The Science of the Big Bang
Many of the major questions that exist about the big bang model of cosmology—such as what came before the big bang, do other universes exist, and how did the fundamental forces unite in those first fractions of a second—are simply curiosities to many people outside of the science world.
And yet, the answers, when we find them, will fundamentally shape the way we understand how we came to be where we are today. Few questions matter more.
Before the Scientific Revolution, there were significant knowledge gaps and technological barriers to understanding the first moments of the universe. Understanding the universe’s early history required telescopes and spectroscopes, among other equipment. It required a nuanced understanding of the properties of light, chemical elements, and atoms.
It required a dramatic twentieth-century revision of the scope of the universe. All of these scientific elements came together when Albert Einstein proposed a new theory of gravity that raised curious questions about the future—and past—of the universe.
OPPONENTS of the BIG BANG THEORY
The big bang theory, like most scientific theories, has its opponents. While most of the opposition comes from the realm of religious people who favor a literal interpretation of their religious texts, there have been small camps of scientists who held out against the big bang model of cosmology into the twentieth century.
The big bang theory of cosmology is the standard model accepted by a majority of scientists. However, the steady state theorist Fred Hoyle continued to oppose the big bang theory throughout his life, as did his Synthesis of the Elements in Stars coauthors Margaret and Geoffrey Burbidge.
Geoffrey Burbidge created a revision of the steady state theory called the “quasi-Steady State.” The new version of the theory proposes that the universe expands and contracts over one-hundred-billion-year cycles.
According to the Burbidges, if stars can eject new types of matter as their paper with Hoyle showed, perhaps galaxies could also eject huge collections of matter to create new galaxies. Margaret Burbidge spent years observing quasars, theorizing that they could be a candidate for these ejected collections of matter.
In a 2005 interview with Discover magazine, Geoffrey Burbidge said:
The present situation in cosmology is that most people like to believe they know what the skeleton looks like, and they’re putting flesh on the bones. And Fred [Hoyle] and I would continuously say, we don’t even know what the skeleton looks like.
We don’t know whether it’s got 20 heads instead of one, or 60 arms or legs. It’s probable that the universe we live in is not the way I think it is or the way the Big Bang people think it is.
In 200 years, somebody is going to say how stupid we were. In other words, Burbidge believes that too many scientists have prematurely accepted the current big bang model of cosmology. Geoffrey Burbidge has since died, and Margaret Burbidge is in her late nineties. Few other scientists have continued to oppose the big bang theory.
The predominant opposition to the big bang comes from those who disagree due to religious reasons.
The Institute for Creation Research, which bills itself as a “leader in scientific research within the context of biblical creation,” publishes articles such as “The Big Bang Theory Collapses” that characterize the big bang theory as irreparably flawed—though scientific studies show otherwise.
The ICR ultimately argues against any scientific cosmology, including the quasi-steady state model, because they all contradict the ICR’s belief that the Christian god created heaven and Earth.
The ICR is just one example of literal religious thinkers who oppose the big bang theory. There are many others who dismiss the model for similar reasons.
There are also many religious people who do not dismiss the big bang theory. Georges Lemaitre was himself a Catholic priest, and many religious thinkers from various faiths see no opposition between the big bang model of cosmology and their religious beliefs.
Some see their creator as the creative force that sparked the big bang, while others, as Lemaitre, consider the religious and scientific realms as entirely separate and able to exist separately without conflict.
THE BIG BANG THEORY Chronology
13.8 billion years ago Our universe begins with a big bang followed by cosmic inflation; light elements from within the first three seconds
13.76 billion years ago Recombination takes place, and light can travel freely through the universe; the cosmic dark ages begin
13.57 billion years ago The first stars form, ending the cosmic dark ages
5 billion years ago The sun is born
3.8 billion years ago Earliest life-forms appear on Earth
13th century Glass lenses developed
1543 Nicolaus Copernicus publishes On the Revolutions of the Heavenly Spheres with his heliocentric theory of the solar system
1572 Tycho Brahe observes a supernova, which shows that changes do happen in the celestial realm
1577 Brahe observes a comet and calculates that it had passed by Venus, another crack in the Aristotelian model of unchanging, crystalline spheres
1608 First two patents are filed for telescope designs, both by spectacle makers in the Netherlands
1609 Galileo Galilei builds a telescope and begins observing the sky; Johannes Kepler publishes his first two laws of planetary motion
1610 Galileo discovers Jupiter’s four largest moons and the phases of Venus
1633 Galileo is found guilty of heresy for supporting the heliocentric model of the universe and sentenced to house arrest for the rest of his life
1665 Sir Isaac Newton shows that white light contains all of the colors of the rainbow
1668 Newton builds the first reflecting telescope
1676 Ole Römer measures the speed of light
1800 Sir William Herschel discovers the infrared light
1911 Ernest Rutherford discovers the atomic nucleus
1915 Albert Einstein publishes his general theory of relativity
1924 Edwin Hubble discovers that other galaxies exist outside of the Milky Way
1927 Georges Lemaitre publishes his first paper on an expanding universe
1929 Hubble discovers that galaxies are receding at speeds directly correlated to their distance
1931 Lemaitre publishes an article in the journal Nature with his theory of the “primeval atom”
1948 George Gamow and Ralph Alpher publish “On the Origin of Chemical Elements” theorizing how elements are formed from the big bang
1957 Fred Hoyle and three colleagues publish “Synthesis of the Elements in Stars” showing how the heavier elements are formed
1965 Arno Penzias and Robert Wilson discover the cosmic microwave background radiation
1989 George Smoot’s team launches the COBE satellite to study the CMB for the seeds of galaxies
1992 Smoot announces that COBE’s data showed small fluctuations in the CMB
Scientists believe that the initial cosmic inflation should have magnified quantum fluctuations in the early universe’s gravitational field, resulting in gravitational waves.
