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Knots of Light

  1. Feb 1, 2014 #1
    The strangest science news of 2011 might have been when scientists reported having made a knot of light. I found that hard to believe: doesn't light always go in a straight line? The article was published in a reputable journal though, so it is likely true. Unfortunately in the new era of for-profit science the journal wanted $39 to view the article. From so sketchy popular accounts one could gather that the knot was made by making a hologram that contained a knot shape, then shining a laser through it. The knot would have fallen apart instantly, so it wasn't that exciting. What was exciting was that they said that natural light is full of vortices. What?!?! That's something new in this world. But I couldn't get more info.

    Then in 2013 out comes another article about knotted light but with a knot that is theoretically stable. http://arxiv.org/abs/1302.0342v1 I have learned while reading science that "stable" depends on context and can mean just about anything. I think such a knot would be fragile, but could exist for a short time. The knot is like nothing I've seen before. It changes shape constantly as the light moves around. Take a look at

    https://www.youtube.com/watch?v=gS8rkOELpPU .

    The knot is on the surface of a torus.

    How does it work? I don't know, but here is my best guess. For a long time it was a mystery how light could move through space at all. Light is a wave, and waves always move through a medium like air or water or whatever. But light had no medium. I still don't understand how it works, but it is something like this. There is a magnetic field that decays to create an electric field that decays to create a magnetic field that decays to create an electric field and so forth. Usually these fields are at right angles to one another so the light moves in a straight line, but it doesn't have to be that way. If the fields are at a different angle then the light curves.

    Scientists have fads and fashions and knots are cool these days. Knots have been tied from other unlikely things, my favorite being water. Dolphins beat us to it, though.


    Whales make water vortex knots as a group in order to catch fish. But hah! Let's see them make a trefoil knot.


    A theoretical knot of light has been known since the 30's or so, but seems impractical to make. There is a video of a model of the Hopf fibration at

    https://www.youtube.com/watch?v=1yJ5EvV0K70 .

    Pretty! Well, at least I think so...
  2. jcsd
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