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Physicist discovered an escape from Hawking’s black hole paradox

255 points by theafh 5y ago

andreareina 5y ago
Netta Engelhardt on Sean Carrol's Mindscape podcast: https://www.youtube.com/watch?v=m-6mcLX_v2I https://www.youtube.com/watch?v=m-6mcLX_v2I
ChrisArchitect 5y ago
Recent discussion about confirming Hawking's Black Hole theorem: https://news.ycombinator.com/item?id=27696774 https://news.ycombinator.com/item?id=27696774
- prof-dr-ir 5y ago
  That is an unrelated result, although the confusion is understandable. You refer to a theorem, named after Hawking, that states that in classical general relativity the area of black hole horizons must always increase. The experimental confirmation of this theorem refers to the fact that the total area indeed appears to have increased for the black hole merger event observed by LIGO (which should indeed fall well within the realm of classical general relativity). However, once quantum gravitational effects are taken into account this black hole theorem no longer holds. Indeed, since the real world should be quantum, it is expected that the area of black holes eventually does decrease: they evaporate by emitting Hawking radiation. This is however purely a theoretical expectation, since these evaporation effects are a loooong way from being observable; evaporation probably only becomes a significant effect on time scales far beyond the current age of the universe. In quantum gravity there are nevertheless plenty of theoretical paradoxes and open questions, and the above article describes some recent progress by the theoreticians in this area.
hondo77 5y ago
> Engelhardt set her sights on quantum gravity when she was 9 years old. I tried to come up with a witty comment about that but words fail me. Wow.
- _Microft 5y ago
  What about: "I'm glad she did run not across the Men in Black in the middle of the night..."
  - felipemnoa 5y ago
    https://www.youtube.com/watch?v=K3hAVT2sDqQ&ab_channel=OscarKoeroo https://www.youtube.com/watch?v=K3hAVT2sDqQ&ab_channel=Oscar...
- handrous 5y ago
  Picking very difficult, specific topics like this to be interested in as a kid is pretty common. Sticking with it—that's unusual.
duxup 5y ago
> information about particles’ past states gets carried forward as they evolve So I was curious and googled and found: > the value of a wave function of a physical system at one point in time should determine its value at any other time Is there a layman's explanation about what this ... is?
- nerdponx 5y ago
  This is where my layperson's intuition totally breaks down. Matter goes into black hole. Black hole destroys everything because too much gravity and spacetime itself might or might not literally have a break in it. Eventually the remnants of said matter radiates out as random particles. That seems totally logical and not paradoxical at all to me. My uneducated mental models of black holes and information theory are so crude that I can't even see what the problem with this is. All I can figure is that the conclusions of a theorem in Research Area A turn out to violate an axiom that is used and dependend-on in Research Area B. I did however find this very interesting document that seems to cover some of what I'm missing: https://plato.stanford.edu/entries/spacetime-singularities/ https://plato.stanford.edu/entries/spacetime-singularities/. I'll have to make my way through it over the next few days, maybe it will benefit other people, too.
- ABeeSea 5y ago
  Mathematically, thee solutions to the differential equation have a “time evolution operator” that allow the quantum states to be pushed forward or backward in time.
- jwally 5y ago
  I'm a layman, so I'm not 100% certain on this, but I think this is a quantum version of Laplace's Demon; where if you know all the information about the state of a system, you can calculate what the system will look like at any point in the past, present, or future.
  - ctlachance 5y ago
    Does this imply that if we knew the total state of the universe, we could calculate its future state? Basically, does this imply the universe is deterministic, or that we're living in a simulation?
syncsynchalt 5y ago
> In the past two years, a network of quantum gravity theorists, mostly millennials, There you have it: millennials are killing the Hawking Information Paradox industry. (It's always been said that mathematicians do their best work when they're young, it seems weird to mix generational cohorts into it)
- coliveira 5y ago
  It is a favorite pastime of journalists to attribute events to a particular "generation", as if there was any kind of explanatory power in doing this.
- FatalLogic 5y ago
  Maybe it's a subtle reference to Planck's Principle [0], which is often summarized as "Science advances one funeral at a time"? In this case, suggesting that younger scientists might invest their time into new ideas that older scientists would dismiss. [0] https://www.chemistryworld.com/news/science-really-does-advance-one-funeral-at-a-time-study-suggests/3010961.article https://www.chemistryworld.com/news/science-really-does-adva...
