3 ms·

Right, most people think of mass energy equivalence which is E=mc^2 but this only describes energy for a mass at rest, with a momentum of zero. The full equatio

Right, most people think of mass energy equivalence which is E=mc^2 but this only describes energy for a mass at rest, with a momentum of zero. The full equation relating energy to intrinsic mass and momentum is E^2=(pc)^2+(mc^2)^2 which is why smashing particles in a collider works. The momentum of two particles colliding at relativistic speeds is "conserved" in the classical sense but it is really converted to photons and massive particles, among other things. What I meant in my original post was that intuition regarding conservation of momentum in classical mechanics may not apply here because as long as the total energy of the system is conserved, the EM drive is free to convert energy to particles and motion because momentum will still be conserved between the drive and the new particles (which is how regular chemical propulsion works). The system experiences a net change in momentum of zero but what matters is that the total energy of the EM drive slowly falls as energy is converted to particles that provide propulsion.

pdonis 10y ago
> the EM drive is free to convert energy to particles and motion because momentum will still be conserved between the drive and the new particles I agree that this would conserve momentum if if were what was happening in the EmDrive. But all of the papers I have read insist that it is not what is happening; no particles are being ejected from the test device; there is no "rocket exhaust".
- akiselev 10y ago
  How do they measure the exhaust? With the EM field in the cavity I would imagine precisely measuring the photon emissions would be very difficult and the SNR might not be high enough to draw a conclusion. If the force is generated by new massive particles it would be headline news in experimental physics as the most efficient energy-mass converter ever made but if it's somehow generated by high energy photons, what are the chances they have adequate imaging to measure UV, X, and gamma rays, especially if the emissions have some sort of complex interference pattern? (although the theoretical maximum for force/power input is much lower with photon pressure than the results in this paper so it's still unlikely)
  - pdonis 10y ago
    > How do they measure the exhaust? I don't know that they are specifically looking for any exhaust other than RF emissions (which they say are not observed). If there were in fact an exhaust at some other frequency I don't know that it would be detected. (If such were present it would still be rather unexpected, in my view; there is nowhere near enough energy being pumped into the apparatus to start creating particle-antiparticle pairs, or to trigger any kind of process that would produce UV or X or gamma rays.)

pdonis 10y ago

> the EM drive is free to convert energy to particles and motion because momentum will still be conserved between the drive and the new particles I agree that this would conserve momentum if if were what was happening in the EmDrive. But all of the papers I have read insist that it is not what is happening; no particles are being ejected from the test device; there is no "rocket exhaust".

akiselev 10y ago
How do they measure the exhaust? With the EM field in the cavity I would imagine precisely measuring the photon emissions would be very difficult and the SNR might not be high enough to draw a conclusion. If the force is generated by new massive particles it would be headline news in experimental physics as the most efficient energy-mass converter ever made but if it's somehow generated by high energy photons, what are the chances they have adequate imaging to measure UV, X, and gamma rays, especially if the emissions have some sort of complex interference pattern? (although the theoretical maximum for force/power input is much lower with photon pressure than the results in this paper so it's still unlikely)
- pdonis 10y ago
  > How do they measure the exhaust? I don't know that they are specifically looking for any exhaust other than RF emissions (which they say are not observed). If there were in fact an exhaust at some other frequency I don't know that it would be detected. (If such were present it would still be rather unexpected, in my view; there is nowhere near enough energy being pumped into the apparatus to start creating particle-antiparticle pairs, or to trigger any kind of process that would produce UV or X or gamma rays.)