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> 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

> 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. So, again, I don't see the problem. 1. http://www.eng.fsu.edu/~dommelen/quantum/style_a/consem.html http://www.eng.fsu.edu/~dommelen/quantum/style_a/consem.html

roywiggins 8y ago
I found this paper pretty convincing. Any "reactionless" drive more efficient than a photon drive is probably a perpetual motion machine: https://arxiv.org/abs/1506.00494 https://arxiv.org/abs/1506.00494 The claimed thrust of the EMDrive was incompatible with photon thrust- it was much too powerful.
- mojomark 8y ago
  Again, this paper acknowledges the operating principles of an EM drive, but simply argues that the efficiency isn't sufficient to achieve a significant acceleration. "Significance" is relative to the application and efficiency can certainly be improved. For example (and I'm just spit-balling here), using expensive superconducting materials or perhaps a metamaterial could drastically improve the q-factor (1) of the engine. 1. https://en.m.wikipedia.org/wiki/Q_factor https://en.m.wikipedia.org/wiki/Q_factor
  - roywiggins 8y ago
    The paper argues that any reactionless drive that produces more force per newton than a perfect photon drive can be turned into a perpetual motion machine, regardless of how it's built: "Since applying a constant force results in a constant acceleration, the kinetic energy of a mass driven by such a device increases quadratically with time, while the energy input increases only linearly with time. Thus, at some point, the kinetic energy of the device-driven mass exceeds the energy input, and if this energy is collected via decelerating the mass (via regenerative electromagnetic braking, for example), then there would be a net gain in energy." With a photon drive, the break-even point is at the speed of light (which you can never actually achieve), but with any drive that's more power-efficient, the break-even point will be less, and you will be able to extract limitless free energy by accelerating the drive past that point.
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roywiggins 8y ago

I found this paper pretty convincing. Any "reactionless" drive more efficient than a photon drive is probably a perpetual motion machine: https://arxiv.org/abs/1506.00494 https://arxiv.org/abs/1506.00494 The claimed thrust of the EMDrive was incompatible with photon thrust- it was much too powerful.

mojomark 8y ago
Again, this paper acknowledges the operating principles of an EM drive, but simply argues that the efficiency isn't sufficient to achieve a significant acceleration. "Significance" is relative to the application and efficiency can certainly be improved. For example (and I'm just spit-balling here), using expensive superconducting materials or perhaps a metamaterial could drastically improve the q-factor (1) of the engine. 1. https://en.m.wikipedia.org/wiki/Q_factor https://en.m.wikipedia.org/wiki/Q_factor
- roywiggins 8y ago
  The paper argues that any reactionless drive that produces more force per newton than a perfect photon drive can be turned into a perpetual motion machine, regardless of how it's built: "Since applying a constant force results in a constant acceleration, the kinetic energy of a mass driven by such a device increases quadratically with time, while the energy input increases only linearly with time. Thus, at some point, the kinetic energy of the device-driven mass exceeds the energy input, and if this energy is collected via decelerating the mass (via regenerative electromagnetic braking, for example), then there would be a net gain in energy." With a photon drive, the break-even point is at the speed of light (which you can never actually achieve), but with any drive that's more power-efficient, the break-even point will be less, and you will be able to extract limitless free energy by accelerating the drive past that point.
- deleted 8y ago
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