10.II: The Big Bang

In the big bang, fundamental particles were synthesized while space began expanding. In this image, a high energy proton is shown producing several new particles. 1

A. Looking into the Past

B. The Stuff of Physics

C. Understanding the Moment of Creation

D. The Early Moments after the Big Bang

E. Upshot: Why Believe the Big Bang?

F. Citations

A. Looking into the Past

How far can you see into the dark night sky?

Of course, you can see unimaginable distances.  More interestingly, you can also see incredible spans of time back into the past.  In the vast emptiness of the cosmos, light itself takes measurable time to travel from place to place.  Sunlight takes eight minutes just to reach Earth, so the image of the sun that you see in the sky shows you where the sun actually was eight minutes earlier.

Looking out to greater distances involves ever-greater time lags, offering us glimpses into an increasingly remote past.  The basic unit of astronomical distance, in fact, is called the light-year, which is the distance that light travels in one year.  A light-year is approximately 10 trillion kilometers. 1 That is an incomprehensible distance to us humans, but it is modest on the grand scale of things.  Outer space is almost completely empty within a few light-years of our solar system. 

With telescopes and other modern instruments, astronomers can peer much farther than the naked eye.  If you pay attention to astronomical discoveries, you will hear stories about supernovae hundreds of millions of light-years away, active galaxies and quasars five billion years old, or gamma ray bursts that exploded over ten billion years ago!  Some of these are extinct astronomical structures that have not even existed for billions of years.  Their ghosts are strangely imprinted on our sky.     

Yet that’s where the time-travel ends.  You can stargaze all you want, but you will never find a celestial body a trillion years old, or 100 billion, or even 15 billion.  Nothing in our observable universe is that old.  The remotest light 2 is dated to a little more than 10 billion years ago (more precisely somewhere around 13 or 14 billion years, a figure that is still being refined). 2

The universe is expanding, with all regions of space receding away from each other.  If we ran time backward and watched space contract in reverse, we would see all the galaxies rushing toward each other until the whole universe was compacted into the same place at the same time.  Play the movie forward again and … BANG!  Hence the universe’s beginning point is called the big bang.  The big bang and its ten-billion-year age are 20th-century discoveries; 3 a complete history of the universe was not even possible much before our lifetime.

B. The Stuff of Physics

The newborn universe bore no resemblance to anything we can imagine today.  It might seem natural to argue that the universe is too complex to have formed spontaneously. But the big bang was not a colossal spewing forth of stars, galaxies, planets, and dinosaurs, no matter what you might see in cartoons.  The universe that emerged from the big bang was simple in the extreme.  In the moment of creation, there was no “stuff” as we know it, not even gas, dust, fire, or light.  All that existed were space-time, forces, and fundamental particles of matter and energy.  These phenomena are the subject matter of physics.  What are they, anyway?  That is a simple question with no simple answer.

The most familiar force is gravity.  It is a cause that pushes or pulls nearby matter.  You are constantly in Earth’s gravitational field.  If you stepped off a tall building, that field would cause you to fall and gain speed.  Then you’d have energy.  Thus, matter has potential energy simply by virtue of being in a force field.

Energy is the ultimate substance of the universe, because matter is simply a concentrated form of energy.  Movement and heat are other manifestations of energy in matter.  Freed from matter, pure energy is radiated in the form of light or similar rays.

Space-time is the framework of the universe, the stage on which everything is played out.  Physicists think of space-time as a unified four-dimensional reference system.  Space is not as inert as people used to think.  Space-time interacts with matter and energy.  The expansion of the universe is an expansion of space itself. 4

space time inertial frame reference relativity Taylor Wheeler meter clock big history coordinates
A classic representation of a space-time framework. The meter sticks mark off space in three spatial dimensions. The fourth dimension, time, is marked by synchronized clocks at each lattice point. Image by Taylor & Wheeler. 5

Most people today know that matter is made of atoms.  An atom consists of protons, neutrons, and electrons, and the protons and neutrons are themselves formed from quarks.  Quarks and electrons are examples of fundamental particles.  They are not made of smaller sub-units.  These are the particles that came immediately out of the big bang.  Ultimately, each fundamental particle is a tiny, standardized little knot of energy.

