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"More than one hundred years after he published his paper setting out the equations of general relativity, Einstein has been proved right once more — in a much

"More than one hundred years after he published his paper setting out the equations of general relativity, Einstein has been proved right once more — in a much more extreme laboratory than he could have possibly imagined!" This sounds somewhat like an insult to Einstein's imagination.

laretluval 8y ago
Up to his death Einstein denied that black holes could physically form.
- 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.
- ars 8y ago
  And he is right. Time dilation means it's impossible for them to form. (From the POV of me, here on earth.)
  - deleted 8y ago
    [deleted]
  - opportune 8y ago
    yeah, and Zeno's ship never reaches its destination
    - oldandtired 8y ago
      Interesting you bring that up. "Black hole" formation is based on a similar idea. An inversion is used for sure. But the argument used is similar. How about that. I haven't considered that example as a logical means of ruling against "black holes".
  - codethief 8y ago
    Considering astrophysical evidence to the contrary as well as multiple simplifications(∆) underlying your argument, I'd say he was probably wrong. ∆) (Some of) the assumptions underlying your argument are the following: Assumption 1: We're observers at infinity, observing time as given by the usual Schwarzschild/Kerr coordinate t (let's focus on Schwarzschild for simplicity). Yes, the argument in favor of this is that such observers observe Schwarzschild spacetime to be flat at infinity (which is more or less what we see) but there are certainly other[1] asymptotically flat foliations of Schwarzschild spacetime which don't have a coordinate singularity at the horizon and thus don't exhibit the behavior you describe. I have yet to see a convincing argument for why we, as observers, couldn't perceive any of these other foliations of Schwarzschild spacetime and for why we definitely wouldn't live to see someone else cross the event horizon. (I mean, the fact that this doesn't work in the usual Schwarzschild coordinates is really a consequence of their singular behavior at the horizon, so should be resolved by any smooth/non-singular choice of coordinates—of which there are infinitely many.) Assumption 2: You're talking about a static black hole solution (or a simple spherical shell collapsing) while realistic scenarios of black hole formation are an entirely different beast. Assumption 3: You cannot superpose / easily glue together solutions of Einstein's field equations. So I'd be at least careful making a statement about us, here on Earth, when it comes to a distant black hole. [1] https://en.m.wikipedia.org/wiki/Gullstrand–Painlevé_coordinates https://en.m.wikipedia.org/wiki/Gullstrand–Painlevé_coordina...
- andrewflnr 8y ago
  He could still imagine them, though.
- laretluval 8y ago
  Do you doubt this? https://en.wikipedia.org/wiki/Einstein%27s_unsuccessful_investigations#Black_holes https://en.wikipedia.org/wiki/Einstein%27s_unsuccessful_inve...
- carapace 8y ago
  https://arxiv.org/pdf/physics/9905030.pdf https://arxiv.org/pdf/physics/9905030.pdf "On the Gravitational Field of a Mass Point according to Einstein’s Theory" by K. Schwarzschild, January 13th, 1916 (English translation) Black holes are fiction. The whole mess started with people misunderstanding Schwarzschild's paper. Yes, there's a singularity in the math, but you can avoid it by changing the origin. This is one of those cases where conventional "science" has been gummed up by human foibles. (And the concept is so damned romantic and compelling. And that movie! It was like the opposite of "Jaws" for sharks.) If you can't read the paper don't bother arguing with me. If you can, show me where the math says "black holes". I'm pretty sure it says "translate the origin and ignore the singularity".
  - adrianN 8y ago
    Even if there is no actual singularity, those objects exist, once you get too close you can't get back out and that is true for light as well, so they are pretty much black. I think black hole is fitting name.
    - NihilumExNil 8y ago
      > those objects What are you talking about, quasars? They emit heaps of light for all I know.
      - SiempreViernes 8y ago
        Not from behind the event horizon they don't, the light comes from outside.
        NihilumExNil 8y ago
        That's not easy to prove, because nobody can look into the quasar. The question still stands. What are "those objects"?
        SiempreViernes 8y ago

laretluval 8y ago

Up to his death Einstein denied that black holes could physically form.

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.
ars 8y ago
And he is right. Time dilation means it's impossible for them to form. (From the POV of me, here on earth.)
- deleted 8y ago
  [deleted]
- opportune 8y ago
  yeah, and Zeno's ship never reaches its destination
  - oldandtired 8y ago
    Interesting you bring that up. "Black hole" formation is based on a similar idea. An inversion is used for sure. But the argument used is similar. How about that. I haven't considered that example as a logical means of ruling against "black holes".
- codethief 8y ago
  Considering astrophysical evidence to the contrary as well as multiple simplifications(∆) underlying your argument, I'd say he was probably wrong. ∆) (Some of) the assumptions underlying your argument are the following: Assumption 1: We're observers at infinity, observing time as given by the usual Schwarzschild/Kerr coordinate t (let's focus on Schwarzschild for simplicity). Yes, the argument in favor of this is that such observers observe Schwarzschild spacetime to be flat at infinity (which is more or less what we see) but there are certainly other[1] asymptotically flat foliations of Schwarzschild spacetime which don't have a coordinate singularity at the horizon and thus don't exhibit the behavior you describe. I have yet to see a convincing argument for why we, as observers, couldn't perceive any of these other foliations of Schwarzschild spacetime and for why we definitely wouldn't live to see someone else cross the event horizon. (I mean, the fact that this doesn't work in the usual Schwarzschild coordinates is really a consequence of their singular behavior at the horizon, so should be resolved by any smooth/non-singular choice of coordinates—of which there are infinitely many.) Assumption 2: You're talking about a static black hole solution (or a simple spherical shell collapsing) while realistic scenarios of black hole formation are an entirely different beast. Assumption 3: You cannot superpose / easily glue together solutions of Einstein's field equations. So I'd be at least careful making a statement about us, here on Earth, when it comes to a distant black hole. [1] https://en.m.wikipedia.org/wiki/Gullstrand–Painlevé_coordinates https://en.m.wikipedia.org/wiki/Gullstrand–Painlevé_coordina...
andrewflnr 8y ago
He could still imagine them, though.
laretluval 8y ago
Do you doubt this? https://en.wikipedia.org/wiki/Einstein%27s_unsuccessful_investigations#Black_holes https://en.wikipedia.org/wiki/Einstein%27s_unsuccessful_inve...
carapace 8y ago
https://arxiv.org/pdf/physics/9905030.pdf https://arxiv.org/pdf/physics/9905030.pdf "On the Gravitational Field of a Mass Point according to Einstein’s Theory" by K. Schwarzschild, January 13th, 1916 (English translation) Black holes are fiction. The whole mess started with people misunderstanding Schwarzschild's paper. Yes, there's a singularity in the math, but you can avoid it by changing the origin. This is one of those cases where conventional "science" has been gummed up by human foibles. (And the concept is so damned romantic and compelling. And that movie! It was like the opposite of "Jaws" for sharks.) If you can't read the paper don't bother arguing with me. If you can, show me where the math says "black holes". I'm pretty sure it says "translate the origin and ignore the singularity".
- adrianN 8y ago
  Even if there is no actual singularity, those objects exist, once you get too close you can't get back out and that is true for light as well, so they are pretty much black. I think black hole is fitting name.
  - NihilumExNil 8y ago
    > those objects What are you talking about, quasars? They emit heaps of light for all I know.
    - SiempreViernes 8y ago
      Not from behind the event horizon they don't, the light comes from outside.
      - NihilumExNil 8y ago
        That's not easy to prove, because nobody can look into the quasar. The question still stands. What are "those objects"?
        SiempreViernes 8y ago