18 ms·

Curious Link Between the Fly-By Anomaly and the “Impossible” EmDrive Thruster

435 points by scrumper 11y ago

baltcode 11y ago
So is there any microwave radiation escaping the cone? If more of it escapes from one side than the other, won't the momentum of the escaping photons (radiation) be the reaction of the thrust produced? Why does it need special physics? I am probably missing something here, but what is it?
adekok 11y ago
The hard part for physicists to accept is that the theory requires the speed of light to change. It would be interesting to see how the theory behind the Unruh radiation works with "The quantum vacuum as the origin of the speed of light" (http://arxiv.org/abs/1302.6165# http://arxiv.org/abs/1302.6165#) Or also MOND (https://en.wikipedia.org/wiki/Modified_Newtonian_dynamics https://en.wikipedia.org/wiki/Modified_Newtonian_dynamics) Which also has predictions based on very low accelerations. It seems like the theories could be related. (says an ex Nuclear physicist who's now doing computers).
- daeken 11y ago
  > The hard part for physicists to accept is that the theory requires the speed of light to change. I'm a complete layman here, so I don't understand how the link you shared says that the speed of light is changing; it seems more like a change in the way we define the speed of light. Is that right? If the actual speed of light is to change, how is that possible? We've experimentally verified it up one side and down the other, so this seems like a huuuuuge discovery.
  - leblancfg 11y ago
    A large part of theoretical physics is getting to grips with the terminology -- not that you should imply that I'm in any way an expert. I think I'd go with the wording "it seems more like a change in the way we understand the speed of light". From that, it implies that, yes, its definition would change, but it's something much bigger! So yes, this seems like a huge discovery. Pretty much all of our understanding of relativity is based on the fact that c is, well, immutable. Changing the way we understand c means that we'll need to completely change the way we grok the last century of theoretical physics.
  - lisivka 11y ago
    Sagnac effect shows that speed of light is not constant and can be changed. [1] http://arxiv.org/pdf/physics/0609222.pdf http://arxiv.org/pdf/physics/0609222.pdf
  - empath75 11y ago
    So there's c, which is essentially a conversion factor between space and time, and also happens to be the speed at which massless particles move. If photons happen to not be massless, the speed of light might change, though 'c' wouldn't have to.
- awinter-py 11y ago
  doesn't refraction also require the speed of light to change? I'm guessing you mean something subtler.
  - danbruc 11y ago
    In case of refraction it is a macroscopic illusion. If you look closely enough, you will see photons traveling at the speed of light between atoms, getting absorbed by atoms and reemitted later. The macroscopic speed of light is just the result of absorption and emission probabilities and the microscopic geometry of the material. But there is another layer below but I am less sure about that, it may be (slightly) wrong. In quantum electro dynamics photon take, figuratively spoken, all possible paths from source to detector, also paths that require going slower and faster than the speed of light. All those possible paths interfere with each other and the net result is that the photon seems to move with the speed of light with very high probability. But really take that with a large grain of salt.
    - cperciva 11y ago
      If you look closely enough, you will see photons traveling at the speed of light between atoms, getting absorbed by atoms and reemitted later. That's a story we tell kids who ask too many awkward questions. If it were true we would see sharp changes in the observed speed of light at wavelengths depending on the absorption spectrum of the material in question. My understanding is that the real answer involves photons gaining inertia via coupling with particles in the material they are passing through (cf. Higgs) ... but I'm probably mangling that explanation horribly.
      - danbruc 11y ago
        I shouldn't have written »absorbed by atoms and reemitted later«, that is really a different thing, interacting with the atoms is better. The superposition of all possible paths and interactions results in a wave function that effectively travels slower than the speed of light.
      - wnoise 11y ago
rimunroe 11y ago
> Since then, something interesting has happened. Various teams around the world have begun to build their own versions of the EmDrive and put them through their paces. And to everyone’s surprise, they’ve begun to reproduce Shawyer’s results. The EmDrive, it seems, really does produce thrust. That's a misleading statement. I'm passingly familiar with a few of the experiments they're referring to, and none of them both produced significant results and were performed by groups which seemed un-suspect. I'm not aware of any peer reviewed paper on this stuff, and I don't personally know any non-laypeople who believe there is anything actually remarkable happening here. [edit] fixed some grammar
- rybosome 11y ago
  Fair points. Paul March of Eagleworks has claimed that a peer reviewed paper is under review for publishing currently, but who knows what the rigor of this publisher is. I badly, badly want this to be real, but I've accepted that it likely isn't.
- martinflack 11y ago
  The article mentions NASA tested it. Is that untrue or less true than it sounds? Genuinely curious.
  - TrevorJ 11y ago
    It's true - I think the general issue is that the forces produced are tiny, so it's hard to rule out some other effect coming into play and for the EM drive to work would mean overturning a decent amount of 'settled' physics understanding so the evidence needs to be pretty incontrovertible.
  - rybosome 11y ago
    Here is a good summary of the state of EmDrive testing (as of a year ago): https://www.reddit.com/comments/34cq1b/ https://www.reddit.com/comments/34cq1b/ TL;DR - a small, experimental division within NASA called Eagleworks tested the device. They are a very small group with very limited funding tasked with exploring unconventional theories around advanced propulsion. Their results were not published in a peer-reviewed journal, and there is considerable disagreement as to the validity of their experiment. They are continuing to refine their experiments, and the last update provided is that they intend to publish a peer-reviewed paper describing an experiment that successfully breached 100uN of thrust, which was the target needed for JPL and others to attempt to replicate their results.
drudru11 11y ago
This is fascinating stuff. It is also good to see more and more respectable names looking at this. Good things will come from that regardless of the overall outcome of the emdrive.
jimmcslim 11y ago
