essay on how the universe began

How did the universe begin—and what were its early days like?

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.

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.

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.

A tiny, ghostly particle called a neutrino and its antimatter counterpart, an antineutrino, could shed some light on the matter, and two big experiments, called DUNE and Hyper-Kamiokande , are using these chargeless, nearly massless particles to try to solve the mystery.

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.

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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. Scientists have tried to glimpse this “cosmic dawn,” but the results have been mixed. Back in 2018, an Australian team announced detected signs of the first stars forming around 180 million years after the big bang, though other groups haven't been able to recreate their results. By 300 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 . To astronomers' surprise, the pace of expansion is accelerating . Estimates of the expansion rate vary, but data from the James Webb Space Telescope adds to a growing body of evidence that it's significantly faster than it should be.

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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Origins of the Universe 101

How old is the universe, and how did it begin? Throughout history, countless myths and scientific theories have tried to explain the universe's origins. The most widely accepted explanation is the big bang theory. Learn about the explosion that started it all and how the universe grew from the size of an atom to encompass everything in existence today.

Earth Science, Astronomy

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The early universe

All matter in the universe was formed in one explosive event 13.7 billion years ago – the Big Bang

The Big Bang

In 1929 the American astronomer Edwin Hubble discovered that the distances to far-away galaxies were proportional to their redshifts. Redshift occurs when a light source moves away from its observer: the light's apparent wavelength is stretched via the Doppler effect towards the red part of the spectrum. Hubble’s observation implied that distant galaxies were moving away from us, as the furthest galaxies had the fastest apparent velocities. If galaxies are moving away from us, reasoned Hubble, then at some time in the past, they must have been clustered close together.

Hubble’s discovery was the first observational support for Georges Lemaître’s Big Bang theory of the universe, proposed in 1927. Lemaître proposed that the universe expanded explosively from an extremely dense and hot state, and continues to expand today. Subsequent calculations have dated this Big Bang to approximately 13.7 billion years ago. In 1998 two teams of astronomers working independently at Berkeley, California observed that supernovae – exploding stars – were moving away from Earth at an accelerating rate. This earned them the Nobel prize in physics in 2011 . Physicists had assumed that matter in the universe would slow its rate of expansion; gravity would eventually cause the universe to fall back on its centre. Though the Big Bang theory cannot describe what the conditions were at the very beginning of the universe, it can help physicists describe the earliest moments after the start of the expansion.

In the first moments after the Big Bang, the universe was extremely hot and dense. As the universe cooled, conditions became just right to give rise to the building blocks of matter – the quarks and electrons of which we are all made. A few millionths of a second later, quarks aggregated to produce protons and neutrons. Within minutes, these protons and neutrons combined into nuclei. As the universe continued to expand and cool, things began to happen more slowly. It took 380,000 years for electrons to be trapped in orbits around nuclei, forming the first atoms. These were mainly helium and hydrogen, which are still by far the most abundant elements in the universe. Present observations suggest that the first stars formed from clouds of gas around 150–200 million years after the Big Bang. Heavier atoms such as carbon, oxygen and iron, have since been continuously produced in the hearts of stars and catapulted throughout the universe in spectacular stellar explosions called supernovae.

But stars and galaxies do not tell the whole story. Astronomical and physical calculations suggest that the visible universe is only a tiny amount (4%) of what the universe is actually made of. A very large fraction of the universe, in fact 26%, is made of an unknown type of matter called " dark matter ". Unlike stars and galaxies, dark matter does not emit any light or electromagnetic radiation of any kind, so that we can detect it only through its gravitational effects. 

An even more mysterious form of energy called “dark energy” accounts for about 70% of the mass-energy content of the universe. Even less is known about it than dark matter. This idea stems from the observation that all galaxies seems to be receding from each other at an accelerating pace, implying that some invisible extra energy is at work.

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Astronomy > How Did the Universe Begin?

How Did the Universe Begin?

When you look up at the night sky, what do you see?

If it's a clear night, you might see hundreds of thousands of tiny points of light, too numerous to count. Some are planets, some are stars, and some are even galaxies!  Where did all these cosmic objects come from? Discover the answer below and  play a game ! 

Edwin Hubble looking through the telescope at Mt. Wilson Observatory in 1924.

In the 1920s in California, astronomer  Edwin Hubble observed distant galaxies using an extremely powerful telescope . He made two mind-boggling discoveries.

First, Hubble figured out that the Milky Way isn’t the only galaxy.  He realized that faint, cloud-like objects in the night sky are actually other galaxies far, far away. The Milky Way is just one of billions of galaxies.

Second, Hubble discovered that the galaxies are constantly moving away from each other.  In other words, the universe is expanding. The biggest thing that we know about is getting bigger all the time.

A few years later,  Belgian astronomer Georges Lemaître used Hubble‘s amazing discoveries to suggest an answer to a big astronomy question: How did the universe begin?

If the universe is always getting bigger, then long ago it was smaller. And long, LONG ago, it was much smaller. That means billions of years ago, everything in the universe was contained in a tiny ball that exploded! Wow!

This breakthrough idea later became known as the  Big Bang!

The  Big Bang  was the moment 13.8 billion years ago when the universe began as a tiny, dense, fireball that exploded. Most astronomers use the Big Bang theory to explain how the universe began. But what caused this explosion in the first place is still a mystery.

So, what has happened since the Big Bang?

Since the Big Bang, the universe has been expanding. In the early years, everything was made of gas. This gas, mostly hydrogen and helium, expanded and cooled. Over billions of years, gravity caused gas and dust to form galaxies, stars , planets, and more.

