How did the universe evolve, and more importantly, how might it end? To find out, Dr. Charles Liu and co-host Allen Liu welcome theoretical cosmologist and astrophysicist, Dr. Katie Mack, author of the recently published book, “The End of Everything (Astrophysically Speaking).” In Part 2, we look at dark matter, Gravitational Memory Effect, and more. (You can listen to Part 1 here.)

We dive right in with a question from David: “I was wondering if any physicists have looked into the idea that the “empty” space in an atom is actually “filled” with dark matter. What experiments could be done to prove or disprove this hypothesis?”

In order to answer David, first Katie explains the science supporting the idea that dark matter exists, including gravitational lensing and other evidence. The fact that there are indications of dark matter in areas where there is sparse regular matter suggests that dark matter is an entirely different kind of particle. Katie describes many of the ways that that dark matter is unrelated to the empty space in atoms, including the fact that dark matter has no real interaction with atoms at all.

Chuck asks whether the amount of dark matter still holds the key to how the universe evolves as he was taught or have new understandings made it entirely irrelevant? Katie explains that dark energy has replaced dark matter in importance, and that’s what’s making the universe expand faster. But we really don’t know what it is, or what it’s doing, or even if it will remain constant.

Our next question comes from Aileen Balderas: “I recently read about something called the Gravitational Memory Effect. This talks about how space remembers certain things. Gravitational wave signals have the power to make it so that the universe remembers what happens to it. How can scientists say that the universe is able to remember things?”

Katie unpacks this fascinating phenomenon which she only learned about five years ago. It turns out that, as Chuck puts it, “The universe has memory the way that memory foam has memory, not like the way elephants have memory.”

Chuck asks Katie about flying planes, which she learned to do in late 2020 during the pandemic, after her book came out. Talk about a lockdown hobby! Katie shares why she loves flying so much, and what she gets out of it. And while she doesn’t own her own plane, she has a share in a single engine airplane with 4 other people.

Chuck also asks the inevitable question: Star Trek or Star Wars? Katie’s answer: Star Trek!

We end the show with Katie describing what she’s doing at The Perimeter Institute, an independent research institute that’s dedicated to stretch the boundaries of our understanding of physics in areas like cosmology, particle physics, quantum information and various areas of theoretical physics. Katie’s been working with them to create some short videos. Check out Perimeter Institute for Theoretical Physics on YouTube to watch "Quantum Physics 101" and "Cosmology 101."

If you’d like to know more about Dr. Kathryn Mack and her work, check out her website, https://www.astrokatie.com/ where you can also sign up for her newsletter, “Watch this Spacetime.” You can also find her on Bluesky at astrokatie.com, Instagram and TikTok at @astrokatiemack, and Twitter (X), YouTube, and Facebook at @astrokatie.

You can also find Katie on John Green’s “Crash Course Pods: The Universe” on Complexly, YouTube, Spotify, Simplecast and more.

We hope you enjoy this episode of The LIUniverse, and, if you do, please support us on Patreon.

Credits for Images Used in this Episode:

• Galaxy group "Stephan's Quintet" seen by NASA's James Webb Space Telescope – NASA, ESA, CSA, and STScI


• NGC 4826, otherwise known as M64— a spiral galaxy. – NASA / Hubble Heritage Team


• Hubble image showing light distortions from the collective gravity of dark matter. – NASA, ESA, and J. Lotz and the HFF Team (STScI)


• The expansion of the universe over time. – NASA


• The End of Everything (Astrophysically Speaking) – Scribner


• Dr. Katie Mack in the cockpit of her plane – Image via Katie Mack’s Instagram

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