- PartiallyTyped 5y ago
  There is also the statement that when an old scientist tells something is possible, then it is certainly possible, but if they express it is impossible, then it is possible.
- pvarangot 5y ago
  I think the blurry line for millennials put the oldest of us at something like 34 to 38 years old now? So yeah most people that got into academia after their bachelors and just finished their post-doc should be a millennial.
- hanniabu 5y ago
  Classic millennials and their cancel culture /s
TheCowboy 5y ago
Has anyone else (without a background in physics) kind of given up trying to understand developments in physics? It seems like the reporting is usually completely inaccurate or a metaphor at best. And that to have some grasp of it requires having a solid foundation in undergrad physics at a minimum. I'm just wondering if I'm being lazy by not trying hard enough or efficient. It's definitely not for lack of curiosity, but I also don't like to fool myself into thinking I understand something that I don't.
- abeppu 5y ago
  > I'm just wondering if I'm being lazy by not trying hard enough or efficient. Leonard Susskind at Stanford has a series of courses specifically aimed at helping people get up to speed in understanding modern physics. Every several months I work up the enthusiasm to watch several lectures, and then I get distracted and forget it all. Clearly, it's because I'm not trying hard enough because there are so many other things to also be curious about. https://theoreticalminimum.com/ https://theoreticalminimum.com/ But I also wish that physics were less focused on understanding extremes, and more interested in understanding physical systems closer at hand. There are interesting recent-ish results found in the behavior of crumpling paper, collapsing piles of sand, or the 'legs' of wine in a glass. I suspect that we could have much richer conceptual tools for thinking about the physical world actually around us if only more resources went into looking at it, rather than into exploring how laws do or don't break down in extreme conditions that don't naturally exist near earth.
  - TheCowboy 5y ago
    I can relate to this. It might seem stupid but understanding this made me change the way I tied my shoes, and my laces come undone way less frequently now. https://news.berkeley.edu/2017/04/11/shoe-string-theory-science-shows-why-shoelaces-come-untied/ https://news.berkeley.edu/2017/04/11/shoe-string-theory-scie... (Also thanks to everyone for their responses, a lot of good stuff to check out.)
    - fho 5y ago
      Mandatory link to Ian's Shoelace Site: https://www.fieggen.com/shoelace/ https://www.fieggen.com/shoelace/
thriftwy 5y ago
Our visible universe has event horizon around it, which has thousands of galaxies falling away from it and becoming unobservable every day, due to cosmological redshift. For some reason, physicists are not concerned with information loss via this one. I would be glad if somebody explained the difference.
- isk517 5y ago
  Black holes are thought to be information destruction not loss. Things moving super far away are lost but should still be out there, things falling into a black hole disappear and then once the black hole evaporates are gone forever. Or at least that use to be the theory.
  - thriftwy 5y ago
    It sounds a mistake to me, thinking that black holes' contents are still "out there". They are no longer observable, just like the galaxies that are no longer observable due to expanding universe. In both cases it is due to curvature of space, so I think these are essentially the same case. I would definitely like to hear something verifiable on why there's a difference and why only one of these susceptible to information paradox.
    - HellzStormer 5y ago
      My take on the difference (not a physicist): Take that galaxy that just crossed our "observable universe horizon" so that we can't see it. If there is a civilization halfway between Earth and that galaxy, they can still see that galaxy. The galaxy can see that second civilization and so can we. There isn't a single fixed "observable universe" boundary in space, it's just relative to the observer. With a black hole, it is different. There is no point that can see both sides while being seen from both sides,. If you are outside the black hole, you see nothing from within. If you are inside, then you can see the inside (this is speculation) and you also see the outside. It's a very clear boundary.
      - 5y ago
fallingknife 5y ago
> In the past two years, a network of quantum gravity theorists, mostly millennials, has made enormous progress on Hawking’s paradox. Wonder why they feel the need to mention that they are mostly millennials?
phn 5y ago
So, layman's question about black holes, almost 100% sci-fi derived. Starting from the time mechanics shown in, e.g., Interstellar. If when you're near a massive black hole time passes differently (more time passes away form the hole, so to speak), couldn't it be said that the regions near and far the black hole are drifting apart in the "time dimension"? If we take the black hole to be an extreme case of that, isn't the black hole a region that is drifting away so "fast" that light isn't fast enough to reach "us" on the outside? In that case, there would be no paradox, right? Whatever is inside the black hole is still there, but with no way to communicate.
