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Author Topic: Black holes are forever?  (Read 13316 times)

Offline DoctorBeaver

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Re: Black holes are forever?
« Reply #25 on: 03/12/2005 12:58:57 »
quote:
If you could watch the universe from inside a black hole (and you can't) you would see galaxies be created and die almost instantly.


 
quote:
I suppose that just before gravity ripped you to shreds you could see the universe ourside appear to speed up.


It depends on the size of the black hole. In the case of a super-massive black hole the gravitational force at the event horizon would be negligible. You could, in theory, hang around there quite a while before gravity sucked you in.
 

another_someone

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Re: Black holes are forever?
« Reply #26 on: 04/12/2005 12:43:38 »
Going off at a slight, but related, tangent, what happens when two large black holes of similar mass collide.  In the final result, one would expect an even larger black hole to be created; but during the process of collision, as the separate black holes approach each other, one would expect a region of space between them to exist with reduced gravitational force, and even a point that is possible between the converging black holes where there would be zero nett gravity, and a trajectory between the two black holes where a projectile could pass being equally attracted to both black holes, and so engulfed by neither.

At some point in time, as the black holes are sufficiently close that their original event horizons would overlap, but they are still distinct and separate gravitational attractors, one would expect this path of balanced gravity would actually be inside the spheres that once defined the respective event horizons of the black holes.  What would be the effect of this collision on matter that had previously been trapped by the event horizon, and upon new matter entering the system?
« Last Edit: 04/12/2005 13:12:05 by another_someone »
 

Offline DoctorBeaver

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Re: Black holes are forever?
« Reply #27 on: 04/12/2005 14:35:58 »
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I don't think that I ever said or suggested that the escape velocity suddenly increased at any point in fact precisely the opposite I described a contiuous process of gradually increasing escape velocity. Let me put what I am trying to say a different way just insde the event horizon a photon can just about get to (but not cross) the event horizon into our universe. If it originates from deeper inside the hole it can't get near the event horizon into our universe but it CAN travel some distance and take some time about doing it


I fully accept all that. But I still don't understand how you can say that this would cause a succession of smaller & smaller event horizons inside the original 1.
 

Offline Soul Surfer

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Re: Black holes are forever?
« Reply #28 on: 04/12/2005 23:36:13 »
OK heres a third way of trying to describe the same point that I am trying to get over

An event horizan is an area of space beyond which it is impossible to go beyond once one has entered it  even if one was able to travel at the spped of light or use a light beam.  As you go deeper into a black hole the distance that light can get becomes less than when you have just entered the hole, so going into a black hole is not like going into a sphere within which there is a strongly gravitating object and one could in theory move around inside this sphere it is a one way trip all the way down but because of this  "contraction of event horizons"  the horizons would eventuially he hot enough to sap the energy of the hole to become a dynamic and stable object and not a static mathematical singularity.

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Offline DoctorBeaver

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Re: Black holes are forever?
« Reply #29 on: 05/12/2005 01:14:24 »
quote:
...but because of this "contraction of event horizons"...


I'm fine with everything you say until you get to the part I've quoted. By the very definition of an event horizon, there can be only 1 per black hole. I'll grant that what you say subsequently sounds plausible; but do you think that maybe "event horizons" is not a good choice of name for what you're trying to describe?
 

another_someone

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Re: Black holes are forever?
« Reply #30 on: 05/12/2005 08:24:44 »
quote:
Originally posted by Soul Surfer

OK heres a third way of trying to describe the same point that I am trying to get over

An event horizan is an area of space beyond which it is impossible to go beyond once one has entered it  even if one was able to travel at the spped of light or use a light beam.



Actually, I was thinking a little more about this, and with my limited understanding, do not see this to be true.

As I understand the definition of an event horizon, it is the point in space at which the escape velocity is equal to the speed of light, such that anyone entering beyond the event horizon will never be able to escape the pull of the black hole.  It is not a point one may never rise above, it is merely a point which if one were to rise above, one would inevitably fall back to.  Thus, a body just below the event horizon may emit light, and that light might be seen by someone outside the event horizon (albeit, such an observer must also be be doomed to fall into the event horizon themselves), but that light simply could never travel an infinite distance away from the black hole, since it will inevitably be drawn back to the black hole.

As I say, it is my limited understanding of things, but it seems subtly different to what I understand others to have said, and even the underlying assumption in some of own previous speculations on the matter.
« Last Edit: 05/12/2005 08:32:48 by another_someone »
 

Offline Soul Surfer

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Re: Black holes are forever?
« Reply #31 on: 05/12/2005 09:40:05 »
I agree that there is only one event horizon with our universe.  but say you entered a very large quiet black hole like the ones in the middle of many galaxies.  (they are so big that you could get inside without being spaghettified by the gravity gradient)  what you see would be a smallish "universe" (cos you can't see out)containig a few particles possibly and having one black hole in the middle of it.  As you progressed on your way down the plughole you would keep seeing much the same thing untill you came to the "singularity"  as suggested by most experts on the subject.  Or as I am suggesting a hawking radiation fuzzball of energy caused by the intense gravity gradient.  This would have incredibly high energy states existing for a long time near the centre in which conditions would be ideal for the creation of a new big bang as a quantum uncertainty "accident"

One of the suggestions for the existence of our universe is that it started as a quantum mechanical fluctuation in the vacuum and grew from that.  In the vacuum as we know it this would seem to be an impossibly unlikely event but in the conditions that I described above it would seem to be much more probable and possibly inevitable.

