Apocalypse When? Solar System Constraints on an Imminent Big Rip

Abstract

Phantom dark energy models with an equation of state parameter $w < -1$ lead generically to a future big rip singularity, in which the dark energy density becomes infinite in a finite time. Current limits on dark energy constrain $w$ to be close to $-1$, and if $w$ is assumed constant, then a future big rip cannot occur in less than the order of a Hubble time in the future. However, many models allow $w$ to decrease rapidly with time. In that case, or if one assumes an additional phantom component with current energy density far below the dark energy density and $w << -1$, it is possible to achieve an imminent big rip, which we define to be a future singularity occuring in much less than the Hubble time. Such a possibility cannot be constrained by any cosmological measurements, as these are all based on light emitted billions of years in the past. Indeed, it is not possible, on the basis of cosmological observations, to rule out a future big rip tomorrow. However, solar system dynamics are sensitive to the behavior of phantom dark energy on timescales of decades rather than billions of years. Using solar system measurements, we are able to derive limits on the timescale for a future big rip independent of the dynamics of the phantom component. We obtain $t_{rip} - t_0 > 30$ years. While admittedly a poor limit, these results are likely to be improved by future more precise measurements of solar system dynamics. Our results also show that evidence for an imminent big rip would show up first in solar system data, rather than in any cosmological observation.