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What is light exactly?

  1. Nov 24, 2012 #1
    Sorry to be so ignorant!
    I have heard that light is a type of electro-magnetic radiation but I was also under the apprehension that photons were particles of light.
    Is that latter assertion too loose?

    Are photons just one of the many kinds of particles and do they just show up when electro- magnetic radiation is created ?

    Also ,if there are different frequencies of EM radiation can they all be classed as some form of light? Or are they just some class of EM radiation?
  2. jcsd
  3. Nov 24, 2012 #2
    Light acts as a particle AND as a wave. This behavior is known as wave-particle duality. Any type of electro-magnetic radiation is a light, including radio waves, x-rays, infrared etc.
    It's simply different wavelength. What we see and call as visible light, is simply photons with wavelengths from 400nm to 800nm (i don't remember exact numbers).
  4. Nov 24, 2012 #3
    Is sound a form of light?
  5. Nov 24, 2012 #4
    sound is a longitudinal wave - very different indeed.
  6. Nov 24, 2012 #5
    No, sound travels in medium such as air. It doesn't travel at the speed of light. You can see a lightning first, and sound later. The speed of sound is determined by the medium, in air it's somewhere around 300m/s.
  7. Nov 24, 2012 #6
    That was a major misapprehension on my part!
    But what about the other part of my question?

    Are photons special types of particles or just one amongst many? Are they even primus inter pares (first among equals).

    In my mind light seems primordial but is it really so? (I don't want to sound like I am making a philosophical point)
  8. Nov 24, 2012 #7


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    Electromagnetic radiation is just one of the components of our Universe. It can be a bit fruitless to try to put EM in some sort of hierarchy, along with matter, gravity, space and time. They are all part of the same structure. Change something about one of them and all the others would change too. It would be a different Universe.
    One of the aims of Science is to link them up in a 'theory of everything' (TOE).
  9. Nov 24, 2012 #8
    In the standard model of particle physics there are three fundamental forces: Strong Nuclear Interaction, Weak Nuclear Interaction, and Electromagnetism. Each of these forces has a given force carrying particle. The Gluon for the strong interaction, the W± and Z bosons for the weak interaction, and the Photon for the electromagnetic force. So yes, it can be considered special in the sense that it is a carrier of a major force but there are countless other particles that have been discovered or hypothesized.

    For reference:

    **Gravity is considered a fundamental force but the cause of gravity is still debated, which is why it is not mentioned in the standard model.
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