The matter that spread out from the Big Bang developed into everything in the universe, including you. You are made of star stuff!

Timeline of the Universe

Astronomers have figured out that the universe is about 13 billion years old. (We’d better skip the candles on the birthday cake!) They have also determined, approximately, when different cosmic events happened, such as when our galaxy and our planet formed.

Can you put these cosmic events in order from the oldest to the most recent? To play, click and drag the pictures left or right to place them in the correct order. 

Can you put these cosmic events in order from the oldest to the most recent? To play, click and drag the pictures up or down to place them in the correct order.

You got it!  Check out the timeline below to explore exactly when these cosmic events occurred. See how the earliest humans didn't even appear until 1.8 million years ago? That's just a blink of an eye in the history of the universe!

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Image Credits:

Milky Way over Thailand, ©  Matipon Tangmatitham ; Hubble at telescope, courtesy of NASA; George LeMaitre illustration by Amanda Duffy © AMNH; Icon illustrations by Daryl Collins © AMNH.

The history of the universe: Big Bang to now in 10 easy steps

Take a trip through time to discover the history of the universe.

Step 1: How it all started

Step 2: the universe's first growth spurt, step 3: too hot to shine, step 4: let there be light, step 5: emerging from the cosmic dark ages, step 6: more stars and more galaxies, step 7: birth of our solar system, step 8: the invisible stuff in the universe, step 9: the expanding and accelerating universe, step 10: we still need to know more, additional resources, bibliography.

The history of the universe and how it evolved is broadly accepted as the Big Bang model, which states that the universe began as an incredibly hot, dense point roughly 13.7 billion years ago. So, how did the universe go from being fractions of an inch (a few millimeters) across to what it is today? Here is a breakdown of the Big Bang to now in 10 easy-to-understand steps.

The Big Bang was not an explosion in space, as the theory's name might suggest. Instead, it was the appearance of space everywhere in the universe, researchers have said. According to the Big Bang theory, the universe was born as a very hot, very dense, single point in space. Cosmologists are unsure what happened before this moment, but with sophisticated space missions, ground-based telescopes and complicated calculations, scientists have been working to paint a clearer picture of the early universe and its formation. A key part of this comes from observations of the cosmic microwave background , which contains the afterglow of light and radiation left over from the Big Bang. This relic of the Big Bang pervades the universe and is visible to microwave detectors, which allows scientists to piece together clues of the early universe. In 2001, NASA launched the Wilkinson Microwave Anisotropy Probe (WMAP) mission to study the conditions as they existed in the early universe by measuring radiation from the cosmic microwave background. Among other discoveries, WMAP was able to determine the age of the universe — about 13.7 billion years old.

When the universe was very young — something like a hundredth of a billionth of a trillionth of a trillionth of a second (whew!) — it underwent an incredible growth spurt. During this burst of expansion, which is known as inflation, the universe grew exponentially and doubled in size at least 90 times.

"The universe was expanding, and as it expanded, it got cooler and less dense," David Spergel, a theoretical astrophysicist at Princeton University in Princeton, N.J., told SPACE.com. After inflation, the universe continued to grow, but at a slower rate. 

As space expanded, the universe cooled and matter formed.

Light chemical elements were created within the first three minutes of the universe's formation. As the universe expanded, temperatures cooled and protons and neutrons collided to make deuterium, which is an isotope of hydrogen. Much of this deuterium combined to make helium.

For the first 380,000 years after the Big Bang, however, the intense heat from the universe's creation made it essentially too hot for light to shine. Atoms crashed together with enough force to break up into a dense, opaque plasma of protons, neutrons and electrons that scattered light like fog.

About 380,000 years after the Big Bang, matter cooled enough for electrons to combine with nuclei to form neutral atoms. This phase is known as "recombination," and the absorption of free electrons caused the universe to become transparent. The light that was unleashed at this time is detectable today in the form of radiation from the cosmic microwave background. Yet, the era of recombination was followed by a period of darkness before stars and other bright objects were formed.

Roughly 400 million years after the Big Bang, the universe began to come out of its dark ages. This period in the universe's evolution is called the age of re-ionization. This dynamic phase was thought to have lasted more than a half-billion years, but based on new observations, scientists think re-ionization may have occurred more rapidly than previously thought. During this time, clumps of gas collapsed enough to form the very first stars and galaxies. The emitted ultraviolet light from these energetic events cleared out and destroyed most of the surrounding neutral hydrogen gas. The process of re-ionization, plus the clearing of foggy hydrogen gas, caused the universe to become transparent to ultraviolet light for the first time.

Astronomers comb the universe looking for the most far-flung and oldest galaxies to help them understand the properties of the early universe. Similarly, by studying the cosmic microwave background, astronomers can work backwards to piece together the events that came before. Data from older missions like WMAP and the Cosmic Background Explorer (COBE), which launched in 1989, and missions still in operation, like the Hubble Space Telescope, which launched in 1990, all help scientists try to solve the most enduring mysteries and answer the most debated questions in cosmology.

Our solar system is estimated to have been born a little after 9 billion years after the Big Bang, making it about 4.6 billion years old. According to current estimates, the sun is one of more than 100 billion stars in our Milky Way galaxy alone, and orbits roughly 25,000 light-years from the galactic core.

Many scientists think the sun and the rest of our solar system was formed from a giant, rotating cloud of gas and dust known as the solar nebula. As gravity caused the nebula to collapse, it spun faster and flattened into a disk. During this phase, most of the material was pulled toward the center to form the sun.