This is probably incredibly naive... but couldn't this all be put to bed by someone putting such a drive on a cubesat, lifting it into orbit, and seeing if it works under practical conditions? Maybe Hawking and Milner should be considering this for Starshot?
- losteric 11y ago
  Sure, the tricky part is finding funding
  - jimmcslim 11y ago
    Yuri Milner of Breakthrough Starshot should be a contender?
  - funkju 11y ago
    Any ideas on a ballpark of what it would cost?
    - losteric 11y ago
      It takes about $100k to get a cubesat into orbit, plus costs for building the sat itself (custom fabricating a miniaturized drive plus a suite of sensors). So not much, but the larger problem is we don't know how this drive works. Miniaturizing it could impact performance, as could other electronics in the satellite... given the unknowns it makes sense to let NASA do some more terrestrial due-diligence before going to space.
  - mabbo 11y ago
    How much funding? A Falcon 9 can lift 10,000 kg to LOE (or more). Let's say we could get a simple Em-drive and basic satellite and solar panel in for under 100kg. (We can do better, but let's start there). That's 1/100 of the load, so (in theory) we could maybe pay 1/100 of the $60m cost for a Falcon 9 lift, or $600,000. Half a million bucks plus some change, let's say. Edit: Less if we can get on board a previously-enjoyed rocket!
trhway 11y ago
> inertia must quantized at small accelerations. as everything does :) I think it is quantized at all levels, it just becomes noticeable at low levels as usually.
- outworlder 11y ago
  Everything seems to be limited by the precision our simulation is running on :)
deftnerd 11y ago
I think what I most enjoy about the possibility of the EmDrive is that it's similar to how things were often discovered during the "golden age" of science. Often, engineers or inventors would create something and then scientists would have to explain why it happened. In the last few generations, physicists and mathematicians would come up with theories and engineers would have to build equipment to test those theories. The EmDrive is one of the rare modern situations where someone has engineered a device that shouldn't work according to what we know and the scientists are having to come up with the explanation. Personally, solving a mystery is more exciting than purely intellectual theories and the EmDrive has created a very interesting mystery.
- rimunroe 11y ago
  I don't think really any scientists in the relevant fields actually think it's an interesting mystery. Lots of people make extraordinary claims about new theories or perpetual motion machines, but those claims frequently get reported on a disproportionately large amount. This is from the perspective of a former physicist who is grumpy about the endless torrent of "Einstein was wrong!"-type articles. I personally feel like it's risky to allow people to pin their hopes on something that's pretty obviously bunk, but I imagine it does have some benefits. I just don't think it's worth it.
  - maaku 11y ago
    > Lots of people make extraordinary claims about new theories or perpetual motion machines. Such claims don't often get replicated by multiple, independent labs, as is the case here.
    - moron4hire 11y ago
      And they seem to be basing their work on "Einstein was right, we just didn't fully understand what it meant."
    - crusso 11y ago
      I'm not up on every instance of "replication" -- but so far, the ones I've read about have been really shoddily performed. http://io9.gizmodo.com/no-german-scientists-have-not-confirmed-the-impossibl-1720573809/1720737686 http://io9.gizmodo.com/no-german-scientists-have-not-confirm... I'd love for this phenomenon to be real, but the Technology Review article did not present a realistic picture of the verification attempted to date.
russdill 11y ago
One of the main issues I see with the EmDrive in general is time invariance. And especially with the theory Mike McCulloch put forward. If photons cause this process for a positive change in momentum, the same process should happen in reverse with a negative change in momentum.
scrumper 11y ago
I'm curious to what degree Unruh radiation (and the resulting consequences this idea relies on) 'established physics'? By extension, I think this is the most interesting article I've seen to date on the EmDrive: it seems to have a basis in a fairly non-controversial result of GR, which in turn is something which nicely explains an otherwise bizarre physical phenomenon. And, to top it off, there are a number of falsifiable predictions which are within our ability to test. I'm interested in whether any of my assumptions are wrong.
- gaur 11y ago
  > I'm curious to what degree Unruh radiation (and the resulting consequences this idea relies on) 'established physics'? Most theorists think Hawking–Unruh radiation has to exist, I guess because the calculation is relatively straightforward. You just need special relativity and some basic field theory. Hawking–Unruh radiation has never been observed in a gravitational system, and doing so would be very difficult because it requires a truly enormous acceleration in order to produce a horizon with a temperature that is an appreciable fraction of 1 K. There are certain regimes in fluid mechanics where the mathematics governing the fluid looks like the mathematics governing relativity. Some people have produced phenomena in those systems that look like Hawking–Unruh radiation. Some people further claim that this demonstrates the existence of Hawking–Unruh radiation for gravitational systems, but I find that reasoning to be specious.
- tremon 11y ago
  This. Self-consistent theories and falsifiable predictions is how our understanding of the universe moves forward.
- pdonis 11y ago
  Unruh radiation itself is well established theoretically, though it has not been observed experimentally. However, the theory behind Unruh radiation says one thing that creates an obvious problem for anyone trying to use it to explain something like the EmDrive or the flyby anomaly: Unruh radiation is felt by objects that are undergoing proper acceleration. That is, they have to already be experiencing thrust. And according to the theory, the thrust they are experiencing has to be very, very small, so that the wavelength of the Unruh radiation is of the same order as the size of the observable universe. In the case of the flyby anomaly, the spacecraft passing by the Earth were in free-fall orbits--i.e., zero thrust. That means zero Unruh radiation. In the case of the EmDrive, technically the apparatus was feeling "thrust", in the sense that it was sitting on the surface of the Earth and therefore feeling weight. (Weight counts as "thrust" in this connection.) But the weight of the EmDrive apparatus is many orders of magnitude larger than the small accelerations that would be required for the Unruh radiation explanation to work--the wavelength of Unruh radiation associated with a 1 g acceleration is about one light-year, much, much smaller than the radius of the observable universe. So, bottom line, whether or not the EmDrive results themselves are valid (I am skeptical, but the whole thing is still being hashed out so it's too early to know for sure), it doesn't look to me like Unruh radiation can account for results of this sort. (Btw, as gaur pointed out, Unruh radiation actually is a result of quantum field theory in flat spacetime, i.e., not GR, as the article claimed.)
