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B Why does time only move forward and not backwards?

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  1. May 24, 2018 #1

    Tech2025

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    Probably an unanswered question , just wondering what people have to say.
     
  2. jcsd
  3. May 24, 2018 #2

    anorlunda

    Staff: Mentor

  4. May 24, 2018 #3
    I'm sure the brilliant minds of this forum can explain what is known this far. I believe it has to do with entropy, where everything goes from order to disorder, at the same time our perception of time is skewed. Past, present, and future all existing at once. Glad you asked also interested in the opinions on this forum.
     
  5. May 24, 2018 #4

    anorlunda

    Staff: Mentor

    You too should read the Wikipedia article.
     
  6. May 24, 2018 #5
    lol, I am.

    After doing a quick Google search and reading what is quoted below I feel more confused. Down the rabbit hole I go.

    "There is no connection between classical thermodynamic entropy(which is real) and “time” (which is an illusion), there never was, and there never will be.

    No form of "time travel" is possible, for the simple reason that there is no "time," no "time direction," no "flow of time," there is only now — there are no “pasts” and no “futures” to go to! In physics (and in QM), there is only a measure of durations of events, and of the intervals between events: the "fourth dimension of time" in mathematical physics is an abstraction — invented to enable manipulation of "Minkowski space" metrics —- it does not exist in our real Universe.

    Recommended reading: J.C.N. Smith's Time — Illusion and Reality.

    “Time” has nothing to do with any form of entropy (see What is the Easiest Definition of "Entropy"?), which in turn has nothing to do with “order” or “disorder”: Entropy is measured in units of energy over temperature (i.e, in joule per kelvin (J/K)), as Wikipedia (correctly) states in the article Entropy:

    Entropy is an extensive property. It has the dimension of energy divided by temperature, which has a unit of joulesper kelvin in the International System of Units But the entropy of a pure substance is usually given as an intensive property — either entropy per unit mass or entropy per unit amount of substance

    I challenge all disinformed fans of the unscientific notion that “entropy is a measure of disorder,” to explain exactly how a “degree of order — or disorder, as the case may be — can possibly be expressed in units of energy and temperature!"
     
  7. May 24, 2018 #6

    jbriggs444

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    As long as time moves in the same direction for everything, it does not matter whether that direction is labelled "forward" or "backward". Ripples from a rock dropped in a pond will appear to move outward either way.
     
  8. May 24, 2018 #7

    anorlunda

    Staff: Mentor

    Don't drag us into the hole also. It appears that you hopped all over on the Internet, sometimes to sources unacceptable on PF. Please give a link to every assertion that you make. (If this was not a B level thread, even Wikipedia is not acceptable.)

    The OP asked about the direction of time. not "what is time". We have had many threads about "what is time" here on PF. They tend to get philosophical and get shut down quickly, so stay away from that.
     
  9. May 24, 2018 #8
    Ahh I see, I see. Good to know. Do not want to get banned, relatively new here.
     
  10. Sep 7, 2018 #9
    What about an exploding rocket? Time reversal there is obviously connected with entropy ... and the two directions are distinguished.
     
  11. Sep 8, 2018 #10

    jbriggs444

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    If the direction of low entropy is in the direction that somebody has chosen to label as "future" then time will proceed in "reverse". The two directions are only distinguished by the direction in which low entropy is located.
     
  12. Sep 8, 2018 #11
    Then
    is not true
     
  13. Sep 8, 2018 #12

    jbriggs444

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    If a rock spontaneously rises from a pond in the middle of a circle of converging ripples, the ripples will appear to move outward because the direction of low entropy is in the direction that you have chosen to call "future".
     
  14. Sep 8, 2018 #13
    The smaller the circles the lower the entropy ... thus more into the "future", thus inwards. q.e.d
     
  15. Sep 8, 2018 #14

    jbriggs444

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    So your claim is that ripples in ponds always converge inwards over time? That certainly does not match my experience.

    Edit: I see now the scare quotes around "future" and agree with what you wrote.
     
    Last edited: Sep 8, 2018
  16. Sep 8, 2018 #15
    No, only if you choose the false direction, as you suggested.
    "Time reversal" is a tricky thing! ...
    [In Particle Physics it may be a symmetry, but not in everyday life ...]
     
  17. Sep 8, 2018 #16
    Time as a scalar quantity measurement (clock time) can be negative (or reversed) as often is the case in in mathematical equations.

    The OP implicitly (or explicitly) is teetering to time as it is experienced in life, which is a manifestation of memory moving from the past towards the future and never is experienced in reverse. This time is probably more of a philosophical discussion than a scientific discussion.
     
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