The standard model describes the dozens of fundamental particles in an organized scheme, something like the periodic table of chemistry. (See table). It is an incredibly interesting and important model because it describes matter, energy, and most forces all at the same time.

The “Standard Model,” accounting for the fundamental particles of matter, energy, and forces. 6

One of the simplest but most profound facts of nature is that fundamental particles are identical everywhere.  All of the electrons flowing through your brain and your computer are perfect copies of one another.  Fundamental particles across the universe, billions of years ago, had the same properties as today on Earth. 7 The universal interchangeability of fundamental particles is vital for the consistent development of the universe, because it means that basic physical patterns (like atoms or light rays) can be duplicated over and over again. 

The consistency of matter-energy, space-time, and forces makes them obey physical “laws”.  If we put chemicals into a test tube, electromagnetic forces will cause them to react in predictable ways, with no need for conscious control.  The best way to describe physical laws is with numbers and mathematics.  This does not mean that particles or a guiding hand is “doing math”.  Physical things simply do what physics constrains them to do.  We humans do the math to understand, predict, and communicate about them.  Mathematics occupies a special position in the grand scheme of things.  It is a language that describes reality, a bridge between the mental and physical worlds. 3

C. Understanding the Moment of Creation

1. Philosophical Issues

2. The theory of everything

1. Philosophical issues

Even though the big bang was immeasurably brief and unimaginably distant, it is undeniably the most important event of all time!  It has also become a portal between major belief systems today.  It’s the first and greatest frontier question in science.  Therefore, it demands deep attention in a philosophical history of the universe. 

A complete understanding of the big bang – what may have preceded or caused it, and what physical laws governed it – remains elusive.  It raises some obvious conundrums.  Where did all this matter and energy come from?  Why was the universe born with certain laws, which support life on Earth, instead of other laws?  These remain some of the most frustratingly difficult questions of all time.  Almost every culture has a creation myth.  It seems that people feel a deep-seated need to answer these questions. 

At first glance, it seems natural to assume that the universe was created by God(s).  Most people feel satisfied “explaining” the universe this way, without stopping to consider that it raises an even harder question:  how did God come into being?!  I call this oversight the secret trillionaire fallacy.  How would you respond to a friend who made this argument?

I don’t believe that anyone could become a billionaire.
Yet there are thousands of billionaires.
Therefore, I believe that they are getting their money from a secret trillionaire

Well, how about this parallel argument?

I don’t believe that the natural world could spontaneously come into being
Yet the natural world does exist
Therefore, I believe that it came from an invisible, supernatural realm, which spontaneously came into being

When we follow this line of reasoning, we talk ourselves into believing something that’s even farther fetched than what we didn’t believe initially!  Later chapters of this book will discuss the psychology of why we think this way.

In any event, if you believe in God, then aren’t you curious about how God made nature?  Let’s all join together, then, at the point where we can at least agree on something indisputable:  the universe came to be. 

2. The theory of everything

Glimpsing the universe’s first moments will require a synthesis of two powerful but disparate 20th century theories: quantum physics and general relativityQuantum physics is the study of matter and energy on the smallest scale, at the atomic and sub-atomic levels.  It is the realm of the Standard Model discussed above.  General relativity is the description of gravity as the interaction between matter-energy and space-time.  Note that the Standard Model says nothing about gravity.  Likewise, general relativity does not extend to the microscopic scale.  To fully understand an early universe when a great deal of matter, energy, and gravity was all crammed into a microscopic space, scientists need to make a connection between these two theories. If they are ever successfully unified into what physicists call the “Theory of Everything,” it could help us understand matter / energy, space-time, and forces under all possible conditions, including black holes and even the big bang.