jaekwon 11y ago
How does this relate to the spinning black/white thing?
- gerbilly 11y ago
  The Black White thing is a Crookes Radiometer[1] and it rotates because of differential heating of the black and white sides of the plates interacting with air molecules to create a tiny air flow from the light side to the dark side of the plate. The device is under _partial_ vacuum. Under total vacuum, no rotation will occur, if the air pressure is too high, drag forces outpace the tiny thrust. https://en.wikipedia.org/wiki/Crookes_radiometer https://en.wikipedia.org/wiki/Crookes_radiometer
apsec112 11y ago
I don't think there's anything real here. McCulloch's papers on arXiv seem very confused. Eg., this paragraph: "In this scheme there is a minimum allowed acceleration which depends on a Hubble scale Θ, so, if Θ has increased in cosmic time, there should be a positive correlation between the anomalous centripetal acceleration seen in equivalent galaxies, and their distance from us, since the more distant ones are seen further back in time when, if the universe has indeed been expanding, Θ was smaller. The mass to light ratio (M/L) does seem to increase as we look further away. The M/L ratio of the Sun is 1 by definition, for nearby stars it is 2, for galaxies’ it is 50, for galaxy pairs it is 100 and for clusters it is 300. As an aside: equation (11) could be used to model inflation, since when Θ was small in the early universe the minimum acceleration is predicted to be larger." (http://arxiv.org/pdf/astro-ph/0612599v1.pdf http://arxiv.org/pdf/astro-ph/0612599v1.pdf) If an effect was stronger in the early universe, you'd expect to see a big correlation between the effect size in a galaxy, and that galaxy's redshift z. It wouldn't make any sense to say that "galaxies" have a ratio of 50, since there are galaxies at every redshift; many are nearby and have redshifts of almost zero, while the Ultra Deep Field galaxies have very large redshifts of up to ~10. If the number is really the same for "galaxies" in general, that means there's no distance dependence, but McCulloch doesn't seem to realize this. He seems to imply that nearby stars have a higher mass/luminosity ratio because of their distance compared to the Sun (?!), but the time-delay effect for anything in the Milky Way is negligible (< 0.0005% of the universe's age). In reality, nearby areas of space will have higher ratios than the Sun just because they contain many objects which, unlike the Sun, don't emit much light (red/brown/white dwarfs, gas and dust, etc.). Likewise, he seems to imply that "galaxy clusters" are farther away than "galaxies", but most galaxies are part of clusters, and we can observe both galaxies and galaxy clusters at both small and large redshifts.
- anentropic 11y ago
  Isn't he saying the 'standard' M/L ratio for galaxies is 50... and that by looking at a lot of galaxies at different distances you see a trend that the more distant ones are more >50 ?
th0ma5 11y ago
The sentiment I hear in this thread is like those that dismiss cold fusion. Sure, we can all make statements like "obviously, someone screwed up" but it is another thing entirely to have to the patience to simply cite the experiments that disprove the proposed effect. I don't know what to make of cold fusion, but I also know for a fact that neither do physicists, and instead of studying it, they're just simply saying because there is no theory it must not work. Same with this stuff. The one YouTube guy discovered the beaded-chain lifting effect, and then it had to be studied to find out what was going on. Obviously that was an easily reproduced experiment. So with this thing, we must find conclusively the unmeasured heat or ions or whatever and show a repeatable method for such mistakes. That is my opinion about science, of course I probably lost most scientists with my first sentence.
- greglindahl 11y ago
  Extraordinary claims require extraordinary proof, and the history of physics is littered with intentional fraudsters and sloppy experimentalists. Disproving every perpetual motion machine via experiment would take a lot of effort from scientists who don't want to do it. If you think those experiments should be done, then by all means do them.
  - th0ma5 11y ago
    Fair enough, but the problem with perpetual motion stuff is that no energy can be extracted or the time until the device stops is very long, not that they don't do what people claim that they do, which is work more or less perpetually. We need to find that kind of explanation for this supposed propulsion.
    - taneq 11y ago
      These devices work "more or less perpetually" the same way 1000.0f is "more or less infinite".
      - th0ma5 11y ago
PaulHoule 11y ago
People have been doing "research" into reactionless propulsion for a long time, such as this science fiction writer: http://rexresearch.com/dean/stine.htm http://rexresearch.com/dean/stine.htm
wmeredith 11y ago
> At very small accelerations, the wavelengths become so large they can no longer fit in the observable universe. When this happens, inertia can take only certain whole-wavelength values and so jumps from one value to the next. So the EmDrive glitches the universe size? This is hilarious.
- tremon 11y ago
  This was also my first reaction. I don't see how energy could be quantized with the inverse of the diameter of the observable universe. Could someone explain the current thinking around how energy quanta relate to the size of the universe, or rather why wavelengths larger than the universe are impossible? If the latter were true, I'd expect that an energy quantum corresponding to 0.99 * universe would be equally impossible as 1.01 * universe, and that only integer multiples of the corresponding frequency would be allowed (i.e. a harmonic series across the universe).
  - TheOtherHobbes 11y ago
    The corollary is that you'd be able to measure the size of the universe by observing quantisation effects. This seems unlikely, because - unless I've missed something obvious - you'd have to be able to set up a wave with a phase velocity > c.
- gcb0 11y ago
  yeah, i quit reading after the condescending intro ended with "In other words, inertia must quantized at small accelerations."
33a 11y ago
Man, this is the perfect news story for 4:20.
dnautics 11y ago
wonder if this inertial/acceleration effect is what is responsible for "dark matter" in the universe, i.e. galaxy-scale gravitational anomalies that don't agree with existing newtonian and GR models.
mcnamaratw 11y ago