Gravitational waves were first predicted by Albert Einstein in his 1915 general theory of relativity. Gravitational waves, from the collision of two black holes, were first detected by LIGO (the Laser Interferometer Gravitational-Wave Observatory) in 2015.
The gravitational waves LIGO picked up confirmed Einstein’s prediction and also showed that black holes do collide. However, scientists are still on the hunt for gravitational waves specifically from cosmic inflation.
Inflation-caused gravitational waves would be too weak for the LIGO detector to pick up, but they would slightly twist the orientation of light, creating an effect called polarization.
In 2012, a group behind the BICEP2 radio telescope at the South Pole thought they had detected big bang gravitational waves. Their data had shown a curlicue pattern in the polarization of the CMB, which greatly excited the science community and made news headlines around the world.
However, the pattern turned out to be from dust in the Milky Way, which emits polarized light with the same curling pattern.
Research is still underway using an upgraded version of the original technology called BICEP3 whose observation period ran through much of 2016. BICEP3 includes more detectors and a finer resolution but also a broader spectrum of light that will help the team discern any signals from inflation from galactic dust.
One of the major questions about the history of our universe is whether our universe is the sole universe.
If you currently have a basic assumption that our universe is the only universe, it can be challenging to imagine what it means for other universes to exist. But at one time, people thought our planet was the only planet, and then that the sun was the only sun, and then that our galaxy was the only galaxy.
According to Brian Greene, one of the most prominent theoretical physicists who studies and speaks on the idea of multiple universes:
An illustration of the gravitational waves (disruptions in space-time) caused by two black holes orbiting one another
What we have found in research … is that our mathematical investigations are suggesting that what we have thought to be everything may actually be a tiny part of a much grander cosmos. And that grander cosmos can contain other realms that seem to rightly be called universe just as our realm has been called the universe.
One relatively simple example Greene gives begins by considering whether the universe is finite or infinite. Currently, physicists do not know which is true. Thus, an infinite universe can be considered a viable option.
Next, consider shuffling a deck of cards an infinite number of times. Eventually, the order of the cards will begin to repeat. So, too, would the configuration of particles in an infinite universe. If space goes on for infinity, there would inevitably be repeating configurations of matter just as there are repeating configurations of cards.
While these other universes have not yet been observed, there have been other successful theories that started in a similar way. Einstein’s general theory of relativity, for example, started as a theoretical set of equations and was later tested in various ways before becoming a well-supported, accepted theory.
The collection of multiple universes is called a multiverse. It is also sometimes called a bubble universe because the term describes how physicists imagine multiple universes forming.
To imagine a bubble universe, picture a boiling pot of water. The pot has bubbles of varying sizes. Some appear and pop immediately, others grow larger and last longer.
In this model, our region of space underwent its early cosmic expansion, which ended 13.8 billion years ago. While inflation in our region ended, inflation continued in other regions or “bubbles.”
The different inflation regions separated, creating an infinite number of universes. As they inflate, the bubbles grow apart and make room for more inflating bubbles.
The idea of a multiverse or bubble universe is controversial, in part because initially, scientists had no way to prove or disprove that a multiverse exists.
A core component of the scientific method is the ability to test a hypothesis, and without that component, a hypothesis essentially becomes a question of philosophy, not of science.
Scientists are looking for impact marks that could show other universes have collided with ours. These marks would validate the multiverse theory.
However, in recent years, astrophysicists have thought of a way to test the multiverse theory. Consider again the pot of boiling water analogy—as water boils, some of the bubbles that rise up will collide. We don’t know how dense the theoretical multiverse would be, but it is possible that another universe could have collided with our own.
Astrophysicists think that such a collision would be observable as imprints or “bruises” on the cosmic microwave background. The collision point would be around the spot of either higher or lower radiation intensity.
While it’s not a guarantee that our (hypothetical) bubble universe has collided with another bubble universe, finding such an imprint would lend significant support to the multiverse theory.
The Big Bang Theory’s Influence Today
The big bang may have taken place almost fourteen billion years ago, but as a society, we’re far from past it. The big bang theory is the standard model taught in astronomy and cosmology courses around the world.
Significant funding and research time is dedicated to understanding more about the big bang and filling in the remaining questions in the cosmological model.
It’s currently impossible to look back past the time of recombination (the moment when free electrons paired up with nuclei to form neutral atoms and photons of light were finally able to travel freely) with telescopes.
That means the first four hundred thousand years or so of the universe can be studied only indirectly, such as by observing and analyzing the cosmic microwave background radiation for clues to the early universe or by re-creating the conditions of the big bang.
Physicists use particle accelerators to reproduce those incredibly hot, incredibly dense early conditions of the universe. Particle accelerators are powerful instruments that produce and accelerate a beam of particles, typically protons or electrons, but occasionally entire atoms such as gold or uranium.
The particles are accelerated inside a beam pipe to greater and greater energies. When the particles have reached the desired energy levels, they collide with another beam or a fixed target, such as a thin piece of metal.
The collision produces a shower of exotic particles. Detectors record the particles and the paths they take after the collision, which gives physicists a wealth of data to sort through in the aftermath.
The most famous particle accelerator studying the early conditions of the universe is the Large Hadron Collider, which is buried underground along the French and Swiss border at CERN (the European Organization for Nuclear Research). The Large Hadron Collider (LHC) is also the world’s largest particle accelerator with a ring 17 miles (27 km) long.
The LHC has four detectors at different collision points on the ring that physicists use for different purposes. ATLAS is a general-purpose detector designed to investigate new physics, such as searching for extra dimensions and dark matter. CMS looks for similar things as ATLAS using different technology.
ALICE is a heavy ion detector used to study the physics of strongly interacting matter at extreme energy densities similar to those just after the big bang. LHCb investigates the differences between matter and antimatter.
