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View Full Version : what would happen if there were no matter outside a black hole?

WaxRubiks
2009-Jan-03, 06:29 PM
if there was just the Universe with one black hole in it what would happen.
If time is dilated for matter falling into a blackhole, as compared to time outside the blackhole, and there is nothing outside the black hole, what would happen?

Would the black hole explode as a Hawking radiation burst as the BH evaporated in an instant? as there is no matter outside the BH and thus no way of measuring time...

matthewota
2009-Jan-03, 07:40 PM
Seems to me it would just sit there....by itself.

tommac
2009-Jan-03, 07:40 PM
if there was just the Universe with one black hole in it what would happen.
If time is dilated for matter falling into a blackhole, as compared to time outside the blackhole, and there is nothing outside the black hole, what would happen?

Would the black hole explode as a Hawking radiation burst as the BH evaporated in an instant? as there is no matter outside the BH and thus no way of measuring time...

Who would be thre to witness it? Isnt this like a tree in a forest?

tommac
2009-Jan-03, 07:50 PM
Seems to me it would just sit there....by itself.

what do you mean by itself ... like our universe just sits here by itself?

The BH is really just a state of our perception of space-time. Without us here to observe it its curvature of space time doesnt mean anything.

Its existance though would be internal and be different to our existance.

Hornblower
2009-Jan-03, 08:27 PM
Let's forget the philosophical question for now and treat this as a thought-experiment exercise in physics.

I would expect it to evaporate by Hawking radiation. How long that would take depends on the mass at the present time.

tommac
2009-Jan-03, 08:30 PM
Let's forget the philosophical question for now and treat this as a thought-experiment exercise in physics.

I would expect it to evaporate by Hawking radiation. How long that would take depends on the mass at the present time.

How exactly does that work? Wouldnt the radiation need to travel faster than the speed of light just to escape the black hole?

tommac
2009-Jan-03, 08:42 PM
Does Hawking radiation assume that there are some particles outside of the black hole?

I thought it had to do with particles splitting into a pair of virtual particles ... the negative part ends up getting swallowed by the black hole and the positive escapes ... consuming the negative reduces the mass of the black hole ???

I am of course no expert ( really in anything ) ... but wouldnt you need to have particles outside of the BH for this effect to happen?

This scenario clearly states that there is no mass outside of the black hole so I am not sure what particles would split? It is my understanding that nothing can escape the speed of light space-time recession of the black hole. So even if the particle was in the black hole and split ... unless it could travel faster than the speed of light it would not escape.

grant hutchison
2009-Jan-03, 09:50 PM
These are virtual particle pairs, produced from the vacuum under the terms of Heisenberg's Uncertainty Principle. They are generated everywhere, constantly, but annihilate again within the timespan stipulated by HUP. The black hole's tidal gravity is able to separate them and provide enough energy to "promote" them to reality.
So, no, you don't need any matter outside the black hole for Hawking radiation to be generated. Just vacuum.

Grant Hutchison

astromark
2009-Jan-04, 09:12 AM
The problem with this sort of question is that understanding it is imposible...
Outside a black hole is never going to be nothing. Black holes rotate, some very quickly. Stable orbits are the norm. There is always going to be mater outside a black hole. The very manor in which they form are rotational, and thus orbiting is not unusual. If per chance of this question such were to be found then nothing would happen as nothing is there to happen with... just the black hole doing what it is they do.

mugaliens
2009-Jan-04, 09:16 AM
Even if you did manage to cram the universe into a black hole, it would continually be radiating (Hawking). It would take a very, very long time to radiate itself out of existence, but eventually, that is the fate of all black holes.

tommac
2009-Jan-04, 03:27 PM
These are virtual particle pairs, produced from the vacuum under the terms of Heisenberg's Uncertainty Principle. They are generated everywhere, constantly, but annihilate again within the timespan stipulated by HUP. The black hole's tidal gravity is able to separate them and provide enough energy to "promote" them to reality.
So, no, you don't need any matter outside the black hole for Hawking radiation to be generated. Just vacuum.

