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Thread: Time and Relativity.

  1. #31
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    Quote Originally Posted by TyroJack View Post
    Yes, "Time as a dimension always exists." but as you point out space as a dimension can exist, being the framework against which the length of bodies or spaces can be measured...
    So we almost agree. Spacetime always exists. The ability to measure space or time needs a clock or ruler. Time exists even if nothing changes (a empty universe). Or we could have an observer with a broken clock - time passes but they cannot measure it.
    The dimensions of spacetime are a mathematical abstraction (not "imagined framework") of our understanding of space and time derived from empirical evidence from rulers and clocks.

    I will check this with a formal question:
    IF01: Do you agree that time is not generated by change (time is an dimension of spacetime tat exists even if nothing is changing)?

  2. #32
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    Quote Originally Posted by TyroJack View Post
    Hmm...

    When I try to set out my understanding of time and relativity to check my understanding, the usual response is that I have it all wrong! So I find your question quite refreshing.

    A pole lying on the ground has a length that is a property of the pole. Add another pole and the length increases - but the dimension in that direction continues on beyond the poles. A process of change, such as a clock's 'tick' has a duration. Add more ticks and the duration of the clock's ticking increases, but that duration is limited by the clock's ticks even though the time dimension continues. The time measured can only be what has happened, future time is yet to come...

    If the process of change, the ticking of the clock were to stop - by the removal of the clock - and nothing was left that was changing, would time continue?
    To take this a step further I would ask a further question: if the ticking clock was to be returned, could the interval without the clock be measured? I would opine that the interval where there was no clock could not be measured as there would be nothing to measure - there being nothing changing, no time could be measured to pass within that system.

    If the time that we experience passing were to be interrupted: if time were frozen, then could we tell? If there were no way to measure it how can we say it does not happen?

    It is an unrealistic situation that could never happen. But then so are all the rocket travelling at near the speed of light; at the speed of light; so far from anything that there are no external forces...
    Well, the idea that this particular universe is empty except for the clock doesn't hold, since even empty space exists and things are happening within this empty space. Call it dark energy, virtual particles, quantum foam, whatever. These things are happening in time. The fact is that even empty space exists. It is NOT nothing. For your example to hold true, this empty universe would have to actually NOT exist. I think you see where this leads.

  3. #33
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    Quote Originally Posted by Strange View Post
    But each of those equations will describe a different rate of change or time; so why doesn't time depend how we measure it?
    But doesn't it?
    When time is measured by an observer at rest with a clock he measures a different time from when he is in motion with the clock.

  4. #34
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    Quote Originally Posted by AGN Fuel View Post
    Agree. Length as a dimension doesn't cease to exist just because there isn't a ruler in an otherwise vacant universe to measure it. Time doesn't cease to exist as a dimension just because there isn't a clock in an otherwise vacant universe to measure it.
    So what is a dimension? 3 infinite spatial dimensions go on for ever, but does space?
    Similarly a temporal dimension can be infinite but is time?

  5. #35
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    Quote Originally Posted by Reality Check View Post
    Spacetime is a foundation in which events happen, not something that is created by events.
    Is it? If there were no events, no big bang, would spacetime exist?

  6. #36
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    Quote Originally Posted by TyroJack View Post
    But doesn't it?
    When time is measured by an observer at rest with a clock he measures a different time from when he is in motion with the clock.
    There is no difference between being at rest with a clock and moving with a clock. In both cases, the observer and the clock are in the same frame of reference.

  7. #37
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    Does TyroJack mean by "in motion with a clock", moving relative to the clock?

    If so, just regarding that clock as it moves is no way to measure time -- unless you also do the required transformation.

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  8. #38
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    Quote Originally Posted by Strange View Post
    But each of those equations will describe a different rate of change or time; so why doesn't time depend how we measure it?
    Quote Originally Posted by TyroJack View Post
    But doesn't it?
    When time is measured by an observer at rest with a clock he measures a different time from when he is in motion with the clock.
    Quote Originally Posted by Strange View Post
    There is no difference between being at rest with a clock and moving with a clock. In both cases, the observer and the clock are in the same frame of reference.
    Sorry - semantics - I meant when the clock is in motion relative to the observer.

    When the clock is at rest relative to the observer - in the same frame of reference - the observer reads proper time on the clock.
    When the clock is in motion relative to the observer - in different frames of reference (requiring Lorentz transformation) - the observer is measuring coordinate time for the clock rather than what the clock is displaying.

