EmDrive

[trekkie_]

From my understanding, this is already a proven technology, even if we aren't entirely sure how it works.

With particles popping in and out of existence, they get trapped in the EM field, accelerated, and expelled as thrust.

But the quark with that, is does speed change the 'absorption' of particles? We don't really know this yet since its only been tested in a stationary mounted scenario, not along track in a vacuum or anything.

You'd think that the more space it covers in a given amount of time, the more particles that will get trapped into the EM fields in a given amount of time and the more material you could use to produce thrust.

But if the particle is stationary and you're moving at an incredible speed compared to it, you may not have the EM strength to capture the particle. So you may only be getting the particles that happen to pop into existence within the space of the EM field at a given moment in time.

But what I've never heard described about particles that pop in and out of existence, is if they're at an absolute speed of zero or if they're aligned with the rotation of the earth or the sun or anything else. If a particle were to pop into existence on earth, one would assume that it would have some predefined speed and direction before gravity can act on it, or no speed and direction at all.....which compared to the perspective of a person on rotating earth, would still appear to be moving the opposite direction of rotation at well over 1000mph.

Either way, it's going to take more power to capture more particles the faster you go otherwise they will just shoot through your EM field. Widening the EM field instead of just making it stronger could ensure a larger area to trap more particles.

Edited September 1, 2014 by trekkie_

[Jesrad]

But the quark with that, is does speed change the 'absorption' of particles?

Doesn't seem to, in the case of Hawking Radiation.

[Z-Man]

It has to be pointed out that the 'particles popping in and out of existence' picture is about as suitable for reasoning about quantum vacuum effects as the 'series of tubes' picture is for the Internet. With that in mind:

But what I've never heard described about particles that pop in and out of existence, is if they're at an absolute speed of zero or if they're aligned with the rotation of the earth or the sun or anything else.

They are most certainly not aligned with any large object that just happens to be near on astronomical scales. The QED vacuum is Lorentz invariant. Any hypothetical device using the QED vacuum as propulsion "medium" will have to have a trust/power ratio that is independent of the current velocity.

A bit more detail on the virtual particles: The virtual particles always pop in in groups, the most frequent one being electron, positron and photon. Total momentum of the group is always zero, as is total energy (1). That is true wherever they appear and from whatever frame of reference you measure their effects. The momenta of the individual particles that contribute to your process depend on your process: the higher your general energy scale, the higher the momenta of the virtual particles you have to take into account. In this case, the energy scales are really, really low; the virtual particles will still mostly have relativistic momentum, though (2).

Note that I carefully avoid discussing speed/velocity. That is a property virtual particles simply do not have in any meaningful way. Very naively put, they are simply not around long enough to get two position measurements done that differ by more than the inherent quantum uncertainty of the measurements.

1: That is, of course, classically impossible. That is the reason why they have to vanish again before the universe notices something is amiss.

2: If you are violating classical laws to spirit an electron into existence, you may as well ask for a little more and get an electron with a lot of momentum.