Episode 25: The No Bear Theorem with Anne Casselman

Well, after the time I took off to write about Cthulhu, I decided to call this episode the start of season 2. It’s been about a year since our first episode was recorded, after all. I made a new intro, too.

After we recorded this episode, jocelyn and dave and I had a bear drawing contest, and jocelyn won. Hey Everyone, it’s MEATBALLS!

Today’s topic is lovely. We talk about throwing crap into black holes, one of my favourite topics because I don’t need to do any prep. Also because I love black holes.

Anyway, today our guest is Anne Casselman, the science writer! we are excited to have her on. When I suggested the topic, she said “… And answer the question that keeps me up at night? Yes please! ”

So this week we’re throwing bears at black holes.

Listen through past the end. we talk about a lot of different black hole things after the credits including the no hair theorem, black hole evaporation and uh… what to name the bear.

Physicists: Jocelyn Read, David Tsang

Intro Music: Ted Leo and the Pharmacists 

Exit Music: John Vanderslice 

8 thoughts on “Episode 25: The No Bear Theorem with Anne Casselman

  1. Not sure this is the place for lively discussion, but I had another question you were dancing around but didn’t quite hit on: Is there anything in the universe right now that’s at the center of a black hole? In other words, the bear sees himself falling right into the center in a short amount of time, but if time in a black hole slows down an infinite amount relative to an outside observer, then will it take an infinite amount of our time for a bear to reach the center? Or is this the sort of comforting notion of simultaneity that general relativists have no time for?

    • actually, it takes an infinite amount of our time for the bear to reach the event horizon! we’ll never see him even get close to the center.

      but he’ll approach the center in a finite amount of time.

      and what’s in the center? a singularity.
      what’s that?
      another topic for a different episode :p

      • Thanks so much for the reply! My confusion has always been that everyone talks about what you see from outside rather than what ‘is’ relative to the outside. But this motivated me to spend a couple evenings fumbling my way through the rest of the Schwarzschild solution, and with the notable exception of the Riemann tensor, it makes a bit more sense now. Key sentence: “In fact, one can say that the entire evolution of the physical universe has occurred by the time the body passes the surface r=2m.” So the bear experiences hitting the center very quickly, but doesn’t even pass the event horizon until after the entire physical evolution of the universe? Now THAT’S a trip!

        Oh, and thanks for the continued motivation! This stuff is so cool! Since listening to your podcast, I remembered how much I used to love this stuff and have worked through most of a quantum mechanics textbook and the basics of general relativity and cosmology. I hope it stimulates this much curiosity in your younger audience!

      • Hey, wait a minute—If black holes evaporate in a finite amount of time via Hawking radiation, is the black hole gone before you hit the event horizon? Seems like, relative to the outside, you’d hover right at the ever-shrinking horizon until the black hole finally blows up in your face. So if you jump into a black hole, do you manage to avoid the singularity?

        • good question, the short answer is that no one knows.
          hawking radiation is kind of like unruh radiation. it comes from the fact that if you stand still next to a black hole, you are accelerating relative to someone falling into the BH, and you will detect particles.
          then when people hear that they say “oh, i guess the BH is losing mass”.

          as far as i am aware, you would need a good theory of quantum gravity to actually make the BH evaporate from hawking radiation.

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