Ethan Siegel is a theoretical astrophysicist and science communicator. He received his PhD from the University of Florida and held academic positions at the University of Arizona, University of Oregon, and Lewis & Clark College before moving on to become a full-time science writer. Ethan is the author of the book Beyond The Galaxy, which is the story of “How Humanity Looked Beyond Our Milky Way And Discovered The Entire Universe” and he has contributed numerous articles to ScienceBlogs, Forbes, and BigThink. Today, Ethan is the face and personality behind Starts With A Bang, both a website and podcast by the same name that is dedicated to explaining and exploring the deepest mysteries of the cosmos. In this episode, Ethan and I discuss the mysterious nature of dark matter: the evidence for it and the proposals for what it might be. Patreon: https://www.patreon.com/timothynguyen Part I. Introduction 00:00:00 : Biography and path to science writing 00:07:26 : Keeping up with the field outside academia 00:11:42 : If you have a bone to pick with Ethan... 00:12:50 : On looking like a scientist and words of wisdom 00:18:24 : Understanding dark matter = one of the most important open problems 00:21:07 : Technical outline Part II. Ordinary Matter 23:28 : Matter and radiation scaling relations 29:36 : Hubble constant 31:00 : Components of rho in Friedmann's equations 34:14 : Constituents of the universe 41:21 : Big Bang nucleosynthesis (BBN) 45:32 : eta: baryon to photon ratio and deuterium formation 53:15 : Mass ratios vs eta Part III. Dark Matter 1:01:02 : rho = radiation + ordinary matter + dark matter + dark energy 1:05:25 : nature of peaks and valleys in cosmic microwave background (CMB): need dark matter 1:07:39: Fritz Zwicky and mass mismatch among galaxies of a cluster 1:10:40 : Kent Ford and Vera Rubin and and mass mismatch within a galaxy 1:11:56 : Recap: BBN tells us that only about 5% of matter is ordinary 1:15:55 : Concordance model (Lambda-CDM) 1:21:04 : Summary of how dark matter provides a common solution to many problems 1:23:29 : Brief remarks on modified gravity 1:24:39 : Bullet cluster as evidence for dark matter 1:31:40 : Candidates for dark matter (neutrinos, WIMPs, axions) 1:38:37 : Experiment vs theory. Giving up vs forging on 1:48:34 : Conclusion Image Credits: http://timothynguyen.org/image-credits/ Further learning: E. Siegel. Beyond the Galaxy Ethan Siegel's webpage: www.startswithabang.com   More Ethan Siegel & Timothy Nguyen videos: Brian Keating’s Losing the Nobel Prize Makes a Good Point but …https://youtu.be/iJ-vraVtCzw Testing Eric Weinstein's and Stephen Wolfram's Theories of Everythinghttps://youtu.be/DPvD4VnD5Z4   Twitter: @iamtimnguyenWebpage: http://www.timothynguyen.org