The article leaves out all the numbers and so skips over one little problem. The momentum some people think they might have observed (if it's not experimental error) is compatible with what you'd get by using a microwave antenna as a thruster. Just ordinary radiation pressure, with the puzzle of how the radiation could be escaping the cavity. But the minimal measurement results I've seen are not compatible with the radiation pressure multiplied by some large factor for the Q of the cavity, which seems to be the claim from some. That really would violate our understanding of conservation of momentum, rather than violating our assumptions about where the momentum goes in this experiment. And that seems to be ruled out experimentally so far.
spottedquoll 11y ago
Extraordinary claims require extraordinary yada yada. A working reactionless drive isn't just extraordinary. It's utterly mind-boggling. The least interesting thing is that it's a free-energy device. It requires breaking spatial symmetry. If it works, it's not some edge-case theoretical law that's being broken. It's the geometry of space. https://en.wikipedia.org/wiki/Noether%27s_theorem https://en.wikipedia.org/wiki/Noether%27s_theorem
- api 11y ago
  Even if this works, reactionless drive would be my last hypothesis after exhausting all possible things it might be interacting with via some as-yet-unknown means: dark matter, nearby gravitational bodies, etc. The infinite energy device claim is easy enough to test. Since a working infinite energy device would be perverse, I'd predict that an EmDrive rigged up so as to produce infinite energy would fail to do so. Exactly how it fails to do so might tell us what's going on. Do the energy requirements rise with momentum (as they should in a sane universe), or do you pass a point at which the effect ceases, or does something truly wacky occur like space-time distortion in such a way as to cancel the effect? My reading of the McCullough hypothesis is that it's pushing against all matter in the universe at once, or some such thing, but that could be way off. I'm not a physicist.
ridgeguy 11y ago
For anybody who's interested, there's a NASA forum devoted to the EmDrive: http://forum.nasaspaceflight.com/index.php?topic=39772.1440 http://forum.nasaspaceflight.com/index.php?topic=39772.1440
Joof 11y ago
Inertia is quantized? Do we actually live inside a computer, because that's really weird. Physicists, help explain this outside of the universe uses a lookup table to approximate inertia.
api 11y ago
"Yes, they're still using warp drives to heat food..." - alien observers
est 11y ago
refuted by reddit https://www.reddit.com/r/EmDrive/comments/4fm2ac/the_curious_link_between_the_flyby_anomaly_and/ https://www.reddit.com/r/EmDrive/comments/4fm2ac/the_curious... > ... (McCulloch) proposes a constant term that modifies the acceleration corresponding to the inertial mass. He says torsion balance experiments can't detect it because torsion balance experiments measure differences in acceleration. But he's wrong because since it's a constant term he "predicts", it should manifest in the Eotvos parameter. Torsion balance experiments have gone well beyond the limit to detect this. But it's irrelevant because he completely misunderstands all the theory he bases this on.
alfiedotwtf 11y ago
Meta: Wow that drop down menu at the top is really annoying
323454 11y ago
Supposing this theory is true, how big an emdrive does it predict is needed to lift a reasonable payload, say 100kg?
- codeduck 11y ago
  The EmDrive would never be powerful enough to be a lifting engine; but what it would be is an incredibly useful engine once your mass is in orbit.
lunchTime42 11y ago
Is there a thing that allows for Science Annonymous?
aalexgabi 11y ago
Humans have learned a lot of things. However they still have to learn about the universe because there are non-naturally-observable physical phenomena and we have no evidence that we discovered them all. Edit: These so called "laws" are laws in our minds and things like EmDrive show us that our minds can expand forming new "laws".
askvictor 11y ago
I can't help but look at things like this as hacks in/of the simulation we are probably living in.
- josephagoss 11y ago
  Interestingly, that would imply we are possibly living in an imperfect simulation, one that hypothetically does not replicate the physics of a real non-simulated universe. If that is true, why? I can think of four possible reasons: 1) Is it because the simulation was designed in such a way that it leaves its inhabitants clues that reveal the true nature of the universe? This lets them figure out the truth once their society and knowledge become sufficiently advanced. 2) That it's impossible to simulate a real universe? This would imply any sufficiently advanced society will be able to detect that they do in fact live within a simulation. 3) That the creators made a mistake and it's not a fundamental limitation. It's simply an error made by whatever civilisation created this simulation, they messed something up. 4) That it's possible to create a perfect simulation, but for some reason they decided to make a simulation that used less resources and this brings errors or the need of hacks to get it working. Now we might be exploring these hacks.
- bitL 11y ago
  Looks that way. So now we are going to hunt for rounding errors of the Simuverse. Should be fun. It's likely simulation would be ended if we beat its purpose by hacking it. End of the world coming?
kempe 11y ago
Would be very interesting to see an actual implementation.
phkahler 11y ago
Photons must behave as if they have mass. From TFA: McCulloch’s theory could help to change that, although it is hardly a mainstream idea. It makes two challenging assumptions. The first is that photons have inertial mass. When I was taking college physics, there was a question on the exam about radiation pressure. I missed that day, so had no idea how to solve it. "a 5mW laser is reflected off a mirror (perpendicular) what is the force exerted on the mirror"? Later looking it up in the book there was a page on this and a derivation using electromagnetic theory. In the exam however, I decided to convert 1 second of laser energy to mass, bounce it off the mirror at speed=c, compute the force and change in momentum (over change in time which was 1s). I got the right answer of course. The logic is simple. If we can convert back and forth between matter and energy, any experimental setup must obey conservation of momentum and it's CG must not move. So a laser inside a closed spaceship would actually be tranfering mass (as energy) from one end to the other. The net effect must be the same as if that mass was moved any other way. I derived a general expression for radiation pressure after the exam and it's identical to the EM one from the book. Photons behave - and must behave - as if they have mass with a velocity of c. By the same reasoning, gravity must bend light rays, though I have not compared this prediction to that of relativity.

