4 ms·

OK, I'm officially interested. I'm a physics undergrad. What paper should I be reading that more or less summarizes the mechanism at work?

rtpg 10y ago
The EmDrive website (http://www.emdrive.com/ http://www.emdrive.com/) has papers. Quickly flipping through this paper[0], I think it explains the principles. http://www.emdrive.com/FeasibilityStudytechnicalreportissue2.pdf http://www.emdrive.com/FeasibilityStudytechnicalreportissue2...
- leni536 10y ago
  The theory is simply wrong, it neglects the electromagnetic pressure between the electromagnetic field and the tapered wall of the waveguide, it should produce the missing force component for a net force of 0. It's impossible to arrive at a non-zero net Force with classical electrodynamics. It's theoretically proven that it conserves momentum. Very possible reasons for measuring non-zero force: > Systematic measurement errors. > Leaking EM field carrying momentum. > Energy channel from outside carrying momentum (failing measurements including battery mentioned in comments) Unlikely explanation: All currently used theories of electrodynamics are wrong. But explaining non-zero force from classical ED is simply impossible. Also note that breaking conservation of momentum + relativity means that conservation of energy is broken as well. edit: typo edit 2: I mean the theoretical approach presented in the paper makes obvious mistakes. I'm not arguing that breaking conservation of momentum is impossible (although I think it's really unlikely), I argue that even if it would happen it couldn't be described by classical electrodynamics (or even QED). We would have to come up with better laws for electrodynamics.
  - epicureanideal 10y ago
    This is exactly the kind of comment I would expect to read shortly before some presumed law of the universe were broken. Reminds me of the "maybe in thousands of years people will fly" newspaper comment the same year the Wright brothers flew. I'm not treating it lightly that conservation of energy etc. would be broken. I'm just saying... it's a law until it's discovered that it's not. Or rather, that the law is only applicable within certain conditions, or needs some asterisks on it.
    - JonnieCache 10y ago
      I think the issue is that if it were possible to break conservation laws using such setups, we would have seen nature doing it by now.
      - estefan 10y ago
        Perhaps we have: https://en.wikipedia.org/wiki/Flyby_anomaly https://en.wikipedia.org/wiki/Flyby_anomaly
      - epicureanideal 10y ago
        Maybe that's how the universe came into existence at all, is "breaking the law" of conservation of energy? I'm not even arguing this, I'm just saying maybe we haven't been looking at things the right way or the proof will be obvious after we know about a new effect.
    - varjag 10y ago
      There were decades of manned flight prior to Wright bros.
      - tossaway1 10y ago
        Also, there were birds flying all over the place so it was obvious to everyone that it was possible...
        Caprinicus 10y ago
        There were a fuckton of people who thought heavier than air flight was not possible until it was done. Not sure how they reconciled birds, but that was a common opinion even among scientists at the time
    - Dylan16807 10y ago
      That's not what the comment addresses. Could the current theory be wrong? Sure. But any explanation within the current theory is someone doing math incorrectly.
  - onion2k 10y ago
    The fact that several teams of very highly qualified physicists bothered to look at it makes me believe the physics involved is non-obvious and can't be written off with a simple "the theory is simply wrong". Dismissing it out of hand does a disservice to all those people. That's not to say it'll prove to be true, I doubt it will, but this is something that has so much potential it's worth investigating the tiny possibility that it's real, and "all currently used theories of electrodynamics are wrong", just in case.
    - csirac2 10y ago
      Worryingly, the 2015 paper didn't seem to have anything about measuring the mass of the device before and after the experiment. An old radar technician asked me to take a look... apparently "boiling" waveguides are a thing when it comes to high-power RF.
      - jschwartzi 10y ago
        If the waveguide boils at a certain rate at certain power levels, then it should be possible to estimate how much force this would produce. If that force is on the same order, then it's likely the reason for what we're seeing.
    - megalodon 10y ago
      > Dismissing it out of hand does a disservice to all those people. Or maybe they all know its impossible, but continue because they are perfectly happy with the amount of funding thrown at them. Not saying it's true, but it's the other side of the coin.
      - estefan 10y ago
        > Or maybe they all know its impossible How could they know? That's the point of the scientific method isn't it, experimentation and valuing observation over preconceptions?
  - rtpg 10y ago
    Has anyone bothered to write your counterargument in more detail? I think I understand your argument but I wonder if anyone's really done the calculation... though I suppose the conservation of momentum itself a theoretical proof that the "other forces" have to cancel out. Is it possible that classic electrodynamics are not wrong, but there's some other fundamental thing in play here? I'd be a bit surprised, given that this just seems to be such a simple setup, but maybe? One can dream....
lutusp 10y ago
> What paper should I be reading that more or less summarizes the mechanism at work? As to the NASA paper, it's yet to be published according to the linked article, but publication is imminent. And the mechanism is not clear, only the measurement (which remains a topic of debate). The possibility remains, because of the small size of the effect being measured, that it has a pedestrian explanation, not new physics. It's essential to keep this in mind.
kowdermeister 10y ago
I've followed the topic on Reddit for quite a while. You won't find the mechanism because no real working theory exists why this effect might be real. There are a few theories floating, but none of the stood the test of scientific inquiry. Current state is still at the stage to prove without doubt that the effect is real. Nobody demonstrated it so far with high enough signal to noise ratio. The EmDrive is not a real thing with a high certainty.
baq 10y ago
i'm waiting for a cubesat(-ish craft) with the device attached so NORAD or whoever can measure how orbital elements change over time, or more likely not.
- clouddrover 10y ago
  Cannae plan to launch a cubesat in a couple of years to demonstrate their drive: https://news.ycombinator.com/item?id=12402915 https://news.ycombinator.com/item?id=12402915

rtpg 10y ago

The EmDrive website (http://www.emdrive.com/ http://www.emdrive.com/) has papers. Quickly flipping through this paper[0], I think it explains the principles. http://www.emdrive.com/FeasibilityStudytechnicalreportissue2.pdf http://www.emdrive.com/FeasibilityStudytechnicalreportissue2...