As far as the “something from nothing” mystery, space is not as “nothing” as our senses perceive it to be.  It naturally seethes with force fields and energy. 8 If you zoomed in closely on a point in empty space, you would find space twisting itself into fundamental particles, which decay back into space. These interactions are called vacuum fluctuations. They have actually been indirectly observed: “Something” arising out of “nothing”! 9 Many of the fluctuations cancel each other out: a particle with positive charge and an anti-particle with negative charge will pop into existence as twins. Added together, their total charge is zero, just like the empty space from which they were born.

Ordinary vacuum fluctuations are small and fleeting.  According to the inflation hypothesis, a particularly large vacuum fluctuation could have gravitational consequences that make it blow up, generating matter and energy in the process. 10

Interestingly, gravitational energy is considered negative, 11 so it cancels the positive energy of matter.  All told, the total amount of energy in the universe could be zero! 12 If these hypotheses are correct, then the creation of the universe only required simple prerequisites like space and gravity.  Do space and gravity have a cause?  Or are they eternal?  When we search for beginnings, the questions never end.                    

D. The Early Moments after the Big Bang

Even though the genesis moment itself lies beyond today’s physical models, the rest of the big bang is well understood.  Current 21st-century physics has done an incredible job of retracing the early universe as far back as 10-36 seconds after the big bang (a trillionth of a trillionth of a trillionth of a second)!  The best way to describe the newborn universe is as a clump of elementary particles at unimaginable temperature and density.  As the universe has continued to expand ever since, its long-term trend has been to thin out and cool down. 

As far as we are concerned, the most important elementary particles to come out of the big bang were quarks, electrons, and photons.  All tangible everyday objects, and we ourselves, are made of quarks and electrons.  Photons are bizarre particle-waves that make light and related forms of electromagnetic radiation.   

The electromagnetic spectrum of photons. Visible light is a narrow band in the middle. 13

Once matter was created, forces immediately went to work combining the fundamental particles into more complex, coherent structures.  Each quark generates a strong nuclear force that attracts other quarks.  This force caused quarks to instantly clump together in triplets to form protons and neutrons.  One proton by itself is also called a hydrogen nucleus because, in today’s world, a proton now forms the small central core of a hydrogen atom. 

You might think that the strong nuclear force would pull all protons together into one universal ball.  Fortunately, protons also generate an electromagnetic force that makes them repel each other.  Already, some complexity in the universe!  As two protons approach a head-on collision, their electromagnetic repulsion slows them down, stops them, and finally pushes them apart.  If they are fast enough, though, they will collide, and then the strong nuclear force will keep them together.  Shortly after the big bang, protons were still hot and fast enough to fuse in a process called big bang nucleosynthesis.     

Neutrons also produce the strong nuclear force, but they are electrically neutral.  This makes them great facilitators of nuclear fusion.  However, solitary neutrons decay in just a few minutes.  Just 20 minutes after the big bang, all the neutrons were either gone or bound to protons, and nucleosynthesis stopped. 14 There had only been enough time for protons and neutrons to get together in small numbers.  For hundreds of millions of years afterward, the chemical composition of the universe was fixed at 75% hydrogen, 25% helium, and trace amounts of the next two elements on the periodic table, lithium and beryllium.  These light nuclei are so stable that they have not changed since their formation.  They still carry a “signature” of the big bang, the oldest forensic evidence in the universe. 

The light nuclei, electrons, photons, and other fundamental particles swarmed madly together in a big hot ball of soup, or what is more technically termed a plasma.  It took about 400,000 years of expansion, thinning, and cooling to reach the next major event, recombination.  At that time, nuclei and electrons, which are electromagnetically attracted to each other, finally cooled down enough to start settling down together.  They formed complete atoms of hydrogen, helium, lithium, and beryllium.  With an equal number of protons and electrons, each atom was electrically neutral.

