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Stephen Hawking's Theory of Everything and Imaginary Time

  1. Dec 20, 2006 #1
    Hi, I am new here and have been lurking awhile. I have been reading Stephen Hawkings Theory of Everything and it brought up imaginary time. ( I got this from the library and just saw online he did not endorse this book) It got me thinking. Time is based on Earth's observations to the solar system. So then say we do eventually "colonize" outside earth- earth's time can't be imposed onto a different planet/ place- it wouldn't work. And for the big picture isn't it hard to try to figure the universe out when the current time dimension is really just "earth time" and not "universe time" so to speak. Then when you factor in speed "altering" earth time - well it gets a bit boggling!! Any opinions or ideas on this.
     
    Last edited: Dec 20, 2006
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  3. Dec 20, 2006 #2

    EL

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    No, time is defined through atomic processes:

    http://en.wikipedia.org/wiki/Time#Standards
     
  4. Dec 23, 2006 #3

    disregardthat

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    Isnt time decided in planck metres?
     
  5. Dec 24, 2006 #4
    thinking of time as a dimension or co-ordinate system is much easier than thinking of it as some etherial force that drives things. In this way the dimention is the same everywhere in the universe, its just the scale of the coords is different (for different civilisations and effects of relativity etc)
     
  6. Dec 24, 2006 #5
    So if time is based atomically then a second is a second- but a "day" is said to be different on each planet based on sun and orbit. So from a different perspective in the universe then time woiuld be same. It almost seems as though it is putting us incorrectly at the center of the universe because "time" as we know it follows our day/night/year albeit not perfectly. I am trying to think of time as a dimension- but it just isn't working :)
     
  7. Dec 24, 2006 #6
    i hate using a thing im trying to define in its own definition but here i kinda have to. time is simply a measurement of the delay between events occuring. how you choose to measure these or what sort of unit you choose as your base is up to you and varies from civilisation to civilisation, ie days on different planets, water through a bucket whatever. What you need to realise is that we all experience the same actual gap in 'time' but we call it different things (assuming SR doesnt come into it). just think of time as an axis on a graph as you would any other dimension, and you have a scale etc
     
  8. Dec 24, 2006 #7

    disregardthat

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    I think this is a good way of seeing it:
    Think of a one dimensional line, it only goes back and forth, each planckmeter on that line decides where each 0-dimensional point is on it.
    If you think of a 3 dimensional space it is standing still. nothing is moving in it. adding the 4th dimension (1 dimension = a straight line) would be to place a 3rd dimension ot each "planckmeter" (plancksecond) on that line. We experience this as "time". So the 3dimensional volume is changing every plancksecond, (planckmeter on the 1dimensional line that we add to the 3 dimensions we have)
     
  9. Dec 26, 2006 #8
    Not every planck second, it depends on your velocity.
    Time Dilation causes this.
    General relatively must be accounted for.
     
  10. Dec 27, 2006 #9

    disregardthat

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    You are probably right, but i don't understand what you mean. Could you explain?
     
  11. Dec 28, 2006 #10
    well...Time dilation expands space/time right?
    Thats why objects seem to become infinite and time inside the object appears to come to a halt.
    So I guess that the plank-meter and those velocities is expanded too.
     
  12. Dec 28, 2006 #11

    disregardthat

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    I will look into time dialation in wikipedia

    One thing, does it have a meaning to say that a planck meter is expanding. Since 1 planck meter is the smallest unit you could have in length, so "expanding" them would not make any sense, since you have nothing to put between, if you get me.
     
  13. Dec 28, 2006 #12

    chroot

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    There are tons of misconceptions in this thread.

    Time is a "subjective" phenomenon, because every observer can only measure time with his own stopwatch, and the universe does not require that any two stopwatches agree. This is the effect of relativity -- every observer has his own personal experience of time, different from everyone else's experience of time, depending upon how he is moving with respect to the others.

    Despite all of this, everyone will measure time and distance the same way, inside their own co-moving laboratories, as anyone else. Everyone will agree that light moves a light-second in a second, etc. As EL pointed out, time is defined with reference to atomic behavior, and everyone, no matter how they are moving, will measure atomic behavior in their own laboratory to be the same.

    The ancient, Newtonian view of time is that every watch, everywhere in the universe, ticks at the same rate. If this were true, then there is a concept of a "universal instant," the same on everyone's watches, everywhere in the unvierse. This concept is no longer valid in relativity. Now, every observer has his own personal concept of "now," and it is not possible to somehow synchronize everyone's watches, everywhere in the universe, and expect them to remain synchronized.

    - Warren
     
  14. Dec 28, 2006 #13

    russ_watters

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    Well, the second is defined in the way it is because it lined-up well with the way we had it defined before atomic clocks - which is according to our planet's rotation and motion through the solar system.

    However, by defining it according to oscillations of a cesium atom, we could tell any intelligent being from anywhere in the universe and they'd understand what we meant. Otherwise, just saying "day" wouldn't mean anything to them.
    Well, the earth is the center of our universe because we can only see what we can see. So we might as well define the units of time in a way convenient to us, right?

