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The choice of coordinate is Earth. From the point of view of Earth black holes can never merge because it would take an infinite amount of time to do so. I do

by ars 4y ago

The choice of coordinate is Earth. From the point of view of Earth black holes can never merge because it would take an infinite amount of time to do so. I do not care about the point of view of the black hole itself, or the point of view of an object falling into the black hole. And it most definitely has physical meaning, and while gravitational waves could be emitted, they can never actually get to the merger. The gravitational waves would essentially slow down and fade out if it was a black hole. And since that is not what we see, I do not find the data compelling for black holes, but rather for ultra massive objects.

pdonis 4y ago
> From the point of view of Earth black holes can never merge because it would take an infinite amount of time to do so. This is not correct. What is correct is that from Earth you cannot see events on or inside the horizon of a black hole (or of a merger). But the fact that you cannot see those events does not mean they don't happen or that you cannot have indirect evidence for them, any more than the fact that you cannot see objects over your horizon on Earth itself means that objects can't travel there. > I do not care about the point of view of the black hole itself, or the point of view of an object falling into the black hole. Nothing I am saying has anything to do with any "point of view". I am stating invariant facts about the spacetime geometry and events in it. > it most definitely has physical meaning No "point of view" has physical meaning. "Points of view" are mathematical conveniences that we humans use for calculations. They are not physical things. > while gravitational waves could be emitted, they can never actually get to the merger. > The gravitational waves would essentially slow down and fade out if it was a black hole. Neither of these claims correctly reflect what GR predicts for black holes and black hole mergers. What GR predicts matches observations.
- ars 4y ago
  I strenuously disagree about what you're saying about relativistic point of view. It is not merely a mathematical calculation it is a description of reality. From our point of view if something has not happened then as far as we are concerned it has not happened in reality. In a different reality, i.e. in a different point of view, it may have happened. And this is not a contradiction, it is merely the way the universe works. And not only what can we not see beyond the event horizon, as things approached the event horizon they slow down tremendously. Even at quite a distance they slow down so much that our lifetime is insufficient to see them change. In our lifetime it is impossible to see black holes merge because the time dilation is sufficient to slow that down to imperceptibility.
  - pdonis 4y ago
    > From our point of view if something has not happened then as far as we are concerned it has not happened in reality. Sorry, but this is simply wrong as a description of what the actual theory of relativity says. So is the rest of your post. I've already explained why.
    - hnfong 4y ago
      The GP's statement sounds like a tautology. Is there a substantial difference between "from our point of view" and "as far as we are concerned ... in reality" under the theory of relativity? Using the mathematics of a physics theory to deny a tautological(?) statement seems to get at the very issue that Sabine is raising in the original article. Alternatively, you're literally arguing that the mathematics of the theory of relativity bears no meaning in reality. (i.e. "The effect you are talking about is an artifact of a particular choice of coordinates and has no physical meaning.") I'm not sure whether your statement is true, but if it is, it seems to prove Sabine's point...
      - pdonis 4y ago
        > The GP's statement sounds like a tautology. Maybe it does to you, but it isn't a tautology. It's a false claim. See below. > Is there a substantial difference between "from our point of view" and "as far as we are concerned ... in reality" under the theory of relativity? Yes. A "point of view" in relativity (by which is meant something like a coordinate chart or a reference frame) might not be capable of describing all of reality. So you cannot infer, just from the fact that a "point of view" does not contain some particular event, that that event is not part of reality. Before you can draw that inference, you first have to show that the "point of view" in question is capable of describing all of reality (which in relativity means all of whatever spacetime manifold you are dealing with). The "point of view" the GP is trying to use is not capable of describing all of the spacetime manifold we are dealing with. So it does not justify the claim the GP is making, that any event not described by that point of view cannot be part of the spacetime manifold. > Using the mathematics of a physics theory to deny a tautological(?) statement Is not what I am doing. I am using the mathematics of relativity to correct a wrong claim by someone who (apparently) doesn't understand that mathematics properly. Everything I am saying is basic general relativity and can be found in any GR textbook.

by ars 4y ago

pdonis 4y ago

> From the point of view of Earth black holes can never merge because it would take an infinite amount of time to do so. This is not correct. What is correct is that from Earth you cannot see events on or inside the horizon of a black hole (or of a merger). But the fact that you cannot see those events does not mean they don't happen or that you cannot have indirect evidence for them, any more than the fact that you cannot see objects over your horizon on Earth itself means that objects can't travel there. > I do not care about the point of view of the black hole itself, or the point of view of an object falling into the black hole. Nothing I am saying has anything to do with any "point of view". I am stating invariant facts about the spacetime geometry and events in it. > it most definitely has physical meaning No "point of view" has physical meaning. "Points of view" are mathematical conveniences that we humans use for calculations. They are not physical things. > while gravitational waves could be emitted, they can never actually get to the merger. > The gravitational waves would essentially slow down and fade out if it was a black hole. Neither of these claims correctly reflect what GR predicts for black holes and black hole mergers. What GR predicts matches observations.

ars 4y ago
I strenuously disagree about what you're saying about relativistic point of view. It is not merely a mathematical calculation it is a description of reality. From our point of view if something has not happened then as far as we are concerned it has not happened in reality. In a different reality, i.e. in a different point of view, it may have happened. And this is not a contradiction, it is merely the way the universe works. And not only what can we not see beyond the event horizon, as things approached the event horizon they slow down tremendously. Even at quite a distance they slow down so much that our lifetime is insufficient to see them change. In our lifetime it is impossible to see black holes merge because the time dilation is sufficient to slow that down to imperceptibility.
- pdonis 4y ago
  > From our point of view if something has not happened then as far as we are concerned it has not happened in reality. Sorry, but this is simply wrong as a description of what the actual theory of relativity says. So is the rest of your post. I've already explained why.
  - hnfong 4y ago
    The GP's statement sounds like a tautology. Is there a substantial difference between "from our point of view" and "as far as we are concerned ... in reality" under the theory of relativity? Using the mathematics of a physics theory to deny a tautological(?) statement seems to get at the very issue that Sabine is raising in the original article. Alternatively, you're literally arguing that the mathematics of the theory of relativity bears no meaning in reality. (i.e. "The effect you are talking about is an artifact of a particular choice of coordinates and has no physical meaning.") I'm not sure whether your statement is true, but if it is, it seems to prove Sabine's point...
    - pdonis 4y ago
      > The GP's statement sounds like a tautology. Maybe it does to you, but it isn't a tautology. It's a false claim. See below. > Is there a substantial difference between "from our point of view" and "as far as we are concerned ... in reality" under the theory of relativity? Yes. A "point of view" in relativity (by which is meant something like a coordinate chart or a reference frame) might not be capable of describing all of reality. So you cannot infer, just from the fact that a "point of view" does not contain some particular event, that that event is not part of reality. Before you can draw that inference, you first have to show that the "point of view" in question is capable of describing all of reality (which in relativity means all of whatever spacetime manifold you are dealing with). The "point of view" the GP is trying to use is not capable of describing all of the spacetime manifold we are dealing with. So it does not justify the claim the GP is making, that any event not described by that point of view cannot be part of the spacetime manifold. > Using the mathematics of a physics theory to deny a tautological(?) statement Is not what I am doing. I am using the mathematics of relativity to correct a wrong claim by someone who (apparently) doesn't understand that mathematics properly. Everything I am saying is basic general relativity and can be found in any GR textbook.