Relativity drive

[TheFaithfulStone]

Just because it's trivial to you Q, doesn't mean it's trivial to us hoi-ploi. Even if it is obvious after a little thought.



TFS

[Erasmus00]

If momentum is conserved, then an object is incapable of moving its own center of mass. This follows trivially from the deffinition of the center of mass (the place where the total momentum sums to 0. If momentum is conserved, this place always has 0 momentum). From this, we can easily see that this device simply can't work.
-Will

[KickAssClown]

Your assuming that the EM radiation is part of the mass, and that it moves with the frame. As I understand special relativity though, the photon's frame is invariant, where as the mass's is variant.

Also, for a partial possible answer to the absorbing aspect of the em bouncing inside the construct, if you use the right material you could end up with sides that minimally absorb the microwave radiation and ends that absorb it greatly. Energy is only absorbed in discrete packets.

Furthermore, it should be noted that he uses Microwave radiation, which can be used to induce electric current in some materials.

Erasmus, how then do I move my center of mass? I am an object, I have mass, and I have a center of mass. I walk and that changes my momentum, correct? As I understand it, how I do that is by difference of potentials. Is it so improbable that you can power a thruster without ejecting things out the tail end?

[Erasmus00]

Originally Posted by KickAssClown

Your assuming that the EM radiation is part of the mass, and that it moves with the frame. As I understand special relativity though, the photon's frame is invariant, where as the mass's is variant.

For light



So the momentum is related to the frequency, which doppler shifts.

Erasmus, how then do I move my center of mass? I am an object, I have mass, and I have a center of mass. I walk and that changes my momentum, correct? As I understand it, how I do that is by difference of potentials. Is it so improbable that you can power a thruster without ejecting things out the tail end?

You don't move your own center of mass. You push off the Earth, and you move relative to the Earth. The center of mass of the you-Earth system does not move.

It is impossible to power a thruster without ejecting something IF momentum is conserved.
-Will

[Qfwfq]

Certainly Will but some here have been challenging the premise that momentum is conserved, speculating that wave-particle duality might provide some legal loop-hole...

As usual, I'm tight on time to bend down to the, uhm, "hoi-ploi", so perhaps you could excercise your ever unlimited patience here, and educt them on how there's no getting away with it.

In the pool-ball argument of course it is simple, no matter what the angle of the surface and ball motion one can always take the x and y components. This may help to understand exactly how, in any case, the change in the vehicle's momentum will always be opposite to the change in that of the ball. Therefore, if the ball is to never escape, a prolonged increase in the vehicle's (time-averaged) momentum would imply the same for the ball, in the same way instead of the opposite way. Although it's less simple to eviscerate the details for photons in quantum formalism, there is no escaping momentum conservation.

[Aireal]

Qfwfq
Thanks for pointing out that EM is basicly massless so a lot of energy is used for a given thrust when compaired to a normal reaction drive. That is one of the reasons why I felt it would be impracticle as an engine. Nor do I believe that the conversation momentum is being circumvented by a loophole of wave theory, such loopholes do not exist that I am aware of. Rather I am trying to find out how the thrust is achived without voilating conversation of momentum. This device was created by respectable scientists, so I doubt that the recordings of observed thrust are in error, or that the concept is compleatly crackpot. So the question remains, How this this effect occur?

One of the things I would like to check is to see if the is any red shifting of the EM radiation from this process to account for the lost energy of momentum. Without access to their research notes and a working model to use in testing, all I can do is conjecture as to its cause. I have a couple of ideas, some of them the math will drive me crazy trying to solve, others I can not test without experimentation.

So back to what I said in my first post. I think this might make a good research tool, or a device for grad students to test classroom theory on, but as an engine for space travel, not, it is too inefficent and impracticle.

[wade_b]

Another way to think of the em-drive....

Does a laser exhibit recoil?

Yet, it emits a large amount of directed energy from one side...

So - doesn't it stand to reason, that the emission of nearly massless particles from the magnetron into a tuned cavity, can impart mass to the far wall of the tuned cavity?

Newtonian physics don't apply here - again, does the laser exhibit a force vector in direct opposition to it's directed energy?

[modest]

Originally Posted by wade_b

Does a laser exhibit recoil?

Yes.

In stimulated emission an excited state atom emits a photon in the direction of an incident photon and returns to the ground state. The incident photon causes no recoil in the atom but the emitted photon causes a recoil opposite the incident photon. Figure 1.4 shows conservation of momentum in stimulated emission. We can see that although the total momentum of the system is zero the atom has a recoil opposite the incident photon.

Section I: Theoretical Principles

Is this what you were thinking?

~modest

[wade_b]

Originally Posted by modest

Yes.

Is this what you were thinking?

~modest

That is interesting but expected behavior on the particle level.

The real question: is that recoil measurable in the laser itself, and does it follow the rules of Newtonian physics?

I'm searching really for a good abstraction for the relativistic notion of an "open system" as applied to the emission device in the tuned cavity.

[wade_b]

This really does seem impossible, even when applying the Einstein Elevator and changing the reference frame.

If I understand correctly, the law of conservation of momentum still applies inside the elevator.

The model I studied shows a force vector being applied from outside the elevator; the perception of momentum inside the elevator would be 0.

So I'm not quite seeing how a force generated inside the elevator could translate into momentum measured outside of it?