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posted by martyb on Friday June 17 2016, @12:39AM   Printer-friendly
from the invisible-light dept.

International Business Times writes:

A new peer-reviewed paper (open, DOI: 10.1063/1.4953807) on the EmDrive from Finland states that the controversial electromagnetic space propulsion technology does work due to microwaves fed into the device converting into photons that leak out of the closed cavity, producing an exhaust.

So how could something come out that you can't detect? Well, the photons bounce back and forth inside the metal cavity, and some of them end up going together in the same direction with the same speed, but they are 180 degrees out of phase. Invariably, when travelling together in this out-of-phase configuration, they cancel each other's electromagnetic field out completely.

That's the same as water waves travelling together so that the crest of one wave is exactly at the trough of the other and cancelling each other out. The water does not go away, it's still there, in the same way the pairs of photons are still there and carrying momentum even though you can't see them as light.

If you don't have electromagnetic properties on the waves as they have cancelled each other out, then they don't reflect from the cavity walls anymore. Instead they leak out of the cavity. So we have an exhaust – the photons are leaking out pair-wise.


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  • (Score: 1, Informative) by Anonymous Coward on Friday June 17 2016, @06:41AM

    by Anonymous Coward on Friday June 17 2016, @06:41AM (#361433)

    I am a physicist.
    I have no idea how this got past peer review; I guess I have to start doubting AIP journals in general.

    The concept of photons that cancel each other's EM fields makes no sense. If something like this could happen, we would have seen it before.

    First thing: as another poster noted, this would mean the EM drive is no better than just pointing a laser/maser whatever in some direction, and then happily accelerating the other way (which is perfectly possible and real, except that the acceleration is minuscule).

    Second thing: two photons overlapping exactly would mean that their location is "known" with infinite precision (it's known by the other photon). That would mean that their momentum could have any value possible, just because of Schrodinger. Being photons, their energy is proportional to the momentum, therefore the probability of the two photons having the same energy (thus the EM fields cancelling each other out) is zero.

    Luckily, this EM drive thing is testable. I say we should not spend any public funds on testing it, but if there are enough idiots out there to believe it's worth investing time and money, whatever. I will be the one only checking the news from time to time to laugh when they finally admit it's a scam.

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  • (Score: 0) by Anonymous Coward on Friday June 17 2016, @07:03AM

    by Anonymous Coward on Friday June 17 2016, @07:03AM (#361441)

    Second thing: two photons overlapping exactly would mean that their location is "known" with infinite precision (it's known by the other photon).

    Umm, no. It means that the wave functions of the two photons are exactly opposite in phase. It is the opposite of how a laser works. Photons produced by lasers are just about exactly in phase, which is why their light is so coherent and so bright because their wave functions experience constructive interference. According to the article the photons generated are just about exactly out of phase, and so their wave functions experience destructive interference and as such there is hardly any electromagnetic field at all. You fail elementary quantum mechanics.

    • (Score: 0) by Anonymous Coward on Friday June 17 2016, @03:34PM

      by Anonymous Coward on Friday June 17 2016, @03:34PM (#361602)

      fucking made me read the fucking article.
      article is junk, like I said.

      there are a total of 4 equations, with a bunch of handwaving for 8 pages, no actual proofs.

      I really have no idea how this article passed peer review.

  • (Score: 0) by Anonymous Coward on Friday June 17 2016, @08:07AM

    by Anonymous Coward on Friday June 17 2016, @08:07AM (#361455)

    Here is a thought experiment; consider two EM waves with nearly equal phase; we get the classical interference pattern. Now consider the effect in the limit that the two phases approach each other; we get peaks and troughs in the interference pattern (beat pattern), with the beat wave length large (infinite in the limit of two phases equal). This is like neutrino oscillation.

  • (Score: 0) by Anonymous Coward on Friday June 17 2016, @08:46AM

    by Anonymous Coward on Friday June 17 2016, @08:46AM (#361463)

    If something like this could happen, we would have seen it before.

    I have a feeling of scientific déjà vu.

    • (Score: 0) by Anonymous Coward on Friday June 17 2016, @10:16AM

      by Anonymous Coward on Friday June 17 2016, @10:16AM (#361479)

      It's called the Double Penetration Experiment.

  • (Score: 2) by GreatAuntAnesthesia on Friday June 17 2016, @09:34AM

    by GreatAuntAnesthesia (3275) on Friday June 17 2016, @09:34AM (#361469) Journal

    > Second thing: two photons overlapping exactly would mean that their location is "known" with infinite precision (it's known by the other photon). That would mean that their momentum could have any value possible, just because of Schrodinger.

    OK, so to vreate your magic spacedrive you get two photons overlapping exactly, and then you persuade them to choose the highest of the possible values for momentum using a photonic vector plotter suspended in strong brownian motion producer (say, a nice hot cup of tea)...

    • (Score: 0) by Anonymous Coward on Friday June 17 2016, @09:50AM

      by Anonymous Coward on Friday June 17 2016, @09:50AM (#361474)

      Presto changeo. Infinite improbability drive.