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Taking Time as the Fourth Coordinate What are the implications?

  1. Jul 25, 2004 #1
    As Einstein said, when we talk of higher speeds close to the speed of light, time becomes an important factor...So much that the time coordinate that was almost non-existent before, becomes a dominant force...

    So if we move at speeds close to the speed of light, the time coordinate become much more important...But I aint clear about the implications of this phenomenon..Can anybody shed some light on this topic?

  2. jcsd
  3. Jul 25, 2004 #2

    Fact is that when moving at the speed of light, Special relativity says that time-dilatation and length-contraction occur. Time dilatation means that clocks slow down when moving at the speed of light. Think of the twin-paradox. The brother that stays on earth has aged more then the one that was moving at the speed of light during the space trip (here the time evolved slower then on earth).

    Length-contraction is an analogue phenemenon but for lengths of objects. This means that moving objects appear shorter as the are when looked at in rest.

    These two effects are a consequence of the fact that the speed of light is an universal constant in special relativity.

    nikolaas van der heyden
  4. Jul 25, 2004 #3
    Speed is not the only important factor. When it comes to simultaneity, distance is important too, even at low speeds. Look at the time part of the Lorentz transformation

    [tex] t' = \gamma(t - vx/c^2) [/tex]

    when v << c

    [tex] t' \approx t - vx/c^2 [/tex]

    If x is small compared to v/c2 then t' ~ t. But for huge distances we must keep the spatial term.

  5. Jul 25, 2004 #4
    Well I know about Time Dilation & Length Contraction...But I was looking for some other implications that wud be there...
  6. Jul 25, 2004 #5
    Hi HT

    Your first, opening, post started with an invalid assumption, i.e. your statement
    is incorrect. Einstein never said that. He said that time is a 4-component in spacetime but he didn't say that this only becomes important at high speeds. You asked what the implications are so I'm responding to the implications of time as the 4-component in spacetime - the non-simultaneity of events isd very important in relativity. In fact it is one of the most important things that relativiity has taught us. But this important fact does not mean that for v << c that we can forget about it. We can only do that when v <<c and x << v/c2.

  7. Jan 27, 2009 #6
    What i want to know is how this affects human kind.

    For example with reference to time dilation, if we reach high enough speeds we could travel to distant planets with out fear of dying of old age of fly around for 50 years and come back to Earth to recieve the world record for oldest living person.

    So how would length contraction benefit of hinder human kind?
  8. Jan 27, 2009 #7


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    Talk about digging an old and dead thread! You did know that you're responding to a thread that had its last activity in 2004, didn't you?

    In any case, the effects of General and Special Relativity can be directly related to your GPS system, which is now used in commercial flights and most other positioning systems. So that's one obvious example on how it has affected "human kind". There are others. Many of the semiconductors you are using in your modern electronics require relativistic corrections to arrive at the accurate band structure that we measure in experiments. Without such relativistic corrections, what we observe does not match what theory predicts, which would have hindered our progress in using those materials.

  9. Jan 27, 2009 #8
    Time dilation and length contraction also bcome singifiant in cosmology....things like the cosmological horizon.
    But the major impact of relativity should not be thought of as time in vacuum....the major insight: not only is time not constant...nor is distance....the only "fixture" is the speed of light...and all curve via gravitational potential....
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