Dead Stars Don’t Radiate

https://johncarlosbaez.wordpress.com/2025/05/17/dead-stars-dont-radiate-and-shrink/

by thechao • 1 year ago

246 148 1 year ago

johncarlosbaez.wordpress.com

As best I can tell there's no paywall on TFA, so I really don't think there's any reason to go through archive.is, which adds its own advertisements (if you don't block them).

Out_of_Characte• 1 year ago

archiving isn't just to circumvent a paywall. There's also the HN hug of death, possible geoblocks or an actual interest in archiving the article as it was written at the time these comments.

nimish• 1 year ago

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.

kurthr2• 1 year ago

Well, there's another aspect which is that the original authors and pop-sci journalists don't seem to be able to understand where they went wrong or how outrageous their claims are, precisely because their jobs depend on not understanding. The could have corrected it. We could not still be circling this drain 2 years later, but we are.

Kinda classic. Kinda boring.

EA-31672• 1 year ago

It helps that this is a genuinely difficult process to understand and requires an enormous fluency with QFT. Most people who fit that bill have better things to do with their time than write popular science articles or correct them.

tekla• 1 year ago

99.999999999% of people do not have enough knowledge to even dream of beginning to understand a majority of research. Adults can barely read, much less be able to pass Calc 1.

lupire2• 1 year ago

Wher are you hiding 92 Billion people?

coolcase2• 1 year ago

That percentage of the human population is everyone.

ajross• 1 year ago

It certainly wasn't in "silos", it's all on arxiv!

But yes: the world is complicated and it's easy to make mistakes outside your core field. The point of the scientific process is to get things in front of eyeballs who can spot the mistakes, c.f. the linked blog post. Then everyone fights about it or points and laughs or whatever, and the world moves on. The system worked.

What the process is not good at is filtering new ideas before people turn them into news headlines. And sure, that sucks. But it's not a problem with "academia failing", at all. The eyeballs worked!

moefh• 1 year ago

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 discussion explaining why the paper is nonsense and pointing to one of the replies objecting to it mentioned in the article from this post. That comment was downvoted by HN readers. I know because it was greyed out when I upvoted it days ago.

So there's no knowledge silo -- us simple folk just want to discuss the newest breakthrough without looking too hard, because that spoils the fun.

[1] https://news.ycombinator.com/item?id=43961226

gnramires• 1 year ago

I also think this kind of idea can be fun speculation, but I think there are better things to have fun that aren't promoting wrong ideas (like literal Science Fiction speculation!). When we can build fun on top, the physics of our reality doesn't need to be (academically) fun by itself :)

ryandrake• 1 year ago

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 naysayers. Starting out your comment with "It's nonsense." is about as conducive to a productive conversation as starting it out with "You're wrong."

jhalstead• 1 year ago

Direct link to A_D_E_P_T's comment: https://news.ycombinator.com/item?id=43964524

gus_massa2• 1 year ago

It's a good comment, but too technical. It's difficult to know if it makes sense. I think it's good, but I'm used to read weird stuff in papers. Anyway, my level of general relativity is too low to understand all the details.

I skip that whole thread because I was expecting an overhyped result and I have to sleep from time to time https://xkcd.com/386/ . I'd have upvoted that comment, especially if it was gray.

The comment is like ELI35[1], but for HN it's better to write a ELI25[2] version. Or perhaps a ELI25 introduction and a second ELI35 part with even more technical details. (I never liked ELI5[3].)

[1] I just finished my postdoc in General Relativity.

[2] I just finished my major in Geology. I know atoms and calculus, but I have no idea what covariant is. Moreover, whatever gauge means is not the type of gauges I know.

[3] I just want a lollipop.

kmm• 1 year ago

Is it really that siloed? The condition mentioned in the article (there being a global timelike Killing field) is discussed in all introductory texts on quantum field theory in curved spaces, it's even present in the first few paragraphs of the relevant Wikipedia article[1]. Even if it doesn't apply here, the authors ought to have mentioned why not.

I don't think they were stupid per se, nor malicious, but perhaps cavalier in pushing a result with such unexpected consequences without getting a consult.

1: https://en.wikipedia.org/wiki/Quantum_field_theory_in_curved...

boznz• 1 year ago

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.

michaelmrose2• 1 year ago

We call every model no matter how well founded a theory. An untested theory might be better called a hypothesis.

This mistake of language plays into the weirdos who opine we should disregard inconvenient ideas because they are just a theory failing to understand the difference between their own usage and the scientific usage.

grues-dinner• 1 year ago

clearly a lot of knowledge held in silos.

