essay of universe

Origins of the universe, explained

The most popular theory of our universe's origin centers on a cosmic cataclysm unmatched in all of history—the big bang.

The best-supported theory of our universe's origin centers on an event known as the big bang. This theory was born of the observation that other galaxies are moving away from our own at great speed in all directions, as if they had all been propelled by an ancient explosive force.

A Belgian priest named Georges Lemaître first suggested the big bang theory in the 1920s, when he theorized that the universe began from a single primordial atom. The idea received major boosts from Edwin Hubble's observations that galaxies are speeding away from us in all directions, as well as from the 1960s discovery of cosmic microwave radiation—interpreted as echoes of the big bang—by Arno Penzias and Robert Wilson.

Further work has helped clarify the big bang's tempo. Here’s the theory: In the first 10^-43 seconds of its existence, the universe was very compact, less than a million billion billionth the size of a single atom. It's thought that at such an incomprehensibly dense, energetic state, the four fundamental forces—gravity, electromagnetism, and the strong and weak nuclear forces—were forged into a single force, but our current theories haven't yet figured out how a single, unified force would work. To pull this off, we'd need to know how gravity works on the subatomic scale, but we currently don't.

It's also thought that the extremely close quarters allowed the universe's very first particles to mix, mingle, and settle into roughly the same temperature. Then, in an unimaginably small fraction of a second, all that matter and energy expanded outward more or less evenly, with tiny variations provided by fluctuations on the quantum scale. That model of breakneck expansion, called inflation, may explain why the universe has such an even temperature and distribution of matter.

After inflation, the universe continued to expand but at a much slower rate. It's still unclear what exactly powered inflation.

Aftermath of cosmic inflation

As time passed and matter cooled, more diverse kinds of particles began to form, and they eventually condensed into the stars and galaxies of our present universe.

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By the time the universe was a billionth of a second old, the universe had cooled down enough for the four fundamental forces to separate from one another. The universe's fundamental particles also formed. It was still so hot, though, that these particles hadn't yet assembled into many of the subatomic particles we have today, such as the proton. As the universe kept expanding, this piping-hot primordial soup—called the quark-gluon plasma—continued to cool. Some particle colliders, such as CERN's Large Hadron Collider , are powerful enough to re-create the quark-gluon plasma.

Radiation in the early universe was so intense that colliding photons could form pairs of particles made of matter and antimatter, which is like regular matter in every way except with the opposite electrical charge. It's thought that the early universe contained equal amounts of matter and antimatter. But as the universe cooled, photons no longer packed enough punch to make matter-antimatter pairs. So like an extreme game of musical chairs, many particles of matter and antimatter paired off and annihilated one another.

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Somehow, some excess matter survived—and it's now the stuff that people, planets, and galaxies are made of. Our existence is a clear sign that the laws of nature treat matter and antimatter slightly differently. Researchers have experimentally observed this rule imbalance, called CP violation , in action. Physicists are still trying to figure out exactly how matter won out in the early universe.

the spiral arms in the galaxy Messier 63.

Building atoms

Within the universe's first second, it was cool enough for the remaining matter to coalesce into protons and neutrons, the familiar particles that make up atoms' nuclei. And after the first three minutes, the protons and neutrons had assembled into hydrogen and helium nuclei. By mass, hydrogen was 75 percent of the early universe's matter, and helium was 25 percent. The abundance of helium is a key prediction of big bang theory, and it's been confirmed by scientific observations.

Despite having atomic nuclei, the young universe was still too hot for electrons to settle in around them to form stable atoms. The universe's matter remained an electrically charged fog that was so dense, light had a hard time bouncing its way through. It would take another 380,000 years or so for the universe to cool down enough for neutral atoms to form—a pivotal moment called recombination. The cooler universe made it transparent for the first time, which let the photons rattling around within it finally zip through unimpeded.

We still see this primordial afterglow today as cosmic microwave background radiation , which is found throughout the universe. The radiation is similar to that used to transmit TV signals via antennae. But it is the oldest radiation known and may hold many secrets about the universe's earliest moments.

From the first stars to today

There wasn't a single star in the universe until about 180 million years after the big bang. It took that long for gravity to gather clouds of hydrogen and forge them into stars. Many physicists think that vast clouds of dark matter , a still-unknown material that outweighs visible matter by more than five to one, provided a gravitational scaffold for the first galaxies and stars.

Once the universe's first stars ignited , the light they unleashed packed enough punch to once again strip electrons from neutral atoms, a key chapter of the universe called reionization. In February 2018, an Australian team announced that they may have detected signs of this “cosmic dawn.” By 400 million years after the big bang , the first galaxies were born. In the billions of years since, stars, galaxies, and clusters of galaxies have formed and re-formed—eventually yielding our home galaxy, the Milky Way, and our cosmic home, the solar system.

Even now the universe is expanding , and to astronomers' surprise, the pace of expansion is accelerating. It's thought that this acceleration is driven by a force that repels gravity called dark energy . We still don't know what dark energy is, but it’s thought that it makes up 68 percent of the universe's total matter and energy. Dark matter makes up another 27 percent. In essence, all the matter you've ever seen—from your first love to the stars overhead—makes up less than five percent of the universe.

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October 1, 1994

17 min read

The Evolution of the Universe

Some 15 billion years ago the universe emerged from a hot, dense sea of matter and energy. As the cosmos expanded and cooled, it spawned galaxies, stars, planets and life

By P. James E. Peebles , David N. Schramm , Edwin L. Turner & Richard G. Kron

GALAXY CLUSTER is representative of what the universe looked like when it was 60 percent of its present age. The Hubble Space Telescope captured the image by focusing on the cluster as it completed 10 orbits. This image is one of the longest and clearest exposures ever produced. Several pairs of galaxies appear to be caught in one another’s gravitational field. Such interactions are rarely found in nearby clusters and are evidence that the universe is evolving.

Editor’s Note (10/8/19): Cosmologist James Peebles won a 2019 Nobel Prize in Physics for his contributions to theories of how our universe began and evolved. He describes these ideas in this article, which he co-wrote for Scientific American in 1994.

At a particular instant roughly 15 billion years ago, all the matter and energy we can observe, concentrated in a region smaller than a dime, began to expand and cool at an incredibly rapid rate. By the time the temperature had dropped to 100 million times that of the sun’s core, the forces of nature assumed their present properties, and the elementary particles known as quarks roamed freely in a sea of energy. When the universe had expanded an additional 1,000 times, all the matter we can measure filled a region the size of the solar system.

At that time, the free quarks became confined in neutrons and protons. After the universe had grown by another factor of 1,000, protons and neutrons combined to form atomic nuclei, including most of the helium and deuterium present today. All of this occurred within the first minute of the expansion. Conditions were still too hot, however, for atomic nuclei to capture electrons. Neutral atoms appeared in abundance only after the expansion had continued for 300,000 years and the universe was 1,000 times smaller than it is now. The neutral atoms then began to coalesce into gas clouds, which later evolved into stars. By the time the universe had expanded to one fifth its present size, the stars had formed groups recognizable as young galaxies.

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When the universe was half its present size, nuclear reactions in stars had produced most of the heavy elements from which terrestrial planets were made. Our solar system is relatively young: it formed five billion years ago, when the universe was two thirds its present size. Over time the formation of stars has consumed the supply of gas in galaxies, and hence the population of stars is waning. Fifteen billion years from now stars like our sun will be relatively rare, making the universe a far less hospitable place for observers like us.

Our understanding of the genesis and evolution of the universe is one of the great achievements of 20th-century science. This knowledge comes from decades of innovative experiments and theories. Modern telescopes on the ground and in space detect the light from galaxies billions of light-years away, showing us what the universe looked like when it was young. Particle accelerators probe the basic physics of the high-energy environment of the early universe. Satellites detect the cosmic background radiation left over from the early stages of expansion, providing an image of the universe on the largest scales we can observe.

Our best efforts to explain this wealth of data are embodied in a theory known as the standard cosmological model or the big bang cosmology. The major claim of the theory is that in the largescale average the universe is expanding in a nearly homogeneous way from a dense early state. At present, there are no fundamental challenges to the big bang theory, although there are certainly unresolved issues within the theory itself. Astronomers are not sure, for example, how the galaxies were formed, but there is no reason to think the process did not occur within the framework of the big bang. Indeed, the predictions of the theory have survived all tests to date.

Yet the big bang model goes only so far, and many fundamental mysteries remain. What was the universe like before it was expanding? (No observation we have made allows us to look back beyond the moment at which the expansion began.) What will happen in the distant future, when the last of the stars exhaust the supply of nuclear fuel? No one knows the answers yet.

Our universe may be viewed in many lights—by mystics, theologians, philosophers or scientists. In science we adopt the plodding route: we accept only what is tested by experiment or observation. Albert Einstein gave us the now well-tested and accepted Theory of General Relativity, which establishes the relations between mass, energy, space and time. Einstein showed that a homogeneous distribution of matter in space fits nicely with his theory. He assumed without discussion that the universe is static, unchanging in the large-scale average [see “How Cosmology Became a Science,” by Stephen G. Brush; SCIENTIFIC AMERICAN, August 1992].

In 1922 the Russian theorist Alexander A. Friedmann realized that Einstein’s universe is unstable; the slightest perturbation would cause it to expand or contract. At that time, Vesto M. Slipher of Lowell Observatory was collecting the first evidence that galaxies are actually moving apart. Then, in 1929, the eminent astronomer Edwin P. Hubble showed that the rate a galaxy is moving away from us is roughly proportional to its distance from us.

MULTIPLE IMAGES of a distant quasar ( left ) are the result of an effect known as gravitational lensing. The effect occurs when light from a distant object is bent by the gravitational field of an intervening galaxy. In this case, the galaxy, which is visible in the center, produces four images of the quasar. The photograph was produced using the Hubble telescope.

The existence of an expanding universe implies that the cosmos has evolved from a dense concentration of matter into the present broadly spread distribution of galaxies. Fred Hoyle, an English cosmologist, was the first to call this process the big bang. Hoyle intended to disparage the theory, but the name was so catchy it gained popularity. It is somewhat misleading, however, to describe the expansion as some type of explosion of matter away from some particular point in space.

That is not the picture at all: in Einstein’s universe the concept of space and the distribution of matter are intimately linked; the observed expansion of the system of galaxies reveals the unfolding of space itself. An essential feature of the theory is that the average density in space declines as the universe expands; the distribution of matter forms no observable edge. In an explosion the fastest particles move out into empty space, but in the big bang cosmology, particles uniformly fill all space. The expansion of the universe has had little influence on the size of galaxies or even clusters of galaxies that are bound by gravity; space is simply opening up between them. In this sense, the expansion is similar to a rising loaf of raisin bread. The dough is analogous to space, and the raisins, to clusters of galaxies. As the dough expands, the raisins move apart. Moreover, the speed with which any two raisins move apart is directly and positively related to the amount of dough separating them.

The evidence for the expansion of the universe has been accumulating for some 60 years. The first important clue is the redshift. A galaxy emits or absorbs some wavelengths of light more strongly than others. If the galaxy is moving away from us, these emission and absorption features are shifted to longer wavelengths—that is, they become redder as the recession velocity increases. This phenomenon is known as the redshift.

Hubble’s measurements indicated that the redshift of a distant galaxy is greater than that of one closer to the earth. This relation, now known as Hubble’s law, is just what one would expect in a uniformly expanding universe. Hubble’s law says the recession velocity of a galaxy is equal to its distance multiplied by a quantity called Hubble’s constant. The redshift effect in nearby galaxies is relatively subtle, requiring good instrumentation to detect it. In contrast, the redshift of very distant objects—radio galaxies and quasars—is an awesome phenomenon; some appear to be moving away at greater than 90 percent of the speed of light.

Hubble contributed to another crucial part of the picture. He counted the number of visible galaxies in different directions in the sky and found that they appear to be rather uniformly distributed. The value of Hubble’s constant seemed to be the same in all directions, a necessary consequence of uniform expansion. Modern surveys confirm the fundamental tenet that the universe is homogeneous on large scales. Although maps of the distribution of the nearby galaxies display clumpiness, deeper surveys reveal considerable uniformity.

The Milky Way, for instance, resides in a knot of two dozen galaxies; these in turn are part of a complex of galaxies that protrudes from the so-called local supercluster. The hierarchy of clustering has been traced up to dimensions of about 500 million light-years. The fluctuations in the average density of matter diminish as the scale of the structure being investigated increases. In maps that cover distances that reach close to the observable limit, the average density of matter changes by less than a tenth of a percent.

To test Hubble’s law, astronomers need to measure distances to galaxies. One method for gauging distance is to observe the apparent brightness of a galaxy. If one galaxy is four times fainter in the night sky than an otherwise comparable galaxy, then it can be estimated to be twice as far away. This expectation has now been tested over the whole of the visible range of distances.

HOMOGENEOUS DISTRIBUTION of galaxies is apparent in a map that includes objects from 300 to 1,000 million light-years away. The only inhomogeneity, a gap near the center line, occurs because part of the sky is obscured by the Milky Way. Michael Strauss of the Institute for Advanced Study in Princeton, N.J., created the map using data from NASA’s Infrared Astronomical Satellite .

Some critics of the theory have pointed out that a galaxy that appears to be smaller and fainter might not actually be more distant. Fortunately, there is a direct indication that objects whose redshifts are larger really are more distant. The evidence comes from observations of an effect known as gravitational lensing. An object as massive and compact as a galaxy can act as a crude lens, producing a distorted, magnified image (or even many images) of any background radiation source that lies behind it. Such an object does so by bending the paths of light rays and other electromagnetic radiation. So if a galaxy sits in the line of sight between the earth and some distant object, it will bend the light rays from the object so that they are observable [see “Gravitational Lenses,” by Edwin L. Turner; SCIENTIFIC AMERICAN, July 1988]. During the past decade, astronomers have discovered more than a dozen gravitational lenses. The object behind the lens is always found to have a higher redshift than the lens itself, confirming the qualitative prediction of Hubble’s law.

