To every action there is always opposed an equal reaction: or the mutual actions of two bodies upon each other are always equal, and directed to contrary parts.
In a closed system, the total momentum is constant.
Except for the EmDrive.
Those laws are Newton’s 3rd Law and his law of conservation of momentum. The EmDrive is an electromagnetic thruster that theoretically uses microwaves in a resonant cavity to produce thrust without propellant. Followers of Newton’s laws say it can’t exist. NASA thought it had created one but couldn’t really say how it happened. Mike McCulloch thinks he has an explanation for how it can really work.
Dr. McCulloch is a physicist at Plymouth University and author of Physics from the Edge and he’s truly at the edge or possible over it when it comes to the EmDrive. McCullough brings a new component into the EmDrive picture – the Unruh effect. Canadian physicist William Unruh theorized that accelerating bodies will observe the universe warming up as they accelerate, while stationary bodies won’t see it. That warming is Unruh radiation and McCulloch claims that it puts pressure on the accelerating body, causing inertia which would generate thrust. Thus, inside the EmDrive cone, the inertia of photons changes as they bounce back and forth. To conserve momentum, they generate thrust and the EmDrive works.
McCulloch even gives a real-life example of this – the so-called flyby anomaly. This refers to the small increase in momentum spacecraft experience when they fly past Earth on the way to their destinations. This has never been duplicated in the lab but McCulloch thinks adjustments to the wavelengths of Unruh radiation would accomplish this.
McCulloch also suggests two tests to prove his predictions. One would be to place a dielectric (electrical insulator) inside the cavity of the EmDrive which should increase the thrust. The second is to change the frequency of the Unruh radiation waves to simulate changes in the conical size of the EmDrive, creating an artificial “narrow end” for the thrust.
Should we address the next Nobel Prize for Physics to Dr. McCulloch c/o Plymouth University? Not so fast. Unruh radiation and the Unruh effect are theoretical. Claimed observations of the Unruh effect are so tiny that they don’t exceed the margin of error. There are other more conventional explanations for the flyby anomaly. McCulloch assumes that the speed of light must change inside the EmDrive.
McCulloch's proposed EmDrive explanation is an interesting idea. Will it hold up under tougher scrutiny? Can it be created in a lab? Are we ready to break Newton’s Third Law? Then what?