I have some questions about the cosmic inflation. As I tried to find the answers, I got little more confused. I have mentioned all the quotes from relevant articles which I found confusing. I understand that there are quite a few questions but they are all related to each other and I thought that asking them together might be a good idea so you can see where I'm having the difficulty.
Also please keep in mind that I'm only trying to understand it from basic layman point of view.
Thank you for your time and help, in advance!Quote 1:
In physical cosmology, cosmic inflation, cosmological inflation, or just inflation, is a theory of exponential expansion of space in the early universe. The inflationary epoch lasted from 10−36 seconds after the conjectured Big Bang singularity to some time between 10−33 and 10−32 seconds after the singularity. Following the inflationary period, the universe continued to expand, but at a slower rate. The acceleration of this expansion due to dark energy began after the universe was already over 7.7 billion years old (5.4 billion years ago).[1] https://en.wikipedia.org/wiki/Inflation_(cosmology)
Quote 2:
Detailed measurements of the expansion rate of the universe place the Big Bang singularity at around 13.8 billion years ago, which is thus considered the age of the universe.[6] https://en.wikipedia.org/wiki/Big_Bang
Quote 3:
Immediately after the Big Bang, the universe was a hot, dense plasma of photons, leptons, and quarks: the quark epoch. At 10−6 seconds, the Universe had expanded and cooled sufficiently to allow for the formation of protons: the hadron epoch. This plasma was effectively opaque to electromagnetic radiation due to Thomson scattering by free electrons, as the mean free path each photon could travel before encountering an electron was very short. This is the current state of the interior of the Sun. As the universe expanded, it also cooled. Eventually, the universe cooled to the point that the formation of neutral hydrogen was energetically favored, and the fraction of free electrons and protons as compared to neutral hydrogen decreased to a few parts in 10,000. https://en.wikipedia.org/wiki/Recombination_(cosmology)
Quote 4:
Extrapolation of the expansion of the universe backwards in time using general relativity yields an infinite density and temperature at a finite time in the past.[20] This irregular behavior, known as the gravitational singularity, indicates that general relativity is not an adequate description of the laws of physics in this regime. Models based on general relativity alone can not extrapolate toward the singularity—before the end of the so-called Planck epoch.[5]
This primordial singularity is itself sometimes called "the Big Bang",[21] but the term can also refer to a more generic early hot, dense phase[22][notes 2] of the universe. https://en.wikipedia.org/wiki/Big_Bang#Singularity
Quote 5:
The earliest phases of the Big Bang are subject to much speculation, since astronomical data about them are not available. In the most common models the universe was filled homogeneously and isotropically with a very high energy density and huge temperatures and pressures, and was very rapidly expanding and cooling. The period from 0 to 10−43 seconds into the expansion, the Planck epoch, was a phase in which the four fundamental forces — the electromagnetic force, the strong nuclear force, the weak nuclear force, and the gravitational force, were unified as one.[25] In this stage, the characteristic scale length of the universe was the Planck length, 1.6×10−35 m, and consequently had a temperature of approximately 1032 degrees Celsius. Even the very concept of a particle breaks down in these conditions. A proper understanding of this period awaits the development of a theory of quantum gravity.[26][27] The Planck epoch was succeeded by the grand unification epoch beginning at 10−43 seconds, where gravitation separated from the other forces as the universe's temperature fell.[25]
At approximately 10−37 seconds into the expansion, a phase transition caused a cosmic inflation, during which the universe grew exponentially, unconstrained by the light speed invariance, and temperatures dropped by a factor of 100,000. Microscopic quantum fluctuations that occurred because of Heisenberg's uncertainty principle were amplified into the seeds that would later form the large-scale structure of the universe.[28] At a time around 10−36 seconds, the electroweak epoch begins when the strong nuclear force separates from the other forces, with only the electromagnetic force and weak nuclear force remaining unified.[29]
Inflation stopped at around the 10^−33 to 10^−32 seconds mark, with the universe's volume having increased by a factor of at least 1078. Reheating occurred until the universe obtained the temperatures required for the production of a quark–gluon plasma as well as all other elementary particles.[30][31] Temperatures were so high that the random motions of particles were at relativistic speeds, and particle–antiparticle pairs of all kinds were being continuously created and destroyed in collisions.[4] At some point, an unknown reaction called baryogenesis violated the conservation of baryon number, leading to a very small excess of quarks and leptons over antiquarks and antileptons—of the order of one part in 30 million. This resulted in the predominance of matter over antimatter in the present universe.[32] https://en.wikipedia.org/wiki/Big_Bang#Inflation_and_baryogenesis
Quote 6:
According to inflation theory, during the inflationary epoch about 10−32 of a second after the Big Bang, the universe suddenly expanded, and its volume increased by a factor of at least 10^78 (an expansion of distance by a factor of at least 1026 in each of the three dimensions). This would be equivalent to expanding an object 1 nanometer (10−9 m, about half the width of a molecule of DNA) in length to one approximately 10.6 light years (about 10^17 m or 62 trillion miles) long. A much slower and gradual expansion of space continued after this, until at around 9.8 billion years after the Big Bang (4 billion years ago) it began to gradually expand more quickly, and is still doing so. Physicists have postulated the existence of dark energy, appearing as a cosmological constant in the simplest gravitational models, as a way to explain this late-time acceleration. According to the simplest extrapolation of the currently favored cosmological model, the Lambda-CDM model, this acceleration becomes more dominant into the future. In June 2016, NASA and ESA scientists reported that the universe was found to be expanding 5% to 9% faster than thought earlier, based on studies using the Hubble Space Telescope.[2] https://en.wikipedia.org/wiki/Expansion_of_the_universe Question 1:
It's related to the first paragraph of Quote 4.