Grant Hutchison

Hmmmm ... but wouldnt they be considered mass?

Can things that are small travel faster than light?

using HUP you would need to have some mass to start with right?

tommac
2009-Jan-04, 03:30 PM
Even if you did manage to cram the universe into a black hole, it would continually be radiating (Hawking). It would take a very, very long time to radiate itself out of existence, but eventually, that is the fate of all black holes.

OK lets assume that you are right ( I currenty am not convinced that it would radiate ... but lets take that as fact. )

What would happen to the radiation? It would all just wander out into space? Would any of it eventually make it back to the black hole via being the sole gravitational force in the universe other than the radiation that escaped.

tommac
2009-Jan-04, 03:32 PM
The question is WHY are they created everywhere contanty?

These are virtual particle pairs, produced from the vacuum under the terms of Heisenberg's Uncertainty Principle. They are generated everywhere, constantly, but annihilate again within the timespan stipulated by HUP. The black hole's tidal gravity is able to separate them and provide enough energy to "promote" them to reality.
So, no, you don't need any matter outside the black hole for Hawking radiation to be generated. Just vacuum.

Grant Hutchison

trinitree88
2009-Jan-04, 04:02 PM
The creation of temporary pairs of virtual particles occurs as a result of the uncertainty in the mass,m.. or E/c2,over short time intervals, if you view it that way, of an existing particle, not from an empty vacuum, which has no uncertainty in it's mass or energy. The ability of a nucleon to fluctuate between states of itself, and states of itself plus a virtual particle, which could be more and more massive over shorter and shorter time intervals, enabled Yukawa to pick a time interval short enough to allow a particle to travel almost at ~c to it's nuclear neighbor, about a Fermi away.
As the following well done applet shows, his prediction was thought to be verified by discovery of the mu-meson (really a heavy electron) in cosmic ray tracks. Later it was realized that it interacted too weakly to be the carrier of the strong force, and it was with the discovery of the pions, that he was vindicated in his analysis.
One of the little secrets of the Nobel committee, was that his prize was awarded prematurely, and was at the time physically incorrect...but then we all make a few boo-boos in life.
Virtual particles do not arise out of the vacuum from nothingness as a result of the Heisenberg Uncertainty Principle, and matter can not be created that way. They are associated with the periphery of pre-existing particles, and like Cinderella, they must return to the other state before midnight (the constraints of the Heisenberg Uncertainty Principle)..
For every virtual particle pair, they annihilate to return the mass/energy to a stable limit as the time interval marches on.
Creating a real particle out of a virtual one requires that we add sufficient energy to the transitory "particle/virtual particle state" to shake it loose, and promote it into reality. Then it is real, but we didn't violate conservation of mass, or energy to do so...we added it, usually in the form of a collision....which is what an accelerator labs does...accelerate incoming particle/strike target/ watch the debris shower for created particles that were shook loose in the collision. Kind of like studying antique pocket watches by throwing them against a steel wall, and photographing the debris in superslow motion ...Enter Doc Edgerton.

see:http://www.sjsu.edu/faculty/watkins/yukawa.htm

tommac
2009-Jan-04, 04:10 PM
Yes ... so does this support my argument against Grants radiation thing?

My thought here is that if there is NO mass outside of the back hole, and NOTHING can travel faster than the speed of light.

Then HUP does not allow a virtual particle to be created external to the BH from the mass within the BH.

It is my understanding that Hawking radiation must include virtual particles that are create from mass/energy that is outside of the black hole.

