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Getting to the Bottom of Time

  1. Dec 28, 2007 #1
    "What is time?" I am aware that the question is age-old and has loomed in the background of physics as long as the subject has been around. I am also aware that cosmologists, who devote their lives to studying the concept of time and the evolution of this universe, struggle to put a finger on an exact definition of this elusive concept. But, nevertheless, I would like to start a new thread devoted to the search for "What we actually mean when we use the word ‘time.’"
    I hope to create an environment in which we all can collaborate to get to the root of this. For those of you who might think this a frivolous and irrelevant chase, it is recognized by greatly respected physicists that this problem may be the root of our current stagnation in theoretical physics. When Tony Leggett, Nobel laureate and expert on superfluids, was asked where he believes the next breakthrough in theoretical physics to be, he told us that it would be in a change of our notion of time. Lee Smolin, famed theoretical physicist researching quantum gravity at the Perimeter Institute, states in his book, The Trouble with Physics:

    "More and more, I have the feeling that quantum theory and general relativity are both deeply wrong about the nature of time. It is not enough to combine them. There is a deeper problem, perhaps going back to the origin of physics."

    I believe the reason for this obscurity is the fact that our muddled concept of time is so intertwined with the way we communicate and is the foundation of our rationalization, that we have no way to discuss it without bringing in presupposed meanings of the concept.
    I recognize that it will be challenging for everyone to keep all posts progressive while discussing this topic, but I ask everyone to scrutinize your own posts before submitting them, making sure that you have not implied assumptions that will cause digression in the thread.

    I look forward to seeing what we can put forth here. This is a topic that I have always held close and hope to research later in life.

    -PJ
     
  2. jcsd
  3. Dec 28, 2007 #2

    Fra

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    I agree that this is a key question.

    The most obvious idea is that time is what we "measure with a clock".

    But if one analysis what "measure a clock" means, then classicaly it is somehow just monitoring the state of the clock device, and this thus provides a parametrisation of relative change.

    But where does the clock come from? and what if the clock itself is a quantum mechanical system and the identity and the state of the clock is itself uncertain.

    Indeed, if we can not distinguish a clock, how can we measure time?

    I don't have a complete answer but my personal take on this is along these lines. First the observer/system trying to measure time, need to be able to relate to, and distinguish a clock structure. But I figure that in general a clock could be any stable structureformation in the information patterns than we can use as references.

    But what the formalism is to implement this into a consistent working model is I thinks still open?

    The standard formulation of QM becomes very ambigous unless you have reliable clocks and rods, because this provides the parameters and background from which we related.

    /Fredrik
     
  4. Dec 28, 2007 #3

    Fra

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    more ponderings

    It seems on one hand, any kind of statement about something need a reference. There is always an implicit framework where the statement itself is defined.

    On the other hand, there is an ongoing feedback that seems to suggest that anything is just relating to something else because if there was a fixed reference, what would this relate to?

    This translates IMO to the task of building relations and at the same time try to avoid a fixed starting point for the relations.

    I see two ways, one way is to consider an arbitrary starting point, and simply consider how that can evolve, grow or shrink. But what does an arbitrary starting point look like?

    The other approach which I try to figure out, is to find the minimal non-trivial starting point and try to understand how it can evolve and grow and how structure can be emergent. My association to emergence of time and space is to self-organisation and learning, and to understand how complete "chaos" or ignorance is unstable.

    /Fredrik
     
  5. Dec 28, 2007 #4

    Fra

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    In the end I think there is a way to unite the two starting points, but showing that the arbitrary chosen starting point can be reduced to the minimal starting point in a certain sense. This relates to the old question also what is the smallest element or "block" that exists in our universe? I think the question is, what is the smallest element we can _relate to_. This I think has properties similar to the minimal starting point (minimum speculation).

