I Expanding universe needs a big bang?

[PeterDonis]

doesn't anything shorter than the length of Planck Time foreclose knowing what happened at the moment of the Big Bang.

The "moment of the Big Bang" in our best current cosmological model is not an "initial singularity". It's the hot, dense, rapidly expanding state that is the earliest state of the universe for which we have good evidence. In inflationary models, it's the state at the end of inflation, just after "reheating" has occurred.

 

[Drakkith]

ed
Pardon my impertinence, but doesn't anything shorter than the length of Planck Time foreclose knowing what happened at the moment of the Big Bang.

You're confusing the big bang as a single 'event' (creation of the known universe) with the big bang as a 'process' (rapid expansion from a hot, dense state). Bandersnatch is referring to the latter.