The creation of temporary pairs of virtual particles occurs as a result of the uncertainty in the mass,m.. or E/c2,over short time intervals, if you view it that way, of an existing particle, not from an empty vacuum, which has no uncertainty in it's mass or energy. The ability of a nucleon to fluctuate between states of itself, and states of itself plus a virtual particle, which could be more and more massive over shorter and shorter time intervals, enabled Yukawa to pick a time interval short enough to allow a particle to travel almost at ~c to it's nuclear neighbor, about a Fermi away.
As the following well done applet shows, his prediction was thought to be verified by discovery of the mu-meson (really a heavy electron) in cosmic ray tracks. Later it was realized that it interacted too weakly to be the carrier of the strong force, and it was with the discovery of the pions, that he was vindicated in his analysis.
One of the little secrets of the Nobel committee, was that his prize was awarded prematurely, and was at the time physically incorrect...but then we all make a few boo-boos in life.
Virtual particles do not arise out of the vacuum from nothingness as a result of the Heisenberg Uncertainty Principle, and matter can not be created that way. They are associated with the periphery of pre-existing particles, and like Cinderella, they must return to the other state before midnight (the constraints of the Heisenberg Uncertainty Principle)..pete

see:http://www.sjsu.edu/faculty/watkins/yukawa.htm

trinitree88
2009-Jan-04, 05:31 PM
Yes ... so does this support my argument against Grants radiation thing?

My thought here is that if there is NO mass outside of the back hole, and NOTHING can travel faster than the speed of light.

Then HUP does not allow a virtual particle to be created external to the BH from the mass within the BH.

It is my understanding that Hawking radiation must include virtual particles that are create from mass/energy that is outside of the black hole.

tommac. My thinking is that for your scenario, you are correct. Remember there is no known physics inside the black hole's EH, and in the absence of anything outside the BH, it's kind of like the kid in the art room showing the teacher the black paper...it's a black cat eating licorice off tarpaper on a moonless night...:shifty:...thing. pete

Tensor
2009-Jan-04, 05:52 PM
tommac. My thinking is that for your scenario, you are correct. Remember there is no known physics inside the black hole's EH, and in the absence of anything outside the BH, pete

Pete, tommac, you're both under a slight misunderstanding here. Under General Relativity, there has to be somehting outside the BH. The warpage of spacetime. When the BH was formed by the collapse of a star, the event horizon forms inside the star and expands as the surface of the star shrinks. As the star shrinks, spacetime warps outside the star. The smaller is shrinks, the larger the warpage of spacetime. The event horizon breaks through the star, just as the surface shrinks to the Schwartzchild radius. At that point, the event horizon stops growing and the star stops shrinking. But you still have the spacetime warpage outside the star. Because the GR equations are so non-linear, the energy in that warped spacetime keeps regenerating, keeping the blackhole together. So, in the case of Hawking radiation, the energy is coming from the warped spacetime outstide the star, which is included in the BH mass, as in GR it's energy, not just mass that warps spacetime to produce gravity.

grant hutchison
2009-Jan-04, 05:57 PM
Hmmmm ... but wouldnt they be considered mass? No. That's why they're "virtual" particles.

Can things that are small travel faster than light?No.

using HUP you would need to have some mass to start with right?No. That's the point of Hawking radiation.

Grant Hutchison

grant hutchison
2009-Jan-04, 06:02 PM
The question is WHY are they created everywhere contanty?Because they're not forbidden.
Heisenberg allows any quantity of energy to pop into existence, so long as it does so for a sufficently short period of time.
These virtual particles have demonstrable physical effects, by their transient interaction with other matter. Try Googling up "Lamb shift" and "Casimir effect".

Grant Hutchison

trinitree88
2009-Jan-04, 06:06 PM
Pete, tommac, you're both under a slight misunderstanding here. Under General Relativity, there has to be somehting outside the BH. The warpage of spacetime. When the BH was formed by the collapse of a star, the event horizon forms inside the star and expands as the surface of the star shrinks. As the star shrinks, spacetime warps outside the star. The smaller is shrinks, the larger the warpage of spacetime. The event horizon breaks through the star, just as the surface shrinks to the Schwartzchild radius. At that point, the event horizon stops growing and the star stops shrinking. But you still have the spacetime warpage outside the star. Because the GR equations are so non-linear, the energy in that warped spacetime keeps regenerating, keeping the blackhole together. So, in the case of Hawking radiation, the energy is coming from the warped spacetime outstide the star, which is included in the BH mass, as in GR it's energy, not just mass that warps spacetime to produce gravity.

