The Epic Chronology blog will have all future posts at:
https://epicchronology.wordpress.com/
from now on. Over the weekend I will work on moving all my original posts to the new site. I'm also working on a new post after the long break.
From 10 seconds to 20 minutes after the Big Bang, a process of primordial nucleosynthesis occurred. Nucleosynthesis is the process in which the baryons (protons and neutrons) combine with each other to form atomic nuclei. The first ever element was hydrogen, with its atomic number of 1. The atomic number of an element signifies how many protons it has in its nucleus. The atomic number is the single determining factor for what type of element an atom is. However, the amount of neutrons in an atom can change and still be the same element. For example, the element hydrogen can have no neutrons, 1 neutron, or 2. Neutrons and protons are held together by the strong nuclear force.
At this point in the universe's history the temperature was so high that the protons had so much energy, that they could overcome their electromagnetic repulsions (they are positively charged and hence repulse) and form heavier and heavier atomic nuclei. However, it was too high. Earlier in the universe's history, the energy of each photon was so high that it would collide with any atomic nuclei heavier than hydrogen, forcing them to decay into lighter forms. This was known as the "deuterium bottleneck", named after the hydrogen isotope of deuterium (with 1 neutron instead of none). As the temperature of the universe cooled the photons didn't have enough energy to cause these violent events, and heavier elements could continue to form.
Note: During this period, the ratio between baryons and photons was being determined, This ratio played a key rule in nuclear reactions, specifically the transformation of deuterium into helium-4 (an isotope of helium with 2 neutrons). For more information on how this ratio affected nuclear reactions, and other ratios like the proton-neutron ratio, see here.
The deuterium and tritium collide to form helium-4, with an extra neutron breaking loose.
Image by Kirill Borisenko / CC BY-SA 4.0
These protons came about from a process of radioactive decay. Many were originally neutrons which, through the weak interaction, decayed into an electron, a neutrino, and a proton. This specific decay involving the loss of an electron is known as beta decay. Yes, protons are very slightly less massive than neutrons. Once the protons via their immense energies were forced close enough to each other, the strong nuclear force was able to interact between the 2 protons and overcome the electromagnetic repulsions. This led to the creation of the next element with its atomic number of 2: helium. This was specifically helium-4, meaning it had 2 protons and 2 neutrons. It was created out of the fusion reaction of deuterium and tritium, isotopes of hydrogen, colliding into each other. This type of collision could only be possible in these immense temperatures such as the early universe, as the electromagnetic repulsions were just that strong.
Diagram of the progression of primordial nucleosynthesis. Neutrons don’t have no charge,their charge is just balanced between positive and negative. So they can decay an electron, and effectively become a proton. In this early stage of the universe because it was all plasma,a single proton was effectively hydrogen. Add a neutron, and you have deuterium. Before this period in the universe the temperature was so high that the photons (y) would have so much energy, that they would rip up the deuterium. At this point the deuterium could become tritium or helium-3, which themselves can form helium-4. This process continued into the heaviest elements of lithium-7 and beryllium-7. However, these quickly decayed back into helium-4.
Image by Pamputt / CC BY-SA 4.0
Altogether, after this incredibly short period of primordial nucleosynthesis, the universe's mass was about 75% hydrogen, 24% helium, and trace amounts of deuterium, tritium, and even lithium and beryllium. Deuterium and tritium are isotopes of hydrogen having, instead of only 1 neutron, rather 2 and 3 neutrons respectively. Lithium, however, is an entirely new element with an atomic number of 3. Byrrelium has an atomic number of 4. As the universe continued to expand the temperature continued to drop and nucleosynthesis on such a wide scale was no longer possible.
What followed was the matter dominated Epoch. In this special time, the temperature of the universe was cool enough for matter to finally exist in a long term sense, however the universe was still so small that everywhere you looked was mostly matter. The universe was entirely a plasma, the 4th modern state of matter. A plasma is when the temperature is so hot that the atomic nuclei float alone, without any electron orbitals (note that the quark-gluon plasma from even earlier was so hot that not even atomic nuclei existed). About 380,000 years after the Big Bang, the temperature of the universe was finally cool enough for this plasma state to fall into the gas state of matter.
