1. Standard memberKellyJayonline
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    13 Jun '13 09:03
    Does "now" have a beginning and end?
    Kelly
  2. Germany
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    13 Jun '13 16:18
    No.
  3. Joined
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    13 Jun '13 18:028 edits
    anyone;

    I know that, due to the language we use for physics, we define Plancks time as a certain "length" of time which makes it verbally sound very much like it must have a beginning and an end. But that is just because of the language we use.
    So does Planck's time literally have a “beginning” and an “end”?

    https://en.wikipedia.org/wiki/Planck_time

    I honestly don't know. I don't even know if it could make any sense to say that Planck's time “has a beginning and an end” because, if it does make sense, wouldn't that imply that there is a meaningful time period less than Planck's time (which would be a contradiction of Planck's time) else the beginning of a Planck's time happens at the 'same' moment of time as the end (which would also be a contradiction?) of the Planck's time?. But, if it does make sense and Planck's time has a beginning and an end, then isn't “now” always just one Planck's time in temporal length and thus has a “beginning” and an “end”? Anyone?
  4. Standard memberDeepThought
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    13 Jun '13 21:47
    Originally posted by humy
    anyone;

    I know that, due to the language we use for physics, we define Plancks time as a certain "length" of time which makes it verbally sound very much like it must have a beginning and an end. But that is just because of the language we use.
    So does Planck's time literally have a “beginning” and an “end”?

    https://en.wikipedia.org/wiki/Planck_time

    ...[text shortened]... lanck's time in temporal length and thus has a “beginning” and an “end”? Anyone?
    A beginning and end imply boundaries, a single point has no boundary because the boundary of a space has dimension one less than the space it bounds, a point has dimension zero, and there are no spaces (afaik) that have negative dimension.
  5. Joined
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    13 Jun '13 21:511 edit
    Originally posted by DeepThought
    A beginning and end imply boundaries, a single point has no boundary because the boundary of a space has dimension one less than the space it bounds, a point has dimension zero, and there are no spaces (afaik) that have negative dimension.
    Should we think of a single Planck's time being a "single point" in time thus without boundaries or a "period of time" thus with boundaries?
  6. Standard memberlemon lime
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    13 Jun '13 22:48
    Originally posted by KellyJay
    Does "now" have a beginning and end?
    Kelly
    No. "Now" is not a line with a beginning and end point. "Now" is simply a point.

    And here comes one of those "nows" right... now!

    .

    There! Did you see it?
  7. Standard memberDeepThought
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    13 Jun '13 23:10
    Originally posted by humy
    Should we think of a single Planck's time being a "single point" in time thus without boundaries or a "period of time" thus with boundaries?
    The Planck time is a numbers game. One combines some physical constants and calls it a time. The importance of the Planck time is that it is representative of the scale at which we expect quantum gravity effects to be important. This makes experiment challenging as event horizons proliferate at those scales. If space-time is continuous and there is no shortest distance between two points then my argument above holds. If, as for example Loop Quantum Gravity predicts, space time is essentially discrete, then for a given ideal point-like observer "now" is a discrete point and either has no boundaries or is it's own boundary in which case the beginning and end of now is now.

    As an aside loop quantum gravity involves a step where they compactify the Lorentz group, and then predict discrete states. I'd like to see a convincing argument as to why the discretization of space-time isn't an artifact of the compactification (which may exist - I haven't done a literature review).
  8. Standard memberKellyJayonline
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    14 Jun '13 10:491 edit
    I'm not trying to setup a debate I thought it interesting that "now" is so
    small if that word can be used to describe it, has some qualities of a
    eternal time limit, boundless/boarderless. Of course I may be way off
    here....I'll await someone else to show me how they differ in that respect.
    Kelly
  9. Standard memberRJHinds
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    15 Jun '13 00:20
    Originally posted by KellyJay
    Does "now" have a beginning and end?
    Kelly
    Of course "now" has a beginning and end. There was a time in the past in which the present "now" was not and a time in the future in which the present "now" will no longer be now. So each "now" in time has a beginning and end.

    The Instructor
  10. Standard memberKellyJayonline
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    15 Jun '13 04:03
    Originally posted by RJHinds
    Of course "now" has a beginning and end. There was a time in the past in which the present "now" was not and a time in the future in which the present "now" will no longer be now. So each "now" in time has a beginning and end.

    The Instructor
    With "now" isn't the beginning the same as the end?
    Kelly
  11. Cape Town
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    15 Jun '13 07:08
    Originally posted by DeepThought
    A beginning and end imply boundaries, a single point has no boundary because the boundary of a space has dimension one less than the space it bounds, a point has dimension zero, and there are no spaces (afaik) that have negative dimension.
    Mathematically, a single point on the number line is a bounded set, with the point being both upper bound and lower bound.
    http://en.wikipedia.org/wiki/Bounded_set

    I would say that on the time line, the lower bound corresponds to a beginning and the upper bound to an end, although it must be noted that the bounds are not always members of the set.
  12. Standard memberKellyJayonline
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    15 Jun '13 08:35
    Originally posted by DeepThought
    The Planck time is a numbers game. One combines some physical constants and calls it a time. The importance of the Planck time is that it is representative of the scale at which we expect quantum gravity effects to be important. This makes experiment challenging as event horizons proliferate at those scales. If space-time is continuous and there is n ...[text shortened]... n artifact of the compactification (which may exist - I haven't done a literature review).
    I missed the part of your post where you said, "...a discrete point and either has no boundaries or is it's own boundary in which case the beginning and end of now is now."

    I said it later, not seeing this.
    Kelly
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