From: nuny@bid.nes   
      
   On Wednesday, August 10, 2016 at 12:16:25 PM UTC-7, 0something0 wrote:   
   > I think I know a way to create a reactionless drive without violating any   
   laws   
   > of physics, the way it works is there is a photon sail at the front, and   
   > lasers fed by a nuclear reactor or something, and the lasers hit the sail to   
   > creat momentum. I'm guessing it's an existing idea, but isn't this possible?   
      
     Yes, it's an existing idea, and yes, it's possible, but there are details   
   you didn't cover.   
      
     First, generating photons requires the expenditure of energy, depleting   
   whatever runs the laser. Whatever it is you can only carry a finite amount, so   
   when it runs out, you're done just like an ordinary rocket that runs out of   
   LOX or whatever.   
      
     Second, what happens to the photons when they hit the sail?   
      
     If the sail absorbs them you get no net movement because the photons carry   
   momentum as they leave the laser, meaning the laser recoils a bit per each   
   photon it emits. When the sail absorbs a photon it also absorbs its momentum,   
   canceling the recoil    
   from the photon's launch. If the laser's bright enough you might measure a   
   tiny tension in the sail shrouds proportional to the brightness as the laser   
   tries to push the sail away...   
      
     If the sail reflects the photons into free space, they carry their momentum   
   away from the ship just like any other kind of rocket and you might as well   
   discard the sail and turn the whole ship around.   
      
     In neither case is conservation of momentum violated.   
      
     If you don't get it because it's, like, a LASER, man!, remember that your   
   laser is just a photon rocket. Replace it with an ordinary chemical rocket and   
   your sail then catches the "wind" from the rocket exhaust. What will happen?   
      
      
     Mark L. Fergerson   
      
   --- SoupGate-Win32 v1.05   
    * Origin: you cannot sedate... all the things you hate (1:229/2)