When neutral atoms formed, the photons that had been madly swarming in the plasma were finally released.  For the first time, light traveled freely through space.  The universe became transparent!  The photons that were released at this time still inundate space and are therefore referred to as the cosmic background radiation of the universe.  Originally, these photons assumed highly energetic forms like X-rays and ultra-violet light.  Now that they have been stretched out by the expansion of space, they have cooled down to microwaves with medium-low energy.

Even after recombination, the universe was still literally in its “dark ages” for almost a billion years.  It was an eerily empty universe compared to what we know today, consisting primarily of hot hydrogen and helium gas.  Initially, there were no stars or solid matter.  There must have been a time when the background radiation would have been visible to our eyes, making the whole universe glow blindingly brightly for millions of years before fading to black.

E. Upshot: Why Believe the Big Bang?

The big bang is a mind-blowing concept that has been trickling into public discourse for less than a century.  Many religious people feel that it came out of left field, and they dismiss it out of hand. 15 The whole universe bursting out of a hot dense point?  Why do scientists believe in such a cockamamie idea?

The truth is, big bang theory does a good job of accounting for the universe as it is actually observed.  It accounts remarkably well for three key conditions: the expansion of the universe, the cosmic background radiation, and the proportion of light nuclei in the universe.  It would be difficult to explain any of these phenomena in a steady state universe.

What’s more, all three of these key discoveries were predicted by big bang theory before they were observed. 161718 Skeptics might assume that scientists simply fabricated data to fit predictions.  Yet the cosmic background radiation was discovered accidentally, by antenna engineers who had never heard of the concept.

This is not to say that the theory is finalized.  There are major questions still to be resolved, like the nature of dark matter and energy.  But mainstream scientists see the big bang as a theory to be completed and refined, not overturned. 

