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Real time video of light moving: applications for biomedical science

Discussion in 'Other Health News and Research' started by Cheesus, Feb 9, 2017.

  1. Cheesus

    Cheesus Senior Member

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    According to the abstract, this will be super helpful in biomedical science. I don't know much about that, really I just wanted to show you guys this ridiculously awesome video of light moving. It is filmed at 100 billion frames per second

    https://i.imgur.com/gKfHroL.gifv

    Here is the corresponding abstract:

    https://www.researchgate.net/public..._Mach_cone_induced_by_a_scattered_light_pulse
     
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  2. Hip

    Hip Senior Member

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    That's pretty amazing that we have cameras that can film at that speed.

    By my calculation, in a 100 billionth of a second, a light particle will move 3 mm.
     
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  3. Jonathan Edwards

    Jonathan Edwards "Gibberish"

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    It is a very clever piece of filming but light does not actually move. Nor is it made of particles. The weird thing about a photon of light is that it is a connection between one place at one time with another place at a later time but it takes no time to get from one place to the other. Once the connection has started it has also finished.

    What the video shows is lots of photons being scattered out from a path that if they were not scattered would bounce back near to where they started. I assume there is a short burst of photons, which means that photons that get scattered out of the path later connect to the camera later. You cannot see or detect with a camera a photon that is following a path that is not to the camera so the apparent movement in the video is just like the apparent movement on a TV screen or a neon sign or Christmas lights. It seems to move because light is coming from a different place as time goes by.

    Imaging using scattered light has been going on for a couple of decades. It is used to study infant brains. Surprisingly you can shine a light straight through a baby's brain and get a picture of what the internal structure is. It is just that you have to clean up the image hugely. I guess this fast tracking camera might help in calibrating such techniques.
     
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  4. Cheesus

    Cheesus Senior Member

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    Physics is so cool.
     
  5. Cheesus

    Cheesus Senior Member

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    @Jonathan Edwards

    So would it be correct to say that it is a video of light travelling, rather than to say it is a video of light moving?
     
  6. TiredSam

    TiredSam The wise nematode hibernates

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    A photon checks into a hotel.

    The receptionist asks "do you have any luggage sir?"

    The photon replies "no, I'm travelling light."
     
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  7. Jonathan Edwards

    Jonathan Edwards "Gibberish"

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    No I don't think it travels either, and the apparent movement or travel in the picture is not 'light travelling' any more than the 'movement' of a bright spot in a neon display is anything travelling. Light comes in units called photons but these are not particles. They are never in one place or another. They are causal connections between two places in spacetime. And they are not even strings, just causal connections.
     
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  8. sb4

    sb4 Senior Member

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    Wouldn't this be true only in a vacuum, gravity and other things slow down light meaning it's not travelling at c meaning it experiences time?
     
  9. Jonathan Edwards

    Jonathan Edwards "Gibberish"

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    No, it has nothing to do with general relativity. It is a basic feature of quantum theory - confirmed by the Aspect experiments that tested Bell's theorem. Light does not travel any more than anything travels in QM. There are no trajectories. It is basic to the theory. As Bohr pointed out, the dynamic connection that is a quantum system cannot be divided into a 'particle' being in one place at one time and another place at another.
     
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  10. sb4

    sb4 Senior Member

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    So the photon is a wave (in a super position?) but why does the wave not experience time when slowed down(in gravity for example )?
     
  11. Jonathan Edwards

    Jonathan Edwards "Gibberish"

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    No a photon is not a wave. That is a trivial analogy often used but it is unhelpful. I am not sure that anything experiences time, in the sense of time in physics as a component of spacetime. We have an experience of 'time' that is a sign created by parts of our brains to indicate to other parts of the brain a story about the world. As pointed out by Newton that is not time in the sense used in physics. Time is never slowed down or speeded up. Again that is a misinterpretation of SR. All these myths are ways of trying to make physics seem like our experiences, but 300 years ago the people who invented physics, like Descartes, Newton and Leibniz understand that this is a pointless exercise.

    It's a long story.
     
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