What is the EM Drive? And Does it Really Work?

hello and Scott Manley here and today I would like to talk to you about to the emdrive yes it's that a copper can which has been somehow making science writers get very excited and talk about flying to the moon in a few hours our to Mars any week or so so let's rewind things a little let's actually talk about where the emdrive started so originally it was invented by a guy called Roger Shire in 1999 and the idea is that it would generate thrust purely from electricity no reaction mass needed which would of course be fantastic for spacecraft it would mean that you wouldn't have to carry around that very heavy reaction mass however it's not so good for people that like physics because this does kind of break the laws of physics interestingly another guy called Guido feta came up with a variation on this again uses electrical power to generate thrust he called his the canny drive which was supposedly some reference to Hannibal crossing the Alps but more likely it's a reference to Scotty from Star Trek who was often heard to say you can't change the laws of physics captain it's back in the news because an academic paper on the experiment has finally passed peer review and been studied so if you're not an academia you may not actually know what this means when you write up your experiment into a paper form you will then send it to the publisher who will then pass it out to people that are supposed to know what they're talking about people that are experts in the field and these people will read the paper they will perhaps find problems with the paper and they will send this feedback back and then of course you are supposed to address these problems and then send a revised version and eventually either the paper gets published or it gets rejected so having it passed through a peer-review process is generally a good sign it means that it's no longer on the fringes of crazy crank you know physics however doesn't really mean that they prove that things work I mean to start with the people that are reviewing these papers this is an they haven't gone out and done their own version of the experiment to verify what they've done is they've kind of looked at what's been written up and said well you know do you have a control experiment or did you test this did you tell you know we'd like you to cite this particular paper it doesn't really necessarily prove this work it works in any wave and I personally still believe there's highly likely that there we will they will find a flaw the reviewers of the paper they looked through it and that they've clearly had a lot of feedback because there's a whole section where the authors of the paper try to address possible modes for operation which are possible things that were not accounted for and then provide some justification for why they were accounted for and we perhaps more on that later let's talk about how it's supposed to work so it's actually called a resonant cavity electromagnetic thruster what it is is you have a sealed space and you inject microwaves at a specific frequency and they bounce around in all sorts of directions and when you generally have sealed spaces you can have the walls at just the right distance so it resonates at particular frequencies hence the resonance this is useful because it means that the microwaves can bounce back and forth several times and you see they hang around longer which is a good thing so in the case of the emdrive you're supposed to pump in the microwaves and somehow you feel a force in one direction so the emdrive is different from many other resonant cavities in that the walls are not all parallel you have a parallel front and rear wall and then it's a conical shape a frustum is the technical term so it is narrower one end than it is at the other end and the inventor claims that this is essentially a waveguide and the narrower waveguide at one end means that the group velocity of the waves is lower and therefore the momentum is lower so the reflection at one end is reflecting less momentum than the other end which is wider and therefore has higher group velocity and therefore higher mentum so you should feel a thrust in one direction that's the that's the claim and it's not just the Eagle Works team that has built it three at least three teams I've seen have built this and done experiments on it perhaps most high-profile was a team in China led by someone called professor yang they built a system and they they ran it they rode up a paper on it they claim to have measured thrust but later they retracted that paper after they figured out that they were getting induced thrust I believe through cables any thrust that was left over was below the level that they would be able to measure with their apparatus there's another team in Germany layer led by a guy called Martin Taj Maher times my I probably mispronounced his name and they claim to have seen thrust and I've also heard somewhere that they may have retracted that claim but I couldn't find that on the internet so people in the comments please you know citations would be good but yeah the one we're really talking about is the NASA team Eagle works team who kinda like to do stuff out in the fringes like warp drive there's another thing they've looked at so the nice thing about NASA of course is that it's in the business of spaceflight it knows it has the hardware sitting around it's like oh do you mind if we use your vacuum team chamber and torsion balance you know there nobody else is using them right now so the team were able to exploit this and it was a pretty cheap thing I mean they literally built their emdrive in their dining room so they took their device and put it on a torsion balance which is a device which measures very small forces by rotation you have it hanging from a very thin cable and the twisting of the cable provides the spring that pushes your scales back torsion balances were used for the original Cavendish measurement of the constant of gravitation I believe so there there's a long history of them being used to measure very very small and weak forces the original test campaign was carried out in an atmosphere and that led to many criticisms because of course the atmosphere could be generating convective forces and things like that so instead they eventually managed to get at vacuum capable microwave generating hardware put it inside a vacuum chamber and the well that's what this paper is about in this current set of results they claim that they observe a small force in one direction when they turn on the device they also say that when the power is increased the amount of force observed increases and flipping the device to point it in the opposite direction generates force in the opposite direction the magnitude of this force is 1.2 micro Newton's per watt and this is important because that is significantly higher than what you would expect from photon thrust so there is actually a real device which generates thrust purely through electricity is called a photon thrust or what you're really doing is you're generating light and you're shooting it out in one direction and it generates recoil in the other direction because photons while they are massless they carry momentum the amount of energy required is pretty staggering you need 300 megawatts for one Newton of force and all the