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Follow up video on Eternal Inflation:
References:
Gary Felder’s Wondrium lectures on Big Bang: https://t.ly/emdPY
Alan Guth paper summary and lecture: https://t.ly/WqKQ
Alan Guth paper: https://t.ly/wF3x
Paul Steinhardt list of articles on Inflationary cosmology: https://t.ly/ZqmH
Excellent article on Inflation: https://t.ly/rrZU
Chapters:
0:00 – Popular models of Big Bang are incorrect
2:27 – Observations not explained by original Big Bang model
4:37 – Common misunderstandings of Big Bang
7:12 – How Inflation “fixes” the Big Bang
11:56 – What caused cosmic Inflation?
15:23 – Next video: Eternal Inflation!
Summary:
The Big Bang theory: In the beginning, the universe was packed tightly together into a point of infinite density. It then exploded into the universe we see today. This is actually INCORRECT.
There was no explosion. There was no substance like stars, galaxies, or even atoms that went flying. The universe did not have zero size or infinite density. It is just a moment in time when the universe was very hot and very dense.
And contrary to popular belief, the big bang model is not a theory of how the universe began. We don’t know how it began.
The early model of the BB failed to explain some later observations about the universe – its homogeneity, its flatness, and no magnetic monopoles. The theory of cosmic inflation proposed by Alan Guth and others, solved these puzzles.
What is this theory of Inflation? How does it fix the big bang? What caused Inflation to happen?
Cosmic Inflation is a sudden expansion, faster than the speed of light, whcih happend from about 10^-36 seconds after the beginning to 10^-32 seconds. It expanded a factor of at least 10^78x
How could inflation occur faster than speed of light? Einstein’s theory of special relativity shows that speed limit applies only to things moving within space, not the expansion of space itself.
Some descriptions of inflation say the universe started out smaller than an atom, then expanded to the size of a grapefruit. This is misleading because it implies that the universe has an edge. It doesn’t.
Other common misunderstandings about the Big Bang: The universe did not come from a point of infinite density and heat. This is purely due to mathematical extrapolation. A singularity is probably not a physical thing.
Universe is expanding, but galaxies aren’t actually moving at that expansion rate, only the space between galaxies is becoming larger, and only on very large scales. But on smaller scales gravity still holds stars together within a galaxy, and certain galaxies are still attracted to each other.
There is no center of the universe or location. Every point moved away from every other point.
The universe is extremely homogenous and isotropic which means that it appears roughly the same anywhere. This can be seen in the cosmic microwave background, or CMB, where the tiny differences you see on its image represent temperature fluctuations of only 0.0001 Kelvin.
How did the universe smooth out? Imagine it like the surface of deflated balloon. There may be tiny imperfections like wrinkles randomly distributed on it. If the balloon is suddenly inflated to a very large size, the wrinkles get smoothed out.
How does inflation explain the flatness issue? If you were the size of an ant on a small balloon, and the balloon expanded to the size of the Earth, it would appear flat to you, even though it is still a sphere, that it’s flat. Note “curvature” means an overall curvature of the universe in FOUR dimensions. This is usually shown as 2D surface on a 3D object like a balloon.
How does inflation solve the fact that we observe no magnetic monopoles?
Monopoles can only theoretically form at very high temperatures, that were only present during the big bang. But once they formed they would be stable enough to survive. Since Inflation would have quickly cooled the universe, no new monopoles would be created after inflation. These would have been distributed so broadly that there would be hardly any left in any given part of space.
The universe is not completely smooth. CMB shows that there were small temperature differences. This anisotropy explains the large scale structures of the universe.
How did inflation start? What was responsible for inflation?
This is not well understood. It is thought that there may have been a scalar inflation field during the time of the big bang, called the inflation field.
#cosmicinflation
#bigbang
This field would have been in a false vacuum at very high temperatures, but moved to its true vacuum at lower temperatures, with the help of quantum tunneling. When the field reached the lowest minimum energy density in the potential, Inflation came to a stop. This is a very short process.