- philipov 5y ago
  > isn't the black hole a region that is drifting away so "fast" that light isn't fast enough to reach "us" on the outside? I've seen some models of black holes that are similar to this. Specifically, what is happening in those models is that the space inside the event horizon is growing faster than the speed of light, so more space is created than light can traverse. This is the inverse of how cosmological horizons work. The reason we can only observe a limited portion of the universe is because objects are uniformly moving away from all other non-gravitationally bound objects. Space is being created between them. The farther you look, the faster galaxies are moving away from us because space is being created at every point in between. If you try to look far enough, the speed that objects are moving away from us becomes faster than the speed of light: space is being created faster than light can traverse it. This sort of faster-than-light travel doesn't break the relativistic speed limit because these objects aren't inertially accelerating inside their frame of reference, the frame of reference itself is expanding.
  - hinkley 5y ago
    > space is being created faster than light can traverse it. Which is precisely the sort of behavior one might expect if they lived inside of a black hole.
    - alasdair_ 5y ago
      Isn’t this what is happening in our universe as well? Space is expanding faster than light can traverse it?
f154hfds 5y ago
For those of you like me having trouble with the abstract nature of modern physics, I have to recommend the relevant PBS Space Time on the subject: https://www.youtube.com/watch?v=HF-9Dy6iB_4 https://www.youtube.com/watch?v=HF-9Dy6iB_4
gigatexal 5y ago
Amid the pandemic and the increasingly scary bits of international politics and increasing nationalism I’m just so happy that very exotic science continues to happen.
yawaworht1978 5y ago
While I find pbs space time very good and entertaining, I am wondering if I am the only one who thinks the content is a bit towards the complex side?
- wrycoder 5y ago
  That's great - there is a massive amount of overly simplified physics popular journalism.
- dvsfish 5y ago
  This is hardly a bad thing. Not all content should necessarily be easy to digest.
pcj-github 5y ago
I recently heard somewhere that the cosmic background radiation (CMR, 2.7 kelvin or so) is so much hotter than the "temperature" generated by Hawking radiation of black holes (apparently on the order of a billionth of a kelvin) such that they effectively do not radiate, and are not expected to do so for a loooong time (until expansion of the universe drops the background temp to an incredibly cold temperature). What I have not been able to determine is when they might be expected to occur? How far in the future will black holes start evaporating? (I believe the answer depends on the size of the black hole as well)
- cdumler 5y ago
  According to this, on the order of million trillion trillion trillion trillion trillion years [1]. [1] https://www.youtube.com/watch?v=uD4izuDMUQA https://www.youtube.com/watch?v=uD4izuDMUQA
- mr_toad 5y ago
  Some of the larger black holes could take 10^100 years to evaporate even after the universe grows cold. I don’t know how long that would take, but the whole process will take an unimaginably long time.
- T-A 5y ago
  You can easily find out yourself. First use a black hole temperature calculator like https://www.omnicalculator.com/physics/black-hole-temperature https://www.omnicalculator.com/physics/black-hole-temperatur... or https://www.vttoth.com/CMS/physics-notes/311-hawking-radiation-calculator https://www.vttoth.com/CMS/physics-notes/311-hawking-radiati... to find the Hawking temperature T_BH of your black hole. Then use the fact that CMB temperature T_CMB is inversely proportional to the cosmological scale factor a(t), where t is time: https://physics.stackexchange.com/questions/76241/cmbr-temperature-over-time https://physics.stackexchange.com/questions/76241/cmbr-tempe... Set a(t_now) = 1 for convenience; then T_CMB(t) = T_CMB(t_now) / a(t) and you want to find the time t when T_BH = T_CMB(t). That depends on how the scale factor will change over time: https://en.wikipedia.org/wiki/Scale_factor_(cosmology) https://en.wikipedia.org/wiki/Scale_factor_(cosmology) We don't know that, but if we assume for simplicity that dark energy will keep dominating, a(t) will grow exponentially, i.e. a(t) = a(t) / a(t_now) ~ exp(H_0 * (t - t_now)) where H_0 is Hubble's constant. So T_CMB(t) = T_CMB(t_now) / a(t) ~ T_CMB(t_now) / exp(H_0 * (t - t_now)) Numbers: T_CMB(t_now) ~ 2.7 K H_0 ~ 71 km/s/Mpc ~ 2.3e-18 s^-1 t_now ~ 14 Gyr ~ 3.2e16 s so, with t expressed in seconds, T_CMB(t) ~ 2.7 / exp(2.3e-18 * (t - 3.2e16)) K Setting this equal to T_BH and solving for t, I get t = 3.2e16 + ln(2.7 / T_BH) / 2.3e-18 s So let's say you have a solar mass black hole. Then T_BH ~ 6.16871e-8 K and so t ~ 7.7e18 s ~ 2.4e11 years i.e. 240 billion years (17 times the current age of the universe). That's actually not a humongous number, thanks to the exponential expansion of a(t). It would take a lot longer with the expansion rate of a matter-dominated universe (exercise for the reader!)
