Cosmological Constant

The cosmological constant was initially a mathematical fudge factor in Einstein’s field equation for general relativity, inserted to allow a static universe before Edwin Hubble’s discovery of expansion. Now it is taken seriously as a physical force (dark energy) driving the accelerating expansion of the universe. Some idealist-minded cosmologists thought the cosmological constant should be exactly zero. (But then, some even found reason to marvel that the gravitational constant differs from zero!) However, despite perennial interest in tidy numbers, there is no a priori reason to expect nature to involve them. It is nature that must determine theory, not the other way around. To determine the cosmological constant empirically requires many assumptions regarding methods for gathering data from observations. Such a measurement, in other words, is highly theory dependent. A blatant problem posed by the cosmological constant is the huge difference between its observed value, based on astronomical observations, and predictions from theoretical physics regarding the quantum vacuum, to which the cosmological constant is assumed to correspond. It is possible to explain away this discrepancy using anthropic reasoning—in other words, as a selection effect. That is, a typical theoretical value would lead to a universe that would not support life (for example, because it would be too short-lived for evolutionary time scales). So, because in fact we are present in it, our “region” of space must exist as an extremely unlikely part of a vastly larger meta-space where life cannot arise. The discrepancy between theory and observation spans many orders of magnitude. It is literally astronomical. On this view, it implies the extravagance of a universe many orders of magnitude larger than the known universe (our region). While such is possible, it seems ontologically more economical to question quantum field theory on the one hand, and the measured values, on the other.