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What is time?

  1. Jul 22, 2007 #1

    One of the great marvels of science appears to be the existence of time.

    I have been searching for the scientific evidence of such physical existence of time but I have foundd none.

    This is amazing for me because I understand that several tests have been made to proved a dilatation of time but time itself has been never prove as existing by experimental methods.

    How is this possible?

    As far as I can understand science in general, at this step in our knowledge, the physical existence of time should be a priority goal.

    I went inclusive to Wikipwedia as my last resort and the only definition of time is given as data or quantities of data, but nothing that guide us to the certainty of such physically existing and flowing time.

    Wikipedia appears to recognize that time cannot be defined by physical means, and this bothers me a lot. If time is not physically existent, then how we say that time flows and dilates?

    Does someone have any contribution which can lead us to establish a solid definition of time with its correspondent evidence through the requirements established by the scientific method to prove its physical existence and flowing?

    Last edited: Jul 22, 2007
  2. jcsd
  3. Jul 22, 2007 #2
    The only truism I can come up with is that it must be something, since we experience it.

    I believe that this is a precept of most philosophies; that human experience has some basis in 'real' 'reality', even if it isn't the most direct representation.

    Can anyone with experience in GUTs tell me whether there are any that consider time to be an otherwise identical dimension, or is it fundamentally different to the spatial dimensions in all theories?
  4. Jul 22, 2007 #3
    lol, are you searching for the ether of time? space and time are dimensions, information needed in order to specify location in our universe... time does not flow or change, you move through time, just as you move through space, the main difference is that you have some default motion through time but not through space, you can't however move through space without affecting time. When one says... time dilates, all that means is that they are moving slower through time (thus time passes slower) because they are moving faster through space. There's sort of an equilibrium between space and time. We are at one end were we move full speed through time and stand still spatially, and at the other the photon who moves at full speed through space and thus does not move through time. There is nothing mystical here, but this is a cool quote... "time is nature's way of keeping everything from happening at once" The fact that things change can be your physical proof of time.
  5. Jul 22, 2007 #4
    Although there is a mathematical basis to "dimensions," we really do not have evidence that time is a dimension. In statistical thermodynamics, kinetics, etc., time is something that is not all-permeating but rather judged based off of temperature, the motions of particles, etc.

    * The physical basis of time

    - Bryan
  6. Jul 22, 2007 #5


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    Have you checked your watch?
    I'm not sure what you mean by that, but their definition seems reasonably good to me - and directly contradicts your assertion that it can't be measured:
    As it says, there is no more difficulty in measuring and/or accepting the reality of time than there is of other physics fundamentals such as length and mass. We get a lot of people here who question the existence of time, but for the above reason, I never understand why they have so much trouble with it.
    Last edited: Jul 22, 2007
  7. Jul 22, 2007 #6
    The main problem with time in physics is whether time flows, ie whether time is static like a spacial dimension or whether we really move through it like common experience suggests. In Brian Greene's Fabric of the Cosmos he quotes Einstein as saying that time is static and the the perceived flow of time is an illusion caused by our own minds. He says there is no physical basis for believing that time does flow. Spacetime is thought of as a 4-dimensional structure with points corresponding to each event, where time is one of the axes.
  8. Jul 22, 2007 #7
    because a lot of physical "laws" are time independant, in that they work the same backwards and forwards "in time".
  9. Jul 22, 2007 #8


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    i nearly completely agree with you, Russ, particularly for someone doing "operational" physics as opposed to existential and metaphysical philosophy. we know it's there (or something is there, that we detect with our own consciousness, and measure with clocks), we don't know precisely what it is (just as we don't know precisely what space is or what reality really is), but, at least for us operational or rational or empirical folks, we sorta skip over that issue and start describing it and how it is related empirically to the rest of reality that we observe. we observe some coupling of motion in space to time, that this coupling is linear for inertial movement, and we observe this arrow of time that, so far, has not been shown to be violated outside of the mystery of black holes, as far as i know. this arrow of time has, i believe, no counterpart to the 3 spacial dimensions, and for that reason is sufficient to differentiate it qualitatively from space (which is a belief challenged by relativity, depicting time as the same kinda "stuff" that space is but with mathematical values that are imaginary numbers, but not sufficiently challenged for my money).