paulpauper 5y ago
Reading quanta magazine always makes me feel like a failure inside . All these ppl doing cutting edge research about things that matter. Thank God for crypto investments , stock investments or else i'd have nothing going for me.
bryan0 5y ago
How are these extremal surfaces related to the event horizon? How are these surfaces related to the "firewall" solution to the blackhole information paradox that everyone was talking about a few years ago? https://en.wikipedia.org/wiki/Firewall_(physics) https://en.wikipedia.org/wiki/Firewall_(physics)
- zachf 5y ago
  The question about firewalls is such a good one. In short, physicists identified this problem involving three parts of an evaporating black hole, and all three seemed to be entangled according to the usual understanding, but that was bad because “entanglement is monogamous”, meaning that a system A can’t be “married” (maximally entangled) to system B and system C at the same time. So it was proposed that maybe spacetime just ends, just inside the event horizon, and so the metaphorical third wheel, system C, is killed off or actually just never existed. It’s not like anyone’s been inside a black hole and then came out to tell us if spacetime ends there. So that’s a firewall, and it was a hypothesis for how to resolve the non-monogamy issue. But it does require a bizarre new phenomenon where spacetime ends suddenly in a region of low curvature where nothing was supposed to happen. So many people did not like this idea. However, there was an alternative idea, which was that C was the “same person” as B, in which case its perfectly legal to be married to B and C at the same time. But B and C are really far apart, so that seemed weird. It would have to be that spacetime was joining these distant systems together via their entanglement. This was called ER=EPR, or roughly speaking the idea that the connectivity of space is defined by entanglement, so that these distantly separated systems B and C were actually connected via a very quantum sort of wormhole and thus were the same thing. This new work on the evaporation paradox, amazingly, makes it clear that at least in some cases, ER=EPR is actually happening in an unexpected but concrete way—in these models, there is the emergence of a spacetime bridge of the distant entangled systems. And that’s what’s so awesome. We always suspected the firewall paradox would prove something about what spacetime is, because it was a very sharp paradox. And now, in this unexpected and un-firewally way, it has!
  - GoblinSlayer 5y ago
    The black hole model used here is the elephant in the room, namely the no-hair conjecture. It's derived for the classic black hole, which has a problem that it's assumed into existence and has no means of formation (collapsars are only asymptotically close, but not exactly classic black holes, they are furry and the no-hair conjecture doesn't hold).
phendrenad2 5y ago
So in layman's terms, we just redefine the surface of the black hole until the equations work? (I'm sure I'm wrong, but maybe this'll help kick off the discussion)
- steve76 5y ago
  Telescopes have improved. Jupiter has stayed the same since Galileo. May be the same as particles appearing in a vacuum as a property of a black hole and not the vacuum.
steve76 5y ago
Electromagnetism, or light, is the interaction, or heat transfer, between two things with no medium in between. The medium of interaction is the the insides of the two things themselves. In order to exist, insides need to be able to interact, outside needs to stay the same. The surroundings have a thermometer. It moves a little. It only has one place to go. Wherever it goes, the outside of it gets stuck glowing red before glowing orange. Insides and how they interact with the surroundings can not only cause outsides to get stuck, but go backwards. There's nothing the surroundings can do to get the outside to change. The insides can handle anything thrown at it. The insides themselves can't get anything beyond the outside. Whatever the insides are doing, it's easier to go back in than to simply fall out into the surroundings. Why? Things have no mind. They take the easy way. They don't make fast decisions to what's easiest. The way they took is the easiest way because they have no choice in the matter. If you consider empty space as not empty, but two things canceling each other out, that's an easier way than going back inside. It's possible to say that's a property of the inside, and not the surroundings. You have a way to limit insides where the outside does not change. That provides insights on what nature does when it lacks composite structure.

