Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

There is no present

  1. Dec 5, 2003 #1
    ok...i am quite tired now so pardon me for any errors...let goes
    my agruement is that there is no present becos of two reasons.
    firstly there is still no clear cut definition for time.hence we cannot define present.it is not an qulaitive value.
    second, when one say present it have alredi become a past n so there is no present.
    so to sum it all up there is no present no now, but onli past n future becos i tink tis 2 area overlap..
    anyone with any other agruements?
     
  2. jcsd
  3. Dec 5, 2003 #2

    hypnagogue

    User Avatar
    Staff Emeritus
    Science Advisor
    Gold Member

    There is quite obviously a subjective experience of time, at least, that involves perception of the present. It is simply what you are perceiving right now, at this instant.

    The subjective experience of the present has also been called the specious present, since it actually encompasses a short duration of time rather than an instananeous point in time. A proof of this is simple. TV presents dynamic images to us by consecutively refreshing its image in a series of horizontal lines from the top of the screen to the bottom, but when we watch TV we do not notice this line-by-line refresh; rather we just see a single, coherent image. So photons that impress the new image on us first from the top of the screen and later from the bottom of the screen are actually perceived as striking our eyes at the same point in time. This brief duration of time where two non-simultaneous events are perceived as simultaneous is the specious present.
     
  4. Dec 5, 2003 #3
    so am i right to sae that the present is nothing more than an experience and therefore it does not exist?
     
  5. Dec 6, 2003 #4

    hypnagogue

    User Avatar
    Staff Emeritus
    Science Advisor
    Gold Member

    Well first of all, it depends on what you mean by "present." Are you talking about the subjective, specious present which actually encompasses a brief duration of time or are you talking about an instaneous moment in time?

    Second, who says that just because something is an experience that it doesn't exist? Perhaps you mean it doesn't exist in an objective sense, but that is something else entirely.

    In any case, when people talk about the present they are almost always talking about the specious present. Assuming you mean the present in your argument to be an instantaneous moment in time, I still don't see a problem with the notion. I think your difficulty arises by combining the two: you cannot reconcile how what is really a brief duration of time can be durationless, for good reason. They can't be reconciled. But this is just because we are really working with two definitions: the specious present, and the instantaneous present. Once we recognize these differences our problem vanishes.

    For instance, you say:

    In this instance, the recitation of the word "present" occurs over a brief duration of time that we perceive (roughly) as the specious present. Since this perceived 'present' is actually a duration of time, many moments (instananeous presents) will pass by in the duration of one specious present. But these are two distinct things, so there really is no paradox.
     
  6. Dec 6, 2003 #5
    wow
    man that took a while to digest haha
    ok when i thought of the present i think it as an instaneous moment.so perhaps defining the present as an experience does not work here since it does not exisit
    second u mentioned the present as the instaneous moment which mean it cannot be measured by time since it is well, instantaneoous. since it cannot be measured by time, wouldnt it be apporiate to classify the present as non exisitent ?
    this arguement is kinda fun so keeping on sending in yr agruements...=>
     
  7. Dec 6, 2003 #6
    Do 'instantaneous presents' exist? I thought Zeno (and more recently Peter Lynds) showed us that they didn't?
     
  8. Dec 6, 2003 #7
    arh... didnt see that...can u tell mi about it?
     
  9. Dec 6, 2003 #8
    Briefly the argument is that if spacetime is a continuum them 'instants' are infinitessimals and don't exist. There is just Hypnagogue's 'specious present' (which is not made out of instants).
     
  10. Dec 6, 2003 #9

    selfAdjoint

    User Avatar
    Staff Emeritus
    Gold Member
    Dearly Missed

    Where do you get that points don't exist in a continuum ("infinitesimals" is a red herring)? Th3e curve in the plane intersects points and it's perfectly reasonable to ask _which_ points. That's the basis of coordinates and equations. So the world line of your life passes theough the points (here-now) of spacetime, in the spacetime model.
     
  11. Dec 6, 2003 #10
    Wasn't the calculus invented specifically to get around the problem of the infinities and infintessimals that crop up in continuous curves and continuous space?
     
  12. Dec 6, 2003 #11
    Aside from this, most of the candidates for the QG theory require that a Plank's length be the smallest possible unit of spacetime, and thus spacetime itself is quantized.
     
