Could dark matter be made of gravitons?
<p>One of the most puzzling observations about the Universe is that there isn’t enough matter — at least, matter that we know of — to explain how we see things are gravitating. On Solar System scales, General Relativity and the masses we observe do the job just fine. But on larger scales, the internal motions of individual galaxies indicate the presence of more mass than we observe. Galaxies in clusters move around too quickly, while X-rays reveal an insufficient amount of normal matter. Even on cosmic scales, extra mass has to be present to explain gravitational lensing, the cosmic web, and the imperfections in the Big Bang’s leftover glow.</p>
<p>While we typically invoke a new particle of some type, one intriguing idea is purely gravitational: could dark matter be made of gravitons alone? After all, the other known forces in the Universe — the electromagnetic force, the strong nuclear force, and the weak nuclear force — are all inherently quantum in nature, and those forces are mediated by particles that we’ve detected.</p>
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