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Dead Stars Don’t Radiate

johncarlosbaez.wordpress.com

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Re: Dead Stars Don’t Radiate

#51

Post by molticrystal »

cvoss wrote: post #13

> It would also mean that quantum field theory in curved spacetime can only be consistent if baryon number fails to be conserved! This would be utterly shocking. Is it really shocking (today)? I mean, isn't this a logical consequence of Hawking radiation for black holes? I thought we were shocked by this a long time ago, but now we're ok with it. The authors of the paper in question may very well be wrong in their ca…

>That kind of emotional writing does not become someone whose profession should focus on scientific persuasion.

What you'd probably prefer reading is one of the sources John Carlos Baez cites [0]:

Comment on “Gravitational Pair Production and Black Hole Evaporation” Antonio Ferreiro1, José Navarro-Salas, and Silvia Pla

Where they take the equation used in the paper, and outline how there is a better way than using that equation

"... is obtained to the lowest order in a perturbative expansion, while the standard way to obtain the non-perturbative Schwinger effect using the weak field approximation is to perform a resummation of all terms"

and how the one in the paper being critiqued can't handle situations arising from electromagnetic cases, much less the gravitational one properly. These are the statements Baez makes but the cited paper gives in a much more professional tone and method.

https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.13...

Re: Dead Stars Don’t Radiate

#52

Post by boznz »

nimish wrote: post #4

There'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.

A Lot of these physics papers are interesting but ultimately just noise. An untested Theory is NOT fact, it's just someone (with or without a PhD) pulling something out of their arse that might explain things. Most of cosmology and physics is still theory (even the big bang, and string theory) and even if 90% of theory fits facts, they could still be wrong. I am seeing more and more of these un-testable theories, built on other un-testable theories, citing other un-testable theories, this is why theoretical physics is in a crisis IMHO.

MY mother and father also have an untested theory that explains all this too it's called "God", most Sci-Fi authors have plenty, and I am sure AI's will soon add to this pile.

Kudos to those scientists that create testable papers or experimentally prove stuff.

Re: Dead Stars Don’t Radiate

#53

Post by quantadev »

jiggawatts wrote: post #28
jodrellblank wrote: post #26

Earlier quoted context omitted.

> " To maintain consistency with outside observers, this evaporation must occur fast enough that the victim can never reach any surface. Instead, the black hole recedes from them, evaporating faster and faster. " If this is radiating a star's mass worth Hawking radiation particles, is it like the Solar Wind, and if it's happening ever faster is there a point where it would start pushing the victim away from the black…

Yes, infalling victims will have a rather unpleasant time as they discover that black holes are secretly supernovas frozen in time. Outside observers see the victim's own black body radiation become extremely redshifted, asymptotically matching the black hole's black body radiation. If you mathematically "undo" this distortion for both, then what you are really observing from the outside is a star's worth of matter g…

How are they getting blasted in the face when such a blast would necessarily have to be moving faster than light?

Re: Dead Stars Don’t Radiate

#54

Post by disentanglement »

A_D_E_P_T wrote: post #47

lol, 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.

Although that paper even made it to PRL. I guess I should have written up some similar nonsense and sent it to PRL, might have improved my career chances.

Re: Dead Stars Don’t Radiate

#55

Post by jiggawatts »

feoren wrote: post #30
jiggawatts wrote: post #22

Earlier 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…

This claim is different from the overwhelmingly accepted scientific consensus, so it's on you to provide evidence. You say the two observers can't disagree on whether the victim falls in in finite time; tens of thousands of Ph.D. physicists say they can disagree. Where is literally any citation, any evidence at all of what you're claiming?

> overwhelmingly accepted scientific consensus

There is no consensus, quite the opposite: it was very well known that neither classical GR nor quantum mechanics are able to model a black hole!

People like to argue this as if it is settled science, right after saying two contradictory things about it, both from simplified, incomplete models.

Re: Dead Stars Don’t Radiate

#56

Post by GuB-42 »

thayne wrote: post #43

The 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…

I second that. A more accurate title would be "Only black holes emit Hawking radiation".

AFAIK everything above above absolute zero radiates, which effectively means that everything radiates. Black holes would be an exception if it wasn't for Hawking radiation.

