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Time dilation for slower objects

  1. Nov 17, 2015 #1
    Good day,
    I'm a high schooler so my knowledge of physics is futile and still expanding. Please correct me when I'm wrong, I love physics.

    Now to my question. I'm still a bit fuzzy on this theory of time dilation and the speed of light etc. But if time dilation happens at the speed of light can it also happen at slower speeds such as the speed of sound? If this is true does the amount of time dilation change within a different medium or a vacuum all together?

    My understanding of time dilation is that if you (or an object) that is traveling at the speed of light moves or emits a beam of light then that beam/movement will still move at the speed of light regardless of your motion prior to said event while everything else observing it sees it slower. Because the speed of light is constant and nothing can move faster than it. This raises another question. If this is so; your moving at the speed of light and you move just your hand, will time then slow down for the rest of your body as your hand is moving?

    I am very lost.
  2. jcsd
  3. Nov 17, 2015 #2


    Staff: Mentor

    It doesn't. The concept of "time dilation" isn't applicable to light. It's only applicable to things that move slower than light.

    It only makes sense as a concept at slower speeds.

    ...appears to be garbled. Can you give the references you are using? It appears that you have misunderstood or misinterpreted quite a few things.

    To briefly outline some of the misconceptions in your post:

    (1) Nothing except light, or other radiation that has zero rest mass, can move at the speed of light. You can't, and an ordinary object (meaning, anything with nonzero rest mass) can't. So saying "if you (or an object) that is traveling at the speed of light" makes no sense.

    (2) Time dilation is not the same thing as the speed of light being the same in all inertial frames.

    (3) As above, time dilation as a concept does not apply to light, or anything that moves at the speed of light. It only applies to things that move slower than light, i.e., things with nonzero rest mass.
  4. Nov 17, 2015 #3
    The references are from various places,
    http://galileo.phys.virginia.edu/classes/252/time_dil.html being one.
    I also came across the train example. Being that all this is theoretical/conceptual so were my questions.
  5. Nov 17, 2015 #4


    Staff: Mentor

    That reference looks fine to me. But I don't see how you are getting from what you read there to any of the questions you ask in the OP. I think you might want to take a step back and read the article again.
  6. Nov 17, 2015 #5


    User Avatar
    Gold Member

    At a quick glance, I see nothing wrong with the presentation in that link, but your understanding of it is, as Peter said, totally garbled. It does not present anything that I can see that would lead to any of your erroneous conclusions/beliefs.

    Perhaps some of your other references were more confusing than this one.

    At any rate, I suggest that you start with a simple presentation on Special Relativity from the ground up. I don't have a good reference off hand to point you to, but a forum search will likely turn something up since such recommendations occur here from time to time.

    I don't understand you point about your questions being theoretical/conceptual.

    EDIT: I see Peter beat me to it :smile:
  7. Nov 17, 2015 #6

    Mister T

    User Avatar
    Science Advisor
    Gold Member

    That's not time dilation. If you watch a moving clock, you will observe that it runs slow. A clock running slow is not the same thing as an object moving slow. A clock running slow means time itself has slowed. An object moving at a slow speed is something else, like a car moving at 30 mi'h is slow compared to a car moving at 60 mi/h.

    A clock in motion relative to you runs slower than a clock that's not moving relative to you. The faster the clock moves, the slower it runs.

    Nothing with mass can move as fast as light. It's the absolute speed limit.
  8. Nov 20, 2015 #7
    Thank you everyone.
    I will go back and start from the ground up. I must have missed or misinterpreted a large part in properly understanding. I'll revise and try rebuilding the proper paradigm for a subject this complex.
    Thank you.
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