Still lower noise radio astronomy (was: low-noise amplifiers for radio astronomy )

In article ,
"John (Liberty) Bell" writes:
The operative phrase here is "seems to be". In order to change that to
"is", we would need to have comparable data over a solid angle of 4 pi
steradians to be conclusive.

For most purposes in astronomy, we have to be satisfied with
statistical samples.

... we know that, in detail, the universe contains large
clumps and filaments of galaxies with large volumes of vacuum in
between. Sampling different angular portions of the spacetime continuum
at a given time does reveal such variability.

This problem is generically known as "cosmic variance." Statistical
samples have to be large enough. The principles for calculating
cosmic variance are known, but answers depend on the statistics of
galaxy clustering (the "galaxy correlation function"), which in
principle depends on galaxy type and cosmic age. Nevertheless,
enough is known to obtain reasonable estimates for the likely sample
variance. The relevant quantity is survey volume, not area, but
that's a detail. Calculating survey volume depends, of course, on
the cosmological parameters one assumes.

I would recommend extreme caution to anyone who assumes that
observations at high z shifts must necessarily be interpreted
within the context of [classical big bang theory]

The theory is well enough established that interpreting observations
in its context no longer needs justification. That is not to say
that no one should look for contradictions, but any interpretation
these days has to at least start by looking at what is expected if
the "concordance big bang model" is valid.

In message :
Several examples of such unpredicted, or at least unexpected,
observational results (in the context of then established theory)
occur to me immediately.

Yes, there are some questions remaining; not all of astronomy is
understood. :-) However, I think you need to get up to date on all
the things the big bang model does predict. There's a reason it's
known as the "concordance" model.

Steady state is entirely hopeless. The high-redshift Universe (seen
as it was billions of years ago) looks nothing at all like the local
Universe. One can argue about details -- and believe me, we
astronomers do! -- but the fact of cosmic evolution is undeniable.

--
Steve Willner Phone 617-495-7123
Cambridge, MA 02138 USA
(Please email your reply if you want to be sure I see it; include a
valid Reply-To address to receive an acknowledgement. Commercial
email may be sent to your ISP.)

Steve Willner wrote:
In article ,
"John (Liberty) Bell" writes:
The operative phrase here is "seems to be". In order to change that to
"is", we would need to have comparable data over a solid angle of 4 pi
steradians to be conclusive.

For most purposes in astronomy, we have to be satisfied with
statistical samples.

Absolutely. But the level of confidence does depend on the size of the
statistical set.

... we know that, in detail, the universe contains large
clumps and filaments of galaxies with large volumes of vacuum in
between. Sampling different angular portions of the spacetime continuum
at a given time does reveal such variability.

This problem is generically known as "cosmic variance." Statistical
samples have to be large enough. The principles for calculating
cosmic variance are known, but answers depend on the statistics of
galaxy clustering (the "galaxy correlation function"), which in
principle depends on galaxy type and cosmic age. Nevertheless,
enough is known to obtain reasonable estimates for the likely sample
variance. The relevant quantity is survey volume, not area, but
that's a detail.

Agreed.

Calculating survey volume depends, of course, on
the cosmological parameters one assumes.

A very important point.

I would recommend extreme caution to anyone who assumes that
observations at high z shifts must necessarily be interpreted
within the context of [classical big bang theory]

The theory is well enough established that interpreting observations
in its context no longer needs justification.

That is true.

That is not to say
that no one should look for contradictions, but any interpretation
these days has to at least start by looking at what is expected if
the "concordance big bang model" is valid.

Quite. When examining presented data, I automatically assume that the
researchers have already done precisely that. Unexpected results then
mean one of two things. New physics, or distortions introduced by the
accepted model, which I guess amounts to the same thing.

In message :
Several examples of such unpredicted, or at least unexpected,
observational results (in the context of then established theory)
occur to me immediately.

Yes, there are some questions remaining; not all of astronomy is
understood. :-) However, I think you need to get up to date on all
the things the big bang model does predict. There's a reason it's
known as the "concordance" model.

Steady state is entirely hopeless.

I entirely agree.

The high-redshift Universe (seen
as it was billions of years ago) looks nothing at all like the local
Universe. One can argue about details -- and believe me, we
astronomers do! -- but the fact of cosmic evolution is undeniable.

Again, I completely agree.

Nevertheless, when you have a field equation which predicts a creation
and evolution of the universe at high z, which is significantly
different to standard big bang theory, what can you do easily to
evaluate the new astronomical data, as presented? One thing you can do
simply, is confirm that the observed results deviate from established
theory and expectations in the predicted direction. That is what I did,
in practice, by employing that one relevant aspect of the steady state
model (survey volume, or more precisely, matter within that survey
volume), as an extreme limit of that predicted direction.

John Bell