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Momentum for Free?

 Laser-beam through electron beam through BEC.
 
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Slow photons (i.e. photons that pass through a Bose-Einstein Condensate) have more momentum than fast photons. Photons that hit electrons give the electrons more momentum. Electrons that go from a small anode to a large cathode supposedly gains momentum (Biefeld-Brown effect).

Imagine that we make an electron beam go through a BEC on its way from the anode to the cathode. Then we shine a laser beam through the electron beam (in the same direction, through the BEC). The photons would gain momentum from being slowed down, and they would transfer momentum to the electrons, which would also gain momentum through the Biefeld-Brown effect.

Could this reactionless increase in momentum be used for propulsion?

—rips, Jan 15 2004

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       The problem with both photons and electrons is they don't have much mass so you would need a lot of ejecta to create any meaningful thrust. Could be a slight improvement to the ion rocket for deep space tho. My suggestion is you throw some dirt in there.
—thrival, Jan 15 2004
   

       Hmmm, "reactionless increase in momentum..." There's a law against that.
—ATP, Jan 15 2004
   

       I know there's a law against it, and the Biefeld-Brown effect does seem like fringe stuff. But mainstream physics acknowledge that photons gain momentum as they slow down, and that electrons gain momentum when you shine a laser beam through them. I'm not a physicist, so I can't point to the rulebook on this... Would be fun if something could be gained from this, though. I.e. as a better low-specific-impulse-engine than the ion engines in use now.
—rips, Jan 16 2004
   

       //mainstream physics acknowledge that photons gain momentum as they slow down// I'm not up-to-date on recent physics, but I've done a bit of a search and can't find this claim elsewhere. Can you provide me with a link? I fear they aren't taking relivistic effects into account or I'm missing something. I've always thought photons have no rest mass, and therefore no rest momentum.
—Worldgineer, Jan 16 2004
   

       Worldgineer   

       I asked a friend about this, and he quoted a physics formula:   

       p=hf/c. If c (the speed of the photons) decreases, p will increase, but the energy (E=hf) remains the same.   

       He also said: 'remember that in any collision, the energy is decreased or retained', which pertains to the part where I hit the electrons with a laser.   

       He does not think the effect will be very large, though.
—rips, Jan 20 2004
   

       //remember that in any collision, the energy is decreased or retained//   

       That's on a macroscopic scale. When you're down at the fundamental levels, there aren't many ways for energy to be lost due to inelastic collisions. In fact, the idea of an inelastic collision is kind of absurd in the context of particle physics.
—Detly, Jan 22 2004
   

       The biggest problem with this idea isn't so much the increase of momentum for the photons, it's the laser.   

       You aren't getting momentum for free, because you're using the laser to speed up the electrons. The laser costs energy, and in order to increase the momentum of the electrons enough to make a difference (or power a big freaking space boat), you'd need a really strong laser. REALLY strong. The energy for that would have to come from somewhere.   

       Regardless of the fringeness of B-B, the energy required for the laser makes this too inefficient to be a frequent-use drive. Perhaps for short bursts, it MIGHT be a decent addendum to a pre-existing propulsion system. But for the main drive? Not so much.
—shapu, May 11 2004
   


 

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