  9. #39
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    Quote Originally Posted by TyroJack View Post
    But doesn't it?
    When time is measured by an observer at rest with a clock he measures a different time from when he is in motion with the clock.
    That is not what I meant. If you measure time by using the decay rate of different radioactive elements then they will have different rates of change. But they all measure the same time.

  10. #40
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    Quote Originally Posted by Krankor View Post
    Well, the idea that this particular universe is empty except for the clock doesn't hold, since even empty space exists and things are happening within this empty space. Call it dark energy, virtual particles, quantum foam, whatever. These things are happening in time. The fact is that evenempty space exists. It is NOT nothing. For your example to hold true, this empty universe would have to actually NOT exist. I think you see where this leads.
    I guess it depends on one's definition of empty space. My take would be if "things" are happening in "empty space" then the space is not truly empty. I'm not sure if this is what TyroJack is arguing or not?

  11. #41
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    Quote Originally Posted by Krankor View Post
    Well, the idea that this particular universe is empty except for the clock doesn't hold, since even empty space exists and things are happening within this empty space. Call it dark energy, virtual particles, quantum foam, whatever. These things are happening in time. The fact is that even empty space exists. It is NOT nothing. For your example to hold true, this empty universe would have to actually NOT exist. I think you see where this leads.
    We can model an empty universe using GR. Time and space still exist even though there is nothing happening.

  12. #42
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    Quote Originally Posted by TyroJack View Post
    Is it? If there were no events, no big bang, would spacetime exist?
    You know that the example of an empty universe in GR shows this. No events. No Big Bang. Spacetime exists.

  13. #43
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    Quote Originally Posted by Reality Check View Post
    You know that the example of an empty universe in GR shows this. No events. No Big Bang. Spacetime exists.
    I can't get my head around how time can exist in empty space, in fact how any dimension can exist in empty space. Or rather what the concept of dimension means in empty space. But then my idea of empty space (probably completely incorrect) is an infinite void of nothingness, the opposite to a singularity. If I'm interpreting TyroJack correctly then I believe this is one of the points of the O.P?
    Last edited by cosmocrazy; 2017-May-16 at 07:56 AM. Reason: corrected quote tag

  14. #44
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    Quote Originally Posted by cosmocrazy View Post
    I can't get my head around how time can exist in empty space, in fact how any dimension can exist in empty space. Or rather what the concept of dimension means in empty space. But then my idea of empty space (probably completely incorrect) is an infinite void of nothingness, the opposite to a singularity.
    Your infinite void of nothingness is, presumably, three dimensional; i.e. you can apply a coordinate system to it. GR just adds another dimension to these coordinates, labelled time.

  15. #45
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    Quote Originally Posted by Strange View Post
    Your infinite void of nothingness is, presumably, three dimensional; i.e. you can apply a coordinate system to it. GR just adds another dimension to these coordinates, labelled time.
    That's the crux of it though, it may well be possible to model it that way, but is it absolutely necessary to do so? Can it not also be modelled in much the same way as a singularity, in that the concept of dimension can be not applicable?

  16. #46
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    Let's be careful here folks. ATM is not for general discussions, it is for a single person to present their non-mainstream idea. Questions to clarify that are what we are looking for. Cosmocrazy and others, if you would like to have a discussion of mainstream relativity and how it applies to empty space, please start your own thread on the topic (I'd suggest in Astronomy). Thank you.
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  17. #47
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    Quote Originally Posted by cosmocrazy View Post
    I can't get my head around how time can exist in empty space, in fact how any dimension can exist in empty space. Or rather what the concept of dimension means in empty space. But then my idea of empty space (probably completely incorrect) is an infinite void of nothingness, the opposite to a singularity. If I'm interpreting TyroJack correctly then I believe this is one of the points of the O.P?
    The key is that they are not separate. They are not space and time. It is one thing called spacetime. They cannot be separated. The OP suggests that you can have empty space without time. This is not possible.

  18. #48
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    Quote Originally Posted by TyroJack View Post
    Yes, "Time as a dimension always exists." but as you point out space as a dimension can exist, being the framework against which the length of bodies or spaces can be measured...
    So, the dimension of time will exist as a 'scale' against which intervals in time, or durations can be measured...

    Space and time, the dimensions of Spacetime are no more than an imagined framework providing structure to our concept of Spacetime, against which we can measure space and time.

    Length is the spatial property that bodies possess.
    Duration is a temporal property that processes of change possess.
    I tend to agree with your conclusion, but we do not have such a universe. Even if all matter would be removed we would still have the expansion and the quantum vacum fluctuations...

  19. #49
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    In this universe time does move on, sneakily past 30 days... thread closed.
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