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Considering astrophysical evidence to the contrary as well as multiple simplifications(∆) underlying your argument, I'd say he was probably wrong. ∆) (Some of)

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...

ars 8y ago
> Considering astrophysical evidence to the contrary There is none. The only things that has been observed are supermassive objects. No event horizon or black hole has been seen. Every observation so far is also consistent with Neutron stars. In fact some observations attributed to black holes are actually more consistent with neutron stars because of the same time dilation issues. i.e. we observe the event occurring in finite time. > I have yet to see a convincing argument for why we, as observers, couldn't perceive any of these other foliations of Schwarzschild spacetime For the simple reason that we are not free falling into a black hole. > 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. Forget mathematical coordinateness. Use the real world. In the real world you can not see a black hole form (or something fall into one) because time dilates to infinity. The fact that there are solutions where it doesn't, hardly matters when none of those solutions are physical. > You're talking about a static black hole solution while a black hole forming is an entirely different matter. That's even worse. The matter falls inward so fast that every atom is massively time dilated (due to velocity) relative to the others, and it perceives them as taking infinite time to reach the center. > So I'd be at least careful making a statement about us, here on Earth, when it comes to a distant black hole. I said that because last time I raised this object people told me "But yah, there are solutions where you do see the black hole form", so I figured I'd preempt that by specifying a POV. It didn't help - you did the exact same thing, told me there are other solutions.
- pdonis 8y ago
  > Every observation so far is also consistent with Neutron stars. This is not correct. Neutron stars have a maximum mass limit which is somewhere between 1.5 and 3 solar masses. Any compact object over that limit must be a black hole. The hole at the center of our galaxy, which is the subject of the article, is a million or so solar masses, way over the limit. > some observations attributed to black holes are actually more consistent with neutron stars because of the same time dilation issues. i.e. we observe the event occurring in finite time. This is not correct either. Events that happen outside the event horizons of black holes will also emit light signals that reach us in a finite time. > The matter falls inward so fast that every atom is massively time dilated (due to velocity) relative to the others, and it perceives them as taking infinite time to reach the center. This is not correct. You have a flawed understanding of time dilation. Relative to each other, the atoms in an object falling into a black hole are moving very slowly, and the time dilation they see each other to have due to relative motion is negligible.
  - ars 8y ago
    > Neutron stars have a maximum mass limit which is somewhere between 1.5 and 3 solar masses. Yes, but after that they can become Quark stars (if such things exist). We do not have enough knowledge of quark degeneracy pressure to be able to tell. So we should not make assumption that they become physics-breaking black holes. > Any compact object over that limit must be a black hole. And how do you know the object is compact? Our telescopes do not have anywhere near sufficient resolution to distinguish that. > Events that happen outside the event horizons of black holes will also emit light signals that reach us in a finite time. OK, and what sort of events would that be? The only known signals are black hole mergers, which obviously can not be black hole mergers since such an event would take infinite time. We could see blazars perhaps, but those are not necessarily caused by black holes. > Relative to each other, the atoms in an object falling into a black hole are moving very slowly, and the time dilation they see each other to have due to relative motion is negligible. You are forgetting the objects on the other side of the black hole. Or even at small angles. Your objection would only apply to object right next to each other, and such objects are obviously not forming black holes by themself. They need all the mass nearby to make a black hole, but time dilation makes such mass unavailable.
oldandtired 8y ago
From our perspective and according to the general consensus idea that the universe is of finite age and fully in accordance with all black hole models and general relativity, blacks holes cannot exist in our universe. That does not mean what we have observed is not interesting, It is, but we don't know what it is, though we know it is not the "black hole" of theory. There are no circumstance under the prevailing theories for which any kind of "black hole" can come into existence anywhere in our universe. Black holes are wonderful "flights of fancy" just like the Stargate and the Ancients Hyperdrive and just like the Star Trek Warp Drive. "Black Holes" require certain assumptions for their formation in the theoretical sense and since those assumptions are not found in our universe, all models of "black holes" have an automatic failure point. All discussions about "black holes" being real, ignore those discrepancies and assume that they can exist. If you fail to agree with the "reality" of "black hole" formation, you become persona non grata. The problem with the "black hole reality" assumption is that we cut off entire streams of investigation into what the observed phenomena may be. We are stuck in a very little corner of the universe and we cannot see many things up close. Our model assumptions colour our understanding of what we see. There are many of our observations that are anomalous to the prevailing theories that are considered "correct". Yet, if you (as an observational or experimental scientist) raise questions in relation to the consensus models, you will be quickly put in your place. It is quite interesting that for a supposedly advanced civilisation, much of our technology and scientific endeavour is ruled by dogma. This does not lead to the advancement of our understanding of the universe around us. Just as other people have said before me and as I have said before - "There are no silly or stupid questions". Science is one useful tool we have for investigation of the universe around us. But the outcomes we find using it in our investigations of the universe around us are predicated on the basic assumptions we bring to the table in those investigations. It is one tool among many that we have and when people use it as the only tool that has meaning, they have moved it from being a useful tool to being a dogmatic tool. they have made science into a religion.
- pdonis 8y ago
  > There are no circumstance under the prevailing theories for which any kind of "black hole" can come into existence anywhere in our universe You are peddling misinformation here. You really need to get a correct understanding of black holes.

