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Q:
Is it possible that dark matter is not dark at all? According to
Einstein's theory of relativity, energy has mass. Although this is a
special theory limited to bodies moving in the absence of a
gravitational field, the idea that energy has mass should still
persist. Light and other rays from the electromagnetic spectrum are
seemingly everywhere, but obviously more condensed in galaxies. These
rays obviously have energy and possible very small amounts of mass
each. Can this ambient energy-mass (if not already included) account
for the seeming presence of dark matter??
A:
Einstein's equation linking energy and mass holds in all of spacetime,
at all energies. It is true that photons (or light rays) have a small
amount
of mass associated with them. However, there are about 2 billion
photons
for every hydrogen nucleus, or proton, in the universe, and their mass
equivalent is about one trillionth that of a proton, so the mass
equivalent
of the photons is about 500 times less than that of the protons. Thus
there is not enough mass to explain the mystery of dark matter. Please
visit the Chandra field guide to dark matter for more information:
http://chandra.harvard.edu/xray_astro/dark_matter.html
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