1Only a century ago, most astronomers firmly believed that the whole universe was static and eternal.
2However, careful telescopic observations of very distant galaxies would soon overturn that comfortable and familiar assumption.
3Astronomers noticed that light from faraway galaxies is stretched toward the red end of the spectrum.
4This redshift reveals the surprising fact that nearly every galaxy in the sky is moving away from us.
5The farther away a galaxy lies from our own, the faster it appears to recede from us.
6From this simple pattern, scientists were forced to conclude that the fabric of space itself must be expanding.
7If we run the cosmic film backwards in time, everything converges on a single point of infinite density.
8That unimaginably dense and astonishingly hot beginning is the great event we now call the Big Bang.
9Remarkably, the faint radiation left over from that ancient fire still fills the entire sky today.
10Orbiting far above us, sensitive satellites have now mapped this faint afterglow with truly extraordinary precision.
11Strangely, the expansion of the universe is actually accelerating, driven by a mysterious force called dark energy.
12Understanding the true nature of dark energy is perhaps the greatest challenge in all of modern cosmology.