Rewriting the textbooks: Einstein's cosmological fudge:
Albert Einstein's towering reputation is only enhanced by his self-styled biggest blunder. It might not have been a blunder after all.Einstein did not derive those equations, he got them from Grossmann and Hilbert. The expansion of the universe was shown by LeMaitre before Hubble, and explained here and here. Einstein attacked LeMaitre for being wrong, and did not accept the expansion until years later.
At stake is the fate of the universe. In 1915, Einstein derived the equations of general relativity that describe the workings of a gravity-dominated cosmos. He added a fudge factor called the cosmological constant to ensure that, in keeping with contemporary tastes, the universe described neither expanded nor contracted. Soon after, though, Edwin Hubble showed that distant galaxies were receding from us, blowing the static universe apart. Einstein reputedly disowned his idea.
He might now want to disown the disowning. The discovery in 1998 that very distant supernovae appear to be not just receding but accelerating away from us suggests the presence of a mysterious "dark energy" that counteracts gravity's pull (The Astronomical Journal, vol 116, p 1009). And it turns out that a good way to reproduce this effect is to add the fudge back into Einstein's cosmological recipe.
Add the fudge back in? Einstein was as wrong as he could be. It is funny how his reputation can be enhanced by blunders.