255 points by theafh 5y ago

Netta Engelhardt on Sean Carrol's Mindscape podcast: https://www.youtube.com/watch?v=m-6mcLX_v2I https://www.youtube.com/watch?v=m-6mcLX_v2I

ChrisArchitect 5y ago

Recent discussion about confirming Hawking's Black Hole theorem: https://news.ycombinator.com/item?id=27696774 https://news.ycombinator.com/item?id=27696774

prof-dr-ir 5y ago
That is an unrelated result, although the confusion is understandable. You refer to a theorem, named after Hawking, that states that in classical general relativity the area of black hole horizons must always increase. The experimental confirmation of this theorem refers to the fact that the total area indeed appears to have increased for the black hole merger event observed by LIGO (which should indeed fall well within the realm of classical general relativity). However, once quantum gravitational effects are taken into account this black hole theorem no longer holds. Indeed, since the real world should be quantum, it is expected that the area of black holes eventually does decrease: they evaporate by emitting Hawking radiation. This is however purely a theoretical expectation, since these evaporation effects are a loooong way from being observable; evaporation probably only becomes a significant effect on time scales far beyond the current age of the universe. In quantum gravity there are nevertheless plenty of theoretical paradoxes and open questions, and the above article describes some recent progress by the theoreticians in this area.

hondo77 5y ago

> Engelhardt set her sights on quantum gravity when she was 9 years old. I tried to come up with a witty comment about that but words fail me. Wow.

_Microft 5y ago
What about: "I'm glad she did run not across the Men in Black in the middle of the night..."
- felipemnoa 5y ago
  https://www.youtube.com/watch?v=K3hAVT2sDqQ&ab_channel=OscarKoeroo https://www.youtube.com/watch?v=K3hAVT2sDqQ&ab_channel=Oscar...
handrous 5y ago
Picking very difficult, specific topics like this to be interested in as a kid is pretty common. Sticking with it—that's unusual.

duxup 5y ago

> information about particles’ past states gets carried forward as they evolve So I was curious and googled and found: > the value of a wave function of a physical system at one point in time should determine its value at any other time Is there a layman's explanation about what this ... is?

nerdponx 5y ago
This is where my layperson's intuition totally breaks down. Matter goes into black hole. Black hole destroys everything because too much gravity and spacetime itself might or might not literally have a break in it. Eventually the remnants of said matter radiates out as random particles. That seems totally logical and not paradoxical at all to me. My uneducated mental models of black holes and information theory are so crude that I can't even see what the problem with this is. All I can figure is that the conclusions of a theorem in Research Area A turn out to violate an axiom that is used and dependend-on in Research Area B. I did however find this very interesting document that seems to cover some of what I'm missing: https://plato.stanford.edu/entries/spacetime-singularities/ https://plato.stanford.edu/entries/spacetime-singularities/. I'll have to make my way through it over the next few days, maybe it will benefit other people, too.
ABeeSea 5y ago
Mathematically, thee solutions to the differential equation have a “time evolution operator” that allow the quantum states to be pushed forward or backward in time.
jwally 5y ago
I'm a layman, so I'm not 100% certain on this, but I think this is a quantum version of Laplace's Demon; where if you know all the information about the state of a system, you can calculate what the system will look like at any point in the past, present, or future.
- ctlachance 5y ago
  Does this imply that if we knew the total state of the universe, we could calculate its future state? Basically, does this imply the universe is deterministic, or that we're living in a simulation?

syncsynchalt 5y ago

> In the past two years, a network of quantum gravity theorists, mostly millennials, There you have it: millennials are killing the Hawking Information Paradox industry. (It's always been said that mathematicians do their best work when they're young, it seems weird to mix generational cohorts into it)

coliveira 5y ago
It is a favorite pastime of journalists to attribute events to a particular "generation", as if there was any kind of explanatory power in doing this.
FatalLogic 5y ago
Maybe it's a subtle reference to Planck's Principle [0], which is often summarized as "Science advances one funeral at a time"? In this case, suggesting that younger scientists might invest their time into new ideas that older scientists would dismiss. [0] https://www.chemistryworld.com/news/science-really-does-advance-one-funeral-at-a-time-study-suggests/3010961.article https://www.chemistryworld.com/news/science-really-does-adva...
PartiallyTyped 5y ago
There is also the statement that when an old scientist tells something is possible, then it is certainly possible, but if they express it is impossible, then it is possible.
pvarangot 5y ago
I think the blurry line for millennials put the oldest of us at something like 34 to 38 years old now? So yeah most people that got into academia after their bachelors and just finished their post-doc should be a millennial.
hanniabu 5y ago
Classic millennials and their cancel culture /s

