There is much debate about the arrow time. (Related disciplines are thermodynamics, statistical physics, quantum mechanics, gravity, inflation, so it gets technical.)

Here are some good papers, look them up at http://arxiv.org

Hollands and Wald. An Alternative to Inflation. arXiv (2002) vol. gr-qc

Wald. The Arrow of Time and the Initial Conditions of the Universe. arXiv (2005) vol. gr-qc

Kofman et al. Inflationary Theory and Alternative Cosmology. arXiv (2002) vol. hep-th

Carroll. Is Our Universe Natural?. arXiv (2005) vol. hep-th

Carroll and Chen. Spontaneous Inflation and the Origin of the Arrow of Time. arXiv (2004) vol. hep-th

Lebowitz. Boltzmann's Entropy and Time's Arrow. Physics Today (1993) pp. 1-7

Wallace. Gravity, Entropy, and Cosmology: In Search of Clarity. arXiv (2009) vol. cond-mat.stat-mech

Maccone. A quantum solution to the arrow-of-time dilemma. arXiv (2008) vol. quant-ph