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Astro-Anouar
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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 said: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 said:and Why the White Hole is the Opposite Of the Black hole ?
phinds said: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 said:I didn't ask "What is" I ask 'Why'
phinds said: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 said: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
A white hole is a time-reversed black hole, and is thus unphysical (it means you got the arrow of time wrong).Astro-Anouar said: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 ?
Actually finding out if they exist would be quite simpleNugatory said: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.
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 said: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)
taiyo said:Actually finding out if they exist would be quite simple
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 holePeterDonis said:How so?
Chalnoth said: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).
taiyo said: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
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 holePeterDonis said: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.
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).PeterDonis said: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.
taiyo said:Another machine determining if its solid
taiyo said: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
Chalnoth said:the white hole's horizon can decrease if it expels matter
actually yes in a way because matter would be forced to go around like light because nothing can enter white holePeterDonis said: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".
taiyo said:actually yes in a way because matter would be forced to go around like light because nothing can enter white hole
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.PeterDonis said: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 said: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?
A white hole is a theoretical object in space that is considered to be the opposite of a black hole. While a black hole has a strong gravitational pull, a white hole is thought to have a strong repulsive force, pushing matter and energy away from it.
Currently, there is no scientific evidence to support the existence of white holes. They are purely hypothetical and have not been observed or detected in the universe. However, some physicists continue to study and explore the concept of white holes as a possible solution to understanding the mysteries of the universe.
White holes and black holes are considered to be opposite in many ways. While black holes are known for their strong gravitational pull, white holes are thought to have a strong repulsive force. Additionally, matter and energy are believed to be able to escape from a white hole, while they cannot escape from a black hole's event horizon.
As of now, there are no known methods or technologies that can detect white holes. Since they have not been observed in the universe, it is difficult to determine how they would be detected. However, scientists are constantly working on new technologies and theories that could potentially help detect white holes in the future.
While the existence of white holes is still a topic of debate among scientists, they could potentially play a significant role in our understanding of the universe. Some theories suggest that white holes could be connected to black holes and may be responsible for the creation of new universes. However, more research and evidence is needed to fully understand the role of white holes in the universe.