Of course, as noted researcher Eskil Simonsson teaches, Dead stars still burn.
Dead Stars Don’t Radiate
111–120 of 155 posts
Re: Dead Stars Don’t Radiate
#112Earlier quoted context omitted.
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.
The horizon is the distance at which escape velocity is c.
Closer to the centre, including your feet, the escape velocity is higher.
Electrical impulses wouldn’t be able to travel from the bottom of your brain to the top, so you’d be unconscious anyway.
Re: Dead Stars Don’t Radiate
#113Earlier quoted context omitted.
> Because that's not how relativity works! Two observers can disagree only on the order and relative timing of events, not what the events are or the total number of events. No, and this has nothing to do with quantum mechanics or the no-hair theorem or anything particularly fancy. As a toy example, suppose you have a frame with a (co-moving, but it doesn’t really matter) time coordinate t. A series of events happen…
> Nothing to see in the sky, and you may well survive your visit to the event horizon. Then, dramatically less than one second later for any credibly sized black hole, you will meet the singularity, and IIRC you should probably expect to be squashed by tidal forces before that. Don't we know about a bunch of black holes best measured in AU? Won't you have a good chunk of time inside those? Does time dilation work sev…
I vaguely recall doing this calculation on a problem set. For a black hole roughly the size of the one at the center of our galaxy, IIRC you have well under a microsecond. I could be remembering wrong.
Even worse: the way to maximize how long you have before you hit the singularity, you should do nothing. Firing your rocket in any direction gets you to the singularity in an even smaller amount of proper time: the singularity isn’t in front of you in space — it’s ahead of you in time.
Keep in mind that all of this is for the Schwarzchild metric, which is a nice solution to Einstein’s equations in the sense that you can derive it on a blackboard. It can’t describe what we think of as a real black hole for plenty of reasons, including the major one that a Schwartzchild black hole has existed forever and therefore could not have formed in a supernova. You need a different solution for a black hole that has only existed for a finite time.
Re: Dead Stars Don’t Radiate
#114Earlier quoted context omitted.
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.
The horizon is the distance at which escape velocity is c. Closer to the centre, including your feet, the escape velocity is higher. Electrical impulses wouldn’t be able to travel from the bottom of your brain to the top, so you’d be unconscious anyway.
...and tidal forces may have reduced your body to red goo, so there's that
Re: Dead Stars Don’t Radiate
#115lol, I wrote a very similar comment here a few days ago: https://news.ycombinator.com/item?id=43964524 It's true, that paper is nonsense. There's not really much else to say. Preprint servers sometimes publish the sort of stuff that wouldn't pass peer review. (Remember that S.Korean "superconductor" from about two years ago!?) The press should be cautious when writing about it.
Whether it’s nonsense or not, this quote in the critical assessment is concerning: > If I were a science journalist writing an article about a supposedly shocking development like this, I would email some experts and check to see if it’s for real. An attitude like that would have us all believing the earth is flat or that the sun revolves around the earth. After all, experts of the time believed both wrongly.
I agree with that comment. Experts can be wrong, of course, but the null hypothesis is that their opinion is 'more correct' than that of a science journalist.
As an aside, nobody really believed the earth was flat: https://en.wikipedia.org/wiki/Myth_of_the_flat_Earth.
Re: Dead Stars Don’t Radiate
#116The title is... odd. White dwarfs and neutron stars are generally considered "dead stars", since they no longer have active fusion processes. But they do radiate from energy left over from the star's "death". (Mostly thermal energy for a white dwarf, for neutron stars there is also a lot in angular momentum and the spinning magnetic field.) In theory, they will eventually radiate all of their energy away and become b…
> The title is... odd.
Not if you know the reputation of John Baez: Anyone familiar with him or his writings would know without hesitation that he understands black-body and E&M radiation, so his choice of title is clearly meant to be provocative.
It says to the reader "I wonder what he means?" To this reader, I'll also say that he delivered a terrific blog post.
Re: Dead Stars Don’t Radiate
#117Earlier quoted context omitted.
And black holes are much colder then their surroundings, i.e. the Cosmic Microwave Background. And they will be for trillions of years.
Do you mean singularities are much colder? Because everything outside of that is super hot, no?
We can only talk about the surface. The surface emits basically no radiation at all. The amount of Hawking radiation it emits is practically non-existent. It's truly black.
The temperature inside could be anything. You could well be inside a black hole right now.
Even if we were inside one we couldn't really talk about the temperature of the singularity. The singularity is a divide-by-zero error. It probably doesn't physically exist at all, and whatever does exist is beyond our ability to model.
Re: Dead Stars Don’t Radiate
#118Earlier quoted context omitted.
What I meant to say was "asymptotically approaches infinity" for 'f(x)' at some limiting value 'x' and thus a left/right mirroring of the function. I shouldn't assume people know I mean vertical just because I say asymptotic, so thanks for catching that imprecision in my wording. As you probably know, horizontal asymptotes are never what we think of as the 'problematic' parts of Relativity, because when something app…
1/sqrt(x) is a vertical asymptote?
Replace "is a" with "has one".
Re: Dead Stars Don’t Radiate
#119Earlier quoted context omitted.
Whether it’s nonsense or not, this quote in the critical assessment is concerning: > If I were a science journalist writing an article about a supposedly shocking development like this, I would email some experts and check to see if it’s for real. An attitude like that would have us all believing the earth is flat or that the sun revolves around the earth. After all, experts of the time believed both wrongly.
I agree with that comment. Experts can be wrong, of course, but the null hypothesis is that their opinion is 'more correct' than that of a science journalist. As an aside, nobody really believed the earth was flat: https://en.wikipedia.org/wiki/Myth_of_the_flat_Earth .
> nobody really believed the earth was flat
Your link only debates that during the Middle Ages people thought the earth was flat.
Those living in ancient Mesopotamia and Egypt believed we all lived on a flat disc or plane floating in the ocean.
Re: Dead Stars Don’t Radiate
#120> 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.
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