In one recent experiment, the scientists at CERN used the ALICE detector to study the collision of heavy ions (such as gold and lead nuclei) at energies of a few trillion electron volts each.
The resulting collision, which CERN described as a “miniscule fireball,” recreated the hot, dense soup of particles moving at extremely high energies in the early universe.
The particle mixture was primarily made up of subatomic particles called quarks and gluons that moved freely. (Quarks are particles that make up the matter; gluons carry the strong force that binds quarks together.)
For just a few millionths of The quark-gluon plasma existed for a few microseconds after the universe began before cooling and condensing to form protons and neutrons. a second after the big bang, the bonds between quarks and gluons were weak and the two types of particles were able to move freely in what’s known as a quark-gluon plasma.
The LHC’s man-made fireball cooled immediately, and the individual quarks and gluons recombined and created many different types of particles, from protons, neutrons, antiprotons, and antineutrons to tiny particles called pions and kaons.
One early finding from the analysis of the quark-gluon plasma showed scientists that the plasma behaves more like a fluid than a gas, contrary to many researchers’ expectations.
Scientists at CERN are also using the Large Hadron Collider’s LHCb detector to determine what caused the imbalance between matter and antimatter after the big bang.
Other Uses for Accelerators
Particle accelerators were invented by experimental physicists to study particle physics, but they have since been used in many useful applications.
From Splitting the Atom to the Atomic Bomb
The first particle accelerator was built in 1929 by John Cockcroft and Ernest Walton in pursuit of splitting the atom to study the nucleus. They succeeded in 1932 when they bombarded lithium with high-energy hydrogen protons. Their experiment was the first time humans split an atom, a process called fission.
The experiment also confirmed Einstein’s law E=mc 2. Walton and Cockcroft found that their experiment produced two atoms of helium plus energy. The mass of the helium nuclei was slightly less than the mass of the combined lithium and hydrogen nuclei, but the loss in mass was accounted for by the amount of energy released.
In 1939, German physicists discovered how to split a uranium atom. Scientists across the world feared that the Nazis would build an atomic bomb capable of terrible destruction. (When the uranium-235 isotope is split, the fission begins a chain reaction that can grow large enough to cause an enormous explosion.)
At the urging of Einstein and other top physicists, in 1941 the United States government launched an atomic bomb development effort code-named the Manhattan Project.
Over 120,000 Americans worked on the Manhattan Project, and the government spent almost $2 billion on research and development. The effort was so top secret that Vice President Harry
Nuclear fission creates a chain reaction
Truman didn’t learn about the Manhattan Project until President Theodore Roosevelt died in office and Truman became president.
When Japan refused to surrender in 1945, Truman authorized two atomic bombs that were dropped on Hiroshima and Nagasaki on August 6 and August 9, respectively.
The bombs effectively ended World War II, but hundreds of thousands of Japanese people were killed and many more suffered terrible health effects from the radiation.
For example, particle accelerators are used to deliver radiation therapy, which is one of the standard methods for treating cancer. In one form, high energy X-rays are generated by beaming high-energy electrons at a material such as tungsten.
These X-rays are then directed at the site of the patient’s cancerous tumor to kill the cancer cells. Healthy tissue is also damaged by the radiation beam, however, and researchers are continually looking for ways to deliver the right dose of radiation to destroy the tumor while minimizing the impact on healthy cells.
Particle accelerators are also used to generate X-rays for medical imaging, such as when we have our teeth X-rayed at the dentist’s office or have a full-body magnetic resonance imaging (MRI) scan.
Outside of the medical world, particle accelerators are used for industrial purposes, such as manufacturing computer chips and producing the plastic used in shrink-wrap, for security purposes, such as inspecting cargo, and in many other applications.
Physicists are able to study many aspects of the big bang using particle accelerators, but their work is by no means over. There are still many enormous questions about the beginning of the universe. The major questions include:
How did all four forces combine in the first fraction of a second?
What gave particles their mass?
Why did particles outnumber antiparticles?
How can we detect and study the neutrinos believed to have been created in the big bang, and what will they tell us if we find them?
How can we detect and study the gravitational waves that are believed to have been created by the big bang?
Is our universe the only universe?
The Four Forces
The Standard Model of particle physics has been developed since the 1930s, with significant help from particle accelerators and their cataclysmic investigations into atoms and their component parts.
According to the Standard Model, everything in the universe is made of a few fundamental particles (such as the building blocks of matter, quarks, and leptons), governed by four fundamental forces (the gravitational, electromagnetic, weak, and strong forces).
The Standard Model explains how these particles and three of the forces relate to one another.
The electromagnetic force, which governs the propagation of light and the magnetism that allows a magnet to pick up a paper clip, reaches over great distances, as evidenced by starlight reaching Earth.
The weak force governs beta decay (a form of natural radioactivity) and hydrogen fusion and acts at distances smaller than the atomic nucleus. The strong force holds together the nucleus and acts at very small distances.
The electromagnetic, weak, and strong forces result from the exchange of a force-carrying particle that belongs to a larger group of particles called bosons. Each force has its own boson: the strong force is carried by the gluon, the electromagnetic force is carried by the photon, and the weak force is carried by W and Z bosons.
The Standard Model is able to explain the forces other than gravity, all of which operate on microscopic scales. Gravity, however, operates across large distances, and as of yet, there is only a theoretical boson called the graviton that corresponds to the gravitational force.
Even without gravity, however, the Standard Model is able to explain particle physics very well because the gravitational force has little effect at the small scale of particles.
Research has shown that at very high energies, the electromagnetic and weak forces unite into a single force. Scientists believe that at even higher energies the strong force converges with the electroweak force to create a grand unified theory (GUT).
It is thought that at the extreme conditions immediately after the big bang all four forces would have been unified, but scientists do not yet understand how this could work.
