View Full Version : Antimatter Torch Drive

17th-August-2013, 07:56 PM
Consider a ship that accelerates by annihilating antimatter. The energy released in its engine equals the mass of annihilated antimatter multiplied by the speed of light squared. As the ship approaches the speed of light, its mass exponentially increases, but so does the mass of its propellant. The ship can therefore annihilate an ever greater mass of antimatter per unit time to compensate for the increasing inertia of its own growing mass or annihilate the same absolute mass of antimatter for a very long time (forever?). Ignoring such concerns as melting engines or structural warping, could such a drive work?


17th-August-2013, 09:45 PM
I don't think so...

I know a block of matter doesn't gain more atoms as its velocity increases, so it doesn't gain atomic mass, rather it gains relative mass, or perhaps to be more accurate "relative energy", I mean to accelerate an object is to effectively store energy in it so, by storing, that energy somehow...



The energy released by the annihilating matter continues in motion and thus from the frame of reference of the ship the explosion was stationary, even though if used as a weapon against a stationary target the relativistic speed explosion would have more energy to give than one that simple happened next to the target.

Although how velocity factors into it given the lack of mass is....


17th-August-2013, 11:08 PM
This annihilation is not about relativistic mass... It's about mass at zero velocity, or the amount of protons neutrons and electrons in the atom.

F****** original idea though

18th-August-2013, 12:28 AM
No this has been thought of before unfortunately. I forget the discussion (I covered it back in physics school somewhere), the problem is the rest frame as Cooly says. Consider from the viewpoint of the engineer on the ship. He has x pounds of antimatter and x pounds of matter to drive his ship. The rest of the universe zips by faster and faster, but his engine has a maximum output (0-10 say) and so all he can do is dial in some power. At some time he will run out of fuel. He'd better turn the ship backwards before the fuel gets to the halfway mark too.

External observers see them accelerate closer and closer to c regardless of the propulsion.

18th-August-2013, 12:59 AM
Thanks for the feedback, guys, and thanks for the compliment, Cooley. :) You touched upon my worry regarding this design: turning velocity into rest mass seems like a rather strange feat because the hypothetical engineer (who I suppose, if crazy enough to ride an antimatter engine, is crazy enough to use pounds in rocket science :p) can still walk around on a ship that is travelling at 0.9c.