AboutPhilip A. Stahl Expertise I specialize in stellar and solar astrophysics. Can answer any questions pertaining to these areas, the spectroscopic analysis of stars – as well as the magneto-hydrodynamics of sunspots and solar flares. Sorry – No homework problems done or research projects! I will provide hints on solutions.
Experience Have published papers on the relationship between sunspot morphology and solar flares; discovery of SID flares related to this, constructed computerized stellar models; MHD research.
Organizations American Astronomical Society (Solar physics and Dynamical astronomy divisions), American Geophysical Union, American Mathematical Society, Intertel.
Publications Solar Physics, Journal of the Royal Astronomical Society of Canada, Journal of the Barbados Astronomical Society, Meudon Solar Flare Proceedings (Meudon, France)
Education/Credentials B.A. degree in Astronomy; M.Phil. degree in Physics - specializing in solar physics.
Awards and Honors Postgraduate research award- Barbados government; Studentship Award in Solar Physics - American Astronomical Society
Expert: Philip A. Stahl Date: 7/3/2008 Subject: White holes -- my favorite astronomical object
Question QUESTION: Hi:
What about white holes makes their existence impossible?
A white hole is the opposite of a black hole. If one can exist, then why not the other?
Thanks,
Green
ANSWER: Hello,
Your question introduces the critical notion of the difference between what is theoretically "allowed" and what can actually exist, or be detected. For example, tachyons - hypothetical particles that *always* travel faster than light, are allowe- but we've no evidence at all that they really exist.
Just as the tachyon always moves faster-than-light, in the white hole nothing can get in (as in the case of the black hole) it can only come *out*. Thus, it is the mirror image of the black hole. On the surface, because of this seeming symmetry, rudimentary logic would suggest the white hole must exist.
Despite this, no one knows exactly how a white hole could actually form in the real universe. A black hole's origin is well known: the collapse of a massive star that is reduced to such a tiny volume (collapsar) that its gravity is large enough to suck up anything and everything in its vicinity.
While we may speculate that the BH's singularity admits into the white hole (say via a wormhole) this is only speculation. This is not the same as hard evidence, or proof.
Much more plausibly, the WH would need to be introduced into the universe as an initial condition. E.g. certain conditions of temperature, pressure, density allow their formation. In effect, they come about from the original state of the universe, not from any subsequent states of stellar collapse to black holes.
Now, the bottom line: all our data and cosmological observations thus far show no objects that conform to the behavior of "white holes". Even quasars, once believed to be the outpourings of white holes, were ditched decades ago as certain discrepancies arose, and we now suspect they are unique ancient objects in themselves. Of extraordinary luminosity for sure, but not in the white hole class.
In the absence of any hard evidence to the contrary we can therefore say with some degree of confidence that it is improbable that white holes actually exist. (Again, please note this is not the same as assserting it is "impossible" that they exist!)
No doubt they will remain in the public imagination for some time, however, as well as provide a rich basis for science fiction themes.
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QUESTION: Hi:
Thanks for your response.
I've heard one reason white holes can't exist is because they violet the second law of thermodynamics.
Just would while holes violate the 2nd law?
Thanks again,
Green
Answer Hello,
The 2nd law of thermodynamics or "entropy law" states that the tendency of a closed thermodynamic system will always tend toward greater disorder, not less. A quaint way to portray this is to say: "the toothpaste once squeezed out, cannot be put back into its tube".
Associated with this is the so-called "arrow of time". In our universe at least this is always toward greater disorder. Thus, the arrow of time points in this direction - as opposed to the tendency for increased order.
In terms of white holes, if they are treated as cosmic information *sources* (e.g. locations in space-time where mass-energy is emerging INTO, not out of) then many have insisted this means they are the "time reversals" of the black hole.
But if the "arrow of time" (and hence, the entropy law) defines one direction for time, it is hard to see how one can get a "time reversal" that would not violate the 2nd law.
I suspect this is what is meant when it is said WHs "violate the 2nd law".
