The small anomalous acceleration of the emdrive (which is like a microwave oven built into a copper cone) towards its narrow end, may or may not be a real effect, but is proving to be a lot of fun to think about. I've written before about 'thinking in the context of a real experiment' and I think that is lacking in mainstream theoretical physics where people incessantly drop objects into imaginary black holes. Looking for new physics one must look for 'direct' observations that disagree with the old physics, and the emdrive is a great example of that, and one that has been reproduced in three different labs. It turns out (see 2 blogs ago) that MiHsC predicts an emdrive thrust of

F = PQ/f * ((1/w_big)-(1/w_small)) (1)

where P is power input, Q is the number of photon 'bounces' before they are absorbed, f is the input microwave frequency and w_big and w_small are the diameters of the big and small emdrive end plates. The important point is that this formula works quite well when compared with the data. Also, last night I worked out how to prove this formula from first principles so I'm now much happier about it. I've also tried replacing f with c/CavityLength=c/s, where c is the speed of light. This is because in the derivation the f is the frequency of Unruh radiation seen by the photons, and this is determined not by the microwave frequency (which is admittedly close), but by the cavity length which forces the microwave photons to change direction back and forth, and it is this that does the accelerating. This gives the similar formula

F = PQs/c * ((1/w_big)-(1/w_small)) (2)

Now, you may be saying 'for photons the rules are different', but ultimately, causes must be universal and photons do have inertial mass, since they carry momentum and if they have inertia, then according to MiHsC this is caused by Unruh radiation (which is more than just em radiation) and for the huge accelerations of these photons as they bounce between the ends of the cavity the Unruh waves are short enough to 'see' the cavity and be damped by its walls (as electrons move to cancel the field there). They will be more damped at the narrow end, meaning they will have less inertial mass at that narrow end. This means that, for each photon bounce, more mass is going from the narrow to wide end than the other way around, and so to balance the books the conservation of momentum demands a force towards the narrow end of a size as shown in Eq. 1 or Eq. 2. The best defence of all this is that it works quite well. For the results of Eq. 1 see two blogs back, and Eq. 2 predicts the following for the five experiments for which complete information is available (excluding the Chinese experiments whose geometry is unknown):

Experiment P Q s w_big w_small Observd Predictd

(see refs) W dl m m m (mN) (mN)

-------------------------------------------------------------------------------------------------------------

Shawyer (expt) 850 5900 0.156 0.16 0.11 16 7

Shawyer (demo) 1000 45000 0.345 0.28 0.17 147 123

Brady

*et al*. A 16.9 7320 0.23 0.25 0.165 0.09 0.19

Brady

*et al*. B 16.7 18100 0.23 0.25 0.165 0.05 0.47

Brady

*et al*. C 2.6 22000 0.23 0.25 0.165 0.06 0.09

More emdrive experiments are needed, but the reasonable agreement between MiHsC (last column) and the data (second to last column), except for the problematic 4th row, suggests that MiHsC can be applied to light in cavities, and this opens up a whole new area for testing. I have submitted a paper on this, so let's see what the reviewers say. Note: Thanks to Dr Jose Rodal and aero (NSF forum) for clarifying the emdrive geometry, which is crucial.

References

Brady, D.,

*et al*., 2014. Anomalous thrust production from an RF test device measured on a low-thrust torsion pendulum. Conference proceedings, see Table page 18. Link

Shawyer, R., 2008. Microwave propulsion - progress in the emdrive programme. See section 6, page 6. Link

McCulloch, M.E., 2013. Inertia from an asymmetric Casimir effect. EPL, 101, 59001. http://arxiv.org/abs/1302.2775

McCulloch, M.E., 2014. Physics from the Edge, published by World Scientific. Link