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Thread: Light....

  1. #1 Light.... 
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    The speed of light is constant. the speed of wich you are traveling effects your perception of time.

    Light slows down when it travels throught water and other substances so what happens to time right there when the speed of light changes


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  3. #2  
    Moderator Moderator Janus's Avatar
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    The constant is the speed of light in a vacuum. This is the only speed of light that counts in Relativity. The fact that the apparent speed of light changes in different mediums is not a factor.


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  4. #3  
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    maybe the perception of time is also effected by your age, or by what kind of organism you happen te be.
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    Forum Masters Degree Numsgil's Avatar
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    When we talk of time in physics, we're talking about things like the half life of some given isotope, or the period of a pendulum under some given acceleration. Something that can be counted definitively and non subjectively.
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    What I donít understand about light and time and the whole idea about the special theory are to contradicting themselves, otherwise, logical truths. When light approaches the theoretical max c speed it is gathering energy along, right? Higher the speed higher the inertia, thus energy is growing as light moves faster and increases to infinity. Then, suddenly as it hits c-its max speed, its energy is gone and reduced to 0 because in vacuum energy will not exist. I understand that in the real world light can never reach c since the infinite increase of energy makes it impossible, although I donít fully understand or know the math equation that backs it up.
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  7. #6  
    Forum Masters Degree Numsgil's Avatar
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    Light always travels at c. When it slows down by passing through a substance, it's because the substance is absorbing and reemitting the light, and that process reduces the net distance the light travels.
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    How can it travel at c when the only condition for Light to catch that speed is for Light to travel through Vacuum and Vacuum doesnít exist, even in space there is a matter, presumably remnants from the big bang, if you believe in a big bang, anyway there is some energy in space that wouldnít allow Light to travel at c, I donít know, I suppose it is possible to measure the distance Light travels in space and prove without a doubt that its speed is exactly the same everywhere and conform those results with the theory.
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    There are three problems with that idea.

    First, space may not be a 100% vacuum, but it's close enough to not really matter in general. If the average distance between particles is measured on the order of meters or more, the time a beam of light will spend interacting with those particles will be practically nonexistent.

    Second, there is a true vacuum between the particles of matter. During those parts of the trip, no matter what the medium is, light moves at c. As the density of the medium increases, the proportion of the time spent between particles decreases, along with the apparent velocity. (Ok, I know it's not strictly density that matters, but I can't remember the right word ATM.)

    Third, only particles matter here. Things like the cosmic microwave background and other beams of light won't do anything to a beam of light. Gravity will bend it, but won't slow it down. (Correct me if I'm wrong about that though.)
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  10. #9  
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    I've been told there are some mediums through which light will travel *faster* than C. Supposedly when this happens there's a special effect that accompanies it, though I forget what that effect is.
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  11. #10  
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    Another thing that is difficult to grasp is the bending of Light by Gravity. Gravity can only attract another body with its own mass and energy, Light travels between particles at c, so it travels without energy and mass and I canít see how it can be affected by Gravity.

    It begins the travel without the need to be propelled by any source as it spreads instantly at the same constant speed. When it hits a wall, depending on the material it will be absorbed, dispersed, refracted, reflected, or everything at the same time. It will never slow down but will be bouncing between particles that have become denser at the same speed c. that is its particles will keep traveling at its constant speed.
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  12. #11  
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    I've been told there are some mediums through which light will travel *faster* than C. Supposedly when this happens there's a special effect that accompanies it, though I forget what that effect is.
    kojax, I'm surprised you of all people came up with this faulty piece of information. There are no mediums where light can travel faster than C; if that were so, it would violate the laws of refraction and relativity.

    Perhaps you refer to refraction? Light goes slower than c there.

    Another thing that is difficult to grasp is the bending of Light by Gravity. Gravity can only attract another body with its own mass and energy, Light travels between particles at c, so it travels without energy and mass and I canít see how it can be affected by Gravity.
    This is because of an obsolete understanding of gravity. Gravity is no longer a force that affects masses; it is quite literally curved space-time. i.e. a graviational field resembles the surface of a sphere. Light, in such an environment, will be forced to curve as it attempts to move in a straight line, as you can't draw a truly straight line on a curved surface.

    This is Einstein's general theory of relativity, if you wish to know more about it.

    When it hits a wall, depending on the material it will be absorbed, dispersed, refracted, reflected, or everything at the same time.
    No; never at the same time. It takes some time for light to be emitted after being absorbed, you should know.

    It will never slow down but will be bouncing between particles that have become denser at the same speed c.
    Why will the particles become denser?

    that is its particles will keep traveling at its constant speed.
    Correct. So?
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  13. #12  
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    Quote Originally Posted by Liongold
    I've been told there are some mediums through which light will travel *faster* than C. Supposedly when this happens there's a special effect that accompanies it, though I forget what that effect is.
    kojax, I'm surprised you of all people came up with this faulty piece of information. There are no mediums where light can travel faster than C; if that were so, it would violate the laws of refraction and relativity.

    Perhaps you refer to refraction? Light goes slower than c there.
    http://en.wikipedia.org/wiki/%C4%8Cerenkov_radiation
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  14. #13  
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    Quote Originally Posted by JaneBennet
    Quote Originally Posted by Liongold
    I've been told there are some mediums through which light will travel *faster* than C. Supposedly when this happens there's a special effect that accompanies it, though I forget what that effect is.
    kojax, I'm surprised you of all people came up with this faulty piece of information. There are no mediums where light can travel faster than C; if that were so, it would violate the laws of refraction and relativity.

    Perhaps you refer to refraction? Light goes slower than c there.
    http://en.wikipedia.org/wiki/%C4%8Cerenkov_radiation
    Yes. This is the light emitted when a particle travels through a medium at a speed faster than the speed of light through that medium. It still does not at any time travel faster than C in a vacuum and neither does the light itself.
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  15. #14  
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    Thanks for clearing that up.

    I had found this possibility quite confusing, because of pretty much the same reason why everyone else objects. It would confuse all the relativity concepts. So, C in a vacuum is still the maximum.
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