"Roedy Green" wrote in message
...
How would you tell the difference between an expanding universe and
light slowing down over time? I would think since light is your
yardstick, they would look the same.

If the speed of light was changing over time (by enough to create the
appearance of an expanding universe) then the fine structure constant
"alpha" would be changing. If that happened all of atomic and nuclear
physics would have been radically different in the past. However,
observations of distant quasars and of the Oklo natural nuclear reactor of
about 2 billion years ago imply that alpha has not varied by very much if at
all, over cosmological time scales.


Second question, is there any evidence on a local scale of an
expanding universe, or does it all come from the Doppler shift of
distant galaxies? Is there any way to notice the meter bar in Paris
has grown a tad, or anything comparable?

No, you can't observe cosmological expansion effects locally on the Earth or
within our own galaxy. Space is expanding, not the objects within it. And
the metre bar in Paris is now a historical artifact, because the metre is
defined using light itself (as is the second).

--
Roedy Green Canadian Mind Products
http://mindprod.com

"The industrial civilisation is based on the consumption of energy
resources that are inherently limited in quantity, and that are about to
become scarce. When they do, competition for what remains will trigger
dramatic economic and geopolitical events; in the end, it may be
impossible for even a single nation to sustain industrialism as we have
know it in the twentieth century."
~ Richard Heinberg, The Party's Over: Oil, War, and the Fate of
Industrial Societies


--
Mike Dworetsky

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