leni536 10y ago
The theory is simply wrong, it neglects the electromagnetic pressure between the electromagnetic field and the tapered wall of the waveguide, it should produce the missing force component for a net force of 0. It's impossible to arrive at a non-zero net Force with classical electrodynamics. It's theoretically proven that it conserves momentum. Very possible reasons for measuring non-zero force: > Systematic measurement errors. > Leaking EM field carrying momentum. > Energy channel from outside carrying momentum (failing measurements including battery mentioned in comments) Unlikely explanation: All currently used theories of electrodynamics are wrong. But explaining non-zero force from classical ED is simply impossible. Also note that breaking conservation of momentum + relativity means that conservation of energy is broken as well. edit: typo edit 2: I mean the theoretical approach presented in the paper makes obvious mistakes. I'm not arguing that breaking conservation of momentum is impossible (although I think it's really unlikely), I argue that even if it would happen it couldn't be described by classical electrodynamics (or even QED). We would have to come up with better laws for electrodynamics.
- epicureanideal 10y ago
  This is exactly the kind of comment I would expect to read shortly before some presumed law of the universe were broken. Reminds me of the "maybe in thousands of years people will fly" newspaper comment the same year the Wright brothers flew. I'm not treating it lightly that conservation of energy etc. would be broken. I'm just saying... it's a law until it's discovered that it's not. Or rather, that the law is only applicable within certain conditions, or needs some asterisks on it.
  - JonnieCache 10y ago
    I think the issue is that if it were possible to break conservation laws using such setups, we would have seen nature doing it by now.
    - estefan 10y ago
      Perhaps we have: https://en.wikipedia.org/wiki/Flyby_anomaly https://en.wikipedia.org/wiki/Flyby_anomaly
    - epicureanideal 10y ago
      Maybe that's how the universe came into existence at all, is "breaking the law" of conservation of energy? I'm not even arguing this, I'm just saying maybe we haven't been looking at things the right way or the proof will be obvious after we know about a new effect.
  - varjag 10y ago
    There were decades of manned flight prior to Wright bros.
    - tossaway1 10y ago
      Also, there were birds flying all over the place so it was obvious to everyone that it was possible...
      - Caprinicus 10y ago
        There were a fuckton of people who thought heavier than air flight was not possible until it was done. Not sure how they reconciled birds, but that was a common opinion even among scientists at the time
  - Dylan16807 10y ago
    That's not what the comment addresses. Could the current theory be wrong? Sure. But any explanation within the current theory is someone doing math incorrectly.
- onion2k 10y ago
  The fact that several teams of very highly qualified physicists bothered to look at it makes me believe the physics involved is non-obvious and can't be written off with a simple "the theory is simply wrong". Dismissing it out of hand does a disservice to all those people. That's not to say it'll prove to be true, I doubt it will, but this is something that has so much potential it's worth investigating the tiny possibility that it's real, and "all currently used theories of electrodynamics are wrong", just in case.
  - csirac2 10y ago
    Worryingly, the 2015 paper didn't seem to have anything about measuring the mass of the device before and after the experiment. An old radar technician asked me to take a look... apparently "boiling" waveguides are a thing when it comes to high-power RF.
    - jschwartzi 10y ago
      If the waveguide boils at a certain rate at certain power levels, then it should be possible to estimate how much force this would produce. If that force is on the same order, then it's likely the reason for what we're seeing.
  - megalodon 10y ago
    > Dismissing it out of hand does a disservice to all those people. Or maybe they all know its impossible, but continue because they are perfectly happy with the amount of funding thrown at them. Not saying it's true, but it's the other side of the coin.
    - estefan 10y ago
      > Or maybe they all know its impossible How could they know? That's the point of the scientific method isn't it, experimentation and valuing observation over preconceptions?
- rtpg 10y ago
  Has anyone bothered to write your counterargument in more detail? I think I understand your argument but I wonder if anyone's really done the calculation... though I suppose the conservation of momentum itself a theoretical proof that the "other forces" have to cancel out. Is it possible that classic electrodynamics are not wrong, but there's some other fundamental thing in play here? I'd be a bit surprised, given that this just seems to be such a simple setup, but maybe? One can dream....

lutusp 10y ago

> What paper should I be reading that more or less summarizes the mechanism at work? As to the NASA paper, it's yet to be published according to the linked article, but publication is imminent. And the mechanism is not clear, only the measurement (which remains a topic of debate). The possibility remains, because of the small size of the effect being measured, that it has a pedestrian explanation, not new physics. It's essential to keep this in mind.

kowdermeister 10y ago

I've followed the topic on Reddit for quite a while. You won't find the mechanism because no real working theory exists why this effect might be real. There are a few theories floating, but none of the stood the test of scientific inquiry. Current state is still at the stage to prove without doubt that the effect is real. Nobody demonstrated it so far with high enough signal to noise ratio. The EmDrive is not a real thing with a high certainty.

baq 10y ago

i'm waiting for a cubesat(-ish craft) with the device attached so NORAD or whoever can measure how orbital elements change over time, or more likely not.

clouddrover 10y ago
Cannae plan to launch a cubesat in a couple of years to demonstrate their drive: https://news.ycombinator.com/item?id=12402915 https://news.ycombinator.com/item?id=12402915