The End of Everything (Astrophysically Speaking)

by Katie Mack

As an aside, the fact that pretty much all the hydrogen in the universe was produced in the first few minutes means that a pretty large fraction of what you and I are made of has been hanging around the universe in one form or another for almost as long as the universe has been here. You may have heard that “we are made of stardust” (or “star stuff” if you’re Sagan), and this is absolutely true if we measure by mass. All the heavier elements in your body—oxygen, carbon, nitrogen, calcium, etc.—were produced later, either in the centers of stars or in stellar explosions. But hydrogen, while the lightest, is also the most abundant element in your body by number. So, yes, you hold within you the dust of ancient generations of stars. But you are also, to a very large fraction, built out of by-products of the actual Big Bang. Carl Sagan’s larger statement still stands, and to an even greater degree: “We are a way for the cosmos to know itself.”