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Ask Marilyn: How Much of the Known Universe Is Occupied by Matter?

K. Key, ­Moreno Valley, California, writes:

Marilyn: How much of the known universe is occupied by matter?

Marilyn responds:

Consider the vastness of the cosmos, readers. What portion of its mass is composed of familiar (atomic) matter?

(a) 1/1000 percent
(b) 1/100 percent
(c) 1/10 percent
(d) 1 percent
(e) 5 percent

Surprise: (e). While that’s not much, the portion appears to be a fraction of that because we view the immensity of space in terms of distance. Outer space is thin but not empty.

Almost everything else—called “dark” matter and energy because we can’t actually see any of it—is implied by the behavior of gravity. This means that the ­content of about 95 percent of the ­universe is inferred with our fertile minds and fevered ­imaginations.



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