Tensor. I will not dispute the warpage of spacetime due to the mass/energy content of the BH, and that in GR, that must still be there, even if the rest of the universe is missing.
There's something else there, too. A neutrino sink. A place where neutrinos could go in, if they existed in our missing-universe-scenario, and not come out. So if suddenly, supernatural beings were to place a sun-like star near the BH, it would experience the warpage of spacetime from GR, and the disappearance of neutrinos it emitted....unlike our sun's neutrinos which are merely redshifted as they passage the Earth (SNO results).

dgavin
2009-Jan-04, 06:23 PM
Me -feelings- on this OP, is that BH's play an import part in cyclic universe therories.

For example, the all the Matter and Energry and Dark Matter/Energy of a universe collapsed into a black hole, then the exact conditions that existed before that universes big bang, will have been reformed.

In otherwards, the BH would reach a point of univeral signularity, all enery concetrated into a single point of space/time, and then it would explode as a White Hole. (AKA: A new Big Bang).

WaxRubiks
2009-Jan-04, 06:30 PM
Me -feelings- on this OP, is that BH's play an import part in cyclic universe therories.

For example, the all the Matter and Energry and Dark Matter/Energy of a universe collapsed into a black hole, then the exact conditions that existed before that universes big bang, will have been reformed.

In otherwards, the BH would reach a point of univeral signularity, all enery concetrated into a single point of space/time, and then it would explode as a White Hole. (AKA: A new Big Bang).

Yes, I have wondered something like this.

tommac
2009-Jan-04, 07:14 PM
Pete, tommac, you're both under a slight misunderstanding here. Under General Relativity, there has to be somehting outside the BH. The warpage of spacetime. When the BH was formed by the collapse of a star, the event horizon forms inside the star and expands as the surface of the star shrinks. As the star shrinks, spacetime warps outside the star. The smaller is shrinks, the larger the warpage of spacetime. The event horizon breaks through the star, just as the surface shrinks to the Schwartzchild radius. At that point, the event horizon stops growing and the star stops shrinking. But you still have the spacetime warpage outside the star. Because the GR equations are so non-linear, the energy in that warped spacetime keeps regenerating, keeping the blackhole together. So, in the case of Hawking radiation, the energy is coming from the warped spacetime outstide the star, which is included in the BH mass, as in GR it's energy, not just mass that warps spacetime to produce gravity.

References please. I agree that you have warped space-time exists outside of the BH but I disagree that the gravity itself is a form of energy. the gravity is just the topology that is created from the energy.

In any case the question as stated says taht there is no mass ( I assume no energy ) outside the BH.

tommac
2009-Jan-04, 07:19 PM
explode as a white hole? Huh? I thought a white hole was just the time reversal of a black hole?

Me -feelings- on this OP, is that BH's play an import part in cyclic universe therories.

For example, the all the Matter and Energry and Dark Matter/Energy of a universe collapsed into a black hole, then the exact conditions that existed before that universes big bang, will have been reformed.

In otherwards, the BH would reach a point of univeral signularity, all enery concetrated into a single point of space/time, and then it would explode as a White Hole. (AKA: A new Big Bang).

Tensor
2009-Jan-04, 10:04 PM
References please. I agree that you have warped space-time exists outside of the BH but I disagree that the gravity itself is a form of energy. the gravity is just the topology that is created from the energy.

Any good GR textbook. Other than that, a good non-techical reference would be Kip Thorne's "Black Holes and Time Warps: Einstein's Outrageous Legacy". Just for your info, the motion of the perihelion of Mercury can be though of as the inclusion of the gravitational energy of the Sun. Something that Newtonian Gravity doesn't take into account.

In any case the question as stated says taht there is no mass ( I assume no energy ) outside the BH.

Sorry, can't happen under our current gravitational theory. If there is no energy, there is no curvature, then there is no black hole.

tommac
2009-Jan-04, 11:41 PM
Pages and paragraphs please. I have read BH + TW and dont see any reference to this.

Any good GR textbook. Other than that, a good non-techical reference would be Kip Thorne's "Black Holes and Time Warps: Einstein's Outrageous Legacy". Just for your info, the motion of the perihelion of Mercury can be though of as the inclusion of the gravitational energy of the Sun. Something that Newtonian Gravity doesn't take into account.

