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Is Light a State of Matter?

  1. Nov 17, 2009 #1
    Is Light a State of Matter? This is a question many people have asked for a long time. What is your opinion on this topic?

    I believe that light IS a state of matter contrary to popular belief. Because all energy needs something to carry it through. I think light is an extremely high energy form of matter.
  2. jcsd
  3. Nov 17, 2009 #2


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    I don't think anyone has asked this question before, except possibly when they are still learning what the words mean.

    Light is not a form of matter. It is a form of energy; but quite different from matter. Matter, at a minimum, is made up of material which has non-zero rest mass. This is not a question for "beliefs", but simply understanding what the words mean.

    Welcome to physicsforums, by the way!

    Cheers -- sylas
  4. Nov 17, 2009 #3


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    This is much like the original theory of "ether". It has been refuted.

    While there are similarities between forms of kinetic energy travelling through for example, air or water, that does not mean that all energy must have a medium. Be careful of carrying an analogy too far.

    If you wish, you can think of photons as light's medium.
  5. Nov 17, 2009 #4
    Are x-rays a form of matter? What about ultraviolet radiation? Light is just the range in the EM radiation spectrum that can be observed by human eyes. It is definitely a form of energy, not matter. But this doesn't mean that it can't affect matter; read more about the photoelectric effect and you'll see this. As DaveC said, you can think of photons as the medium through which light propagates. It seems you haven't had much formal instruction on matter/energy properties, so this may be a good starting point in understanding the nature of the light, which can be tricky initially.
  6. Nov 18, 2009 #5
    Energy and matter have two different definitions, so no, light is not a form of matter.

    At the same time....E=mc^2. So while light is not not matter and matter is not light...they are still two different forms of the same thing.

    Kind of like a Honda is not a Toyota, and a Toyota is not a Honda...but they are both cars.
  7. Nov 18, 2009 #6


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    "In an attempt to explain the meaning of “empty space” to a young child, I said “space is something not made of atoms.” He replied “Then you were wrong to tell me last time that only light is not made of atoms.” Indeed, light and gravity are two singular forms of “matter” which are very different from other forms of matter such as
    atoms, electrons, etc . (Here I assume space = gravity.) The existences of light and gravity – two massless gauge bosons – are two big mysteries in nature."

    Wen, http://arxiv.org/abs/hep-th/0109120
  8. Nov 18, 2009 #7
    minor correction, light is light- regardless of whether or not our human eyes can see it. X-rays and Ultraviolet light are still light, albeit with different wavelength.
  9. Nov 18, 2009 #8


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    What an odd thing to say. Light and gravity are not forms of matter.

    Light is a form of energy and gravity is a field that permeates space.
  10. Nov 18, 2009 #9
    (Visible) Light is usually just the name given to the visible portion of the EM spectrum. You're right though, they're all different wavelengths of EM radiation, and they're all composed of photons. I've never heard of gamma rays (for example) referred to as light, but I suppose that's one way of thinking of it.
  11. Nov 18, 2009 #10
    I'm glad I entered these forums with enough knowledge to know that light is not a 'state of matter'. (:
  12. Nov 18, 2009 #11

    I've heard, but I'm not sure about, a new theory that larger objects fire gravitons which attract objects emitting weaker gravitons.. or something along those lines. I am a supporter of the 'field that permeates space' theory, but I'm interested in the new suggestion.
  13. Nov 18, 2009 #12


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    In the http://en.wikipedia.org/wiki/Standard_Model" [Broken] all elementary particles can be classified as bosons or fermions. The fermions are considered matter and the bosons are considered forces (or at least the carriers of force). Light is fundamentally composed of photons which are bosons and therefore not matter.
    Last edited by a moderator: May 4, 2017
  14. Nov 18, 2009 #13
    When we get to a reasonable "theory of everything" perhaps we'll have a better understanding of the relationship between matter, energy, space, time, etc. Right now about all we have is a general idea that a phase transition during the big bang (or little cyclic bang) resulted in the variety of apparently different entities that we observe today, but which all may evolve from something singular and fundamental...like strings, perhaps.

    For the time being light is hardly a 'state of matter" but light and matter are perhaps each a state of another entity.
  15. Nov 18, 2009 #14


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    Quantum theory models gravity as gravitons - the force-carrying particle that acts between bodies. It is another valid way of looking at the same thing.
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