Figuring out this unified force could help scientists understand more about the big bang and where our universe came from.
Matter Versus Antimatter
Matter and antimatter particles are created in pairs, which means that the big bang should have created equal amounts of matter and antimatter.
Matter and antimatter annihilate one another upon contact, and in the first fractions of a second, the universe was filled with particle and antiparticle pairs popping in and out of existence.
At the end of this process, when all the annihilations were complete, the universe should have been filled with pure energy—and nothing else.
This is clearly not the case. We are made of matter, and we inhabit a world and universe made of matter. What, then, happened such that matter survived?
Scientists calculate that about one particle per billion particles of matter survived. It’s unknown why this is the case, but observations of particles at the LHC give one potential explanation:
Due to a weak interaction process, particles can oscillate between their particle and antiparticle state before decaying into other particles of matter or antimatter. It could be that in the early universe an unknown mechanism caused oscillating particles to decay into matter slightly more often than they decayed into antimatter.
The survival of matter over antimatter is a topic of an ongoing investigation at physics institutions across the world.
When you look up at the sky at night with your unaided eye, you can see a beautiful array of stars and constellations. Without a telescope, it’s hard to garner any information from those stars beyond their position in the night sky and their relative brightness.
A crucial precursor to the invention of the telescope was the invention of the glass lens within it that created the necessary magnifying effect.
Light permeates and illuminates our daily lives, but it also has the power to reveal vast amounts of information about the cosmos. Knowing the speed of light, the different types of light, and what light spectra can tell us has been essential to studying the beginnings of the universe.
The Speed of Light
The speed of light is a significant metric in cosmology because when we know how fast light travels, we can use that speed in calculations of how far away different stars, galaxies, nebulae (clouds of gas and dust), and other phenomena are.
Aristotle thought that light traveled instantly, but today we know that light does have a finite speed. The first person to measure the speed of light with relative accuracy was the Danish astronomer Ole Römer in 1676.
Römer had studied Jupiter’s moon Io (discovered a half-century earlier by Galileo), which is regularly eclipsed by Jupiter as Io moves behind Jupiter in its orbit. Sometimes, the eclipse happened sooner than expected or later than expected.
Römer realized that the early or late appearance of Io from behind Jupiter was due to the varying distance between Earth and Jupiter. When Earth was farther away from Jupiter, the light had to travel farther and thus arrived at Earth later than astronomers had expected. Though Io’s orbit around Jupiter is regular, the timing of the eclipse varied by about an
White light is composed of different wavelengths of light that refract at different angles when passing through a prism. hour throughout the year due to the varying distance between the two planets.
Römer estimated that the speed of light was 186,000 miles per second (299,344 km/s), which isn’t far off from its modern-day measurement of 186,282 miles per second (299,792 km/s).
Visible Light Spectra
Another misconception of light was that it was a pure, white substance. As far back as Aristotle, scientists had believed that light creates a rainbow when passed through a prism because the light itself is modified.
In 1665, Isaac Newton proved differently with a simple but convincing experiment. On a sunny day at Cambridge University, Newton darkened his room and made a small hole in the shutter for a beam of light to pass through.
Newton then took the second prism and placed it upside down in front of the first prism. The spectrum of light, with all of its component colors, passed through the second prism and combined back into white light. In this way, Newton showed that white light contains all of the colors of the rainbow.
A NEW GRAVITY
One of the most astounding developments in physics of the twentieth century was Albert Einstein’s general theory of relativity. Published in 1915, the theory presented a geometric theory of gravity that revised the common understanding of gravity based on Isaac Newton’s work centuries earlier.
Newton’s theory of gravity held that gravity is a tugging force between two objects that directly depends on the mass of each object and how far away those two objects are from one another. The moon and Earth both attract one another, for example, but the more massive Earth exerts a relatively stronger attractive force on the moon.
In 1905, Einstein had published his special theory of relativity, which in part stated that space and time are inextricably connected in a four-dimensional continuum called space-time.
In his 1915 general theory of relativity, Einstein hypothesized that a massive object will create a distortion in space-time much like a bowling ball distorts the surface of a trampoline.
Just like a marble placed on the trampoline will roll inward toward the bowling ball, objects in space follow the distortions in space-time toward more massive objects. In broader terms, matter tells space-time how to curve, and curved space-time tells matter how to move. Light, too, Einstein predicted, would follow any warps in space-time.
On May 29, 1919, a solar eclipse proved Einstein’s theory of gravity was more accurate than Newton’s. During this particular eclipse, astronomers knew the sun would be passing through the Hyades star cluster.
The light from the stars would have to pass through the sun’s gravitational field en route to Earth, and because of the darkness from the eclipse, scientists could observe and measure this light when it arrived.
The English physicist and astronomer Sir Arthur Eddington, leader of the experiment, first measured the true positions of the stars in January and February of 1919.
When the solar eclipse happened, he measured the star positions again. The star positions appeared shifted due to the path-altering effect, known as gravitational lensing, of the sun’s gravitational field.
Einstein’s theory of general relativity didn’t just change the way we view gravity. It also created enormous new cosmological questions. Depending on how the equations in his theory were solved, the universe was either expanding or contracting.
Einstein preferred to believe it was staying static, so he added a term he called the “cosmological constant” to his equations to force it into stability. He would later come to regret this modification of his otherwise elegant equations.
Georges Lemaitre was born in Charleroi, Belgium, in 1894. Lemaitre initially studied engineering before volunteering for the Belgian army and serving as an artillery officer during World War I. During the war, Lemaitre witnessed the first poison gas attack in history and was decorated with the Croix de Guerre (Cross of War).
Post-war, Lemaitre switched his scientific focus from engineering to mathematics and physics. He obtained a doctorate from the University of Louvain in 1920 and was ordained as a priest in 1923.
