Note on the emergence of cosmic space in modified gravities.

Intrigued by the holographic principle, Padmanabhan recently proposed a novel idea, saying that our cosmic space is emergent as cosmic time progresses. In particular, the expansion rate of the Universe is related to the difference between the surface degrees of freedom on the holographic horizon and the bulk degrees of freedom inside. In this note, we generalize this interesting paradigm to brane world, scalartensor gravity, and f(R) theory, respectively, and find that in the cosmological setting the Friedmann equations can be successfully derived. [ABSTRACT FROM AUTHOR]