The Arrow of Time Forbids a Positive Cosmological Constant $\Lambda$

TL;DR

The paper argues that a positive cosmological constant leads to a reversal of the thermodynamic arrow of time in our universe, implying that such a constant is fundamentally forbidden or requires modifications to general relativity.

Contribution

It demonstrates that gravitational entropy dynamics in a DeSitter universe imply a reversed arrow of time, challenging the existence of a positive cosmological constant.

Findings

Reversal of the thermodynamic arrow of time in DeSitter states

Finite lifetime of a DeSitter patch due to gravitational instabilities

Implication that a positive cosmological constant is incompatible with observed physics

Abstract

Motivated by the mounting evidence for dark energy, here we explore the consequences of a fundamental cosmological constant $\Lambda$ for our universe. We show that when the gravitational entropy of a pure DeSitter state ultimately wins over matter, then the thermodynamic arrow of time in our universe must reverse in scales of order a Hubble time. We find that due to the dynamics of gravity and nonlocal entanglement, a finite size system such as a DeSitter patch with horizon size $H_0^{-1}$ has a finite lifetime $\Delta t$. This phenomenon arises from the dynamic gravitational instabilities that develop during a DeSitter epoch and turn catastrophic. A reversed arrow of time is clearly in disagreement with observations. Thus we are led to conclude: Nature forbids a fundamental $\Lambda$. Or else general relativity must be modified in the IR regime when $\Lambda$ dominates the expansion of the Universe.