Hubble’s law has great significance not only because it describes the expansion of the universe but also because it can be used to calculate the age of the cosmos. To be precise, the time elapsed since the big bang is a function of the present value of Hubble’s constant and its rate of change. Astronomers have determined the approximate rate of the expansion, but no one has yet been able to measure the second value precisely.

Still, one can estimate this quantity from knowledge of the universe’s average density. One expects that because gravity exerts a force that opposes expansion, galaxies would tend to move apart more slowly now than they did in the past. The rate of change in expansion is therefore related to the gravitational pull of the universe set by its average density. If the density is that of just the visible material in and around galaxies, the age of the universe probably lies between 12 and 20 billion years. (The range allows for the uncertainty in the rate of expansion.)

Yet many researchers believe the density is greater than this minimum value. So-called dark matter would make up the difference. A strongly defended argument holds that the universe is just dense enough that in the remote future the expansion will slow almost to zero. Under this assumption, the age of the universe decreases to the range of seven to 13 billion years.

DENSITY of neutrons and protons in the universe determined the abundances of certain elements. For a higher density universe, the computed helium abundance is little different, and the computed abundance of deuterium is considerably lower. The shaded region is consistent with the observations, ranging from an abundance of 24 percent for helium to one part in 1010 for the lithium isotope. This quantitative agreement is a prime success of the big bang cosmology.

To improve these estimates, many astronomers are involved in intensive research to measure both the distances to galaxies and the density of the universe. Estimates of the expansion time provide an important test for the big bang model of the universe. If the theory is correct, everything in the visible universe should be younger than the expansion time computed from Hubble’s law.

These two timescales do appear to be in at least rough concordance. For example, the oldest stars in the disk of the Milky Way galaxy are about nine billion years old—an estimate derived from the rate of cooling of white dwarf stars. The stars in the halo of the Milky Way are somewhat older, about 15 billion years—a value derived from the rate of nuclear fuel consumption in the cores of these stars. The ages of the oldest known chemical elements are also approximately 15 billion years—a number that comes from radioactive dating techniques. Workers in laboratories have derived these age estimates from atomic and nuclear physics. It is noteworthy that their results agree, at least approximately, with the age that astronomers have derived by measuring cosmic expansion.

Another theory, the steady state theory, also succeeds in accounting for the expansion and homogeneity of the universe. In 1946 three physicists in England—Hoyle, Hermann Bondi and Thomas Gold—proposed such a cosmology. In their theory the universe is forever expanding, and matter is created spontaneously to fill the voids. As this material accumulates, they suggested, it forms new stars to replace the old. This steady state hypothesis predicts that ensembles of galaxies close to us should look statistically the same as those far away. The big bang cosmology makes a different prediction: if galaxies were all formed long ago, distant galaxies should look younger than those nearby because light from them requires a longer time to reach us. Such galaxies should contain more shortlived stars and more gas out of which future generations of stars will form.

The test is simple conceptually, but it took decades for astronomers to develop detectors sensitive enough to study distant galaxies in detail. When astronomers examine nearby galaxies that are powerful emitters of radio wavelengths, they see, at optical wavelengths, relatively round systems of stars. Distant radio galaxies, on the other hand, appear to have elongated and sometimes irregular structures. Moreover, in most distant radio galaxies, unlike the ones nearby, the distribution of light tends to be aligned with the pattern of the radio emission.

Likewise, when astronomers study the population of massive, dense clusters of galaxies, they find differences between those that are close and those far away. Distant clusters contain bluish galaxies that show evidence of ongoing star formation. Similar clusters that are nearby contain reddish galaxies in which active star formation ceased long ago. Observations made with the Hubble Space Telescope confirm that at least some of the enhanced star formation in these younger clusters may be the result of collisions between their member galaxies, a process that is much rarer in the present epoch.

DISTANT GALAXIES differ greatly from those nearby—an observation that shows that galaxies evolved from earlier, more irregular forms. Among galaxies that are bright at both optical ( blue ) and radio ( red ) wavelengths, the nearby galaxies tend to have smooth elliptical shapes at optical wavelengths and very elongated radio images. As redshift, and therefore distance, increases, galaxies have more irregular elongated forms that appear aligned at optical and radio wavelengths. The galaxy at the far right is seen as it was at 10 percent of the present age of the universe. The images were assembled by Pat McCarthy of the Carnegie Institute.

So if galaxies are all moving away from one another and are evolving from earlier forms, it seems logical that they were once crowded together in some dense sea of matter and energy. Indeed, in 1927, before much was known about distant galaxies, a Belgian cosmologist and priest, Georges Lemaître, proposed that the expansion of the universe might be traced to an exceedingly dense state he called the primeval “super-atom.” It might even be possible, he thought, to detect remnant radiation from the primeval atom. But what would this radiation signature look like?

When the universe was very young and hot, radiation could not travel very far without being absorbed and emitted by some particle. This continuous exchange of energy maintained a state of thermal equilibrium; any particular region was unlikely to be much hotter or cooler than the average. When matter and energy settle to such a state, the result is a so-called thermal spectrum, where the intensity of radiation at each wavelength is a definite function of the temperature. Hence, radiation originating in the hot big bang is recognizable by its spectrum.

In fact, this thermal cosmic background radiation has been detected. While working on the development of radar in the 1940s, Robert H. Dicke, then at the Massachusetts Institute of Technology, invented the microwave radiometer—a device capable of detecting low levels of radiation. In the 1960s Bell Laboratories used a radiometer in a telescope that would track the early communications satellites Echo-1 and Telstar. The engineer who built this instrument found that it was detecting unexpected radiation. Arno A. Penzias and Robert W. Wilson identified the signal as the cosmic background radiation. It is interesting that Penzias and Wilson were led to this idea by the news that Dicke had suggested that one ought to use a radiometer to search for the cosmic background.

Astronomers have studied this radiation in great detail using the Cosmic Background Explorer (COBE) satellite and a number of rocket-launched, balloon-borne and ground-based experiments. The cosmic background radiation has two distinctive properties. First, it is nearly the same in all directions. (As George F. Smoot of Lawrence Berkeley Laboratory and his team discovered in 1992, the variation is just one part per 100,000.) The interpretation is that the radiation uniformly fills space, as predicted in the big bang cosmology. Second, the spectrum is very close to that of an object in thermal equilibrium at 2.726 kelvins above absolute zero. To be sure, the cosmic background radiation was produced when the universe was far hotter than 2.726 degrees, yet researchers anticipated correctly that the apparent temperature of the radiation would be low. In the 1930s Richard C. Tolman of the California Institute of Technology showed that the temperature of the cosmic background would diminish because of the universe’s expansion.

The cosmic background radiation provides direct evidence that the universe did expand from a dense, hot state, for this is the condition needed to produce the radiation. In the dense, hot early universe thermonuclear reactions produced elements heavier than hydrogen, including deuterium, helium and lithium. It is striking that the computed mix of the light elements agrees with the observed abundances. That is, all evidence indicates that the light elements were produced in the hot, young universe, whereas the heavier elements appeared later, as products of the thermonuclear reactions that power stars.

The theory for the origin of the light elements emerged from the burst of research that followed the end of World War II. George Gamow and graduate student Ralph A. Alpher of George Washington University and Robert Herman of the Johns Hopkins University Applied Physics Laboratory and others used nuclear physics data from the war e›ort to predict what kind of nuclear processes might have occurred in the early universe and what elements might have been produced. Alpher and Herman also realized that a remnant of the original expansion would still be detectable in the existing universe.

Despite the fact that significant details of this pioneering work were in error, it forged a link between nuclear physics and cosmology. The workers demonstrated that the early universe could be viewed as a type of thermonuclear reactor. As a result, physicists have now precisely calculated the abundances of light elements produced in the big bang and how those quantities have changed because of subsequent events in the interstellar medium and nuclear processes in stars.

Our grasp of the conditions that prevailed in the early universe does not translate into a full understanding of how galaxies formed. Nevertheless, we do have quite a few pieces of the puzzle. Gravity causes the growth of density fluctuations in the distribution of matter, because it more strongly slows the expansion of denser regions, making them grow still denser. This process is observed in the growth of nearby clusters of galaxies, and the galaxies themselves were probably assembled by the same process on a smaller scale.

The growth of structure in the early universe was prevented by radiation pressure, but that changed when the universe had expanded to about 0.1 percent of its present size. At that point, the temperature was about 3,000 kelvins, cool enough to allow the ions and electrons to combine to form neutral hydrogen and helium. The neutral matter was able to slip through the radiation and to form gas clouds that could collapse to star clusters. Observations show that by the time the universe was one fifth its present size, matter had gathered into gas clouds large enough to be called young galaxies.

A pressing challenge now is to reconcile the apparent uniformity of the early universe with the lumpy distribution of galaxies in the present universe. Astronomers know that the density of the early universe did not vary by much, because they observe only slight irregularities in the cosmic background radiation. So far it has been easy to develop theories that are consistent with the available measurements, but more critical tests are in progress. In particular, different theories for galaxy formation predict quite different fluctuations in the cosmic background radiation on angular scales less than about one degree. Measurements of such tiny fluctuations have not yet been done, but they might be accomplished in the generation of experiments now under way. It will be exciting to learn whether any of the theories of galaxy formation now under consideration survive these tests.

The present-day universe has provided ample opportunity for the development of life as we know it—there are some 100 billion billion stars similar to the sun in the part of the universe we can observe. The big bang cosmology implies, however, that life is possible only for a bounded span of time: the universe was too hot in the distant past, and it has limited resources for the future. Most galaxies are still producing new stars, but many others have already exhausted their supply of gas. Thirty billion years from now, galaxies will be much darker and filled with dead or dying stars, so there will be far fewer planets capable of supporting life as it now exists.

The universe may expand forever, in which case all the galaxies and stars will eventually grow dark and cold. The alternative to this big chill is a big crunch. If the mass of the universe is large enough, gravity will eventually reverse the expansion, and all matter and energy will be reunited. During the next decade, as researchers improve techniques for measuring the mass of the universe, we may learn whether the present expansion is headed toward a big chill or a big crunch.

In the near future, we expect new experiments to provide a better understanding of the big bang. As we improve measurements of the expansion rate and the ages of stars, we may be able to confirm that the stars are indeed younger than the expanding universe. The larger telescopes recently completed or under construction may allow us to see how the mass of the universe affects the curvature of spacetime, which in turn influences our observations of distant galaxies.

We will also continue to study issues that the big bang cosmology does not address. We do not know why there was a big bang or what may have existed before. We do not know whether our universe has siblings—other expanding regions well removed from what we can observe. We do not understand why the fundamental constants of nature have the values they do. Advances in particle physics suggest some interesting ways these questions might be answered; the challenge is to find experimental tests of the ideas.

In following the debate on such matters of cosmology, one should bear in mind that all physical theories are approximations of reality that can fail if pushed too far. Physical science advances by incorporating earlier theories that are experimentally supported into larger, more encompassing frameworks. The big bang theory is supported by a wealth of evidence: it explains the cosmic background radiation, the abundances of light elements and the Hubble expansion. Thus, any new cosmology surely will include the big bang picture. Whatever developments the coming decades may bring, cosmology has moved from a branch of philosophy to a physical science where hypotheses meet the test of observation and experiment.

What is the Universe?

The universe is everything. It includes all of space, and all the matter and energy that space contains. It even includes time itself and, of course, it includes you.

Earth and the Moon are part of the universe, as are the other planets and their many dozens of moons. Along with asteroids and comets, the planets orbit the Sun. The Sun is one among hundreds of billions of stars in the Milky Way galaxy, and most of those stars have their own planets, known as exoplanets.

The Milky Way is but one of billions of galaxies in the observable universe — all of them, including our own, are thought to have supermassive black holes at their centers. All the stars in all the galaxies and all the other stuff that astronomers can’t even observe are all part of the universe. It is, simply, everything.

Though the universe may seem a strange place, it is not a distant one. Wherever you are right now, outer space is only 62 miles (100 kilometers) away. Day or night, whether you’re indoors or outdoors, asleep, eating lunch or dozing off in class, outer space is just a few dozen miles above your head. It’s below you too. About 8,000 miles (12,800 kilometers) below your feet — on the opposite side of Earth — lurks the unforgiving vacuum and radiation of outer space.

In fact, you’re technically in space right now. Humans say “out in space” as if it’s there and we’re here, as if Earth is separate from the rest of the universe. But Earth is a planet, and it’s in space and part of the universe just like the other planets. It just so happens that things live here and the environment near the surface of this particular planet is hospitable for life as we know it. Earth is a tiny, fragile exception in the cosmos. For humans and the other things living on our planet, practically the entire cosmos is a hostile and merciless environment.

How old is Earth?

Our planet, Earth, is an oasis not only in space, but in time. It may feel permanent, but the entire planet is a fleeting thing in the lifespan of the universe. For nearly two-thirds of the time since the universe began, Earth did not even exist. Nor will it last forever in its current state. Several billion years from now, the Sun will expand, swallowing Mercury and Venus, and filling Earth’s sky. It might even expand large enough to swallow Earth itself. It’s difficult to be certain. After all, humans have only just begun deciphering the cosmos.

While the distant future is difficult to accurately predict, the distant past is slightly less so. By studying the radioactive decay of isotopes on Earth and in asteroids, scientists have learned that our planet and the solar system formed around 4.6 billion years ago.

