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

a bit more advanced

[User 956]

"The latest New Scientist has an article about an engine that exploits relativity and microwaves to generate thrust.

That sounds a bit more advanced than these two guys, who exploit explosives and a microwave to generate thrust.

Aditional Features

[celardore]

It also warms soup, and is great for reheating food.

attempt #2

[User 956]

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

Of course, his first effort was to create a drive that ran purely on improbability, but you could never be sure where you'd end up or even what species you'd be when you get there.

Re:attempt #2

[Jhon]

Heisenberg gets stopped by a cop for speeding.

"Do you have any idea how fast you were going?", asks the cop.

"No. But I know exactly where I am!"

Save New Scientist!

[exp(pi*sqrt(163))]

The complete and utter bogosity of this story has prompted Greg Egan to try to start a movement to save New Scientist. Anyway, check out this story.

Re:Forgetting some things?

[jonnyelectronic]

I think you're forgetting that it involves relativity, therefore doesn't need to make sense. Plus I seem to remember that conservation of momentum was a by product of that 4-vector thing, so maybe something funny happens. Maybe.

Oblig comment

[QuantumFTL]

"In this house we obey the Laws of Conservation of Momentum!"

Comment removed

[account_deleted]

Comment removed based on user account deletion

Re:'bout damn time I get my flying cars

[Azarael]

Joke well taken, but in all honesty the bigger joke is that we technically could have had flying cars already. You know what the problem is? the general public couldn't be trusted not to crash the things left and right. In no time there would be more flying lawsuits than cars.

Awesome!

[LewsKinslayer]

Now I can have what I've always dreamed of, a flying car with a Phantom game console running Duke Nuke'em Forever on HURD with Copland running in virtualization on a BitBoys Oy Glaze3D graphics system whose driver was programmed in Perl 6 running on top of Parrot!

I love it when dreams come true.

The aRocket post with paragraphs...

[Anonymous Coward]

Peter Fairbrother zenadsl6186 at zen.co.uk
Tue Sep 19 17:56:42 PDT 2006

Russell McMahon wrote:

As already noted on ARocket - it "*can't* work - but wouldn't it be nice if he was right, even though he's not :-(.

I don't know that a reactionless drive can't work - although I don't know how to build one :( - but I do know that this particular one doesn't work.

For those who haven't met the emdrive before - it's not your usual snake oil and mirrors type device - the inventor is highly capable and has convinced a number of substantial organisations, including the US Air Force, British Govt research granters and NASA to be cautiously interested. All of which just means that it's not yet obvious to all where the hole in his theory is.

Without having gone into it in detail, his math seems okay up to eq 6 (when he is quoting well-known math), but thereafter he veers into the realms of error and fantasy.

Eqation 7 is incorrect in so far as it purports to describe the total forces on the waveguide - while it does correctly describe the sum of the forces on the ends of the waveguide, it does not take into account the forces produced on the sides of the tapered waveguide.*

All by itself that is enough to blow the conclusions of the paper completely out of the water. It is simply wrong. It doesn't work. You can stop reading here.

Now we get into the rather more dubious portion of the paper.

Eq. 8 is also in error - it is based on the incorrect statement "...as the two forces Fg1 and Fg2 are dependent upon the velocities vg1 and vg2, the thrust T should be calculated according to Einsteins law of addition of velocities." - but the conclusion does not follow, and use of Einstein's equation is inappropriate. There is no real-world summing of velocities, it is a mathematical trick (and there is an error int the math too). The ends of the waveguide are stationary relative to each other.

That is an elementary schoolboy (or snake-oil salesman's) mistake.

There are several other obvious mistakes in the paper, and he frequently states as fact things that are unjustified and on occasion untrue. There are also parts of it which seem to be meaningless.

For example, this is also incorrect: "The second effect is that as the beam velocities are not directly dependent on any velocity of the waveguide, the beam and waveguide form an open system."

The conclusion does not follow.

This is actually very confused - I don't think he even knows what he is saying. Relativity theory does not (directly) come into it at all.

I stopped looking for more errors about here.

Snake oil or error?

There was some mention of licencing the technology, but as it is in the UK patenting it here would be impossible - it is, after all, a perpetual motion machine (or it would be if Q approached infinity, which there seems no theoretical reason to suppose impossible), and you cannot patent a perpetual motion machine in the UK.

Even if it worked.

The question of how he got a grant is still ... puzzling, but not totally unexpected. Grants are often assigned by managers and politicians rather than scientists or engineers.

To the DTI, NASA etc: Please can I have half his grant for pointing out his mistakes? I promise I will use it do space r+d. :)

*Of course if you want to consider the waveguide as two pieces, forces on the tapered walls do not affect the result - but the math in eq7 would be wrong if you are looking at it that way, eg the lambda-g1 and lambda_g2 figures are for the ends of the waveguide, not the middle.

I think he first went wrong in his mind here - in fig 2.4 there is a vertical line in the middle of the diagram, implying that he was looking at the waveguide as two pieces, rather than as two ends and a tapered middle. You can of course look at it in either way, but in his analysis (even before we get into the error-full "relativity" stuff) he is trying to do both at once, and that will and has lead to error.

--
Peter Fairbrother

--a different AC

This is complete bollocks

[LauraScudder]

By the way, this engine would violate conservation of momentum, and is thus incredibly dubious. On top of that, the "working" prototype was measured to generate an incredibly tiny force, a measurement which was given without error bars in the only numbers I've seen, so he's probably just measured his noise floor. It has never been published in a peer reviewed journal. Because of this article, John Baez has posted an open letter from Greg Egan to the editors of New Scientist, which includes gems like "I really was gobsmacked by the level of scientific illiteracy in the article".

In other words, reader beware. Crackpots abound.

Re:'bout damn time I get my flying cars

[Azarael]

It's a bit harder to drive your car into the side of a highrise buidling.

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.