The Big Bang and the Beginning of Interaction

Last week we discussed the various hypothetical ideas for the infinitely distant past, before the Big Bang, the conventional beginning of not only the universe, but time itself. Where we left off I hinted about another side of cosmic inflation that we will touch on now. The inflationary model did not always regard a multiverse. As it was first proposed by Alan Guth, Old Inflationary Theory was simply supposed to be an explanation for the horizon problem. As Old Inflation Theory goes, the universe underwent exponential expansion (under the similar metastable conditions we described last week) sometime between t=10^-36 and t=10^-32 (between 10^-36 seconds and 10^-32 seconds after the Big Bang). This was the Inflationary Epoch, and we will call it the Old Inflationary Epoch to differentiate it from the more debatable multiverse from last week. However, this does not make Old Inflation Theory any more "true", just less conflicting and troubling. After all, it was originally supposed to be the most simple and elegant explanation for an existing problem (Angelo, 2012).

t = 0 to t = 10^-43 seconds

But before the Old Inflationary Epoch, there was still something else. The Plank Epoch was a peculiar time. In fact, it was the shortest possible unit of time for any physical event to occur. The Plank Epoch lasted at about t=0 to t=10^-43. This period of time, this shortest period of time, represents our deepest misunderstandings on the nature of physics in such highly unusual circumstances. The extremely dense environment that was this very first Epoch, we simply cannot explain (Angelo, 2020). During this mysterious period, the temperature was so high (the energy density was so high) that all four of the fundamental interactions might have been one in the same. We do not understand what this would mean.

Visualization of gravity curving space in 3 spatial dimensions.  Notice how the grid would have had perfect 90 degree angles if not for the massive object.  The clocks on the vertices of the grid represent the curvature of time.  The closer you are to the center of gravity, the more distorted time becomes.  

Image by Lucas Vieira Barbosa / CC BY-SA 4.0

t = 10^-43 to t=10^-32 seconds

After the Plank Epoch, the gravitational interaction was formed. Gravity is a strange thing, as to our current understanding it is not like the other fundamental interactions. According to the famous Theory of General Relativity, gravity is actually the outcome of the geometry of spacetime and the tendency of objects to follow a straight line (Daintith and Gould, 2006). Whenever an object of mass exists in spacetime, it curves the "fabric" of it to a certain way that alters what constitutes a straight line, and neighboring masses follow it. Because the universe is so homogeneous in its spread of matter, spacetime and especially space is mostly isotopic. Indeed there are deviations, but they are astonishingly small.

Note:  This behavior of objects is described in the Principle of Least Action.  For more information on this principle, see here.

Although the gravity may have formed almost immediately, that is not true for the other interactions. Grand Unified Theory asserts that three of the four interactions (not including gravity) act as a single force under extremely high energies. This would mean this period immediately after the Plank Epoch was the Grand Unification Epoch (Angelo, 2020). Uniting the fourth fundamental interaction, gravity, would require a literal "Theory of Everything", a truly ambitious project for the physicist.

Note: A Theory of Everything is probably one of the most contested areas of physics. The issue

is that Quantum Field Theory, the most fundamental theory of quantum mechanics, conflicts

with the Theory of General Relativity. For more information on one such proposed idea, String Theory, see here.

t = 10^-32 to t = 10^-12 seconds

About 10^-32 seconds after t=0, the interactions that we know of in the universe were almost born, beginning with the Electroweak Epoch (Sardar, 2015). The period of exponential inflation ended and the universe from then on would only expand via a mysterious anti-gravity energy not related to the inflaton field. This expansion since 10^-32 seconds started to steadily accelerate. With the inflaton field subsided the three gauge interactions that govern our universe formed. 

The forces of the universe were at this time, the strong force, the electroweak force, and the force of gravity. At this time the temperature of the universe was low enough that the electronuclear force, the unification of the strong and electroweak forces, broke down. This is known as symmetry breaking. In physics, symmetry doesn’t refer to the thing that equilateral triangles or butterflies have, but an invariance, or independence to a factor. The strong nuclear force was the first to break off. These forces were carried by particles called gauge bosons. The strong force, the strongest of the 4 forces, is carried by gluons which “glue” (quark) particles that interact with this force together in immensely strong bonds. However, at this point in the universe’s history the temperature was so high that particles would collide into each other at insanely high energies, resisting binding. The electroweak force was a unification of the massless photon and the W and Z bosons. These were produced at incredible rates as the energy was high enough for near constant particle Interaction.

Visualization of the quantum fluctuations of a field - the excited states of energy are oscillations.  They vanish when they oscillate back into antimatter form, causing a collision and converting the masses in energy in the form of photons.

