4 ms·

Sabine’s post on this topic might be relevant here: http://backreaction.blogspot.com/2020/11/the-black-hole-information-loss-problem.html?m=1 http://backreacti

by bryan0 5y ago

Sabine’s post on this topic might be relevant here: http://backreaction.blogspot.com/2020/11/the-black-hole-information-loss-problem.html?m=1 http://backreaction.blogspot.com/2020/11/the-black-hole-info... > The Black Hole information loss problem is unsolved. Because it’s unsolvable. > The black hole information loss problem is not a math problem. It’s not like trying to prove the Riemann hypothesis. You cannot solve the black hole information loss problem with math alone. You need data, there is no data, and there won’t be any data. Which is why the black hole information loss problem is for all practical purposes unsolvable.

ericmay 5y ago
> "You need data, there is no data, and there won’t be any data." Why won't there be any data? Is it just physically impossible to collect or is it an engineering problem?
- zehaeva 5y ago
  Because data comes from experiments. Unless we figure out how to create a black hole in the lab (spoiler, you wouldn't want to) or could get close to a natural black hole (spoiler, you wouldn't want to) you're not going to get any data for this.
  - vl 5y ago
    >create a black hole in the lab (spoiler, you wouldn't want to) Current understanding is that there is nothing dangerous about creating black hole in the lab: it’s going to be so small that it will evaporate quickly, and event horizon is so small that it will be very unlikely to capture new matter.
    - a9h74j 5y ago
      > Current understanding I.e., if a tiny black hole had formed at LLC and swallowed the Earth, that would have been data. Recall all the arguments quoting rates of Hawking Radiation from small black holes as if it were proven fact.
      - vl 5y ago
        >if a tiny black hole had formed at LLC and swallowed the Earth The point is that tiny black hole, man-made or from the outer space, can't swallow Earth in any reasonable amount of time: when it's gravitationally captured and orbits through Earth internals "forever", it's event horizon is so small, that it's very rarely interacts and captures new matter (after all, matter is not "dense" on the atomic level), so it grows very very slowly, even if it doesn't evaporate at all. Any light black hole has really minuscule size. For comparison: black hole of mass of Earth is couple centimeters in diameter. Now, if such black hole comes from outer space and hits Earth, almost nothing will be left.
        solveit 5y ago
        You're right, unless there is unknown physics that happens near a black hole.
        simiones 5y ago
        It's still important to note that black holes at the atomic level, and gravitational effects of any kind at that level in fact, are entirely speculative science. QM doesn't allow for any kind of gravitational attraction, and GR doesn't account for any of the effects observed at atomic level, so we are left with only speculation. Microscopic black holes are an entire extra level of speculation over any other gravitational effects. Even in GR, black holes are not exactly consistent with the theory - they are singularities, indicating that (even if we knew nothing of QM) GR can't be a complete theory of nature. So, discussing what microscopic black holes can or can't do is not much more than discussing what effect photon torpedoes would have on a Holtzman shield (Star Trek x Dune fanfic).
    - zehaeva 5y ago
      I was thinking of a black hole that would be large enough to do any sort of science with. I personally wouldn't be concerned with it consuming the world, I would be more concerned with it evaporating! Because the smaller the blackhole is the faster it evaporates, below a certain energy the blackhole would turn all the energy/mass that was put into it into energy close to instantly, i.e. it basically turns into a bomb.
- simiones 5y ago
  All of the black holes we know for sure exist (those produced by supernovae) are predicted to dissolve so slowly that it would take thousands of years or perhaps even millions of years of observation to produce any data on Hawking radiation. If small black holes can actually form (which is currently just a theory) there may be some chance to observe and measure them dissolving. However, I believe this requires energies far higher than any particle collider we can expect to build in the next hundred years, so this avenue is also closed. So, perhaps "never" is a bit pessimistic, but not far off in human terms.
  - SkyBelow 5y ago
    >All of the black holes we know for sure exist (those produced by supernovae) are predicted to dissolve so slowly that it would take thousands of years or perhaps even millions of years of observation to produce any data on Hawking radiation. Isn't there also an issue that the background temperature of space is still too high compared to the temperature of Hawking Radiation and thus blackholes are still growing, even in 'empty space', because the temperature is greater than what they would lose from Hawking radiation? And this temperature difference will continue for the foreseeable future, even on galactic time scales.
- JumpCrisscross 5y ago
