Equivalence of the Einstein and Jordan frames
  No experiment can measure an absolute scale: every dimensionfull quantity has
to be compared to some fixed unit scale in order to be measured, and thus only
dimensionless quantities are really physical. The Einstein and Jordan frame are
related by a conformal transformation of the metric, which amounts to rescaling
all length scales. Since the absolute scale cannot be measured, both frames
describe the same physics, and are equivalent. In this article we make this
explicit by rewriting the action in terms of dimensionless variables, which are
invariant under a conformal transformation. For definiteness, we concentrate on
the action of Higgs inflation, but the results can easily be generalized. In
addition, we show that the action for f(R)-gravity, which includes Starobinsky
inflation, can be written in a frame-independent form.