    Edit: (Addition)

    I try to elaborate this and associate speculation, risk and expectations with the action ideas and try to give this a more proper foundation, that is also consistent with a learning perspective. I always found these things - while very nice and plausible - quite ambigous and lacking logical reasoning, the lack of reasoning is compensated with empirical support. Nothing wrong with that in itself, but I've got a strong feeling that this can be understood far better than what is currently the case.

    I think there is a deeper understanding of the so called "minimum action" principle that has a deeper meaning. The probabilistic analysis is still cloudy and ambigous for me at least.

    /Fredrik
     
    Last edited: Dec 28, 2007
  6. Dec 31, 2007 #5
    Gee Fra well it's now 1.1.2008, maybe that's why I'm having trouble understanding...
    Anyway the question was "What is time?". Well we know some things>>

    Time runs at 90 degrees to space... er we call it orthogonal (?)
    1 second and 300,000 km can be interchanged mathematically
    Any object some distance away is "detached" by an amount of time.

    Is there any real evidence that time is intrinsically different to distance except as an expression of our own perception?

    Imagine a 4d space where all 4 dimensions were spatial ones. Enter you and me (3d spatial objects). That is, there is a dimension "left over". This additional dimension is time (?) and it's direction is a function of your own personal orientation/rotation.

    Now review special relativity where (check it out) all dilation can be considered/viewed as a rotation.

    Question is what constant "force" drives time? The only thing I can think of is spatial expansion. Expansion of the universe. The big R at "c".
     
  7. Jan 3, 2008 #6
    Thank you, muccasen!
    But, I'm afraid that phrases like, "time runs" and "detached by an amount of time" are the ones that I am trying to avoid. These are simply idioms that we have come to associate with the concept of time. Of all the "concepts" we think we understand, "time" is the most interesting, abstract, and fundamental to the way we think. I would prefer not to feed into this abstractness. We should dig deeper into what we mean by phrases like, "time passes" and "before and after".

    First some notes on your comments:
    I don't think anyone would disagree with you, I've for one pondered the "facts" you've brought up as well.
    However,
    1 second and 300,000 km are interchangeable mathematically by definition!
    The importance lies in the fact that there is a limit to the ratio of number of rods passed to change in readings of a clock made by any observer. That is, if any observer lays rods in a line, notes changes in a clock, remains in the same reference frame as the rods and clock, and observes something traversing the length of the rods, they will find that there is a limit of traversed rods to clock ticks.

    I don't want to get to this yet though.
    First I want to understand the clock, because that is what we are using to "measure" time.

    The simplest clock I can come up with is this:

    With 3 particles: A, B, C observing the change of particle C changing it's location from the vicinity of A to the vicinity of B.

    A and B are some distance apart.
    C begins lined up with A as shown:

    A B
    C

    Then*, we notice a change:

    A B
    C

    C is now lined up with B.

    We observe other particles and scenarios:

    First Scenario:
    1 A B
    C
    D

    2 A B
    C (Here, C has reached B, D has not arrived at B yet, but another C _ is simultaneously (in the reference frame of A and B) at A)
    C

    3 A B

    D
    C

    So we find that 2 C's changing position when 1 D changes position.
    But, in repeating the experiment, we find that this is not always the case. Sometimes D shows up at B before* the second C does. But, C always "beats" D.
    And in repeating this experiment by substituting different particles for D and repeating the experiment with 2 C's facing off, we find that C is the only particle that is consistent (that is, when any two C's face off, they are at A together and then* at B together).

    Thus, we define the event of C moving from A to B to be one unit of "change"

    This becomes our clock!

    This is similar to our definition of the second, in which we observe a number of periods in the radiation from a caesium-133 atom.

    *this kills me to use these word because they obviously imply a time change, but for the sake of argument and despite the lack of understanding I have when I use this word, I continue

    The time we talk about is obviously completely involved with change and seems to be our way of comparing different changes.

    I am getting very tired now and would like to sleep on some of the ideas I am thinking of such as, we ascribe change to be due to interactions between matter or does change cause interactions between matter, or is there even a difference? We only "detect" photons because of the "change" it causes... and now to sleep.
     
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