Lemaitre received a traveling scholarship from the Belgian government, awarded for a thesis he wrote on relativity and gravitation, that allowed him to spend the subsequent years studying at Cambridge University, the Harvard College Observatory, and the Massachusetts Institute of Technology.
He returned to the University of Louvain in 1925 and became a full professor of astrophysics there in 1927.
That same year, Lemaitre proposed that the universe had begun at a finite moment in a highly condensed state and had expanded ever since. He published his theory in the Annals of the Scientific Society of Brussels, which was not widely read outside of Belgium.
Some who did read it dismissed his work as influenced by his theological studies, as the idea of a beginning could imply a divine creator. Lemaitre disliked religious readings of his cosmology, however, arguing that his theory “remains entirely outside any metaphysical or religious question.”
Everything changed for Lemaitre when his former Cambridge University professor Sir Arthur Eddington began to champion Lemaitre’s work. Eddington, who had observed the 1919 eclipse, had seen the initial publication but forgot about it for some time.
In 1930, three years after Lemaitre first published his expansion theory and one year after Hubble released his data on the expanding universe, Eddington wrote a letter to the journal Nature drawing attention to Lemaitre’s work. In hindsight, with Hubble’s data as evidence, Lemaitre’s work was significantly easier to accept.
Einstein had read Lemaitre’s 1927 paper and originally told him that his math was correct but his physics were abominable. After Hubble’s data was published, however, Einstein was much more interested in what Lemaitre had to say about cosmology, and the two had many walks and talks together over the following years.
After publishing on his primeval atom theory, Lemaitre’s academic work included cosmic rays, celestial mechanics, and pioneering work on using computers to solve astrophysical problems. He received numerous awards, including the Royal Astronomical Society’s first Eddington Medal in 1953. Lemaitre died in 1966.
Einstein, Hubble, and Lemaitre laid the foundation for modern cosmology. Einstein’s general theory of relativity raised curious questions about the universe, Lemaitre published a theory of a universe with a finite beginning and original highly condensed state, and Hubble’s data provided evidence that the universe was indeed expanding over time.
Over the subsequent decades, numerous scientists would propose theories that built on that foundation and make discoveries that helped create the standard big bang model of cosmology. George Gamow and Ralph Alpher proposed a modification of Lemaitre’s work in which all of the elements were formed in the big bang.
Fred Hoyle opposed the big bang model, but his work on stellar nucleosynthesis helped fill in scientific gaps in the theory. Arno Penzias and Robert Wilson unintentionally discovered strong evidence of the big bang, and George Smoot designed a massive experiment to find whether that evidence could also explain the formation of stars and galaxies over time.
George Gamow was born in Odessa, Ukraine (it was part of the Russian Empire at the time), in 1904. He loved science from a young age, growing interested in astronomy when his father gave him a telescope for his thirteenth birthday.
Gamow graduated from the University of Leningrad in 1928 and moved to Göttingen, Germany, where he developed a theory of radioactive decay as a function of quantum mechanics. He was the first to successfully explain why some
Like Lemaitre, Alexander Friedmann also solved Einstein’s equations of general relativity and proposed an expanding model of the universe in the 1920s.
Friedmann and his theory received significantly less attention than Lemaitre, however, due to Friedmann’s background as a mathematician (not a physicist) and his death in 1925, before Hubble had shown that the universe was indeed expanding.
Friedmann was born in 1888 in St. Petersburg, Russia. As a student, Friedmann showed a remarkable talent for mathematics and coauthored a paper published in Mathematische Annalen in 1905. During World War I, Friedmann joined the volunteer aviation detachment and flew in bombing raids.
After the war, Friedmann worked in various positions including as head of the Central Aeronautical Station in Kiev, as a professor at the University of Perm, and as director of the Main Geophysical Observatory in Leningrad. The cosmologist George Gamow briefly studied under Friedmann at the observatory.
Friedmann became interested in Einstein’s general theory of relativity and published an article, “On the Curvature of Space,” in 1922 that proposed a dynamic, expanding universe. Einstein quickly rejected Friedmann’s work in the same journal, Zeitschrift für Physik, though he retracted his rejection again in the journal in 1923.
Friedmann’s equations for the expansion of space, known as the Friedmann equations, show the fate of the universe as either expanding forever, expanding forever at a decreasing rate, or collapsing backward (dependent on its density).
Friedmann’s career in cosmology was cut short in 1925 when he died of typhus.
Gamow became a professor at the University of Colorado at Boulder in 1956 and worked there until his death.
radioactive elements decay in seconds while others slowly decay over millennia.
The theoretical physicist Niels Bohr offered Gamow a fellowship at the Theoretical Physics Institute of the University of Copenhagen where, among other work, Gamow worked on calculations of stellar thermonuclear reactions.
Gamow also convinced the experimental physicist Ernest Rutherford of the value in building a proton accelerator, which was later used to split a lithium nucleus into alpha particles.
As much of Europe faced the pressures of communism and fascism in the 1930s, many intellectuals fled the continent (including Einstein). Gamow made several attempts to escape the Soviet Union, including an attempted crossing of the Black Sea into Turkey via kayak in 1932.
He finally got his chance to escape when he was invited to give a talk in Brussels on the properties of the atomic nuclei. Gamow arranged for his wife, Rho, also a physicist, to accompany him.
From there, the Gamows traveled through Europe and then to America in pursuit of an academic career outside of the Soviet Union.
Though he hoped for a prestigious position at a school known for its physics program, Gamow ended up accepting a position at George Washington University, which at the time didn’t have a strong reputation in physics.
Gamow quickly changed that, however, as his terms of acceptance involved expanding the physics department at GWU and establishing a theoretical physics conference series.
