Thrust from Microwaves - The Relativity Drive 567
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."
Forgetting some things? (Score:3, Insightful)
and
B) Conservation of Momentum
Re:Save New Scientist! (Score:5, Insightful)
It does seem rather bogus
His references include an undergrad level textbook on physics, as opposed to the usual slew of papers outlining new developments in the field. Undergrad physics books are geared towards undergrad courses... which is why you see things like: "assume no friction due to air" in trajectory problems. His second reference is Maxwell's treaty on electricity and magnetism... hardly a new work.
In short, odds are he picked up a textbook and started playing with simplified equations and figures he's made a "discovery" that no one else has noticed until now.... HUGE HUGE Kudos if it's true.... but the magic 8-ball's sayin "outcome not likely"
Is anyone else reminded... (Score:3, Insightful)
Comment removed (Score:5, Insightful)
Re:'bout damn time I get my flying cars (Score:5, Insightful)
The Rocket Monopolist Conspiracy! (Score:4, Insightful)
I hope his invention is better than his explanations for why he has no investors (I know, I know, it's not).
Re:Key points from TFA (Score:3, Insightful)
Now, admittedly, one is as much in violation of the laws of physics as the other. We have no theoretical basis for reactionless propulsion. In the case of two black boxes acting on each other without being physically connected, the laws of reaction still apply (ie, you can apply force to a maglev train and have it carry over to the rail, despite the fact they never come into contact with each other). I'm not sure how this hypothetical drive could hover without repelling the ground in some way.
Side note - as I mentioned in another post, we've known how to extract momentum from laser light for decades. Light sails and photon drives, both found in sci-fi and both supported by the laws of physics, use exactly that very principle. But the characteristics of these propulsion systems is nothing like what's described in TFA. Either this guy has found something new, or he's made a mistake. I would not give very good odds on the former, sadly.
Re:'bout damn time I get my flying cars (Score:3, Insightful)
TW
Re:Save New Scientist! (Score:3, Insightful)
Re:Erm... I don't get it. (Score:5, Insightful)
Assuming that part of TFA is true, then he's already way ahead of the usual "free energy" crowds.
Typically when somebody's claims violate the laws of physics, the usual challenge is for them to provide a repeatable experiment for others to test the theory in question with. This challenge is most often met with weaseling or silence. When such theories are tested from outside, they most often do not pan out (see the cold fusion experiments as an example).
If he's willing to get outside review already, then I at least will acknowledge that he is an honest crackpot rather than a snake oil salesmen. And it's always better to actually test the blue sky ideas than it is to dismiss them out of hand.
Re:'bout damn time I get my flying cars (Score:5, Insightful)
Re:'bout damn time I get my flying cars (Score:2, Insightful)
Re:Forgetting some things? (Score:5, Insightful)
It's possible that it's covered more accurately in his paper, I haven't got around to reading that yet, but TFA is certainly not the place to go for a serious treatment of this information.
Re:Slashdot - where science makes no sense (TM) (Score:3, Insightful)
Yeah. Get the prototype tested. Evidence beats theory any day, well almost.
Re:Key points from TFA (Score:4, Insightful)
He's claiming that the effect depends on the absolute velocity of the engine - a concept that has been meaningless ever since we did away with the coelestial aether and Maxwellian electrodynamics.
He's not using relativity, he's using the exact opposite.
Comment removed (Score:5, Insightful)
Re:Forgetting some things? (Score:5, Insightful)
But, he does claim to have a working prototype, and it will be interesting to see if anything does come of it. I've been known to be wrong in the past, after all.
Re:Not possible (Score:2, Insightful)
Re:'bout damn time I get my flying cars (Score:3, Insightful)
TW
Re:'bout damn time I get my flying cars (Score:3, Insightful)
A flying car would have to use more energy, hence fuel of course, and cost an insane amount of money to fly. Yes, there would be the inherent risks of flying cars etc, but VTOL eats up a good deal of fuel, unless you use standard fixed wing, which requires landing space. Rotary wing works, but is not as efficent as fixed wing at speed.
I would say it comes down more to the costs of energy than liability. After all, many ppl have ultralites, and a guy near me commutes about 70 km every day across the Georgia Straight via personal helicopter. But then, he can afford it, he is a Neurosurgeon at a Vancouver hospital.
Re:journalist, at least, is totally clueless (Score:4, Insightful)
Some
"by mounting it on a sensitive balance, he has shown that it generates about 16 millinewtons of thrust, using 1 kilowatt of electrical power."
One of the many problems here is how incredibly easy it is to stuff up sensitive measurements. For example, I have seen electronic balances and other equipment read a lot more than 16mN in error due to em interference (could be the microwaves, could be slop-over RF, could be induction into the mains. Remember Cold Fusion? Did you know the neutron detectors they were using were incredibly sensitive to temperature? No? Nor did Pons and Fleischmann, unfortunately...
That actually works - kinda... (Score:5, Insightful)
That actually works. A little bit.
But it works MUCH BETTER if you just point the fan to the rear.
