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Please explain to me 'why' light is part defined by velocity

  1. May 6, 2015 #1
    Rhetorical Question: I have never understood why light (primarily a form of information or data) is often assumed to have velocity.

    We would never in any other process, attempt to give the quality/definition of speed to any other form of information and rather look to the platform or mechanism.

    Did we just assume light could travel on its own, without ever considering that there was some other entity involved?

    And just to round off this 'devil's advocate' opener; what would light truly be to us in scientific terms, if we were a highly evolved race of Earthworms i.e. blind by nature?
  2. jcsd
  3. May 6, 2015 #2


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    Staff: Mentor

    I don't understand your objection; speed of sound...?
  4. May 6, 2015 #3


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    Staff: Mentor

    Welcome to the PF.

    What is your educational background? That will help us tune our responses to your level of understanding of science & physics. :smile:
  5. May 6, 2015 #4


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    Staff Emeritus
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    Light is not assumed to have a velocity. It was determined to have a measurable velocity as the result of careful observations made of the planets in the solar system following the invention of the telescope in the 17th century.

    The astronomer Cassini was the first to notice that light did not travel instantaneously, but unfortunately, he did not pursue the implications of his observation further. The Danish astronomer Roemer made observations about light similar to those of Cassini, and did explore the matter further:


    Roemer was the first scientist to estimate the speed of light, although his estimate was about 25% lower than the currently measured value:


    Water waves and sound waves are readily observed to travel at finite speeds.

    It's not clear what you mean by "other entity".

    We can't "see" things like radio waves or X-rays, but we know they exist.
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