In addition to developing a theory of element formation in the big bang, Gamow’s research included stellar evolution, supernovas, and red giants. In later years, Gamow made contributions in biochemistry as well as a foray into what he called “the physics of living matter.”
After reading about Watson and Crick’s work on the structure of DNA in the journal Nature, he wrote his own note to Nature proposing the existence of a genetic code within DNA that was determined by the “composition of its unique complement of proteins” made up of chains of amino acids. Gamow’s ideas inspired Watson, Crick, and many other researchers to begin researching how DNA coded proteins.
Gamow also wrote numerous popular blogs designed to give non-physicists access to complex topics, including the Mr. Tomkins series about a toy universe with properties different from our own and One, Two, Three…Infinity. Gamow died in 1968.
Arno Penzias was born in Munich, Germany, in 1933 to a Jewish family. His family was rounded up for deportation to Poland when he was a young boy, but they returned to Munich after a number of days. His parents, aware of the danger they faced, sent Arno and his younger brother on a train to England in 1939.
His parents were able to join the two boys in England and, after six months there, they moved to New York City. Penzias attended the City College of New York, a municipally funded college dedicated to educating the children of New York’s immigrants.
After college, he spent two years in the Army Signal Corps, which develops and manages communication and information systems for the command and control of the military.
When he began his graduate studies in physics at Columbia University in 1956, that army experience helped Penzias gain research projects in the Columbia radiation laboratory. For his thesis, he built a maser amplifier, a device that amplifies electromagnetic radiation, for a radio astronomy experiment.
Penzias and Wilson made their discovery of the CMB on the Holmdel Horn Antenna, which detects radio waves. After finishing his Ph.D., Penzias began working at Bell Labs in Holmdel, New Jersey. There, Penzias was able to continue his work in radio astronomy, which led to his work with fellow radio astronomer Robert Wilson.
In an attempt to measure the radiation intensity of the Milky Way, the two accidentally discovered the cosmic microwave background (CMB) radiation, the relic radiation left over from the big bang.
Penzias rose through numerous levels of leadership at Bell Labs, eventually becoming vice president of research. As his own astrophysics research wound down, he wrote a blog called Ideas and Information on the creation and use of technology in society.
When he approached mandatory retirement age, Penzias left the research and development world for Silicon Valley, where he became involved in the venture capital world.
Robert Wilson was born in Houston, Texas, in 1936. His father worked for an oil well service company, and while in high school Robert often accompanied his father into the oil fields.
His parents were both “inveterate do-it-yourselfers,” Wilson wrote, and he gained a particular fondness for electronics from his father. As a high school student, Robert enjoyed repairing radios and television sets.
Wilson attended Rice University, where he majored in physics. He obtained his Ph.D. in physics at Caltech, where he worked with radio astronomer John Bolton on expanding a radio map of the Milky Way. After graduation, he joined Bell Labs’ radio research department.
Together, Wilson and Penzias made numerous discoveries using radio astronomy, including a surprising abundance of carbon monoxide in the Milky Way and their Nobel Prize-winning discovery of the CMB.
Today, Wilson continues to live in Holmdel, NJ, with his family.
George Smoot grew up attending university biology courses with his mother. Both parents had resumed their college educations after World War II and two children, and watching his parents study, learn, and dedicate time to education had a strong influence on George.
After some financial difficulties, the family moved to Alaska, where George spent his time outside exploring and studying the night sky.
George’s father worked for the United States Geological Survey, and as his reputation, as a field scientist grew, he traveled around the world to gather data on the properties and water flow of rivers.
George’s parents played a shaping role in his life through high school, as his father tutored him in trigonometry and calculus while his mother gave him lessons in science and history.
Smoot attended the Massachusetts Institute of Technology (MIT), where he majored in mathematics and physics. He stayed at MIT for his Ph.D. and then moved to Berkeley to work on particle physics at the Lawrence Berkeley National Laboratory.
There, he worked on the High-Altitude Particle Physics Experiment, in which Smoot and his colleagues searched for evidence of the big bang using balloon-borne detectors that would look for antimatter in cosmic rays.
Smoot eventually changed his focus to studying the CMB for more information about the early universe, which led to his Nobel Prize-winning discovery of fluctuations in the CMB.
Putting It Together
Over the twentieth century, the big bang theory slowly fell into place. In the next chapter, we’ll discuss the initial versions of the theory and the current big bang model of cosmology. The structure in the universe has become increasingly complex over time.
The Discovery of the Big Bang
As scientists studied the origins of the universe, their cosmological research focused on three major pillars: the expanding universe, nucleosynthesis, and the cosmic microwave background radiation. Today, all three give strong support for the big bang model while also providing clarity into how the universe evolved over time.
The EXPANDING UNIVERSE
“The whole story of the world need not have been written down in the first quantum-like a song on the disc of a phonograph. The whole matter of the world must have been present at the beginning, but the story it has to tell may be written step by step.”
In the 1920s, two academics independently worked through Einstein’s general relativity equations and found that the solutions suggested an expanding universe. One was Alexander Friedmann, whose work in the field was cut short by his untimely death from typhoid fever in 1925.
The other was Georges Lemaitre, who went on to become the first scientist to propose a theory of an expanding universe with a discrete beginning. Today, Lemaitre is known as the father of the big bang theory.
The Primeval Atom
Lemaitre was an avid scholar of general relativity and studied under one of its foremost experts, Sir Arthur Eddington, at Cambridge University in England. Lemaitre began writing about an expanding universe in the 1920s. In the early 1930s, he added the concept of a discrete origin to his theory.
In a 1931 letter published in the journal Nature, Lemaitre began by writing, “Sir Arthur Eddington states that, philosophically, the notion of a beginning of the present order of Nature is repugnant to him …”
For many scientists like Eddington, any cosmology with a finite beginning had too much of a creation narrative, which harkened back to mythology and supernatural forces, to be scientifically acceptable.
