A. The initial universe did not come from anywhere. The expansion of space from a highly dense state is the first event. There is no before this priordial event.
B. The universe is cyclic, and the initial singularity of our universe was preceded by a contracting phase of the universe. Or, see the cyclic model proposed by Steinhardt and friends. The universe is cyclic in this model because an extra dimension collapses every few trillion years or so.
C. See the no boundary proposal. The notion of causality is out the window, so the question of before the big bang is meaningless.
D. Chatoic eternal inflation, where our universe emerges from a pre existing, infinite, expanding universe that itself is without a beginning.
As it stands, there is no way to tell which scenario is correct. Recall that science is limited to the study of the observable universe, which data suggests has a beginning at the big bang. Speculation about anything before that seems more like metaphysics.
[This message has been edited by Beercules, 04-11-2004]
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