The Cartesian Cafe

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 Everything
  https://youtu.be/DPvD4VnD5Z4

Twitter: @iamtimnguyen
Webpage: http://www.timothynguyen.org