TheCowboy 5y ago

Has anyone else (without a background in physics) kind of given up trying to understand developments in physics? It seems like the reporting is usually completely inaccurate or a metaphor at best. And that to have some grasp of it requires having a solid foundation in undergrad physics at a minimum. I'm just wondering if I'm being lazy by not trying hard enough or efficient. It's definitely not for lack of curiosity, but I also don't like to fool myself into thinking I understand something that I don't.

abeppu 5y ago
> I'm just wondering if I'm being lazy by not trying hard enough or efficient. Leonard Susskind at Stanford has a series of courses specifically aimed at helping people get up to speed in understanding modern physics. Every several months I work up the enthusiasm to watch several lectures, and then I get distracted and forget it all. Clearly, it's because I'm not trying hard enough because there are so many other things to also be curious about. https://theoreticalminimum.com/ https://theoreticalminimum.com/ But I also wish that physics were less focused on understanding extremes, and more interested in understanding physical systems closer at hand. There are interesting recent-ish results found in the behavior of crumpling paper, collapsing piles of sand, or the 'legs' of wine in a glass. I suspect that we could have much richer conceptual tools for thinking about the physical world actually around us if only more resources went into looking at it, rather than into exploring how laws do or don't break down in extreme conditions that don't naturally exist near earth.
- TheCowboy 5y ago
  I can relate to this. It might seem stupid but understanding this made me change the way I tied my shoes, and my laces come undone way less frequently now. https://news.berkeley.edu/2017/04/11/shoe-string-theory-science-shows-why-shoelaces-come-untied/ https://news.berkeley.edu/2017/04/11/shoe-string-theory-scie... (Also thanks to everyone for their responses, a lot of good stuff to check out.)
  - fho 5y ago
    Mandatory link to Ian's Shoelace Site: https://www.fieggen.com/shoelace/ https://www.fieggen.com/shoelace/

thriftwy 5y ago

Our visible universe has event horizon around it, which has thousands of galaxies falling away from it and becoming unobservable every day, due to cosmological redshift. For some reason, physicists are not concerned with information loss via this one. I would be glad if somebody explained the difference.

isk517 5y ago
Black holes are thought to be information destruction not loss. Things moving super far away are lost but should still be out there, things falling into a black hole disappear and then once the black hole evaporates are gone forever. Or at least that use to be the theory.
- thriftwy 5y ago
  It sounds a mistake to me, thinking that black holes' contents are still "out there". They are no longer observable, just like the galaxies that are no longer observable due to expanding universe. In both cases it is due to curvature of space, so I think these are essentially the same case. I would definitely like to hear something verifiable on why there's a difference and why only one of these susceptible to information paradox.
  - HellzStormer 5y ago
    My take on the difference (not a physicist): Take that galaxy that just crossed our "observable universe horizon" so that we can't see it. If there is a civilization halfway between Earth and that galaxy, they can still see that galaxy. The galaxy can see that second civilization and so can we. There isn't a single fixed "observable universe" boundary in space, it's just relative to the observer. With a black hole, it is different. There is no point that can see both sides while being seen from both sides,. If you are outside the black hole, you see nothing from within. If you are inside, then you can see the inside (this is speculation) and you also see the outside. It's a very clear boundary.
    - 5y ago

fallingknife 5y ago

> In the past two years, a network of quantum gravity theorists, mostly millennials, has made enormous progress on Hawking’s paradox. Wonder why they feel the need to mention that they are mostly millennials?

phn 5y ago

So, layman's question about black holes, almost 100% sci-fi derived. Starting from the time mechanics shown in, e.g., Interstellar. If when you're near a massive black hole time passes differently (more time passes away form the hole, so to speak), couldn't it be said that the regions near and far the black hole are drifting apart in the "time dimension"? If we take the black hole to be an extreme case of that, isn't the black hole a region that is drifting away so "fast" that light isn't fast enough to reach "us" on the outside? In that case, there would be no paradox, right? Whatever is inside the black hole is still there, but with no way to communicate.