To Lemaitre, the notion of a beginning of the universe was not only quite acceptable, but it was also the logical conclusion from quantum theory.
If there was a constant total amount of energy in the universe and that number of distinct quanta were increasing, as theory held, then the implication must be that there were once much fewer quanta, perhaps a single quantum, that held all of the energy in the universe.
In the letter to Nature, Lemaitre suggested the possibility of a single unique radioactive atom that held all the mass in the universe before decaying into smaller and smaller atoms.
“The last two thousand million years are slow evolution: they are ashes and smoke of bright but very rapid fireworks,” he wrote in a paper called “The Evolution of the Universe.”
In a later text, The Primeval Atom, he wrote: “We can compare space-time to an open, conic cup … The bottom of the cup is the origin of atomic disintegration; it is the first instant at the bottom of space-time, the now which has no yesterday because, yesterday, there was no space.”
Lemaitre was the first physicist to propose a widely discussed model of cosmology with a finite beginning and expansion from a single atom.
However, his theory of cosmology wasn’t the big bang we think of today, which involves an explosion of pure energy that converts into all of the matter in the known universe. Lemaitre’s model was a colder, disintegrating model of the universe. The hot big bang model that we know today arrived seventeen years later.
Lemaitre worked on his cosmology in the years between World War I and World War II. World War II temporarily interrupted astrophysics as it diverted many top physicists to war projects and isolated others.
Lemaitre himself was cut off in Belgium after the Germans invaded, and he nearly died in an Allied forces’ bombing of his apartment building.
After the war, Lemaitre turned his focus to other scientific pursuits, including mathematical computing. Einstein turned his attention to finding a unified field theory that would unite general relativity with quantum mechanics.
Sir Arthur Eddington died in 1944. One generation of scientists stepped away from the cosmological question; a new generation of scientists stepped up.
Roughly a decade after Lemaitre proposed a primeval atom that decayed into all the matter in the universe, George Gamow and Ralph Alpher published a paper detailing the foundation of the modern big bang theory.
Gamow’s early work included studying radioactivity and stellar physics. When World War II broke out, Gamow had plenty of time to focus on the implications of nuclear physics on cosmology.
While other American scientists were drafted to support the war effort, Gamow was left out because he had briefly served in the Red Army before fleeing Ukraine.
Years later, as a professor at George Washington University, Gamow and his doctoral student Ralph Alpher published a paper outlining their theory of the beginning of the universe and synthesis of matter.
The physicists Carl von Weizsäcker and Hans Bethe had both showed how stars convert hydrogen into helium through what is called the carbon-nitrogen-oxygen cycle, but at the time no physicist could explain how heavier elements, or even carbon, were formed within stars. Gamow believed they could have formed at the beginning of the universe.
Gamow and Alpher proposed that the universe did not begin as a single super atom but as hot, highly compressed neutron gas that underwent a rapid expansion and cooling.
The initial primordial matter decayed into protons and electrons as the gas pressure dropped due to the expansion. (Gas pressure is a function of molecular collisions. As the gas density of the early universe decreased, the particles collided less frequently and the pressure dropped.)
This began a process called big bang nucleosynthesis in which protons “captured” neutrons to form deuterium (an isotope of hydrogen). Neutron capture continued and formed heavier and heavier elements by adding one neutron and one proton at a time.
The relative abundance of elements was determined by the time allowed by the universe’s expansion (that is, the time in which the universe had the right conditions for nucleosynthesis to proceed).
This capped window of time, Gamow and Alpher believed, explained why light hydrogen was so prevalent and heavy elements like gold so rare.
Their 1948 paper contained a model for only the abundances of hydrogen and helium, but as these two elements account for 99 percent of the atoms in the universe, it was enough to make their paper credible.
In Alpher’s Ph.D. thesis, he wrote that the nucleosynthesis of hydrogen and helium took just three hundred seconds.
Over time, large stars fuse successively heavier elements, creating “shells” of different elements that are eventually released into the universe.
Alpher’s calculations showed that there should be about ten hydrogen nuclei for every helium nucleus at the end of the big bang, which matches modern observed abundances and lent further support to the model.
In another 1948 paper, Alpher and his coauthor Robert Herman calculated that the radiation from the beginning of the universe should today be about 5 degrees K. This prediction provided a way to test the theory and provide strong supporting evidence for its validity.
Gamow and Alpher’s work created a buzz in the scientific community because it explained the origin of the most abundant elements and provided a compelling narrative of the big bang. Their work created the basic model of the big bang theory we know today.
The Age of the Universe
One other roadblock that had to be cleared before the big bang model was embraced by the scientific community was the age of the universe.
After Hubble’s discovery of the expanding universe, astronomers used his measurements to calculate the age of the universe. Galaxies move away from each other at a velocity represented by v = H0 x D. V is the observed velocity of the galaxy as it moves away from us, D is the distance to the galaxy, and H is the Hubble constant.
The Hubble constant represents the expansion rate of the universe, and Hubble’s 1929 estimate of this value was about 500 kilometers per second per megaparsec (Mpc). (Parsecs are measurements of distance in astronomy. One parsec is 3.26 light-years long, and one megaparsec is 3.26 million light-years long.)
The Hubble constant can be used to infer the age of the galaxy. If the universe had been expanding at a rate of 500 km/s/Mpc to the present day, the universe was about 1.8 billion years old.
However, geologists had shown through examinations of radioactive rocks that Earth was older than 1.8 billion years, and it was assumed that stars were even older than our planet. This timescale difficulty, as it was called, was a major flaw in the big bang models proposed by Lemaitre and Gamow.
It turned out, however, that Hubble’s measurements weren’t entirely accurate. The German astronomer Walter Baade discovered that there were two major types of Cepheid variable stars, which Hubble didn’t know when he used Cepheid variables to calculate the distance to the Andromeda galaxy.