I don't think it's quite that, since the eventual goal is to publish, not only publicly, but as publicly as possible. More like it seems like everyone tends to hold their cards quite close to their chest until the moment of pre-print publication. Which means you can be working on something that someone could have told you months or years ago you have a problem.

The scientific equivalent of polishing a branch before making a pull request, only to be told "this has a huge memory leak and moreover what you want already works if you use this other API".

I'm not really sure there's a human-scale solution: the research landscape is so vast that you can't connect everyone to everyone else and have everyone in need of valuable input get it, and have everyone able to give it not be inundated with half-baked rubbish. Even if you assume everyone from the top to bottom has pure motivations and incentives for doing the research in the first place (in the pull request analogy CVE spammers, for example).

Perhaps not having the universities themselves so keen for PR that they'll slap a press release together about anything that looks clickable without due diligence would at least prevent making a public spectacle outside of the academic circle now and then, but it wouldn't solve the fundamental issues.

bmitc• 1 year ago

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.

gruturo2• 1 year ago

Without a gravity well whose escape velocity exceeds c, how are they supposing hawking radiation happens in this scenario?

Both virtual particles-antiparticles survive (and promptly disappear because one didn't just cross an event horizon).

Sharlin• 1 year ago

That one's a big white lie of how Hawking radiation works. It's not even an approximation, just a far-fetched metaphor that Hawking made up, presumably to satisfy science journalists.

raattgift2• 1 year ago

Hawking 1974, "Black hole explosions?" (Nature paywall) <https://www.nature.com/articles/248030a0> (sci-hub antipaywall) <https://sci-hub.se/https://www.nature.com/articles/248030a0> ("... the time dependence of the metric during the collapse will cause a certain amount of mixing of positive and negative frequencies [...] Part of this wave will be scattered by the curvature of the static Schwarzschild solution outside the black hole ... Another part of the wave will propagate backwards into the star") was certainly not for science journalists and is not at all "far-fetched". The only missing piece here is possibly discussion of his particular approach to second-quantization of the matter fields and how one might interpret that; Hawking's peers fifty years ago did not need assistance there.

This was followed in detail by Hawking 1975 (open access via Project Euclid) <https://projecteuclid.org/journals/communications-in-mathema...> where the most relevant bit surrounds eqns (2.27-28) and there is nothing wrong with talking about signed "contributions to the probability flux into the collapsing body" (as opposed to identifying those contributions as particles).

Hawking himself wrote simpler pop-sci explanations in a number of places, including his book, where a reader would not be expected to understand how canonicalizations of wave functions in other than position space and directly-measured particles differ. However none of those works is the equivalent of the brief "explosions?" letter and its follow-on.

EA-31672• 1 year ago

You have to remember the "one particle in the pair fails to escape the event horizon" explanation is a simplification of the alleged reality, which is the scattering of particles (or fields) in the presence of an event horizon. As far as I know there is no intuitive, non-mathematical way to describe this accurately, so science communicators of all stripes tend to approximate it in ways that can mislead the audience.

The man himself (Hawking) said: "One might picture this negative energy flux in the following way. Just outside the event horizon there will be virtual pairs of particles, one with negative energy and one with positive energy. It should be emphasized that these pictures of the mechanism responsible for the thermal emission and area decrease are heuristic only and should not be taken too literally."

gruturo2• 1 year ago

Thanks! I just learned something!

bryan0• 1 year ago

Not a physicist, but the more accurate “intuitive” explanation I read is that an accelerating observer sees thermal radiation in a vacuum. This is called the Unruh effect [0]. And since a black hole requires an accelerated observer to not be pulled in you will always have thermal radiation coming from the black hole UNLESS you are free falling into it. Physicists please correct me where I’m wrong!

[0] https://en.m.wikipedia.org/wiki/Unruh_effect

detourdog• 1 year ago

I couldn't really make heads or tails of this but if they aren't are emitting are they absorbing instead?

I feel like the only way not to emit is to absorb.

kurthr2• 1 year ago

Naw, this is Hawking Radiation a "quantum phenomena" that in the original paper doesn't conserve mass/baryons. It's weird that it was originally published (fantastic claims require fantastic evidence). I don't really like the headline of TFA either since it seems conflate all sorts of radiation.

The original paper is 2023 (Phys Review Letters). There was a rebuttal in PRL in 2024. I don't know why this is still a big deal now in 2025 other than Science Alert decided to write (another?) hyperbolic article based on crap. Still boring.

cvoss• 1 year ago

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 calculations (I can't say), but this blog post doesn't smell good to me because of doubtful statements like these, passed off as so obviously true that you must be an idiot not to agree. That kind of emotional writing does not become someone whose profession should focus on scientific persuasion.

