3 ms·

It probably depends what one means by "black hole". Physical singularities are predicted by GR+other theorems but haven't been established.

by Jach 8y ago

SiempreViernes 8y ago
Uh, ain't no ambiguity here: a black hole is a thing with an event horizon.
- Jach 8y ago
  What do you mean by an "event horizon"? If you're a physicist I would expect you to drill down to the math and assumptions and theorems, not just English, but as I'm not a physicist you don't need to humor me even if you are one. Still supposing you did, would what you mean jive with our best known physical theories? What sorts of implications[0] to the actual observable cosmos would there be which are comfortable and uncomfortable? To a layman there's not much ambiguity. And so things a layman would recognize as describing a "black hole" were posited before general relativity existed, but if you modeled them mathematically you would be able to find contradictions with other established theory. Therefore it is important to know what a physicist like Einstein means, precisely, if they think a "black hole" doesn't exist. In the wiki link someone else provided (full of "citation needed"s) it's reasonable to infer that at least one component of a denial of the reality of black holes is that formation implies infinite energy, infinite energy cannot be, therefore formation cannot be. The belief of non-existence is then really belief in the faulty logical implication, not so much a layman "black hole". In any case scientists now know many things that Einstein didn't about what the best theories say about objects both laymen and physicists might understand as "black holes" and "event horizons" as well as what the best observational evidence says about events in the cosmos -- some of that evidence being very recent (gravity waves). It's not very fruitful to cite Einstein authoritatively on any supposed dispute without taking into account modern knowledge. [0] Tegmark's paper here https://arxiv.org/abs/astro-ph/0302131 https://arxiv.org/abs/astro-ph/0302131 is probably my favorite paper drilling home the idea that theories can predict unobservable entities. We don't seem to have problems with positing the continued existence of a spaceship that escapes our future light cone even though we'll never be able to interact with it again, but implications of other theories (especially around "parallel universes") seem to make people very uncomfortable.
  - SiempreViernes 8y ago
    Jeez man, I mean what one always means when saying event horizon in the context of black holes: the surface that separates causally disconnected inner region around very compact objects from the rest of the universe. Now, the term "black hole" is admittedly from after Einstein died, but since he what he actually didn't believe was anything physical could be compact enough to have a size comparable to its Schwarzschild radius this is simply a difference in naming: clearly we are talking about the same sort of object. The math does little difference to the discussion, but if you want it then I suggest you find a book like Wald or Shutz.

It probably depends what one means by "black hole". Physical singularities are predicted by GR+other theorems but haven't been established.

by Jach 8y ago

It probably depends what one means by "black hole". Physical singularities are predicted by GR+other theorems but haven't been established.

SiempreViernes 8y ago

Uh, ain't no ambiguity here: a black hole is a thing with an event horizon.

Jach 8y ago
What do you mean by an "event horizon"? If you're a physicist I would expect you to drill down to the math and assumptions and theorems, not just English, but as I'm not a physicist you don't need to humor me even if you are one. Still supposing you did, would what you mean jive with our best known physical theories? What sorts of implications[0] to the actual observable cosmos would there be which are comfortable and uncomfortable? To a layman there's not much ambiguity. And so things a layman would recognize as describing a "black hole" were posited before general relativity existed, but if you modeled them mathematically you would be able to find contradictions with other established theory. Therefore it is important to know what a physicist like Einstein means, precisely, if they think a "black hole" doesn't exist. In the wiki link someone else provided (full of "citation needed"s) it's reasonable to infer that at least one component of a denial of the reality of black holes is that formation implies infinite energy, infinite energy cannot be, therefore formation cannot be. The belief of non-existence is then really belief in the faulty logical implication, not so much a layman "black hole". In any case scientists now know many things that Einstein didn't about what the best theories say about objects both laymen and physicists might understand as "black holes" and "event horizons" as well as what the best observational evidence says about events in the cosmos -- some of that evidence being very recent (gravity waves). It's not very fruitful to cite Einstein authoritatively on any supposed dispute without taking into account modern knowledge. [0] Tegmark's paper here https://arxiv.org/abs/astro-ph/0302131 https://arxiv.org/abs/astro-ph/0302131 is probably my favorite paper drilling home the idea that theories can predict unobservable entities. We don't seem to have problems with positing the continued existence of a spaceship that escapes our future light cone even though we'll never be able to interact with it again, but implications of other theories (especially around "parallel universes") seem to make people very uncomfortable.
- SiempreViernes 8y ago
  Jeez man, I mean what one always means when saying event horizon in the context of black holes: the surface that separates causally disconnected inner region around very compact objects from the rest of the universe. Now, the term "black hole" is admittedly from after Einstein died, but since he what he actually didn't believe was anything physical could be compact enough to have a size comparable to its Schwarzschild radius this is simply a difference in naming: clearly we are talking about the same sort of object. The math does little difference to the discussion, but if you want it then I suggest you find a book like Wald or Shutz.