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Thread: so how can an event horizon model be falsified over a non-event horizon model?

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    so how can an event horizon model be falsified over a non-event horizon model?

    I don't believe specifically in a collapsed massive body that is just a bit bigger than the Schwarzschild radius, but how can such a body be distinguished from an event-horizon model?

    How can a SC radius model be falsified?
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    Quote Originally Posted by WaxRubiks View Post
    I don't believe specifically in a collapsed massive body that is just a bit bigger than the Schwarzschild radius, but how can such a body be distinguished from an event-horizon model?

    How can a SC radius model be falsified?
    I think the best test is one that's already been done; I've discussed it here before. A team led by Ron Remillard compared observations of accretion disks of possible neutron stars and black holes. For the ones that are believed to be neutron stars, the gas impacts on the surface from time to time, and creates an explosive burst of X-rays that we can see. For the ones believed to be black holes, this never happens, strongly suggesting that gas does not impact on any kind of surface.

    Any compact body that does not have something like a black hole's event horizon would seem to have a hard time explaining this.

    Similarly, thinking about the recent pictures from M87, not seeing the shadow there would have definitely required at least some rethinking. Remember that outside the event horizon, light could still make it to us if it was headed directly our way. The reason we don't see anything is that there isn't anything there that could be emitting that light. But if there were any kind of surface at all just outside the event horizon, it presumably should be able to emit light, and we see something.

    A model that suggests that "black holes" are actually compact bodies with a surface just outside an event horizon would have to explain why they instead appear to behave like a black hole without such a surface. We'd have to look at a specific model of such a thing to see how it could be differentiated by observation.
    Conserve energy. Commute with the Hamiltonian.

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    Quote Originally Posted by Grey View Post
    I think the best test is one that's already been done; I've discussed it here before. A team led by Ron Remillard compared observations of accretion disks of possible neutron stars and black holes. For the ones that are believed to be neutron stars, the gas impacts on the surface from time to time, and creates an explosive burst of X-rays that we can see. For the ones believed to be black holes, this never happens, strongly suggesting that gas does not impact on any kind of surface.

    Any compact body that does not have something like a black hole's event horizon would seem to have a hard time explaining this.

    Similarly, thinking about the recent pictures from M87, not seeing the shadow there would have definitely required at least some rethinking. Remember that outside the event horizon, light could still make it to us if it was headed directly our way. The reason we don't see anything is that there isn't anything there that could be emitting that light. But if there were any kind of surface at all just outside the event horizon, it presumably should be able to emit light, and we see something.

    A model that suggests that "black holes" are actually compact bodies with a surface just outside an event horizon would have to explain why they instead appear to behave like a black hole without such a surface. We'd have to look at a specific model of such a thing to see how it could be differentiated by observation.
    well I think that a body that was just outside the Schwarzschild radius would be really heavily time dilated....anything that impacted with it would produce radiation that at was very red shifted...

    and btw I believe in a heavily time dilated on going collapse....for what it's worth.
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    You should know by now not to espouse such beliefs in the Q&A forum. Ask questions. Get answers.
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    That is exactly what he is doing.

    Asking good questions and getting good answers.

    Every good question, without exception, is based on beliefs.
    It isn't possible to formulate a good question without having
    beliefs about whatever subject is being asked about. And if
    some or all of those beliefs are wrong, the quickest way to
    find that out is to ask good questions about them.

    That's what science is, not conformity to someone else's
    beliefs.

    -- Jeff, in Minneapolis

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    Please do not reply to Jeff Root’s post. It’s a rule breaker and he won’t be able to respond since he has been permanently banned.
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    Quote Originally Posted by WaxRubiks View Post
    well I think that a body that was just outside the Schwarzschild radius would be really heavily time dilated....anything that impacted with it would produce radiation that at was very red shifted...
    WaxRubiks, even though you phrased it as more of a statement than a question, I wanted to respond to it. You can certainly consider some kind of object that has a surface just outside of the event horizon at least hypothetically. I want to point out that something even quite close to the event horizon has a relatively small level of redshift. For example, for a surface just 0.1% further out from a black hole than where an event horizon would form, the time dilation is a factor of about 31. That is pretty big, but an X-ray burst like the one in Remillard's study would still be an X-ray burst. You'd need a time dilation factor that was much larger to be able to shift x-rays down to unobservably faint radio waves. The surface would have to form very, very close to the potential event horizon indeed. For such a model to stand up, I think you'd need a plausible mechanism to support the collapsing proto-black hole.

