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Why time is a separate physical quantity

  1. Aug 6, 2010 #1

    I have a question about time.

    I don't understand why everyone thinks of a time as some coordinate like x,y,z. I don't get it. From my point of view the time as some physical quantity doesn't exist. Because there is only moving matter. And we can talk about time by observing changes in that matter. So we can talk about time only when the hand of a clock moves from one position to another. And time dilation is just a different type of matter movement. And so time travel is impossible because one must change all matter to it's previous position. I really don't understand why we talk about time as some existing entity.

    I suppose I have some major flow in my understanding. So can anyone explain to me this issues or point to some books, articles?

    Thank you
  2. jcsd
  3. Aug 7, 2010 #2


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    What does this mean?
  4. Aug 7, 2010 #3
    What exactly you don't understand?
  5. Aug 7, 2010 #4


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    What do you mean by "time dilation is just another matter movement"?
  6. Aug 7, 2010 #5
    I don't know if I can say it right. One says that time slows down when an object's velocity is approaching a speed of light. And I don't understand why we are talking about 'time'? Why not particles start to move slowly and because of that we perceive time differently. But my main point is why we are talking about time like any other real quantity like mass or position. What is a base for that assumption? Why one thinks that time actually exists? I can only see that particles/atoms/whatever are changing their positions. And because of that changing we can talk about time. But the time doesn't really exist. I'm not trying to prove my point, I just want to understand where I'm getting wrong. I hope you understand what I am talking about.
  7. Aug 7, 2010 #6


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    The particles don't begin to move slowly though.

    In classical mechanics, we define some abstract concept called "time" as some parameter that we can have as an invariant quantity. This is invariant because going from different reference frames, we always have this time ticking away at the same rate whereas other quantities change. Kinetic energy typically changes going from one inertial frame to the next. Velocity changes as well. Time doesn't.

    However, this doesn't jive well with observations of high speed systems. Enter Relativity and it helps explain everything we know to be true today.

    If you're really looking for a concrete example, look at high energy physics. Particles having lifetimes of [tex]10^-6s[/tex], a pure "time" quantity. However, when accelerated to near the speed of light, they take far far longer until they decay which allows us to actually do particle collisions and high energy physics. Time being an invariant quantity would not allow this.
  8. Aug 7, 2010 #7
    time has existence even if there is no significant movement you see time is not some thing that you see on the clock einstine imagined time as a dimension it self
    so yes there is a flaw in your understanding .time is the most essential ''ingredient'' for any process to proceed in the universe if there is no time there is no movement time allows movement time is not dependent on the movement of a object for its description its the other way around . what you see on the clock is actually the mathematical evaluation of time the clocks dont create time they are measuing tool of time if there be no clocks time would still have an existance.
  9. Aug 7, 2010 #8


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    Time keeps everything in the universe from happening all at once. It is inexorably tied to the finite speed of light and clearly has a place as a coordinate system in astrophysics. A universe without a time dimension is irrelevant.
  10. Aug 7, 2010 #9
    FizixFreak, yes that's exactly what I'm talking about. I know this point of view. But I don't understand it at all. What is the base for such assumptions? Why one thinks that time exists without movement? Is there some experimental data that proves that time is actually another dimension? Or maybe theoretical explanation?
  11. Aug 7, 2010 #10
    Chronos, why there is a need of such thing as time to keep everything from happening at once? Isn't it sufficient that there is matter (atoms and stuff) that moves at different speed thus creating different states one after another. Because speed is fixed (not infinite), there is no possible way to make all this states at once. They just follow one after another. Where am I wrong. And please consider answering my questions to FizixFreak.
  12. Aug 7, 2010 #11


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    What is 'speed' without time?
  13. Aug 7, 2010 #12
    Ok you made me thinking. We define speed through distance and time. That's odd. But what the time is anyway? I though of it as changings in a matter. So there is no 'time' at all. But FizixFreak says that time exists even if matter is not moving. So it's kind of 4-th dimension. But is there any scientific proof of time existing as separate entity? Had anyone made such effort? Had anyone explained in detail what time is and why it is what it is? Or we just rely on some intuitive understanding of 'time'?

    Speed without a time. How about speed is just a movement of matter perceived by other matter (aka observer). So we can talk about speed just because we participate in that movement ourselves. If nobody is watching is there any speed at all? Yes it is messy but I hope you'll get my point.
  14. Aug 7, 2010 #13
    And I'm hoping there is someone out there who is as confused as I am so he can contribute to my questions...
  15. Aug 7, 2010 #14


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    And what does the matter change with respect to? Do you understand the mathematical concept of a derivative, which encapsulates the idea of changing?
  16. Aug 7, 2010 #15
    Time is generally not considered separate from space. In fact, they are considered to be a part of the same thing, space-time.