How old is the universe?

The universe, on the other hand, appears to be about 13.8 billion years old. Scientists arrived at that number by measuring the ages of the oldest stars and the rate at which the universe expands. They also measured the expansion by observing the Doppler shift in light from galaxies, almost all of which are traveling away from us and from each other. The farther the galaxies are, the faster they’re traveling away. One might expect gravity to slow the galaxies’ motion from one another, but instead they’re speeding up and scientists don’t know why. In the distant future, the galaxies will be so far away that their light will not be visible from Earth.

Put another way, the matter, energy and everything in the universe (including space itself) was more compact last Saturday than it is today.

Put another way, the matter, energy and everything in the universe (including space itself) was more compact last Saturday than it is today. The same can be said about any time in the past — last year, a million years ago, a billion years ago. But the past doesn’t go on forever.

By measuring the speed of galaxies and their distances from us, scientists have found that if we could go back far enough, before galaxies formed or stars began fusing hydrogen into helium, things were so close together and hot that atoms couldn’t form and photons had nowhere to go. A bit farther back in time, everything was in the same spot. Or really the entire universe (not just the matter in it) was one spot.

Don't spend too much time considering a mission to visit the spot where the universe was born, though, as a person cannot visit the place where the Big Bang happened. It's not that the universe was a dark, empty space and an explosion happened in it from which all matter sprang forth. The universe didn’t exist. Space didn’t exist. Time is part of the universe and so it didn’t exist. Time, too, began with the big bang. Space itself expanded from a single point to the enormous cosmos as the universe expanded over time.

What is the universe made of?

The universe contains all the energy and matter there is. Much of the observable matter in the universe takes the form of individual atoms of hydrogen, which is the simplest atomic element, made of only a proton and an electron (if the atom also contains a neutron, it is instead called deuterium). Two or more atoms sharing electrons is a molecule. Many trillions of atoms together is a dust particle. Smoosh a few tons of carbon, silica, oxygen, ice, and some metals together, and you have an asteroid. Or collect 333,000 Earth masses of hydrogen and helium together, and you have a Sun-like star.

For the sake of practicality, humans categorize clumps of matter based on their attributes. Galaxies, star clusters, planets, dwarf planets, rogue planets, moons, rings, ringlets, comets, meteorites, raccoons — they’re all collections of matter exhibiting characteristics different from one another but obeying the same natural laws.

Scientists have begun tallying those clumps of matter and the resulting numbers are pretty wild. Our home galaxy, the Milky Way, contains at least 100 billion stars, and the observable universe contains at least 100 billion galaxies. If galaxies were all the same size, that would give us 10 thousand billion billion (or 10 sextillion) stars in the observable universe.

But the universe also seems to contain a bunch of matter and energy that we can’t see or directly observe. All the stars, planets, comets, sea otters, black holes and dung beetles together represent less than 5 percent of the stuff in the universe. About 27 percent of the remainder is dark matter, and 68 percent is dark energy, neither of which are even remotely understood. The universe as we understand it wouldn’t work if dark matter and dark energy didn’t exist, and they’re labeled “dark” because scientists can’t seem to directly observe them. At least not yet.

How has our view of the universe changed over time?

Human understanding of what the universe is, how it works and how vast it is has changed over the ages. For countless lifetimes, humans had little or no means of understanding the universe. Our distant ancestors instead relied upon myth to explain the origins of everything. Because our ancestors themselves invented them, the myths reflect human concerns, hopes, aspirations or fears rather than the nature of reality.

Several centuries ago, however, humans began to apply mathematics, writing and new investigative principles to the search for knowledge. Those principles were refined over time, as were scientific tools, eventually revealing hints about the nature of the universe. Only a few hundred years ago, when people began systematically investigating the nature of things, the word “scientist” didn’t even exist (researchers were instead called “natural philosophers” for a time). Since then, our knowledge of the universe has repeatedly leapt forward. It was only about a century ago that astronomers first observed galaxies beyond our own, and only a half-century has passed since humans first began sending spacecraft to other worlds.

In the span of a single human lifetime, space probes have voyaged to the outer solar system and sent back the first up-close images of the four giant outermost planets and their countless moons; rovers wheeled along the surface on Mars for the first time; humans constructed a permanently crewed, Earth-orbiting space station; and the first large space telescopes delivered jaw-dropping views of more distant parts of the cosmos than ever before. In the early 21st century alone, astronomers discovered thousands of planets around other stars, detected gravitational waves for the first time and produced the first image of a black hole.

With ever-advancing technology and knowledge, and no shortage of imagination, humans continue to lay bare the secrets of the cosmos. New insights and inspired notions aid in this pursuit, and also spring from it. We have yet to send a space probe to even the nearest of the billions upon billions of other stars in the galaxy. Humans haven’t even explored all the worlds in our own solar system. In short, most of the universe that can be known remains unknown .

The universe is nearly 14 billion years old, our solar system is 4.6 billion years old, life on Earth has existed for maybe 3.8 billion years, and humans have been around for only a few hundred thousand years. In other words, the universe has existed roughly 56,000 times longer than our species has. By that measure, almost everything that’s ever happened did so before humans existed. So of course we have loads of questions — in a cosmic sense, we just got here.

Our first few decades of exploring our own solar system are merely a beginning. From here, just one human lifetime from now, our understanding of the universe and our place in it will have undoubtedly grown and evolved in ways we can today only imagine.

Next: The Search for Life: Are We Alone?

The Universe

The Universe is everything we can touch, feel, sense, measure or detect. It includes living things, planets, stars, galaxies, dust clouds, light, and even time. Before the birth of the Universe, time, space and matter did not exist.

The Universe contains billions of galaxies, each containing millions or billions of stars. The space between the stars and galaxies is largely empty. However, even places far from stars and planets contain scattered particles of dust or a few hydrogen atoms per cubic centimeter. Space is also filled with radiation (e.g. light and heat), magnetic fields and high energy particles (e.g. cosmic rays).

The Universe is incredibly huge. It would take a modern jet fighter more than a million years to reach the nearest star to the Sun. Travelling at the speed of light (300,000 km per second), it would take 100,000 years to cross our Milky Way galaxy alone.

No one knows the exact size of the Universe, because we cannot see the edge – if there is one. All we do know is that the visible Universe is at least 93 billion light years across. (A light year is the distance light travels in one year – about 9 trillion km.)

The Universe has not always been the same size. Scientists believe it began in a Big Bang, which took place nearly 14 billion years ago. Since then, the Universe has been expanding outward at very high speed. So the area of space we now see is billions of times bigger than it was when the Universe was very young. The galaxies are also moving further apart as the space between them expands.

Story of the Universe

Extreme life
In the beginning
The Big Bang
The birth of galaxies
What is space?
Black Holes
The mystery of the dark Universe
Cosmic distances

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Introduction to the universe.

The Solar System is a collection of planets, moons, asteroids and comets and other rocky objects orbiting the Sun. The Solar System is believed to extend out to at least 150 000 million km from the Sun, although the planets are all found within about 6000 million km.

Our Solar System is thought to have formed 4.6 x 10 9 years ago from a vast, rotating cloud of gas and dust known as the solar nebula. As the solar nebula rotated, its gravity began to attract gas and dust towards the centre, eventually forming our Sun.

The Sun is the powerhouse of the Solar System. Without it, life on Earth simply would not exist. Despite burning its hydrogen fuel for the best part of 5 billion years, the Sun is still only half way through its life cycle.

The study of the Sun, its environment and how the material it discharges interacts with other worlds in the Solar System is of great interest to us all. ESA has a number of mission that analyse various aspects of this solar emission.

Solar Mission

Planets and moons.

The formation of the Sun had a dramatic effect on the temperatures across the solar nebula, introducing a temperature range that stretched from about 2000K near the Sun to less than 50K at the outer regions. The heat in the inner Solar System only allowed materials with high condensation temperatures to remain solid. These particles eventually gathered to form the four terrestrial planets: Mercury, Venus, Earth and Mars.

A similar process formed the outer planets of the Solar System: Jupiter, Saturn, Uranus, and Neptune. Yet, they are different because icy materials such as frozen water, carbon dioxide and methane were also available. Consequently, these outer Jovian planets are much larger than the terrestrial planets. In addition these giant planets were able to enhance their atmospheres by capturing gas atoms moving more slowly due to the colder temperatures.

Each planet travels around the Sun in an elliptical orbit that is held in place by the gravitational attraction between the Sun and the planet. Some of the planets, including, of course, Earth, have moons orbiting them. Mars has just two moons in orbit around it, while Jupiter has 63 moons known to be orbiting it. Kepler's three laws of planetary motion define the motion of the planets around the Sun, and the movement of moons around their parent planet.

Table 1.1: Distance and Orbital Parameters for the Planets

Table 1.2: Observational Characteristics of the Planets

Asteroids and Comets

There was some material left over from the solar nebula once the Sun and the planets had formed. Some of this debris remains in our Solar System in the form of asteroids and comets.

Asteroids, which are sometimes called minor planets, are rocky bodies mostly found in the planetary region between Mars and Jupiter. This region is known as the asteroid belt, and it stretches from about 250 million km to about 600 million km from the Sun. The largest known asteroid is Ceres with a diameter of roughly 1000 km. Only around a dozen are more than 250 km across. Over 100 000 asteroids larger than one kilometre in diameter are known to exist, with more being discovered all the time.

We often hear of asteroids on the news, when near-Earth asteroids pass close enough to our planet to cause concern of a potential impact either now, or in the future. These near-Earth objects have highly elliptical orbits, which bring them into the inner Solar System, crossing the orbit of Mars and occasionally coming close to Earth.

Comets are often referred to as 'dirty snowballs', as they are made up of ice and dust. The ones we can see travel around the Sun in highly elliptical orbits taking from a few years to thousands of years to return to the inner Solar System. Typically comets are just a few kilometres across, which makes them very difficult to spot for most of their orbit. As they approach the Sun, however, solar radiation vaporizes the gases in the comet and the characteristic comet 'tail' is formed. The tail of a comet consists of two parts: a whiter part made of dust, which always points away from the Sun, and a blue part consisting of ionised gas. Comets are mainly found in two regions of the Solar System: the Kuiper belt, a region that extends from around the orbit of Pluto to about 500 AU from the Sun, and the Oort Cloud (from the Kuiper Belt to about 50 000 AU from the Sun).

Occasionally small rocks or dust particles enter the Earth's atmosphere. The dust particles and small rocks burn up in the atmosphere leaving behind brief trails in the sky witnessed as meteors. It is estimated that more than 200 million kg of meteoritic material is swept up by the Earth each year, with around 10% reaching the ground.

Much of this material orbits the Sun in distinct streams, usually as debris from different comets. At various times throughout the year the Earth crosses these streams and for a few nights an observers can witness a meteor shower.

Table 1.3: Dates of Primary Meteor Showers

Sometimes larger fragments survive their passage through the atmosphere and impact the surface, where they become known as meteorites. Most impacting fragments are tiny and cause little or no damage. Historically, however, there have been several major impacts, which may be responsible for changes in climate and the mass extinction of species.

Figure 1.1: Barringer Meteor Crater (credit: NASA)

Bodies of the Universe

It is hard to comprehend the enormity of our Universe. Our Sun is only one of billions of stars in our galaxy, known as the Milky Way. But beyond the Milky Way, there are billions of other galaxies, too. Collectively, all these galaxies, along with the vast amount of space found in between them, are called the Universe.

Extragalactic

Other components.

Dark Energy

Stellar Clusters & Constellations

We are familiar with the constellations that we see regularly in the night sky - a distinctive pattern of stars. However, although these stars may form shapes that are recognisable to us here on Earth, they do not usually have any real link to each other, as they are often at different distances from the Earth, and are in fact very far away from each other.

Figure 1.2: View of Orion and Actual Distance to Stars

Stellar clusters, on the other hand, are systems of stars that are held together by the gravity of their members. Eventually these clusters slowly evaporate. After a few billion years, the relatively loose collections of stars known as open clusters will no longer be held together by gravity and the cluster will stop existing. More highly compacted stellar clusters, known as globular clusters, which are typically about 15 billion years old, have not yet evaporated. Due to their relatively well-known distances, and the similarities that tend to exist among their stars, stellar clusters play an important role in astrophysics. Some of the nearest stellar clusters are visible with the naked eye. The most visible open clusters are the Pleiades and Hyades, both to be found in the constellation of Taurus.

Table 1.4: List of the brightest Open and Globular Clusters

Relative Distances To Objects

A light year is the distance light travels through empty space in the course of one year.

1 light year = 9.461 x 10 12 km = 5.878 x 10 12 miles

In order to comprehend the enormity of space, astronomers use a variety of methods to measure the distances between stars and between galaxies.

Our own galaxy, the Milky Way, is around 120 000 light years across and the Sun occupies a position roughly 28 000 light years from the centre. Within the Milky Way, the nearest star to the Sun is Proxima Centauri, which is about 4.4 light years away. But most of our nearest stars are between 100 and 1000 light years away from Earth.

From any given location on Earth it is possible to view around 7000 stars with the naked eye and countless more with a telescope. In all, our galaxy contains over 1 billion stars.

The distance to stars in our galaxy is obtained using a technique called parallax. By identifying certain stellar properties it is then possible to calibrate a distance scale out to our galactic neighbours.

The nearest galactic objects are the Magellanic Clouds. The Large Magellanic Cloud is 170 000 light years away, while the Small Magellanic Cloud is at a distance of 210 000 light years. The next nearest galaxy is Andromeda (M31 in the Messier catalogue), at a distance of 2.3 million light years.

Galaxies are usually part of a larger group of galaxies. The group of galaxies that includes the Milky Way and Andromeda, plus several other smaller companion galaxies, is known as the Local Group. The other galaxies in the Local Group are between 80 000 to three million light years away from the Milky Way.

