CalTech’s Sean Carroll at Google shows that the kind of matter with which we are familiar — atoms and molecules, and indeed every particle we have ever created in a laboratory — only makes up about 5% of the universe. Another 25% is dark matter, a kind of particle that is massive and weakly interacting. The remaining 70% is dark energy, which is not even a particle — it’s a smoothly-distributed energy field that remains persistent in density even as the universe expands.
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The Invisible Universe – Google on Dark Matter