The younger Population I stars are hotter, brighter, and bluer than the older Population II stars. Hubble had observed Population I Cepheid variable stars in Andromeda but mistook them for dimmer Population II stars. He saw a relatively bright star and, with the dimmer stars in mind, though it must be much closer than it really was.
Baade recalculated the distance to Andromeda using the knowledge of both types of Cepheid variables. His new calculation showed that Andromeda was twice as far away as previously thought.
It also opened up a new look at the big bang model’s timeline: if the recession speeds remained the same but the distances doubled, the age of the universe was now around 3.6 billion years.
Baade formally announced his results in 1952, just four years after Gamow and Alpher published their first paper on big bang nucleosynthesis.
This was much better for the big bang model as it allowed for a universe that was older than Earth, but it wasn’t yet a complete success. There were other elements of the universe thought to be older than 3.6 billion years.
Baade’s student Allan Sandage took on the task of measuring the distances to the farthest galaxies. Previously, due to technological limitations, astronomers had to use a variety of assumptions to measure the distance to very far-off galaxies. One of those assumptions rested on finding the brightest star in a faraway galaxy.
By comparing its apparent (observed) brightness to the apparent brightness of the brightest stars in a closer galaxy, astronomers could come up with a rough estimate of how far away the distant galaxy was. However, Sandage showed that what astronomers thought was the brightest star was actually often an enormous, very luminous cloud of hydrogen gas.
That meant that the actual brightest star in the distant galaxies was much dimmer than was previously known and the galaxies were much farther off than previously calculated. Sandage revised the age of the universe to first 5.5 billion years in 1954 and eventually to an age between 10 billion and 20 billion years.
The new timeline allowed for all of the planets, stars, and galaxies to form and thus made the big bang model compatible with observations of the universe.
Today, the age of the universe is estimated to be 13.8 billion years, within Sandage’s later estimated range. (The Hubble constant, H0, is now estimated to be somewhere between 45 km/sec/Mpc to 90 km/sec/Mpc.)
The current age estimate has been calculated using a variety of methods, including measurements of stellar evolution, expansion of the universe, and radioactive decay, with all three methods in agreement of the universe’s age.
Mapping the CMB
Those who supported the big bang model believed that the early universe must not have been perfectly uniform, for otherwise stars and galaxies couldn’t have formed.
Instead, they imagined a universe where some areas were denser than others, creating regions where gravity would eventually attract more matter and cause the regions to collapse under their own weight.
There was no proof of these variations in density when Penzias and Wilson first discovered the CMB. The signal they picked up was uniform across time and space. The American astronomer George Smoot hoped that if he measured the CMB with more powerful instruments, he would find the predicted density variations.
Smoot worked at the University of California at Berkeley, where he participated in several 1970s experiments using giant balloons to lift radiation detectors tens of kilometers above Earth.
The scientists hoped that this high altitude would remove any radiation from microwaves in Earth’s atmosphere. However, the cold temperatures at that altitude could wreak havoc on the detectors and the balloons were prone to a crash-landing.
In efforts to find other means of studying the CMB from high altitudes, Smoot used a United States Air Force spy plane to take a detector up. The data gathered ended up showing that the Milky Way was moving through the universe at a speed of 600,000 kilometers per second, which was new and interesting information, but not the data Smoot intended to find.
While his 1976 spy plane experiment was underway, Smoot began working on designing a satellite detector called COBE, or the Cosmic Background Explorer.
COBE contained several detectors including a Differential Microwave Radiometer (DMR) that measured the CMB radiation from two separate directions and found the difference. The DMR could thus detect whether the CMB was perfectly smooth or had small fluctuations.
COBE was scheduled to launch in 1988, but the experiment ran into a problem when the Challenger space shuttle exploded in January of 1986. NASA upended its flight schedule and called off the scheduled COBE launch.
The COBE team explored opportunities to launch on a foreign rocket, namely with the French, but NASA objected. Eventually, NASA agreed to send COBE up in a Delta rocket, which was much smaller than they had initially planned for.
The team quickly redesigned COBE to be smaller and lighter so the sophisticated equipment could fit in the rocket.
COBE launched on November 18, 1989. It took about six months to complete an initial rough, full-sky survey. The initial data showed no variations, but when the first thorough full-sky map was completed in December of 1991, the data showed something more.
The peak wavelength of the CMB radiation varied by 0.001 percent, a tiny variation but significant enough to show that the early universe was inhomogeneous. The variations were big enough to cause matter to clump and, eventually, galaxies to form.
Smoot’s team announced their results in April of 1992. It was one of the most significant discoveries in the history of cosmology, for the COBE results showed that the big bang model of cosmology could explain the history of the universe from its birth to the formation of galaxies to present day. Subsequent missions by the WMAP and Planck satellites confirmed and refined COBE’s measurements of the CMB.
By the 1990s, all three pillars of the big bang model were in place and the big bang became the standard cosmological model for our universe. Over the past few decades, scientists have arrived at a sophisticated, detailed standard model of those first few moments in the infant universe.
The STANDARD MODEL
In the first half of this chapter, we looked at how the discovery of the big bang fell into place, piece by piece. Now, let’s dig in deeper to the details of how it worked.
The standard model of the big bang today contains details of the first fractions of a second. The numbers at this time in the universe’s history are both astronomically small and astronomically large.
As a quick refresher on scientific notation, 10-43 seconds is the equivalent of a decimal place followed by 42 zeroes and a one. Conversely, 1032 degrees K is 10 with 32 zeroes after it.
The scale of these numbers shows the rapid speed at which the universe was changing and the extreme conditions present in that early period. As the universe expanded and cooled, the changes began to happen within more comprehensible timescales and environmental conditions.