upside of photon rocket is that it does have the best possible specific impulse of the speed of light you can't get any faster than that this actually has been observed in many systems solar sails actually make use of it but interestingly the pioneer anomaly is commonly cited by emdrive advocates as an example of new physics where the pioneer probe was experience an extra force pushing it back towards the solar system that was because of the radioisotope thermoelectric generator being on one side of the spacecraft and therefore the photons the thermal photons coming off of the radiators were preferentially going off in one direction and producing a thrust in the other direction so be under no illusion that pioneer 10 anomaly is not new physics it is photon thrust physics which is well understood so coming back yes the emdrive appears to generate more thrust than this based upon the experiments but yeah I'm a little skeptical because hey I'm a physicist ice spent a long time studying physics and I'm not about to have them change physics out from underneath me having dark energy come in that really messed up my view of the universe look the emdrive fundamentally has this problem with conservation of momentum that you know you really don't want to break that and the proponents the advocates of the drive say well maybe it's generating thrust by coupling to the quantum vacuum maybe is pushing against quantum vacuum virtual particles that's their exact phrase and I believe that John Byers an expert in quantum vacuum pretty much called this claim bool reactional drives are just not things you want to have around you know there's a quote on atomic rockets friends don't let friends used reaction lists drives because they just brake too much physics to be seen if you have a reaction let's drive that works by generating force when you put electricity into it without recoil then hey you end up being able to do things like generate perpetual motion machines and nothing freaks physicists out more than claiming you have a perpetual motion machine or claiming that you are getting overall unity out of your system the way this works is that Newton's law says that the amount of work done by a system is equal to the force times the velocity so as the emdrive system would accelerate the amount of energy that it is putting into the system in terms of kinetic energy would increase but the amount of electrical energy it's generating would stay the same so eventually it reached some velocity where the amount of kinetic energy is getting out is greater than the amount of electrical energy it's putting in so you can just build a wheel with a bunch of e/m drives around the outside to drive that up to the critical speed and then it would go faster and faster and you could just tap off that energy and get free energy back that is just something that physicists do not like so the emdrive proponents they say well maybe it generates less thrust as it goes faster and that then runs into problems with relativity because relativity of course says that velocity is measured relative the observer so different observers would see the emdrive at different speeds but they would somehow measure it generating it would somehow accelerate differently depending upon the observer that would of course cause all sorts of problems to special relativity in special relativity has been pretty well established to work pretty darn well they've also said that hey maybe it's better at hovering because you're basically staying still no change in velocity you know anti-gravity that would be fantastic but that then runs into general relativity general relativity says if you're standing inside a closed room and you can't see outside it and you're feeling a force of 9.8 m/s poun you to the ground you cannot tell the difference between that being inside a rocket accelerating at that speed or standing on the surface of a planet getting cooled down at that speed this is like a fundamental part of a formulation of general relativity which has been pretty well tested so having it hover that yet that would again all cause issues hovering is the same as accelerating so obviously I'm not convinced but I'm prepared to wait for more data however the device as demonstrated even if it does work is still not that useful and to be fair they did say that they had not optimized their device for performance they're getting 1.2 micronewtons per what and I believe the best numbers I've seen from a nuclear reactor in space has been 200 watts per kilogram so that works out to about 20 meters per second of acceleration per day this device it's not going to be able to carry you to the moon in a few hours or to Mars at least at this performance level it works out a bit seven kilometers per second per year ion engines are way better at this level first start they're a lot lighter and they can work you know they work with fuel you have to get up to like 30 40 50 kilometers per second of Delta V and missions that are lasting 5 10 years before an e/m drive becomes even slightly compared and there aren't there aren't any missions with those requirements right now so I don't see that displacing ion thrusters unless they could make it work better and certainly not causing things to fly or getting you to Mars very quickly yeah maybe they can optimize as I said they they literally built this in a dining room if you look at resonant cavities you know electromagnetic resonant cavities that are actually used in science for good science these things are built to incredibly high tolerances they are typically machined from a solid block of copper and the end plates are bolted on with really heavy tight bolts so this thing does not change shape at all because they want to get the highest quality factor out of the device the thing that was built I believe I heard one scientist describe it as something my mother-in-law might hang off a tree to scare away wild animals and they think this is somehow you're gonna change the laws of physics look at this stage it is little more than a curiosity I don't believe it's going to change the laws of physics but obviously I'm a skeptic the paper does have flaws as well that been identified for example one of the author's claims that there are no analytical solutions for standing waves inside a frustum of that design and I believe that Greg Egan scientist a science fiction author he presented analytical solutions for this you know he's not just an author he's a mathematical physicist so he knows his stuff there's other problems with the paper and miu they'll hopefully be follow-up work it'd be really nice to see them actually build a control device on a copper cylinder which had doesn't have a taper and then put that on the device on the the balance to see if it generates thrust but yeah at this point I really think the experimental error is most likely thing if they do fly it in space then and they do generate thrust no one would be more pleased than me it would not only mean that everything I'd learned was wrong but it would actually mean that we could fly spaceships around and stuff like that at some point I fully expect to see action and physics going back to boring old physics with no flying cars then again not having flying cars is probably a good thing given the skills of some of the drivers around here I'm Scott Manley fly safe you

