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That is not true. General relativity concerns itself with mass, and gravitational waves are function of mass. Quark stars have plenty of mass, why would you th

by ars 4y ago

That is not true. General relativity concerns itself with mass, and gravitational waves are function of mass. Quark stars have plenty of mass, why would you think they would not generate gravitational waves? I don't understand what you could be thinking of. In fact a black hole would make things more complicated because of the infinite time dilation. If anything gravitational waves are evidence for extraordinarily massive objects, but against black hole singularities with their problematic infinite time dilation.

pdonis 4y ago
> General relativity concerns itself with mass, and gravitational waves are function of mass. This is way too simplistic. Gravitational waves are waves of propagating spacetime curvature. They can certainly be produced by "mass", i.e., by objects with nonzero stress-energy, as long as those objects (or mergers of such objects) have time-varying quadrupole moments. But they can also be produced by objects like black holes (or mergers of such objects), which have zero stress-energy and are made purely of spacetime curvature. > a black hole would make things more complicated because of the infinite time dilation There is no such thing. The effect you are talking about is an artifact of a particular choice of coordinates and has no physical meaning. It certainly does not prevent black hole mergers from emitting gravitational waves.
- 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.

by ars 4y ago

pdonis 4y ago

> General relativity concerns itself with mass, and gravitational waves are function of mass. This is way too simplistic. Gravitational waves are waves of propagating spacetime curvature. They can certainly be produced by "mass", i.e., by objects with nonzero stress-energy, as long as those objects (or mergers of such objects) have time-varying quadrupole moments. But they can also be produced by objects like black holes (or mergers of such objects), which have zero stress-energy and are made purely of spacetime curvature. > a black hole would make things more complicated because of the infinite time dilation There is no such thing. The effect you are talking about is an artifact of a particular choice of coordinates and has no physical meaning. It certainly does not prevent black hole mergers from emitting gravitational waves.

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.