This event was known as decoupling, when electrons could finally resist the incredible amount of energy and through their electromagnetic force attract toward the positively charged protons of nuclei and form orbitals around them. I use the term orbital, but it was nothing like the path a planet would take to orbit the sun. It was not a circle, but a fog of probability, the general area of the whizzing proton. The first orbital of an atom is called the s orbital, which can have a maximum of 2 electrons. After that electrons would gather around another s orbital, followed by a p orbital which can hold 6 electrons.
The Cosmic Microwave Background as seen by telescopes. For more information on the amazing discovery of the cosmic microwave background, see here.
Image by NASA / WMAP Science Team
Another thing happened in this moment of decoupling. During the last 380,000 years, all the way back to the initial annihilation of antimatter, a massive array of photons were created. However, due to the immense density of the matter dominated era, this could not be appreciated. They were stuck in an endless loop of ping pong between tightly packed atomic nuclei. Now, 380,000 years later, the universe was large enough that these photons could finally gain their freedom. With that, the famous Cosmic Microwave Background which made this incredible journey for us to understand possible. And with that, our chapter of the Big Bang and the early universe is finally over (until the next big discovery!). We’ve traveled far back in the infinite past, before the beginning of time. We explored the mysteries of the very beginnings, and discovered the very origins of our reality. Now it is time to look at our much more familiar recent past and even the far future. Thank you for reading along.
P.S.: I will be taking a break to plan out the next set of posts which will see the formation of more concrete and familiar astronomical bodies. There is simply so much though that I have to take time to plan it out. I will also be spending this time to revise my older posts so stay tuned for that on the discord server (you can join in the about page). See you then!
Where we left off the fundamental forces of the universe were being defined and the universe continued to be an extremely high energy soup of constant collision. The universe at this point was in a constant state of high energy photons converting into matter-antimatter pairs only to annihilate with each other back into photons (Das & Ferbel, 2013). Antimatter has the same mass but opposite electric charge of their matter component. So you can have a quark and an antiquark, or an electron and an antielectron (also called a positron). The universe was basically a photon gas, as well as a "quark-gluon soup" of tightly packed matter and antimatter continuing this process.
Diagram of pair production. γ is “gamma” or the term for a high energy photon. The energy it contains is so high that it converts into a pair of an electron and an antielectron (positron). At this point, the universe was so hot that photons would also convert into pairs of quarks and antiquarks. Note, you would actually need a pair of photons, not just one, to collide with one another and produce this pair.
Image by Christian Nölleke / CC BY-SA 3.0
That would change. Sometime in the early universe (we don't exactly know when this happened) the temperature of the universe dropped to a point where this photon matter creation process would happen en masse for one last time. This critical temperature was 2x10^12 K, leading to the final annihilation which is called Baryogenesis (baryo- meaning baryon). Mysteriously, even though a particle and antiparticle are seemingly always created together in pairs, this final annihilation left us with mostly matter and almost no antimatter (Cline, 2004). This is the great mystery of Baryogenesis, the asymmetry between matter and antimatter. It has been calculated that there must have been an extra particle for every 5 billion particle-antiparticle pair.
Note: This baryonic asymmetry has actually been observed in our own experiments. In 2010, Fermilab managed to generate 1% more matter than antimatter. The reason why this happens is still not known. To learn more about the experiment and other modern quantum experiments, see here.
Diagram of annihilation. The matter and antimatter attract each other and collide, converting back into high energy photons. Note again, there would not be a single photon in this transition, but a pair. This should happen, but for some reason a small amount of matter is left over.
Image by Iamion / CC BY-SA 4.0
There are many ideas, though unverified, for how this could have occured. Within the Standard Model, it is possible that when the electroweak force was splitting into the weak and electromagnetic forces symmetry breaking occured. Symmetry breaking famously occurs during phase transitions (as in the phases of matter). When an object decreases in temperature it reaches a critical point where it stops decreasing in temperature and instead transitions to a new phase of matter. Objects of lower temperature phases are less symmetrical than objects of higher energy phases. So as the universe cooled and the symmetry of the electroweak force broke, then it would lead to the change in how matter and antimatter are created and eventually annihilated. This could have led to the matter-antimatter asymmetry that we observe today.
