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E=MC^2 question about the M

  1. Oct 1, 2011 #1
    E=MC^2 question about the "M"

    So, energy equals mass times the speed of light squared.

    Energy can determine speed, because the energy is transferred into the 3 spacial dimensions.

    My question is with E=MC^2 itself, Energy of light would equal zero mass times the speed of light squared, right? But that would mean light had zero energy. Care to help explain? I really wanna figure this out, and I'm reading the Elegant Universe right now so it would help to understand this before going in too much further.

    Thanks,

    -Lazer
     
  2. jcsd
  3. Oct 1, 2011 #2

    WannabeNewton

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    Re: E=MC^2 question about the "M"

    This question actually comes up a lot. [itex]E = m_{0}c^{2}[/itex] is only valid for particles in their rest frames (the [itex]m_{0}[/itex] is the rest mass). A photon has no rest frame so the equation does not apply to it. In general, [itex]E = \sqrt{(m_{0}c^{2})^{2} + (pc)^{2}}[/itex] so for a photon [itex]E = pc[/itex] where p is the momentum.
     
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