    That brings me to a misconception chroot didn't mention - "time" is a dimension, "seconds" are a unit of time. People have been using the concepts interchangeably. The units are subjective because anyone can define any units however is convenient for them - inches, feet, meters, rods, furlongs - it doesn't have anything to do with what the concept of "length" really is. What was discovered with Relativity, as croot mentioned, is that not only are the units subjective, but the dimension itself is subjective too. Even using the same definition of a "second", people in different places will not necessarily agree on how many seconds elapsed between two events they both observe.
     
    Last edited: Dec 28, 2006
  15. Dec 29, 2006 #14

    disregardthat

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    Which means that one dimension doesn't differ from another, right?

    I just want to make something clear, and not that I have misconceptet that too: zero dimensional is a point, one dimensional is a straight line with infinitial length, two dimensional is a flatwith infinitial area, three dimensional is space with infinial volume. That I understand, and think is correct.

    But what means the fourth dimension? I read it is 'time'. Time to me must be that the three dimensional space is in constant "movement", measured by the planck seconds. Which to me would be the whole result of the fourth dimension.

    But we also say that the fourth dimension is the reason to gravity, the "dent's" in three dimensional space. How can the fourth dimension be both change in three dimensional space, AND constant "movement" of space?
     
  16. Dec 29, 2006 #15

    chroot

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    Four dimensional spacetime is a very simple concept. It labels each event (like meeting a friend for dinner) with three spatial coordinates (Asena Restaurant, Alameda, CA) and one time coordinate (7:30 pm). When futher equipped with an appropriate metric, one can also measure the distances between one event in spacetime and another event in spacetime.

    That's it. That's all there is to it.

    It has nothing to do with movement, or "planck seconds," which don't even exist. Relativity deals with transformations in this four-dimensional spacetime, which mix space and time coordinates. That's it. That's what gives rise to everything from the twin paradox to gravity, and its the mathematical formalism that lets us make explicit calculations. It's nowhere near as philosophical or abstract as people always want to make it out to be.

    - Warren
     
  17. Dec 30, 2006 #16

    disregardthat

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    Yeah, I guessed the answer would be something like that :P

    So, what effect does mass have on spacetime? It 'bends' the three dimensional space as we see as gravity, but in four dimensional space? Does time get 'bended'?

    And another thing. in a two dimensional coordinate system, a point must have two coordinates to be located. like x=5 and y=3. If you set this up in a three dimensional coordinate system, the coordinates for this point must be x=5, y=3 and z=0, (since we have no information of the pint location in the three dimensional system we assume it is 0) isn't this correct? If you search the entire two dimensional system at z=1 you will find no point. Ok, that's how I understand a coordinate system must work.

    If you have a point x=5, y=3 and z=1 and put these in a fourdimensional coordinate system 'time' then it would be x=5, y=3, z=1 and t(time)=0(assuming it is 0 since we have no information).

    Ok, with this said, on to the question. Let's say one coordinate is the planck constant, and moving one plancksecond in the fourdimensional coordinate system, you would have no information of the point. What makes the point, or any mass present at all times? Yeah, it's changing but what makes it not disappear for each coordinate at the fourdimensional coordinate system?
     
    Last edited: Dec 30, 2006
  18. Jan 17, 2007 #17
    This is circular cq. tautological, (light moves a light-second per second), you probably mean every observer can measure the speed of light to be the same (in vacuum), independent of their coordinate frame.


    Yeah, but somehow, we can know our 'relative' speed vice versa the CMBR, and can not all observers trace back their past worldline starting out in the Big Bang, which then brings us back somehow at some form of universal time?
     
  19. Jan 17, 2007 #18

    chroot

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    The CMBR rest frame is no more a "universal standard of time" than anyone's wristwatch. It's an important standard of time, much like the USNO's atomic clocks, but no more absolute.

    - Warren
     
  20. Jan 17, 2007 #19
    Isn't it the case the the Big Bang 'happened' the "same time ago" (in sofar that can be acurately measured) for all observers which are at rest relative to the CMBR, and that you can recalculate your measurements, since you can detect your relative speed relative to the CMBR?

    If it is not 'absolute' like you state, for what reason is that?
    a. Because also non-moving observers (relative to CMBR) can have different outcomes for that time they calculte of the Big Bang (of course we assume they have same data from which to obtain that data and also use same calculation), although they in the same rest frame at the 'same' time.
    b. Because we can not know our speed relative to the CMBR.
    c. Other?
     
  21. Jan 21, 2007 #20
    heusdens,

    the CMBR rest frame is important like chroot said, but it doesn't constitute a fundamental rest frame. It is nice because no matter where you are in the universe you can measure your motion with respect to it, but that doesnt mean that it is a 'more valid' rest frame than any other. It would be like choosing Earths rest frame as Universal. Its nice because everyone on earth can convienently use it, but it is no more fundamental physically than Jupiters rest frame. The point of relativity is that there is no special rest frame.

    An interesting side note: there was an article recently (in Harpers I think) called "battle of the time lords" describing the disagreements between some astronomers and physicists at NIST about the definition of time. Not a mathematical definition, but a standard to use for our planet. NIST wants to use the cesium atom clocks and insert leap seconds whenever we need to resynchronize with our historical clock (the earths motion around the sun). While the astronomers would like a system that doesnt require adjustment, but is tied to the earths motion.
     
    Last edited: Jan 21, 2007
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