Yes the actual laws of physics can't be broken. We don't know those. We know an approximation of them based on centuries of careful observation and analysis. That approximation is incredibly good, too. It lets us make microchips with 7nm features, synthesize high atomic weight elements, and build spacecraft that have traversed the solar system. Even so, there are things we know we don't know and there are bound to be things we don't know we don't know.
It would be nice if the EmDrive turned out to be a ground breaking demonstration of a hole in our model. We could probably squeeze a century of amazing science out of it. Not to mention the potential practical applications.
But groundbreaking new discoveries that shake the foundations of a developed scientific theory are incredibly rare. So, as awesome as it could be if it were right, the odds were always against it.
It is also much more likely for such a discovery to appear at the edge of our knowledge where our understanding of the rules is at least a bit fuzzy (like near black holes and whatnot). Something like EmDrive, which is in a regime that has been exhaustively tested, would be like discovering that Bin Laden was hiding in the Oval Office all along.
Conservation laws should be considered more as powerful analysis tools than as foundations of reality. So more Newtonian gravity than Relativity. In fact, you can regard Newtonian orbital mechanics as elaborations on conservation of energy and momentum. Conservation laws themselves have an underlying principle:
Another analogy: Conservation laws are like Euclidian geometry. On the scale of building a cabinet or an office building, Euclidian geometry rules! On intergalactic scales, it simply fails. So too, with the conservation of energy. If someone tries to sell you a perpetual motion or over unity machine, it is pretty rock solid. But if you're going to try to make some kind of cosmological argument using conservation of energy, that's just plain facepalm territory there. (Some HNer actually reported me for using <facepalm> in response to conservation of energy
in a cosmological argument.)
I've been curiously watching this story although, like many other folks, I realized that the chances were greater than 99% that it wouldn't work out.
What saddened me is the glee that some scientists and students took with dismantling all of these home experimenters. It was shameful to watch. What could have been a great opportunity for many to learn more about science and experimentation turned into a bunch of jackasses mocking a bunch of interested laymen. Not exactly the public image you want for your field of study.
Such a drive would necessarily be a perpetual motion machine. Perpetual motion machines are a dime a dozen and we don't test all of them rigorously because approximately none of them will ever work.
you have to be careful, many experimentally verified observations could have been called quackery, too (an electric current has an effect on a magnet only if it's out of the plane of the magnet? QUACKERY!) If you go to biology and biochemistry, there's plenty of things that still have zero (or very tenuous) basis in underlying theory that are observationally verified (lots of sweet-tasting compounds, basically all anaesthetics, tylenol, e.g.)
Just because one cannot explain a phenomenon using known physics doesn't mean they should outright dismiss it. A good many discoveries started with, "Hmmm, that's odd...".
And, science mistakes are good lessons, such as "why didn't we think to check that?"
Why is it impossible? Is it the amount of thrust that's generated that's impossible, or the mere concept of generating thrust from electromagnetic waves?
The reason that I'm asking is because light has momentum. If I shine a beam of light out the back of my spacecraft, then I will accelerate in the opposite direction. Not a lot, just a little.
Was EmDrive impossible because it was claimed to generate way more thrust than could be explained from the energy levels involved? (Edit: It looks like an additional reason it's impossible is because the EmDrive was claimed not to emit radiation, and rather keep it bouncing around in the cavity. Thanks for the replies and explanations!)
Imagine that I attach a 1 megawatt laser in the 630 nm spectrum to my spacecraft. From some rough calculations based on (1), it looks like the laser will generate about 0.003 newtons of thrust (equal to the weight of 0.2 pounds on Earth), which is very little thrust, and impractical for accelerating a spacecraft over regular time scales.
> Of course it is. Nearly every physicist knew this was quackery from day one.
Source of disproof?
From two years of atomic physics study at my university, I don't see any reason you can't generate thrust using EM emission from an anetenna attached to the object being propelled. No laws are violated.
First of all, before getting to conservation laws, the author's statement that an EM drive requires no fuel, right after stating the engine is powered by microwaves (generated by some stored energy source, a.k.a. fuel) is nonsensical.
So, about those conservation laws. EM drives absolutely fully conserve energy and momentum in the system. Anyone who studied physics at the university level should have a firm understanding that photons do not "launch" themselves off of the surface from which they are emitted, like a rocket from a platform. Instead, the energy and momentum change forms as they transfer from the source (e.g. an atom) to the photom (e.g. a microwave).
In atomic orbital decay (say spontaneous emission from an exciton), emitted photons recieve their energy and momentum from the atom's decaying orbital energy and angular momentum. That's it. See here (1) for a deeper breakdown of what's going on, but if you're generally trying to figure out where the energy and momentum are coming from, at the high level that's all there is to it - no quackery here.