    as human beings, our concept of time was shaken up a little by Einstein in such a way that its alledged absolute, universal, and eternal nature is challenged. for people or objects in frames of reference that are not stationary relative to each other, neither is their perception or observation of time identical.

    if it is true that time itself had no existence "before" the big bang, it could also be true that if there would ever be a "big crunch" (i am not saying that such would ever happen), that time itself would have no existence "following" the big crunch.

    but we don't know exactly what time is just as we don't know exactly what reality is, although most of us accept the existence of both. and then, once we get past that, the only thing that an empiricist can do is, from observation, try to discern relationships between this thing we measure with clocks to any other physical phenomena. we have such relationships (of "stuff" vs. time) in Newtonian physics, Einsteinian physics, "Schrödingerian physics" (a.k.a. Quantum Mechanics, there is a time-dependant version of Schrödinger's equation, even though it wasn't used much when i was learning some of this stuff in college), and i s'pose in any TOE or GUT or cosmology (although what they say about time is far beyond my pay grade, being an engineer).

    Newtonian physics had no intrinsic natural coupling factor between this thing we call "time" and anything else. well, i guess it does in the same way that General Relativity does with the Gravitational constant, [itex]G[/itex]:

    [tex] t = \frac{1}{\sqrt{G}} \cdot \sqrt{ \frac{d^3}{m} } [/tex]

    where [itex]d[/itex] is distance (or length, the measure of "stuff" in one spacial dimension), [itex]d^3[/itex] would be volume, and [itex]m[/itex] is mass.

    Special and General Relativity ("Einsteinian physics") intrisically or naturally couples time to distance by use of a scaling factor we commonly called the speed of light, [itex]c[/itex]:

    [tex] t = \frac{1}{c} \cdot d [/tex]

    And Quantum Mechanics (or "Wave Mechanics" or what i've been calling "Schrödingerian physics") intrinsically naturally couples time to energy by use of a scaling factor we commonly called Planck's Constant, [itex]\hbar[/itex]:

    [tex] t = \hbar \cdot \frac{1}{E} [/tex]

    but we already have a relationship that defines the stuff called "energy" in terms of stuff we call time, mass, and distance, ([itex] E = F \cdot d = (m d/t^2) \cdot d [/itex]) which turns the scaling factor around so that, more fundamentally:

    [tex] t =\frac{1}{\hbar} \cdot d^2 m [/tex]

    Now all of these scaling factors, [itex] 1/G, 1/c, 1/\hbar [/itex] are there only because of the (most commonly) anthropocentric (or, more precisely, "anthropometric") units we came up with as a consequence of the clocks, (meter) sticks, and weighing scales we use. We can (and do, with "Planck Units") make these all go away from our known laws of physics (which are really just mathematical expressions of what we observe). For instance, with relativily (special or general), when we choose units so to set c=1, does that mean that time and distance are the same thing (time, expressed as a spacial dimension, picks up a dimensionless mathematical constant factor of the imaginary unit, i, so "time" would be "imaginary distance" i s'pose)? But if you look at the other two relationships (with natural units), is time the same thing as area times mass? or the square root of volume divided by mass? i don't think so (i could manipulate those relationships above to show that time is the same as its reciprocal and same for all other fundamental quantities), but there are physicists who think that there really is no dimensional difference between that stuff.

    sorry, if i am creating more questions than answers, but maybe the answer to the OP's question is "we don't exactly know".
    Last edited: Jul 22, 2007
  10. Jul 22, 2007 #9
    Thank you very much for your reply.

    I have thought about your words and I asked myself, how do we "experience it?"

    I checked the philosophical thoughts and most of them appear to direct a time which flows, but scientifically such event is not validate by any experiment made exclusively for it. Other philosophical thoughts say that "we are time", something which also won't guide us scientifically to any place.