The next nearest rich cluster of galaxies, the Virgo cluster, is around 60 million light years away. It is believed that the Milky Way-Andromeda cluster is part of an even bigger supercluster along with Virgo-Coma cluster.

Stellar Motions

Diurnal effects.

During the course of one night, the constellations appear to move across the sky. Stars rise above the eastern horizon and set below the western horizon. The stars appear to rotate around one point in the sky. This optical effect occurs because the Earth itself is rotating about axis.

View the sky changing over 24 hours

Annual Effects

If you observe the night sky regularly over the course of one year, you will notice that the constellations appear to change their position slightly from one night to the next at any given time, only returning to their original positions once a year. This is due to the difference between a calendar day (24 hours) and a sidereal day (23 hours 56 minutes), or the time the Earth actually takes to spin once on its axis.

View the sky changing over 1 year

Annual Parallax

Annual Parallax is the difference between the position of a star observed from the Earth and by a hypothetical observer at the Sun. The effect is a tiny shift in the positions of relatively close stars against the background of distant stars. If the position of a nearby star is plotted during the course of a year it sweeps out an ellipse, called the parallactic ellipse, across the sky. This change in position is very small and requires high precision instruments to make the observation.

This effect, which can be observed for example with a spinning top, is caused by the gravitational pull from the Sun and Moon on the Earth's equatorial bulge. (Note - if the Earth were a perfect sphere precession would not occur.)

Precession causes the Earth's rotation axis to sweep out a circle on the sky with an angular radius of 23° 27' (this value corresponds to the axial tilt of the Earth). The circle is traced out at the rate of 1° every 71.6 years, taking 25 800 years to complete a full circle.

This means that the celestial pole, which currently points at the star Polaris, changes with time. Careful examination of the 'View of the sky changing over 24 hours' animation (above) shows the Pole Star also leaving a star trail since it is ¾ of a degree away from the celestial pole.

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Teacher Notes 1

The composition of the Universe

The chemical composition of the Universe and the physical nature of its constituent matter are topics that have occupied scientists for centuries. From its privileged position above the Earth’s atmosphere Hubble has been able to contribute significantly to this area of research.

All over the Universe stars work as giant reprocessing plants taking light chemical elements and transforming them into heavier ones. The original, so-called primordial, composition of the Universe is studied in such fine detail because it is one of the keys to our understanding of processes in the very early Universe.

Helium in the early Universe

Shortly after the First Servicing Mission successfully corrected the spherical aberration in Hubble’s mirror a team led by European astronomer Peter Jakobsen investigated the nature of the gaseous matter that fills the vast volume of intergalactic space. By observing ultraviolet light from a distant quasar, which would otherwise have been absorbed by the Earth’s atmosphere, they found the long-sought signature of helium in the early Universe. This was an important piece of supporting evidence for the Big Bang theory. It also confirmed scientists’ expectation that, in the very early Universe, matter not yet locked up in stars and galaxies was nearly completely ionised (the atoms were stripped of their electrons). This was an important step forward for cosmology.

Quasar lighthouses

This investigation of helium in the early Universe is one of many ways that Hubble has used distant quasars as lighthouses. As light from the quasars passes through the intervening intergalactic matter, the light signal is changed in such a way as to reveal the composition of the gas.

The results have filled in important pieces of the puzzle of the total composition of the Universe now and in the past.

During the servicing mission in 2009 , astronauts installed a new instrument dedicated to studying this field. The Cosmic Origins Spectrograph is designed to break up ultraviolet light from faraway quasars into its component wavelengths, and study how intervening matter absorbs certain wavelengths more than others. This reveals the fingerprints of different elements, telling us more about their abundances at various locations in the Universe.

Dark Matter

Today astronomers believe that around one quarter of the mass-energy of the Universe consists of dark matter . This is a substance quite different from the normal matter that makes up atoms and the familiar world around us. Hubble has played an important part in work intended to establish the amount of dark matter in the Universe and to determine where it is and how it behaves .

The riddle of what the ghostly dark matter is made of is still far from solved, but Hubble’s incredibly sharp observations of gravitational lenses have provided stepping stones for future work in this area.

Dark matter only interacts with gravity, which means it neither reflects, emits or obstructs light (or indeed any other type of electromagnetic radiation). Because of this, it cannot be observed directly. However, Hubble studies of how clusters of galaxies bend the light that passes through them lets astronomers deduce where the hidden mass lies. This means that they are able to make maps of where the dark matter lies in a cluster.

One of Hubble’s big breakthroughs in this area is the discovery of how dark matter behaves when clusters collide with each other. Studies of a number of these clusters have shown that the location of dark matter (as deduced from gravitational lensing with Hubble) does not match the distribution of hot gas (as spotted in X-rays by observatories such as ESA’s XMM-Newton or NASA’s Chandra). This strongly supports theories about dark matter: we expect hot gases to slow down as they hit each other and the pressure increases. Dark matter, on the other hand, should not experience friction or pressure, so we would expect it to pass through the collision relatively unhindered. Hubble and Chandra observations have indeed confirmed that this is the case.

In 2018 astronomers used Hubble's sensitivty to study intracluster light in the hunt for dark matter . Intracluster light is a byproduct of interactions between galaxies. In the course of these interactions, individual stars are stripped from their galaxies and float freely within the cluster. Once free from their galaxies, they end up where the majority of the mass of the cluster, mostly dark matter, resides. Both the dark matter and these isolated stars — which form the intracluster light — act as collisionless components. These follow the gravitational potential of the cluster itself. The study showed that the intracluster light is aligned with the dark matter, tracing its distribution more accurately than any other method relying on luminous tracers used so far.

A 3D map of the dark matter distribution in the Universe

In 2007 an international team of astronomers used Hubble to create the first three-dimensional map of the large-scale distribution of dark matter in the Universe. It was constructed by measuring the shapes of half a million galaxies observed by Hubble. The light of these galaxies traveled — until it reached Hubble — down a path interrupted by clumps of dark matter which deformed the appearance of the galaxies. Astronomers used the observed distortion of the galaxies shapes to reconstruct their original shape and could therefore also calculate the distribution of dark matter in between.

This map showed that normal matter, largely in the form of galaxies, accumulates along the densest concentrations of dark matter. The created map stretches halfway back to the beginning of the Universe and shows how dark matter grew increasingly clumpy as it collapsed under gravity. Mapping dark matter distribution down to even smaller scales is fundamental for our understanding of how galaxies grew and clustered over billions of years. Tracing the growth of clustering in dark matter may eventually also shed light on dark energy.

Dark energy

More intriguing still than dark matter is dark energy. Hubble studies of the expansion rate of the Universe have found that the expansion is actually speeding up. Astronomers have explained this using the theory of dark energy, that pushes the Universe apart ever faster, against the pull of gravity.

As Einstein's famous equation, E=mc 2 tells us, energy and mass are interchangeable. Studies of the rate of expansion of the cosmos suggests that dark energy is by far the largest part of the Universe’s mass-energy content, far outweighing both normal matter and dark matter: it seems that dark energy makes almost 70% of the known Universe.

While astronomers have been able to take steps along the path to understanding how dark energy works and what it does, its true nature is still a mystery.

The page on " measuring the age and size of the Universe " also has information on dark energy and how it relates to the expansion of the cosmos.

What is the universe made of?

Matter and energy are the two basic components of the entire Universe. An enormous challenge for scientists is that most of the matter in the Universe is invisible and the source of most of the energy is not understood. How can we study the Universe if we can’t see most of it?

As our tools for observation grow more sophisticated, scientists at Center for Astrophysics | Harvard & Smithsonian will continue to be at the forefront of dark matter and dark energy research.

NASA’s Chandra X-ray Observatory and optical telescopes help map the distribution of dark matter in colliding galaxy clusters, like the Bullet Cluster. X-ray observations show a heated shock front where the gas from the clusters collided and slowed down, but gravitational lensing measurements show that dark matter was unaffected by the collision and separate from the normal matter.

It is theorized that when some dark matter particles collide, they annihilate and disappear in a flash of high-energy radiation. The Very Energetic Radiation Imaging Telescope Array System (VERITAS) in Arizona, which can detect gamma-ray radiation, is looking for the signature of dark matter annihilation.

The South Pole Telescope in Antarctica and Chandra are placing limits on dark energy by looking for its effects on galaxy cluster evolution throughout the history of the Universe. By comparing observations of galaxy clusters with experimental models, researchers are studying how dark energy competed with gravity throughout the history of the Universe.

Scientists at CfA have led the Baryon Oscillation Spectroscopic Survey (BOSS), analyzing millions of galaxies and charting their distribution in the Universe. The distribution has been shown to trace sound waves from the early Universe, like ripples in a pond, where some regions have higher numbers of galaxies, and others have less. Looking at these distributions, we can more accurately measure the distance to galaxies and map the effects of dark energy.

On the horizon, the Dark Energy Spectroscopic Instrument (DESI) will create a 3D map of the Universe, containing millions of galaxies out to 10 billion light years. This map will measure dark energy’s effect on the expansion of the Universe. And the Large Synoptic Survey Telescope (LSST) will observe billions of galaxies and discover unprecedented numbers of supernovae, constraining the properties of dark matter and dark energy.

Dark Matter and Dark Energy

Astronomer Fritz Zwicky was the first to notice the discrepancy between the amount of visible matter in a cluster of galaxies and the motions of the galaxies themselves. He suggested that there may be invisible matter, or what he called “dark matter”, interacting gravitationally with the visible matter. Later, astronomers noticed similar incongruities when observing nearby spiral galaxies. The outer edges of the galaxies rotated much faster than expected, suggesting “dark matter” existed throughout and extended beyond the visible galaxy.

Today, we can estimate the amount of dark matter in a galaxy based on how it causes light from a background source to bend. Using this “gravitational lensing” technique, we can measure the severity of that bend to get an idea of the galaxy’s mass. When the mass we calculate from the bend and the mass we can observe directly don’t agree, we know dark matter must be present.

Modern calculations say dark matter comprises about 27% of the Universe. We don’t yet know what it is, but we are searching for answers.

We have known that the Universe is expanding since the early 20th century. But recent observations of distant supernovae and other observations show that the Universe is not only expanding, but the expansion is accelerating. This astonishing discovery came as a complete surprise because the expansion of the Universe should slow down with time because of the gravitational attraction between galaxies and clusters of galaxies. The unseen repellant force required to explain this observation has been labelled “dark energy,” and current models say it makes up about 68% of the Universe.

That leaves only 5% of the Universe that is visible to us.

Supernova 1994D in this image from NASA's Hubble Space Telescope might look like a star, but it's the explosion of a white dwarf that nearly outshone an entire galaxy. Such supernovas — known as type Ia — are extremely similar to each other, allowing astronomers to use them to measure the rate of the expansion of the universe.

What We Know and What We Think

While we can’t see dark matter, we know it’s there. And we can investigate some of dark matter’s properties using gravitational lensing. This technique measures the gravitational pull galaxies exert on light from more distant sources. The warping and magnification of this light gives us insight into the amount, density, and distribution of dark matter in any given lensing galaxy. Theoretically, the current best explanation we have for dark matter is the existence of WIMPs, or Weakly Interacting Massive Particles. These theoretical particles should have certain predictable behaviors, but directly observing them and their byproducts so far has proved elusive.

As for dark energy, Einstein had assumed the Universe was static, neither expanding nor collapsing. However, his Theory of General Relativity predicted that the Universe was not static, and so he added a “cosmological constant,” to oppose gravity. He later called it the “biggest blunder” of his life after Hubble demonstrated that the Universe was expanding.

The discovery that the expansion of the Universe is accelerating revived the idea of the cosmological constant. The simplest interpretation of this constant is that it represents the energy of empty space. This “vacuum energy” is constant throughout space and time.

Another interpretation is that dark energy might be an energy field that varies over time and space. Or, perhaps we do not fully understand gravity. For example, maybe it acts differently on enormous scales. Astronomers are currently testing modifications to General Relativity to see if they can explain the Universe’s accelerating expansion.

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Where Is Everybody in Our Universe?

Two physicists contemplate life on other planets in this excerpt from “Exoplanets”

Michael Summers and James Trefil

The story is that it all started one day in 1950, when a group of prominent physicists— all veterans of the Manhattan Project—were walking to lunch at the Fuller Lodge in Los Alamos. They were discussing the spate of recent UFO sightings that had been claimed in the area, and the conversation turned to the topic of extraterrestrial civilizations. Out of the blue, Enrico Fermi (1901–54), a man well known for his ability to see to the heart of a problem, asked a simple question: Where is everybody? In the years since then, scientists have come to realize that Fermi’s offhand question is, in fact, the deepest question we can ask about life in our galaxy. The fact that there is no evidence for the existence of extraterrestrials in spite of the calculations suggesting that they should exist is known as the Fermi paradox.

So why has his offhand question played such an important role in the debate about extraterrestrials? To understand this, we can go back to our old device of compressing the lifetime of the universe into a single year. In this scheme, the Sun and our solar system formed in the late summer (Labor Day is a convenient approximation), modern humans showed up a few minutes before midnight on New Year’s Eve, and all of recorded history took place while the ball is descending in Times Square, with modern science appearing in the last second of that descent.

The point is this: if there really are other technological civilizations out there, it is extremely unlikely that they developed science after we did—after all, they had the whole year to discover the laws of nature. To understand what follows from this statement, let’s look at a possible future for the human race.

Exoplanets: Diamond Worlds, Super Earths, Pulsar Planets, and the New Search for Life beyond Our Solar System

In Exoplanets, astronomer Michael Summers and physicist James Trefil explore remarkable recent discoveries: planets revolving around pulsars, planets made of diamond, planets that are mostly water, and numerous rogue planets wandering through the emptiness of space.