In the 1960s and 1970s, astronomers began thinking that there might be more mass in the universe than what is visible. Vera Rubin , an astronomer at the Carnegie Institution of Washington, observed the speeds of stars at various locations in galaxies. Basic Newtonian physics implies that stars on the outskirts of a galaxy would orbit more slowly than stars at the center, but Rubin found no difference in the velocities of stars farther out. In fact, she found that all stars in a galaxy seem to circle the center at more or less the same speed. This mysterious and invisible mass became known as dark matter . Dark matter is inferred because of the gravitational pull it exerts on regular matter. One hypothesis states the mysterious stuff could be formed by exotic particles that don't interact with light or regular matter, which is why it has been so difficult to detect. 

In the 1920s, astronomer Edwin Hubble made a revolutionary discovery about the universe. Using a newly constructed telescope at the Mount Wilson Observatory in Los Angeles, Hubble observed that the universe is not static, but rather is expanding. Decades later, in 1998, the prolific space telescope named after the famous astronomer, the Hubble Space Telescope , studied very distant supernovas and found that, a long time ago, the universe was expanding more slowly than it is today. This discovery was surprising because it was long thought that the gravity of matter in the universe would slow its expansion, or even cause it to contract.

– How big is the universe?

– What is the coldest place in the universe?

– How many black holes are there in the universe?

– What color is the universe?

Dark energy is thought to be the strange force that is pulling the cosmos apart at ever-increasing speeds, but it remains undetected and shrouded in mystery. The existence of this elusive energy, which is thought to make up 80% of the universe, is one of the most hotly debated topics in cosmology.

While much has been discovered about the creation and evolution of the universe, there are enduring questions that remain unanswered. Dark matter and dark energy remain two of the biggest mysteries, but cosmologists continue to probe the universe in hopes of better understanding how it all began.

The James Webb Space Telescope (JWST), launched in 2021, will continue the hunt for the elusive dark matter, as well as peering back to the beginning of time and the evolution of the universe using its infrared instruments.

For more information about the evolution of the universe check out, " The History of the Universe " by David H. Lyth or " A Brief History of Time " by Stephen Hawking. You can also keep up to date with the discoveries of JWST, visit NASA's dedicated webpage or the European Space Agency's dedicated webpage . 

Scientific American, " The Evolution of the Universe ", October 1994. 

Walter Perry, " Origin and Evolution of the Universe ", Journal of Modern Physics, Volume 12, November 2021.

Bharat Ratra and Michael S. Vogeley, " The Beginning and Evolution of the Universe ", Publications of the Astronomical Society of the Pacific, Volume 120, March 2008, 

NASA, " Brief History of the Universe ", December 2006. 

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Denise Chow is a former Space.com staff writer who then worked as assistant managing editor at Live Science before moving to NBC News as a science reporter, where she focuses on general science and climate change. She spent two years with Space.com, writing about rocket launches and covering NASA's final three space shuttle missions, before joining the Live Science team in 2013. A Canadian transplant, Denise has a bachelor's degree from the University of Toronto, and a master's degree in journalism from New York University. At NBC News, Denise covers general science and climate change.

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The Big Bang Theory: How the Universe Began

The Big Bang theory represents cosmologists ' best attempts to reconstruct the 14 billion year story of the universe based on the sliver of existence visible today.

Different people use the term "Big Bang" in different ways. Most generally, it illustrates the arc of the observable universe as it thinned out and cooled down from an initially dense, hot state. This description boils down to the idea that the cosmos is expanding, a broad principle analogous to survival of the fittest in biology that few would consider debatable.

More specifically, the Big Bang can also refer to the birth of the observable universe itself — the moment something changed, kickstarting the events that led to today. Cosmologists have argued for decades about the details of that fraction of a second, and the discussion continues today. [ From Big Bang to Present: Snapshots of Our Universe Through Time ]

The classic Big Bang theory

For most of human history, observers of the sky assumed it eternal and unchanging. Edwin Hubble dealt this story an experimental blow in the 1920s when his observations showed both that galaxies outside the Milky Way existed, and that their light appeared stretched — a sign that they were rushing away from Earth .

George Lemaître, a contemporary Belgian physicist, interpreted data from Hubble and others as evidence of an expanding universe, a possibility permitted by Einstein's recently published field equations of general relativity . Thinking backwards, Lemaître inferred that today's separating galaxies must have started out together in what he called the "primeval atom."

The first public use of the modern term for Lemaître's idea actually came from a critic — English astronomer Fred Hoyle. On March 28, 1949, Hoyle coined the phrase during a defense of his preferred theory of an eternal universe that created matter to cancel out the dilution of expansion. Hoyle said the notion that "all matter of the universe was created in one big bang at a particular time in the remote past," was irrational. In later interviews, Hoyle denied intentionally inventing a slanderous name , but the moniker stuck, much to the frustration of some.

"The Big Bang is a really bad term," said Paul Steinhardt, a cosmologist at Princeton. "The Big Stretch would capture the right idea." The mental image of an explosion causes all kinds of confusion, according to Steinhardt. It implies a central point, an expanding frontier, and a scene where light shrapnel flies faster than heavier chunks. But an expanding universe looks nothing like that, he said. There's no center, no edge, and galaxies large and small all slide apart in the same way (although more distant galaxies move away faster under the cosmologically recent influence of dark energy).

Regardless of its name, the Big Bang theory found widespread acceptance for its unparalleled ability to explain what we see. The balance of light with particles like protons and neutrons during the first 3 minutes, for instance, let early elements form at a rate predicting the current amounts of helium and other light atoms.

"There was a small window in time where it was possible for nuclei to form," said Glennys Farrar, a cosmologist at New York University. "After that, the universe kept expanding and they couldn't find each other, and before [the window] it was too hot."

