[HN Gopher] Dead Stars Don't Radiate
___________________________________________________________________
Dead Stars Don't Radiate
Author : thechao
Score : 237 points
Date : 2025-05-17 17:54 UTC (1 days ago)
(HTM) web link (johncarlosbaez.wordpress.com)
(TXT) w3m dump (johncarlosbaez.wordpress.com)
| fishsticks89 wrote:
| https://archive.is/mG1KS
| Wowfunhappy wrote:
| 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 wrote:
| 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 wrote:
| 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.
| kurthr wrote:
| 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-3167 wrote:
| 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 wrote:
| 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.
| lupire wrote:
| Wher are you hiding 92 Billion people?
| coolcase wrote:
| That percentage of the human population is everyone.
| saagarjha wrote:
| I guess they left out a bit for Einstein's brain (but not
| the rest of his body).
| ajross wrote:
| 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 wrote:
| > 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 wrote:
| 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 wrote:
| 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."
| andrewflnr wrote:
| 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.
| twothreeone wrote:
| I'd agree if it was just another arxiv draft. But, honestly
| I appreciate the clarity and brevity of the comment in this
| case. And I think that tone is warranted given the paper
| was published in a well known journal, lending it quite
| some credibility as clearly demonstrated by the high-stakes
| PR it received. Especially, since any retraction of that
| paper will likely not be followed up by the same articles.
| jhalstead wrote:
| Direct link to A_D_E_P_T's comment:
| https://news.ycombinator.com/item?id=43964524
| gus_massa wrote:
| 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 wrote:
| 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 wrote:
| 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.
| grues-dinner wrote:
| > 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 wrote:
| 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.
| gruturo wrote:
| 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 wrote:
| 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.
| EA-3167 wrote:
| 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."
| gruturo wrote:
| Thanks! I just learned something!
| pixl97 wrote:
| Arvin Ash just did an episode on exactly this effect. The
| modern way we understand it is much to simplified.
|
| https://www.youtube.com/watch?v=UxVssUb0MsA
| coolcase wrote:
| Now I am confused as what he says at the end seems to
| agree with the paper
|
| "Hawking radiation doesn't just come from black holes but
| from any collapsed star"
| bryan0 wrote:
| 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 wrote:
| 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.
| kurthr wrote:
| 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 wrote:
| > 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
| jiggawatts wrote:
| > 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 wrote:
| > " _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)
| jiggawatts wrote:
| 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 getting converted to pure energy and the
| infalling victims getting blasted in the face by that.
|
| The victims can't make it back out "whole and intact" in
| the same sense that you're not going to keep your atomic
| integrity if you're up close and personal to a supernova.
|
| Your quantum numbers however... those can be preserved
| nicely.
| quantadev wrote:
| How are they getting blasted in the face when such a
| blast would necessarily have to be moving faster than
| light?
| hparadiz wrote:
| Because time slows down relative the outside observed as
| you get closer to the event horizon any matter falling
| inwards starts to compress blocking the matter above it
| until eventually that matter is compressed to an extreme
| against the event horizon. The photons that get fired off
| from that interaction away from the black hole are able
| to escape and that's why we can see some black holes as
| being extremely bright. However matter that is spiraling
| inwards will be blasted by hundreds of years worth of
| photons from every direction while inside this matter and
| energy goop and all sorts of other particles in a matter
| of moments relative to how it is experiencing time.
| quantadev wrote:
| Ah, I gotcha, thanks for explaining. Yeah the 'accretion
| disk' are what this is normally called. Lots of matter is
| getting smashed right outside the EH, creating heat
| energy, and like you said it's able to blast out photons.
| Ygg2 wrote:
| > black holes are secretly supernovas frozen in time.
|
| I don't think that's true. What kills you isn't radiation
| of the singularity, but cosmic microwave background (and
| other infalling radiation) turned to visible light, then
| x-rays, then gamma rays.
| pixl97 wrote:
| I don't think the hawking radiation occurs at the edge of
| the event horizon itself.
|
| Arvin Ash just did a video on this
|
| https://www.youtube.com/watch?v=UxVssUb0MsA
|
| It appears to occur outside the event horizon in a large
| area.
| amluto wrote:
| > 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!
| jiggawatts wrote:
| > 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!?_
| amluto wrote:
| > 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 at the origin (x=y=z=0 in this
| frame) at various times t.
