Causality Implies Inflationary Back-Reaction

Understand

There is a widespread belief among inflationary cosmologists that a local observer cannot sense super-horizon gravitons.

• The argument goes that a local observer would subsume super-horizon gravitons into a redefinition of his coordinate system.
• We show that adopting this view for pure gravity on de Sitter background leads to time variation in the Hubble parameter measured by a local observer.
• It also leads to a violation of the gravitational field equation $R = 4 \Lambda$ because that equation is obeyed by the full metric, rather than the one which has been cleansed of super-horizon modes.