    Maybe this will help. Consider the following example:
    Particle A is at position (x,y,z). Particle B interacts with particle A. The interaction causes Particle A to move to (x2,y2,z2).

    Note that I didn't use any time words. I just used the word "causes." By using this word, you understand that one event happens before the other. If there is no time, how can I know what happened first? Without time, A and B are simply particles moving in space. With time, it seems like B causes A to move.

    Time helps us to understand how events happen in sequence. This helps us to understand which events are the results of other events.

    We need a certain frame of reference in which to describe events. It turns out that we can describe many events with an arbitrary number of spacial dimensions, but we also need time for these events to make much sense to us.

    I don't claim to understand time. We're in the same boat here. These are just my thoughts. I hope I explained them clearly enough.
  17. Aug 7, 2010 #16
    DaleSpam, yes I understand derivatives and I know that v=ds/dt. But my explanation was descriptive not formal.

    To make it clear can anyone answer this questions:
    1. Is there some experimental data that proves that time is actually another dimension? Or maybe theoretical explanation?
    2. Had anyone (i mean scientist) explained in detail what time is and why it is what it is? Or we just rely on some intuitive understanding of 'time'?

    I don't think that this questions are so hard to answer if there is an answer to them of course.
  18. Aug 7, 2010 #17
    adaptation, thank you for your explanation. But than I have another question. Does time actually exist? Or is it just how we perceive things? Is there a 'time' without us? Had any scientist answered such questions?
  19. Aug 7, 2010 #18
    This is really a very deep and subtle and complicated question. It hasn't been answered yet. It may in fact be unnecessary to use time to describe the physical phenomena we observe. One thing that's for certain though, time is a very useful concept, it makes theories far easier to write if you use it!

    Take at look at Julian Barbour's website: http://www.platonia.com - he has investigated the nature of time, you might find it interesting. Another good place to look is the FQXi site: http://www.fqxi.org/community/essay/winners/2008.1 There are lots of essays about the nature of time there, quite a few say time doesn't exist on a fundamental level.

    It's certainly a very interesting question. Whether anyone will find a good answer any time soon is another matter...
    Last edited by a moderator: Apr 25, 2017
  20. Aug 7, 2010 #19
    Thank you very much, Tomsk. I have suspected that there is something wrong with 'time' in physics. Now I see that it is simply an open question and has no concrete answer yet. I'll definitely check out those essays. Thanks again, your post was very helpful.

    I suggest if anyone finds interesting links on that subject he will post them here.
  21. Aug 7, 2010 #20

    Do you think all masses (say the elements) are related? Why?

    Do you think the weak force and the electromagnetic force are related? Why?

    Well, it turns out they are related: we think that way because we have some underlying understanding...you could say, for example, all the elements are related because they are different combinations of electrons, protons and neutrons; and the two forces we know are related from electroweak unification (mathematics). It's like being able to tell you and a brother, for example, are related because it's imprinted in your DNA.

    It's likely that all those "different" components that appear distinct now are derived from 'spontaneous symmetry breaking' at the the origin of the universe...the evolution of what you observe currently from an incredibly high energy and very unstable initial conditions near the beginning of the universe....so it is assumed gravity, the strong force and electroweak forces, for example, originate from a single entity....likewise, it's quite possible time and space, as well, spring from that "fundamental" entity.....but we don't know much about time at all and not nearly enough about space to understand exactly how they are related.

    All the above is obscured by the fact that so far the BIG BANG is outside our best theories...it's a singularity we do not know how to model.....that's a big reason black holes are of such interest, because they,too, are singularities which we think exist now and it is hoped studying them will provide some clues as to how gravity and space, for example, are linked. Then we'll have to figure out how the big bang singularity at the beginning of the universe is related to black holes at the end of the universe.

    Finally, it just might be that the common "element" among everything we observe (space, time, matter, energy, etc) is INFORMATION in disguise....but that is beyond currently accepted and widely held theory.

    It may help you to remember most of the statements in your original post are contrary to the best current scientific understanding: for example:

    "And time dilation is just a different type of matter movement."

    not so; differences in gravitational potential also affect the observed passage of time....For example, time appears to stop at the horizon of a black hole as viewed by a distant stationary external observer....so both velocity and gravitational potential are factors.....

    This stuff is NOT obvious nor intuitive; if it were, everybody would be a physicst.
    Last edited: Aug 7, 2010
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