Richard Easther | The Big Bang, Inflation, and Gravitational Waves

Richard Easther is a scientist, teacher, and communicator. He has been a Professor of Physics at the University of Auckland for over the last 10 years and was previously a professor of physics at Yale University. As a scientist, Richard covers ground that crosses particle physics, cosmology, astrophysics and astronomy, and in particular, focuses on the physics of the very early universe and the ways in which the universe changes between the Big Bang and the present day.
In this episode, Richard and I discuss the details of cosmology at large, both technically and historically. We dive into Einstein's equations from general relativity and see what implications they have for an expanding universe alongside a discussion of the cast of characters involved in 20th century cosmology (Einstein, Hubble, Friedmann, Lemaitre, and others). We also discuss inflation, gravitational waves, the story behind Brian Keating's book Losing the Nobel Prize, and the current state of experiments and cosmology as a field.
Patreon: https://www.patreon.com/timothynguyen
Originally published on May 3, 2022 on YouTube: https://youtu.be/DiXyZgukRmE
Timestamps:

00:00:00 : Introduction
00:02:42 : Astronomy must have been one of the earliest sciences
00:03:57 : Eric Weinstein and Geometric Unity
00:13:47 : Outline of podcast
00:15:10 : Brian Keating, Losing the Nobel Prize, Geometric Unity
00:16:38 : Big Bang and General Relativity
00:21:07 : Einstein's equations
00:26:27 : Einstein and Hilbert
00:27:47 : Schwarzschild solution (typo in video)
00:33:07 : Hubble
00:35:54 : One galaxy versus infinitely many
00:36:16 : Olbers' paradox
00:39:55 : Friedmann and FRLW metric
00:41:53 : Friedmann metric was audacious?
00:46:05 : Friedmann equation
00:48:36 : How to start a fight in physics: West coast vs East coast metric and sign conventions.
00:50:05 : Flat vs spherical vs hyperbolic space
00:51:40 : Stress energy tensor terms
00:54:15 : Conservation laws and stress energy tensor
00:58:28 : Acceleration of the universe
01:05:12 : Derivation of a(t) ~ t^2/3 from preceding computations
01:05:37 : a = 0 is the Big Bang. How seriously can we take this?
01:07:09 : Lemaitre
01:11:51 : Was Hubble's observation of an expanding universe in 1929 a fresh observation?
01:13:45 : Without Einstein, no General Relativity?
01:14:45 : Two questions: General Relativity vs Quantum Mechanics and how to understand time and universe's expansion velocity (which can exceed the speed of light!)
01:17:58 : How much of the universe is observable
01:24:54 : Planck length
01:26:33 : Physics down to the Big Bang singularity
01:28:07 : Density of photons vs matter
01:33:41 : Inflation and Alan Guth
01:36:49 : No magnetic monopoles?
01:38:30 : Constant density requires negative pressure
01:42:42 : Is negative pressure contrived?
01:49:29 : Marrying General Relativity and Quantum Mechanics
01:51:58 : Symmetry breaking
01:53:50 : How to corroborate inflation?
01:56:21 : Sabine Hossenfelder's criticisms
02:00:19 : Gravitational waves
02:01:31 : LIGO
02:04:13 : CMB (Cosmic Microwave Background)
02:11:27 : Relationship between detecting gravitational waves and inflation
02:16:37 : BICEP2
02:19:06 : Brian Keating's Losing the Nobel Prize and the problem of dust
02:24:40 : BICEP3
02:26:26 : Wrap up: current state of cosmology


Notes:
Easther's blogpost on Eric Weinstein: http://excursionset.com/blog/2013/5/25/trainwrecks-i-have-seen
Vice article on Eric Weinstein and Geometric Unity:
https://www.vice.com/en/article/z3xbz4/eric-weinstein-says-he-solved-the-universes-mysteries-scientists-disagree

Further learning:
Matts Roos. "Introduction to Cosmology"
Barbara Ryden. "Introduction to Cosmology"
Our Cosmic Mistake About Gravitational Waves: https://www.youtube.com/watch?v=O0D-COVodzY