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