ars 8y ago

> Considering astrophysical evidence to the contrary There is none. The only things that has been observed are supermassive objects. No event horizon or black hole has been seen. Every observation so far is also consistent with Neutron stars. In fact some observations attributed to black holes are actually more consistent with neutron stars because of the same time dilation issues. i.e. we observe the event occurring in finite time. > I have yet to see a convincing argument for why we, as observers, couldn't perceive any of these other foliations of Schwarzschild spacetime For the simple reason that we are not free falling into a black hole. > 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. Forget mathematical coordinateness. Use the real world. In the real world you can not see a black hole form (or something fall into one) because time dilates to infinity. The fact that there are solutions where it doesn't, hardly matters when none of those solutions are physical. > You're talking about a static black hole solution while a black hole forming is an entirely different matter. That's even worse. The matter falls inward so fast that every atom is massively time dilated (due to velocity) relative to the others, and it perceives them as taking infinite time to reach the center. > So I'd be at least careful making a statement about us, here on Earth, when it comes to a distant black hole. I said that because last time I raised this object people told me "But yah, there are solutions where you do see the black hole form", so I figured I'd preempt that by specifying a POV. It didn't help - you did the exact same thing, told me there are other solutions.

pdonis 8y ago
> Every observation so far is also consistent with Neutron stars. This is not correct. Neutron stars have a maximum mass limit which is somewhere between 1.5 and 3 solar masses. Any compact object over that limit must be a black hole. The hole at the center of our galaxy, which is the subject of the article, is a million or so solar masses, way over the limit. > some observations attributed to black holes are actually more consistent with neutron stars because of the same time dilation issues. i.e. we observe the event occurring in finite time. This is not correct either. Events that happen outside the event horizons of black holes will also emit light signals that reach us in a finite time. > The matter falls inward so fast that every atom is massively time dilated (due to velocity) relative to the others, and it perceives them as taking infinite time to reach the center. This is not correct. You have a flawed understanding of time dilation. Relative to each other, the atoms in an object falling into a black hole are moving very slowly, and the time dilation they see each other to have due to relative motion is negligible.
- ars 8y ago
  > Neutron stars have a maximum mass limit which is somewhere between 1.5 and 3 solar masses. Yes, but after that they can become Quark stars (if such things exist). We do not have enough knowledge of quark degeneracy pressure to be able to tell. So we should not make assumption that they become physics-breaking black holes. > Any compact object over that limit must be a black hole. And how do you know the object is compact? Our telescopes do not have anywhere near sufficient resolution to distinguish that. > Events that happen outside the event horizons of black holes will also emit light signals that reach us in a finite time. OK, and what sort of events would that be? The only known signals are black hole mergers, which obviously can not be black hole mergers since such an event would take infinite time. We could see blazars perhaps, but those are not necessarily caused by black holes. > Relative to each other, the atoms in an object falling into a black hole are moving very slowly, and the time dilation they see each other to have due to relative motion is negligible. You are forgetting the objects on the other side of the black hole. Or even at small angles. Your objection would only apply to object right next to each other, and such objects are obviously not forming black holes by themself. They need all the mass nearby to make a black hole, but time dilation makes such mass unavailable.

oldandtired 8y ago

From our perspective and according to the general consensus idea that the universe is of finite age and fully in accordance with all black hole models and general relativity, blacks holes cannot exist in our universe. That does not mean what we have observed is not interesting, It is, but we don't know what it is, though we know it is not the "black hole" of theory. There are no circumstance under the prevailing theories for which any kind of "black hole" can come into existence anywhere in our universe. Black holes are wonderful "flights of fancy" just like the Stargate and the Ancients Hyperdrive and just like the Star Trek Warp Drive. "Black Holes" require certain assumptions for their formation in the theoretical sense and since those assumptions are not found in our universe, all models of "black holes" have an automatic failure point. All discussions about "black holes" being real, ignore those discrepancies and assume that they can exist. If you fail to agree with the "reality" of "black hole" formation, you become persona non grata. The problem with the "black hole reality" assumption is that we cut off entire streams of investigation into what the observed phenomena may be. We are stuck in a very little corner of the universe and we cannot see many things up close. Our model assumptions colour our understanding of what we see. There are many of our observations that are anomalous to the prevailing theories that are considered "correct". Yet, if you (as an observational or experimental scientist) raise questions in relation to the consensus models, you will be quickly put in your place. It is quite interesting that for a supposedly advanced civilisation, much of our technology and scientific endeavour is ruled by dogma. This does not lead to the advancement of our understanding of the universe around us. Just as other people have said before me and as I have said before - "There are no silly or stupid questions". Science is one useful tool we have for investigation of the universe around us. But the outcomes we find using it in our investigations of the universe around us are predicated on the basic assumptions we bring to the table in those investigations. It is one tool among many that we have and when people use it as the only tool that has meaning, they have moved it from being a useful tool to being a dogmatic tool. they have made science into a religion.

pdonis 8y ago
> There are no circumstance under the prevailing theories for which any kind of "black hole" can come into existence anywhere in our universe You are peddling misinformation here. You really need to get a correct understanding of black holes.