Einstein's Cosmological Constant

Albert Einstein's General Theory of Relativity laid the groundwork for our current understanding of the universe, and indeed for much of modern high energy physics. The math of the basic theory demanded an expanding universe, however, and in the early twentieth century physicists believed in a steady state universe, so Einstein introduced a cosmological constant into his equations that essentially zeroed out any expansion. Later in the century astronomers showed the universe was, in fact, expanding, and Einstein called the cosmological constant the "biggest blunder" of his career.

Now, theoretical physicists are struggling to understand dark matter and build an overall theory that takes dark matter into account-- and it turns out that Einstein's cosmological constant fits into current approaches that includes dark matter.

At first thought, we might argue that Einstein stumbled on a deeper truth with his cosmological constant, one he never grasped and we are just now glimpsing. However, the essence of dark matter is that it powers universal expansion; Einstein used the constant to stop that expansion. Therefore, saying Einstein was right the first time is likely insufficient. Rejecting that explanation, however, would seem to say a factor introduced into one theory fits into another theory out of blind luck. The math is probably saying we still don't understand a large part of the puzzle.