White Holes: Real or Hypothesis?

[Astro-Anouar]

The White Hole is Real ? or Just a hypothesis with a mathematical model ? and Why the White Hole is the Opposite Of the Black hole ?

 

[Nugatory]

Assuming that by a "white hole" you meant the thing described by the bottom wedge of a Kruskal-Szeres diagram...

None have ever been observed, and there are good reasons to doubt that any exist.

 

[Astro-Anouar]

Assuming that by a "white hole" you meant the thing described by the bottom wedge of a Kruskal-Szeres diagram...

None have ever been observed, and there are good reasons to doubt that any exist.

and Why the White Hole is the Opposite Of the Black hole ?

 

[phinds]

and Why the White Hole is the Opposite Of the Black hole ?

There is this REALLY neat facility for doing a little of your own research ... it's called Google Search. I suggest you learn how to use it.

https://www.physicsforums.com/blog.php?b=3588

 

[Astro-Anouar]

There is this REALLY neat facility for doing a little of your own research ... it's called Google Search. I suggest you learn how to use it.

https://www.physicsforums.com/blog.php?b=3588

I didn't ask "What is" I ask 'Why'

 

[phinds]

I didn't ask "What is" I ask 'Why'

Yes, and if you had done a simple search you would have found the following in wikipedia:

A white hole, in general relativity, is a hypothetical region of spacetime which cannot be entered from the outside, but from which matter and light have the ability to escape. In this sense, it is the reverse of a black hole, which can be entered from the outside, but from which nothing, including light, has the ability to escape

 

[Mordred]

As phinds pointed out its easy to google search. Type in google "how do white holes form" will pull up numerous sites such as this one.

http://garrettmaster1.homeip.net:82/BlackHoleReview/WhiteHoles.htm

 

[Astro-Anouar]

Yes, and if you had done a simple search you would have found the following in wikipedia:

A white hole, in general relativity, is a hypothetical region of spacetime which cannot be entered from the outside, but from which matter and light have the ability to escape. In this sense, it is the reverse of a black hole, which can be entered from the outside, but from which nothing, including light, has the ability to escape

Thank for search and Sorry For harassment But I red This Before and this didn't answer my question ' Why the White Hole push the matter and energy why matter and light have the ability to escape' for example: nothing even light could escape from Black Hole Why ? Because it had a Great Density and an incredible Gravitational Field.

 

[Astro-Anouar]

As phinds pointed out its easy to google search. Type in google "how do white holes form" will pull up numerous sites such as this one.

http://garrettmaster1.homeip.net:82/BlackHoleReview/WhiteHoles.htm

Thank You I'll Read it

 

[Chalnoth]

The White Hole is Real ? or Just a hypothesis with a mathematical model ? and Why the White Hole is the Opposite Of the Black hole ?

A white hole is a time-reversed black hole, and is thus unphysical (it means you got the arrow of time wrong).

 

[taiyo]

Assuming that by a "white hole" you meant the thing described by the bottom wedge of a Kruskal-Szeres diagram...

None have ever been observed, and there are good reasons to doubt that any exist.

Actually finding out if they exist would be quite simple

 

[newjerseyrunner]

A white hole is the opposite of a black hole because a black hole can be entered from the outside but once inside, it can never escape. A white hole is a region of space that can be exited, but never entered.

 

[ChrisVer]

I don't see any problem with the repulsion from a white hole ... except for that you either need negative mass-squared matter (exotic matter) or something similar to dark energy (with this strange equation of state relationship leading to negative pressure)

 

[Chalnoth]

I don't see any problem with the repulsion from a white hole ... except for that you either need negative mass-squared matter (exotic matter) or something similar to dark energy (with this strange equation of state relationship leading to negative pressure)

The white hole has positive mass, just like a black hole. It's simply that the time coordinate is reversed. This is a perfectly valid solution to the field equations, it's just that it violates the second law of thermodynamics (i.e., a white hole's entropy decreases over time).

 

[ChrisVer]

well, I connected the white hole existence with wormhole and referred to its instability. So yes I think it wasn't the right way to answer that

 

[PeterDonis]

Actually finding out if they exist would be quite simple

How so?

 

[taiyo]

Create a d

How so?

by building a device that detects anomalies in space when light is being pushed or pulled to or from an unknown source that another device can figure out if it is solid or a black or white hole

 

[PeterDonis]

This is a perfectly valid solution to the field equations, it's just that it violates the second law of thermodynamics (i.e., a white hole's entropy decreases over time).

No, actually, its entropy is constant, since the area of its horizon is constant--at least if we're talking about an idealized white hole that never loses any mass from things getting out (the time reverse of an idealized black hole that never gains any mass from things falling in). So this solution doesn't violate the second law (but that's not to say it's physically reasonable--see below).

If we want to talk about a white hole with changing entropy, then the area of its horizon has to change with time, and that requires putting some nonzero stress-energy somewhere into the solution. For example, we could look at the outgoing Vaidya metric, which is basically a "white hole" that constantly emits null radiation and has a horizon that shrinks with time as a result of this. But this solution doesn't violate the second law, because we have to count the entropy of the emitted radiation as well as the entropy of the hole. Since the solution is exactly time reversible (the time reverse is just the ingoing Vaidya metric, which is basically a black hole that constantly absorbs null radiation and has a horizon that grows), the entropy does not change in either direction, as with any process that is exactly reversible.

The reason white holes are considered unphysical is the initial singularity. For black holes, the singularity is in the future, and we have an idealized model (the Oppenheimer-Snyder model) of how such an object could be formed by the gravitational collapse of a massive object. We know massive objects exist that could in principle undergo such a collapse, so it is at least physically reasonable that something similar to it has happened in our universe. (That still leaves the issue of whether the final singularity is still there when quantum gravity effects are taken into account, but that's a separate question that doesn't make the overall model unphysical--it just means there is an open question for further research.)