If you need a mental image, just try to imagine throwing (imparting a force on) a photon emitted from a light bulb in your hand. You can't do it. A photon travels at the speed of light in a vacuum the instant it is created at the bulb's filament. Because you're hand and the lightbulb (both made of matter and traveling in the same direction as the photon) cannot travel at the speed of light, the photon will always be forward of your hand/light bulb and no energy can be transferred from your hand/light bulb to the photon, and vice versa. There is no "recoil" felt by your hand. That's exactly the same for the EM drive's antenna (or any antenna or emitter for that matter). However, that same photon can certainly interact with matter and transfer it's energy and 'linear' (angular) momentum to an incident piece of matter, for a kinetic reaction.
The last time I tried to tell the story behind the academic community's attempts to stop this in its tracks I was downvoted. Rest assured, academia tried its best.
Yes, sort of, but that’s mainly useful for torque rather than thrust as thrust relies on (if I’m getting this right) field gradients rather than absolute field strength. It’s not nothing, but it might as well be.
I back-of-enveloped a launch system with a very big magnet on the ground, supplying a much steeper gradient to push against, and it was still crazy expensive.
"It is also impossible to control attitude in all three axes even if the full three coils are used, because the torque can be generated only perpendicular to the Earth's magnetic field vector."
the non-earth orbiting mission i worked on didn't have any; it used little thrusters to desaturate its reaction wheels.
Yes there are various forms of electromagnetic drives that use the earths magnetic field for small tasks like rotation and (maybe) station keeping. There are a few types, some which use propellant, and some that do not. More info here: https://en.m.wikipedia.org/wiki/Electrically_powered_spacecr...
It would have been a perpetual motion machine of the first kind (you could get an unlimited amount of energy out of it): https://arxiv.org/abs/1506.00494
The evidence for it was no better than the evidence for any other perpetual motion machine, there was nothing that made it special other than not claiming to be a perpetual motion machine (despite being one).
I wanted to believe it could be true, but that's the beauty of science.
Test. Test and re-test. If the conclusion isn't want you want it to be, refine the accuracy of your test and increase sample size. If you test is already at maximum resolution, then tough tacos buddy.
[+] [-] daotoad|7 years ago|reply
Yes the actual laws of physics can't be broken. We don't know those. We know an approximation of them based on centuries of careful observation and analysis. That approximation is incredibly good, too. It lets us make microchips with 7nm features, synthesize high atomic weight elements, and build spacecraft that have traversed the solar system. Even so, there are things we know we don't know and there are bound to be things we don't know we don't know.
It would be nice if the EmDrive turned out to be a ground breaking demonstration of a hole in our model. We could probably squeeze a century of amazing science out of it. Not to mention the potential practical applications.
But groundbreaking new discoveries that shake the foundations of a developed scientific theory are incredibly rare. So, as awesome as it could be if it were right, the odds were always against it.
[+] [-] WJW|7 years ago|reply
[+] [-] stcredzero|7 years ago|reply
Conservation laws should be considered more as powerful analysis tools than as foundations of reality. So more Newtonian gravity than Relativity. In fact, you can regard Newtonian orbital mechanics as elaborations on conservation of energy and momentum. Conservation laws themselves have an underlying principle:
https://www.youtube.com/watch?v=04ERSb06dOg
Another analogy: Conservation laws are like Euclidian geometry. On the scale of building a cabinet or an office building, Euclidian geometry rules! On intergalactic scales, it simply fails. So too, with the conservation of energy. If someone tries to sell you a perpetual motion or over unity machine, it is pretty rock solid. But if you're going to try to make some kind of cosmological argument using conservation of energy, that's just plain facepalm territory there. (Some HNer actually reported me for using <facepalm> in response to conservation of energy in a cosmological argument.)
[+] [-] DanielBMarkham|7 years ago|reply
What saddened me is the glee that some scientists and students took with dismantling all of these home experimenters. It was shameful to watch. What could have been a great opportunity for many to learn more about science and experimentation turned into a bunch of jackasses mocking a bunch of interested laymen. Not exactly the public image you want for your field of study.
[+] [-] SubiculumCode|7 years ago|reply
[+] [-] gaze|7 years ago|reply
[+] [-] roywiggins|7 years ago|reply
https://arxiv.org/abs/1506.00494
[+] [-] dnautics|7 years ago|reply
[+] [-] tabtab|7 years ago|reply
And, science mistakes are good lessons, such as "why didn't we think to check that?"
[+] [-] Pyxl101|7 years ago|reply
The reason that I'm asking is because light has momentum. If I shine a beam of light out the back of my spacecraft, then I will accelerate in the opposite direction. Not a lot, just a little.
