Categories: AstronomyPhysics

Don’t Be Surprised if EmDrive Experiments Never Work

Every few years the “EmDrive”, a proposed method of generating rocket thrust without any exhaust, hits the news. Each time, everyone asks: could this be it? Could this be the technological leap to revolutionize spaceflight?

Don’t hold your breath.

Here’s the basic idea behind the EmDrive. You take a chamber with a funky shape (usually narrower on one end than the other). You let a bunch of microwave radiation bounce around inside it. Accordingly to some – ahemcontroversial experiments, the device begins to move, with no emission from the drive at all. This runs counter to the usual rocket setup, which requires the expulsion of a propellent to push a spacecraft around.

Proponents of the EmDrive claim that it represents a revolution in physics and technology, a great leap for mankind that frees us from the shackles of…well, needing a propellent. Sure, the claimed thrust is incredibly tiny – not even enough to push a piece of paper – but anything other than 0 would be a big deal.

Big deal indeed. Assuming that the EmDrive works as advertised, it completely violates known physics. And not just in a small way – it breaks one of the most important, fundamental, cornerstone aspects of physics: conservation of momentum.

Things can’t just start moving on their own. According to literally everything we know about physics, the EmDrive can’t just go all by itself. It has to push something out in the opposite direction, or react to something else, in order to generate thrust.

Momentum conservation isn’t just a cool idea. It underscores almost the entirety of modern physics. Everything from quantum field theory to general relativity are really just expressions of conservation of momentum in specialized contexts. Conservation of momentum has been experimentally confirmed countless times in everything from high-energy particle colliders to the expansion of the universe itself.

Yeah, sure, momentum conservation could be broken in a new, exotic case that we haven’t encountered before. But it’s unlikely to show up as a tiny thrust in an EmDrive, where the observed thrust is so small that there many other, more plausible, explanations: microwave leakage, reactions with the Earth’s magnetic field, miscalibration, etc.

We may someday find that we need to update our understanding of momentum conservation. But not today.

Paul M. Sutter

Astrophysicist, Author, Host |

Recent Posts

A map of River Beds on Titan for Dragonfly to Explore

Explorers either have the benefit of having maps or the burden of creating them.  Similarly,…

13 hours ago

I Could Look at James Webb Unboxing Pictures all Day

Crews at the Guyanese Space Center recently "unboxed" the James Webb Space Telescope and are…

18 hours ago

Uh oh, one of Lucy’s Solar Arrays Hasn’t Latched Properly

As we’re fond of saying here at UT, space exploration is hard. Many things can…

24 hours ago

Meteorites Found With Little Pieces of Other Stars

When Carl Sagan said, “We are all made of star stuff,” he didn’t just mean…

1 day ago

There are 6×10^80 Bits of Information in the Observable Universe

A new study based on Information Theory has produced the first estimate on just how…

2 days ago

The Large Magellanic Cloud Stole one of its Globular Clusters

Astronomers have known for years that galaxies are cannibalistic. Massive galaxies like our own Milky…

2 days ago