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Stellar Drive

Interesting idea. Is the physics really OK on this one? It sounds dodgy. I
don't follow the author's attempt to keep Newton's third. What if there
were no charged matter in the direction of the escaping fields? If there
were charged matter, would it not make a difference if it was mainly
negative or positive? The magnetic forces would be in opposite directions
for opposite charges. If there were no charged matter moving relative to
the electromagnets, there would again be no possibility of future magnetic
forces making up lost momentum. Does the concept depend on the statistical
distribution of charge and velocity throughout the universe surrounding the
magic drive? Surely the principle of reaction is not statistical in the
sense thermodynamics is. I have a few other points. Timothy wrote:

>Magnetic fields is just EM-radiation, usually magnetic fields are very low
>frequency radiation, in some cases almost non-alternating. In any case
>photons are exchanged.
>So you  could just as well (even better) use a laser to generate "local

How would you make a laser pull? Lasers, indeed all real photons, only
push. The force on the target would be cancelled by the reaction to the
laser emission in the emitter, and the system would experince no net force.
With pulling virtual photons, the idea seems to imply an odd free lunch -
the action and reaction are in the same direction. But we still pay for

I think Kevin made a good point about the second electromagnet's field
interacting with the first electromagnet by inducung a current in it. I
don't think that shielding it with a superconductor would help - a current
would be induced in the superconductor, and you would still have your
unwanted reaction force. It would be like a bar magnet hovering over the
eddy currents it produces in a superconductor.

My final point is that if the system doesn't violate Newton's Third Law,
what's the point of it? Its not really a 'stellar drive' (how did
reactionless drives get that name?) at all. I assume the point of a
reactionless drive is to save a starship from using up its energy on
reaction mass - one would prefer that it convert all its stored energy into
KE for itself. But if the magnetic fields created eventually do accelerate
a distant 'reaction mass', no energy has been saved. So is the concept
really helpful for us?

Just out of interest, is there any way of focussing virtual photons to
concentrate a magnetic field in one direction? I doubt it's possible
without making the photons real first.