Mike McCulloch's MiHsC Theory

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Mike McCulloch's theory is that the EmDrive thrust results from an internal pressure differential in Unruh Radiation.[1][2][3] See also: http://physicsfromtheedge.blogspot.co.uk/

Explanation of MiHsC Theory

Modification of inertia by a Hubble-scale Casimir effect, or MiHsC, is a theory developed by Mike McCulloch, a physicist at Plymouth University in Plymouth, England. The theory attempts to explain the cause of inertia, which is not completely explained by general and special relativity. MiHsC theory relies on Mach's Principle, which states that distant objects can influence inertial mass. But there is a boundary as to how far away the objects influencing inertia can be. This boundary is the point at which light (and therefore any information) will never be able to reach an object because either cosmic acceleration or its own acceleration outpaces the speed of light. Anything beyond this boundary (called the Hubble or Rindler event horizons respectively) is outside the observable universe and therefore can't affect the object at the center of the Rindler space. The Rindler event horizon is effectively the same as a black hole's event horizon. At a black hole's event horizon, quantum virtual particle pairs are occasionally separated by gravity resulting in particle emissions known as Hawking Radiation. For a Rindler horizon, a similar radiation is suspected to exist called Unruh radiation. MiHsC posits that Unruh radiation causes inertia. As a particle accelerates, the Rindler information horizon expands in the direction of acceleration, and contracts behind it. This results in a pressure differential in the Unruh radiation experienced by the accelerating object. More Unruh radiation hits the object from the direction of acceleration, resulting in the effect we observe as inertia. In addition to explaining the EmDrive's motion without violating Conservation of Momentum, MiHsC theory also notably resolves the observed discrepancies in galactic rotation and cosmological acceleration without the need for dark matter or dark energy.

Application to EmDrive

In the case of the EmDrive, the metal walls act as the event horizon for Unruh radiation created within the cavity. The wavelengths of this radiation are normally light-years across, but inside the EmDrive they are compressed to roughly the size of the EmDrive. Fewer Unruh waves will fit at the small end of the frustum, resulting in a pressure differential. Photons at the larger end therefore have higher inertial mass, and to conserve momentum in our reference frame, its frame, the cavity, must move towards the narrow end. The predicted thrust is, approximately, for a truncated cone cavity:

[math]F = {P \cdot Q \cdot L\over c} \times \left({1 \over Ds} - {1 \over Db}\right)[/math]

where c is the speed of light in the medium inside the cavity (m/s), P is input power (Watts), Q is the quality factor of the resonance, L is the cavity length (meters), Ds is the small end diameter (meters) and Db the big end diameter (meters).


Dr. McCulloch is still refining his theory with respect to the EmDrive and intends to publish additional papers which may include testable predictions for the EmDrive.

Predictions & Evidence

The derivation & comparisons with the data are given in this paper: Can the emdrive be explained by quantised inertia? and this one: Testing quantised inertia on the emdrive and in the Table below. The predictions are in rough agreement with the observed thrust of various experiments. Further testing is necessary to exclude environmental artifacts.

Experiment Observed Thrust (mN) Predicted Thrust (mN)
Shawyer 1 16 4.2
Shawyer 2 80-214 216
Cannae 9 5.3
NASA 1 0.091 0.22
NASA 2 0.05 0.53
NASA 3 0.05 0.1
NASA vac'm 0.03 0.7
Tajmar1 0.02 0.02

MiHsC predicts that thrust can be increased by increasing either the input power, Q factor, taper of the cone, or use of a dielectric. In addition, by changing the cavity's aspect ratio (and the input Rf frequency to maintain resonance) it should be possible to cause the Unruh radiation to better fit in the small end than the large. This would result in thrust in the opposite direction.