Before the Big Bang

The question of what was before the universe even came into existence is a peculiar one.  Albert Einstein posited that asking this question would be ridiculous, just as ridiculous, he added, as asking what is north of the north pole.  This is because time is relative and as the universe continues it diverges.  If you go back into the past instead, time converges into a single point.  You cannot discuss the time before it, because there simply was no time before it.  So there simply was no time before the Big Bang.  However, this didn't stop physicists from forming various hypotheses for not only explaining what was before the Big Bang, but also what is waiting for the universe in the far future. 

Note:  A hypothesis, such as the Big Bounce Hypothesis, is a testable idea to explain a physical phenomenon.  A theory, such as the Big Bang Theory, is a type of hypothesis that has been thoroughly tested already with positive results.  This is different from casual language where a theory is simply a hunch or a guess.  In science, a theory has already been tested.  A law simply describes a natural phenomenon in the form of an equation, but lacks an explanation that a hypothesis or theory has.  For more on the philosophy of science and epistemology, see here.

Before discussing the various models, it is important to understand the various points of confusion that require an explanation.  One is the fact that we do not understand how physics behaves in the cosmological singularity, the point of infinite density that the Big Bang supposedly began with.  Another issue is the homogeneity of the universe’s contents, the flatness or lack of curvature of space, and the isotropic nature in its view (Carrigan and Trower, 1983).  Scientists consider all three of these remarkable coincidences, and ones that require more fundamental explanations on the origins of the universe.

Note:  Mathematics is extremely fundamental to physics and some even consider it the innate language of the universe.  To learn more about isotropy, see here.

Think of a reverse Big Bang

Image by Ævar Arnfjörð Bjarmason / CC BY-SA 2.0

t = -∞ to t = 0 seconds

One such idea for what was that before the Big Bang is the Big Bounce Hypothesis.  It is a continuation of the Big Crunch Hypothesis which concerns the end of the universe.  The Big Bounce refers to a cycle, possibly even a never ending one, that the universe takes.  It begins with a big bang, leading to the expansion of a universe, until it reaches a certain point where the universe begins to contract instead of expand.  The hypothesis explains that this contraction would be due to gravity forcing not only matter, but also space itself back into the small point that it once started as (Daintith, 2006).  

Once the universe would crunch into a singularity - an infinitely small point with infinity energy - we don’t know how physics operates in such an environment.  The specifics of that specific predicament will be discussed next week.  The Big Bounce Hypothesis claims that quantum fluctuations - random fluctuations of energy in a quantum field - behave differently, and universal constants begin to vary.  This idea fell short to many because the universe’s expansion was in fact accelerating, with no apparent sign of stopping.

Visualization of the quantum fluctuations of a field - notice the irregular lumps of energy

Image by Ahmed Neutron / CC BY-SA 4

Another explanation for what happened before the Big Bang is the Eternal Inflation Model.  This was derived from Old Inflation Theory which we will discuss next week.  We begin with a field - the inflaton field. It is a type of quantum field, a scalar field meaning its energy state is not dependent on location in space (Rennie, 2002).  It is in a constant struggle to reach a vacuum state, a state with minimum potential energy and the absence of particles.  The inflaton field slowly decays its potential energy into exponential expansion, however many regions of it at random intervals and random quantities shoot the inflaton field back into higher decays.  These random happenings are known as quantum fluctuations, so really they are random fluctuations of energy state in the field (Daintith, 2006).  The inflaton field also releases its immense potential energy into the exponential inflation of space. However, at a certain point regions of it in their own time start to rapidly decay into inflaton particles, ceasing rapid space inflation (Rennie, 2002). This also has the effect of causing neighboring regions of the inflaton field to more quickly fall into this rapidly decaying state (Brandenburger, 2001). 

Overtime, across the inflaton field there are regions or bubbles of space in which these processes occur. In the surrounding regions outside the bubble, exponential inflation continues to occur until those regions also reach rapid decay in their own times. This creates a  structure in which the expansion of the bubbles can never fully encompass the slow rolling inflaton field.  Think of fractals.  In this environment not only was our universe born, but many universes within their own bubbles of expansion. The inflaton field is truly infinite, and our universe is just one of the bubbles.  

This model championed over the Big Bounce Hypothesis for decades, but not without issues.  Namely, the Eternal Inflation Model describes a multiverse which is problematic because it does not predict the physical properties of our universe, but simply equates it to random chance, in an infinite pool of universes (Witze, 2012).  The inflaton field was also never directly observed, although since we do have direct observations of a scalar field in nature, this is not so much an issue.  Returning in various forms, the Big Bounce Hypothesis is being currently tested in its merits, including Ekpyrotic Universe Theory which states that the uniformity and flatness of space in the universe is not a product of "random intervals" in some field, but a testable explanation.  However, the Eternal Inflation Model is still backed by the very concrete Quantum field Theory, whilst the Ekpyrotic Universe Model partly requires String Theory which itself remains controversial (Cowen, 2001).   

Even more contemporary theories do not require “new physics”.  One such idea attempts to explain the aforementioned observed expansion of the universe in terms of metastability within another scalar field.  Metastability is similar to the slow-rolling phenomenon we saw in the inflaton field.  If scalar fields wish to reach a vacuum state through converting potential energy into kinetic energy, then metastability is a false vacuum state where the field is not at its most minimum possible potential energy, yet it does not decay - it acts stable when it is not.  Once a quantum fluctuation randomly takes this field out of metastability, the field will decay into true stability, which its minimum potential energy could be low enough for the universe to begin to contract (Rennie, 2002). The Big Bounce Model is ultimately much more interesting to many current physicists compared to the Eternal Inflation Model because of its much more concrete power of predictability, rather than random chance. 

Note:  Dark energy is a fun idea we’ve all heard of before, but do not confuse it with the inflaton field.  In fact all of these supposed scalar fields could all be describing the only scalar field we have detected so far, the Higgs field.  If you’ve heard of sensationalist news stories exclaiming the universe will end because of the discovery of the Higgs field, it’s possible they were describing this exact phenomenon of contraction.  Others include relations to the fundamental forces.  All of these we will cover next week.  

Whether it be an endless cycle of expansions and contractions, or a vast field of infinitely many universes, there is no question that the "time" before the beginning is one of the most mysterious questions of cosmology.   Next week we will observe our more concrete understanding of the immediate phenomena after the Big Bang.

References:

Carrigan, R. A., & Trower, W. P. (1983). Magnetic monopoles. New York: Plenum Press.

Daintith, J., & Gould, W. (2006). Big crunch. In Dictionary of Astronomy, Fifth Edition. New York: Facts On File. Retrieved from online.infobase.com/Auth/Index?aid=103612&itemid=WE40&articleId=290061.

Rennie, R. (2002). In Dictionary of Atomic and Nuclear Physics. New York: Facts On File. Retrieved from online.infobase.com/Auth/Index?aid=103612&itemid=WE40&articleId=292865.

Brandenberger, R. (2001, January). A Status Review of Inflationary Cosmology. Retrieved from https://ui.adsabs.harvard.edu/abs/2001hep.ph....1119B/abstract

Witze, A. (2012). Inflation on trial: Astrophysicists interrogate one of their most successful theories. Science News, 182(2), 20-21. doi:10.1002/scin.5591820224

Cowen, R. (2001). When Branes Collide. Science News, 160(12), 184. doi:10.2307/4012670