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Photons and their purpose

  1. Jan 20, 2015 #1
    I am knew only in year 9 but am doing some research on photons and was wondering how they have a mass of 0 as I thought every thing had to have a mass to be within the realms of reality or general relativity.
    but I might just be wrong and if so could you explain it to me simply why and the correct reasons.
    Last edited by a moderator: Jan 20, 2015
  2. jcsd
  3. Jan 20, 2015 #2


    Staff: Mentor

    Congratulations Evenus1 for thinking about such things at age 9.

    No it is not true that everything needs mass to be real. You already have the number one example - photons. Photons are very real a
    Yet they have zero mass.

    It is better to think that all particles have energy. Mass is just the energy of the particle that remains when the particle is not moving (momentum zero). Photons never stop moving. They have energy, but no mass.

    Later, you will learn that energy and mass are related.
  4. Jan 20, 2015 #3


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    Excellent question at your age. Anorlunda has addressed part of your question but I'd like to address the other part of your subject line "what is their purpose". In science, basically, fundamental things don't HAVE a purpose, they just exist. Purpose is something ascribed to those things by humans, but nature doesn't really care what we think it just does what it does. We say that light has the purpose of allowing humans to see, but nature creates photons whether we are here to use them or not.

    That is, a baseball HAS a purpose because it is a macro object designed by humans FOR a purpose, but it is made up of fundamental particles called quarks and electrons and THEY don't have a purpose, they just exist. The goal of physics is to identify such fundamental objects and learn how they came about and how they work and how they interact with other objects to make up the universe we live in.
  5. Jan 20, 2015 #4
    hi its me agian i am not nine but 14 soz but in uk and there school system is in years not grades lol
  6. Jan 21, 2015 #5


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    Photons fit in as gauge particles. That is, they are what the electromagnetic field is made of. Light, radio waves, magnetism, electric charge, all of that involves photons.

    They are massless because they have gauge symmetry. I know that sounds like so much gobble-dee-gook now. But basically, symmetry is the argument. If they had mass they would spoil this symmetry. And this symmetry is what makes electromagnetism a long-distance interaction. Or to put it another way, Maxwell's equations imply an interaction involving a massless vector field.

    You probably won't make much traction on that at your level. You will need to study some calculus at least. You may get to start that in year 11 or 12 if you are keen.
  7. Jan 22, 2015 #6


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    For someone 14 years old in UK, your knowledge of physics (English) is much above (below) average. No one's perfect, I guess. ;)
  8. Jan 25, 2015 #7
    i dont understan your brackets they dont make sence
  9. Jan 25, 2015 #8
    i am sort of trying to lern some basic calculus as. i need it for some of my algorithms
  10. Jan 25, 2015 #9


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    He is saying

    physics above average
    English below average

    This reflects the fact that your spelling is atrocious and your grammar is only slightly better.
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