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Haven’t we basically proven that even horizon is real? At which point, isn’t anything inside sealed off by gravity, the fact that time slows down infinitely, th

Haven’t we basically proven that even horizon is real? At which point, isn’t anything inside sealed off by gravity, the fact that time slows down infinitely, the hypothesised firewall, etc? I.e. if a black hole has a singularity or a super heavy pokemon, there is no distinguishable difference in our universe?

pdonis 2y ago
> Haven’t we basically proven that even horizon is real? No. All we have shown is that there are compact regions in our universe that look like event horizons--but could also be just apparent horizons. To know that they are actual, true event horizons, we would have to know the entire future of the universe, since an event horizon is a globally defined surface in spacetime and its presence and location cannot be known unless you know the entire spacetime, i.e., the entire future. If you don't know that--and of course we don't--you can't tell an actual event horizon from an apparent horizon. > isn’t anything inside sealed off by gravity, the fact that time slows down infinitely, the hypothesised firewall, etc? None of these are actual features of actual event horizons (or apparent horizons, for that matter). The first is a missatement--the gravity of the object is not "sealed off" and can still be detected outside. The second is an illusion caused by an unfortunate choice of coordinates. The third is pure speculation, and speculation which does not appear to have gained much traction. > if a black hole has a singularity or a super heavy pokemon, there is no distinguishable difference in our universe? Most physicists do not believe that either of these (if I take "super heavy pokemon" to mean "some kind of ordinary compact object like a neutron star") is what actually happens.
mr_toad 2y ago
> Haven’t we basically proven that even horizon is real? We haven’t observed event horizons except as fuzzy highly processed images. They look a lot like what you’d expect from a black hole, but we have hardly ruled out all possibilities. And there are theoretical effects near an event horizon for charged and spinning black holes, that as far as I know we’ve never been able to observe. It doesn’t seem out of the question that a black hole without a singularity might exhibit behaviour near the event horizon that is measurably different from the theories we have now.

pdonis 2y ago

> Haven’t we basically proven that even horizon is real? No. All we have shown is that there are compact regions in our universe that look like event horizons--but could also be just apparent horizons. To know that they are actual, true event horizons, we would have to know the entire future of the universe, since an event horizon is a globally defined surface in spacetime and its presence and location cannot be known unless you know the entire spacetime, i.e., the entire future. If you don't know that--and of course we don't--you can't tell an actual event horizon from an apparent horizon. > isn’t anything inside sealed off by gravity, the fact that time slows down infinitely, the hypothesised firewall, etc? None of these are actual features of actual event horizons (or apparent horizons, for that matter). The first is a missatement--the gravity of the object is not "sealed off" and can still be detected outside. The second is an illusion caused by an unfortunate choice of coordinates. The third is pure speculation, and speculation which does not appear to have gained much traction. > if a black hole has a singularity or a super heavy pokemon, there is no distinguishable difference in our universe? Most physicists do not believe that either of these (if I take "super heavy pokemon" to mean "some kind of ordinary compact object like a neutron star") is what actually happens.

mr_toad 2y ago

> Haven’t we basically proven that even horizon is real? We haven’t observed event horizons except as fuzzy highly processed images. They look a lot like what you’d expect from a black hole, but we have hardly ruled out all possibilities. And there are theoretical effects near an event horizon for charged and spinning black holes, that as far as I know we’ve never been able to observe. It doesn’t seem out of the question that a black hole without a singularity might exhibit behaviour near the event horizon that is measurably different from the theories we have now.