Oops....forgot to carry the two.

One of the great cautionary tales from science is Albert Einstein's "Cosmological Constant", which was basically a constant that Einstein shoehorned into his theory of relativity (I can never remember which one, General or Special Relativity). In really simplified terms, Einstein didn't like the implications of his theory for the evolution of the universe, so he stuck in a number he called the "Cosmological Constant", in order to make the theory fit the way he wanted the universe to behave. (My understanding is that the Constant was intended to balance the implications of his theory that the Universe would either be expanding or contracting, with the empirical evidence of Einstein's day that the Universe was static, or "steady state", as it was described then.)

Einstein later regarded the Cosmological Constant as a colossal blunder that impeded the natural beauty of his theory, but it now turns out that he may have been right all along. A team using the Hubble Space Telescope to examine distant supernovae for gravitational effects, and what they observe now appears to confirm the existence of dark energy.