Was EmDrive impossible because it was claimed to generate way more thrust than could be explained from the energy levels involved? (Edit: It looks like an additional reason it's impossible is because the EmDrive was claimed not to emit radiation, and rather keep it bouncing around in the cavity. Thanks for the replies and explanations!)
Imagine that I attach a 1 megawatt laser in the 630 nm spectrum to my spacecraft. From some rough calculations based on (1), it looks like the laser will generate about 0.003 newtons of thrust (equal to the weight of 0.2 pounds on Earth), which is very little thrust, and impractical for accelerating a spacecraft over regular time scales.
(1) Momentum of a laser beam: http://umdberg.pbworks.com/w/page/50455623/Momentum%20of%20a...
[+] [-] mojomark|7 years ago|reply
Source of disproof?
From two years of atomic physics study at my university, I don't see any reason you can't generate thrust using EM emission from an anetenna attached to the object being propelled. No laws are violated.
First of all, before getting to conservation laws, the author's statement that an EM drive requires no fuel, right after stating the engine is powered by microwaves (generated by some stored energy source, a.k.a. fuel) is nonsensical.
So, about those conservation laws. EM drives absolutely fully conserve energy and momentum in the system. Anyone who studied physics at the university level should have a firm understanding that photons do not "launch" themselves off of the surface from which they are emitted, like a rocket from a platform. Instead, the energy and momentum change forms as they transfer from the source (e.g. an atom) to the photom (e.g. a microwave).
In atomic orbital decay (say spontaneous emission from an exciton), emitted photons recieve their energy and momentum from the atom's decaying orbital energy and angular momentum. That's it. See here (1) for a deeper breakdown of what's going on, but if you're generally trying to figure out where the energy and momentum are coming from, at the high level that's all there is to it - no quackery here.
If you need a mental image, just try to imagine throwing (imparting a force on) a photon emitted from a light bulb in your hand. You can't do it. A photon travels at the speed of light in a vacuum the instant it is created at the bulb's filament. Because you're hand and the lightbulb (both made of matter and traveling in the same direction as the photon) cannot travel at the speed of light, the photon will always be forward of your hand/light bulb and no energy can be transferred from your hand/light bulb to the photon, and vice versa. There is no "recoil" felt by your hand. That's exactly the same for the EM drive's antenna (or any antenna or emitter for that matter). However, that same photon can certainly interact with matter and transfer it's energy and 'linear' (angular) momentum to an incident piece of matter, for a kinetic reaction.
So, again, I don't see the problem.
1. http://www.eng.fsu.edu/~dommelen/quantum/style_a/consem.html
[+] [-] selimthegrim|7 years ago|reply
[+] [-] bitL|7 years ago|reply
[+] [-] alan|7 years ago|reply
[+] [-] ben_w|7 years ago|reply
I back-of-enveloped a launch system with a very big magnet on the ground, supplying a much steeper gradient to push against, and it was still crazy expensive.
(I wonder if it would be useful for skyhooks?)
[+] [-] sigstoat|7 years ago|reply
https://en.wikipedia.org/wiki/Magnetorquer
"It is also impossible to control attitude in all three axes even if the full three coils are used, because the torque can be generated only perpendicular to the Earth's magnetic field vector."
the non-earth orbiting mission i worked on didn't have any; it used little thrusters to desaturate its reaction wheels.
[+] [-] cheesepizza1077|7 years ago|reply
[+] [-] hooo|7 years ago|reply
[+] [-] db48x|7 years ago|reply
[+] [-] roywiggins|7 years ago|reply
The evidence for it was no better than the evidence for any other perpetual motion machine, there was nothing that made it special other than not claiming to be a perpetual motion machine (despite being one).
[+] [-] searine|7 years ago|reply
Test. Test and re-test. If the conclusion isn't want you want it to be, refine the accuracy of your test and increase sample size. If you test is already at maximum resolution, then tough tacos buddy.
[+] [-] tabtab|7 years ago|reply
Indeed. Star Trek dreams shatnered, I mean shattered. Sorry, no visiting green Orion space-babes. Live long and cuss.
And, wouldn't somebody typically check electrical interaction with Earth's magnetic field? It's a factor already known about.
[+] [-] jwilk|7 years ago|reply
https://news.ycombinator.com/item?id=17096175
[+] [-] ballenf|7 years ago|reply
[+] [-] yummybear|7 years ago|reply
[+] [-] larkeith|7 years ago|reply
[+] [-] nategri|7 years ago|reply
[+] [-] the-pigeon|7 years ago|reply
[+] [-] 21|7 years ago|reply