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The Question
(Submitted July 17, 2003)
Could WIMPs be virtual in nature? If virtual particles can melt away a
black hole (ala Stephen Hawking), couldn't they also have momentary mass?
This would solve the WIMP problem in that they would send out gravitons,
but they wouldn't react much with ordinary matter as they disappear rapidly
and mostly inhabit empty space.
Therefore, couldn't empty space have its own gravity?
I wonder if this'll have applications in solving the cosmological constant
discrepancy. It'd surely explain the acceleration of universal expansion.
Could this also have value to the quantum theory/gravity conundrum?
The Answer
This is a nice thought, and one that theoretical physics have thought
about in the past; the best brains in the world are struggling over the
detailed maths to see if a similar idea can actually be made to work, though.
Virtual particles certainly aren't the explanation for WIMPs. For one
thing, we need something that stay billions of years, long enough to cluster
into galaxies and the like. Virtual particles disappear too quickly to do so.
[By the way, the key part of Hawking radiation is not the virtual particles,
but the fact that virtual particles can turn into real particles in the
extreme conditions around a small black hole. If they stayed virtual,
they won't do anything to the black hole.] For another, theorists have plenty
of ideas as to what real particles can make up WIMPs --- the problem is
that we don't have big enough accelerators (or other similarly expensive
experiments) capable of determining which of the various possibilities
is correct.
On the other hand, theorists do think that the Cosmological Constant has
to do with vacuum energy, which is basically what you are suggesting.
As we mentioned, the problem is working out the math --- naive calculations
come out 120 orders of magnitude off, which is enough to embarrass even
theoretical cosmologists:
http://pancake.uchicago.edu/~carroll/preposterous.html (http://pancake.uchicago.edu/%7Ecarroll/preposterous.html)
Hope this helps,
Koji & Scott
for "Ask a High Energy Astronomer"
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