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Light as Energy

  1. Jan 17, 2012 #1
    If our eyes can perceive light and light is energy then why is energy defined as an indirectly observed quantity?
  2. jcsd
  3. Jan 17, 2012 #2
    It is incorrect to say "light is energy".

    Energy is a property of physical systems. For example, energy is a property of light.
  4. Jan 17, 2012 #3
    So is light instead matter?

    I thought it was electromagnetic radiation which is energy.
  5. Jan 17, 2012 #4


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    Light is an electromagnetic wave with properties of both particles and waves. It carries energy with it. It is not matter.
    Similarly, a water wave carries energy with it yet it is not energy itself.
  6. Jan 17, 2012 #5
    I was under the impression that everything in the physical universe could be deduced down to either matter or energy. If light is not matter and also not energy then I was under the wrong impression.
  7. Jan 17, 2012 #6


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    This is strange.

    Light isn't JUST energy. It also has other characteristics, such has having a momentum, and in the quantum picture, it also has a spin quantum number. Saying light is just energy is like saying all there is to you is your face, while the rest of your body is irrelevant.

    Matter and energy are equivalent, but NOT IDENTICAL.

  8. Jan 17, 2012 #7


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    No, energy isn't a "thing". It is carried with objects but isn't something that exists on its own. Light is considered a Boson, which is not normal matter. But there are plenty of other particles that are the same way, such as gluons, the W and Z bosons, and more.
  9. Jan 18, 2012 #8
    Isn't a boson a subatomic particle? Aren't subatomic particles forms of matter?
  10. Jan 18, 2012 #9


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    You seem to think that it's just down to categorising things*. There's more to it than that. The relationships between things count too.
    You also seem to be pointing out inconsistencies and errors in 'the System' (as you see it). Whilst it's by no means complete, do you really thing that it's as full of holes as you imply?

    *You were probably taught about Solids, Liquids and Gases, at School. How long did it take for you to spot that a lot of things fall into none of those categories? It like that only more so with QM and fundamental particles.
  11. Jan 18, 2012 #10


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    No, not all subatomic particles are forms of matter. Photon's are not matter.
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