Should it be a big embarrassment for Phys. Rev. Lett., a big dip in their reputation?
The whole point of respectable journals is that they filter out bad quality papers.
Dead Stars Don’t Radiate
81–90 of 155 posts
Re: Dead Stars Don’t Radiate
#82Is there a simple way to understand why massive objects don't radiate gravitationally? Accelerating observers see a bath of thermal radiation via something called the Unruh effect. If you're standing on a planet, you're accelerating under gravity, and therefore don't you see Unruh radiation? Does this have any connection to Hawking radiation?
> If you're standing on a planet, you're accelerating under gravity, and therefore don't you see Unruh radiation?
Layman here, but if you're standing, you're not actually accelerating, right? You'd only be accelerating if there was nothing under you holding you up, meaning if you were falling down.
Re: Dead Stars Don’t Radiate
#83Earlier quoted context omitted.
> The current "pop science" (nearly science fiction) statement is that it is possible to fall into a black hole and there is "nothing special" about the event horizon. How is this not true? From the point of view of whoever is falling, and supposing the black hole is very large
Consider that every "surface" inside the event horizon is like a stronger event horizon so passing through you'd certainly notice things like not being able to see your feet any more as the light wouldn't be able to travel out to your eyes! There would be a lot of other stuff happening too so you may not notice exactly, but the event horizon is definitely noticeable!
Why wouldn't you be able to see your feet? Your head is also falling through the horizon (hopefully - otherwise you are going to be very unhappy), so the light from your feet doesn't need to escape the horizon for you to see it.
Re: Dead Stars Don’t Radiate
#84Earlier quoted context omitted.
> There's an issue this highlights [...] there's clearly a lot of knowledge held in silos. I think the real issue this highlights -- which is something everyone knows and still everyone does -- is that people love to spread and discuss sensational stories, and no one likes to hear naysayers ruining the fun. Look the discussion of the original story here in HN[1]. There's a comment by A_D_E_P_T way down in the discuss…
I don't think there's a lack of skepticism on HN of all places. Every article that gets posted that discusses even a mild scientific result brings at least one HN commenter out of the woodwork to dunk on it. You can bank on it--there is always That Guy who has to argue against it, whether he's right or not. Also, the comment you reference was probably downvoted because of the tone, not because of some HN bias against…
The point of a statement like "it's nonsense" is to prevent a conservation that should not happen, because it will be dumb. It's the right thing to say iff it's correct.
Re: Dead Stars Don’t Radiate
#85Is there a simple way to understand why massive objects don't radiate gravitationally? Accelerating observers see a bath of thermal radiation via something called the Unruh effect. If you're standing on a planet, you're accelerating under gravity, and therefore don't you see Unruh radiation? Does this have any connection to Hawking radiation?
> If you're standing on a planet, you're accelerating under gravity, and therefore don't you see Unruh radiation? Layman here, but if you're standing, you're not actually accelerating, right? You'd only be accelerating if there was nothing under you holding you up, meaning if you were falling down.
Ah yeah there are multiple definitions of 'acceleration' here. Unruh radiation occurs when you're not 'in an inertial reference frame,' loosely meaning that you feel acceleration. So in a rocket in space or (presumably) standing on Earth's surface.
What you say makes intuitive sense, but it was actually the opposite logic that lead Einstein to his general theory of relativity. Here's a slightly dorky but very good Veritasium video that explains this issue and general relativity https://youtu.be/XRr1kaXKBsU?si=1iudoAx5kWgWHHt-
Re: Dead Stars Don’t Radiate
#86Is there a simple way to understand why massive objects don't radiate gravitationally? Accelerating observers see a bath of thermal radiation via something called the Unruh effect. If you're standing on a planet, you're accelerating under gravity, and therefore don't you see Unruh radiation? Does this have any connection to Hawking radiation?