philipov 5y ago
> isn't the black hole a region that is drifting away so "fast" that light isn't fast enough to reach "us" on the outside? I've seen some models of black holes that are similar to this. Specifically, what is happening in those models is that the space inside the event horizon is growing faster than the speed of light, so more space is created than light can traverse. This is the inverse of how cosmological horizons work. The reason we can only observe a limited portion of the universe is because objects are uniformly moving away from all other non-gravitationally bound objects. Space is being created between them. The farther you look, the faster galaxies are moving away from us because space is being created at every point in between. If you try to look far enough, the speed that objects are moving away from us becomes faster than the speed of light: space is being created faster than light can traverse it. This sort of faster-than-light travel doesn't break the relativistic speed limit because these objects aren't inertially accelerating inside their frame of reference, the frame of reference itself is expanding.
- hinkley 5y ago
  > space is being created faster than light can traverse it. Which is precisely the sort of behavior one might expect if they lived inside of a black hole.
  - alasdair_ 5y ago
    Isn’t this what is happening in our universe as well? Space is expanding faster than light can traverse it?

f154hfds 5y ago

For those of you like me having trouble with the abstract nature of modern physics, I have to recommend the relevant PBS Space Time on the subject: https://www.youtube.com/watch?v=HF-9Dy6iB_4 https://www.youtube.com/watch?v=HF-9Dy6iB_4

gigatexal 5y ago

Amid the pandemic and the increasingly scary bits of international politics and increasing nationalism I’m just so happy that very exotic science continues to happen.

yawaworht1978 5y ago

While I find pbs space time very good and entertaining, I am wondering if I am the only one who thinks the content is a bit towards the complex side?

wrycoder 5y ago
That's great - there is a massive amount of overly simplified physics popular journalism.
dvsfish 5y ago
This is hardly a bad thing. Not all content should necessarily be easy to digest.

pcj-github 5y ago

I recently heard somewhere that the cosmic background radiation (CMR, 2.7 kelvin or so) is so much hotter than the "temperature" generated by Hawking radiation of black holes (apparently on the order of a billionth of a kelvin) such that they effectively do not radiate, and are not expected to do so for a loooong time (until expansion of the universe drops the background temp to an incredibly cold temperature). What I have not been able to determine is when they might be expected to occur? How far in the future will black holes start evaporating? (I believe the answer depends on the size of the black hole as well)

cdumler 5y ago
According to this, on the order of million trillion trillion trillion trillion trillion years [1]. [1] https://www.youtube.com/watch?v=uD4izuDMUQA https://www.youtube.com/watch?v=uD4izuDMUQA
mr_toad 5y ago
Some of the larger black holes could take 10^100 years to evaporate even after the universe grows cold. I don’t know how long that would take, but the whole process will take an unimaginably long time.
T-A 5y ago
You can easily find out yourself. First use a black hole temperature calculator like https://www.omnicalculator.com/physics/black-hole-temperature https://www.omnicalculator.com/physics/black-hole-temperatur... or https://www.vttoth.com/CMS/physics-notes/311-hawking-radiation-calculator https://www.vttoth.com/CMS/physics-notes/311-hawking-radiati... to find the Hawking temperature T_BH of your black hole. Then use the fact that CMB temperature T_CMB is inversely proportional to the cosmological scale factor a(t), where t is time: https://physics.stackexchange.com/questions/76241/cmbr-temperature-over-time https://physics.stackexchange.com/questions/76241/cmbr-tempe... Set a(t_now) = 1 for convenience; then T_CMB(t) = T_CMB(t_now) / a(t) and you want to find the time t when T_BH = T_CMB(t). That depends on how the scale factor will change over time: https://en.wikipedia.org/wiki/Scale_factor_(cosmology) https://en.wikipedia.org/wiki/Scale_factor_(cosmology) We don't know that, but if we assume for simplicity that dark energy will keep dominating, a(t) will grow exponentially, i.e. a(t) = a(t) / a(t_now) ~ exp(H_0 * (t - t_now)) where H_0 is Hubble's constant. So T_CMB(t) = T_CMB(t_now) / a(t) ~ T_CMB(t_now) / exp(H_0 * (t - t_now)) Numbers: T_CMB(t_now) ~ 2.7 K H_0 ~ 71 km/s/Mpc ~ 2.3e-18 s^-1 t_now ~ 14 Gyr ~ 3.2e16 s so, with t expressed in seconds, T_CMB(t) ~ 2.7 / exp(2.3e-18 * (t - 3.2e16)) K Setting this equal to T_BH and solving for t, I get t = 3.2e16 + ln(2.7 / T_BH) / 2.3e-18 s So let's say you have a solar mass black hole. Then T_BH ~ 6.16871e-8 K and so t ~ 7.7e18 s ~ 2.4e11 years i.e. 240 billion years (17 times the current age of the universe). That's actually not a humongous number, thanks to the exponential expansion of a(t). It would take a lot longer with the expansion rate of a matter-dominated universe (exercise for the reader!)