We’ll start at Princeton University in the 1970s, where physicist Gerard O’Neill (1927–92) was teaching a seminar centered around an interesting question: is the surface of a planet really the best place for a technological civilization? The answer the class came up with was “no,” and from their deliberations came the design for a structure now called an O’Neill colony.

Imagine a hollow doughnut, a mile or more across, rotating slowly in space. In O’Neill’s vision, people live inside the doughnut, and the centrifugal force associated with its rotation substitutes for gravity. Using solar or nuclear power, possibly with ancillary doughnuts for raising crops, such a system could be self-sustaining, a true move of humanity away from our home planet. It is almost within our technological capabilities to build such a structure right now, if not within our budgets. In any case, we should expect that any extraterrestrial race that has come to our level of technical sophistication should also be able to build something like an O’Neill colony.

Let’s imagine how something like O’Neill colonies might play out in our future. Eventually, we can expect that people in colonies like this would leave the space around Earth and move to the truly prime real estate in the solar system, the asteroid belt, where ample material and solar power are available.

It’s the next step that has enormous implications for the Fermi paradox. After a few generations have spent their lives in something like an O’Neill colony, will it really matter to them if their colony is on the way to another star system rather than in the asteroid belt? As the best locations in our own system fill up, it is reasonable to suppose that future space colonists will follow the example of their forebears and “light out for the territories,” except that, in this case, that would mean moving to other solar systems. In essence, we suggest that they would turn their colonies into interstellar starships. How hard would that be?

Let’s make two extraordinarily conservative assumptions. Let’s assume that (1) there is no way to get around the speed-of-light barrier—no “warp drive”—and (2) no major technological advances will be made in the next couple of centuries. The immense distance between stars would require travel times of a century or more, which would mean that the starship would be multigenerational—you get on, your grandchildren get off. Several propulsion systems for such a trip have been proposed—for example, one in which the ship scoops up rarefied interstellar hydrogen to run its power and propulsion systems. The idea of such a multigenerational starship is already a staple of science fiction.

The point of this exercise in futurology is that once a civilization reaches our level of sophistication, it is only a matter of a few centuries before it can start colonizing other star systems. If we can imagine ourselves doing it, then there’s no reason extraterrestrials couldn’t do it as well. The important point for our discussion is that we are talking about a time span of only a few hundred years. In terms of our galactic year analogy, this amounts to only one second. Basically, as soon as the ball touches down in Times Square, Earth could be the center of an expanding wave of human colonization. No one would even have time to say, “Happy New Year.”

How long would it take that wave to engulf the entire galaxy? Most calculations give times on the order of 30 million years or so. And while this is an extremely long time on a human scale, it is only one day in our galactic year. So if extraterrestrial civilizations have been popping up throughout the galactic year, and if at least some of those civilizations are as scientifically adept as we are, there should have been multiple waves of colonization sweeping over the solar system.

So . . . where is everybody?

That, in essence, is a modern look at the question Fermi asked over a half century ago, one we still haven’t been able to answer. His point can be stated this way: we shouldn’t be looking for extraterrestrials out there, as we do in SETI (the search for extraterrestrial intelligence)—we should be looking for them right here. And if we ignore the silliness of UFOs and ancient astronauts, we can say that there is no evidence whatsoever for extraterrestrials being here now or in the past.

Where is everybody? Why the Great Silence?

William of Ockham was an English scholar who is famous for one throwaway line in an otherwise turgid theological treatise. Called Occam’s razor, it says, “Plurality must never be posited without necessity.” In essence, it tells us that when we have a question to answer, the simplest solution is the one we should choose. The concept shaves away complexity; hence the word razor .

There is no doubt that the simplest answer to the questions “Why the Great Silence? Why don’t we hear any SETI signals?” is that we don’t hear signals because no one is sending them. There are a number of other explanations that have been put forward, and we can look at them briefly before taking William of Ockham seriously. Basically, the explanations can be divided into three categories:

1. They really are out there, but they’re not interested in us.

2. They really are out there, but they’re protecting us.

3. They really are out there, and we’re going to get it unless we mend our ways.

An example of the first category would be a race of extraterrestrials living in a Dyson sphere, happy as clams with their star’s energy and supremely uninterested in anyone else. Another possibility would be extraterrestrials on a rogue planet who can’t imagine a planet near a star being inhabitable. An example of the second item in the list is seen in the Star Trek series, where spacefarers obey the Prime Directive, which forbids them from interfering with the development of other life forms. The last category is portrayed in the classic 1950s film The Day the Earth Stood Still , in which an extraterrestrial visitor warns that Earth will be destroyed unless we control our use of atomic weapons:

Klaatu barrada nikto!

All these schemes have two things in common. First, there is no evidence to support any of them, and, second, they are all somewhat improbable in a galaxy with thousands of different advanced civilizations. Some might indeed retreat to Dyson spheres or refuse to go near stars, but to suppose that all of them would is something of a stretch. Similar arguments can be made for the other explanations.

One way to approach the question posed by the Great Silence is to think of each term in the Drake equation as a gateway or valve on the way to an advanced technological civilization. If even one of those terms has a numerical value much less than we have assumed, the effect would be to greatly reduce our estimate of the number of extraterrestrials out there. In essence, that term would act as a kind of filter, blocking the orderly progression implied in the equation. To use a term introduced by economist Robin Hanson, our colleague at George Mason, somewhere in the chain of events in the Drake equation there might be a “Great Filter” that effectively blocks the development of civilizations that might be trying to communicate with us.

Some scientists have argued that the existence of periodic ice ages played an important role in producing the kind of social interactions needed to take humans beyond the hunter-gatherer stage. In one scenario, for example, the need to protect the nutritionally rich shellfish beds along the African coast—a dependable source of food—during an ice age is what led to both the kind of cooperativeness and the kind of aggressiveness that have characterized our species ever since. Again, if you accept this sort of argument, you are saying that the Great Filter is located at the point where intelligence progresses into advanced society. If this is true, there will be lots of planets with the equivalent of dinosaurs out there, but none (or very few) with radio telescopes.

Arguments that say, in effect, that there is something special about Earth that is unlikely to be duplicated elsewhere in the galaxy—go under the name of the Rare Earth Hypothesis. They are put forward most completely in a book titled Rare Earth , by geologist Peter Ward and astronomer Donald Brownlee. Ward and Brownlee’s central thrust is that we have been blindly accepting the Copernican principle—the idea that Earth is not special—and ignoring the fact that there are many unusual things about our home planet. In essence, they look at all the things that are unique about Earth and argue that if they are all necessary for an advanced civilization to develop, then we could well be the only such civilization in the galaxy. For example, if, besides an Earth-sized planet in the CHZ of its star, you need a star located a certain distance from the galactic center, a Jupiter farther out, plate tectonics, the right planetary tilt to produce ice ages, and a large moon to stabilize the planet’s axis of rotation and produce tidal pools (Darwin’s warm little pond), Earth might well be the only planet like that in the galaxy. The Rare Earth answer to the Fermi paradox is thus quite simple: there’s nobody here because there’s nobody there. We are indeed alone.

Those who don’t accept the Rare Earth Hypothesis assert that any specific event you want to talk about is extremely unlikely, and that simply reciting that fact proves nothing. Think, for example, of the chain of unlikely events that led to your reading these words. Your parents had to meet, you had to attend a certain school, learn to read, acquire an interest in science, and so on. There’s no point in harping on this improbability, though, because if you weren’t reading this book, you’d be doing something else equally improbable. In the same way, other types of improbable intelligences could have developed in the galaxy following their own improbable chain of events, and there could be an infinite number of those improbable paths. For these critics, all the Rare Earth Hypothesis proves is that there is at least one improbable path to an advanced civilization (our own); it says absolutely nothing about the possible existence of other paths.

The scenarios we have considered all have one thing in common: they all assume that the Great Filter is behind us, that by some combination of luck or providence, Homo sapiens has made it through all the filters and bottlenecks that stood in our way. But there is another, much more frightening possibility. What if none of these events in our past constitutes the Great Filter? What if the Great Filter is still in front of us?

To understand the importance of this question, let’s think for a moment about the nature of the evolutionary process. Natural selection is driven by one criterion and one criterion only: the need to get an organism’s genes into the next generation. Winners in the evolutionary game, in other words, are not determined by moral or ethical considerations. Consider the history of our own species as an example of this statement. The appearance of Homo sapiens in any region once we left Africa was accompanied by the disappearance of competing hominids (think Neanderthals and Denisovans) and just about every large animal (think woolly mammoths and giant tree sloths). We became the dominant life form on the planet by wiping out our competitors, either directly or indirectly. Given this history, we think it’s fair to say that Homo sapiens is not the sort of species you’d want to meet in a dark alley, and the same will be true of any other winner of the evolutionary game who became the dominant species on their planet.

The “Great Filter is in front of us” argument goes like this: despite the Rare Earth Hypothesis, there really doesn’t seem to be anything all that special about the way that life developed on Earth, and given the abundance of planets out there, there is no reason that complex life shouldn’t be quite common. On the other hand, from what we know about the process of evolution, we can expect the winners of the evolutionary game on other planets to be no more benevolent than Homo sapiens . In this case, the coming Great Filter is easy to see. Once an aggressive, warlike species discovers science, they are likely to turn their discoveries against one another and, in essence, wipe themselves out.

The picture of galactic history that comes from this argument is a disturbing one. From the very beginning, intelligent, technologically advanced societies have appeared only to disappear in a short time as they succumb to their own dark inner nature—a nature produced by the laws of natural selection. No one is out there, in other words, because they’ve all wiped themselves out long ago, before we started listening.

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Essay on Our Universe

Students are often asked to write an essay on Our Universe in their schools and colleges. And if you’re also looking for the same, we have created 100-word, 250-word, and 500-word essays on the topic.

Let’s take a look…

100 Words Essay on Our Universe

What is the universe.

The universe is a vast space that holds everything we know – from tiny atoms to giant galaxies. It includes all of space, time, energy, and matter. Imagine it as a huge home where all the stars, planets, and moons live. It’s so big that we can’t see the end of it, and it’s always expanding.

Stars and Galaxies

Stars are like giant balls of gas that give off light and heat. They group together to form galaxies. Our sun is a star, and it’s part of a galaxy we call the Milky Way. There are billions of galaxies each with its own stars.

Planets and Moons

Planets are big objects that orbit, or go around, a star. Earth is a planet that goes around our sun. Some planets have moons, which are smaller objects that orbit planets. Just like Earth has one moon, other planets can have many.

The Mystery of Space

Space is full of mysteries. Scientists use telescopes to study far-away stars and planets. They’re trying to learn more about black holes, which are places in space where gravity is very strong, and about the possibility of life beyond Earth.

250 Words Essay on Our Universe

The universe is everything we can touch, feel, sense, measure, or detect. It includes living things, planets, stars, galaxies, dust clouds, light, and even time. Before the birth of the Universe, time, space, and matter did not exist.

The Big Bang

The universe began with a huge explosion called the Big Bang about 13.8 billion years ago. This explosion made all the space, time, matter, and energy in the universe. It started very small and hot, then cooled and stretched to become as big as it is now, and it’s still expanding.

Stars are huge balls of hot gas that give off light and heat. Our sun is a star. There are billions of stars in the universe. Stars group together to form galaxies. Our galaxy is called the Milky Way, and it has billions of stars too. There are so many galaxies we can’t count them all.

Planets are big objects that orbit, or go around, stars. Our Earth is a planet. Some planets have moons that orbit them. Moons are smaller than planets and there are hundreds of moons in our universe.

Exploring the Universe

Scientists use telescopes to look at stars, planets, and galaxies. They use space probes to explore things too far to see with telescopes. By studying the universe, we learn more about where we come from and our place in the cosmos.

500 Words Essay on Our Universe

Introduction to the universe.

The universe is like a huge home with many rooms, each filled with stars, planets, and all sorts of interesting things. Imagine looking up at the night sky. Every star you see is part of our universe. It is everything that exists, from the smallest ant to the biggest galaxy.

What’s in the Universe?

Our universe has lots of galaxies, and our home galaxy is called the Milky Way. Inside it, there’s our solar system, where Earth is just one of eight planets. Besides planets, there are moons, comets, asteroids, and stars. Stars are like giant balls of gas that are so hot they glow and give off light.

The Size of Our Universe

Think of the biggest thing you’ve ever seen. Now imagine something a million times bigger. Our universe is even larger than that! It’s so big that we measure how far things are in it with a special word: “light-year.” A light-year is the distance light travels in one year, and light is super fast!

The Beginning of Everything

A long time ago, scientists believe the universe started with a big bang. It wasn’t an explosion, but more like everything, all the space, time, and stuff that would become galaxies, started expanding from a tiny point. Since then, the universe has been getting bigger and bigger.

The Life of Stars

Stars are born, live, and then die, just like living things on Earth, but their life lasts millions or even billions of years. They start in places called “nebulae,” which are clouds of gas and dust. When they die, they can explode in a huge burst called a supernova, or they can shrink and become really dense, like a “black hole.”

Humans have always been curious about the stars. We’ve used telescopes to look far away, and we’ve sent spacecraft to explore planets and moons. Some spacecraft, like the Voyager probes, have even left our solar system and are sending back information from beyond.

The Mystery of Dark Matter and Dark Energy

There are things in the universe we can’t see called dark matter and dark energy. We know they’re there because they affect how galaxies move and how the universe is growing. But what they are exactly is still a big question.

