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B Planck time at the speed of light

  1. Jul 7, 2016 #1
    I know that if an object moves at the speed of light, from its persepctive time will stop to a halt. However the smallest unit of time should be the plank time. So my question is, will the object (say a photon) experience throughout its life a single still "frame", or will it experience 5.39121e-44 seconds?
  2. jcsd
  3. Jul 7, 2016 #2


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    Gold Member

    I had the same thought some time back and I was reminded here that Plank time / Plank length are numbers that arise from dimensional analysis, and they do not necessarily have specific physical significance.

    Unless I misunderstood what I read at the time - there is no theory that says the smallest unit of time is the Plank time or that the smallest distance is the Plank length.
  4. Jul 7, 2016 #3
    No, it's not true at all, because:
    1. objects with mass cannot move at the speed of light
    2. only massless objects can move at the speed of light and for that objects there is no "perspective", there is no reference frame connected with them (that would violate the fact that light moves at c in all FORs) - and with that, you can't say that time will stop for them. Probably you've read that in some pop-sci book, you shoud totally forget about it :)
    So, your question is based on totally wrong assumptions, so there is no answer to it.
  5. Jul 7, 2016 #4


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    Staff: Mentor

    Both of those statements are wrong, although these misunderstandings are so pervasive that we have FAQ and Insights articles explaining why they're wrong.
    https://www.physicsforums.com/insights/hand-wavy-discussion-planck-length/ (although this discusses the Planck length, similar considerations apply to the Planck time)
    This thread is closed because it is completely based on false premises.
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