@mcc wouldn't call Penrose a crank! Personally I enjoy pbs st more than most other astro youtubers. I believe PhDs are involved in writing every manuscript. PBS Eons is also great
Edit: i am of course highly annoyed by the clickbait titles but unlike others the content never disappoints (unless you watch videos from 5+ years ago)
@OliverUv To be clear, Penrose is the one claiming singularities exist and Roy Kerr is the one calling Penrose a crank. The question I am asking in the first post is whether Kerr is calling Penrose a crank because he is, himself, cranky (now that I have watched the video Kerr's argument seems very reasonable)
@mcc Physicists do not and have not taken the singularities of General Relativity as an accurate prediction of reality. They've generally been viewed as an inevitable result of the theory being incomplete, with a theory of quantum gravity necessary to explain them away. This video is about a recent paper by Kerr that argues that singularities are not an inevitable result of GR, possibly opening the way to a non-quantum model of the interior of black holes
I wonder if the video itself is a good one or a crank one. Some of the videos on this account seem pretty real-science-grounded and some seem… some… some of them I'm not so sure.
The thing nobody mentions is that it's mostly academic. As the black hole collapses, its observable time gets slower and slower, and when it shrinks behind the event horizon, its time as we see it stops, well before it actually gets to a singularity. So if it does eventually become a singularity, it doesn't "matter", because nobody will ever see it.
@TomF 1. I highly respect Sabine's blog work, so I'll trust her videos.
We say "if it becomes a singularity, it doesn't matter, we won't see it", and that all makes sense to me, but then I have one big question: WTF happens during black hole evaporation?
PHYSICISTS: General relativity admits solutions with singularities, it's just not possible to evolve from a state without singularities to one with one or vice versa.
@mcc The way I mentally escape it is to say that evaporation happens at the event horizon, not the singularity. So what actually happens is the black hole shrinks inside the event horizon, and then evaporation happens before it has time to become a singularity.
@TomF Okay. But (I haven't watched the PBS Spacetime video, or Sabine's video, or read whatever Kerr wrote) doesn't that imply that black holes "never actually form", or rather black holes are real but they never form a singularity, and we're back to "singularities aren't real"?
@TomF@mcc I thought we were headed for a cold death of infinite expansion, unless vacuum decay is real and eats us. Damnit, I read Katie Mack’s book, but it didn’t stick.
@c0dec0dec0de@TomF hawking evaporation requires mass falling into the event horizon, right? so if a black hole formed in an otherwise empty universe, would it ever evaporate?
@TomF@mcc black holes are the event horizon. The singularity models what's inside. Whether or not there is a "singularity" is a bit of asymptotic reasoning that's basically untestable.
@mcc@TomF see, space is stretchy and because it is always expanding the blackholes slowly get pulled apart, thus every so often a few steven hawkings are able to escape their celestial prison and the black hole gets smaller as a result
@mcc@TomF the usual description is virtual particle pairs right at the event horizon that suddenly become not-virtual because [mumbles about uncertainty] and one of those carries some energy and momentum away from the singularity
but I don't think that's a very satisfying answer. if anything it might be less satisfying than a geodesic shrug because this framing leaves one wondering what's up with the leftover particles on the unobservable side of the horizon.
@mcc@TomF my personal opinion based on significant reading is that Sabine is 100% a crank, but is occasionally right because she hates everyone else.
(In addition to questionable physics, she's also done "Is capitalism good, actually?" and "Are trans women dangerous for sports, actually?" videos - things she personally knows jack shit about as someone who mostly does fringe physics for a living.)
@tess@TomF I watched her "Are trans women dangerous for sports?" and I thought that video was pretty unambiguously just her taking 15 minutes to say "No. Now: Buy NordVPN" But then she did a second clickbait-title trans women video that everybody seemed a lot more bothered by and I'm so afraid to watch that one I just, uh, haven't. At any rate, I don't think she has any more of a place to comment on biomedicine than I have to comment on physics
@mcc@TomF that was the less offensive of the two videos, for sure.
You should not watch the other one. She was rightly excoriated for it.