paulpauper 5y ago

Reading quanta magazine always makes me feel like a failure inside . All these ppl doing cutting edge research about things that matter. Thank God for crypto investments , stock investments or else i'd have nothing going for me.

bryan0 5y ago

How are these extremal surfaces related to the event horizon? How are these surfaces related to the "firewall" solution to the blackhole information paradox that everyone was talking about a few years ago? https://en.wikipedia.org/wiki/Firewall_(physics) https://en.wikipedia.org/wiki/Firewall_(physics)

zachf 5y ago
The question about firewalls is such a good one. In short, physicists identified this problem involving three parts of an evaporating black hole, and all three seemed to be entangled according to the usual understanding, but that was bad because “entanglement is monogamous”, meaning that a system A can’t be “married” (maximally entangled) to system B and system C at the same time. So it was proposed that maybe spacetime just ends, just inside the event horizon, and so the metaphorical third wheel, system C, is killed off or actually just never existed. It’s not like anyone’s been inside a black hole and then came out to tell us if spacetime ends there. So that’s a firewall, and it was a hypothesis for how to resolve the non-monogamy issue. But it does require a bizarre new phenomenon where spacetime ends suddenly in a region of low curvature where nothing was supposed to happen. So many people did not like this idea. However, there was an alternative idea, which was that C was the “same person” as B, in which case its perfectly legal to be married to B and C at the same time. But B and C are really far apart, so that seemed weird. It would have to be that spacetime was joining these distant systems together via their entanglement. This was called ER=EPR, or roughly speaking the idea that the connectivity of space is defined by entanglement, so that these distantly separated systems B and C were actually connected via a very quantum sort of wormhole and thus were the same thing. This new work on the evaporation paradox, amazingly, makes it clear that at least in some cases, ER=EPR is actually happening in an unexpected but concrete way—in these models, there is the emergence of a spacetime bridge of the distant entangled systems. And that’s what’s so awesome. We always suspected the firewall paradox would prove something about what spacetime is, because it was a very sharp paradox. And now, in this unexpected and un-firewally way, it has!
- GoblinSlayer 5y ago
  The black hole model used here is the elephant in the room, namely the no-hair conjecture. It's derived for the classic black hole, which has a problem that it's assumed into existence and has no means of formation (collapsars are only asymptotically close, but not exactly classic black holes, they are furry and the no-hair conjecture doesn't hold).

phendrenad2 5y ago

So in layman's terms, we just redefine the surface of the black hole until the equations work? (I'm sure I'm wrong, but maybe this'll help kick off the discussion)

steve76 5y ago
Telescopes have improved. Jupiter has stayed the same since Galileo. May be the same as particles appearing in a vacuum as a property of a black hole and not the vacuum.

steve76 5y ago

Electromagnetism, or light, is the interaction, or heat transfer, between two things with no medium in between. The medium of interaction is the the insides of the two things themselves. In order to exist, insides need to be able to interact, outside needs to stay the same. The surroundings have a thermometer. It moves a little. It only has one place to go. Wherever it goes, the outside of it gets stuck glowing red before glowing orange. Insides and how they interact with the surroundings can not only cause outsides to get stuck, but go backwards. There's nothing the surroundings can do to get the outside to change. The insides can handle anything thrown at it. The insides themselves can't get anything beyond the outside. Whatever the insides are doing, it's easier to go back in than to simply fall out into the surroundings. Why? Things have no mind. They take the easy way. They don't make fast decisions to what's easiest. The way they took is the easiest way because they have no choice in the matter. If you consider empty space as not empty, but two things canceling each other out, that's an easier way than going back inside. It's possible to say that's a property of the inside, and not the surroundings. You have a way to limit insides where the outside does not change. That provides insights on what nature does when it lacks composite structure.