Our Place in the Universe

Even though the universe is so vast, our Earth is just a tiny part of it. But it’s a special part because it’s where we live, and so far, it’s the only place we know that has life. We are still learning so much about the universe and our place in it.

Our universe is a fascinating and mysterious place. It’s full of wonders that we are just beginning to understand. As we continue to look up at the stars and learn more, we realize how amazing it is that we are a part of something so vast and incredible. The universe is the biggest adventure waiting for us to explore.

That’s it! I hope the essay helped you.

If you’re looking for more, here are essays on other interesting topics:

Essay on Our Planet Our Health
Essay on Our Nation
Essay on Origin Of Life

Apart from these, you can look at all the essays by clicking here .

Happy studying!

The shape of the cosmos

Henry Gee

Nature volume 402 , page C79 ( 1999 ) Cite this article

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Olaf Stapledon is the great unsung hero of twentieth-century science fiction. His stories are cast on scales of time and space so vast as to inspire nothing short of vertigo or terror. In Star Maker , his hero, in a ‘hawk-flight of the imagination’, journeys through the cosmos and eventually meets the Creator in his workshop. The Star Maker, it seems, is still perfecting his art. Our own cosmos is only provisional. Previous essays in Universe construction litter the room like trash. These essays come in all shapes and sizes, suggesting that we need not live in a great, expanding hypersphere, infinite in all directions.

Our conception of the shape and size of the Universe is based on timescales. The familiar ‘light-year’ is a unit based on the time it takes for a beam of light to get from A to B. But there is a reckoning that is purely geometric, or, rather, trigonometric. This is the ‘parsec’, short for ‘parallax arcsecond’, the distance at which the separation of the Earth and Sun (1 Astronomical Unit) would subtend an angle of one second of arc. A parsec is equivalent to just over three light-years.

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Gee, H. The shape of the cosmos. Nature 402 (Suppl 6761), C79 (1999). https://doi.org/10.1038/35011574

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The Art of Space, Envisioning the Universe (Op-Ed)

Draggerwrist creature - Barlowe gallery, space books, space art

Ron Miller is an award-winning artist and best-selling author who has written more than 50 books, including the recently published " The Art of Space: The History of Space Art, from the Earliest Visions to the Graphics of the Modern Era ." (Zenith Press, 2014). His artwork has been featured in Scientific American, Astronomy, Science et Vie and other publications and has appeared in collections at the Smithsonian Institution and the Pushkin Museum. He has also contributed to Hollywood projects by David Lynch, James Cameron and others. Miller contributed this essay to Space.com's Expert Voices: Op-Ed & Insights .

There are many parallels between artists who devote themselves to recreating the distant ages of the Earth's past and those who recreate distant worlds in space. Both depend on science; both re-create — from many sources and forms — objects, creatures and places not otherwise visible to the human eye; and both allow scientists and others to see what otherwise could not be seen.

Because astronomers have, by and large, treated artists in many respects as colleagues, astronomical art has, in the 400-odd years of its existence, appeared in virtually every media, school and style. While many artists work closely with astronomers in creating scientifically accurate depictions of astronomical subjects, space artists have always felt free to interpret the wonders of astronomy and space exploration as they see fit. And even an artist trying to create a meticulously accurate scene set on, say, Titan will try to make his or her work successful as a landscape painting as well as a useful scientific document. As a result, astronomical art has run the gamut from the photorealistic to the absolutely abstract. And both astronomical art and astronomy have been the richer for it. [ Inspiring Space Art Gallery: Space Foundation's Student Contest Winners 2013 ]

Artwork associated with other sciences does not seem to touch the soul to quite the depths space art does. Medical illustration looks inward to the microcosm, paleontological art into the distant past. But astronomy and astronautics look outward and have no bounds … and the art these sciences inspires does the same.

The evolution of astronomical art

Astronomical art is almost as old as modern astronomy — if one dates the latter back to the invention of the astronomical telescope. After the discovery of planets other than Earth, people wanted to know what these worlds looked like. Donato Creti was one of the earliest artists to satisfy this curiosity, creating a series of paintings in the 17th century that included images of the planets as seen with a Galilean telescope. And A. de Neuville's illustrations for Jules Verne's "From the Earth to the Moon" in 1865 were the first to attempt to depict spaceflight and scenes of other worlds with an inclination toward accuracy. [ Alien Life, Landscapes and the Art of Space (Gallery) ]

The latter part of the 19th century saw the publication of much space art: the artwork that accompanied Verne's "Off on a Comet," John Jacob Astor's "A Journey in Other Worlds," the models that illustrated James Carpenter and James Hall Nasmyth's "The Moon," work by Paul Hardy, Abbe Moreux, Stanley L. Wood, Fred T. Jane and others all helped to interpret the theories and discoveries of the era.

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The first great specialist in space art in the last century was Scriven Bolton, who combined detailed models with painting. He was closely followed by Lucien Rudaux, who can be said to have founded the art of space painting . Working primarily from the late 1920s to the late 1940s, his images of the planets, and especially of the moon and Mars, are so uncannily accurate that they could have been rendered in the last decade. He was a major influence on the grand master of astronomical art, the late Chesley Bonestell, from whom all modern space artists descend.

Art as inspired reality

Astronomy and astronautics owe much to the faithfulness and artistry of space painters, the same way that they owe a debt to science fiction. Artists showed the public the universe in images more real than the most gifted author could ever create. They showed that the Earth's sister planets were not merely an astronomer's speculation— these worlds instead possessed a reality no blurry telescopic photograph could ever convey.

In the mid-1950s, Wernher von Braun wrote a series of articles for the Collier's magazine space symposium series. And, as brilliant and exciting these articles were, what is most memorable are the evocative images created by Chesley Bonestell, Fred Freeman and Rolf Klep. Their work had a realism that was far beyond mere technical virtuosity, and there was a casual matter-of-factness about the pieces that made it seem as if they were painted from life. For the first time, spaceflight and the exploration of the universe seemed not a matter for the distant future, but for tomorrow.

Bonestell's paintings for Life magazine in the late 1940s, and later, for the now-classic books, "The Conquest of Space," "The World We Live In" and others, changed the public's perception, which had been molded by photographic images of planets that looked like pea-sized balls of cotton. Bonestell's renderings depicted what it would be like to actually stand on one of these worlds and see landscapes as real and strange as anything on Earth. "The Conquest of Space" looks more like a collection of postcards than the product of an artist's imagination. [ Cosmic Creativity: A NASA Resident Artist's View of Space ]

Bonestell, while not the first to specialize in astronomical art, was the first to break the mental barrier of artist's "impression" that had existed between viewer and image. So compelling were Bonestell's landscapes of the moon that there was an almost universal sigh of disappointment after the first lunar landing when the moon revealed the lunar surface did not look like a Bonestell painting. This happened even though it had been fairly well-known since the 1920s that lunar mountains were not of an alpine cragginess, as Bonestell had portrayed them.

Astronomical painting is the modern descendant of landscape art from the Hudson River School; in fact, astronomical art is the last bastion of the Romantic approach to painting the universe. Its practitioners carry on this tradition, which was founded by masters like Albert Bierstadt and Thomas Moran. In the latter half of the 19th century, Bierstadt, Moran, Frederick Church and their colleagues were responsible for showing the public the wonders of the American continent. It was through the giant canvases of Moran and Bierstadt that Yellowstone and Yosemite were first seen in the East, eventually convincing the U.S. Congress to preserve these sites as the United States' first national parks.

Accuracy, and passion, in art

Astronomical artists serve the same function today, if any artwork needs a function beyond its existence. Because astronomical art depends so heavily on science to accurately depict its subjects, space painting is often assumed to have a strictly educational role, much like that imposed on early science fiction, most notably by editor Hugo Gernsback, who retained a battery of science experts to approve the accuracy of his stories. While astronomical art should be reasonably accurate, in the same way that a portrait should bear some resemblance to the sitter, there is no requirement that accuracy be the only raison d'être of a painting.

The balance between accuracy for its own sake and a purely imaginative interpretation is not easy to maintain. Kara Szathmary, for example, creates sublime, wholly abstract compositions inspired by astronomical and astronautical subjects. Artwork like his evokes emotions that a purely representative image cannot. [ 'The Art of Space' (US 2014): Book Excerpt ]

Unfortunately, with only three exceptions, no astronomical artist has ever been able to visit the places he or she paints, and no space artist has ever worked from life. The exceptions are Apollo astronaut Alan Bean, whose lunar surface paintings benefit from his first-hand experience, and Vladimir Dzhanibekov and Alexei Leonov, the cosmonaut-artists and long-time collaborators with the late Soviet space painter Andre Sokolov. As long as every other space artist must depend on scientists and astronauts to provide the details of their subjects, astronomical painting will probably have to bear the burden of being thought of as mere illustration, an appendage to science and technology instead of a parallel development.

From landscapes to hardware to extraterrestrials

Space art can be divided into at least two broadly distinct sub-genres: astronomical painting and hardware art. The former is an extension of landscape painting and continues as an art form that has existed for centuries. Astronomical art has roots in the Pre-Raphaelites ,a school of art that demanded precise observation and depiction of nature, and their scrupulous attention to reproducing nature. It follows many of the same precepts as any successful landscape art. Its outstanding practitioners today include Don Davis, Michael Carroll, David Hardy and William Hartmann.

If you're a topical expert — researcher, business leader, author or innovator — and would like to contribute an op-ed piece, email us here.

Hardware art concerns itself with the technology used to explore space, and its practitioners are more interested in how humans are going to get somewhere than in what they are going to find when they get there. Hardware artists have a much more difficult time divorcing themselves from the onus of technical illustration, because their work concerns itself so much with the accurate rendering of technology. Their art has the additional problem of quickly looking dated. Coping with these difficulties very nicely are such well-known artists as Pierre Mion, Pat Rawlings and the late Bob McCall.

There is, of course, a grey area between the two types of art. Nothing prevents an astronomical artist from including spacecraft in a painting or a hardware artist from placing a spacecraft in an interesting location. And there are artists who handle both types of art with equal skill. Those artists who are fortunate enough to be able to combine the two include Pamela Lee, Don Davis, Don Dixon and Rick Sternbach.

Perhaps the smallest division, —and the most difficult to categorize, consists of the few artists who specialize in creating extraterrestrial life forms — not necessarily wholly imaginary creatures, but aliens as well-thought-out as any paleontological recreation. While most space artists have worked in an extraterrestrial now and then, those who specialize in these figures make a very short list, which includes Joel Hagen and Wayne Barlowe.

At either end of the spectrum are artists who use space and space travel as a jumping-off points, allowing the public to see the symbolic, surrealistic and abstract, but always in terms invoking human emotion. They are space artists, too, and their work ranges from the serene mobiles of B.E. Johnson and Joy Alyssa Day to the surrealism of Lynette Cook. Space artists find expression in every medium, too, from traditional oils and acrylics to wood sculpture, glass and even quilting .

Space art seems to be gradually coming into its own, recognized not only by the art community as a legitimate genre in its own right, but, more importantly to the space artist, by scientists as well. Museums, planetariums and other institutions hold major exhibitions of space art every year.

Space art is also an international affair. The membership of the International Association of Astronomical Artists (IAAA) includes artists from around the world. Space art is taking a small, but not insignificant, step toward the realization that all people are passengers on the same space ship. Through trial and tribulation, space artists are creating dreams, inspiring dreamers and expanding the view of the universe.

Follow all of the Expert Voices issues and debates — and become part of the discussion — on Facebook , Twitter and Google+ . The views expressed are those of the author and do not necessarily reflect the views of the publisher. This version of the article was originally published on Space.com.

Join our Space Forums to keep talking space on the latest missions, night sky and more! And if you have a news tip, correction or comment, let us know at: [email protected].

