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Ask Marilyn: Have You Ever Eaten Corvus? Or a Hat?

David Richards of Canton, Ohio, writes:

Marilyn: I'm writing about your response to question about how much of the universe is occupied by matter. (December 2, 2012) The question posed was, "How much of the known universe is occupied by matter?" The question was not, "What portion of its mass is composed of familiar (atomic) matter?" You answered your own question, not the reader's.

While the WMAP results do estimate that about 5 percent of the universe's mass—not 5 percent of the universe—is made up of normal atoms (baryons) and the rest of the total mass of the observable universe is made up of (non-baryonic) dark matter and dark energy, that estimate does not speak to the proportion of the universe that is occupied by mass. While the density of the universe is a matter of debate, if you use an average density of matter to be about that of the Sun, and the "known universe" to be about 28 billion light years across, then the correct answer is that about 0.000000000000000000004 percent of the universe is occupied by matter.

If I'm wrong, I'll eat Corvus.

Marilyn responds:

Well, I liked my question more, so that's what I answered! Thank you for all the zeros, David. (Readers, David Richards is Director of the Hoover-Price Planetarium at the McKinley Museum in Canton, Ohio.)



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