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Offline DoctorBeaver

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Re: Black holes are forever?
« Reply #32 on: 05/12/2005 11:53:52 »
Now that I can go along with - & no succession of event horizons! I'm not enough of a physicist, especially in areas such as Hawking radiation, to know whether or not it's possible.

Another_someone - I don't believe that is the case. As far as I'm aware, the maths says that within the event horizon, spatial & time co-ordinates swap. Therefore space becomes time & vice versa (sort of). So, for any object inside the radius of the event horizon the singularity lies in its future & the event horizon in its past.
I realise that the maths also work "back-to-front" (I forget the scientific term for this) which would allow for backward travel in time; but I don't believe they allow for a sudden flip. Therefore, if the calculations say something is travelling forwards in time, that is the direction in which it must continue.
This seems to me to preclude the possibility of anything emerging from behind the event horizon.
 

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Re: Black holes are forever?
« Reply #33 on: 05/12/2005 16:41:07 »
quote:
Originally posted by DoctorBeaver
Another_someone - I don't believe that is the case. As far as I'm aware, the maths says that within the event horizon, spatial & time co-ordinates swap. Therefore space becomes time & vice versa (sort of). So, for any object inside the radius of the event horizon the singularity lies in its future & the event horizon in its past.
I realise that the maths also work "back-to-front" (I forget the scientific term for this) which would allow for backward travel in time; but I don't believe they allow for a sudden flip. Therefore, if the calculations say something is travelling forwards in time, that is the direction in which it must continue.
This seems to me to preclude the possibility of anything emerging from behind the event horizon.



Thanks for the clarification although I use that term loosely.

I have seen mention of that transposition of space and time within a black hole elsewhere, but I do not regard it as exactly intuitive (at least to my diminutive mind), which is why it was not what came to mind when I made my earlier comment.
 

Offline DoctorBeaver

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Re: Black holes are forever?
« Reply #34 on: 05/12/2005 17:32:49 »
quote:
but I do not regard it as exactly intuitive


There's nothing even remotely intuitive about relativity or quantum theory! [xx(]
 

Offline Mad Mark

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Re: Black holes are forever?
« Reply #35 on: 17/12/2005 01:22:26 »
A singularity as expressed as time is 1 to infinty so jump in enjoy the ride and travel to the end of the universe the quick way.

Tomorrow lies outside our universe without it there would be no tomorrow.
 

Offline DoctorBeaver

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Re: Black holes are forever?
« Reply #36 on: 17/12/2005 02:29:19 »
quote:
A singularity as expressed as time is 1 to infinty so jump in enjoy the ride and travel to the end of the universe the quick way.


That sounds very profound but I'm not sure it actually means anything. Can you clarify it please
 

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Re: Black holes are forever?
« Reply #37 on: 03/01/2006 15:42:09 »
quote:
Originally posted by DoctorBeaver

Now that I can go along with - & no succession of event horizons! I'm not enough of a physicist, especially in areas such as Hawking radiation, to know whether or not it's possible.

Another_someone - I don't believe that is the case. As far as I'm aware, the maths says that within the event horizon, spatial & time co-ordinates swap. Therefore space becomes time & vice versa (sort of). So, for any object inside the radius of the event horizon the singularity lies in its future & the event horizon in its past.
I realise that the maths also work "back-to-front" (I forget the scientific term for this) which would allow for backward travel in time; but I don't believe they allow for a sudden flip. Therefore, if the calculations say something is travelling forwards in time, that is the direction in which it must continue.
This seems to me to preclude the possibility of anything emerging from behind the event horizon.



Sorry about coming back to this again after all this time, but I was looking around at various sites on Special Relativity (yes, I know that gravity is about General Relativity, not SR; but as far as the swap between time and space dimensions, it should be the same).

From what I now think I understand, the flip between time and space is a local phenomena (i.e. subject to the frame of  reference of the observer), not an absolute swap.  Thus, if someone who is outside the event horizon is close enough to someone inside the event horizon, the frames of reference of observer to subject should be sufficiently close (i.e. within the light cone see, I can use big words too, just don't ask me what they mean :)) that they would not perceive a time/space swap.  It is only to an observer who is sufficiently far away from the subject that the subject would be outside their light cone that would then see a swap between space and time in the subject's local co-ordinates.
 

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Re: Black holes are forever?
« Reply #37 on: 03/01/2006 15:42:09 »

 

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