Pre-bangian origin of our entropy and time arrow

Abstract

I argue that, in the chaotic version of string cosmology proposed recently, classical and quantum effects generate, at the time of exit to radiation, the correct amount of entropy to saturate a Hubble (or holography) entropy bound (HEB) and to identify, within our own Universe, the arrow of time. Demanding that the HEB be fulfilled at all times forces a crucial "branch change" to occur, and the so-called string phase to end at a critical value of the effective Planck mass, in agreement with previous conjectures.

Figures (1)

• Figure 1: At the beginning of the DDI era ($t=t_i$) the entropy of the just-formed black hole, $S_{coll}$, coincides with both the BEB, $S_{BB}$, and the HEB, $S_{HB}$, while the entropy in quantum fluctuations, $S_{qf}$, is completely negligible. At the beginning of the string phase, $t=t_s$, both $S_{coll}$ and $S_{HB}$ still have their common initial value. $S_{BB}$ and $S_{qf}$ have grown considerably, but the latter is still negligible if the string coupling is still small at $t=t_s$. During the string phase, $S_{qf}$ catches up with $S_{coll}$ first, and with $S_{HB}$ later, i.e. when the energy in the quantum fluctuations becomes critical and exit to radiation is expected ($t=t_r$). Finally, during the radiation and matter-dominated phases, $S_{HB}$ grows towards $S_{BB}$, while our own entropy $S_{tot}$ lags far behind and increases only slowly as the result of dissipative phenomena and growth of inhomogeneities.