Causality Implies Inflationary Back-Reaction
  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.
