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I Question about massless things

  1. Jan 10, 2017 #1
    Are there any other things/objects in our universe that are massless other than Gluons and Photons? I guess energy is massless, but it's not so much a thing, more-so a property.
     
  2. jcsd
  3. Jan 10, 2017 #2

    Drakkith

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    Staff: Mentor

    Indeed, energy is a property of objects and systems of objects, it is not something in and of itself. But it does have mass. Or, rather, arranging a system such that it has more energy than before will mean it has more mass as well.
     
  4. Jan 10, 2017 #3

    mathman

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    Mass and energy are equivalent. When you say something is mass-less, it usually means that the rest mass is zero. This applies to photons and gluons and gravitons (if they exist).
     
  5. Jan 10, 2017 #4
    Graviton, if it exists at all.
     
  6. Jan 10, 2017 #5
    Don't forget Weyl fermions.
     
  7. Jan 10, 2017 #6
    What about a shadow, or digital information?
     
    Last edited: Jan 10, 2017
  8. Jan 11, 2017 #7
    Those aren't physical objects.
     
  9. Jan 13, 2017 #8
    The OP didn't really qualify what a Thing or an Object was. If you want a macro-sized object, it would have to be an object made of massless particles, like a laser beam.
     
  10. Jan 13, 2017 #9
    Laser is an acronym for light amplification by stimulated emission of radiation. It is made of photons of a specific wavelength, but photons none the less and it does have mass just as all photons do, however small it is.
     
  11. Jan 13, 2017 #10

    Drakkith

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    The mass of the beam is non-zero, but the mass of each photon is zero.
     
  12. Jan 13, 2017 #11
    Each photon has energy which means it has mass. The mass is usually said to be zero in most cases and equations because it is such a small amount of mass.
     
  13. Jan 13, 2017 #12

    Nugatory

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    That is not correct. The mass, energy, and momentum of a particle are related by ##E^2=(mc^2)^2+(pc)^2##. For a photon we have ##E=pc## so a bit of algebra will quickly show that the mass of a photon is precisely exactly zero.
     
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