Re: GR or QED?

George Murphy (
Thu, 30 Apr 1998 07:26:42 -0400

Glenn R. Morton wrote:
> At 02:58 PM 4/29/98 -0400, George Murphy wrote:
> > While there is nothing wrong with noting the high precision of
> >such experiments, it can be a little misleading in the context of
> >anthropic principles because it suggests that the universe must have
> >been fine tuned to this precision in order for intelligent life to
> >develop & that isn't the case.
> I do know that Ross holds that the critical expansion (based upon the
> inflationary view) must be correct to within 1 part in 10^-55 or life
> couldn't exist.
> He says, "How critical is this expansion rate? According to Alan Guth, it
> must be fine-tuned to an accuracy of one part in 10^55." Fingerprint of
> God, p. 124
> What could I learn from you about this claim? As I understand it, there is
> now some significant doubt about the inflationary universe, given the
> evidence for the cosmological constant. While this may not have entirely
> won the day, is Ross' claim correct? Would it contradict your assertion
> above?

My comment referred to the precision of local isotropy, not
necessarily to all physical parameters.
It's true that there would have had to be very precise fine
tuning for a cosmological model in which space (not space-time) is as
close to being flat as it is. (I.e., the density d & Hubble parameter H
are in the ballpark of satisfying H^2 = 8*G*d/3.) Inflationary models
provided an explanation for this. If they don't work then for the time
being we have no scientific explanation for this near coincidence.

George L. Murphy