|
| There's another observer in a frame with a time
| coordinate t'. The frames are related by t' = t - 1/t for
| t<0. The t=-10 event happens at t'=-9.9. The t=-4 event
| happens at t'=-3.25. The t=-1 event happens at t'=0.
| t=-1/100 happens at t'=99.99. t=0 gets closer and closer
| to happening but _never actually happens_. t=1 doesn't
| even come close.
|
| Critically, the t' observer does not observe t=0 or t=1
| in some inconsistent manner. There is no disagreement
| between the observers as to what happens at t>=0. To the
| contrary, those events are simply not present in the t'
| observer's coordinate system!
|
| Note that the transformation above isn't about when light
| from an event gets to the t' observer -- it's the actual
| relativistic transformation between two frames.
|
| The Schwarzchild metric has a nastier transformation than
| this. If you toss a rock into an isolated black hole from
| far away, you will see the rock get progressively closer
| to the event horizon, and you will never see it fall in.
| But the rock is in trouble: its co-movimg coordinate
| system _ends_ not long after it crosses the horizon. That
| latter phenomenon is called the "singularity", it's
| solidly inside the event horizon, and it's not avoidable
| by coordinate system trickery. While general relativity
| does not explain what happens when one encounters the
| singularity, one might imagine that it's fatal to the
| rock the reaches it.
|
| edit: FWIW, you also say:
|
| > 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.
|
| I'm not sure what you're talking about. In a pure GR
| model of an isolated black hole, as you fall in, you will
| observe tidal forces. In a smaller black hole, the tidal
| forces will squash you long before you reach the event
| horizon. In a large enough black hole, they will not!
| Your view of the sky would certainly look very, very
| distorted and delightfully and possibly dangerously blue-
| shifted, but we're talking about an _isolated_ black
| hole. 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. Source: I took the class and did the math. I assume
| this is what the "pop science" you're talking about is
| saying, and it's not wrong.
|
| P.S. I've never tried to calculate how lethal the blue-
| shifted sky would be. Naively considering just the time
| transformation, it should be infinitely lethal at the
| event horizon. But trying to apply intuition based on
| only part of a relativistic transformation is a great way
| to reach incorrect conclusions.
| Dylan16807 wrote:
| > 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 severely against you?
| amluto wrote:
| 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.
| Dylan16807 wrote:
| > For a black hole roughly the size of the one at the
| center of our galaxy, IIRC you have well under a
| microsecond.
|
| You only get one microsecond as you cover over half a
| light minute? Huh.
| feoren wrote:
| 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?
| jiggawatts wrote:
| > 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.
| nextaccountic wrote:
| > 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
| quantadev wrote:
| Nobody knows _what_ happens at the event horizon, but we do
| know from the perspective of an outside observer things
| about physics 'break'. It makes sense that there's a flip-
| side to that 'breakage' (on the inside of the surface, or
| even "only at" the surface) that isn't just normal space as
| if nothing happened.
|
| For example there's no mathematics at all that mankind has
| ever known where an asymptotic approach towards some limit
| doesn't have a mirror version (usually inverted) on the
| other side of the asymptote. If we see time stop, at the EH
| it seems wrong to assume there's nothing "stopped"
| similarly from the other side too. So this means the
| surface has to be very special. You don't just pass by it
| and not notice as you fall in, imo.
| amluto wrote:
| > For example there's no mathematics at all that mankind
| has ever known where an asymptotic approach towards some
| limit doesn't have a mirror version (usually inverted) on
| the other side of the asymptote.
|
| That's a strong statement. 1/sqrt(x), over the reals,
| doesn't have an inverted world for x<0. Maybe you could
| argue that it does exist, weirdly rotated, outside the
| reals?
|
| In any event, the Schwarzchild metric itself is an actual
| example of this. From the perspective of a doomed
| spaceship at the event horizon, the Schwarzchild metric
| is quite civilized.
|
| The stuff _after_ the horizon is a different story, but
| that's not immediately after crossing the event horizon
| -- it might be whole nanoseconds later :)
|
| Go take a GR class. It's fun and mind-bending.
| quantadev wrote:
| 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 approaches a constant
| that's never something that breaks the math.
|
| The Schwarzchild metric, being a relationship of 6
| different variables I think, has some relationships that
| go to infinity asymptotically at the EH radius and some
| things that approach a constant at that radius, so it's
| an example of the kind of asymptotic I was talking about
| _and_ one like your "horizontal" example.
| ubercow13 wrote:
| 1/sqrt(x) is a vertical asymptote?
