Eternal inflation predicts that time will end

TL;DR

The paper argues that in any geometric cutoff used to regulate eternal inflation, time can end for some observers with nonzero probability. By analyzing multiple cutoffs (causal patch, light-cone time, fat geodesic, scale factor time, and proper time), the authors compute the distribution of remaining time before the cutoff and show a finite, nonzero expectation value (e.g., a few to ~5 Gyr) for several measures, while the proper time cutoff yields a severe youngness paradox. They address objections by illustrating that the cutoff defines the ensemble and that the end-of-time outcome is a robust feature of the regulator, not merely an artifact, with the Guth–Vanchurin paradox providing a concrete consistency check. The discussion links the end-of-time phenomenon to observations such as the cosmological constant distribution and offers interpretational options, including a horizon-centered causal patch view that resembles black hole complementarity. Overall, the work highlights how regulator choices shape predictions in eternal inflation and how the end of time could be a testable aspect of cosmological measure proposals.

Abstract

Present treatments of eternal inflation regulate infinities by imposing a geometric cutoff. We point out that some matter systems reach the cutoff in finite time. This implies a nonzero probability for a novel type of catastrophe. According to the most successful measure proposals, our galaxy is likely to encounter the cutoff within the next 5 billion years.

Figures (1)

• Figure 1: A multiverse populated by infinitely many observers (vertical line segments) who first see 1 o'clock (at events labeled "1") and then 2 o'clock ("2"). A geometric cutoff selects a finite set of events, whose relative frequency defines probabilities. Events that are not counted are indicated by dashed lines. The left figure shows a global cutoff: all events prior to the time $t_0$ (curved line) are counted and all later events ignored. (The global time has nothing to do with the observers' clocks, which come into being at a rate dictated by the dynamics of eternal inflation.) The right figure shows the causal patch cutoff, which restricts to the causal past of a point on the future boundary. In both figures, the cutoff region contains observers who see 1 o'clock but not 2 o'clock. Their number, as a fraction of all observers who see 1 o'clock before the cutoff, defines the probability of reaching the end of time between 1 and 2 o'clock.