From http://www.hindu.com/2005/10/23/stories/2005102305241000.htm

J Seymour MacNicely <mac_the_nice@bigstring.com> wrote:

Now, previously I had got about a third of the way into *The Name of
the Rose* before to my distaste, a fine beginning soon turned into
something Eco, from the looks of it, just had to get off his desk in
the form of a Jesuit James Bond thriller, for sake of a few lira in
his pocket, and thereby gain the freedom to finance something new to
pick up from where inspiration ran out.

I found when I forgave the author his detective story and his pomo
stuff, it was fun. Worth reading all the way to the end. But you have to
forgive him first.

Foucault's Pendulum, so far, looks like it came roaring back.

I read the first couple of pages and felt like, am I going to have to
forgive *this* the whole way through? I put it down and haven't
regretted the choice, though I can imagine it might be worth it someday.
It was the same way for me with Ayn Rand. When I was 15 I read to the
very end of _Atlas Shrugged_, and then I picked up _The Fountainhead_
and when I saw where it was heading I just put it down again. And _Lord
of the Rings_, if Tolkien had written another one like that I would
probably have just skipped it.

I begin with a question to anyone familiar enough with physics to
answer this question: What exactly is this bit about Foucault's
pendulum proving, ideally speaking, that any "dimensionless point in
space" from which such a pendulum is suspended is somehow, as I take
it, a proof of Aristotle's metaphysics of the "unmoved mover"?

It demonstrates something from physics. The philosophical
take-home-message you chose to get from that is your choice. If you've
had some physical illusion, something that isn't so, that it challenges,
then that's likely to be the message. But no one can predict what
message that will be unless they know what false belief you started out
with.

Here's one possible interpretation. Newton's laws say that things will
keep moving at the same speed in the same direction unless some outside
force acts on them. In one sense this is just the definition of a force
-- it's anything that keeps something from continuing to move at the
same speed in the same direction. But there's an *idea* behind it which
is more than the operational definition. (And ideas that take more in
than the operational definition puts out, are potentially misleading.)
If you measure the location or the velocity of something moving in a
straight line, it's completely arbitrary where you measure from or the
speed that your reference location itself is moving. This is not just
true, it's something that physicists have consciously chosen. When they
were faced with a situation in which it looked like it might not be
true, they chose with relativity to distort the way they measured space
and time to *make* it true.

But rotations are different. It's true that something will keep rotating
along the same axis at the same speed unless it's acted on by some force
-- and this defines rotational force. And it's true that the angle you
choose to measure the axis of rotation against is arbitrary. But the
speed of rotation is not arbitrary unless you're ready to suppose the
whole universe is rotating around that particular axis. Imasgine one
particular straight line through space, and imagine the whole universe
rotating around that line. Now another and another and another. *More*
arbitrary than imagining the whole universe traveling in some direction.
And a much bigger effect on the physics. Things distant from the line
revolving at great speed around that axis, and it takes a force to keep
them from moving in a straight line....

The math works either way, but imagining the whole universe rotating
with a force to counteract the effects of that rotation is more
complicated than supposing the universe isn't rotating about your
particular axis. Speed of rotation isn't as arbitrary as velocity.

When something is in free fall, then as far as linear movement is
concerned you can treat it like it's motionless. It's completely
arbitrary whether you assume it's moving or assume that everything else
is moving compared to it. You can do whichever makes the math come out
simpler for your particular problem. But not rotation. Rotational forces
can cancel out if they're along the same axis or on different axes that
meet at the same center. Otherwise they don't. In general they don't.
Rotations are more complicated than linear motion.

Foucault's pendulum displays this. Easy to imagine when it's at the
north pole. The pendulum just keeps swinging and the earth turns under
it. What force would we imagine to make the pendulum turn, instead of
supposing that we're turning? Then as you move the pendulum south it is
revolving around the earth's axis, but not around the earth's center.
Finally at the equator it no longer rotates. It does other more subtle
things, because it is being acted on by the earth's gravity and also the
earth's rotation, and they interact.