| quantadev wrote:
| Replace "is a" with "has one".
| bencyoung wrote:
| 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!
| ldunn wrote:
| 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.
| mr_toad wrote:
| 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.
| JoeAltmaier wrote:
| ...and tidal forces may have reduced your body to red
| goo, so there's that
| ldunn wrote:
| It is absolutely untrue that GR predicts that you would
| be knocked unconscious crossing the horizon. In fact one
| of the most fundamental aspects of GR (equivalence)
| predicts the exact opposite - there is no local
| experiment you can do as a freely falling observer to
| detect the horizon.
| machina_ex_deus wrote:
| 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.
| jiggawatts wrote:
| Take a closer look at a picture of Kruskal coordinates,
| e.g.: https://upload.wikimedia.org/wikipedia/commons/1/1c/K
| ruskal_...
|
| 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/Eddingto
| n%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.
| ubercow13 wrote:
| The article you linked says precisely that Kruskal-
| Szekeres coordinates are not singular at the event
| horizon. The event horizon is completely regular: https:/
| /en.wikipedia.org/wiki/Gravitational_singularity#Curv...
|
| You can choose stupid coordinates that introduce a
| singularity wherever you like, in GM or in classical
| mechanics just the same. The coordinates have no meaning.
| mr_mitm wrote:
| > 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).
|
| Is that so? Isn't that a continuous effect? Things falling
| into the black hole appear to be frozen at the event
| horizon only for an observer at infinity.
| AlecBG wrote:
| 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
| lupire wrote:
| 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?
| AlecBG wrote:
| well he certainly mentions a result where if there is an
| everywhere timelike Killing vector field (+ some other
| assumptions) you can prove that Hawking radiation doesn't
| occur and that does not include for example the
| Schwarzschild solution because the Killing vector field
| partial/partial t becomes non-timelike on the horizon.
|
| So for example if you take a dead star in a vacuum with
| nothing else in the universe (and make certain technical
| assumptions) then you can prove that the star does not emit
| Hawking radiation. That's quite a strong result, and
| certainly does make the result seem shocking.
| throwawaymaths wrote:
| > 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 wrote:
| >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, Jose 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_massa wrote:
| >> _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 wrote:
| Also, the Standard Model does allow nonconservation of baryon
| number, nonperturbatively.
| zabzonk wrote:
| But they do fade away? (Blondie)
| dudeinjapan wrote:
| It's better to burn out than to fade away.
| quantadev wrote:
| 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.
| BlueTemplar wrote:
| > 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 ?
| quantadev wrote:
| 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.
| nabla9 wrote:
| > 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.
| quantadev wrote:
| 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 wrote:
| 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
| BlueTemplar wrote:
| > 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 wrote:
| > 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.
| deepsun wrote:
| "As Mark Twain famously never said" (c)
| frogulis wrote:
| 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 wrote:
| 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
| tim333 wrote:
| Quote Investigator was quite interesting on the history.
| The phrase has been evolving over many years going back to
| at least 1710.
| https://quoteinvestigator.com/2014/07/13/truth/
| thayne wrote:
| 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 wrote:
| 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.
| tbrownaw wrote:
| > _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.
| jfengel wrote:
| And black holes are much colder then their surroundings,
| i.e. the Cosmic Microwave Background. And they will be for
| trillions of years.
| dr_dshiv wrote:
| Do you mean singularities are much colder? Because
| everything outside of that is super hot, no?
| jfengel wrote:
| 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.
| m3kw9 wrote:
| He meant dead dead
| davedx wrote:
| Its talking about Hawking radiation
| theandrewbailey wrote:
| Then the title should be:
|
| Dead Stars Don't Hawking Radiate
| alienbaby wrote:
| The article itself explains the title quite well.
| jpmattia wrote:
| > _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.
| nothrabannosir wrote:
| _> 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.
| jpmattia wrote:
| Perhaps, but "Mathematical Physicists HATE when authors
| make THIS ONE ASSUMPTION!!1!" would be more click baity. I
| took it more as Baez writing for his physics audience.
| nothrabannosir wrote:
| Purely out of pedantic interest: is that a meaningful
| distinction, or is it just the same thing for a different
| audience? I'm reminded of chess youtubers who give
| similarly "click baity" titles to their videos which are
| only click bait to people who watch chess videos. Isn't
| it the same?
|
| All the power to them by the way. It's the crushing power
| of the algorithm. No hard feelings, just something I've
| been wondering.
