Re: Expelled: If you don't believe in holy physics dogma ; you're

On Sat, 21 Jun 2008, Bill Miller wrote:

> One of the fundamental laws of mechanics is Newton's law of action and
> reaction, usually stated as : "Whenever a body exerts a force (action)
on a
> second body, the second body exerts an equal and opposite force
(reaction)
> on the first body."
>
> Suppose that a stationary mass is located in the gravitational field of
> another, distant stationary mass.The two m***** exert equal and opposite
> forces on each other. (Action and reaction)  Let us now allow one mass
to
> move under the action of the field of the other mass. ut the second
mass,
> being far away, does not yet "know
> that the first mass has moved. (gravity -- like light -- cannot
propagate
> instantaneously.) The second body continues to experience the same force
as
> before.
>
> In other words, the forces are now unequal in magnitude and direction
and
> Newton's action/reaction law no longer holds! Further, this situation
also
> is in conflict with the very basic law of conservation of momentum.

Hmm. Newton's 3rd law of motion (along with Newton 2, to relate force and 
transfer of momentum) is basically a statement that momentum is conserved.

Yes, if we consider two m***** as above (or two electric charges) to be 
interacting with each other, we have exactly the problem you point out.

Does this mean Newton 3 is wrong? Does this mean momentum is not 
conserved? I would say that it means that we simply don't have a situation

where there are two objects interacting at a distance, but two objects 
each interacting with a field. Perhaps the interaction really is as 
described by field theory, a local interaction between field and body, and

we should throw away the classical mechanics idea of interaction at a 
distance rather than Newton 3.

We know that a force is exerted on each mass. We know that in a static 
case, the force is symmetric. We don't know that it is the other body that

is actually exerting the force. The example you give strongly suggests 
that it isn't.

It wasn't that long ago that I wrote a lot more about this, so I won't 
repeat it here.

But for an example of a "law" by Newton that we know is only an 
approximation: Newton's law of universal gravitation.

-- 
Timo