The Expanding Universe

A new study looking at galaxies in the early universe gives added evidence that the universe is not only expanding, but that the expansion is accelerating.

That acceleration puzzles scientists. By adding up all the matter in the universe, physicists get to the conclusion that the acceleration should be slowing down; the gravity associated with all that mass should eventually pull the universe back into a Big Crunch. The observed facts say otherwise, however. In attempting to explain their observations, physicists have postulated the existence of dark energy. They don't know what it is, and can't detect it directly, but they need it to make their theory work.

In that way, dark energy might be similar to Einstein's cosmological constant. He included that factor in his equation describing the universe even he didn't understand why he needed it. Einstein eventually disavowed his cosmological constant. Now, however, it looks like something akin to the cosmological constant is in fact necessary.

The universe is a strange old place.