The fan sucks air from a lot of directions and ejects it in one direction, creating a net thrust (and reaction - backward - on the boat via the person holding the fan) and a net wind.
Diverting that wind to the rear via the sail produces somewhat more reaction forward on the boat via the sail and the mast than the reaction backward from the fan - IF the trim is good enough that the diverted wind ends up going backward rather than just off to the sides. Result: Slight net forward thrust on the boat.
But pointing the fan to the rear - using it as a jet - eliminates the inefficiencies of using the sail in this way, putting the fan's whole reaction into moving the boat forward.
Re:Forgetting some things? (Score:5, Insightful)
He then proceeds to derive a maximum speed this engine can attain, relative to this arbitrary stationary frame, to illustrate the consequences of this idea. He has, as far as I can see, recreated the ether in his attempt to justify the machine using relativity.
Re:Forgetting some things? (Score:2, Insightful)
Re:Is anyone else reminded... (Score:5, Insightful)
Re:It doesn't violate any laws of physics.... (Score:3, Insightful)
Plausible? Yes. But as the critique said, only to the extent that sending a particle beam in a specific direction will give you thrust. Which is both weak, quite well-known, and anything but what the inventor is claiming.
Now, just what the heck are you talking about with "weak thruster = strong levitator"? Thrust (force) is thrust, no matter if it's pointed down for levitation or not.
Okay, in my opinion, this statement is a big warning sign you should be more careful commenting about what obeys the laws of physics and what doesn't.
Magnets do exchange particles when repelling eachother. They're called "exchange particles" (shock!), and to be specific, the exchange particle for the electromagnetic force is the photon. Even more specifically, virtual photons. They transfer momentum between magnets, both when repelling and attracting. (The latter case is of course harder to visualise, since there's no classical analogy. Nevertheless it's true.)
You also made another pointless distinction: Matter versus particles?
An analogy never ever proves anything in physics. At most you can use it to explain something. Your analogy doesn't do that, though. Nevertheless, conservation of momentum always holds. Or if you like, Newton's third law: For every action there's an equal and opposite reaction. You need two magnets to push against eachother, or they won't move.
And that's the gist of it: What does this thruster push against? The only thing it could ever "push against" are the created particles, and then only if they exit. Any momentum it gains is exactly equal (and opposite) to the momentum of the photons. No bouncing-around, cavity-wall pressure, relativity or other physical concepts can change that. Again, all the forces are equal and opposite: Every force in the engine must be balanced by another force in the engine.
The net effect can't be other than zero unless something else is moving. The only moving things here are the microwave photons, and unless they leave, their net force on the non-moving parts must be zero.
The inventor claims they are not leaving. He also claims that they exert unequal force within the cavity. This is just as wrong as claiming a gas could exert higher pressure on one end of a box (however shaped). In fact, a gas of photons act more like an ideal gas than a real gas does. The concept of photon gases is well studied and understood. (google for it, and while you're at it, you can read up on electron gases, neutron gases, neutrino gases, boson gases, and even entirely fictional substances like jellium.)
Any half-decent physicist, should immediately recognize that you can ignore whatever the purported internal working of the machine is. The thrust will always equal the momentum carried away by the particles leaving the engine, be they rocket exhaust, jet exhaust or a particle beam.
In this case it's entirely trivial. First, nothing is leaving, hence it's bullshit. And if the photons were to leave, the exact momentum is given by P/c (a formula stated in the critique), and the thrust can never be higher than that. (since that would represent creating photons with 100% efficiency, and assume none are absorbed on the way. Which is actually highly unlikely with microwaves, since they're a form of heat radiation, which most materials have quite
Experimental proof (Score:4, Insightful)
If there is a sustained, measurable deviation not explained by known physics, the guy will get a Nobel. That's 1.1 million dollars. If I was sure I had a winner for getting a million, I'd certainly be ready to invest into a vaccum chamber and build a prototype.
If we don't see this happen, then the drive doesn't work. End of story.
Re:Forgetting some things? (Score:3, Insightful)
Conservation of momentum still works in relativistic physics. If this invention is working at all then it's working for some reason the inventor doesn't know about.
Re:Forgetting some things? (Score:2, Insightful)
The system takes an energy input, and uses it to create motion and heat. It probably has something to do with that.
My guess is that this system requires one heck of an energy input, but it can be electrical energy, so you can get massively better efficiencies than you can get by burning liquid hydrogen.
Re:Save New Scientist! (Score:2, Insightful)
From the fact sheet (Score:3, Insightful)
Re:Save New Scientist! (Score:2, Insightful)
Re:Erm... I don't get it. (Score:3, Insightful)
Theory always alters to fit the observed facts. And every now and then, something pops out of the hat that changes everything.
It may be possible to be an honest crackpot by getting the equations wrong, and have that failure obvious to everyone else.. It's also possible to find something that works despite what the equations say..
That's called advancing science..
Wrong or right though, it'll be interesting to see how it pans out..
Re:Save New Scientist! (Score:4, Insightful)
Newton was wrong with his description of gravity. It was the best he could do to describe it, however in the end, its wrong. Could this be the same?
