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In article <1388@trwrb.UUCP> galins@trwrb.UUCP (Joseph E. Galins) writes:
>If the elevator is accelerating, then after a long, long time its speed will
>reach the speed of light then pass it.

No, the speed will approach c but not exceed.

>					...I know that the problem here
>has to do with the fact that F=mA is false when the speed approches 'c'.

That's correct.

>In fact F approches infinity near 'c'.

No, don't forget that F drives the elevator to simulate the gravitation.
It has to be constant and equal to Fg = m0 g (m0 = rest mass).

>				...So with a constant (or even increasing
>but finite) force, wouldn't the acceleration necessarly slow down as the rider
>approched 'c' and hence notice that he was in an elevator? 

There won't be an acceleration, but you can't detect that. Hence you can't
say you are in an elevator. I'll explain that in a minute.

>In other words, with a constant acceleration eventually you would be going
>at a speed of 'c' with no more acceleration therefore losing the 'gravity'
>feeling...

You probably mean 'constant force' not 'constant acceleration' but anyway,
didn't you say F=ma is false for high speeds? Acceleration causes 'gravity'
feeling (F) only at low speeds.

You have to be careful not to mix Newtonian mechanics and relativistic
mechanics.  For velocities comparable to c you have to forget everything
intuitive, all your experiences. Any time you make an inference you better
ask yourself: "Did I derive this from the relativistic laws or do I rely on
ANYTHING else"? It is difficult task and many people won't accept it.

According to Newtonian mechanics, F = ma, therefore if a constant force
acts on a body for a long time, the velocity will increase infinitely.
We know, that it is not true. Relativistic physics says F = dp/dt
where p = mv = GAMMA m0 v, GAMMA = (1-(v/c)^2)^-1/2, m0 = rest mass.
The formula says the following:
	1. The force depends on the change of momentum (p)
	   i.e. BOTH mass and velocity.
	2. If you apply a constant force, the momentum will
	   increase infinitely.

You can see that for low velocities (v<<c) mass is approximately constant
and the force (gravity feeling) depends only on acceleration. For very
high velocities (v -> c) there is almost no acceleration but the momentum
keeps increasing because the mass keeps increasing. Since the momentum or
more precisely its change is what determines the force, you won't feel any
difference. So you are right when you say there won't be any acceleration,
but that has nothing to do with a gravity feeling.

zdenek

P.S.
But I think you'd find out anyway. The human body starts to act really
funny when it moves at the speed of light. The strongest effects are on
the digestive tract.

 -------------------------------------------------------------------------
 Men are four:
 He who knows and knows that he knows, he is wise - follow him;
 He who knows and knows not that he knows, he is asleep - wake him;
 He who knows not and knows that he knows not, he is simple - teach him;
 He who knows not and knows not that he knows not, he is a fool - shun him!

 zdenek@CS.COLUMBIA.EDU  or 	...!seismo!columbia!cs!zdenek
 Zdenek Radouch, 457 Computer Science, Columbia University,
 500 West 120th St., New York, NY 10027