The internet has been buzzing about published by a team of engineers at NASA claiming that they have built a device that creates thrust without propellant. There have been written about it, it鈥檚 spawned a zillion tweets, and I鈥檓 getting plenty of emails asking me about it.
Here鈥檚 the thing: I鈥檓 not convinced. I鈥檓 not saying it鈥檚 wrong, but I am saying it鈥檚 very, very likely to be some sort of measurement or experimental error.
I could write a lot about this, but instead I鈥檒l point you to three people who already have written excellent discussions on what鈥檚 going on here: John Baez on Google Plus (you should read both and ), my old friend , and my friend . All dissect this report, and align pretty well with what I鈥檓 thinking.
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The bottom line here is that what the team is proposing violates a very basic law of physics; all the forces inside the device appear to be balanced, yet a thrust is still generated. says that鈥檚 not possible. The only other way this device could possibly work is if it鈥檚 interacting with 鈥渧irtual particles鈥�, an interesting idea, but a highly speculative one 鈥� and the authors of the paper don鈥檛 discuss the physics. It鈥檚 important to note that the paper is not an official announcement of verified results; it鈥檚 more like a progress report.
I鈥檒l be clear. Of course science has overturned earlier notions of how the universe works. But sometimes, those rules are shown to be true so much and so often that when you come up with an idea that overthrows all of it, you鈥檇 better have iron-clad evidence of it.
This device doesn鈥檛 have that yet. The effect is incredibly small, and one thing we鈥檝e learned many times in history is that very small effects are usually due to something not being built or measured correctly. Steve rightly points out the faster-than-light neutrinos story, which were not real; the measurements were messed up by a faulty cable. And as Baez points out, this new device in question wasn鈥檛 even tested in a vacuum! That鈥檚 extremely important; assuming the measurements are real, the thrust seen could be due to air being warmed up and moving around.
I鈥檓 reminded very strongly of the Pioneer Anomaly. The twin Pioneer spacecraft were slowing down a teeny, tiny bit faster than expected as they sailed through space. A breathless media talked about a fifth force and other exotic explanations鈥� but it turned out to be far more prosaic. One part of the spacecraft was warmer than the other parts. It emitted infrared light, which carried away momentum, slowing the Pioneers down. It was hard to measure, and hard to determine, but once it was figured out it was clearly the right answer.
I suspect that鈥檚 what鈥檚 going on here. It would be fantastic to have a reactionless drive 鈥� something that gets its momentum from the virtual particles swimming into and out of existence in the quantum foam (or some other bizarre concept), and needs no propellant to generate thrust. But the more I want something to be true, the higher I set the bar of evidence to make sure I don鈥檛 get fooled. And if you want to invent new physics, or overthrow the law of conservation of angular momentum, that bar is very, very high. I don鈥檛 think this device has yet cleared it.
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Phil Plait writes Slate鈥檚 Bad Astronomy blog and is an astronomer, public speaker, science evangeliser and author of
