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Does time control light speed?

  1. Aug 21, 2013 #1
    Hi all,

    I am wondering if time has any control over light or is it vice versa?
    For instance, is light speed controlled by time? I have read that it is impossible for anything to travel faster than light and time slows down the closer you get to light speed. Is this because of time being in control?
  2. jcsd
  3. Aug 21, 2013 #2


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    Time does NOT slow down as you approach light speed. That is an artifact of remote observation. Right now, as you read this, you are traveling at .9999999c from some frame of reference. Does your time feel slowed down?
  4. Aug 21, 2013 #3
    Time is relative; space [distance] is relative. The local speed of light in this universe is constant as viewed from inertial reference frames [observers at fixed velocities].

    Your local TIME, say via the wristwatch you carry, never varies but distant observers may well record THEIR local time differently from your time intervals. Two things affect the relative [near and distant] passage of time: relative velocities and differences in gravitational potential. So when in an airplane, for example, time passes ever so differently from a 'stationary' earthbound observer. Yet everyone still sees the same speed of light locally.

    Everything around us has origins in the big bang....everything appears to have erupted from a single unstable entity....light, the mass of the electron, quarks and the nature of forces between them, gravity, vacuum energy, and so forth. So in some way everything is related, since it has a common origin, in some way that we don't yet fully understand
  5. Aug 23, 2013 #4
    Crash course

    Nope, time is a dimension- it doesn't 'control' anything. I suppose you could say rather loosely that it is controlled by the reference frame you take.
    For example take this scenario- the superhero Flash decides to check if he can break the ultimate speed barrier i.e. c while I decide to take him on for a race. Flash starts running and say reaches 0.9999 times c and I being normal take an uniform negligible (w.r.t. c) velocity. What I will then see -keeping in mind that in my reference frame I am at rest- is that Flash's all metabolic activities have moved into an ultra slow-motion and his wristwatch too is barely moving at all 1- Oh that and Flash has become almost paper thin -due to lorentz contraction 2 and enormously heavy 3- because he has an enormous amount of kinetic energy which by mass-energy equivalence exhibits itself as mass, its exactly this fact which stops him from attaining c as his mass increases and more and more energy is required to increase even a small amount of velocity. While Flash who is at rest in his reference frame will see the exact same changes in me.
    Say, now Flash seeing my heart beats so slow rushes back to administer a c.p.r. In doing this Flash leaves his constant velocity frame (I.R.F) and accelerates back in my direction...Now things become interesting...When he then reaches me, he will either see me have grown several years older or altogether dead.:surprised .This is because the race which lasted only for a short period of time for him has been an eternity for me. (This is what gives rise to the twin-paradox.) Then the you may object that Flash has been travelling at the same speed w.r.t. my frame and then he too should have grown old and the effects 'cancel' each other out, but you see Flash did do something that I didn't- he accelerated! Therein lies the mischief, and then the symmetry breaks down.
    The Boring Math Part:
    1) Time dilation
    [itex]t=t_{0}/\gamma [/itex]
    2)Lorentz contraction
    [itex]L=L_{0}/\gamma [/itex]
    3)Apparent mass
    [itex]M=\gamma M_{0}[/itex]

    Where: t0; M0; L0- are in the frame in which flash is at rest
    and t; M;L are in your frame.
    And [itex]\gamma[/itex] is the lorentz factor
    see how as v (speed) approaches c mass M0 becomes larger and altogether infinite at v=c ?
    Last edited: Aug 23, 2013
  6. Aug 23, 2013 #5
    I think what you're trying to ask is whether or not the speed of light can vary due to dilations or fluctuations in an observers' perceived time.

    The answer would be no, Einstein's Special Relativity stipulates that all observers see the speed of light as a constant, which in turn causes time dilation
  7. Aug 24, 2013 #6
    Just to clarify, my post# 3 is general...and describes both special and general relativity, that is, with and without gravity; posts #4 and # 5 are for SR...no gravity.
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