Note: The idea of symmetry is very important in physics. Basically, symmetry describes any situation in which certain features remain unchanged during a sort of transformation, such as a phase change. Sometimes there is a symmetry breaking, meaning these features change. This is what could have happened after the Electroweak Epoch, changing the features of the creation and annihilation of matter and antimatter, possibly allowing for the matter asymmetry we observe today. For more information on symmetry in physics, see here.
A second idea involves this occurring after the Grand Unified Epoch. It states that in order for this baryogenesis asymmetry to occur, there must be a not only a violation (breaking) of the baryon number (a mathematical constant) and violation of charge-symmetry (C Symmetry) and parity-symmetry (P Symmetry), but also thermal equilibrium (Today’s Science, 2015). This means there would be no flow of heat from one part of space to another, that all parts of space had equal amounts of heat. This is how heat acts, it wants to flow from an area of greater heat to an area of lower heat so that both areas have the same amount of heat. In thermal equilibrium the flow of heat does not occur because this state is already reached. This too, has not been verified.
A third, much more daring idea is that there are equal amounts of matter and antimatter, yet they somehow separated without annihilating each other. They would create their own regions, meaning supposedly there are antimatter stars and even antimatter galaxies somewhere out there (Thomsen, 1973). However, this has never been observationally verified.
At this point all matter for the universe has been produced. In this truly Hadron Epoch, quark production had ceased. The remaining quarks would form into various types of hadrons, of which there are baryons and mesons. A baryon is made up of 3 quarks, and they include protons and neutrons, whilst a meson is made up of 2 quarks. These hadrons, and especially the baryons, would become the foundation of nuclear chemistry.
The following Lepton Epoch (t=1 to t=180 or 3 minutes) was very similar. For leptons, a type of fermion just like the quarks but with much smaller masses, the required amount of energy needed for constant photon conversion into lepton and antilepton pairs was much lower. So the universe had to cool for even longer before this too would end. The leptons include the muon, tau, and of course the famous electron. Leptons interact with all the fundamental interactions except for the strong force. So they did not form into heavier hadrons like the quarks did. These leptons have not only corresponding antimatter versions but also neutrino, meaning it does not interact with the electromagnetic force. So there is such a thing as a neutrino electron, though the vast majority of electrons are charged. During the Electroweak Epoch, when electromagnetism and the weak force acted the same, neutrinos were able to interact with the other fermions. This is neutrino decoupling, and it occurred at around this time, as evident of the Cosmic Neutrino Background.
Note: The Cosmic Neutrino Background (CNB), has very recently been directly observed for the first time. For more information on this discovery, see here.
The famous diagram of the Standard Model outlining all the elementary particles of the universe. Note, this diagram is dated and the Higgs boson has been confirmed.
Image by Andres Rojas / CC BY-SA 4
At this point the temperature of the universe was so low that photons no longer had the energy to constantly convert into various quarks and leptons like it used to. These photons made up the majority of the universe and would continue to exist as the catalyst of the electromagnetic force. The quarks and leptons would now be able to exist without constant annihilation, and antimatter would become the ultimate rarity. As the universe continued to cool and space continued to expand, more familiar processes could take hold. That will be next week. For now, the Standard Model is complete.
References:
Das, A., & Ferbel, T. (2013). Introduction to nuclear and particle physics (2nd ed.). World Scientific.
Cline, J. (2004). The Origin of Matter. American Scientist, 92(2), 148. https://doi.org/10.1511/2004.46.926
“Why More Matter Than Antimatter?” Today's Science, Infobase, 2015. Science Online, online.infobase.com/Auth/Index?aid=103612&itemid=WE40&articleId=1009338. Accessed 13 Nov. 2020.
Thomsen, D. E. (1973). Does the Universe Need Antimatter? Science News, 103(13), 211. https://doi.org/10.2307/3958135
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).
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
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.
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.
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.
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
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