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Essay: The Universe

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Abstract The universe is a known place to our young and sensitive eyes. Stars galaxies, planets, comets, asteroids are part of this abundant place that has an end of 13. 8 billion years to us. The age of the universe was known by studying the oldest objects within the universe, which can be studied using binary system or the HR Diagram. Knowing how fast the universe is expanding can be done by knowing how close and far are objects from us and their velocity towards or away from our galaxy. Finally we can know the observable universe by knowing how light and light speed works and travels in space. Introduction What is in the universe? Galaxies, planets, stars, comets, asteroids, and much other chemical composition ‘stuff’ are part of the universe. We are not able to see the entire universe but just the observable part of it. The observable universe is a term referring to the volume of space that we are physically able to detect, it can be defined as what we are potentially able to see, is there more? That is unknown to our eyes. The universe is 13.8 billion years old to us this is until what our eyes can see. The age of the universe was known because of these main reasons, one, by studying the oldest objects within the universe and second, by measuring how fast the universe is expanding, but the one and most important is knowing how light and light speed works and travels in space. Main body Studying the oldest objects within the universe Many countless objects are part of the universe having each a different birthday, one year, ten years and up to a billion years of age. Studying the age of the objects in the universe has some work attached to it. The life cycle of a star is based on its mass (Redd). We can know that if a star is bright it has a bigger mass causing it to have a longer life cycle. Measuring the mass of a star is easier when using a binary system. Binary system is when two (bi) start orbit around each other. By measuring the orbital speed the orbital period and the size of the orbit we can get to know the mass of both the stars. Another easy method to know the mass of the star and therefore the age of it is using the H-R diagram. Depending where the star is in the H-R diagram we can know the mass and therefore its age. Therefore an example can be, if we want to know the age of star ‘A’ and star ‘B’ we first measure the speed, the orbital period between star ‘A’ and star ‘B’, the size of the orbit and we get to know the mass both. The stellar mass is the mass that we have been using and continue to use in order to know determine the age of a star. Hertzsprung’Russell diagram One of the most useful and powerful plots in astrophysics is the Hertzsprung-Russell diagram (hereafter called the H-R diagram). It originated in 1911 when the Danish astronomer, Ejnar Hertzsprung, plotted the absolute magnitude of stars against their colour (hence effective temperature). Independently in 1913 the American astronomer Henry Norris Russell used spectral class against absolute magnitude. Their resultant plots showed that the relationship between temperature and luminosity of a star was not random but instead appeared to fall into distinct groups (Australia). This diagram has several different representation one of which is called the observational Hertzsprung- Russell diagram or color-magnitude diagram (CMD). What this diagram does is that when stars are at the same distance it compares the color, using the color index which can state which star is more luminous. Therefore once we are able to know which star is more luminous we can determine it age. How fast the universe is expanding For a fact we know that stars die but there are some stars that live longer than other and by discovering how old is one star and them discovering that another star is older we have come to know that they may not be the limit and by looking more in to it we may find older objects. The universe is expanding every day away from us and towards us. Galaxies and stars are moving and we can know if a star is close to us, away from us or if it is moving closer or farther away from us. Knowing the wavelength range by using infrared light can answer us where are the stars standing now and once we know where the stars are know we can know their color and therefore their age. Farther stars and galaxies are moving way faster from us that does closer stars and galaxies, this is due to the young age they have which allows them to move in a faster rate. Light The speed of light is what determines our possible visibility of the universe. The speed of light is defines as C= the speed of light= 300,000km/s or 3.0 * 10^8 m/s. A light year is the distance traveled in one year. If you see a star that is 40 light years away, you are seeing it as it was 40 years ago. Thus the deeper you peek into space, the farther you are seeing back in time. Any event that happened beyond a certain point in the past is unknowable to us if the signal from it hasn’t had time to reach us (Observable universe). We can see up to objects that are 13.8 billion light years away from us because 13.8 billion light years is our visible limit. For that reason the universe that old, and there may be more but it has not yet reached our eyes. Conclusion Human beings have a limit of the visibility of the universe. The universe to our yes is enormous with all different stars ‘stuff’ that are part of it. Our eyes and our telescopes can only see back to 13.8 billion years. The light has traveled to us in a speed of 13.8 billion light years, and has not yet seen more. We do not have knowledge of how old or what is beyond what we see, this will be known in several billion years more, if they are to come.

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Essay on Our Universe: Definition, Stars and Solar System!

When we look at the sky, we see different kinds of natural bodies like the sun, the stars, the moon, and so on. The natural bodies in the sky are called celestial bodies or heavenly bodies. They are part of our universe. The universe is a huge space which contains everything that exists. The celestial bodies that we see are just a small fraction of the bodies that exist in the universe. One of the reasons why we do not see more of them is that they are very, very far away.

To measure the large distances in the universe, scientists use a unit of length called the light year. A light year is the distance travelled by light in one year. Light travels 9.46 trillion km in a year (one trillion is 1 followed by 12 zeroes).

One light year represents this huge distance. Proxima Centauri, the star closest to our solar system, is 4.2 light years from us. This means that light from this star takes 4.2 years to reach us. In this article, we shall learn a bit about stars and our solar system. But before that, let us see how the universe was formed.

Scientists believe that the universe was born after a massive explosion called the ‘big bang’. A long time after the big bang, stars like our sun were formed. At that time, clouds of hot gases and particles revolved around the sun. Over time, many particles got stuck together to form large bodies. These bodies pulled in smaller objects near them by gravitational force. This made them larger still. These bodies finally became the planets.

Away from the lights of the city, you can see thousands of stars in the night sky. You can also see some planets and their moons, either with the naked eye or with the help of a telescope. These celestial bodies are different from the stars in one important way. Stars are celestial bodies that produce their own heat and light. Planets and their moons shine by reflecting the light of a star such as our sun.

All stars are huge balls of hydrogen and helium gases. In a star, hydrogen gets converted into helium. In this reaction, a large amount of energy is liberated. This is the source of the heat and light of a star. Stars vary in brightness and size. Some are medium-sized, like our sun. Some are so huge that if they were to be placed in our sun’s position, they would fill the entire solar system!

A star is born in a cloud of gases called a nebula

There are trillions of stars in the universe. They occur in groups called galaxies. The gravitational force between stars keeps the stars of a galaxy together. Apart from stars, a galaxy may have other celestial bodies like planets and moons. So you can say that a galaxy is a group of stars and other celestial bodies bound together by gravitational force.

The distribution of the stars in a galaxy can give it a shape such as spiral, ring or elliptical. Our sun is a part of a spiral galaxy called the Milky Way Galaxy. This galaxy is named after the Milky Way. The Milky Way is a band of stars that we can see on a clear night. These stars are a part of our galaxy. The ancient Romans called this band of stars Via Galactica, or ‘road of milk’. That is how our galaxy got its name.

(a) A ring galaxy and (b) a spiral galaxy

Constellations :

As the earth moves round the sun, we see different stars at different times of the year. In the past, people found many uses for this. For example, they would get ready for sowing when particular stars appeared in the sky. Obviously, it was not possible for them to identify each and every star. So, they looked for groups of stars which seem to form patterns in the sky. A group of stars which seem to form a pattern is called a constellation.

Ancient stargazers made stories about the constellations and named them after the animals, heroes, etc., from these stories. So constellations got names like Cygnus (swan), Leo (lion), Taurus (bull), Cancer (crab), Perseus (a hero) and Libra (scale). You can see many of these constellations on a clear night.

The Great Bear (Ursa Major) is one of the easiest constellations to spot. You can see it between February and May. Its seven brightest stars form the shape of a dipper (a long-handled spoon used for drawing out water). Together, these stars are called the Big Dipper or Saptarshi. These and the other stars of the constellation roughly form the shape of a bear.

The two brightest stars of the Big Dipper are called ‘pointers’ because they point towards the pole star. The pole star lies at the tail of the bear of a smaller constellation called the Little Bear (Ursa Minor).

To find the north direction, ancient travellers would look for the Big Dipper and from there, locate the pole star. While all stars seem to move from the east to the west (as the earth rotates in the opposite direction), the pole star seems fixed. This is because it lies almost directly above the earth’s North Pole [Figure 13.3 (c)].

(a) The Great Bear and the Little Bear (b) The two brightest star of the Great Bear point towards the pole star. (c) The Pole star seems fixed above the north pole of the earth, while the other stars appears to move opposite to the direction of the rotation of the earth

Orion (the Hunter) and Scorpius are two other prominent constellations. There are different stories linking them. According to one, the mighty hunter Orion vowed to kill all the animals of the world. Alarmed at this, the Earth Goddess sent a scorpion to kill Orion. He ran away, and continues to do so even now. This story takes into account the fact that Orion goes below the horizon when Scorpius rises. Orion rises again only when Scorpius sets.

Remember that constellations are imaginary. For our convenience we have picked a few stars that resemble a pattern and called them a constellation. On the other hand, galaxies are real things in which stars and other celestial bodies are held together by gravitational force.

The Solar System :

The sun is the brightest object in the sky. It is huge. It is about 333,000 times heavier than the earth, and you could fit more than a million earths inside it! Its great mass causes a large gravitational force. This keeps the sun, the planets, their moons and some other smaller bodies together as the sun’s family. The sun and all the bodies moving around it are together called the solar system. All the members of the solar system revolve around the sun in almost circular paths, or orbits.

After the sun, the planets are the largest bodies in our solar system. Scientists define a planet as a round body that orbits the sun and which has pulled in all objects near its orbit. Remember that planets were formed when large bodies in space pulled in smaller bodies near it. This cleared the space around a planet’s orbit.

There are eight planets in our solar system. In order of distance from the sun they are Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus and Neptune. You can remember this order as My Very Efficient Maid Just Served Us Noodles.

Apart from revolving around the sun, each planet rotates, or spins, about its axis. The time taken to complete a revolution around the sun is the length of a planet’s year. And the time taken to complete one rotation is the planet’s day.

The four planets closest to the sun—Mercury, Venus, Earth and Mars—are small, rocky planets. They are called terrestrial (earthlike) planets. The other four planets—Jupiter, Saturn, Uranus and Neptune—are giants in comparison.

They are made up mainly of gases. They are called gas giants or Jovian (Jupiter like) planets. All the gas giants have rings around them. Since they are very far from the sun, the gas giants are much colder than the terrestrial planets.

While stars twinkle, planets shine with a steady light. You can see some of the planets with the naked eyes or with the help of a good pair of binoculars. Just remember that as the planets move around the sun, they appear at different positions in the sky at different times of the year. And for the period they are behind the sun, they are not visible.

Mercury, the smallest planet of our solar system, revolves around the sun the fastest. But it rotates on its axis at a much slower speed than the earth. So, a day on Mercury is about 58 times longer than a day on earth.

Although Mercury is the closest to the sun, it is not the hottest planet. Its thin atmosphere cannot trap heat. So, at night, when there is no sun, the temperature can fall to as low as -180°C. You can see Mercury near the eastern horizon before sunrise at certain times of the year. And at certain other times, you can see it near the western horizon after sunset.

The thick atmosphere of Venus makes it the brightest and the hottest planet of the solar system. Its atmosphere has mainly carbon dioxide gas, which reflects a lot of sunlight. But it also traps so much heat that the average temperature on Venus is about 450°C.

Venus takes 243 days to complete one rotation, making its day the longest in the solar system. As a matter of fact, a day on Venus is longer than its year! It is easy to spot Venus because it is so bright. When it is visible in the east before sunrise, it is called a morning star. And when it is visible in the west in the evening, it is called an evening star.

The earth is not the fastest, slowest, hottest, coldest, largest or smallest planet. But it is the only planet on which life is known to exist. The planet’s distance from the sun, the composition of its atmosphere and the fact that liquid water is found on it make life possible on it.

Were it nearer the sun, the water on it would have evaporated. Were it farther away, all our oceans, rivers and lakes would have frozen. The carbon dioxide in the earth’s atmosphere plays two important roles. Plants use it to make food—which feeds, directly or indirectly, all animals. It also traps just enough heat to ensure that the nights on earth do not become freezing cold.

No other planet evokes so much interest as Mars does. This is because scientists have found evidence that liquid water once flowed through the channels visible on its surface. So it is possible that some form of life once existed on this planet. The rust-coloured soil of Mars gives it a red colour. So, it is also called the Red Planet.

When visible, Mars looks like a red sphere. During its two-year orbit, it looks the brightest when the earth is between the sun and Mars. During this time, you can see it rise in the east as the sun sets in the west.

Jupiter is the largest and the heaviest planet of our solar system. It also has the largest number of moons. The strong winds blowing on it, and on the other gas giants, create light and dark areas, giving them a striped look.

If you look through a powerful telescope, you will see a big spot on Jupiter’s surface. This spot is actually a huge storm, which has been raging on Jupiter for more than 300 years. In 1979, the Voyager 1 spacecraft discovered faint rings around Jupiter. These rings are not visible even through the most powerful earth-based telescopes. Jupiter is also visible to the naked eye. It looks like a bright spot in the sky.

You can easily recognise a picture of Saturn because of the planet’s prominent rings. These rings are actually particles of dust and ice revolving around Saturn. Apart from these particles, a large number of moons orbit this planet.

(a) Winds in Jupiter's atmosheres give it a striped look. The Spot its surface is an ancent storm (b) Saturn and its rings

Uranus and Neptune:

Uranus and Neptune are the third and the fourth largest planets respectively. Yet, they were the last two planets to be discovered. That is because they are so far away from us. Even today, we know very little about them.

The moons of planets :

An object revolving around a celestial body is known as a satellite. All planets except Mercury and Venus have natural satellites, or moons, revolving around them. So far, we know of more than 150 planetary moons. Some of them are so small that they were discovered only when spacecraft flew past them. A few of the moons are almost as large as planets. One of Jupiter’s moons, Ganymede, is the largest of them all. It is even larger than Mercury. Of all the moons, we know the most about the earth’s moon.

The earth’s moon:

The earth’s moon is the brightest object in the night sky. It shines by reflecting sunlight. If you look at the moon through a telescope or a good pair of binoculars, you will see a number of craters on its surface. These are large depressions created when huge rocks from space hit the moon. The moon does not have water or an atmosphere. It also does not have life on it.

The moon takes 27 days and 8 hours to complete one revolution around the earth. In this time it also completes one rotation around its axis. We see different shapes of the moon as it travels around the earth.

Stand in front of a lamp in a darkened room. Hold a ball in your outstretched arm and move it around you, just as the moon moves around the earth. A friend standing some distance away from you will always see half of the ball (moon) lit by the lamp (sun). But to you (earth) the shape of the lit portion will keep on changing, like the changing shapes of the moon.

Sunlight lights up half of the moon. As the moon revolves around the earth, we see different parts of the sunlit half. The shapes of these parts are called the phases of the moon. When the entire side facing the earth is sunlit, the moon appears as a full disc. We call this the full moon or purnima. And when the side of the moon facing us gets no sunlight, we do not see the moon.

This is called the new moon or amavasya. After the new moon, the moon appears as a thin crescent. As days pass, we see larger portions of the moon till the full moon appears. After this, the size of the moon visible to us gradually decreases till we once again have the new moon. The whole cycle of one new moon to the next takes 29.5 days. So the new moon and the full moon appear about fifteen days from each other.

The shape of the sunlit half of the moon visible to us changes

Dwarf planets :

A dwarf planet is a small, round body that orbits the sun. At the time of its formation, a dwarf planet could not pull in all other objects near its orbit. So it is not considered a planet. Pluto, which was previously considered a planet, is now considered a dwarf planet. Ceres and Eris are two other dwarf planets.