Channel: Scott Manley

Views: 865,486

Rating: 4.8621144 out of 5

Keywords: emdrive, pseudoscience, space, science, star trek, science fiction, nasa, warp drive

Id: JGcvxg7jJTs

Length: 16min 9sec (969 seconds)

Published: Sun Nov 20 2016

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[u/rfmwguy-]

Entertaining and knowledgeable guy, taking the safe route but he didn't ridicule the researchers.

[u/Kilo1]

I've been following the EM drive on and off for a while now, could somebody please tell me whether it actually works, have they made ANY thrust at all with these?

[u/Anothergen]

Good good summary of it, particularly why we feel it shouldn't work. A pretty fair account of things as they stand.

Oddly enough though, he has the same mistake as /u/crackpot_killer towards the end where he claims that Scott Egan has done an analytical solution to a their design, they they are actually different shapes. Again, whilst there might be analytical solutions to the problem, it's strange that people are going for different cases as their reference.

[u/squirt_aka]

A lot of talk and a lot of firmly taken positions. Let us remember that the scientific method relies on validating one's theories through testing...

Let the results speak for themselves...

As it stands, the device has been shown to work in multiple independent experiments at 1.2 mN / KW. Significant.

[u/IslandPlaya]

He concludes that what is observed is measurement error. It just takes him a long time to get around to it.

[u/crazymanaus]

Wow this guy is no negative.. jeez let's all just stop inventing stuff because we don't need it.. what a moron.