A cloudy plasma filled the universe for the next 378,000 years, until further cooling let electrons and protons form neutral hydrogen atoms, and the fog cleared. The light emitted during this process, which has since stretched into microwaves, is the earliest known object researchers can study directly. Known as the cosmic microwave background (CMB) radiation, many researchers consider it the strongest evidence for the Big Bang.

An explosive update

But as cosmologists pushed farther back into the universe's first moments, the story unraveled. General relativity's equations suggested an initial speck of unlimited heat and density — a singularity. In addition to not making much physical sense, a singular origin didn't match the smooth, flat CMB. Fluctuations in the speck's formidable temperature and density would have produced swaths of sky with different properties , but the CMB's temperature varies by just a fraction of a degree. The curvature of space-time also looks quite flat, which implies an initially near-perfect balance of matter and curvature that most cosmologists find improbable.

Alan Guth proposed a new picture of the first fraction of a second in the 1980s, suggesting that the universe spent its earliest moments growing exponentially faster than it does today. At some point this process stopped, and putting on the brakes produced a dense and hot (but not infinitely so) mess of particles that takes the place of the singularity. "In my own mind I think of that as the Big Bang, when the universe got hot," Farrar said.

The inflation theory, as it's called, now has a plethora of competing models. Although no one knew much about what made the universe expand so rapidly, the theory has grown popular for its ability to explain the seemingly improbable featureless CMB: Inflation preserved minor fluctuations (which developed into today's galaxy clusters), while flattening the major ones. "It's a very sweet story," Steinhardt said, who helped develop the theory. "It's the one we tell our kids."

Beyond inflation

Recent research has introduced two wrinkles into the inflation theory's cosmic narrative. Work by Steinhardt and others suggests that inflation would have stopped in some regions (such as our observable universe) but continued in others, producing an array of separate territories with "every conceivable set of cosmological properties," as Steinhardt puts it. Many physicists find this " multiverse " picture distasteful, because it makes an infinite number of untestable predictions.

On the experimental front, cosmologists expect that inflation should have produced galaxy-spanning gravitational waves in the CMB just as it produced slight temperature and density variations. Current experiments should be sensitive enough to find them, but the primordial space-time ripples haven't shown up (despite one false alarm in 2014 ).

Many researchers await more precise CMB measurements that could kill, or validate , the many inflation models that still stand. Other physicists, however, don't see the cosmos's smoothness as a problem at all — it started off uniform and needs no explanation .

While experimentalists strive for new levels of precision, some theorists have turned away from inflation to seek other ways to squash the universe flat. Steinhardt, for instance, is working on a "big bounce" model, which pushes the starting clock back even further, to an earlier period of contraction that smoothed space-time and set the stage for an explosive expansion. He hopes that before too long, new signatures, in addition to problems like the lack of primordial gravitational waves, will set cosmologists up with a new creation story to tell. "Are there any other observable features to look for?" Steinhardt said, "Ask me again in a few years and I hope to have an answer."

Additional resources :

• Fermilab's Don Lincoln explains exactly what the Big Bang theory does, and doesn't say.
• Read about why some think it's odd how flat the universe is .
• PBS's SpaceTime explains why inflation has proved such an attractive idea .

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Charlie Wood is a staff writer at Quanta Magazine, where he covers physics both on and off the planet. In addition to Live Science, his work has also appeared in Popular Science, Scientific American, The Christian Science Monitor, and other publications. Previously, he taught physics and English in Mozambique and Japan, and he holds an undergraduate degree in physics from Brown University. 

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Early Universe

The universe began 13.8 billion years ago, and in its early years, it looked completely different than it does now. For nearly 400,000 years, the entire cosmos was opaque, which means we have no direct observations of anything that happened during that time. Even after the universe became transparent, it was still a long time before the first stars and galaxies formed, leaving us with limited information about that period. Despite those problems, the early epochs of cosmic history are essential for everything that came after, leading researchers to find ways to figure out exactly what happened when our universe was in its infancy.

Center for Astrophysics | Harvard & Smithsonian scientists study the early universe in a variety of ways:

Hunting for signs of inflation using the twisting of CMB light called polarization. Even though this hypothetical rapid expansion of the universe happened a split-second after the Big Bang, it would have left observable traces behind. CfA researchers lead or are involved in CMB polarization observatories including the South Pole Telescope (SPT), the Keck Array, and the BICEP3 observatory. BICEP3 and Keck Array

Using the Murchison Wide-field Array (MWA) telescope, the Large-Aperture Experiment to Detect the Dark Ages (LEDA), and other observatories to look for the onset of reionization and the first stars. These instruments are designed to detect radio waves emitted by hydrogen gas during the cosmic “dark age”. Preparing to Study the Epoch of Reionization

Looking for different ways to test the predictions of various models of cosmic inflation, along with alternative theories to explain how the early universe behaved. Different theories predict different traces in the CMB, which can potentially be distinguished by sensitive observations. Theorists Propose a New Method to Probe the Beginning of the Universe

Hunting for traces of the first stars in the cosmos in surveys of galaxies and black holes. The earliest stars were likely very massive compared with their modern cousins, which means many exploded as supernovas and collapsed into black holes. Explosion Illuminates Invisible Galaxy in the Dark Ages

The Early Years

Until roughly 380,000 years after the Big Bang, the entire universe was a thick opaque cloud of plasma of electrons and nuclei. As the universe expanded, it cooled off enough to let the plasma become atoms, and the cosmos became transparent. We observe the light from this time as the cosmic microwave background (CMB).

