1. See, for instance, R. Penrose, The Emperor's new mind, Oxford University Press, New York, 1989, Chapter 7.
2. J.D. Bekenstein, Phys. Rev. D 23 (1981) 287; D 49 (1994) 1912, and references therein.
3. E.W. Kolb, M.S. Turner, The early Universe, Addison-Wesley, Redwood City, CA, 1990; A.D. Linde, Particle physics and inflationary cosmology, Harwood, New York, 1990.
4. W. Fischler, L. Susskind, Holography and cosmology, hep-th/9806039; see also D. Bak, S.-J. Rey, Holographic principle and string cosmology, hep-th/9811008; A.K. Biswas, J. Maharana, R.K. Pradhan, The holography principle and pre-big bang cosmology, hep-th/9811051; S.K. Rama, T. Sarkar, Holographic principle during inflation and a lower bound on density fluctuations, hep-th/9812043.
5. G. Veneziano, Phys. Lett. B 265 (1991) 287; K.A. Meissner, G. Veneziano, Phys. Lett. B 267 (1991) 33; Mod. Phys. Lett. A 6 (1991) 3397; M. Gasperini, G. Veneziano, Astropart. Phys. 1 (1993) 317; Mod. Phys. Lett. A 8 (1993) 3701; Phys. Rev. D 50 (1994) 2519. An updated collection of papers on the pre-big bang scenario is available at http://www.to.infn.it/ ̃gasperin/.