Cosmological Constant

When Albert Einstein applied his equations of General Relativity to the observable universe, he found something that he didn't like. His equations were correct, but for some reason, his equations predicted that the universe was dynamic when he and everyone else though the universe was static. This was in 1917, before the Big Bang theory and before Edwin Hubble found that the universe was expanding. To account for what he felt was incorrect, he introduced a fudge factor to take away the dynamic universe solution. He called his fudge factor, the cosmological constant. He hoped and felt that in time, physics and astronomy would be able to allow the cosmological constant to go away. When Hubble found the expansion of the universe and the Big Bang theory were proposed, Einstein thought that his cosmological constant was his biggest blunder. But was it?


Now, with the introduction of dark energy to help explain the expansion of the universe, the cosmological constant was reintroduced. As explained last time, if the dark energy density is constant, the universe will be open and expand forever. With a constant dark energy density, this implies that the universe is homogeneous in both space and time. Remember that this is referred to the Perfect Cosmological Principle which was briefly mentioned here. In other words, the universe appears static and therefore, the cosmological constant may be a physical quantity describing the dark energy density of the universe. Unfortunately, we still don't know what the dark energy density is doing and it may be centuries or millennia before we know.