“For although it is certainly true that quantitative measurements are of great importance, it is a grave error to suppose that the whole of experimental physics can be brought under this heading.” -Hendrik Casimir
Ever since we first discovered that the expansion of the Universe is accelerating, scientists have puzzles as to what’s causing it. Although we’ve measured it precisely and concluded that it’s uniform, static in time, and equivalent in its form to a cosmological constant, we still don’t know why it exists. Moreover, any attempts to calculate what its magnitude should be give nonsensical answers that are a factor of 10^120 too large.
Speculations have abounded that it might be due to an additional force or field in the Universe, or that there should be some experiments or measurements we could make that would surface an anomaly in dark energy. But perhaps the solution lies in a different place entirely: in calculating the Casimir effect for the gravitational force. The Universe isn’t truly empty, but contains huge amounts of matter, and it might be the interplay between the Universe’s large-scale structure and the gravitational fields that exist everywhere in space that causes dark energy to arise.