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Thread: Why does Light not slow down?

  1. #1 Why does Light not slow down? 
    Forum Senior Booms's Avatar
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    I've been thinking and Light exists, it has matter (of sorts) and is a wave so why doesn't it slow down


    Everything else slows down over time as is passes though any kind of matter, and yet light actually speeds up as it exits a dense medium for a less dense one.
    I realise Light is such an impossible speed it would take a very long time to stop, but we should be able to detect some form of speed difference in light from the sun as opposed to light from a star 14 billion light years away if it slowed down. there is no difference therefore light does not slow

    WHY


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  3. #2  
    Forum Ph.D. Darius's Avatar
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    Light does not slow down (to my knowledge), so it never speeds up. Rather, light (visible light in this case) decays into other forms of electromagnetic radiation before completely dissipating when it meets resistance.

    A further answer is shown here, although I am no major in particle physics I believe this is a correct answer.


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    Forum Masters Degree Numsgil's Avatar
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    Light's just funny that way. This and the wave/particle duality are things that aren't explained, but thoroughly demonstrated.
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  5. #4  
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    There is no reason for it to slow down. Without a reason, something will not happen. A ball traveling through the air only slows down because it is unintentionally giving its energy to the air in the form of sound, heat, and general particle movement. Because it is giving it its energy, it must loose its own and therefore slow down. Light works differently. Instead of slowing down, it can either reduce its frequency and therefore energy, or (in terms of a light beam) reduce its number (of photons).

    When traveling through a medium, it does not actually slow down; it is moving at the same speed, but just has to undergo a high number of absorptions and emissions-the more the higher the refractive index. This takes time, therefore causing the light to appear to slow down. Though, in a BEC, it can either be literally slowed down, or caught in a sort of infinite loop between particles (we can stop light in a BEC).

    Instead of light slowing down over long distances, it Red Shifts. This is the nature of the frequency decreasing and wavelength increasing. You could think of this as an equivalent of the light 'slowing down', since both equate to a decrease in energy.

    Remember that a light particle is not a hadron (atoms), it is a boson, controlled by the electro/weak force. This is why it behaves differently than a bullet or ball.
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  6. #5  
    Forum Senior Booms's Avatar
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    ah thanks guys. that clears things up
    It's not how many questions you ask, but the answers you get - Booms

    This is the Acadamy of Science! we don't need to 'prove' anything!
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