Entanglement between pair-created twin universes with opposite time arrows should leave a birthmark on CMB spectrum

TL;DR

This paper proposes that entanglement between a pair-created universe and its twin with opposite time arrows could leave detectable signatures in the CMB spectrum, linking the universe's origin and the arrow of time.

Contribution

It introduces a model where entanglement between twin universes influences the CMB, providing a potential observational test for universe creation scenarios.

Findings

Entanglement enhances the CMB power spectrum at long wavelengths.

A unique global vacuum state is selected by the entanglement.

The model predicts observable signatures in the CMB spectrum.

Abstract

Why (and how) the Universe was born is one of the ultimate questions in physics. Another big puzzle is about the arrow of time: why is there only one direction of time? Are these two issues related? One way to solve both puzzles at one stroke is to posit that our universe was pair-created with a twin, whose time arrow is opposite to ours. If so, then the twins must naturally be quantum entangled. In Euclidean quantum gravity, this implies the existence of a Euclidean wormhole bridging the twin universes. Each universe is then in a mixed-state and the mutual entanglement shall leave signatures in the cosmic microwave background (CMB) power spectrum. Invoking the Klebanov-Susskind-Banks wormhole as a toy model for the sake of tractability, we show that the entanglement selects a novel and unique global vacuum for the total inflaton perturbations in both universes. This is equivalent to imposing a simple harmonic oscillator boundary condition on the Euclidean wavefunction of the total perturbations, and it turns out that the entanglement enhances the CMB power spectrum for long-wavelength modes. Such a birthmark renders our notion refutable.