Thrust from Microwaves - The Relativity Drive

dfenstrate writes "The latest New Scientist has an article about an engine that exploits relativity and microwaves to generate thrust. There is a working prototype." From the article: "Roger Shawyer has developed an engine with no moving parts that he believes can replace rockets and make trains, planes and automobiles obsolete ... The device that has sparked their interest is an engine that generates thrust purely from electromagnetic radiation — microwaves to be precise — by exploiting the strange properties of relativity. It has no moving parts, and releases no exhaust or noxious emissions. Potentially, it could pack the punch of a rocket in a box the size of a suitcase. It could one day replace the engines on almost any spacecraft. More advanced versions might allow cars to lift from the ground and hover."

Comments

Re:Erm... I don't get it.

[RsG]

Because that would be a photon drive. And we already know how well those work - the amount of energy you need to input to get even a tiny amount of thrust out of them is astronomical (pun not intended). We've had the basic idea of light propulsion for at least fifty years, and it's been a major cornerstone of hard science fiction. But it just isn't workable with modern power generation.

You could describe either a photon drive, or it's passive counterpart, the light sail, as a "relativity drive", since they too operate on the oddities of conservation of momentum as it applies to light. Doesn't mean we're going to be using them in lieu of rockets anytime in the next few centuries.

Either this guy has found a revolutionary new way to build a photon drive (and I'm more than a little skeptical), or else the device doesn't actually work. I'm more optimistic about this than I am about the usual lot of crackpot science, since from TFA it sounds like this guy is applying good scientific procedures to his work (documenting, trying to get outside review), but I'm not exactly holding my breath.

Re:Slashdot - where science makes no sense (TM)

[MrSteveSD]

It was a really bad article. It was clearly a dodgy claim and you would think they would have an expert in the area totally vet the article, but alas no.

There are some other worrying things in the article. For example, the author says...

What of the impact of such a device? On my journey home I have plenty of time to speculate. No need for wheels, no friction.

Yet it is precisely the friction between the wheels and road which make a car go forward. Friction with the car wheels is not bad, you need it. Friction with the air is bad, but not the wheels.

If I had do the EM Drive story, a story which sounds highly suspect, I would have looked at some critiques of similar schemes. Within a few minutes of searching I found similar "Reaction-less Drive" schemes which all turned out to be Oscillation drives. It's the same phenomena as when you move across the room in a swivel chair (without touching the floor) by shifting your body-weight around. When you do that you are exploiting the non-linear nature of friction between surfaces. A similar thing can happen with these reaction-less drives interacting with air, water or other surfaces. So it's quite possible that a prototype drive would appear to work. So I would have asked for some kind of proof that this was not an oscillation drive.

Another issue is that it's not clear that this Em Drive prototype has been tested in a vacuum. In one of the other articles on it, it says that the thrust only reaches the maximum after a few seconds. Now that sounds much more like a mechanical oscillation effect (building up to maximum amplitude) than a photon/microwave effect.

Some of what I have said here is re-posted from a discussion I had on the Elmurst Solutions Science forums. (http://www.elmhurstsolutions.co.uk/cgi-bin/yabb2/ YaBB.pl?num=1157719780/0)

Easy to test, no satellite needed

[sehlat]

Easy to test: no satellite needeed. From Jerry Pournelle's web site:

TESTS If anyone does have a candidate device for producing reactionless acceleration -- that is, linear acceleration without throwing mass overboard and without reacting with a medium such as air or water -- the first test is to suspend it on two wires attached so that the plane of the two wires is normal to the direction of thrust-- that is, make a swing and put your gadget on it facing in the normal direction of travel of the swing. Now turn it on. If it will hang non-vertically, get interested. Now cover it with a plastic garbage bag and see if it will still hang non-vertically. If it will still do so, turn it off, and if it settles to a vertical angle, and you can do this repeatedly, and it hasn't lost any mass during the experiments, call your local physics professor. Or call me. I'll take care of notifying the Swedish Academy. But until it will do that, I don't need to look at it...

Re:complete and utter nonsense

[exp(pi*sqrt(163))]

I'm starting to dispair over the state of science in this so called modern world when I see articles like this

It could be a lot worse. People could start claiming completely insane things like that we should replace scientific research in fields like biology and cosmology with the contents of ancient Middle Eastern scrolls. Then we'd really be in trouble.