  > Is it just physically impossible to collect or is it an engineering problem? Engineering as in you’d need to create and measure a shielded black hole. (Shielded because you need to isolate it from the CMB.)
emerged 5y ago
Well she seems to disagree with almost anything any other physicist says.
- Kranar 5y ago
  Not at all true, it's just that most of the time her videos get posted or gain attention is when she has a disagreement with some new "groundbreaking" discovery, and often times her disagreements are well warranted. Most of her videos have nothing to do with disagreeing with others.
- pdonis 5y ago
  No, she is just pointing out something that most other physicists fail to point out, particularly when talking to reporters about things that end up in articles like this one: that when physicists talk about "showing" or "demonstrating" or "discovering" something about black holes, they mean "we built a mathematical model that says X", not "we got actual data that confirms our mathematical model that says X". (There is a similar issue when physicists talk about string theory.)
  - whatshisface 5y ago
    A physical model is way more than a mathematical model. It is based on theories which acquired their epistemic weight elsewhere to lend to the problem being studied. Conclusions made about black holes are made on the basis of QFT and general relativity, unlikely to be overturned so long as the researcher is working far enough from the singularity for the idea of doing QFT on a fixed background spacetime to still apply.
    - pdonis 5y ago
      > A physical model is way more than a mathematical model. Sure, there also have to be rules about how the mathematical quantities in the model correspond to physical quantities that are measured in experiments. > It is based on theories which acquired their epistemic weight elsewhere to lend to the problem being studied. Translated into plain language: you can take a physical model whose predictions have been confirmed over some range, and extrapolate it outside that range. Sure, physicists do this all the time. But that does not mean that the extrapolated predictions are automatically correct. You still have to test them. > Conclusions made about black holes are made on the basis of QFT and general relativity, unlikely to be overturned so long as the researcher is working far enough from the singularity for the idea of doing QFT on a fixed background spacetime to still apply. I understand this is a common belief among physicists. That doesn't change the fact that, unless and until we have actual experimental data, these conclusions have not been confirmed. Also, what is involved in black hole formation and evaporation is not "QFT on a fixed background spacetime". Quantum fields make non-negligible contributions to the gravitational source in these models. That means that, for a fully consistent model, you need a theory of quantum gravity, which we don't have. The actual framework being used basically assumes that a spacetime geometry sourced by the expectation value of the stress-energy tensor of the quantum fields is a sufficiently good approximation. Which is still an assumption, no matter how many physicists believe it, unless and until we have actual data to test it against.
8bitsrule 5y ago
This is a wonderful response in that it points clearly to the modern disconnect between physics theory and the experimentation which led to its greatest advances. Simplifying assumptions can be very useful for didactic purposes, but nature isn't simple. There are many sciences which put observations that threaten the status quo into a (physical or dogmatic) closet. "the problem comes from combining a certain set of assumptions, doing a calculation, and arriving at a contradiction.... without data, the question is not which solution to the problem is correct, but which one you like best."
andrewflnr 5y ago
To the same extent the problem is unsolvable, it also doesn't exist in the first place. No one has observed Hawking radiation. From an empirical standpoint, the whole thing started as a math problem, so it's appropriate to solve it as a math problem.
- simiones 5y ago
  Yes, and as a math problem, it's been solved a thousand times already. This is not like Fermat's last theorem where no one could find a solution that worked, or prove that none existed. This is a situation where we know for sure no solution exists with the axioms of GR or QM. So, you need to add new axioms, and it's easy to add new axioms to solve it, as has been done already in various ways. The remaining problem is to see if any of these axioms are in any way physical, which is a problem of physics, one that can only be solved with data.
chmod600 5y ago
Science requires good hypotheses to contruct good experiments to learn new things. Math is absract, but it can have implications that are testable in the real world.
- JumpCrisscross 5y ago
  > Math is absract, but it can have implications that are testable in the real world The complaint is that there are possibly infinite mathematically-valid solutions to the problem. Without more data we can’t weigh them against each other. The work is interesting. But it should be pitched as a series of thought experiments or philosophical entreaties, not a solution.

