Re: is perpetual motion possible ?

Chipacabra wrote:
"FellKnight" <jordandevenport@xxxxxxxxxxx> wrote in
news:eof9k5xc71.ln2@xxxxxxxxxxxxx:

On Jul 7 2008 12:32 AM, ruylopez wrote:

This is utter digression but I know that you know your ***, and I
like to poke brains around here to see what comes out. I appreciate
your time posting here. I haven't been taught Physics in like 10
years - I was good at it in high school and early college, but I
really couldn't get myself to dig through the math to do something
like major in it.

PS - Can you tell me if the force of gravity has ever been shown to
travel at some speed, like c? That one always bugs me.
It doesn't. In all current tests (difficult to test, admittedly),
gravity is shown to work at infinite velocity. The reason why it is
so difficult to test is because gravity is so weak relative to the
other forces. Just moving an object at high velocity is not perfect,
and the only way we have of removing an item from existence,
matter-antimatter annihilation both produces massive amounts of
energy, and we can only produce submicroscopic amounts of antimatter.

I suggest that you read Physics of the Impossible. It's a new book
from a phycisist who is very good at explaining the universe in
layman's terms.

Actually, Gravity's more complicated then that. The effects of gravity do propogate at (about) the speed of light, we can observe that in the interactions between pulsars as they decay.

One weird observation we've made is that the effects of gravity seem to be predictive. Consider two planetoids, called A and B, orbiting a star. The orbits will be irregular based on A and B interacting with each other. Here's where it gets weird.

A exerts a gravitational force on B (and vice versa) that "travels" at somewhere around the speed of light. Let's say it takes 1 day for light to travel from A to B. Strangely enough, B experiences a force toward where A is NOW, not where it was yesterday. This is where the idea that gravity travels instantly comes from.


That's Newton's interpretation of Gravity, anyhow.

A doesn't exert a gravitational force on B (and vice versa). They influence each other indirectly, by changing the topography of space/time.

Here's an interesting question (IMO): How do they know that mass exerts an attractive force? Couldn't vacuum be exerting a repulsive force instead? Or, in Einstein's language, maybe it isn't that mass creates valleys; maybe vacuum creates mountains.

I think the math would work out the same in either case. I could be wrong.

Cheers.

Now, let's say a comet smashes into A and knocks it off course. It's a magic comet that makes A go in completely the opposite direction. In this case, B will still experience a force toward where A SHOULD be for 1 day, until the information of A's new path is propogated to B, and B begins experiencing gravitational force toward where A has been pushed.
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