435 points by scrumper 11y ago

So is there any microwave radiation escaping the cone? If more of it escapes from one side than the other, won't the momentum of the escaping photons (radiation) be the reaction of the thrust produced? Why does it need special physics? I am probably missing something here, but what is it?

adekok 11y ago

The hard part for physicists to accept is that the theory requires the speed of light to change. It would be interesting to see how the theory behind the Unruh radiation works with "The quantum vacuum as the origin of the speed of light" (http://arxiv.org/abs/1302.6165# http://arxiv.org/abs/1302.6165#) Or also MOND (https://en.wikipedia.org/wiki/Modified_Newtonian_dynamics https://en.wikipedia.org/wiki/Modified_Newtonian_dynamics) Which also has predictions based on very low accelerations. It seems like the theories could be related. (says an ex Nuclear physicist who's now doing computers).

daeken 11y ago
> The hard part for physicists to accept is that the theory requires the speed of light to change. I'm a complete layman here, so I don't understand how the link you shared says that the speed of light is changing; it seems more like a change in the way we define the speed of light. Is that right? If the actual speed of light is to change, how is that possible? We've experimentally verified it up one side and down the other, so this seems like a huuuuuge discovery.
- leblancfg 11y ago
  A large part of theoretical physics is getting to grips with the terminology -- not that you should imply that I'm in any way an expert. I think I'd go with the wording "it seems more like a change in the way we understand the speed of light". From that, it implies that, yes, its definition would change, but it's something much bigger! So yes, this seems like a huge discovery. Pretty much all of our understanding of relativity is based on the fact that c is, well, immutable. Changing the way we understand c means that we'll need to completely change the way we grok the last century of theoretical physics.
- lisivka 11y ago
  Sagnac effect shows that speed of light is not constant and can be changed. [1] http://arxiv.org/pdf/physics/0609222.pdf http://arxiv.org/pdf/physics/0609222.pdf
- empath75 11y ago
  So there's c, which is essentially a conversion factor between space and time, and also happens to be the speed at which massless particles move. If photons happen to not be massless, the speed of light might change, though 'c' wouldn't have to.
awinter-py 11y ago
doesn't refraction also require the speed of light to change? I'm guessing you mean something subtler.
- danbruc 11y ago
  In case of refraction it is a macroscopic illusion. If you look closely enough, you will see photons traveling at the speed of light between atoms, getting absorbed by atoms and reemitted later. The macroscopic speed of light is just the result of absorption and emission probabilities and the microscopic geometry of the material. But there is another layer below but I am less sure about that, it may be (slightly) wrong. In quantum electro dynamics photon take, figuratively spoken, all possible paths from source to detector, also paths that require going slower and faster than the speed of light. All those possible paths interfere with each other and the net result is that the photon seems to move with the speed of light with very high probability. But really take that with a large grain of salt.
  - cperciva 11y ago
    If you look closely enough, you will see photons traveling at the speed of light between atoms, getting absorbed by atoms and reemitted later. That's a story we tell kids who ask too many awkward questions. If it were true we would see sharp changes in the observed speed of light at wavelengths depending on the absorption spectrum of the material in question. My understanding is that the real answer involves photons gaining inertia via coupling with particles in the material they are passing through (cf. Higgs) ... but I'm probably mangling that explanation horribly.
    - danbruc 11y ago
      I shouldn't have written »absorbed by atoms and reemitted later«, that is really a different thing, interacting with the atoms is better. The superposition of all possible paths and interactions results in a wave function that effectively travels slower than the speed of light.
    - wnoise 11y ago

rimunroe 11y ago

> Since then, something interesting has happened. Various teams around the world have begun to build their own versions of the EmDrive and put them through their paces. And to everyone’s surprise, they’ve begun to reproduce Shawyer’s results. The EmDrive, it seems, really does produce thrust. That's a misleading statement. I'm passingly familiar with a few of the experiments they're referring to, and none of them both produced significant results and were performed by groups which seemed un-suspect. I'm not aware of any peer reviewed paper on this stuff, and I don't personally know any non-laypeople who believe there is anything actually remarkable happening here. [edit] fixed some grammar

rybosome 11y ago
Fair points. Paul March of Eagleworks has claimed that a peer reviewed paper is under review for publishing currently, but who knows what the rigor of this publisher is. I badly, badly want this to be real, but I've accepted that it likely isn't.
martinflack 11y ago
The article mentions NASA tested it. Is that untrue or less true than it sounds? Genuinely curious.
- TrevorJ 11y ago
  It's true - I think the general issue is that the forces produced are tiny, so it's hard to rule out some other effect coming into play and for the EM drive to work would mean overturning a decent amount of 'settled' physics understanding so the evidence needs to be pretty incontrovertible.
- rybosome 11y ago
  Here is a good summary of the state of EmDrive testing (as of a year ago): https://www.reddit.com/comments/34cq1b/ https://www.reddit.com/comments/34cq1b/ TL;DR - a small, experimental division within NASA called Eagleworks tested the device. They are a very small group with very limited funding tasked with exploring unconventional theories around advanced propulsion. Their results were not published in a peer-reviewed journal, and there is considerable disagreement as to the validity of their experiment. They are continuing to refine their experiments, and the last update provided is that they intend to publish a peer-reviewed paper describing an experiment that successfully breached 100uN of thrust, which was the target needed for JPL and others to attempt to replicate their results.

drudru11 11y ago

This is fascinating stuff. It is also good to see more and more respectable names looking at this. Good things will come from that regardless of the overall outcome of the emdrive.

jimmcslim 11y ago

This is probably incredibly naive... but couldn't this all be put to bed by someone putting such a drive on a cubesat, lifting it into orbit, and seeing if it works under practical conditions? Maybe Hawking and Milner should be considering this for Starshot?

