light and dark matter

At the risk of uttering complete nonsense, I'd like to describe something
I've been wondering about for a while, namely whether the density of light
in the universe might be related to the problem of dark matter and dark energy.

If one takes all of the light in the universe, it has a certain mass and
therefore it exerts a certain gravitational force on the matter in the
universe. I don't know how much that force is taken into account in
computations of the rate of expansion of the universe. For example,
what is the total gravitational attraction exerted by the light from the
cosmic background radiation?

I realize that dark matter is only supposed to interact gravitationally
with the other stuff we know about in the universe, whereas light
interacts electromagnetically and maybe in other ways, but if the light
is of sufficiently low frequency, I think it wouldn't interact in any way
with matter except gravitationally. Conceivably, there is a lot of light
of much lower frequency than the cosmic background radiation and we can't
detect it except gravitationally and, since it is uniformly distributed
throughout the universe, its primary manifestation has been through its
effects as dark matter. For example, if the light had a wavelength larger than
the solar system, we would have no direct way to sample it with any detector
we could construct.

Since it would not interact electromagnetically, strongly, weakly, etc. with
matter, we could naturally ask what process could produce light of such low
frequency. One way would be for it to be doppler shifted from light of greater
frequency as the universe expands.

The notion of dark energy has been offered to explain recent evidence for
the accelerated expansion of the universe. One other property of light,
at least in Gaussian beams, is its tendency to spread out. So, maybe that
tendency to spread out when it is already densely distributed also
contributes to the accelerated expansion of the universe.

I guess I am saying something like the following: light's tendency to spread
out contributes to the accelerated expansion of the universe; that is what
people have attributed to dark energy. As the expansion proceeds, the light
gets doppler shifted so far down that it can't interact with matter other
than gravitationally. The manifestation of that gravitational interaction
is what people have attributed to dark matter.

This is pure speculation and not well informed. I don't expect any of
it to be right. If someone can explain why it is all wrong, that will
help me forget about it and move on to something else. Maybe a few
relevant numbers are all it takes. I don't intend to argue about it:
I'd just like to hear people's opinions and try to learn from them.

If someone already came up with this crackpot idea and published it,
perhaps someone can provide a reference to it and its refutation.

Ignorantly,
Allan Adler


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* Disclaimer: I am a guest and *not* a member of the MIT Artificial *
* Intelligence Lab. My actions and comments do not reflect *
* in any way on MIT. Moreover, I am nowhere near the Boston *
* metropolitan area. *
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