Robert L. Oldershaw wrote:
Here is a direct, straightforward question that I would like to have answered.

What quantitative or unique qualitative empirical result would lead us
to think that there is a problem with our theoretical model of the
early period of expansion?

I presume that there are some limits to what the existing model could
account for. So what are these "lines in the sand" that do offer clear
and definitive tests of the model?

The standard big bang model requires that the mass distribution in the
universe should become more and more anisotropic over time. We have good
evidence from CMBR observations that the universe was isotropic to within
a few parts per million at the CMBR-last-scattering time (redshift
somewhere around 1100 or so if I recall correctly).

So....

Hypothetical case #1:
If we were to observe some mass tracer to be highly *anisotropic* at
times *earlier* (i.e., redshifts higher) than the CMBR-last-scattering time,
that would be very hard to explain in (i.e., it would be a big problem for)
the big bang model.

Hypothetical case #2:
If we were to observe some mass tracer to be *more* isotropic than
the CMBR at a time *later* than (i.e., at a redshift lower than) the
CMBR-last-scattering time, that would be also be very hard to explain in
(i.e., it would be a big problem for) the big bang model.

Hypothetical case #3:
If we were to observe the distribution of some mass tracer (say,
galaxies, as measured by their 2-point correlation function) to become
*more* isotropic with increasing time over some redshift range, that
would also be hard to explain, i.e., it would be a big problem for,
the big bang model.


[Technically, #2 and #3 might be better characterized as big problems
for our theories of the evolution of anisotropies in an expanding
universe, rather than for the big bang model itself.]

[I suppose there might actually be some theoretical wiggle room around
each of my cases if the "mass tracers" turn out not to accurately trace
mass. One way to reduce that wiggle-room might be to use (galaxy-cluster)
gravitational lensing measurements for #2 and #3, since these directly
sample the mass distribution (at least in theory; in practice these are
very delicate observations to make, and they require elaborate theoretical
modelling of a type of which I don't think Robert Oldershaw approves).]

ciao,

--
-- "Jonathan Thornburg [remove -animal to reply]"
Dept of Astronomy & IUCSS, Indiana University, Bloomington, Indiana, USA
"There was of course no way of knowing whether you were being watched
at any given moment. How often, or on what system, the Thought Police
plugged in on any individual wire was guesswork. It was even conceivable
that they watched everybody all the time." -- George Orwell, "1984"