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Speed of light related to mass

  1. Dec 31, 2014 #1
    Would the speed of light be effected by the mass of light. Is the speed of light relative to mass? In other words if you fuse photons will they be capable of reaching beyond C?
     
  2. jcsd
  3. Dec 31, 2014 #2

    Borg

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    Photons of light have no mass and nothing can travel faster than the speed of light.
     
  4. Dec 31, 2014 #3

    phinds

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    To add to The Borg's response, you are probably under the misapprehension that velocities add linearly and can get something to move faster than c. This is not correct. Google "relativistic velocity addition".
     
  5. Dec 31, 2014 #4
    Relativistic velocity addition already has a constant locking the speed of light into C, I'm attempting to ask what was the speed of light determined by? Was it mass, empirical experiments? Theoretically calculated ideas? Where does it show the speed of light as function of something? Did that something have to do with mass? If so how? And no! E=MC2 will not do for this
     
  6. Dec 31, 2014 #5

    phinds

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    As has already been pointed out, but I will repeat it since you seem to have missed it, light (photons) HAS no mass, so mass has nothing to do with the speed of light. The speed of light has been determined fairly closely by experiment, but is now DEFINED to be exactly 299,792,458 meters per second.
     
  7. Jan 1, 2015 #6
    Photon always travels!It travels with c irrespective of source speed.Photon has rest mass 0.It still has momentum.A gamma photon has momentum much higher than an infrared light photon. If we assume railway engine as a gamma photon and a bicycle as a infrared photon both travelling at same speed then the devastating capability of engine is too high in comparison.
     
  8. Jan 1, 2015 #7

    Borg

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    The speed of light was originally determined by the Danish astronomer, Ole Roemer while observing the orbits of Io around Jupiter. He noticed that the apparent motion Io changed as the Earth moved from one side of the sun to the other in relation to Io. From this, he was able to calculate the first estimates of the speed of light.
    The consistancy of the speed of light is one of the two postulates of Special Relativity:
    These two starting assumptions came about from Einstein trying to resolve two issues in physics:
    In order to completely understand how light and mass mathematically relate to each other, you have to have take college level courses in calculus and electromagnetism in order to have the basics needed to do the math. Proving the relationship comes from the math.

    If you want to dig deeper into how it works, check out the Special Relativity link above or you can try this site which tries to explain all things E=MC2 in laymans terms.
     
  9. Jan 1, 2015 #8

    sophiecentaur

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    You are asking this 'the wrong way round', I think. c is a fundamental constant (at least, all our measurements seem to confirm this). It is tightly bound to the relationship between electric and magnetic fields, so, rather than being "determined by", it is "part of a structure which our present model is based on".
    c was introduced into EM theory long before Relativity came along and early work tells us that the speed of EM waves is independent of frequency. Einstein then tied it in with Space and time, in general.
     
  10. Jan 1, 2015 #9
    Thank you sophiecentaur.
    It seems I have been too indirect and as you say "asking this the wrong way round".

    I do understand very well that c will not be anything but c. Just like π, won't ever be ∞.
    c will always be 299,792,458 meters per second(rounded to 300,000,000 meters per second) and never 1 meter per second more.

    The questions I am proposing is very simple. That is what makes it far too complex.
    The question I proposed earlier was this -"Would the speed of light be effected by the mass of light"
    I see now that it triggers two possible questions, the one I was attempting to get to and the question of whether or not light has mass and if the speed is the direct result of that mass. It seems to me, that I should have been clearer.

    The question i should have asked is this one -"does the speed of light change if the mass of the light change?"
    In other words, if you fuse two photons, will they be capable of travelling faster than the speed of light of one photon? c?
    Perhaps even shorter, if two photons fuse and become a photon(2)? will c than become c(2)? as in the speed of fused light?

    article about scientists fusing photons http://www.nature.com/nature/journal/v502/n7469/full/nature12512.html
     
    Last edited by a moderator: May 7, 2017
  11. Jan 1, 2015 #10

    sophiecentaur

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    There is no experimental evidence at all that light has mass so it seems pretty clear to me that the question has no relevance to the real world.
    You seem to be making up a 'Physics' that is just speculative and that isn't the brief of PF. See the guidelines at the home page of the forum to see that PF is not a platform for this sort of thing.
     
  12. Jan 1, 2015 #11

    phinds

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    In a single sentence, and with a single usage, you are using "the speed of light" to mean two entirely different things. First, there is a "universal speed limit" which is the speed limit of all massless things. We know that light is massless and for historical reasons, we use the term "speed of light" to mean "the universal speed limit" although the universal speed limit is in fact independent of the actual speed of light. Second, if light DID turn out to have mass, no matter how tiny (which it does not) then it would NOT travel at the universal speed limit so in that sense it would not travel at "the speed of light" as used in the first item, it would travel at what I suppose we would come to call "the speed of photons" just as we talk about "the speed of neutrinos".

    As to the second part of your question, all photons travel at the same speed, "c" regardless of their energy. gianeshwar already told you that.

    You have, repeatedly, been given answers to both parts of your question but you seem to be fixated on the idea that you have discovered some new physics that miraculously no other physicists has ever thought of. You would do better studying physics as it is, not as you want it to be.
     
  13. Jan 1, 2015 #12

    Dale

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    If you "fuse" two photons then you get an electron and a positron. They travel with v<c.
     
  14. Jan 1, 2015 #13

    PeterDonis

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    You are getting a lot of responses pointing out that light doesn't have mass (more precisely, a photon's invariant mass is zero); but I suspect what you really mean to ask is whether the speed of light is affected by the energy of the light--e.g., would a gamma ray photon move at a different speed from an infrared photon. The answer is no; all photons move at the same speed.
     
  15. Jan 1, 2015 #14
    I apologize, it seems I cannot present the right question since all of the answers aren't actually going straight to the question I wished to propose.
    I can only presume my own perspective to the topic to be the problem. I ask for this topic to be closed.
    My curiousity has been satisfied, but I apologize to the mighty kind members who kept up with my stubborn, confusing and perhaps ignorant questions.
    I'll retire, for it seems my curiousity has no home here.
     
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