Having been on Mastodon for a while, it's clear she's just continuing a long tradition of white German people wading into heated issues they know nothing about and have no stake in and trying to take a superior, "objective" position.
@TomF@mcc Sabine was getting awfully close to anti-trans videos not that long ago, if not getting explicitly into it. It looks like she hasn't done more videos recently in the same vein, but I got put off around the time she posted https://www.youtube.com/watch?v=oR_RAp73ra0
@ChateauErin@mcc Not everything has to be 100% "pro-trans" or 100% "anti-trans". In general the answer from science is "it's complex". The first six minutes seems pretty clear to me?
@TomF@ChateauErin I think titling a video "is being trans a social fad among teenagers?" is inherently anti-trans literally regardless of the content of the video. The literal best case for that video is going to be she was so excited about, or so dependent on a paycheck of some sort for, making a pop science video she didn't care who she hurt along the way. Nevertheless, I have no reason to trust anything Sabine says about biology, sociology, or queer life, none of which are her academic area.
I do honestly feel like a recurring subplot in physics is "Roger Penrose writes a mathematical proof, it's a really strikingly beautiful mathematical proof and everyone is very impressed with it, you think about it a little longer and realize it doesn't actually say anything about the real universe"
@mcc that’s something Sabine Hossenfelder (sp?) has spoke out about (i’m sure others too…) about that blindness induced by/desire for ‘beautiful’ physics/maths.
He claims he can show that the state of the universe when maximum-entropy heat death is reached is mathematically dual to its state at the moment of the big bang. As if the universe itself were a universe-sized singularity. So you can just continue running the "maths"* from there, and hey, new universe & it doesn't know it's made entirely of vacuum. (1/2)
I love this, it's so philosophically satisfying. It's like the opposite of the Big Bounce theory; the old universe isn't transformed into the new one, rather we reinterpret the old universe and it turns out to be a new universe if you look at it right.
Then Penrose fucked it all up by signing on with a crank paper with highly cooked math claiming to "prove" this idea by finding circles in the Cosmic Microwave Background. His co-author seemed to be trying to prove Hinduism is science (2/2)
Note: Please do not misunderstand my digression at the end here, I want to be clear about my high level of respect for Roger Penrose as a mathematician and Hinduism as theology, it's just, Hinduism is not science and the work of Roger Penrose is only sometimes science. I prefer my magisteria non-overlapping
@mcc Interesting. I haven’t read that, but circa 1991 I did read his book that theorized that as energy levels went to infinity in the last hours of the Big Crunch, a civilization would use that energy to power virtual heaven of historical humans at increasing time-scale so that your and my perceived heaven would last literally forever.
At one point one of my old math professors walked past, saw the cover, and gently said, you know not to trust everything you read, right?
@mcc so i was really mad about this one because in high school i intuited that idea, wrote it down, and then in college went to one of his talks(small group actually got to talk to him) and he presented this theory and it sounded(with more math) just like the thing i had written
@castironflower being able to describe the math exactly is a really big deal tho tbh. like that is the thing that draws the line between a cool science fiction idea and a cool science idea
@mcc He says the scale shift happens when there are no clocks left, but I have to wonder why the presence of clocks matters. Why can't the universes he considers to exist sequentially all exist simultaneously? If time has infinite extent, why not space as well?
@freakazoid The math is a little beyond me, but mathematically I think you might actually have to go to the limit at infinity (of time) for the duality to apply. I think he's using some kinda funky moebius-transform type topology where the "line at infinity" gets moved to a place you can draw a worldline across it. I think the "clocks" might be a way of philosophically rationalizing this mathematical construction. But I'm not sure.
@mcc the channel is hit or miss, but the misses are mostly in the form of, "we didn't have anything interesting to write about this month so we chose... this?" and the conclusion is mostly "huh, that's a nifty idea, here's all the ways it might be wrong".
This is a common problem with astro- and particle physics channels; a new interesting paper comes out but it's just a tiny piece of the puzzle, or an interesting idea, and they wanna talk about it, but there's no definite answer.
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