From Wikipedia [0], itself citing Daniel Harlow, a quantum gravity physicist at MIT:

The conservation of baryon number is not consistent with the physics of black hole evaporation via Hawking radiation.

[0] https://en.m.wikipedia.org/wiki/Baryon_number

jiggawatts5• 1 year ago

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 require non-physical timelike infinities to work.

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.

Quite often, just one paragraph over, the statement is then made that an external observer will never observe the victim falling in.

The two observers can't disagree on such matters!

To say otherwise means that you'd have to believe that the Universe splits (when!?) such that there are two observers so that they can disagree. Or stop believing in logic, consistency, observers, and everything we hold dear as physicists.

This is all patent nonsense by the same person that keeps insisting that brains are "quantum" despite being 309K and organic.

If the external observer doesn't observe the victim falling in, then the victim never falls in, full stop. That's the objective reality.

Penrose diagrams say otherwise because they include the time at infinity, which is non-physical.

Even if the time at infinity was "reachable", which isn't even mathematically sound, let alone physically, Hawking radiation is a thing, so it doesn't matter anyway: Black holes have finite lifetimes!

There is only one logically consistent and physically sound interpretation of black holes: nothing can ever fall in. Inbound victims slow down relative to the outside, which means that from their perspective as they approach the black hole they see its flow of time "speed up". Hence, they also see its Hawking evaporation speed up. 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.

This model (and similar ones), can preserve all quantum numbers, because there is no firewall, no boundary, nothing to "reset" quantum fields. Everything is continuous, consistent, and quantum numbers are preserved. Outside observers see exactly what we currently expect, black holes look and work the same, they evaporate, etc...

jodrellblank• 1 year ago

"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 hole again? (the 'victim' can be a solar sail if that helps)

amluto4• 1 year ago

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… and gets bored and starts doing some math and determines that they could spend literally forever and never actually observe the spacecraft falling through the event horizon, then what’s the inconsistency? You might say “well, the first observer could fire up their communication laser and tell the second observer that ‘yes, the spaceship fell in at such-and-such time’, and the second observer would now have an inconsistent view of the state of the universe”, but this isn’t actually correct: the first observer’s message will never reach the second observer!

feoren• 1 year ago

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?

nextaccountic• 1 year ago

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

machina_ex_deus• 1 year ago

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.

AlecBG2• 1 year ago

I'm not sure what more you want from him, there are many papers and even a textbook linked?

It's bloody John Baez, the man knows his stuff.

On you actual point, it is shocking because its claimed that baryon number is not conserved without black holes getting involved

lupire2• 1 year ago

Are you saying that when Baez referred to "curved spacetime" he was excluding black holes (because the paper was claiming that non--black-holes have Hawking radiation?) or are you saying something else?

throwawaymaths• 1 year ago

shocking because its claimed that baryon number is not conserved without black holes getting involved

Isn't it also speculated that there's hawking radiation caused by the event horizon at the edge of the visible universe in an accelerating frame?

molticrystal• 1 year ago

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...

gus_massa2• 1 year ago

> if baryon number fails to be conserved! This would be utterly shocking.
Is it really shocking (today)?

Moreover, there are a few experiments that try to measure the proton decay (that would break the baryon number conservation.) They are run on Earth, far away form any black hole. For now, all of them failed to find a decay, and the conclusion is that the half life of protons is at least 2.4E34 years. https://en.wikipedia.org/wiki/Proton_decay#Experimental_evid...

I found an old article by quantamagazine explaining one of the experiment. It's a huge pool of very pure water and a lot of detectors. No black hole required. https://www.quantamagazine.org/no-proton-decay-means-grand-u... (HN discussion https://news.ycombinator.com/item?id=13201065 )

pfdietz• 1 year ago

Also, the Standard Model does allow nonconservation of baryon number, nonperturbatively.

zabzonk• 1 year ago

But they do fade away? (Blondie)

dudeinjapan• 1 year ago

It's better to burn out than to fade away.

quantadev9• 1 year ago

In black holes we have essentially a "loss of a dimension" (it's a much bigger story to explain what that even means, that I won't attempt here), so it might be the case that the three-quark arrangement known as 'baryons' only forms according to number of space dimensions (3D == 3 Quarks), making baryons only happen in 3D, so that when stuff reaches an event horizon, the quarks rip apart and rearrange into something where there's simply no such thing as a baryon (i.e. in 2D space). I'm someone who thinks the 'surface' of an event horizon is where the laws are preserved, and that the singularity or even perhaps the entire interior inside black holes may simply not exist at all.