by bryan0 5y ago

ericmay 5y ago

> "You need data, there is no data, and there won’t be any data." Why won't there be any data? Is it just physically impossible to collect or is it an engineering problem?

zehaeva 5y ago
Because data comes from experiments. Unless we figure out how to create a black hole in the lab (spoiler, you wouldn't want to) or could get close to a natural black hole (spoiler, you wouldn't want to) you're not going to get any data for this.
- vl 5y ago
  >create a black hole in the lab (spoiler, you wouldn't want to) Current understanding is that there is nothing dangerous about creating black hole in the lab: it’s going to be so small that it will evaporate quickly, and event horizon is so small that it will be very unlikely to capture new matter.
  - a9h74j 5y ago
    > Current understanding I.e., if a tiny black hole had formed at LLC and swallowed the Earth, that would have been data. Recall all the arguments quoting rates of Hawking Radiation from small black holes as if it were proven fact.
    - vl 5y ago
      >if a tiny black hole had formed at LLC and swallowed the Earth The point is that tiny black hole, man-made or from the outer space, can't swallow Earth in any reasonable amount of time: when it's gravitationally captured and orbits through Earth internals "forever", it's event horizon is so small, that it's very rarely interacts and captures new matter (after all, matter is not "dense" on the atomic level), so it grows very very slowly, even if it doesn't evaporate at all. Any light black hole has really minuscule size. For comparison: black hole of mass of Earth is couple centimeters in diameter. Now, if such black hole comes from outer space and hits Earth, almost nothing will be left.
      - solveit 5y ago
        You're right, unless there is unknown physics that happens near a black hole.
      - simiones 5y ago
        It's still important to note that black holes at the atomic level, and gravitational effects of any kind at that level in fact, are entirely speculative science. QM doesn't allow for any kind of gravitational attraction, and GR doesn't account for any of the effects observed at atomic level, so we are left with only speculation. Microscopic black holes are an entire extra level of speculation over any other gravitational effects. Even in GR, black holes are not exactly consistent with the theory - they are singularities, indicating that (even if we knew nothing of QM) GR can't be a complete theory of nature. So, discussing what microscopic black holes can or can't do is not much more than discussing what effect photon torpedoes would have on a Holtzman shield (Star Trek x Dune fanfic).
  - zehaeva 5y ago
    I was thinking of a black hole that would be large enough to do any sort of science with. I personally wouldn't be concerned with it consuming the world, I would be more concerned with it evaporating! Because the smaller the blackhole is the faster it evaporates, below a certain energy the blackhole would turn all the energy/mass that was put into it into energy close to instantly, i.e. it basically turns into a bomb.
simiones 5y ago
All of the black holes we know for sure exist (those produced by supernovae) are predicted to dissolve so slowly that it would take thousands of years or perhaps even millions of years of observation to produce any data on Hawking radiation. If small black holes can actually form (which is currently just a theory) there may be some chance to observe and measure them dissolving. However, I believe this requires energies far higher than any particle collider we can expect to build in the next hundred years, so this avenue is also closed. So, perhaps "never" is a bit pessimistic, but not far off in human terms.
- SkyBelow 5y ago
  >All of the black holes we know for sure exist (those produced by supernovae) are predicted to dissolve so slowly that it would take thousands of years or perhaps even millions of years of observation to produce any data on Hawking radiation. Isn't there also an issue that the background temperature of space is still too high compared to the temperature of Hawking Radiation and thus blackholes are still growing, even in 'empty space', because the temperature is greater than what they would lose from Hawking radiation? And this temperature difference will continue for the foreseeable future, even on galactic time scales.
JumpCrisscross 5y ago
> Is it just physically impossible to collect or is it an engineering problem? Engineering as in you’d need to create and measure a shielded black hole. (Shielded because you need to isolate it from the CMB.)

emerged 5y ago

Well she seems to disagree with almost anything any other physicist says.