In addition, (stellar) black holes are dead stars. Or at least, that's one way to see them.

Re: Dead Stars Don’t Radiate

#57

Post by jiggawatts »

amluto wrote: post #27
jiggawatts wrote: post #22

Earlier 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…

> The two observers can't disagree on such matters! Why not? If a spaceship fell toward a black hole and, as it approached the event horizon, one observer saw it turn into a horse and the other saw it turn into a cat, that would be very strange indeed, and one would suspect at least one of the observers of being wrong. But if one observer sees it fall through the event horizon and the other observer waits… and waits……

> Why not?

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. There are far more restrictions than that, but those are sufficient for my point.

The whole quantum information loss problem is just this, but dressed up in fancy terminology. It's the problem with black holes that the "number of things" (particles, events, whatever) is "lost" when matter falls into them.

The modern -- accepted -- resolution to this problem is that this information is not lost, preserving quantum numbers, etc...

How exactly this occurs is still being debated, but my point is that if you believe any variant of QM information preservation, then the only logically consistent view is that nothing can fall past an event horizon from any perspective, including the perspective of the infalling observers.

If you disagree and believe the out-dated GR model that an astronaut can't even tell[1] that they've crossed the event horizon, ask yourself this simple question: When does the astronaut experience this "non-event"[1]? Don't start with the mathematics! Instead, start with this simple thought experiment: The non-victim partner far away from the black hole holds up a light that blinks on an off once a second. The victim is looking outward and is watching the blinking speed up. How many blinks do they count at the time they cross the horizon?

Now think through the scenario again, but this time assume the spaceship turns the light off when they observe that the black hole has finished evaporating. When does the in-falling astronaut observe the blinking stop? Keep in mind that every "toy model" makes the simplification here that the blinking rate goes to infinity as the astronaut falls in! (I.e.: "They see the entire history of the universe play out." is a common quote)

[1] Isn't that a strong enough hint for everybody that there is no horizon!?

Re: Dead Stars Don’t Radiate

#58

Post by machina_ex_deus »

jiggawatts wrote: post #22
cvoss wrote: post #13

> It would also mean that quantum field theory in curved spacetime can only be consistent if baryon number fails to be conserved! This would be utterly shocking. Is it really shocking (today)? I mean, isn't this a logical consequence of Hawking radiation for black holes? I thought we were shocked by this a long time ago, but now we're ok with it. The authors of the paper in question may very well be wrong in their ca…

> 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 something like the vaidya metric. The mass function is a function of the ingoing Eddington coordinate v, which takes on a specific value when you cross the event horizon, and so you observe the black hole at a specific mass as you cross the event horizon. Contradicting your layman understanding of time dilation for the observer relative to the black hole.

Once you cross the horizon, the r coordinate becomes timelike, and so you are forced to move to decreasing r value just like a regular observer is forced to move to increasing t value. Your entire future, all your future light cone is within the black hole and it all terminates at the singularity. Minewhile, the t coordinate is space like which is what gives you space like separation from the mess that had happened in the original gravitational collapse. You wouldn't be blasted by a frozen supernova like you have said.

You can kind of say the universe splits at the event horizon, the time like coordinate changes from t to r and the future of the black hole branch of the universe is permanently cut off from the rest of the universe.

In rotating and charged black holes it is different, and you observe the evaporation of the black hole once you cross the Cauchy horizon. If the black hole is eternal (because someone kept feeding radiation to the black hole, maybe by reflecting the hawking radiation inwards), then you would in fact see timelike infinity as you reach the Cauchy horizon, so this time like infinity is quite physical. You would need to avoid being vaporized by blue shifted incoming radiation.

Re: Dead Stars Don’t Radiate

#59

Post by senderista »

layer8 wrote: post #45

This detail caught my eye: > [in their 1975 paper] Ashtekar and Magnon also assume that spacetime is globally hyperbolic Isn’t the modern assumption that spacetime is globally flat?

The term refers to causal structure: https://en.wikipedia.org/wiki/Globally_hyperbolic_manifold

Re: Dead Stars Don’t Radiate

#60

Post by bencyoung »

nextaccountic wrote: post #44
jiggawatts wrote: post #22

Earlier 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…

> 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!
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