In the case of a white hole, however, there is no physically reasonable model of how such an object could come into existence, because the singularity is in the past, not the future--it would have to be part of the initial conditions, and nobody believes such initial conditions (an initial singularity with a past event horizon) are at all reasonable, because nothing like them has ever been observed and we don't even have an idealized model (analogous to the O-S model for black holes) to show how they might be satisfied even in principle.

 

[PeterDonis]

by building a device that detects anomalies in space when light is being pushed or pulled to or from an unknown source that another device can figure out if it is solid or a black or white hole

Ok, and how would you build such a device, and how would you know that the unknown source was a white hole? Just waving your hands isn't enough.

 

[taiyo]

Ok, and how would you build such a device, and how would you know that the unknown source was a white hole? Just waving your hands isn't enough.

Another machine determining if its solid and by launching light and matter if it's not solid and it gets pushed away from no where it is most like a white hole if the light and matter is absorbed and it is not solid it is most likely a black hole

 

[Chalnoth]

No, actually, its entropy is constant, since the area of its horizon is constant--at least if we're talking about an idealized white hole that never loses any mass from things getting out (the time reverse of an idealized black hole that never gains any mass from things falling in). So this solution doesn't violate the second law (but that's not to say it's physically reasonable--see below).

If we want to talk about a white hole with changing entropy, then the area of its horizon has to change with time, and that requires putting some nonzero stress-energy somewhere into the solution. For example, we could look at the outgoing Vaidya metric, which is basically a "white hole" that constantly emits null radiation and has a horizon that shrinks with time as a result of this. But this solution doesn't violate the second law, because we have to count the entropy of the emitted radiation as well as the entropy of the hole. Since the solution is exactly time reversible (the time reverse is just the ingoing Vaidya metric, which is basically a black hole that constantly absorbs null radiation and has a horizon that grows), the entropy does not change in either direction, as with any process that is exactly reversible.

Right, I was being a little bit non-specific. The classical black hole has non-decreasing entropy: its horizon size can never decrease. A white hole has the opposite issue: its horizon size can never increase. But the white hole's horizon can decrease if it expels matter (it can expel anything).

Hawking radiation, of course, complicates the whole situation, and has the effect of making a white hole seem even more unphysical, as the outgoing Hawking radiation from a black hole is purely thermal and therefore high in entropy, while the outgoing matter from a white hole would in general not be thermal.

 

[PeterDonis]

Another machine determining if its solid

How?

by launching light and matter if it's not solid and it gets pushed away from no where it is most like a white hole

A white hole does not have repulsive gravity; it has attractive gravity, just like a black hole (or any other gravitating object). So things launched towards the white hole do not get "pushed away from nowhere".

 

[PeterDonis]

the white hole's horizon can decrease if it expels matter

But, again, as the example of the outgoing Vaidya metric shows, it's not clear that the entropy of the system as a whole (white hole + matter expelled) decreases in this process. One would have to look at an analysis such as Bekenstein's derivation of black hole entropy and see if a "time reverse" of it could be done for the case of a white hole expelling matter.

 

[taiyo]

How?
A white hole does not have repulsive gravity; it has attractive gravity, just like a black hole (or any other gravitating object). So things launched towards the white hole do not get "pushed away from nowhere".

actually yes in a way because matter would be forced to go around like light because nothing can enter white hole

 

[PeterDonis]

actually yes in a way because matter would be forced to go around like light because nothing can enter white hole

No, this is not correct. The reason nothing can enter a white hole is not because the white hole repels things; it attracts things, just like any other gravitating body. The reason nothing can enter a white hole is that its horizon is moving inward at the speed of light, so for anything to enter it, it would have to move inward faster than light.

 

[Jorrie]

The reason nothing can enter a white hole is that its horizon is moving inward at the speed of light, so for anything to enter it, it would have to move inward faster than light.

I suppose it depends on the coordinate chart used, but is it correct to say that the hole's (WH's) horizon has the opposite 'movement' of the BH's horizon? That is whereas the BH horizon moves outward at the local speed of light, the WH's event horizon moves inward at the local speed of light. This may be a difficult concept operationally speaking, but I would like to think of it in terms of "space falling out of the WH" at the local speed of light - a 'fountain effect' rather than the 'waterfall effect' of the BH.
Does this make any sense?

 

[rootone]

I know that a white hole is just a theoretical reverse situation of a black hole which mathematically cannot be ruled out, but unless the 'big bang' is an an example of of a white hole there is no evidence that such things exist.

 

[PeterDonis]

I suppose it depends on the coordinate chart used, but is it correct to say that the hole's (WH's) horizon has the opposite 'movement' of the BH's horizon?

With respect to a local inertial frame that contains the horizon, yes. But it's actually more than that. Any local inertial frame containing a BH horizon must be falling inward (i.e., an object at rest in such an LIF must have a decreasing global radial coordinate); the horizon itself, as a radially outgoing null surface (where here "outgoing" has a different definition which is somewhat technical, involving the tangent vectors and null normals of the horizon considered as a geometric 3-surface in 4-D spacetime), appears in such a LIF to be moving outward at the speed of light.

Conversely, any LIF containing a WH horizon must be "falling" outward (i.e., an object at rest in such an LIF must have an increasing global radial coordinate); the horizon itself, as a radially ingoing null surface (where here "ingoing" has a similar technical definition to "outgoing" above), appears in such a LIF to be moving inward at the speed of light. So not only are the horizon directions "opposite", so are the "directions" of the LIFs themselves.