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Spontaneous Velocity.

  1. Sep 13, 2015 #1
    Hypothetically, a particle p of mass M is sitting at velocity v. Assuming M = 0, and the vi of p is 0 m/s, 0 seconds passes and vf 100 m/s is reached. Since time t is 0, acceleration cannot exist, as no t has passed between the vi and vf states. And, knowing that a = (vf - vi)/ Δt, a = (100 - 0)/0-0, a = 100/0. Because of the divisional zero, would not a be both equal to ∞ m/s^2 and -∞ m/s^2?
     
  2. jcsd
  3. Sep 13, 2015 #2

    Dale

    Staff: Mentor

    Hi TheDarkness, welcome to PF

    The only speed that a massless particle can travel at is c.
     
  4. Sep 13, 2015 #3
    So a massless particle cannot be stationary?
     
  5. Sep 13, 2015 #4

    Dale

    Staff: Mentor

    Correct, it can only move at c never more and never less.
     
  6. Sep 13, 2015 #5
    Yes, but when an electron jumps to a lower shell, and emits a photon, would not the acceleration of the photon from the point of creation be infinite?
     
  7. Sep 13, 2015 #6

    Dale

    Staff: Mentor

    Any real photon is on-shell, meaning that it travels at c at all times. If it traveled at less than c then it would be off shell and could not conserve both energy and momentum.
     
  8. Sep 13, 2015 #7
    I see. Thank you.
     
  9. Sep 13, 2015 #8
    What of virtual particles?
     
  10. Sep 13, 2015 #9

    Dale

    Staff: Mentor

    Virtual particles are off shell, by definition, so all bets are off. Virtual photons can have mass, travel at speeds other than c, and so forth.
     
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