Asteroids :

In a belt between the orbits of Mars and Jupiter, millions of small, irregular, rocky bodies revolve around the sun. These are asteroids, and the belt is known as the asteroid belt. Asteroids are also called minor planets.

Scientists think that asteroids are pieces of material that failed to come together to form a planet when the solar system was being formed. Asteroids can measure a few metres to hundreds of kilometres in width. Some asteroids even have moons.

Meteoroids :

Asteroids were not the only pieces of rock left over from the formation of the solar system. Some others, called meteoroids, still orbit the sun. When they come very close to a planet such as the earth, gravitation pulls them in.

As they enter the earth’s atmosphere, they heat up because of friction with the air, and start burning. As these burning meteoroids fall towards the ground, we see them as streaks of light. The streak of light caused by a burning meteoroid is called a meteor or a shooting star.

Fortunately, the material of most meteoroids burns up completely before it can reach the surface of the earth. However, some large ones fail to burn up completely and strike the earth’s surface. Meteoroids that fall on a planet or a moon are called meteorites. A large meteorite can create a large crater and cause a lot of damage.

Scientists think that dinosaurs were wiped off the earth following a meteorite hit. Meteorite hits are more common on those planets and moons which have little or no atmosphere to burn off the falling rock. The craters on our moon have resulted from meteorite hits.

A comet is a small body of ice and dust that moves around the sun in an elongated orbit. As a comet approaches the sun, it heats up and leaves behind a stream of hot, glowing gases and dust particles. We see this as the ‘tail’ of the comet.

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Home — Essay Samples — Science — Universe — The Beginning of the Universe

The Beginning of The Universe

Categories: Creation Myth Universe

About this sample

Words: 1323 |

Published: Nov 16, 2018

Words: 1323 | Pages: 3 | 7 min read

Works Cited

Greene, B. (2004). The Fabric of the Cosmos: Space, Time, and the Texture of Reality. Knopf.
Guth, A. H. (1997). The Inflationary Universe: The Quest for a New Theory of Cosmic Origins. Perseus Books.
Hawking, S. (1988). A Brief History of Time: From the Big Bang to Black Holes. Bantam Books.
Krauss, L. M. (2012). A Universe from Nothing: Why There Is Something Rather Than Nothing. Free Press.
Lemaître, G. (1931). The Primeval Atom Hypothesis and the Problem of Clusters of Galaxies. Monthly Notices of the Royal Astronomical Society, 91(5), 483-490.
Linde, A. (1990). Particle Physics and Inflationary Cosmology. Contemporary Concepts in Physics, 5, 295-339.
Peebles, P. J. E. (1993). Principles of Physical Cosmology. Princeton University Press.
Penrose, R. (2004). The Road to Reality: A Complete Guide to the Laws of the Universe. Vintage Books.
Rees, M. J. (2000). Just Six Numbers: The Deep Forces That Shape the Universe. Basic Books.
Weinberg, S. (1972). Gravitation and Cosmology: Principles and Applications of the General Theory of Relativity. John Wiley & Sons.

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Every new generation of eyes sees a new version of our galaxy, the Milky Way.

This Impressionistic swirl of color represents the churning magnetic fields in giant dust clouds near the center of the galaxy.

The map, painted in infrared wavelengths, reveals new details in a stretch of our galactic home 500 light-years wide.

The colors represent different temperatures of interstellar dust. Cool, dense dust is green; warmer dust is pink. The magnetic field lines, showing the direction of force, were undetectable before now.

The map is a first step toward understanding how magnetism can shape the universe.

The Magnetic Heart of the Milky Way

By Dennis Overbye

“The nation that controls magnetism will control the universe.” So maintained Dick Tracy, the fictional detective in the comic strip by Chester Gould, in 1962.

But does magnetism control the universe, too?

About seven stars are born each year in the Milky Way, our home galaxy. They come from dust and to dust they eventually return. Now, a celestial image, an Impressionistic swirl of color in the center of the Milky Way, represents a first step toward understanding the role of those magnetic fields in the cycle of stellar death and rebirth.

The image was produced by David Chuss, a physicist at Villanova University and an international team of astronomers. The project is known as FIREPLACE, for Far-InfraRed Polarimetric Large Area CMZ Exploration. The team’s map reveals previously invisible details in a stretch of the central Milky Way 500 light-years wide.

The colors represent different temperatures of interstellar dust: Green indicates cool, dense dust; pink indicates warmer dust. Threaded through these hues are lines showing the directions of magnetic force in the clouds. The yellow streaks are jets of hot ionized gas, which emits radio waves. The jets were first recorded two years ago by the MeerKAT radio telescope in South Africa.

Every new generation of eyes sees a new version of our galaxy.

To map the galaxy’s magnetic field lines, Dr. Chuss and his colleagues flew at 45,000 feet aboard the Stratospheric Observatory for Infrared Astronomy, or SOFIA, a 747 outfitted for astronomy. A special spectrograph measured the direction of polarization of the infrared light emanating from the dust, revealing the directions of the magnetic fields point by point.

The center of the Milky Way is barely noticeable to the right of center in the map, just below a small blob that resembles a sideways figure eight. At the middle of the dusty blob is a monster black hole, around which the entire galaxy rotates like a carousel.

“The next step is to figure out what this all means,” Dr. Chuss said in an interview. Embedded in this map could be clues to some of nature’s deepest, most complex processes, including how stars, the sources of all light and life in the universe, come to be.

“It will provide the ability for new theories to be tested,” Dr. Chuss said, “and guide the development of the next generation of astronomical exploration.”

Produced by Antonio de Luca and Elijah Walker . Image: Villanova University/Paré, Karpovich, Chuss (PI).

An earlier version of this article misidentified the academic affiliation of David Chuss, a physicist. It is Villanova University, not Vanderbilt University.

How we handle corrections

Dennis Overbye is the cosmic affairs correspondent for The Times, covering physics and astronomy. More about Dennis Overbye

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Scientists may have discovered a major flaw in their understanding of dark energy, a mysterious cosmic force . That could be good news for the fate of the universe.

A new set of computer simulations, which take into account the effects of stars moving past our solar system, has effectively made it harder to predict Earth’s future and reconstruct its past.

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The standard cosmological model known as Lambda-CDM (ΛCDM) proposes that dark energy is a constant force in the universe.
However, an early “hint” in a new detailed map from the Dark Energy Spectroscopic Instrument shows that dark energy can actually grow stronger and weaker over time.
While this evidence isn’t enough to be considered a discovery, it does call into question some underlying assumptions about how the universe formed and is expanding.

So, in other words, there’s more than a few mysteries where dark matter and dark energy are concerned. And now, a new cosmological map developed by the Dark Energy Spectroscopic Instrument (DESI) is creating a few more. DESI—outfitted at Kitt Peak National Observatory in Tucson, Arizona—just commenced a five-year effort to make the most detailed map of the known universe, including 40 million galaxies stretched across 11 billion years. The first data release, just recently published online , is already showing that the cosmological model is pretty good, but can’t quite predict everything that the instrument is seeing.

“So far, we’re seeing basic agreement with our best model of the universe, but we’re also seeing some potentially interesting differences that could indicate that dark energy is evolving with time,” Michael Levi, DESI director and a scientist at the Department of Energy’s Lawrence Berkeley National Laboratory, said in a press statement . “Those may or may not go away with more data, so we’re excited to start analyzing our three-year dataset soon.”

Those differences are in reference to the cosmological constant , an idea—first put forward by Albert Einstein in 1915— that suggests the universe is expanding at a constant rate. This is thought to be powered by the unceasing, and unchanging work of dark energy, and has led astronomers to believe that, eventually, the universe will simply expand indefinitely until even the very last atoms are ripped apart. However, DESI’s initial results contradict this idea. Instead, they indicate that dark energy appears to grow stronger and weaker over time.

DESI gathered this data by focusing on Baryon Acoustic Oscillations (BAOs)—“bubbles” formed from the explosive early moments of the universe. Because things were so hot and heavy (literally) when the universe formed, subatomic particles were moving too fast for atoms to form. So, the nuclei of hydrogen and helium—known as baryons—were pervasive on their own. These baryons formed acoustic waves that eventually froze in place when the universe thinned and cooled.

Scientists use these BAOs as a “cosmic ruler,” which allows them to measure the growth of the universe at different times in the past based on their distances. And so far, this technique has found that the cosmological constant isn’t very constant at all.

“We do see, indeed, [see] a hint that the properties of dark energy would not correspond to a simple cosmological constant,” astrophysicist at the Lawrence Berkeley lab Palanque-Delabrouille told The New York Times . “And this is the first time we have that…[but] I wouldn’t call it evidence yet. It’s too, too weak.”

This new data comes at an important time for cosmology’s investigations into the underpinning of everything—and it’s also not the cosmological model’s only competitor. This week, a meeting at London’s Royal Society will question this standard view , with astronomers bringing evidence of the universe’s “lopsidedness” along with groundbreaking (and perplexing) data from the James Webb Space Telescope . All of this comes in preparation for large sky surveys scheduled to come online in the next couple years, including the Vera C. Rubin Observatory and Nancy Grace Roman Space Telescope.

“We are in the golden era of cosmology, with large-scale surveys ongoing and about to be started, and new techniques being developed to make the best use of these datasets,” Arnaud de Mattia, co-leader of DESI’s group interpreting the cosmological data , said in a press statement. “We’re all really motivated to see whether new data will confirm the features we saw in our first-year sample and build a better understanding of the dynamics of our universe.”

Some 2,600 years in the making, that great human journey of universal understanding is entering a new era.

Darren lives in Portland, has a cat, and writes/edits about sci-fi and how our world works. You can find his previous stuff at Gizmodo and Paste if you look hard enough.

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Sophia Bush confirms relationship with Ashlyn Harris: ‘The universe had been conspiring for me’

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Sophia Bush finally feels like she can breathe after coming out as queer and opening up about her long-rumored relationship with soccer star Ashlyn Harris.

“When I take stock of the last few years, I can tell you that I have never operated out of more integrity in my life. I hope that’s clear enough for everyone speculating out there,” the “One Tree Hill” alum wrote Thursday in an essay for the April issue of Glamour .

A collage showing soccer player Ashlyn Harris in yellow sunglasses on the left, and actor Sophia Bush on the right

Sophia Bush, soccer star Ashlyn Harris spark dating rumors after respective divorces

‘One Tree Hill’ alum Sophia Bush and retired USWNT goalkeeper Ashlyn Harris reportedly ‘went out on their first dinner date a couple of weeks ago.’

Oct. 18, 2023

The 41-year-old detailed how her one-year marriage to Grant Hughes felt phony and fell apart amid her grueling fertility issues. She also explained how her recovery from that relationship led her to Harris, who simultaneously had been going through her own divorce from former teammate Ali Krieger.

Bush wrote that after her storybook wedding — which she doesn’t regret — she found herself “in the depths and heartbreak of the fertility process.” She kept all that private as she endured months of ultrasounds, hormone shots, blood draws that led to scar tissue in her veins and numerous egg retrievals, “while simultaneously realizing the person I had chosen to be my partner didn’t necessarily speak the same emotional language I did.”

The “Work in Progress” and “Drama Queens” podcast host said she felt something in her “seismically shift” about six months into that journey and “knew deep down that I absolutely had made a mistake,” ultimately filing for divorce after about 13 months of marriage. Her separation from Hughes, an entrepreneur and real estate investor, saw Bush moving to London “to get out of our house” and doing a play to “jump-start the joy” she had been chasing. (She withdrew from “2:22 A Ghost Story” in July 2023 due to illness.)

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The “Love, Victor” and “Chicago P.D.” actor moved back to her empty home in L.A. last summer and said that an ever-expanding group of women in her life started opening up about their own issues. That group included the “kind ear” of the U.S. Women’s National Team goalkeeper, whom she’d first met in 2019. She didn’t expect to find love there.

“I don’t know how else to say it other than: I didn’t see it until I saw it. And I think it’s very easy not to see something that’s been in front of your face for a long time when you’d never looked at it as an option and you had never been looked at as an option.”

It took other people in their “safe support bubble” to point out to Bush that she and Harris would finish each other’s sentences or be deeply affected by the same things, she wrote.

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Reports about the couple’s romance surfaced in October, months after they each filed for divorce. The “One Tree Hill” alum and the U.S. Women’s National Team goalkeeper reportedly went out on their first dinner date a couple of weeks prior, People reported at the time, and TMZ asserted that they were “officially a thing.”

In her essay, Bush shed light on that purported first date, which she described as a 4½-hour meal that was “truly one of the most surreal experiences of my life thus far.”

“I do know that for a sparkly moment I felt like maybe the universe had been conspiring for me,” she wrote. But navigating the judgment she felt in the public eye was disheartening.

“The ones who said I’d left my ex because I suddenly realized I wanted to be with women — my partners have known what I’m into for as long as I have (so that’s not it, y’all, sorry!),” she wrote, noting that she didn’t leave her marriage because of some random rendezvous but rather after a year of “doing the most soul-crushing work of my life.”

Actress Sophia Bush, right, and her fiancé Grant Hughes, left, take a public tour of the White House, Friday, April 29, 2022, in Washington. (AP Photo/Andrew Harnik)

Sophia Bush files for divorce from husband Grant Hughes after 13 months of marriage

Sophia Bush has filed for divorce from husband Grant Hughes. The news comes seven weeks after Hughes and the ‘One Tree Hill’ alum celebrated their first anniversary.

Aug. 4, 2023

Bush also fawned over her partner‘s integrity and love for her children. As for her identity, the life-long LGBTQIA+ ally described feeling at home with the queer community.

“I think I’ve always known that my sexuality exists on a spectrum. Right now I think the word that best defines it is queer,” she wrote. “I can’t say it without smiling, actually. And that feels pretty great.”

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