Image by Ahmed Neutron / CC BY-SA 4

At this point it is important to explain what Quantum Field Theory exactly is. "Particles" are

commonly understood as points in space which can change their position in space over a period

of time. However, Quantum Field Theory states that all elementary particles have corresponding

fields throughout space (Larson, 2007). Fields work in 3 spatial dimensions, but take a moment to imagine it in 1 dimension. That would be a line. When the line is pulled in one direction, it pushes back the other, and this continues in a vibration/oscillation. This exact oscillation is a particle. There are two types of fields, a force fields (describing the particles responsible for three of the four fundamental interactions), and the matter fields. Keep in mind that when I refer to a gluon, it is not an isolated particle, but a product of this oscillation.

t = 10^-12 seconds to t = 10^-6 seconds

The electroweak force eventually too split by t=10^-12 seconds, into electromagnetism for

photons and the weak force for W and Z bosons, due to the slowly decreasing temperature as

the universe expanded. 

The W and Z bosons should be massless, but are not. As the temperature decreased and the weak force was separated from the electromagnetic force, not only did the electroweak force split, but the higgs field began to interact with particles (Kibblie, 2015). The higgs field is a scalar field like the inflaton field (in fact they might be the same thing) with a non-zero value even in a vacuum state. It is very unstable and, at these immensely high energies, commonly decays into W and Z bosons. The W and Z bosons now had mass. Mass is not being created. Simply, when the higgs field decays it converts its potential energy into mass, which is called the Mass-energy Equivalence Principle, and is described in the famous equation “E=mc^2” (Hale, 2020).

Note:  The higgs field is a fascinating discovery in recent years, and it is important to understand it in a fair light, given all the sensationalism surrounding it.  In the past we’ve talked about the inflation field and even the possibility of the famous dark energy being a scalar field, but in reality these proposed fields may simply be the higgs field for all we know.  For more information on the higgs field, see here.  Also important to note, what exactly is a scalar?  A scalar is a value with no specific sense of direction or place.  So a scalar field has the same value everywhere. A vector is a value that specifies direction or place.  So a vector field, in other words the fields of matter or the other gauge bosons, do have a sense of place or direction.

The other form of particle that developed mass at this time was the fermion, which two of which

cannot occupy the same space. A fermion or matter particle is defined by its color charge, interaction with the strong force, its weak isospin, interaction with the weak force, its electric charge, interaction with the electromagnetic force, and its mass, ability to curve spacetime. A type of fermion is a quark, of which there are up quarks and down quarks, which interact with all four forces. The strong force in particular, binds the up and down quarks into dense hadrons: protons, neutrons and mesons. These protons and neutrons further bind into the nuclei of atoms. The other quarks also contribute to the formation of hadrons. Mass would allow for the fourth force, gravity, to finally interact. However, it is the weakest of the 4 forces, and at this quantum level insignificant. At this state, the temperature would still be so great that the quarks are shooting past and colliding with one another, releasing incredible energies.  There are also leptons, which encompass the very famous electron, but that will be discussed next week.

It is important to note that among the fermions, for every fermion there is an antifermion. Each type of fermion particle has its own quantum matter field as mentioned before, exactly behaving in oscillations. However, when it excites in one direction, it excites at the same magnitude in the other likewise. This creates a situation whereas two particles with equal mass but opposite charge appear. This is matter and antimatter. When antimatter collides with matter it converts its mass into enormous amounts of energy in the form of photons. This has been occurring continuously from where we started until now, filling the universe with a spectacular array of photons.  Because photons do not interact with the Higgs field, they truly have no mass (this causes them to have a constant unchanging speed). This state of constant collision would only last until about t=10^-6 seconds. Next week we will venture into when this will almost completely cease in one of the greatest mysteries of our universe.

References:

Angelo, J. A. (2012). Inflation. In Extreme States of Matter. New York: Facts On File. Retrieved from online.infobase.com/Auth/Index?aid=103612&itemid=WE40&articleId=567093.

Angelo, J. A. (2020). The big bang—source of all energy and matter. In Energy of Matter, Revised Edition. New York: Facts On File. Retrieved from online.infobase.com/Auth/Index?aid=103612&itemid=WE40&articleId=569727.

Sardar, Z. (2015). Postnormal Artefacts. World Futures Review, 7(4), 342-350. doi:10.1177/1946756715627370

Daintith, J., & Gould, W. (2006). General relativity. In Dictionary of Astronomy, Fifth Edition. New York: Facts On File. Retrieved from online.infobase.com/Auth/Index?aid=103612&itemid=WE40&articleId=291290.

Larson, D. T. (2007). Quantum Field Theory. In The Nature of Matter. New York: Facts On File. Retrieved from online.infobase.com/Auth/Index?aid=103612&itemid=WE40&articleId=377745.

Kibble, T. W. (2015). Spontaneous symmetry breaking in gauge theories. Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences, 373(2032), 20140033. doi:10.1098/rsta.2014.0033

Hale, G. (2020). Higgs boson. In Encyclopedia of Physical Science, Revised Edition. New York: Facts On File. Retrieved from online.infobase.com/Auth/Index?aid=103612&itemid=WE40&articleId=559175.

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