The CMB is remarkably uniform in temperature all across the sky, which is surprising. Usually for two things to be exactly the same temperature, they need to be in contact. However, two points on the CMB on opposite sides of the sky would never have been close together since the Big Bang — unless something else was going on to connect them.

The most widely accepted hypothesis for that “something else” is cosmic inflation. In a tiny fraction of a second after the Big Bang, quantum fluctuations drove the universe to “inflate” much faster than the rate we observe at later eras. The part of the cosmos that became our observable universe was smaller than it would seem today, so the points opposite to each other on the sky now would have been in contact before inflation happened.

Much of the research on inflation involves understanding how it worked, and determining how we can detect its effects. For example, inflation would have created gravitational waves in the early universe, leaving small but potentially observable traces in the CMB. Observatories such as the South Pole Telescope (SPT) are looking for these effects.

This artist's impression traces the early history of Universe from with the Big Bang on the left to the first galaxies on the right. The black region in the middle is the "dark ages", the mysterious era setting the stage for the first stars to be born.

Cosmic Dark Ages and First Light

When the CMB formed, the ordinary matter in the universe transitioned from a hot opaque plasma to incandescent hydrogen and helium gas. Astronomers call this the “dark age” of the universe, since no stars had formed yet.

Researchers are using the best observatories in the world both to study the dark age and to find evidence for the first stars in the universe. As the first stars and black holes formed, they turned much of the hydrogen gas in the universe into plasma again , a process astronomers call “reionization”. The environment producing the earliest stars was radically different than star-forming regions today. The raw ingredients were almost exclusively hydrogen and helium, since stars themselves produce heavier elements through nuclear fusion .

Astronomers think the first stars may have been very massive compared with modern stars, and may have formed the first black holes in the cosmos. Individual stars are too small to be seen from so great a distance, so researchers look for indirect evidence about the nature of these objects, through how they influenced their surroundings.

Studying the dark ages and first stars is a way to understand the genealogy of all stars, including our own Sun. These original stars began the process of making most of the elements heavier than helium, which includes the atoms like oxygen and carbon necessary for life. The earliest stars, galaxies, and black holes changed the cloudy universe of the dark ages into the vast cosmic structures we see today.

• What happened in the early universe?
• Laboratory Astrophysics
• Theoretical Astrophysics
• Computational Astrophysics
• Extragalactic Astronomy
• The Energetic Universe
• Atomic and Molecular Physics
• Radio and Geoastronomy

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• 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

May 24, 2023

The Universe Began with a Bang, Not a Bounce, New Studies Find

New research pokes holes in the idea that the cosmos expanded and then contracted before beginning again

By James Riordon

Science History Images/Alamy Stock Photo

How did the universe start? Did we begin with a big bang, or was there a bounce? Might the cosmos evolve in a cycle of expansion and collapse , over and over for all eternity? Now, in two papers, researchers have poked holes in different models of a so-called bouncing universe , suggesting the universe we see around us is probably a one-and-done proposition.

Bouncing universe proponents argue that our cosmos didn’t emerge on its own out of nothing. Instead, advocates claim, a prior universe shrunk in on itself and then regrew into the one we live in. This may have happened once or, according to some theories, an infinite number of times .

So which scenario is correct? The most widely accepted explanation for the history of the universe has it beginning with a big bang, followed by a period of rapid expansion known as cosmic inflation. According to that model, the glow left over from when the universe was hot and young, called the cosmic microwave background (CMB), should look pretty much the same no matter which direction you face. But data from the Planck space observatory, which mapped the CMB from 2009 to 2013, showed unexpected variations in the microwave radiation. They could be meaningless statistical fluctuations in the temperature of the universe, or they might be signs of something interesting going on.

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One possibility is that the CMB anomalies imply that the universe didn’t emerge out of nothing. Instead it came about after a prior universe collapsed and bounced back to create the space and time we live in today.

Bouncing universe models can explain these CMB patterns as well as account for lingering quibbles about the standard description of the universe’s origin and evolution. In particular, the big bang model of the universe begins with a singularity—a point that appeared out of nothing and contained the precursors of everything in the universe in a region so small that it had essentially no size at all. The idea is that the universe grew from the singularity and, after inflation, settled into the more gradually expanding universe we see today. But singularities are problematic because physics, and math itself, doesn’t make sense when everything is packed into a point that’s infinitely small. Many physicists prefer to avoid singularities.

One bouncing model that averts singularities and makes the CMB anomalies a little less anomalous is known as loop quantum cosmology (LQC). It relies on a bridge between classical physics and quantum mechanics known as loop quantum gravity, which posits that the force of gravity peters out at very small distances rather than increasing to infinity. “Cosmological models inspired by loop quantum gravity can solve some problems,” says University of Geneva cosmologist Ruth Durrer, “especially the singularity problem.” Durrer co-authored one of the two new studies on bouncing universes. In it, she and her colleagues looked for astronomical signs of such models .

In an LQC model, a precursor to our universe might have contracted under the force of gravity until it became extremely compact. Eventually quantum mechanics would have taken over. Instead of collapsing to a singularity, the universe would have started to expand again and may even have gone through an inflationary phase, as many cosmologists believe ours did.

If that happened, says physicist Ivan Agullo of Louisiana State University, it should have left a mark on the universe. Agullo, who was not affiliated with either of the recent analyses, has proposed that the mark would turn up in a feature in the CMB data known as the “bispectrum,” a measure of how different portions of the universe would have interacted in a bouncing scenario. The bispectrum would not be apparent in an image of the CMB, but it would show up in analyses of the frequencies in the ancient CMB microwaves.