> If you're standing on a planet, you're accelerating under gravity, and therefore don't you see Unruh radiation? Layman here, but if you're standing, you're not actually accelerating, right? You'd only be accelerating if there was nothing under you holding you up, meaning if you were falling down.
Also a layman. But as long as your temperature is not absolute zero, particles inside you are moving, and if they have mass, they would indeed radiate gravitationally - until they slow down to a stop, that being absolute zero.
My understanding from pop science videos is that they can indeed evaporate, but only through decay mediated by the weak force.
Re: Dead Stars Don’t Radiate
#87Earlier quoted context omitted.
> The conservation of baryon number is not consistent with the physics of black hole evaporation via Hawking radiation. There are other black hole models that can conserve these quantum numbers! Speaking of things that are so obviously true that you must be an idiot not to agree, there are statements so obviously false that you have to be an idiot to agree: People keep repeating the nonsense put out by Penrose, which…
First of all, kruskal coordinates show beyond doubt that the event horizon is just a regular null hypersurface that the observer wouldn't notice crossing locally. (Of course if you look around, at the moment of crossing into the event horizon you see everything else that was falling into it unfreeze and continue crossing). If you want to take into account the evaporation of the black hole, then you should look at som…
Take a closer look at a picture of Kruskal coordinates, e.g.: https://upload.wikimedia.org/wikipedia/commons/1/1c/Kruskal_...
Those closer-and-closer line spacings are hiding a mathematical infinity, which isn't physical for finite-lifetime black holes.
Conversely, look at: https://en.wikipedia.org/wiki/Eddington%E2%80%93Finkelstein_...
The ordinary Schwarzschild metric diagram in that article makes it crystal clear that in-falling observers asymptotically approach the horizon, but never cross it.
Read the next section as well, which uses the "Tortoise coordinate"... which again uses the mathematical infinity to allow the horizon to be crossed.
I really don't understand why people keep arguing about this!
If you find yourself writing an infinity symbol, you've failed at physics. Stop, go back, rethink your mathematics.
Re: Dead Stars Don’t Radiate
#88Earlier quoted context omitted.
> If you're standing on a planet, you're accelerating under gravity, and therefore don't you see Unruh radiation? Layman here, but if you're standing, you're not actually accelerating, right? You'd only be accelerating if there was nothing under you holding you up, meaning if you were falling down.
Ah yeah there are multiple definitions of 'acceleration' here. Unruh radiation occurs when you're not 'in an inertial reference frame,' loosely meaning that you feel acceleration. So in a rocket in space or (presumably) standing on Earth's surface. What you say makes intuitive sense, but it was actually the opposite logic that lead Einstein to his general theory of relativity. Here's a slightly dorky but very good Ve…
Ah gotcha! Yeah I'm familiar with Einstein's happiest thought - it just escaped me what was meant by acceleration here for the Unruh effect. Cool!
Re: Dead Stars Don’t Radiate
#89There's an issue this highlights and it's not that the original authors were stupid so much as there's clearly a lot of knowledge held in silos. That's not a good thing if your goal is to advance everyone's knowledge. Whatever is going on in academia is failing relatively closely related fields which is not good.
I think it's just an intractable problem at this point. There's probably millions of physicists on Earth. Everyone working in a company knows just how hard it is to get even hundreds of people to agree and read and understand the same things.
The fact is, there are just too many people doing too many things. When any technical paper sounds like gobblygook to even people in the same field but in a different specialty, it's no surprise this happens, especially when coupled with the modern pressure to scientifically publish and modern "journalism" trends.
Re: Dead Stars Don’t Radiate
#90> As Mark Twain said, “A lie can travel around the world and back again while the truth is lacing up its boots.” Actually he probably didn’t say that—but everyone keeps saying he did, illustrating the point perfectly. Well played.
In a classic case of the Baader-Meinhof phenomenon, I recently read "The Truth" by Terry Pratchett, which repeatedly makes reference to that phrase, and I am now noticing it everywhere, whereas previously I can't recall being aware of it at all.