    I guess that philosophical thoughts about time must be discarded because these cannot be verified through the scientific method.
  11. Jul 22, 2007 #10
    Your reply is most than interesting. Please allow me to consider time as a dimension, this is to say that time can be understood with coordinates.

    I make 23 lines with the same intervals on my desk earth globe from pole to pole and I called them Longitudes or Hours. Having you correct, I guess that time is what you say, a dimension with coordinates.

    Now well, that is what we humans draw in an earth globe, but in physical reality our planet doesn't have such lines. I guess again that for this reason several books point that such are imaginary lines.

    Still, I can perceive space between the drawn longitudes in my easrth globe and between my physical location in reference with other locations. I perceive that betwen my person and Japan there is a separation. There is no doubt that there is a space between you and planet Mars and between the White House and the Crab Nebula.

    I can't, however, say the same about time, because according to you, time is a dimension only.

    As far as I can check your point, I can obtain the other three dimensions from a physically existing space, and I know it exists because I can perceive it like everybody. Because everybody can perceive it with their senses as I do, this is considered as physically existent.

    I don't know if we can do the same with time. I have no idea that there is a sense or a device which will allow us to perceive the flowing of time.
  12. Jul 22, 2007 #11
    I guess that your point is very different, I can think of it like if time is no more than a measurement.

    Having time as a mesurement and not as a dimension, we cannot measure time but that we can use the units given to this measurement to measure the motion of things.
  13. Jul 22, 2007 #12
    Yes, I did it. I did something more than checking my watch, I opened it.

    I don't see any particular sensor inside my watch which will allow me to measure the physical passage of time. I guess that I better open an old mechanical watch which is more easy to identify its parts.

    I have a pictorial dicctionary, I'm lucky. Let me see. I see the parts of the watch but no sensors to verify that time is flowing in a standard way. Sorry, I guess that a watch cannot measure any passage of time.

    Ok, please check in Wikipedia how the physical flowing of time is measured. If you find it, I'll hope you also post it here. What I understand is that they can define time as many ways is possible but not so under any experimental data.

    Maybe my words can be understood with the following example:

    I perceive space. For this purpose, I say that there is space between me and a wall over there. I extend my arms and I cannot reach the wall. I must walk in order to reach it, so, I have experimentally proved the existence of space. I can use several methods and all of them will prove the same. Then, I measure the separation between me and the wall and called it distance. Distance is not physically existing, the word distance exist as a reference, it it is a concept. On the other hand, what is physically existent is space.

    I think that the autor(s) in Wikipedia cannot show similar experiments about a flowing time. This appears to be a difficulty for the article.

    Perhaps is because the question is not answered yet with the proper scientific support.
  14. Jul 22, 2007 #13


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    "Time is nature's way of making sure that everything doesn't happen all at once."

    "Time flies like an arrow, fruit flies like a banana."

    "Time, time, time
    See what's become of me...
    Time, time, time
    See what's become of me
    While I looked around
    For my possibilities
    I was so hard to please
    Look around
    Leaves are brown
    And the sky
    Is a Hazy Shade of Winter..."
  15. Jul 22, 2007 #14


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    Lol, check again - it's on the outside of the watch! :rofl::rofl:
    Look at your wach. (read aloud the number the second hand is pointing to)

    Now look at your watch again.

    You've just measured the physical flow of time.
    You agreed with wik before when you thought it supported your point - you cited it, not me. Perhaps the problem isn't with wik or with the scientific supoprt for the existence of time. Perhaps if you drop your preconceptions and actually try to understand what time is, you will.
    Last edited: Jul 22, 2007
  16. Jul 22, 2007 #15


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    Why are you picking on time? You can't see mass in the way you can see length either, but yet you do not have the same incredulity about its existence, do you?

    Time is different from length. You don't measure it in the same way and you can't see it with your eyes in the same way. But you can still measure it and perceive it with the proper tools. Just like mass. So why the problem with time?
  17. Jul 22, 2007 #16
    I agree with you, "if" it is true. What happens "if" it is not true? Any alternative from your part?