“If observed,” Agullo says, the bispectrum “would serve as a smoking gun for the existence of a bounce instead of a bang.” Agullo’s group previously calculated the bispectrum as it would have appeared shortly after a cosmic bounce. Durrer and her colleagues took the calculation further, but when they compared it with the present-day Planck CMB data, there was no significant sign of a bispectrum imprint.

Although lots of other bouncing cosmos models may still be viable, the failure to find a significant bispectrum means that models that rely on LQC to deal with the anomalies in the CMB can be ruled out. It’s a sad result for Agullo, who had high hopes of finding concrete evidence of a bouncing universe. He still considers many bouncing universe models viable, however. And Paola Delgado, a cosmology Ph.D. candidate at Jagiellonian University in Poland, who worked on the new analysis that was co-authored by Durrer, says there’s one potential upside. “I heard for a long time that [attempts to merge quantum physics and cosmology] cannot be tested,” Delgado says. “I think it was really nice to see that for some classes of models, you still have some contact with observations.”

Ruling out signs of an LQC-driven cosmic bounce in Planck data means the CMB anomalies remain unexplained. But an even larger cosmic issue lingers: Did the universe have a beginning at all? As far as advocates of the big bang are concerned, it did. But that leaves us with the inscrutable singularity that started everything off.

Alternatively, according to theories of so-called cyclic cosmologies, the universe is immortal and is going through endless bounces. Although a bouncing universe may experience one or more cycles, a truly cyclic universe has no beginning and no end. It consists of a series of bounces that go back for an infinite number of cycles and will continue for an infinite number more. And because such a universe doesn’t have a beginning, there’s no big bang and no singularity.

The study that Durrer and Delgado co-authored doesn’t rule out immortal cyclic cosmologies. Plenty of theories describe such a bouncing universe in ways that would be difficult or impossible to distinguish from the “big bang plus inflation” model by looking at Planck CMB data.

But a critical flaw lurks in the idea of an eternally cycling universe, according to physicist William Kinney of the University at Buffalo, who co-authored the second recent analysis. That flaw is entropy, which builds up as a universe bounces. Often thought of as the amount of disorder in a system, entropy is related to the system’s amount of useful energy: the higher the entropy, the less energy available. If the universe increases in entropy and disorder with each bounce, the amount of usable energy available decreases each time. In that case, the cosmos would have had larger amounts of useful energy in earlier epochs. If you extrapolate back far enough, that implies a big bang–like beginning with an infinitely small amount of entropy, even for a universe that subsequently goes through cyclic bounces. (If you’re wondering how this scenario doesn’t violate the law of conservation of energy, we’re talking about available energy. Although the total amount of energy in the cosmos remains static, the amount that can do useful work decreases with increasing entropy.)

New cyclic models get around the problem, Kinney says, by requiring that the universe expands by a lot with each cycle. The expansion allows the universe to smooth out, dissipating the entropy before collapsing again. Although this explanation solves the entropy problem, Kinney and his University at Buffalo co-author Nina Stein calculated in their recent paper that the solution itself ensures that the universe is not immortal . “I feel like we’ve demonstrated something fundamental about the universe,” Kinney says, “which is that it probably had a beginning.” That implies a big bang occurred at some point, even if that event happened many bouncing universes ago, which in turn suggests that it took a singularity to get everything going in the first place.

Kinney’s paper is the latest in the debate over cyclic universes, but proponents of a universe without beginning or end have yet to respond in the scientific literature. Two leading proponents of a cyclic universe, astrophysicists Paul Steinhardt of Princeton University and Anna Ijjas of New York University, declined to comment for this article. If the history of the debate is any indication , though, we may soon hear of a work-around to counter Kinney’s analysis.

Some physicists say the Planck data only rule out a bounce under a loop quantum cosmology model that can explain away the CMB anomalies through the bispectrum, not other LQC bounce models that address anomalies using different mechanisms. Cosmologist Nelson Pinto-Neto of the Brazilian Center for Physics Research, who has studied bouncing and other cyclic models, agrees that LQC bounces that account for the CMB anomalies are likely off the table now, but he’s more sanguine on the question of a cyclic universe. “Existence is a fact. We are all here and now. Nonexistence is an abstraction of the human mind,” Nelson says. “This is the reason I think that a [cyclic universe], which has always existed, is simpler than one that has been created. However, as a scientist, I must be open to both possibilities.”

Editor’s Note (6/29/23): This article was edited after posting to better clarify scientits’ views on loop quantum cosmology bouncing universe models that account for the cosmic microwave background. The text was previously amended on June 1 to better clarify Ivan Agullo’s position on bouncing universe models.

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National Academy of Sciences (US). Science and Creationism: A View from the National Academy of Sciences: Second Edition. Washington (DC): National Academies Press (US); 1999.

Science and Creationism: A View from the National Academy of Sciences: Second Edition.

• Hardcopy Version at National Academies Press

The Origin of the Universe, Earth, and Life

The term "evolution" usually refers to the biological evolution of living things. But the processes by which planets, stars, galaxies, and the universe form and change over time are also types of "evolution." In all of these cases there is change over time, although the processes involved are quite different.

In the late 1920s the American astronomer Edwin Hubble made a very interesting and important discovery. Hubble made observations that he interpreted as showing that distant stars and galaxies are receding from Earth in every direction. Moreover, the velocities of recession increase in proportion with distance, a discovery that has been confirmed by numerous and repeated measurements since Hubble's time. The implication of these findings is that the universe is expanding.

