The discussion centers on the theoretical existence of white holes in the universe, contrasting them with black holes, which are supported by substantial observational evidence. Participants highlight that while black holes are predicted by models of gravitational collapse, white holes lack a corresponding astrophysical process or observational predictions. The conversation references Einstein's field equations and the historical development of black hole theory, emphasizing that white holes remain a mathematical construct without empirical support. The absence of evidence for white holes does not equate to their non-existence, but current scientific understanding suggests they are not realized in our universe.
PREREQUISITESAstronomers, astrophysicists, and students of theoretical physics who are interested in the nature of black holes and the theoretical implications of white holes.
The black holes in our universe result from the collapse of a sufficiently large star. There is no astrophysical process that would result in a white hole.Slavik Komarova said:lately I have researched the topic white holes and have not found an answer to some questions, among them the absence of evidence of these astrophysic objects
Well I imagine you would calculate the expected spectrum (thermal ?) and compare it with observation. You would look to eliminate other possibilities like black hole accreation disks massive stars etc.Vanadium 50 said:And, at the risk of piling on, if there were a white hole in some distant galaxy, how would you tell?
Picking a glaxy at random, M81 for example has a quarter of a trillion thermal sources (stars), How do you tell which one is actually a white hole?andrew s 1905 said:Well I imagine you would calculate the expected spectrum (thermal ?)
First, the word for "how are you going to tell observationally/experimentally?" is not disparagement. It is science.andrew s 1905 said:One could of course have made such disparaging remarks about black holes
The same could have be said of black holes.Vanadium 50 said:Picking a glaxy at random, M81 for example has a quarter of a trillion thermal sources (stars), How do you tell which one is actually a white hole?
In advance of what? Certainly, not the discussion of if they existed or not. You are reflecting the polished hindsight view of the reality of the the road to the acceptance of the reality of black holes and that they had been observed conclusively.Vanadium 50 said:Second, the observational evidence for BH's was laid out in advance -accretion disks, nearby star orbits, interferometric imaging, GWs, etc.
No, they aren't. To expand on previous comments, the theoretical prediction that we should observe black holes in our universe is based on (a) models of gravitational collapse to black holes, starting with the 1939 Oppenheimer-Snyder 1939 paper, and (b) theoretical work on the possible states of matter, starting with the work of Harrison, Wakano, and Wheeler in the 1950s, which showed that all non-black-hole states of matter that are supported by degeneracy pressure have a maximum mass limit, so that objects over the limit must collapse to black holes.Slavik Komarova said:why does not the same occur in relation to white holes since they are also the result of the same theoretical prediction ?
You can't do this for a white hole, because a white hole is inherently unpredictable: the initial singularity inside the hole could produce anything (or, what comes to the same thing, you could say it does not provide a valid set of initial conditions at all to ground any predictions at all). That is why your comparison with black holes along these lines is not really valid: you can make predictions about what kind of spectrum black holes should produce under various conditions (making reasonable assumptions about its mass, spin, and what kind of matter is falling into it).andrew s 1905 said:I imagine you would calculate the expected spectrum
Yes, this is correct.andrew s 1905 said:On reflection the big difference between black and white holes was that there was/is a theoretical way to created a black hole from what had already been observed or near extrapolation while none exists (as far as I know) for white holes.
I'm not sure the historical development of BH theory and observation is quite that clean; Kip Thorne's Black Holes and Time Warps gives a good overview, in which various theoretical and observational lines proceeded in a rather jumbled fashion until the "golden age" of the 1960s when things started to be tied together into a unified picture. By the time projects like LIGO were under discussion, of course, the unified picture had been in place for some time and was indeed being used to drive various observational efforts.Vanadium 50 said:the observational evidence for BH's was laid out in advance -accretion disks, nearby star orbits, interferometric imaging, GWs, etc.
This is probably a weak analogy, but is it akin in conception to multiplying by zero as opposed to dividing by it?PeterDonis said:You can't do this for a white hole, because a white hole is inherently unpredictable: the initial singularity inside the hole could produce anything (or, what comes to the same thing, you could say it does not provide a valid set of initial conditions at all to ground any predictions at all). That is why your comparison with black holes along these lines is not really valid: you can make predictions about what kind of spectrum black holes should produce under various conditions (making reasonable assumptions about its mass, spin, and what kind of matter is falling into it).Yes, this is correct.
Not really, that I can see. Dividing by zero is a mathematically forbidden/inconsistent operation. A white hole is not a mathematically forbidden or inconsistent solution; the issues with it are issues of physical possibility or reasonableness, not mathematical consistency.swampwiz said:This is probably a weak analogy, but is it akin in conception to multiplying by zero as opposed to dividing by it?