In article ,
Hanroanu wrote:
I have wondered this for a long time now. A discussion with my
physics professor proved unsatisfying. Well, my curiosity goes likes
such. We imagine two objects that are apart but close to each other
in a remote part of the universe. If they are not revolving, then the
objects will come together by gravity. However, if they are revolving
(at the right speed), then the objects will stay apart, like there was
a force between them. Now I ponder, what do you measure the rotation
relative to? The background stars and the rest of the universe? What
if the two objects was the only thing in the universe. How can you
measure the rotation relative to nothing?


Foucalt built a large pendulum that could swing for days, and the
direction that the bob moved turned a circle once per day, proof of the
rotation of the Earth. Today, Sagnac interferometers, made by interfering
laser beams through spools of fiber optics, can be made sensitive enough
to measure the Earth's rotation. Coriolis forces on large pools of water
allowed to still before draining can also show direction of rotation
(although the swirl of toilets has nothing to do with that one).

A more interesting question, I think, is how would the inhabitants
develop a theory of rotation given that what you've described is all they
know. Transform to an accelerated reference frame and you pick up
inertial forces--centrifugal force, Coriolis forces, etc. Science would
have to advance beyond our Galileo and Copernicus before the debates
started flaring about the nature of the force and movement of the planet
and sun.

All the while assuming a Newtonian analysis is sufficient. I don't know
what a cosmos consisting of two objects would be like in general
relativity.

--
"Is that plutonium on your gums?"
"Shut up and kiss me!"
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