Hubble's hypothesis of an expanding universe leads to certain deductions. One is that the universe was more condensed at a previous time. From this deduction came the suggestion that all the currently observed matter and energy in the universe were initially condensed in a very small and infinitely hot mass. A huge explosion, known as the Big Bang, then sent matter and energy expanding in all directions.

This Big Bang hypothesis led to more testable deductions. One such deduction was that the temperature in deep space today should be several degrees above absolute zero. Observations showed this deduction to be correct. In fact, the Cosmic Microwave Background Explorer (COBE) satellite launched in 1991 confirmed that the background radiation field has exactly the spectrum predicted by a Big Bang origin for the universe.

As the universe expanded, according to current scientific understanding, matter collected into clouds that began to condense and rotate, forming the forerunners of galaxies. Within galaxies, including our own Milky Way galaxy, changes in pressure caused gas and dust to form distinct clouds. In some of these clouds, where there was sufficient mass and the right forces, gravitational attraction caused the cloud to collapse. If the mass of material in the cloud was sufficiently compressed, nuclear reactions began and a star was born.

Some proportion of stars, including our sun, formed in the middle of a flattened spinning disk of material. In the case of our sun, the gas and dust within this disk collided and aggregated into small grains, and the grains formed into larger bodies called planetesimals ("very small planets"), some of which reached diameters of several hundred kilometers. In successive stages these planetesimals coalesced into the nine planets and their numerous satellites. The rocky planets, including Earth, were near the sun, and the gaseous planets were in more distant orbits.

The ages of the universe, our galaxy, the solar system, and Earth can be estimated using modem scientific methods. The age of the universe can be derived from the observed relationship between the velocities of and the distances separating the galaxies. The velocities of distant galaxies can be measured very accurately, but the measurement of distances is more uncertain. Over the past few decades, measurements of the Hubble expansion have led to estimated ages for the universe of between 7 billion and 20 billion years, with the most recent and best measurements within the range of 10 billion to 15 billion years.

A disk of dust and gas, appearing as a dark band in this Hubble Space Telescope photograph, bisects a glowing nebula around a very young star in the constellation Taurus. Similar disks can be seen around other nearby stars and are thought to provide the (more...)

The age of the Milky Way galaxy has been calculated in two ways. One involves studying the observed stages of evolution of different-sized stars in globular clusters. Globular clusters occur in a faint halo surrounding the center of the Galaxy, with each cluster containing from a hundred thousand to a million stars. The very low amounts of elements heavier than hydrogen and helium in these stars indicate that they must have formed early in the history of the Galaxy, before large amounts of heavy elements were created inside the initial generations of stars and later distributed into the interstellar medium through supernova explosions (the Big Bang itself created primarily hydrogen and helium atoms). Estimates of the ages of the stars in globular clusters fall within the range of 11 billion to 16 billion years.

A second method for estimating the age of our galaxy is based on the present abundances of several long-lived radioactive elements in the solar system. Their abundances are set by their rates of production and distribution through exploding supernovas. According to these calculations, the age of our galaxy is between 9 billion and 16 billion years. Thus, both ways of estimating the age of the Milky Way galaxy agree with each other, and they also are consistent with the independently derived estimate for the age of the universe.

Radioactive elements occurring naturally in rocks and minerals also provide a means of estimating the age of the solar system and Earth. Several of these elements decay with half lives between 700 million and more than 100 billion years (the half life of an element is the time it takes for half of the element to decay radioactively into another element). Using these time-keepers, it is calculated that meteorites, which are fragments of asteroids, formed between 4.53 billion and 4.58 billion years ago (asteroids are small "planetoids" that revolve around the sun and are remnants of the solar nebula that gave rise to the sun and planets). The same radioactive time-keepers applied to the three oldest lunar samples returned to Earth by the Apollo astronauts yield ages between 4.4 billion and 4.5 billion years, providing minimum estimates for the time since the formation of the moon.

The oldest known rocks on Earth occur in northwestern Canada (3.96 billion years), but well-studied rocks nearly as old are also found in other parts of the world. In Western Australia, zircon crystals encased within younger rocks have ages as old as 4.3 billion years, making these tiny crystals the oldest materials so far found on Earth.

The best estimates of Earth's age are obtained by calculating the time required for development of the observed lead isotopes in Earth's oldest lead ores. These estimates yield 4.54 billion years as the age of Earth and of meteorites, and hence of the solar system.

The origins of life cannot be dated as precisely, but there is evidence that bacteria-like organisms lived on Earth 3.5 billion years ago, and they may have existed even earlier, when the first solid crust formed, almost 4 billion years ago. These early organisms must have been simpler than the organisms living today. Furthermore, before the earliest organisms there must have been structures that one would not call "alive" but that are now components of living things. Today, all living organisms store and transmit hereditary information using two kinds of molecules: DNA and RNA. Each of these molecules is in turn composed of four kinds of subunits known as nucleotides. The sequences of nucleotides in particular lengths of DNA or RNA, known as genes, direct the construction of molecules known as proteins, which in turn catalyze biochemical reactions, provide structural components for organisms, and perform many of the other functions on which life depends. Proteins consist of chains of subunits known as amino acids. The sequence of nucleotides in DNA and RNA therefore determines the sequence of amino acids in proteins; this is a central mechanism in all of biology.

Experiments conducted under conditions intended to resemble those present on primitive Earth have resulted in the production of some of the chemical components of proteins, DNA, and RNA. Some of these molecules also have been detected in meteorites from outer space and in interstellar space by astronomers using radio-telescopes. Scientists have concluded that the "building blocks of life" could have been available early in Earth's history.

