From: gmartin@zia.aoc.nrao.edu (George Martin)
Subject: Re: Are we privileged observers?
Keywords: universe,earth, paradox
Organization: NRAO
Date: Mon, 17 Aug 92 00:39:24 GMT

In article <julian.714000550@sfu.ca> julian@fraser.sfu.ca (Julian Shillcock) writes:
>kring@efes.physik.uni-kl.de (Thomas Kettenring) writes:
  [interesting discussion deleted]
>
>>Huh?  If we can observe them, we can look there if the laws of physics hold.
>
>No you can't, becuse you do not know how to interpret the observations.
>An example: Suppose you measure the spectral shift of starlight, and find
>it has a red-shift. Is this because the light is from a receeding source
>or it is having to escape a strong gravitational field, or perhaps 
>some unknown mechanism? We have to make a "uniformity" assumption
>in order to interpret our observations. Another example: suppose
>Newton's constant (G = 6.67 .10**-11 N.m**2/Kg**2 actually depends
>on position so that it has a different value a few million light years
>away? How can we discover this? Well, you can measure the period of
>a double star and see if the accepted value of G works. But then you
>need the masses to do this and how so you calculate them? You have to
>assume a value for G, so you end up with a circular calculation.
>
I think that astronomers can tell the difference between dopler red
shifted light and gravitationally red shifted "tired" light.  Things
having to do with line shape widths and profiles and etc.  Also
assuming that a line is gravitationaly red shifted should lead to other
consequences which can be tested.  I would note that even Geoff Burbadge
belives that observations of galaxies show that the universe is expanding
even though he doubts Big Bang cosmology.  I will give you a reference to
that if you want.

There have been a number of observations done testing if the standard
physical constants have changed in time and so far the answer is that
things like the electron charge, etc. have not.  You might check out
Astronomy and Astrophsics Abstracts or the equivalent for Phys. Rev.
for more details.

And then large G.  Dirac's Large Number Hypothesis would seem to
require that there is a dG/dt not equal to zero.  This excited a
number of people to look for it in the 70's.  In the Dirac hypothesis
changing G would lead to a number of effects observable today both
in laboratory experiments and geological observations.  Nothing was
found.  I am not aware of anyone who has looked for a dG/dt who
found anything other than zero.  The upper limits for a dG/dt not
equal to zero from the experiments which looked for it would seem to
suggest that the /dt for other physical contants is extermly small, like
maybe zero.

I would have a hard time believing that all of the physical
constants are changing just so, so that we can not measure the change of
one relative to one or more of the others.  Such a hypothesis would
make for an interesting cosmology though, likely one with testable
assumptions.

>We usually make the minimalist aasumption that the laws of physics
>are the same everywhere for all observers, but this is an untestable
>assumption within physics: rather it is the basis on which we do physics.
>It is a matter of faith where the laws of physics apply ( hence my
>statement about needing a meta-physics, ie, a more abstract theory 
>that says where the current theories are valid).

I am not qualified to comment on this but from what I read physicists
like cosmologists do not see this need.

  [rest deleted]
-- 
George Martin
Systems Analyst                     NRAO/VLA                  Socorro NM
Internet: gmartin@something.aoc.nrao.edu
"Skating away on the thin ice of the new day."  (Ian Anderson)
Newsgroups: talk.origins