| jpmattia wrote:
| Well, you got me thinking about "What _exactly_ is
| clickbait? "
|
| So full disclosure: I've directly interacted with John
| Carlos Baez only in social media, with the topics as
| disparate as music and observational astronomy. My own
| QFT & GR background is grad course level but with little
| actual usage in my career. (I've done more solid-state +
| high-speed electronics work, with a bunch of programming
| as well.) With that background, and turning the pedantry
| dial up to 11:
|
| To me, one distinguishing element of clickbait is that
| the post is ultimately disappointing. The usual M.O. for
| clickbait is that the website needs eyeballs for
| advertising, so they beef up a headline of an
| uninteresting article with the expectation of getting
| extra monetization compared to an honest headline.
|
| I would venture a guess that he doesn't actually care
| about monetization, or really even extra clicks, with
| this post. The screenshot with the big red X through the
| popsci article sets the expectation pretty quickly, and
| the tone of the rest of the post is really a rant that
| mediocre science made it into PRL and then into the
| popular science literature. He explicitly calls out the
| popsci journalists for laziness, but in a clever (I'm
| pretty sure Mark Twain would approve of his name being
| taken in vain) and erudite (correct use of the
| subjunctive) way.
|
| Would I have clicked on the title without seeing the
| authorship johncarlosbaez.wordpress.com? Maybe but I
| doubt it. There is so much bad popsci physics out there
| that I'm pretty trained to ignore obviously inadequate
| headlines. So on a scale of 1-10, I'd rate the click-
| baityness of the headline no more than a 3. He got me to
| click, but only because I knew it was his post.
|
| As for others, the set of people who understand that
| Hawking radiation exists has nearly 100% overlap with
| those who know that black bodies and spinning magnets
| radiate, so for those folks who are in the set who are
| also unfamiliar with the author, perhaps it's more
| clickbaity.
|
| [edit: And I can't believe you got me to write that many
| words on the clickbait philosophy. Have I been baited? :)
| ]
| thayne wrote:
| > I took it more as Baez writing for his physics
| audience.
|
| I have a degree in Physics with an emphasis in Astronomy,
| and my thought on reading the title was "that's absurd".
| Even if you somehow infer that "radiate" specifically
| means "emit hawking radiation" which I don't know how you
| would without more context, "dead stars" generally is
| considered to include black holes, which do emit hawking
| radiation.
| jpmattia wrote:
| I wrote in the other reply:
|
| > _As for others, the set of people who understand that
| Hawking radiation exists has nearly 100% overlap with
| those who know that black bodies and spinning magnets
| radiate, so for those folks who are in the set who are
| also unfamiliar with the author, perhaps it 's more
| clickbaity._
|
| So according to my theory, you must in the set that
| understands Hawking radiation + black bodies + E&M, but
| not in the set familiar with Baez.
|
| I worked hard on my theory, please don't let me down and
| be a counterexample. :)
| layer8 wrote:
| 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 wrote:
| The term refers to causal structure:
| https://en.wikipedia.org/wiki/Globally_hyperbolic_manifold
| griffzhowl wrote:
| 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 wrote:
| 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 wrote:
| 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.
| rubitxxx4 wrote:
| 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 wrote:
| 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.
| rubitxxx4 wrote:
| > 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.
| darkerside wrote:
| 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.
| khanan wrote:
| Let's see what Neil deGrasse Tyson says about this.
| w10-1 wrote:
| 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 wrote:
| 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
| ;-)
| globnomulous wrote:
| 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 wrote:
| Good news for boltzmann brains
| m3kw9 wrote:
| One can argue there are 8billion Boltzmann brains on earth
| already
| m3kw9 wrote:
| 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
| qnleigh wrote:
| 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?
| dataflow wrote:
| > 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.
| qnleigh wrote:
| 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-
| dataflow wrote:
| 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!
| nazgul17 wrote:
| 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 wrote:
| No, you are in fact accelerating when you are standing on the
| planet.
| deepsun wrote:
| 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.
| griffzhowl wrote:
| 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
| tbrownaw wrote:
| I've seen proposed perpetual motion machines based on treating
| simplified calculations as if they're the real thing.
| lproven wrote:
| Of course, as noted researcher Eskil Simonsson teaches, Dead
| stars still burn.
| chrz wrote:
| Theres still something in universe that we are missing and I feel
| the grand theories of next billion years are missing that
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