An important new research avenue has opened with the discovery that certain molecules made of RNA, called ribozymes, can act as catalysts in modem cells. It previously had been thought that only proteins could serve as the catalysts required to carry out specific biochemical functions. Thus, in the early prebiotic world, RNA molecules could have been "autocatalytic"—that is, they could have replicated themselves well before there were any protein catalysts (called enzymes).

Laboratory experiments demonstrate that replicating autocatalytic RNA molecules undergo spontaneous changes and that the variants of RNA molecules with the greatest autocatalytic activity come to prevail in their environments. Some scientists favor the hypothesis that there was an early "RNA world," and they are testing models that lead from RNA to the synthesis of simple DNA and protein molecules. These assemblages of molecules eventually could have become packaged within membranes, thus making up "protocells"—early versions of very simple cells.

For those who are studying the origin of life, the question is no longer whether life could have originated by chemical processes involving nonbiological components. The question instead has become which of many pathways might have been followed to produce the first cells.

Will we ever be able to identify the path of chemical evolution that succeeded in initiating life on Earth? Scientists are designing experiments and speculating about how early Earth could have provided a hospitable site for the segregation of molecules in units that might have been the first living systems. The recent speculation includes the possibility that the first living cells might have arisen on Mars, seeding Earth via the many meteorites that are known to travel from Mars to our planet.

Of course, even if a living cell were to be made in the laboratory, it would not prove that nature followed the same pathway billions of years ago. But it is the job of science to provide plausible natural explanations for natural phenomena. The study of the origin of life is a very active research area in which important progress is being made, although the consensus among scientists is that none of the current hypotheses has thus far been confirmed. The history of science shows that seemingly intractable problems like this one may become amenable to solution later, as a result of advances in theory, instrumentation, or the discovery of new facts.

Creationist Views of the Origin of the Universe, Earth, and Life

Many religious persons, including many scientists, hold that God created the universe and the various processes driving physical and biological evolution and that these processes then resulted in the creation of galaxies, our solar system, and life on Earth. This belief, which sometimes is termed "theistic evolution," is not in disagreement with scientific explanations of evolution. Indeed, it reflects the remarkable and inspiring character of the physical universe revealed by cosmology, paleontology, molecular biology, and many other scientific disciplines.

The advocates of "creation science" hold a variety of viewpoints. Some claim that Earth and the universe are relatively young, perhaps only 6,000 to 10,000 years old. These individuals often believe that the present physical form of Earth can be explained by "catastrophism," including a worldwide flood, and that all living things (including humans) were created miraculously, essentially in the forms we now find them.

Other advocates of creation science are willing to accept that Earth, the planets, and the stars may have existed for millions of years. But they argue that the various types of organisms, and especially humans, could only have come about with supernatural intervention, because they show "intelligent design."

In this booklet, both these "Young Earth" and "Old Earth" views are referred to as "creationism" or "special creation."

There are no valid scientific data or calculations to substantiate the belief that Earth was created just a few thousand years ago. This document has summarized the vast amount of evidence for the great age of the universe, our galaxy, the solar system, and Earth from astronomy, astrophysics, nuclear physics, geology, geochemistry, and geophysics. Independent scientific methods consistently give an age for Earth and the solar system of about 5 billion years, and an age for our galaxy and the universe that is two to three times greater. These conclusions make the origin of the universe as a whole intelligible, lend coherence to many different branches of science, and form the core conclusions of a remarkable body of knowledge about the origins and behavior of the physical world.

Nor is there any evidence that the entire geological record, with its orderly succession of fossils, is the product of a single universal flood that occurred a few thousand years ago, lasted a little longer than a year, and covered the highest mountains to a depth of several meters. On the contrary, intertidal and terrestrial deposits demonstrate that at no recorded time in the past has the entire planet been under water. Moreover, a universal flood of sufficient magnitude to form the sedimentary rocks seen today, which together are many kilometers thick, would require a volume of water far greater than has ever existed on and in Earth, at least since the formation of the first known solid crust about 4 billion years ago. The belief that Earth's sediments, with their fossils, were deposited in an orderly sequence in a year's time defies all geological observations and physical principles concerning sedimentation rates and possible quantities of suspended solid matter.

Geologists have constructed a detailed history of sediment deposition that links particular bodies of rock in the crust of Earth to particular environments and processes. If petroleum geologists could find more oil and gas by interpreting the record of sedimentary rocks as having resulted from a single flood, they would certainly favor the idea of such a flood, but they do not. Instead, these practical workers agree with academic geologists about the nature of depositional environments and geological time. Petroleum geologists have been pioneers in the recognition of fossil deposits that were formed over millions of years in such environments as meandering rivers, deltas, sandy barrier beaches, and coral reefs.

The example of petroleum geology demonstrates one of the great strengths of science. By using knowledge of the natural world to predict the consequences of our actions, science makes it possible to solve problems and create opportunities using technology. The detailed knowledge required to sustain our civilization could only have been derived through scientific investigation.

The arguments of creationists are not driven by evidence that can be observed in the natural world. Special creation or supernatural intervention is not subjectable to meaningful tests, which require predicting plausible results and then checking these results through observation and experimentation. Indeed, claims of "special creation" reverse the scientific process. The explanation is seen as unalterable, and evidence is sought only to support a particular conclusion by whatever means possible.

• Cite this Page National Academy of Sciences (US). Science and Creationism: A View from the National Academy of Sciences: Second Edition. Washington (DC): National Academies Press (US); 1999. The Origin of the Universe, Earth, and Life.
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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?

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

The Beginning of The Universe

• Categories: Creation Myth Universe

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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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