A physicist has found yet another reason why NASA's headline-grabbing "warp drive" propulsion system should be impossible and probably won't work: As currently constructed, the so-called EmDrive would be an "absurd" perpetual motion machine capable of solving the Earth's energy woes.
Already, the space propulsion system violates one of Newton's laws of physics, which is why the seeming success of one of its initial experiments was so exciting. Now, another physicist says that such a propulsion system would also defy established laws of thermodynamics, suggesting that the drive is little more than a pipe dream.
The EmDrive is being worked on by a group of scientists at NASA Eagleworks's advanced propulsion laboratory, led by a scientist named Harold White. It purports to work by using solar energy to create microwaves, which are then bounced around in a closed chamber to create thrust, without the use of any propellant whatsoever. By that logic, it'd then be possible for the drive to propel itself forever, as long as it has power.
Understandably, the group's earliest experiments got tons of buzz, simply because they couldn't explain why it appeared to work in violation of the conservation of momentum—that you can get an action (thrust) without a reaction (actually pushing against something, or using propellant). The team later suggested that the drive might work because of some unexplained quantum weirdness.
But now, Andrew Higgins, a mechanical engineering professor at McGill University in Montreal says that there's another problem with the EmDrive that demonstrates the "absurdity of such a device": It also violates the first law of thermodynamics, which says that energy cannot be created out of nothing.
"If it works, we solve all the world's energy problems"
Higgins says that the Eagleworks scientists have proposed what is essentially a perpetual motion machine, an invention that has remained elusive for, well, forever. Because of the way the drive works, it would very quickly accumulate kinetic energy. This energy would quickly exceed the energy input. That energy could then be collected by decelerating the spaceship, resulting in a net gain in energy.
To explain it, Higgins likens it to how a Prius works. The Prius uses the braking energy to help recharge its battery, which is why it gets such good gas mileage. But the Prius only recoups a tiny amount of the actual energy created by burning gasoline—the warp drive would, as presented, gain more energy back than was originally put in.
"I don't work in quantum physics, so I wasn't interested in their sidestepping of the momentum principle—but to have a device you send power into and generate more force out of it bugged me," Higgins, who published a paper debunking the feasibility of the drive on arXiv, told me. "Like a Prius, which collects energy when you brake it, you could do that with one of these propellantless drives to not just violate Newton, but to violate the conservation of energy, which is a more serious challenge."
"If it works, we solve all the world's energy problems," he added. "It sounds wonderful but it's probably not going to work."
"This result suggests that a source of free and infinite energy is already at our technological disposal"
NASA itself has tempered expectations on the EmDrive. Earlier this month, the agency told Space.com that the higher ups at the agency don't believe Eagleworks has made any sort of breakthrough yet. The Eagleworks laboratory is a small lab at Johnson Space Center, and its teams receive just a small fraction of NASA's overall funding.
"While conceptual research into novel propulsion methods by a team at NASA's Johnson Space Center in Houston has created headlines, this is a small effort that has not yet shown any tangible results," NASA officials told Space.com. "NASA is not working on 'warp drive' technology."
He says his paper didn't grow out of any sort of animosity, rather, he thinks it's important for physicists to ask questions and point out flaws in the work of others to more quickly get to the bottom of why certain experiments may or may not work.
"The fact that the EmDrive, or any other reactionless drive that has a thrust-to-power ratio greater than a photon-emitting device, would enable a perpetual motion machine of the first kind suggests that such a device cannot exist," he wrote. "This objection is not as easily explained away as the conservation of momentum objection to a reactionless drive, because this result suggests that a source of free and infinite energy is already at our technological disposal."
Higgins says he's glad there are people working on advanced propulsion techniques, and said that it's important to dream big. But he said it's just as important to debunk others' work.
"It's good to have people make spectacular claims and then think through where they're wrong—sometimes it's fun to sit there and find out where they went wrong or debunk it," he said. "I don't think it's damaging, as long as there's not too much money being spent on it."