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Thread: Wonders of the Universe

  1. #1 Wonders of the Universe 
    Forum Freshman Fatboy Miller's Avatar
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    Great to see Brian Cox back in a new 'wonders' series - love everything he does!

    One point I didn't quite get...

    He raises the point of why the arrow of time runs from present to future, not present to past and 'proves' it by the second law of thermodynamics (order to chaos). Is this not a tautology? If a universe existed with the arrow of time reversed, would any inhabitants have a second law of thermodynamics of chaos to order?


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  3. #2  
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    Well if you refer to the sandcastle example..

    If you start with a pile of sand.. (chaos) why wouldnt it arrange itself like a sandcastle (order).

    Well first of all, there are many orderly ways of arranging the grains of sand.. so why should it tend towards the sandcastle? Why not a sand sculpture of a persons face or whatever? But then for every possible orderly arrangement there are a near infintesimal number of chaotic arrangements.

    If change is guided only by chance and a few basic fundamental laws.. its more likely to arrange itself into one of the chaotic arrangements. Thus order to disorder. (Of course, if change is guided, say by a god, then this wouldn't apply - hmm.. [ponders] does that mean the second law of thermodynamics suggests no god exists?)


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  4. #3  
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    @Fatboy:

    Yeah that's true. If you define the forward direction of time of being the increase of entropy (obeying the 2nd law of thermodynamics), then it will allways be true that if 2nd law is obeyed, then time runs forward.

    But what you can actually prove is that time is directed in any way (forward or backward, as you define it), and this wouldn't be a tautology.
    I am.
    You can't deny it.
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  5. #4  
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    There isn't any arrow of time, fatboy. Not really. Clocks clock up motion. It doesn't matter whether it's an atomic clock at NIST working off the hyperfine transition, a quartz wristwatch driven by an oscillating crystal, a pendulum clock, or a sundial, there's always motion of some kind being accumulated, with some kind of display. When you turn the clock "forward" for daylight saving hours, this "forward" is just a figure of speech. And whilst all the ongoing motion in the universe tends from order to chaos and we talk of entropy, it's not really a "direction" as such. Things that move move in different directions in space, but there is no overall direction associated with all that motion. It makes as much sense as talking about something hot cooling down in the direction of cold.
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  6. #5  
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    Quote Originally Posted by Farsight
    There isn't any arrow of time...
    Horsefeathers

    The symmetry of time (T-symmetry) can be understood by a simple analogy: if time were perfectly symmetric then it would be possible to watch a movie taken of real events and everything that happens in the movie would seem realistic whether it was played forwards or backwards.

    An obvious objection to this assertion is gravity: after all, things fall down, not up.
    (ref. http://en.wikipedia.org/wiki/Arrow_of_time )

    Chris
    It is difficult to say what is impossible, for the dream of yesterday is the hope of today and the reality of tomorrow.
    Robert H. Goddard - 1904
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  7. #6 well 
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    NOT all laws are correct , and not the second
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  8. #7 Re: well 
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    Quote Originally Posted by Water Nosfim
    NOT all laws are correct , and not the second
    Please post what you feel is the correct 2nd law of thermodynamics.

    Thanks
    Chris
    It is difficult to say what is impossible, for the dream of yesterday is the hope of today and the reality of tomorrow.
    Robert H. Goddard - 1904
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  9. #8 Re: well 
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    Quote Originally Posted by CSMYTH3025
    Quote Originally Posted by Water Nosfim
    NOT all laws are correct , and not the second
    Please post what you feel is the correct 2nd law of thermodynamics.

    Thanks
    Chris
    Its hard to me to write in english but time can go backwerd , it can be statistic , and depend on the arya .
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  10. #9  
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    Quote Originally Posted by Farsight
    There isn't any arrow of time, fatboy. Not really. Clocks clock up motion. It doesn't matter whether it's an atomic clock at NIST working off the hyperfine transition, a quartz wristwatch driven by an oscillating crystal, a pendulum clock, or a sundial, there's always motion of some kind being accumulated, with some kind of display. When you turn the clock "forward" for daylight saving hours, this "forward" is just a figure of speech. And whilst all the ongoing motion in the universe tends from order to chaos and we talk of entropy, it's not really a "direction" as such. Things that move move in different directions in space, but there is no overall direction associated with all that motion. It makes as much sense as talking about something hot cooling down in the direction of cold.
    Rubbish, as usual from you. Crank.
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