Kranar 5y ago
Not at all true, it's just that most of the time her videos get posted or gain attention is when she has a disagreement with some new "groundbreaking" discovery, and often times her disagreements are well warranted. Most of her videos have nothing to do with disagreeing with others.
pdonis 5y ago
No, she is just pointing out something that most other physicists fail to point out, particularly when talking to reporters about things that end up in articles like this one: that when physicists talk about "showing" or "demonstrating" or "discovering" something about black holes, they mean "we built a mathematical model that says X", not "we got actual data that confirms our mathematical model that says X". (There is a similar issue when physicists talk about string theory.)
- whatshisface 5y ago
  A physical model is way more than a mathematical model. It is based on theories which acquired their epistemic weight elsewhere to lend to the problem being studied. Conclusions made about black holes are made on the basis of QFT and general relativity, unlikely to be overturned so long as the researcher is working far enough from the singularity for the idea of doing QFT on a fixed background spacetime to still apply.
  - pdonis 5y ago
    > A physical model is way more than a mathematical model. Sure, there also have to be rules about how the mathematical quantities in the model correspond to physical quantities that are measured in experiments. > It is based on theories which acquired their epistemic weight elsewhere to lend to the problem being studied. Translated into plain language: you can take a physical model whose predictions have been confirmed over some range, and extrapolate it outside that range. Sure, physicists do this all the time. But that does not mean that the extrapolated predictions are automatically correct. You still have to test them. > Conclusions made about black holes are made on the basis of QFT and general relativity, unlikely to be overturned so long as the researcher is working far enough from the singularity for the idea of doing QFT on a fixed background spacetime to still apply. I understand this is a common belief among physicists. That doesn't change the fact that, unless and until we have actual experimental data, these conclusions have not been confirmed. Also, what is involved in black hole formation and evaporation is not "QFT on a fixed background spacetime". Quantum fields make non-negligible contributions to the gravitational source in these models. That means that, for a fully consistent model, you need a theory of quantum gravity, which we don't have. The actual framework being used basically assumes that a spacetime geometry sourced by the expectation value of the stress-energy tensor of the quantum fields is a sufficiently good approximation. Which is still an assumption, no matter how many physicists believe it, unless and until we have actual data to test it against.

8bitsrule 5y ago

This is a wonderful response in that it points clearly to the modern disconnect between physics theory and the experimentation which led to its greatest advances. Simplifying assumptions can be very useful for didactic purposes, but nature isn't simple. There are many sciences which put observations that threaten the status quo into a (physical or dogmatic) closet. "the problem comes from combining a certain set of assumptions, doing a calculation, and arriving at a contradiction.... without data, the question is not which solution to the problem is correct, but which one you like best."

andrewflnr 5y ago

To the same extent the problem is unsolvable, it also doesn't exist in the first place. No one has observed Hawking radiation. From an empirical standpoint, the whole thing started as a math problem, so it's appropriate to solve it as a math problem.

simiones 5y ago
Yes, and as a math problem, it's been solved a thousand times already. This is not like Fermat's last theorem where no one could find a solution that worked, or prove that none existed. This is a situation where we know for sure no solution exists with the axioms of GR or QM. So, you need to add new axioms, and it's easy to add new axioms to solve it, as has been done already in various ways. The remaining problem is to see if any of these axioms are in any way physical, which is a problem of physics, one that can only be solved with data.

chmod600 5y ago

Science requires good hypotheses to contruct good experiments to learn new things. Math is absract, but it can have implications that are testable in the real world.

JumpCrisscross 5y ago
> Math is absract, but it can have implications that are testable in the real world The complaint is that there are possibly infinite mathematically-valid solutions to the problem. Without more data we can’t weigh them against each other. The work is interesting. But it should be pitched as a series of thought experiments or philosophical entreaties, not a solution.