Much of where Relativity "breaks" spacetime (i.e. problems with infinities and divide-by-zero) can be solved by looking at things as a loss of a dimension. For example, length contraction is compressing out a dimension (at light speed), and also time dilation (at event horizons, or light speed) is a removal of a dimension as well. Yes, this is similar to Holographic Principle, if you're noticing that. In my view even Lorentz equation itself is an expression of how you can smoothly transform an N-Dimensional space down to an (N-1)-Dimensional space, which happens on an exponential-like curve where the asymptote is reached right when the dimension is "lost". I think "time" always seems like a special dimension, no matter what dimensionality you're in, because it's the 'next one up' or 'next one down' in this hierarchy of dimensionality in spaces. This is the exact reason 'time' in the Minkowski Space distance formula must be assigned the opposite sign (+/-) from the other dimensions, and holds true regardless of whether you assume time to be positive v.s. negative (i.e. called Metric Signature). This of course implies our entire 4D universe is itself a space embedded in a larger space, and technically it's also an "event horizon" from the perspective of higher dimensions.

BlueTemplar2• 1 year ago

I'm someone who thinks the 'surface' of an event horizon is where the laws are preserved, and that the singularity or even perhaps the entire interior inside black holes may simply not exist at all.

Sounds tempting, but then what happens at the transition : when a sphere of matter gets just a little bit too dense ?

quantadev9• 1 year ago

It's just like the Lorentz Tranform or any other of the laws of Relativity. Things can get very massive and/or time can slow way down, but ultimately there's not a "problem" (i.e. mathematical failure requiring the theory to be extended) until the speed of light is reached, as an asymptotic limit.

But you're raising a good point that maybe Lorentz is pointing to 'non-integer dimensionality' where even enough mass crammed into a small enough space causes the "new maths" to begin to noticeably take hold. Like I said I see Lorentz as a way to transform dimensionality from N-D to (N +/- 1)D, but in a continuous and 'differentiable' way.

In super simplistic terms Lorentz is a "compression" function where one dimension of space is compressed perfectly flat, which is the mathematical equivalent of removing that dimension from the 'degrees of freedom' of the system.

nabla92• 1 year ago

I'm someone who thinks the 'surface' of an event horizon is where the laws are preserved,

I don't think this is a good way to think it. If black hole is big enough, there is nothing strange happening in the event horizon, no significant length contraction, nothing.

quantadev9• 1 year ago

Some "infinities" of singularity are at the center sure, but all the maximal Relativistic effects are at the EH surface. It's even proven that the entropy (informational content roughly) is equal to the EH area divided by the number of planc-length square areas, as the amount of quantum arrangements of information that are allowed "inside". That is a HUGE hint everything's remaining on the surface.

For example, when you see a clock fall into a BH you see it stop ticking at the EH, not at the center. It's a common misconception that everything about them is at the center, but everything interesting is at the surface.

cubefox• 1 year ago

HN discussion at the time:

Universe expected to decay in 10⁷⁸ years, much sooner than previously thought (phys.org) https://news.ycombinator.com/item?id=43961226 223 points, 5 days ago, 323 comments

BlueTemplar2• 1 year ago

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.

It was Gandalf who said that of course. And before you try to contradict me, let me point out that Gandalf is a wizard that has no need to bother with silly things like spacetime continuity.

P.S.: https://quoteinvestigator.com/2014/07/13/truth/

In conclusion, there exists a family of expressions contrasting the dissemination of lies and truths, and these adages have been evolving for more than 300 years. Jonathan Swift can properly be credited with the statement he wrote in 1710 [(that does not mention footwear yet)].

mlhpdx• 1 year ago

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.

deepsun2• 1 year ago

"As Mark Twain famously never said" (c)

frogulis• 1 year ago

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.

vlovich123• 1 year ago

I remember this from the Stephen Colbert show where he then goes something like “what was the truth doing with its pants off”

It’s a very old saying but we all learn it at some point

thayne2• 1 year ago

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 black dwarfs or cold neutron stars, but IIRC, that would take longer than the current lifetime of the universe.

GuB-42• 1 year ago

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.

tbrownaw2• 1 year ago

AFAIK everything above above absolute zero radiates, which effectively means that everything radiates.

What really matters is temperature relative to surroundings. Something at the same temperature as everything around it won't lose any net energy to radiation.

m3kw93• 1 year ago

He meant dead dead

verzali3• 1 year ago

Even dead dead stars radiate

davedx• 1 year ago

Its talking about Hawking radiation

theandrewbailey• 1 year ago

Then the title should be:

Dead Stars Don't Hawking Radiate

alienbaby• 1 year ago

The article itself explains the title quite well.

jpmattia4• 1 year ago

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.

nothrabannosir2• 1 year ago

It says to the reader "I wonder what he means?"