    Quote Originally Posted by WaxRubiks View Post
    and btw I believe in a heavily time dilated on going collapse....for what it's worth.
    Well, this is actually just a standard black hole, at least from the perspective of anyone a long way from the black hole. For an observer far away, the collapse of a star to a black hole takes essentially infinite time (there may be some picky details if black holes really do evaporate from Hawking radiation, and some other issues, but they aren't too important here). From the perspective of something falling in (or riding along with the collapse), that's not true, because you never see yourself as slowed in time; you always experience time at a normal rate. So if there's not a surface actually stopping you, and you're just imagining that since it's heavily time dilated it will take a long time, that can't apply to an observer falling in. It certainly does apply to the view from a distant observer's perspective, but that gets you right to a standard black hole as described by general relativity.
    Conserve energy. Commute with the Hamiltonian.

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    Quote Originally Posted by WaxRubiks View Post
    I don't believe specifically in a collapsed massive body that is just a bit bigger than the Schwarzschild radius, but how can such a body be distinguished from an event-horizon model?

    How can a SC radius model be falsified?
    I expect that this very hypothetical object would fail the basic definition of a black hole - it would not be black.
    Neutron stars are very hot and emit mostly X-rays. A hypothetical even denser body should be hotter suggesting higher energy hard x-rays or even gamma-ray radiation. We have observatories looking for X-ray and gamma ray sources. Gravitational redshift puts the output into the range of other observatories, e.g. Hubble.

    The type I X-ray bursts seen from neutron stars and thus this object (and missing from black holes) are not only detected directly. They have effects on any surrounding gas: NASA’s Chandra Captures X-Ray Echoes Pinpointing Distant Neutron Star

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    Quote Originally Posted by Grey View Post
    WaxRubiks, even though you phrased it as more of a statement than a question, I wanted to respond to it. You can certainly consider some kind of object that has a surface just outside of the event horizon at least hypothetically. I want to point out that something even quite close to the event horizon has a relatively small level of redshift. For example, for a surface just 0.1% further out from a black hole than where an event horizon would form, the time dilation is a factor of about 31. That is pretty big, but an X-ray burst like the one in Remillard's study would still be an X-ray burst. You'd need a time dilation factor that was much larger to be able to shift x-rays down to unobservably faint radio waves. The surface would have to form very, very close to the potential event horizon indeed. For such a model to stand up, I think you'd need a plausible mechanism to support the collapsing proto-black hole.

    Well, this is actually just a standard black hole, at least from the perspective of anyone a long way from the black hole. For an observer far away, the collapse of a star to a black hole takes essentially infinite time (there may be some picky details if black holes really do evaporate from Hawking radiation, and some other issues, but they aren't too important here). From the perspective of something falling in (or riding along with the collapse), that's not true, because you never see yourself as slowed in time; you always experience time at a normal rate. So if there's not a surface actually stopping you, and you're just imagining that since it's heavily time dilated it will take a long time, that can't apply to an observer falling in. It certainly does apply to the view from a distant observer's perspective, but that gets you right to a standard black hole as described by general relativity.
    but imagine falling towards a massive body in continual state of collapse. would one even reach the falling surface...I'm not really sure of that.
    ................................

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    Quote Originally Posted by WaxRubiks View Post
    but imagine falling towards a massive body in continual state of collapse. would one even reach the falling surface...I'm not really sure of that.
    If the body is collapsing at less than the free-fall speed then you would eventually reach the surface. If it is collapsing at, or more than, free-fall speed then you wouldn't.

    But if the massive body is continually collapsing then eventually it will be within its event horizon and become a black hole.

    Until that point it will radiate and not appear black.

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    Quote Originally Posted by WaxRubiks View Post
    but imagine falling towards a massive body in continual state of collapse. would one even reach the falling surface...I'm not really sure of that.
    From the perspective of someone far away from the black hole, then no, it would take you infinitely long to reach the surface. And as Strange points out, if both you and the collapsing surface are in free fall, then you'll never really "catch up". But if there's not anything physically stopping you (or the collapsing object) from crossing the event horizon, than you'll certainly do that. Again, even if you seem to be moving progressively more slowly as you approach to someone far away, you won't see yourself slowing down.

    One term that used to be used for black holes was "frozen star", precisely because it would seem to a distant observer like all the matter would wind up "frozen" at the event horizon.* So, I'm not sure there would be any way for you to distinguish what you're describing from a black hole as described by general relativity, because what you're describing pretty much is a black hole as described by general relativity. It's just that you're insisting that the perspective of the person far from the black hole is the only correct one, and that it's not valid to look at the reference frame of an object or observer falling in.


    * It turns out that this isn't quite right, and it doesn't take infinitely long from something to fall in, because the event horizon will expand to encompass an infalling object once it gets close enough, and I believe that actually happens in finite time even from a distant observer's perspective. You can see an extreme example of this in a black hole merger, which from the LIGO observations appears to happen just about exactly the way we predict.
    Conserve energy. Commute with the Hamiltonian.

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