The controversial EM Drive might soon become a lot less controversial if a new hypothesis about how it works is confirmed.
According to a new study, published in AIP Advances, from researchers in Finland, the EM drive is not a true propeller-less engine, so it does not violate the third law of dynamics. The physicists suggest that the microwave photons injected in the engine pair up with out-of-phase photons present in the cavity, creating a disrupting interference between the two.
Waves interfere destructively when a wave’s valleys are perfectly aligned with another wave’s peaks. This might lead to the waves completely canceling each other out, but their energy still being propagated, creating an exhaust.
“Our work on the EM Drive is a side track for me from the study of general principles. From this perspective, the EM Drive must be an engine like any other,” co-author Arto Annila told IFLScience. “It takes in fuel as microwaves and dumps out something that will eventually end up into cold space like thermal waste. It is hard to see the vacuum, that is, the ultimate dump, but it is easy to think that it comprises photons in pairs without net electromagnetic field.”
The paper makes some bold claims about the cosmos as a whole. It suggests that the vacuum energy of the universe is just made out of these out-of-phase photons. Hence, when they form inside the engine, nothing seems to come out.
It's not just about fundamental physics, either; the shape of the engine also plays a role. The EM Drive is a truncated cone, and thanks to a magnetron it can apparently produce thrust in the order of 100 micronewtons (about the weight of a mosquito on Earth). NASA has allegedly been testing it for years, but the technology will soon undergo its first peer-reviewed test.
“The photons will bounce back and forth in the EM Drive's cavity, and invariably some, depending on the shape and other properties of the cavity, will end up propagating along the same path but having opposite phases,” continued Annila.
The researchers suggest how this could be tested in current models, which claim the possibility of taking humans to Mars in 70 days, as well as using this idea to construct different engines.
“The paired photon exhaust can in principle be detected by an interferometer, a similar device used to detect gravitational waves, but I reckon that measurement will be difficult,” added Annila. “Coming up with a better drive when having our proposal in mind will be an indication. The proof of pudding is in its eating.”