Up to Chapter 10

Back to Section 10.I: Introduction

Continue to Section 10.III: The Matter-Dominated Era

F. Citations

  1. Image by US DOE, HD.6B.235 (1973), https://www.flickr.com/photos/departmentofenergy/11069100644 (accessed, saved, and archived 2/23/20. Not subject to copyright, as a US government creative work.
  2. Adam G. Riess et al., “Large Magellanic Cloud Cepheid Standards Provide a 1% Foundation for the Determination of the Hubble Constant and Stronger Evidence for Physics Beyond LambdaCDM,” Astrophysical Journal arXiv:1903.07603v2 (astro-ph.CO) (3/27/2019) , https://arxiv.org/abs/1903.07603v2 , accessed and saved 6/02/19.
  3. Allan R. Sandage, “Current Problems in the Extragalactic Distance Scale”, Astrophysical Journal, vol. 127, p. 513 (May, 1958), http://adsabs.harvard.edu/abs/1958ApJ…127..513S (accessed and saved 6/02/19).
  4. The interaction of space-time with matter-energy, and the expansion of space-time, are described in Einstein’s general theory of relativity.  First complete publication (German): “Die Grundlage der allgemeinen Relativitätstheorie”, Annalen der Physik 49(7):769-822 (March, 1916), http://myweb.rz.uni-augsburg.de/~eckern/adp/history/einstein-papers/1916_49_769-822.pdf (accessed and saved 6/3/19).  First English translation:  “The Foundation of the Generalised Theory of Relativity” in S.N. Bose and M.N. Saha, The Principle of Relativity; original papers by A. Einstein and H. Minkowski, University of Calcutta (1920), Part 2, pp. 89 – 163, https://archive.org/details/theprincipleofre00einsuoft/page/89 (accessed and saved 6/3/19).  Einstein’s own general-audience account of relativity was Relativity: The Special and General Theory, trans. Robert Lawson, Holt (New York, 1920), https://www.ibiblio.org/ebooks/Einstein/Einstein_Relativity.pdf
  5. Edwin F. Taylor and John Archibald Wheeler, Spacetime Physics, W. H. Freeman (1966) 2ed. (1992) p. 37, https://archive.org/details/spacetime_physics/page/n45/mode/2up (accessed 2/23/20). Used with permission of Prof. Taylor.
  6. Image by Wikimedia Commons user “Cush”, released into the public domain, https://en.wikipedia.org/wiki/File:Standard_Model_of_Elementary_Particles_Anti.svg#file (accessed, saved, and archived 10/23/20).
  7. Julija Bagdonaite et al., “A Stringent Limit on a Drifting Proton-to-Electron Mass Ratio from Alcohol in the Early Universe”, Science 339(6115):46-48 (1/04/2013), https://science.sciencemag.org/content/339/6115/46 (accessed and saved 6/03/19).
  8. Helge Kragh, “Preludes to dark energy:  zero-point energy and vacuum speculations”, Archive for History of Exact Sciences 66(3):199-240 (May, 2012), https://www.jstor.org/stable/41472231 (accessed and saved 6/09/19).
  9. S.K. Lamoreaux, “Demonstration of the Casimir Force in the 0.6 to 6 µm Range”, Phys. Rev. Lett. 78(1):5-8 (1/06/1997), https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.78.5 (accessed and saved 6/09/19).
  10. Alan H. Guth, “Inflationary Universe: a possible solution to the horizon and flatness problems”, Phys. Rev. D 23(2):347-356 (1/15/1981), https://journals.aps.org/prd/abstract/10.1103/PhysRevD.23.347 (accessed and saved 3/09/20).
  11. Guth, ibid, Appendix A.
  12. Edward P. Tryon, “Is the Universe a Vacuum Fluctuation?” Nature 246, 396-397 (12/14/1973), https://www.nature.com/articles/246396a0 (accessed and saved 6/09/19).
  13. Electromagnetic spectrum image by The Imagine Team, NASA (11/14/2014), https://imagine.gsfc.nasa.gov/science/toolbox/emspectrum1.html (accessed, saved, and archived 3/01/20).  In the public domain as the creative work of a US government agency.
  14. Ralph Alpher, “A Neutron-Capture Theory of the Formation and Relative Abundance of the Elements”, Physical Review 74, 1577 (12/01/1948), https://journals.aps.org/pr/abstract/10.1103/PhysRev.74.1577 (abstract accessed 6/23/19).
  15. Seth Borenstein and Jennifer Agiesta, “Poll:  Religion Trumps Belief in Big Bang Theory for Most Americans”, Associated Press (4/21/2014), https://www.nbcnews.com/science/science-news/poll-religion-trumps-belief-big-bang-theory-most-americans-n85806 (accessed and saved 6/16/19).
  16. Expansion of the Universe:  Predictions derived from Einstein (1916), op cit., observed by Edwin Hubble, “A relation between distance and radial velocity among extra-galactic nebulae”, PNAS 15(3):168-173 (3/15/1929), https://www.pnas.org/content/15/3/168 (accessed and saved 6/16/19).
  17. Cosmic background radiation:  Predicted by Ralph A. Alpher and Robert Herman, “Evolution of the Universe”, Nature 162, 774-775 (11/13/1948), https://www.nature.com/articles/162774b0 (accessed 6/16/19). Observed by A.A. Penzias and R.W. Wilson, “A Measurement of Excess Antenna Temperature at 2080 Mc/s”, Astrophysical Journal vol. 142, pp. 419-421 (July, 1965), http://adsabs.harvard.edu/abs/1965ApJ…142..419P (accessed 6/16/19).
  18. Nuclear ratios:  This was a more drawn-out process, but predictions were refined in the latter half of the 20th century, and the observations became accurate enough to confirm theory only in the early 21st century.  Good overview by Ethan Siegel, “Big Bang Confirmed Again, This Time By The Universe’s First Atoms”, Forbes (7/11/2017), https://www.forbes.com/sites/startswithabang/2017/07/11/big-bang-confirmed-again-this-time-by-the-universes-first-atoms/#5850116879c2 (accessed and saved 6/16/19). 
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