Almost certainly not. Newton's Laws were incomplete, not wrong. Newton's Laws are today seen as a mere special case of General Relativity, and yet we still use Newton's Laws on a day to day basis, and when some new theory of quantum gravity replaces GR, Newton's Laws will still be used on a day to day basis, because they're not wrong.
The "EMDrive", on the other hand, would throw out one of the most established principles of physics, Conservation of Momentum, a principle found in every coherent system of physics a human being has ever written (at least, those systems of physics meant to describe the universe we live in). And while it's conceivable that we really do need to rewrite the physics textbooks from scratch and add an error bar to Conservation of Momentum (then figure out why it's possible to break it in the first place), the article hardly constitutes a good reason to do so. Science isn't done by asking "Wouldn't it be great if X were possible?"
Read this last week... (Score:5, Insightful)
But what really got me fuming wasn't the author's total failure to notice that any of these were an issue - which I'll grant got me quite livid, being as bad as a football report from someone who doesn't know the offside rule. That it violates basic physics is bad, and should certainly have been seriously raised as an issue in the article, but if it works then that's just too bad for basic physics.
What upset me most of all was the lack of imagination. What if this thing works as advertised? Oh, then we can have planes that work a bit differently. Hovercars, perhaps. For the love of God, man, it's a reactionless drive! Strap a few to a nuclear reactor and go to Saturn and back in a week! A rocket that doesn't have to carry vast tanks of reaction mass around with it? The whole galaxy would open up!
I'll buy this week's New Scientist in the hope of some sort of grovelling apology for this appalling mess of an article. Or at least of a proper flaming of the editors in the letters pages. And then I think I'll see if I can't get a reliable supply of Scientific American - it's quite scarce in UK newsagents but always has some really solid science in it.
Re:Forgetting some things? (Score:3, Insightful)
The photon is the particle that carries momentum from one dipole to another so when the photons strike the surfaces they pass the momentum from the electrons in the syncrotron to the waveguide.
Due to the shape of the waveguide and the position of the entrypoint, the photons are more likely to hit the top.
Due to relativity, as the waveguide moves it does not strike the photons near the bottom more rapidly as they all move up with it.
Since the synchrotron will move with it, the electrons that the momentum was extracted from will move, so this device will not convert fuel into thrust, but fuel into a difference in position. Hence using it for hover cars - For a given energy in the fuel and given gravitational potential, the craft would move a certain distance and no further.
Problems exist like heating of the waveguide and generation of an ever increasing dipole and are apparently yet to be conquered. I don't expect the dipole problem to be conquered as I believe that will turn out to be the manifestation of the displacement limit.
If.... (Score:2, Insightful)
Some simple questions (Score:2, Insightful)
Judging by the drawing, it seems that a lot of microwaves are released into a chamber which they bounce around in, only that one wall is less bouncy than the other walls (i.e. flat and nonreflective) so more of them hit this wall.
My questions are:
- Why can't this be replicated organically, by putting a herd of mice into a room with one hard broad end and the rest padded material, so that most of the mice will exert most force on the broad end?
- Why can't it be replicated with sound waves?
- Why can't it be replicated with photons?
- Why can't it be replicated with a tank of water? (hard jagged wall on one end, rounded on all others, create motion in the water)
- Is the thought behind it that microwaves DO exert force when they hit something, but DO NOT exert backwards force on their point of release? In that case fair enough - sound waves would probably be out - but what about thermal energy? Couldn't you put a match in a room where every wall but one is mirrored and achieve the same effect?
- If the concept is so simple, surely it should have been discussed even in fairly simple textbooks? Basically, if you have a system with a source that generates waves with momentum without itself being subject to the momentum, what happens if you place it inside a box on a trolley and most of the waves are absorbed by one side?
Re:Aditional Features (Score:2, Insightful)
Only if the soup was warm at some time in the past.
Re:Save New Scientist! (Score:3, Insightful)
Re:Key points from TFA (Score:2, Insightful)
Gravitation and acceleration are identical, sure. But no energy is used until work is done, and work isn't done until something accelerates. To use this for hovering you balance potential force from this device (force which comes from the microwave transmitter, and would get converted to heat/velocity) with the potential force from gravity (from the attraction of the masses, and would get converted to heat/velocity) until they are equal. As long as the device doesn't accelerate in the direction of those two forces (relative, of course, to each other), no work is done and therefore no energy is used. (Well, except for heat/friction losses in the unit. For this to be practical those would have to be minimal.) So the only energy you need to input is the loss to heat, and you can keep a specific height against gravitational acceleration. (You are countering gravity's force, only.)
The article does make sense. Energy comes in from electricity, and is output in heat. Momentum does the same, with a directional bias. Total acceleration possible is no higher than the amount of energy input. He's just found a way to convert electrical energy to potential kinetic energy. There are losses, but the advantage is you can use it the same as potential kinetic energy from more normal sources. It just sounds odd because we are used to potential kinetic energy to be 'height above the ground'. There are clear inputs and outputs for all conserved quantities, in all cases.
Couldn't you just... (Score:3, Insightful)