# RE: starship-design: Casimir-Foreward balloon

Timothy,

> Of course the total momentum vector will be zero. But how
> large is total?
> In Connor's design, at the end of the voyage, the volume in
> which the total
> momentum is conserved has become pretty large. Yet the size
> is not a solid
> reason to say (believe) that it won't work.

Well, that is the problem. The total momentum (and energy) must be defined
in the terms of the system, which as you point out is rather large in this
case. I seem to remember that it WAS possible to violate conservation
locally as long as you didn't violate it in terms of the larger system. The
physics for this are beyond me I'm afraid.

Another way to consider it: let's think of this as a pool table where we
throw the balls in from outside the table. The balls bounce around randomly
transferring energy and momentum with each bump, yet it still sums to zero
until the ball finds the single pocket at the end of the table at which
point it leaves the local system, transferring useful momentum with its last
bump (the one that sent it to the pocket). Locally, we just gained momentum
on a vector we wanted (and violated conservation), in terms of the larger
system, I believe it will still sum to zero (and preserve conservation).

Anybody care to check my reasoning on this? Did I screw up somewhere?

BTW, the photons leaving through the exit in his balloon will not
necessarily be coherent, nor is there any real need for them to be coherent,
as long as they all leave in approximately the same direction - backwards!

Lee