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. 
S. Basu (Florida), N. C. Tsamis (Crete) and R. P. Woodard (Florida)
gr-qc astro-ph.CO