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Can you modify this quote regarding time dilation?

  1. May 3, 2013 #1
    The total speed of an object through the dimension of space and the dimension of time equals the speed of light. An object moving through space must subtract from its movement through time for the sum to remain at lightspeed. So an object at the speed of light has all its movement through space and its movement through time must equal zero. Inversly a stationary object has all its movement through time and none through space. Making the quickest way to travel into the future is to stop moving.

    What parts of this quote need to be modified?

    The last sentence seems completely contrary to how I've understood "going into the future." Is this last sentence correct?

    The second sentence, when it uses the word "subtract", is what is hard for me to process. Can someone either modify this or explain it in finer detail? Is there a numeral that can represent one's movement through time? And can it be plugged into an equation that allows for it to be subtracted from or added to the "space numeral" so that the equation always equals the speed of light?
    Last edited: May 3, 2013
  2. jcsd
  3. May 3, 2013 #2


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    Whenever you quote something, you should provide the source.

    The subject of the quote is Four Velocity. Do a search and you will quickly see the quote is beyond redemption.
  4. May 3, 2013 #3


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    The quote assumes there is such a thing as speed through space. The only meaningful speeds are those measured against some other object. So two things may have a relative velocity, but they don't have an absolute velocity individually.

    As George pointed out, the thing that describes relative velocity is called the 4-velocity. Look it up on Wiki.
  5. May 3, 2013 #4

    Meir Achuz

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    It is a somewhat poetic discussion of the 4-velocity and 'proper time'.
    It might be how Lewis Carroll would describe it had he not predated relativity.
    The four-velocity is [itex]U^{\mu}=(c\gamma,\gamma\bf v)[/itex]. Its square is
    [itex]U^2=U^\mu U_\mu=c^2\gamma^2-{\bf v}^2\gamma^2=c^2[/itex]. The square root of this is what the quote calls the "total speed of an object".
    The word "subtract" refers to the minus sign for the space part in the 'length' formula. If v=c, then [itex]U^2=0[/itex], and equals zero as in the quote. "Travel into the future" refers to the increase of the proper time,
    [itex]d\tau^2=dt^2-d{\bf x}^2[/itex]. You can see from that equation that [itex]d\tau[/itex] is maximized if [itex]\bf dx=0[/itex]. This means the twin that never moves ages faster.
    Last edited: May 3, 2013
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