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Aug 9, 2012
In less than 100 seconds, Luke Davies explains how we know dark matter exists.
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And in less than 10 seconds, I explain what dark matter is:=.Dark matter is consist of dark particles.The dark particles are Dirac virtual particles.
The "logical" reasoning offered by Luke Davies is like this: 'I cannot see "dark matter", but I know gravity exists, therefore "dark matter" must exist as well.'Notice the non sequitur: gravity exists, ergo there must be "non-baryonic dark matter".Suppose you go in a china shop and see all (baryonic) porcelain vases and cups arranged in the air, in a perfectly stable configuration, and wonder what the heck has designed and supported such an amazing configuration of fragile stuff. Then physicists  tell you that it is all due to an invisible dark dancing elephant, which is roughly four times larger than all vases and cups combined.If you are a bit reluctant to swallow such 'dark (non-baryonic) dancing elephant', check out a simple, yet non-trivial, explanation here.D. Chakalov----------- Jörg P. Dietrich et al., Nature 487, 202–204 (12 July 2012)
I thought it was a good little presentation. Luke ended up by saying "we can't say much else" which was bang-on. I'm glad he didn't get sucked into the presumption that dark matter must be comprised of particles such as WIMPs. Because as I am fond of saying: space is dark, it has its vacuum energy, that energy has a mass equivalence, and there's a lot of it about!