[geocentrism] For Alan
- From: "Philip" <joyphil@xxxxxxxxxxx>
- To: <geocentrism@xxxxxxxxxxxxx>
- Date: Wed, 4 Aug 2004 11:11:03 +1000
I don't know if it would have made in difference Alan if instead of Immobility
with respect to space, I had used the term fixed frame of reference, or if you
yet know from my subsequent humble attempt to clear it up, so I quote here the
short statement by Michael Fowler which is trying to say the self same thing,
in his lecture on Special Relativity
You had your alien in a couple of frames of reference which were not proven to
be immoble
. Philip
"What exactly do we mean by a frame "at rest" anyway? This seems obvious from
our perspective as creatures who live on the surface of the earth--we mean, of
course, at rest relative to fixed objects on the earth's surface. Actually, the
earth's rotation means this isn't quite a fixed frame, and also the earth is
moving in orbit at 18 miles per second. From an astronaut's point of view,
then, a frame fixed relative to the sun might seem more reasonable. But why
stop there? We believe the laws of physics are good throughout the universe.
Let us consider somewhere in space far from the sun, even far from our galaxy.
We would see galaxies in all directions, all moving in different ways. Suppose
we now set up a frame of reference and check that Newton's laws still work. In
particular, we check that the First Law holds--that a body experiencing no
force moves at a steady speed in a straight line. This First law is often
referred to as The Principle of Inertia, and a frame in which it holds is
called an Inertial Frame. Then we set up another frame of reference, moving at
a steady velocity relative to the first one, and find that Newton's laws are
o.k. in this frame too.
The point to notice here is that it is not at all obvious which--if either--of
these frames is "at rest". We can, however, assert that they are both inertial
frames, after we've checked that in both of them, a body with no forces acting
on it moves at a steady speed in a straight line (the speed could be zero). In
this situation, Michelson would have said that a frame "at rest" is one at rest
relative to the aether. However, his own experiment found motion through the
aether to be undetectable, so how would we ever know we were in the right
frame?
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