4 ms·

It's not a breakthrough in science at all, honestly. It is already well known that you can propel something just by generating photons (generally using nuclear

by lnanek2 12y ago

It's not a breakthrough in science at all, honestly. It is already well known that you can propel something just by generating photons (generally using nuclear power to heat an element, just like a light bulb). Microwaves are just a different wavelength. It is just too inefficient to matter at the moment. The only breakthroughs to be made are in efficiency. Photons still have energy and momentum, just no rest mass, and there is even such a thing as electromagnetic pressure created from photons transferring momentum.

DennisP 12y ago
It's true you can generate thrust by throwing photons out one end, but that's not what this device does. It bounces microwaves around inside a closed, superconducting chamber, with one end wider than the other.
- hliyan 12y ago
  Exactly right. It's an apparent violation of Newton's Third Law, unless the photons are pushing against virtual particle pairs as suggested in the article.
  - madaxe_again 12y ago
    It's not a violation from the reference frame of the rf - just yours.
- tehwalrus 12y ago
  Oh, it's that device? The one that was on the cover of New Scientist at some point? We (i.e. the lecturer) mocked that in physics lectures (mostly on a "look at the shit New Scientist publishes..." sidetrack). It may also have claimed perpetual motion, while it was at it. If there really is some quantum interaction, then this becomes interesting, but from momentum alone the contributions from the sides of the box always exactly cancel the resultant from the mismatched plates (by definition of a closed box).
  - lectrick 12y ago
    Argument from Authority is a thing.
    - tehwalrus 12y ago
      indeed, my PhD supervisor is often wrong about stuff. I don't believe my lecturers per se, but rather I remember the argument about cancelling edge effects (which certainly seems to apply here.)
  - DennisP 12y ago
    If you've got constant thrust from constant energy input, that pretty much implies perpetual motion, since energy input increases linearly with time and kinetic energy with the square of time. If you want to say you get less thrust as velocity increases then you run into trouble with the principle of relativity. So I'm skeptical too, though I think it's worth continuing experiments.
    - aetherson 12y ago
      Wait, I get what you're saying (0.5mv^2), but isn't it relatively straightforward to get constant thrust from constant energy in other situations? Laser --> lightsail, for example.
      - aetherson 12y ago
        To reply to myself, the thrust you'd get from a laser that shoots at you would in fact diminish as you accelerate away from it, as the light would redshift and thus carry less energy to you.
    - tehwalrus 12y ago
      Sure, you can only find the mistake while repeating the experiments (perhaps, as someone else suggested, in a vacuum might be a plan). I hadn't noticed the constant thrust problem you mention, I'm now recursing back through the equations I remember to try and work out why it costs more energy to push something that's already moving fast... wait, force applied was never anything to do with energy to start with, impulse/power were. Brain-fart resolved.
- lnanek2 12y ago
  It's already a kind of well known concept in SciFi to bounce the photon back and forth a lot, getting a little hit of momentum each time (and draining its energy, thus changing its wavelength). Keeping the reflecting pair on the rocket and trying to use asymmetry to pull more off on one side than the other seems a pretty straightforward thing to try.
mrinterweb 12y ago
Considering that photons have a force, I wonder if the force of the photos hitting a craft propelled by an EmDrive would be able to approach a star. The craft with an EmDrive would likely need solar panels to sustain the EmDrive which would increase the craft's surface area to encounter more photons and other energy particles.
- AKifer 12y ago
  There's no need of a solar panel for big spacecraft, US and USSR have designed compact enough nuclear reactor that can generate Mw of power for various submarines,like here http://en.wikipedia.org/wiki/Alfa_class_submarine http://en.wikipedia.org/wiki/Alfa_class_submarine. There has been time that a single US submarine was able to power the entire Hawai island after a natural disater http://news.google.com/newspapers?nid=1755&dat=19821128&id=EZ4cAAAAIBAJ&sjid=SGgEAAAAIBAJ&pg=6758,7135178 http://news.google.com/newspapers?nid=1755&dat=19821128&id=E...

by lnanek2 12y ago

DennisP 12y ago

It's true you can generate thrust by throwing photons out one end, but that's not what this device does. It bounces microwaves around inside a closed, superconducting chamber, with one end wider than the other.

hliyan 12y ago
Exactly right. It's an apparent violation of Newton's Third Law, unless the photons are pushing against virtual particle pairs as suggested in the article.
- madaxe_again 12y ago
  It's not a violation from the reference frame of the rf - just yours.
tehwalrus 12y ago
Oh, it's that device? The one that was on the cover of New Scientist at some point? We (i.e. the lecturer) mocked that in physics lectures (mostly on a "look at the shit New Scientist publishes..." sidetrack). It may also have claimed perpetual motion, while it was at it. If there really is some quantum interaction, then this becomes interesting, but from momentum alone the contributions from the sides of the box always exactly cancel the resultant from the mismatched plates (by definition of a closed box).
- lectrick 12y ago
  Argument from Authority is a thing.
  - tehwalrus 12y ago
    indeed, my PhD supervisor is often wrong about stuff. I don't believe my lecturers per se, but rather I remember the argument about cancelling edge effects (which certainly seems to apply here.)
- DennisP 12y ago
  If you've got constant thrust from constant energy input, that pretty much implies perpetual motion, since energy input increases linearly with time and kinetic energy with the square of time. If you want to say you get less thrust as velocity increases then you run into trouble with the principle of relativity. So I'm skeptical too, though I think it's worth continuing experiments.
  - aetherson 12y ago
    Wait, I get what you're saying (0.5mv^2), but isn't it relatively straightforward to get constant thrust from constant energy in other situations? Laser --> lightsail, for example.
    - aetherson 12y ago
      To reply to myself, the thrust you'd get from a laser that shoots at you would in fact diminish as you accelerate away from it, as the light would redshift and thus carry less energy to you.
  - tehwalrus 12y ago
    Sure, you can only find the mistake while repeating the experiments (perhaps, as someone else suggested, in a vacuum might be a plan). I hadn't noticed the constant thrust problem you mention, I'm now recursing back through the equations I remember to try and work out why it costs more energy to push something that's already moving fast... wait, force applied was never anything to do with energy to start with, impulse/power were. Brain-fart resolved.
lnanek2 12y ago
It's already a kind of well known concept in SciFi to bounce the photon back and forth a lot, getting a little hit of momentum each time (and draining its energy, thus changing its wavelength). Keeping the reflecting pair on the rocket and trying to use asymmetry to pull more off on one side than the other seems a pretty straightforward thing to try.

mrinterweb 12y ago

Considering that photons have a force, I wonder if the force of the photos hitting a craft propelled by an EmDrive would be able to approach a star. The craft with an EmDrive would likely need solar panels to sustain the EmDrive which would increase the craft's surface area to encounter more photons and other energy particles.

AKifer 12y ago
There's no need of a solar panel for big spacecraft, US and USSR have designed compact enough nuclear reactor that can generate Mw of power for various submarines,like here http://en.wikipedia.org/wiki/Alfa_class_submarine http://en.wikipedia.org/wiki/Alfa_class_submarine. There has been time that a single US submarine was able to power the entire Hawai island after a natural disater http://news.google.com/newspapers?nid=1755&dat=19821128&id=EZ4cAAAAIBAJ&sjid=SGgEAAAAIBAJ&pg=6758,7135178 http://news.google.com/newspapers?nid=1755&dat=19821128&id=E...