losteric 11y ago
Sure, the tricky part is finding funding
- jimmcslim 11y ago
  Yuri Milner of Breakthrough Starshot should be a contender?
- funkju 11y ago
  Any ideas on a ballpark of what it would cost?
  - losteric 11y ago
    It takes about $100k to get a cubesat into orbit, plus costs for building the sat itself (custom fabricating a miniaturized drive plus a suite of sensors). So not much, but the larger problem is we don't know how this drive works. Miniaturizing it could impact performance, as could other electronics in the satellite... given the unknowns it makes sense to let NASA do some more terrestrial due-diligence before going to space.
- mabbo 11y ago
  How much funding? A Falcon 9 can lift 10,000 kg to LOE (or more). Let's say we could get a simple Em-drive and basic satellite and solar panel in for under 100kg. (We can do better, but let's start there). That's 1/100 of the load, so (in theory) we could maybe pay 1/100 of the $60m cost for a Falcon 9 lift, or $600,000. Half a million bucks plus some change, let's say. Edit: Less if we can get on board a previously-enjoyed rocket!

trhway 11y ago

> inertia must quantized at small accelerations. as everything does :) I think it is quantized at all levels, it just becomes noticeable at low levels as usually.

outworlder 11y ago
Everything seems to be limited by the precision our simulation is running on :)

deftnerd 11y ago

I think what I most enjoy about the possibility of the EmDrive is that it's similar to how things were often discovered during the "golden age" of science. Often, engineers or inventors would create something and then scientists would have to explain why it happened. In the last few generations, physicists and mathematicians would come up with theories and engineers would have to build equipment to test those theories. The EmDrive is one of the rare modern situations where someone has engineered a device that shouldn't work according to what we know and the scientists are having to come up with the explanation. Personally, solving a mystery is more exciting than purely intellectual theories and the EmDrive has created a very interesting mystery.

rimunroe 11y ago
I don't think really any scientists in the relevant fields actually think it's an interesting mystery. Lots of people make extraordinary claims about new theories or perpetual motion machines, but those claims frequently get reported on a disproportionately large amount. This is from the perspective of a former physicist who is grumpy about the endless torrent of "Einstein was wrong!"-type articles. I personally feel like it's risky to allow people to pin their hopes on something that's pretty obviously bunk, but I imagine it does have some benefits. I just don't think it's worth it.
- maaku 11y ago
  > Lots of people make extraordinary claims about new theories or perpetual motion machines. Such claims don't often get replicated by multiple, independent labs, as is the case here.
  - moron4hire 11y ago
    And they seem to be basing their work on "Einstein was right, we just didn't fully understand what it meant."
  - crusso 11y ago
    I'm not up on every instance of "replication" -- but so far, the ones I've read about have been really shoddily performed. http://io9.gizmodo.com/no-german-scientists-have-not-confirmed-the-impossibl-1720573809/1720737686 http://io9.gizmodo.com/no-german-scientists-have-not-confirm... I'd love for this phenomenon to be real, but the Technology Review article did not present a realistic picture of the verification attempted to date.

russdill 11y ago

One of the main issues I see with the EmDrive in general is time invariance. And especially with the theory Mike McCulloch put forward. If photons cause this process for a positive change in momentum, the same process should happen in reverse with a negative change in momentum.

scrumper 11y ago

I'm curious to what degree Unruh radiation (and the resulting consequences this idea relies on) 'established physics'? By extension, I think this is the most interesting article I've seen to date on the EmDrive: it seems to have a basis in a fairly non-controversial result of GR, which in turn is something which nicely explains an otherwise bizarre physical phenomenon. And, to top it off, there are a number of falsifiable predictions which are within our ability to test. I'm interested in whether any of my assumptions are wrong.

gaur 11y ago
> I'm curious to what degree Unruh radiation (and the resulting consequences this idea relies on) 'established physics'? Most theorists think Hawking–Unruh radiation has to exist, I guess because the calculation is relatively straightforward. You just need special relativity and some basic field theory. Hawking–Unruh radiation has never been observed in a gravitational system, and doing so would be very difficult because it requires a truly enormous acceleration in order to produce a horizon with a temperature that is an appreciable fraction of 1 K. There are certain regimes in fluid mechanics where the mathematics governing the fluid looks like the mathematics governing relativity. Some people have produced phenomena in those systems that look like Hawking–Unruh radiation. Some people further claim that this demonstrates the existence of Hawking–Unruh radiation for gravitational systems, but I find that reasoning to be specious.
tremon 11y ago
This. Self-consistent theories and falsifiable predictions is how our understanding of the universe moves forward.
pdonis 11y ago
Unruh radiation itself is well established theoretically, though it has not been observed experimentally. However, the theory behind Unruh radiation says one thing that creates an obvious problem for anyone trying to use it to explain something like the EmDrive or the flyby anomaly: Unruh radiation is felt by objects that are undergoing proper acceleration. That is, they have to already be experiencing thrust. And according to the theory, the thrust they are experiencing has to be very, very small, so that the wavelength of the Unruh radiation is of the same order as the size of the observable universe. In the case of the flyby anomaly, the spacecraft passing by the Earth were in free-fall orbits--i.e., zero thrust. That means zero Unruh radiation. In the case of the EmDrive, technically the apparatus was feeling "thrust", in the sense that it was sitting on the surface of the Earth and therefore feeling weight. (Weight counts as "thrust" in this connection.) But the weight of the EmDrive apparatus is many orders of magnitude larger than the small accelerations that would be required for the Unruh radiation explanation to work--the wavelength of Unruh radiation associated with a 1 g acceleration is about one light-year, much, much smaller than the radius of the observable universe. So, bottom line, whether or not the EmDrive results themselves are valid (I am skeptical, but the whole thing is still being hashed out so it's too early to know for sure), it doesn't look to me like Unruh radiation can account for results of this sort. (Btw, as gaur pointed out, Unruh radiation actually is a result of quantum field theory in flat spacetime, i.e., not GR, as the article claimed.)

