The Big Picture: On the Origins of Life, Meaning, and the Universe Itself

by Sean Carroll

Normally we’d expect the expansion of the universe to slow down as the gravitational forces between the galaxies worked to pull them together. The observed acceleration must be due to something other than matter as we know it. There is a very obvious, robust candidate for what the culprit might be: vacuum energy, which Einstein invented and called the cosmological constant. Vacuum energy is a kind of energy that is inherent in space itself, remaining at a constant density (amount of energy per cubic centimeter) even as space expands. Due to the interplay of energy and spacetime in general relativity, vacuum energy never runs out or fades away; it can keep pushing forever. We don’t know for sure whether it will keep pushing forever, of course; we can only extrapolate our theoretical understanding into the future. But it’s possible, and in some sense would be simplest, for the accelerated expansion to simply continue without end.