    I ask for your forgiveness because I cut off your whole paragraph , but it was necessary.

    Scientifically we know what reality is: in science Reality is what exist physically. check Wikipedia:

    Reality, in everyday usage, means "the state of things as they actually exist."

    We do know what reality is. As long we perceive it, it is real. You perceive the image and the breeze when you are standing in the sand near the ocean, and also you perceive a rotten lotion which smells like ocean's breeze and you have a picture in a wall showing you the sand and the ocean.

    As long as you perceive them and they can be perceived by others as well, what you perceive is physically existent.

    Now, you imagined both, the breeze and the image, the imaginations still real but in your mind alone. As your imaginations cannot be measured or perceived by others, your imaginations are not accepted as part of science (physics) to validate a theory, to analyze them as a phenomenon and more.

    I must disagree with what you just say. With all my respect, why you seem to jump to conclusions when right in the beginning your points appear to be full of gaps?

    Example: "we don't know exactly what reality is, although most of us accept the existence of both. and then, once we get past that,..."

    Wait please, do not run because you can fall.

    Take it easy. You don't know what reality is but you accept consciouness detections as real things, and with such base you just got pass that.

    I don't see any reason why I can trust what you just said.

    If I accept your words as the answer to define and prove the existence of time, I practically have nothing to verify what I received from you.

    I cannot read your mind, I myself do not detect with my consciousness any physical passage of time, and neither I can find any device which can detect it either.

    I am disappointed with myself, I should like to detect the passage of time with my consciousness as well as you do. Even so, right after that, I should like to prove such detection with a device so I can finally accept its physical existence with a scientific validation.
  18. Jul 22, 2007 #17
    The question is whether or not there is a present moment that is moving forward through time. What is physically different about the present moment from other moments? Do all moments in time simply exist as points on a line or do we flow along the line with only one moment existing at a time? According to both Brian Greene and Paul Davies (and apparently Einstein) there is no such thing as the present moment and time does not flow. Time is static.
  19. Jul 22, 2007 #18
    What's all this blabbering about time? Time is not a physical object. You can't affect it. (I didn't feel like reading all the posts, so here's my 2 cents)

    Before the universe, "time" had always existed and never changed. It doesn't change; it can't change. Time is a constant. If "time" were to freeze, the universe would cease to exist. We only concern ourselves with time because matter is finite, and we must measure how long it has existed with something. Time is far from finite, therefore, you can't affect it. It's like trying to reduce the amount of numbers in existence. You can't.

    Don't go looking for time with "experiments", because all you are going to find is matter, space and energy. Time, by defintion is an object which is impossible to "detect".

    Time is the measurement of the progression of events. It is not anything like jelly or hydrogen (immaterial). It does not cease to exist apart from matter, but it only has a use with matter, being the subject of cause and effect.

    Time does not intersect with space. It is a constant, and by definition unaffectable by anything else.
  20. Jul 22, 2007 #19
    Yes I can't see mass because mass is a measurement of matter and is considered as a concept in physics.

    I can't see lenght itself bbecause is another concept but I can apply this concept in physics and see your lenght, the lenght of an airplane, and more.

    Concepts as lenght, width and depth are given to the structure of things in the universe by their physical appearance. You can see their appearance, and we live in a three perceptable dimensional universe. Don't you think?

    When someone says to me, "look, if you take a point which has one dimension", I immediately disagree with that idea as a fact.

    Actually there is not such thing as one or two dimensional worlds, we use those concepts to make our studies more easy to understand, but when I draw a point in a piece of paper and I use a magnified glass or a microscope I will notice that the paper itself is three dimensional and that the point in the piece of paper is also three dimensional as well. It is understood, however, that used as a reference in a study I can consider the point as one dimensional object, and the drawing in the paper as representing a two dimensional picture or image.

    You say that we can measure and perceive time with the proper tools, I have been loking for those tools and find none. I will please ask you to name those tools.
  21. Jul 22, 2007 #20


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    As would I: points have no dimensions.

    Huh :confused: What's wrong with a watch?
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