jaekwon 11y ago

How does this relate to the spinning black/white thing?

gerbilly 11y ago
The Black White thing is a Crookes Radiometer[1] and it rotates because of differential heating of the black and white sides of the plates interacting with air molecules to create a tiny air flow from the light side to the dark side of the plate. The device is under _partial_ vacuum. Under total vacuum, no rotation will occur, if the air pressure is too high, drag forces outpace the tiny thrust. https://en.wikipedia.org/wiki/Crookes_radiometer https://en.wikipedia.org/wiki/Crookes_radiometer

apsec112 11y ago

I don't think there's anything real here. McCulloch's papers on arXiv seem very confused. Eg., this paragraph: "In this scheme there is a minimum allowed acceleration which depends on a Hubble scale Θ, so, if Θ has increased in cosmic time, there should be a positive correlation between the anomalous centripetal acceleration seen in equivalent galaxies, and their distance from us, since the more distant ones are seen further back in time when, if the universe has indeed been expanding, Θ was smaller. The mass to light ratio (M/L) does seem to increase as we look further away. The M/L ratio of the Sun is 1 by definition, for nearby stars it is 2, for galaxies’ it is 50, for galaxy pairs it is 100 and for clusters it is 300. As an aside: equation (11) could be used to model inflation, since when Θ was small in the early universe the minimum acceleration is predicted to be larger." (http://arxiv.org/pdf/astro-ph/0612599v1.pdf http://arxiv.org/pdf/astro-ph/0612599v1.pdf) If an effect was stronger in the early universe, you'd expect to see a big correlation between the effect size in a galaxy, and that galaxy's redshift z. It wouldn't make any sense to say that "galaxies" have a ratio of 50, since there are galaxies at every redshift; many are nearby and have redshifts of almost zero, while the Ultra Deep Field galaxies have very large redshifts of up to ~10. If the number is really the same for "galaxies" in general, that means there's no distance dependence, but McCulloch doesn't seem to realize this. He seems to imply that nearby stars have a higher mass/luminosity ratio because of their distance compared to the Sun (?!), but the time-delay effect for anything in the Milky Way is negligible (< 0.0005% of the universe's age). In reality, nearby areas of space will have higher ratios than the Sun just because they contain many objects which, unlike the Sun, don't emit much light (red/brown/white dwarfs, gas and dust, etc.). Likewise, he seems to imply that "galaxy clusters" are farther away than "galaxies", but most galaxies are part of clusters, and we can observe both galaxies and galaxy clusters at both small and large redshifts.

anentropic 11y ago
Isn't he saying the 'standard' M/L ratio for galaxies is 50... and that by looking at a lot of galaxies at different distances you see a trend that the more distant ones are more >50 ?

th0ma5 11y ago

The sentiment I hear in this thread is like those that dismiss cold fusion. Sure, we can all make statements like "obviously, someone screwed up" but it is another thing entirely to have to the patience to simply cite the experiments that disprove the proposed effect. I don't know what to make of cold fusion, but I also know for a fact that neither do physicists, and instead of studying it, they're just simply saying because there is no theory it must not work. Same with this stuff. The one YouTube guy discovered the beaded-chain lifting effect, and then it had to be studied to find out what was going on. Obviously that was an easily reproduced experiment. So with this thing, we must find conclusively the unmeasured heat or ions or whatever and show a repeatable method for such mistakes. That is my opinion about science, of course I probably lost most scientists with my first sentence.

greglindahl 11y ago
Extraordinary claims require extraordinary proof, and the history of physics is littered with intentional fraudsters and sloppy experimentalists. Disproving every perpetual motion machine via experiment would take a lot of effort from scientists who don't want to do it. If you think those experiments should be done, then by all means do them.
- th0ma5 11y ago
  Fair enough, but the problem with perpetual motion stuff is that no energy can be extracted or the time until the device stops is very long, not that they don't do what people claim that they do, which is work more or less perpetually. We need to find that kind of explanation for this supposed propulsion.
  - taneq 11y ago
    These devices work "more or less perpetually" the same way 1000.0f is "more or less infinite".
    - th0ma5 11y ago

PaulHoule 11y ago

People have been doing "research" into reactionless propulsion for a long time, such as this science fiction writer: http://rexresearch.com/dean/stine.htm http://rexresearch.com/dean/stine.htm

wmeredith 11y ago

> At very small accelerations, the wavelengths become so large they can no longer fit in the observable universe. When this happens, inertia can take only certain whole-wavelength values and so jumps from one value to the next. So the EmDrive glitches the universe size? This is hilarious.

tremon 11y ago
This was also my first reaction. I don't see how energy could be quantized with the inverse of the diameter of the observable universe. Could someone explain the current thinking around how energy quanta relate to the size of the universe, or rather why wavelengths larger than the universe are impossible? If the latter were true, I'd expect that an energy quantum corresponding to 0.99 * universe would be equally impossible as 1.01 * universe, and that only integer multiples of the corresponding frequency would be allowed (i.e. a harmonic series across the universe).
- TheOtherHobbes 11y ago
  The corollary is that you'd be able to measure the size of the universe by observing quantisation effects. This seems unlikely, because - unless I've missed something obvious - you'd have to be able to set up a wave with a phase velocity > c.
gcb0 11y ago
yeah, i quit reading after the condescending intro ended with "In other words, inertia must quantized at small accelerations."