What does it mean when it's said that all the present physics theories break down if they try to explain what happened before the Planck epoch, i.e. from 0 seconds to 10^-43 seconds. This is also said that the theory of quantum gravity will be able to explain it one day. For example, to put in perspective, I think I understand how at small scale the theory of general relativity fails, one of the reasons from a layman perspective, is that the location of a particle is not fixed at microscopic scale and hence is the curvature of space-time is also not fixed to one location.
Question 2:
During the inflation, the space was able to expand at faster than the speed of light, at almost 3.3 x 10^40 times the speed of light as shown in the "Calculation" below. But how did whatever the 'material' that non-inflated space contained within it before the inflation was able to keep pace with the inflated space. Did the material the space contained in it also inflated at the same rate?
Calculation:
As the Wikipedia article, Quote 6, says that during inflation 1 nm distance expanded to 62 trillion miles over the period of 10^-32 second (assuming inflation lasted from10^-36 second to 10^-32 second).
62 (10^12) miles
62 (10^12) miles / 10^-32 second
62 (10^44) miles/second
speed of light 186000 miles/second
3.3 x 10^40 times the speed of light
For the epoch titled "Inflationary epoch, Electroweak epoch" between 10^-36 to 10^-32 seconds, in green highlight it says, "Cosmic inflation expands space by a factor of the order of 10^26 over a time of the order of 10^−36 to 10^−32 seconds".
For the epoch titled "Electroweak epoch ends" around 10^-12 second, in yellow highlight, it says "The sphere of space that will become the observable universe is approximately 300 light-seconds in radius at this time".
This part has confused me a lot. As it is said the universe was infinite to start with, then the big bang happened everywhere. The visible universe is a subset of the whole universe. If the visible universe is compressed back, it would result into a singularity. Informally speaking at the time of big bang, such singularities were present everywhere in the universe. At the time of big bang, all those singularities exploded.
If the universe was really infinite to start with then how it can expand by a factor of 10^26. Is it infinity expanding by a factor of the order of 10^26?! If it's been estimated that it expanded by a factor of 10^26 then the size of universe at the beginning should have been known.
Question 4:
Under Quote 5, under third paragraph, it says, "Inflation stopped at around the 10^−33 to 10^−32 seconds mark, with the universe's volume having increased by a factor of at least 1078. Reheating occurred until the universe obtained the temperatures required for the production of a quark–gluon plasma as well as all other elementary particles".
How did the reheating occur? I understand that as the universe expanded, its temperature should have dropped. But then how did it reheat itself?
Question 5:
If you look under the column titled "Epoch" of the table, there is a row labelled "Electroweak epoch end" around 10^-12 seconds after the big bang. It seems like induvial particles such bosons and fermions started coming into existence around that time. I've highlighted the terms in blue.
The photons came into existence during the epoch titled "Quark epoch" which occurred between 10^-12 second to 10^-5 second after the big bang.
Do you think I'm understanding it correctly as a layman?
Under Quote 1, in first paragraph, it says, "Following the inflationary period, the universe continued to expand, but at a slower rate. The acceleration of this expansion due to dark energy began after the universe was already over 7.7 billion years old (5.4 billion years ago)".