Sorry, can't happen under our current gravitational theory. If there is no energy, there is no curvature, then there is no black hole.

The energy comes from the mass inside the BH. That energy and mass is what causes the curvature. The curvature itselef is not energy.

One of my stupid questions was to ask if gravity travels at the speed of light then how does it escape from a BH. That was clearly answered that the topology is created by the BH itself. It does not need to continuously propogate. Once it is created it is created. If it changed then the changes happen at the speed of light but the continous existance does not need to be re-propogated.

Tensor
2009-Jan-05, 01:44 AM
Pages and paragraphs please. I have read BH + TW and dont see any reference to this.

Page 362 Box 10-1, Starts toward the bottom of the box and continues on to page 363.

The energy comes from the mass inside the BH. That energy and mass is what causes the curvature. The curvature itselef is not energy.

By GR, nothing inside the EH can affect anything outside the EH. Nothing can escape the EH. The curvature, mathematically, can be shown to have an "energy" in GR. I put that in quotes because it uses a psuedotensor, not a regular tensor.

One of my stupid questions was to ask if gravity travels at the speed of light then how does it escape from a BH. That was clearly answered that the topology is created by the BH itself. It does not need to continuously propogate. Once it is created it is created.

It's created, but it requires regeneration to continue. If there is no energy, there is no curvature. If that was the case, as the sun moved through spacetime, there should be a permanent warpage whereever the sun has been. That hasn't been seen as it would effect the planets, it doesn't.

If it changed then the changes happen at the speed of light but the continous existance does not need to be re-propogated.

Yes it does, check out the box. Technically, it's not energy, it's the second, third, fourth, etc order terms in the Taylor expansion series due to the non-linearity of the equations. The non-linearity is what actually regenerates the curvature. It can be thought of, as a simple understandable explanation for those not familiar with the math, as the energy of the gravitational field adding to the gravity of the object.

Not knowing your math level, I'm going to simplify this a bit. In GR, the field equation is curvature + metric = constant * energy. The metric just tells us how to measure distance along the curvature. The constants are there to make sure GR agrees with Newtonian gravity in the low speed, low gravity realm. So, basically, the equation is curvature = energy. If there is no energy, there is no curvature. So something has to supply the energy to continue to supply the curvature, once the star disappears behind the EH.

tommac
2009-Jan-05, 02:27 PM
Will check the reference ... but have one question.

Are you saying that any gravitational field there is energy? In the void of space there is energy? I am not really questioning it ... just want to make sure that is what you are saying.

Since gravity has infinite reach that means that it would be impossible to have a true vacuum because there would still be small amounts of energy even in an empty universe.

If we had a null universe ... would there be virtual particles?

Page 362 Box 10-1, Starts toward the bottom of the box and continues on to page 363.

By GR, nothing inside the EH can affect anything outside the EH. Nothing can escape the EH. The curvature, mathematically, can be shown to have an "energy" in GR. I put that in quotes because it uses a psuedotensor, not a regular tensor.

It's created, but it requires regeneration to continue. If there is no energy, there is no curvature. If that was the case, as the sun moved through spacetime, there should be a permanent warpage whereever the sun has been. That hasn't been seen as it would effect the planets, it doesn't.

Yes it does, check out the box. Technically, it's not energy, it's the second, third, fourth, etc order terms in the Taylor expansion series due to the non-linearity of the equations. The non-linearity is what actually regenerates the curvature. It can be thought of, as a simple understandable explanation for those not familiar with the math, as the energy of the gravitational field adding to the gravity of the object.

Not knowing your math level, I'm going to simplify this a bit. In GR, the field equation is curvature + metric = constant * energy. The metric just tells us how to measure distance along the curvature. The constants are there to make sure GR agrees with Newtonian gravity in the low speed, low gravity realm. So, basically, the equation is curvature = energy. If there is no energy, there is no curvature. So something has to supply the energy to continue to supply the curvature, once the star disappears behind the EH.