  13. Dec 6, 2003 #12
    So spacetime is quantised because we our theory depends on it? That's not a strong argument. How do you get around Zeno's objections?
     
  14. Dec 6, 2003 #13
    General Relativity and Quantum Mechanics are some of the strongest theories ever to exist. They've got experimental, mathematical, and observational proofs behind them, and so are respected as being "correct" (for the most part). So, if the unification of those theories (which have proven themselves correct at all times in their respective arenas) requires quantized spacetime, then that is what must be postulated.

    There was a thread about Zeno's paradoxes, and they all seemed to be completely non-sensical by the end of the thread...what exactly is Zeno's objection against instantaneous presents? (btw, the quantized spacetime would allow for finite amounts of spacetime as the most discreet units thereof, and thus instantaneous presents aren't required at all for these theories.)
     
  15. Dec 6, 2003 #14
    I don't think that's quite right. My guess is that if space is quantised then it entails that time is also.

    Zeno's paradox of the race between Achilles and the tortoise is a 'reduction ad absurdam' argument against the idea that motion is quantised. To him this was illogical because it gave rise to paradoxes.

    It is not hard to see what he was getting at. If you make the tortoise go as slow as possible, (one quanta of distance (P-length if you like)in one instant of time), and Achilles go faster, then either the race becomes non-computable or you have to accept that at any instant Achilles is not at any particular position.

    This is not quite his argument, but it's equivalent. It suggests that the fabric of reality, whatever it is, is a continuum, and that paradoxes arise from trying to quantise it.

    So far, whenever I work it out, he turns out to be right. But I may be missing something.
     
  16. Dec 6, 2003 #15
    Why is it that we can only remain conscious within the present? Seems to me that's all we really have ... Consciousness and the Present Moment.

    Could it be that consciousness is the cause of which everything else is the effect? Wow! How much easier could it be to say that everything emanates from the Mind of God?
     
  17. Dec 7, 2003 #16

    hypnagogue

    User Avatar
    Staff Emeritus
    Science Advisor
    Gold Member

    You have it kind of backwards. Zeno devised his paradox to show that motion is impossible. That's what makes it a paradox: the logical conclusion of the argument contradicts our everyday perception of the world.

    And if anything, Zeno's paradox goes against the idea that space is a continuum, not the other way around. His paradox relies on the notion that space is infinitely divisible. If you discount this notion by assuming that space is quantized, then the paradox breaks down.
     
  18. Dec 7, 2003 #17
    Instead of just there is no present. For we have not the technology to figure that out yet. Why not just state that the present that we precept is false.
     
  19. Dec 7, 2003 #18

    hypnagogue

    User Avatar
    Staff Emeritus
    Science Advisor
    Gold Member

    In what way is it 'false'? I suppose it gives us a false impression of simultaneity, since non-simultaneous events can be perceived as simultaneous in the specious present. But otherwise our perception of the present cannot be said to be 'true' or 'false' any more than the color red could be called true or false.
     
  20. Dec 7, 2003 #19
    Illogical, not impossible. Zeno was perfectly aware that motion was possible.

    Exactly. Therefore the fault lies somewhere with his scenario, not with the world itself.

    Now I'd say that you have it kind of backwards. His paradox remains a paradox as long as you assume that space is divisible, whether infinitely, or only as far as some fundamental quanta. The paradox only goes away once you say that space is a continuum.

    The confusion arises here because if space is a continuum then it really is infinitely divisible, and therefore any finite division is arbitrary and leads to paradox.
     
  21. Dec 7, 2003 #20

    hypnagogue

    User Avatar
    Staff Emeritus
    Science Advisor
    Gold Member

    No, impossible.

    from http://faculty.washington.edu/smcohen/320/zeno1.htm

    from Zero, by Charles Seife

    But Zeno's paradox does not deal with finite divisions. It deals with infinite divisions. Infinite divisions are only possible on a continuum; if space is quantized, then there comes a point where it cannot be divided any further. This point of indivisibility is where Zeno's paradox would break down, since it requires that you be able to make further divisions of space indefinitely.

    from Zero, by Charles Seife
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?



Similar Discussions: There is no present
  1. The Present. (Replies: 26)

  2. The Present (Replies: 12)

  3. There is no present (Replies: 41)

  4. The present (Replies: 12)

  5. Where is the present? (Replies: 37)

Loading...