Back to: Astronomy & the Cosmos
In the 1920s, astronomers measuring the light of distant galaxies found their spectra shifted toward the red, the light equivalent of a receding siren’s dropping pitch, and discovered that nearly every galaxy is moving away from us, with farther galaxies receding faster. The conclusion, confirmed by a century of observation since: the universe is expanding. Space itself is stretching, carrying galaxies apart like raisins in rising dough.
Run the film backward and everything converges: about 13.8 billion years ago the entire observable universe was compressed into an unimaginably hot, dense state that suddenly began expanding, the event we call the Big Bang. This is not a fringe idea; it makes precise predictions that have been verified. The most spectacular: a faint afterglow of that primordial fireball should still permeate all of space. In 1965 it was found, the cosmic microwave background, glowing from every direction at just under 3 degrees above absolute zero, exactly as predicted.
Two clarifications defuse the common confusions. The Big Bang was not an explosion in space, it was the expansion of space, happening everywhere at once; there is no center and no edge. And the discovery in 1998 that the expansion is accelerating, driven by a mysterious ‘dark energy’ making up most of the universe’s contents, means the story’s ending is still being written. You now know roughly what humanity knows, and, more excitingly, where the map still says ‘here be dragons.’