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Is Light considered Matter? Questions on energy and states of matter.

  1. Aug 26, 2012 #1
    So my initial question was whether or not light was considered matter. While googling this question, I came across this answer:


    In the top answer given, it is inferred that photons (light) are included in the definition of matter by the modern physics definition.

    So if light is matter, in what state is it? I'm very new to physics, and from my understanding matter is characterized by certain qualities, and can be put in a category such as a gas, liquid, etc...

    Thanks in advance for any answers.
  2. jcsd
  3. Aug 26, 2012 #2
    There is no specific physics definition of matter. Its an ill defined term that is not technical. Check out the Wikipedia on it.

    I would not consider light matter. The first line in the wiki says that mass and volume are characteristics of matter. Light has neither.

    In physics we prefer the term 'mass', its is specifically defined.
  4. Aug 26, 2012 #3
    So to consider something as a gas, liquid, or any other phase of matter, would said thing need to have mass?
  5. Aug 26, 2012 #4
    I think so. And it would have to be macroscopic too. I would not consider a proton to be matter. Even a proton and an electron (H atom) is pushing it. A single proton or H atom cannot be in a gas, liquid or solid state. You need a collection of them to start distinguishing between phases. And once you get a collection of them you can start to talk of their volume as well.
  6. Aug 26, 2012 #5


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    Personally I view matter as any particle with rest mass. Some see it as just "normal everyday" particles such as protons, neutrons, and electrons. Still others see it only as particles bound inside atoms. This is a perfect example of an ill defined term. Luckily we have definitions for things such as hadrons, bosons, fermions, etc that are much more specific.
  7. Aug 26, 2012 #6
    Thank you for your help! This has clarified things a lot! :)
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