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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.

Hope this helps,

Koji & Scott
for "Ask an Astrophysicist"

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