33a 11y ago

Man, this is the perfect news story for 4:20.

dnautics 11y ago

wonder if this inertial/acceleration effect is what is responsible for "dark matter" in the universe, i.e. galaxy-scale gravitational anomalies that don't agree with existing newtonian and GR models.

mcnamaratw 11y ago

The article leaves out all the numbers and so skips over one little problem. The momentum some people think they might have observed (if it's not experimental error) is compatible with what you'd get by using a microwave antenna as a thruster. Just ordinary radiation pressure, with the puzzle of how the radiation could be escaping the cavity. But the minimal measurement results I've seen are not compatible with the radiation pressure multiplied by some large factor for the Q of the cavity, which seems to be the claim from some. That really would violate our understanding of conservation of momentum, rather than violating our assumptions about where the momentum goes in this experiment. And that seems to be ruled out experimentally so far.

spottedquoll 11y ago

Extraordinary claims require extraordinary yada yada. A working reactionless drive isn't just extraordinary. It's utterly mind-boggling. The least interesting thing is that it's a free-energy device. It requires breaking spatial symmetry. If it works, it's not some edge-case theoretical law that's being broken. It's the geometry of space. https://en.wikipedia.org/wiki/Noether%27s_theorem https://en.wikipedia.org/wiki/Noether%27s_theorem

api 11y ago
Even if this works, reactionless drive would be my last hypothesis after exhausting all possible things it might be interacting with via some as-yet-unknown means: dark matter, nearby gravitational bodies, etc. The infinite energy device claim is easy enough to test. Since a working infinite energy device would be perverse, I'd predict that an EmDrive rigged up so as to produce infinite energy would fail to do so. Exactly how it fails to do so might tell us what's going on. Do the energy requirements rise with momentum (as they should in a sane universe), or do you pass a point at which the effect ceases, or does something truly wacky occur like space-time distortion in such a way as to cancel the effect? My reading of the McCullough hypothesis is that it's pushing against all matter in the universe at once, or some such thing, but that could be way off. I'm not a physicist.

ridgeguy 11y ago

For anybody who's interested, there's a NASA forum devoted to the EmDrive: http://forum.nasaspaceflight.com/index.php?topic=39772.1440 http://forum.nasaspaceflight.com/index.php?topic=39772.1440

Joof 11y ago

Inertia is quantized? Do we actually live inside a computer, because that's really weird. Physicists, help explain this outside of the universe uses a lookup table to approximate inertia.

api 11y ago

"Yes, they're still using warp drives to heat food..." - alien observers

est 11y ago

refuted by reddit https://www.reddit.com/r/EmDrive/comments/4fm2ac/the_curious_link_between_the_flyby_anomaly_and/ https://www.reddit.com/r/EmDrive/comments/4fm2ac/the_curious... > ... (McCulloch) proposes a constant term that modifies the acceleration corresponding to the inertial mass. He says torsion balance experiments can't detect it because torsion balance experiments measure differences in acceleration. But he's wrong because since it's a constant term he "predicts", it should manifest in the Eotvos parameter. Torsion balance experiments have gone well beyond the limit to detect this. But it's irrelevant because he completely misunderstands all the theory he bases this on.

alfiedotwtf 11y ago

Meta: Wow that drop down menu at the top is really annoying

323454 11y ago

Supposing this theory is true, how big an emdrive does it predict is needed to lift a reasonable payload, say 100kg?

codeduck 11y ago
The EmDrive would never be powerful enough to be a lifting engine; but what it would be is an incredibly useful engine once your mass is in orbit.

lunchTime42 11y ago

Is there a thing that allows for Science Annonymous?

aalexgabi 11y ago

Humans have learned a lot of things. However they still have to learn about the universe because there are non-naturally-observable physical phenomena and we have no evidence that we discovered them all. Edit: These so called "laws" are laws in our minds and things like EmDrive show us that our minds can expand forming new "laws".

askvictor 11y ago

I can't help but look at things like this as hacks in/of the simulation we are probably living in.

josephagoss 11y ago
Interestingly, that would imply we are possibly living in an imperfect simulation, one that hypothetically does not replicate the physics of a real non-simulated universe. If that is true, why? I can think of four possible reasons: 1) Is it because the simulation was designed in such a way that it leaves its inhabitants clues that reveal the true nature of the universe? This lets them figure out the truth once their society and knowledge become sufficiently advanced. 2) That it's impossible to simulate a real universe? This would imply any sufficiently advanced society will be able to detect that they do in fact live within a simulation. 3) That the creators made a mistake and it's not a fundamental limitation. It's simply an error made by whatever civilisation created this simulation, they messed something up. 4) That it's possible to create a perfect simulation, but for some reason they decided to make a simulation that used less resources and this brings errors or the need of hacks to get it working. Now we might be exploring these hacks.
bitL 11y ago
Looks that way. So now we are going to hunt for rounding errors of the Simuverse. Should be fun. It's likely simulation would be ended if we beat its purpose by hacking it. End of the world coming?

kempe 11y ago

Would be very interesting to see an actual implementation.

phkahler 11y ago

Photons must behave as if they have mass. From TFA: McCulloch’s theory could help to change that, although it is hardly a mainstream idea. It makes two challenging assumptions. The first is that photons have inertial mass. When I was taking college physics, there was a question on the exam about radiation pressure. I missed that day, so had no idea how to solve it. "a 5mW laser is reflected off a mirror (perpendicular) what is the force exerted on the mirror"? Later looking it up in the book there was a page on this and a derivation using electromagnetic theory. In the exam however, I decided to convert 1 second of laser energy to mass, bounce it off the mirror at speed=c, compute the force and change in momentum (over change in time which was 1s). I got the right answer of course. The logic is simple. If we can convert back and forth between matter and energy, any experimental setup must obey conservation of momentum and it's CG must not move. So a laser inside a closed spaceship would actually be tranfering mass (as energy) from one end to the other. The net effect must be the same as if that mass was moved any other way. I derived a general expression for radiation pressure after the exam and it's identical to the EM one from the book. Photons behave - and must behave - as if they have mass with a velocity of c. By the same reasoning, gravity must bend light rays, though I have not compared this prediction to that of relativity.