This has become affectionately known as “click bait”.

No disrespect to the pedigree of the clearly distinguished author.

layer8• 1 year ago

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?

senderista• 1 year ago

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

griffzhowl2• 1 year ago

I'm just learning this stuff so the details are hazy, bu my understanding is that there's a difference between spacetime curvature and spatial curvature. You can have a hyperbolic spacetime while at the same time having a flat three-dimensional spatial section of it.

It's not an assumption that space is flat. GR doesn't specify the global space curvature, so it's possible that it has a globally negative or positive curvature, but so far there's no evidence of any.

A_D_E_P_T• 1 year ago

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.

disentanglement• 1 year ago

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.

rubitxxx42• 1 year ago

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.

discoinverno• 1 year ago

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.

darkerside• 1 year ago

I'd like to revise that comment to, "email the experts to better understand how this finding fits into the current scientific worldview."

We shouldn't take the experts on blind faith, but we definitely shouldn't take the challenges on blind faith either.

michaelmrose2• 1 year ago

It is true that revolutionary theories may be both true and controversial but they are rarely friendless or obviously wrong to nearly all practitioners of the relevant fields and those theories are legion and without merit.

Without being up to date in the minutia of every field one will be ill disposed to judge which of 100 piles of nonsense extant at any given time are real discoveries and which bunkum and ones work as a journalist would be so compromised by the 1000 lies one spread that none should believe the one truth they uncovered.

I wouldn't credit anyone so stupid as not to consult ones peers.

khanan• 1 year ago

Let's see what Neil deGrasse Tyson says about this.

w10-1• 1 year ago

Ok, we all understand the ancient problem and its current manifestation.

But what can be done? Science is not supposed to be the realm of disinformation, but it seems to have no real defenses. People are being paid to lie, no one is being paid to say they are liars, and from the outside scientific dispute looks a lot like politics, so scientists lose credibility by association.

That's a real problem.

NKosmatos• 1 year ago

Ah yes, our favorite HN “entertainment”. Scientists, quantum physicists in our case, having a beef about Hawking radiation :-)

Besides some high level ideas, which even us normal people can understand, there are so many details linked in the original post that you need an MSc/PhD to fully understand them.

For the time being, let’s just keep that the universe has a few extra trillion years, and isn’t expected to decay in 10⁷⁸ years ;-)

verzali3• 1 year ago

A few extra trillion years would look like a drop of water against the ocean that is 10⁷⁸ years...

globnomulous• 1 year ago

This is partly why I roll my eyes when people who don't do research in a field start telling me about the "studies [they] found" while researching a topic. Unless you know the field and the research methods and have actually practiced them, reading studies is pointless, because you're too ignorant to evaluate them.

JohnMakin• 1 year ago

Good news for boltzmann brains

m3kw93• 1 year ago

One can argue there are 8billion Boltzmann brains on earth already

m3kw93• 1 year ago

Anyone that predicts an event that far out in the future let alone 100 years out I would bet against any day of the week. This is couple trillion of trillions years using physics no way of proving

qnleigh2• 1 year ago

Is 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?

dataflow2• 1 year ago

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.

qnleigh2• 1 year ago

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-

nazgul17• 1 year ago

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.

varjag• 1 year ago

No, you are in fact accelerating when you are standing on the planet.

deepsun2• 1 year ago

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.

griffzhowl2• 1 year ago

Yes, I think so. As Baez says, it suggests the paper wasn't reviewed by experts in the subject. But that is the point of peer review, so seems to be very sloppy work by the journal

verzali3• 1 year ago

That should be the real issue.

Bluntly, science journalism is not that well paid and most people won't have given the articles he calls out more than a moments thought. Of course journalists are going to be lazy if they aren't paid not to be. (Which is a problem itself, but I don't see many people advocating for better paid science journalists).

But journals should be a kind of guard rail against that. If their peer reviewers were too lazy to find experts or too arrogant to admit they didn't understand what they were reviewing, then that is a real problem.

tbrownaw2• 1 year ago

I've seen proposed perpetual motion machines based on treating simplified calculations as if they're the real thing.

lproven• 1 year ago

Of course, as noted researcher Eskil Simonsson teaches, Dead stars still burn.

chrz• 1 year ago

Theres still something in universe that we are missing and I feel the grand theories of next billion years are missing that

Dead Stars Don’t Radiate

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