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General Relativity

  1. Feb 15, 2005 #1
    I was reading in one of my books today. It brought up an answered that I had when I was talking Modern PHysics over a year ago.

    Sadly our curriculum didn't really allow for us to do modern physics but our class flew through all the old physics for grade 12.

    Basically I had read alot of modern physics off of This Site

    So first day We did Wave-PArtice duality. HE wrote Wave on one side of the board and Particle on the otherside. Then asked which is light? People were like guessing answers. But he would ask why, howcome. I was then able to give an answer for both side. Light is a wave because it can defract and interfere. Light is a particle because it has relative mass, as blackholes and gravity affects the direction of light.

    Then after that I read about how gravity actually warps space. Also that say Starship A, when approaching the speed of light, the relative mass increases. Therefore to be moving at c you need infinite amount of energy.

    Now what my question is.
    If light has no rest mass. but relative mass. But Starship A does have rest mass and inifinity relative mass.

    What makes light not become infinte relative mass when Starship A does?

    Photon is a boson, a fundamental particle. How can a fundamental particle exist but not have any mass. What would it be made of? How could it exist?

    I haven't done string theory all that much, I think Imight get the gist of what its about. If you need to explain this with string theory.
  2. jcsd
  3. Feb 15, 2005 #2
    First and foremost, you have the wrong idea about string theory: In its present stage it can't explain anything. It is quite the opposite of what most people think, it is a theory of nothing. (but math)

    Einstien's Special Relativity predicts that any particle with a non zero rest mass cannot travel at the speed of light. That is, only massless particles can travel at the speed of light.

    The reason we know photons exist is because even though they have zero rest mass (and are restricted to only travel at c) they have non zero energy. The energy of a single photon is:

    E = hf Where f is the frequency, E is the energy of a single photon, and h is planck's constant from quantum mechanics.

    The photon is a very important particle that undoubtedly exists. Its energy is measurable, and its purpose is to mediate the electromagnetic force.
  4. Feb 15, 2005 #3


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    Basically though, everything is both a wave and a particle, including you. Its just that the smaller the particle, the more significant the wave properties. Photons, being massless, have the most distinct wave properties, but they still also have particle properties (as Crosson said).
  5. Feb 15, 2005 #4


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    As a terminology:please use "relativistic mass" for the mass of a moving particle which is not a gravity field...
    The things you mention are pretty well "handled" by the current nonsupersymmetric theories...

  6. Feb 18, 2005 #5
    oh, well the physics book from which i learnt it from said relative mass. I will say relativistic from now on.

    Like i've never learnt much at all of string theory. From what I think I've learnt is that there is 10-11 dimensions and that is because all the fundamental particles are defined by string which "wiggle" in certain dimensions. All particles therefore are different by that.

    Now what makes up those particles like an electron, what gives it rest mass?

    As for the Energy equation.
    So we know Light has Energy obviously. I think there was a very recent experiment where they were able to stop light to a dead spot. I think I read that in my email from These guys.

    So since they were possible to do that. E=mc^2 should be allowed since they got it to rest. Then there MUST be mass. As I would expect. To be made of something, there should be something, if there is something, it should have mass. Maybe not weight.
  7. Feb 19, 2005 #6


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    There is a theory within the Standard Model which accounts for (rest) masses of all fundamental particles in the SM...

  8. Feb 19, 2005 #7
    "how does string theory account for the mass of the electron?"

    It doesn't. String theory is a scam, all they do is play with complex math that they say are analogous to strings vibrating in higher dimensions. The great hope is that if they do enough of this math, an electron will just pop right out. :rolleyes:

    Photons always move at the speed c, that is built in to our universe. We all know that light "slows down" in a medium but all that slows down is the group velocity, each of the individual photons always moved at c (with respect to all observers). I suggest you reread your article because it is probably just a sensationalized title corresponding to a non-shocking result.

    Here is the equation you need to look at:

    E = sqrt[ (mc)^4 + (pc)^2) ] where E is the relativistic (total) energy and p is the relativistic momentum. Notice how this equation allows for a particle of zero mass to have non zero energy. If you move at the speed of light at all, you are massless, and you cannot move at any speed other than c.
  9. Feb 19, 2005 #8


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    You mean
    [tex] E^{2}=(pc)^{2}+m^{2}c^{4} [/tex]

    and not the absurdity you've written there...

    Last edited: Feb 19, 2005
  10. Feb 20, 2005 #9
    well it was in an email with sources and such. I don't think i kept it as it isn't in my inbox anymore.

    However here is a bbc of it. I think,
    The BBC

    Code (Text):
    "Scientists say they have slowed light to a dead stop, stored it and then let it go again."
    So I dunno.

    Michio Kaku I think has like a forum here. He did a show at infidelguy.com and i believe he believes in string theory. or M theory. I forget.
  11. Feb 20, 2005 #10


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    He WORKS in string theory.Now what does that have to do with the topic...?

  12. Feb 20, 2005 #11
    I believe they have slowed light down to like several meters per second in a MEDIUM, something like argon gas or something like that, the bottom line is that even amongst these mediums the photons themselves still always move at c. Basically they are destroyed in the collisions amongst particles from what I understand and the energy from this collision releases another photon in the same direction at c which continues until it hits another particle so to speak.
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