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Simultaneity: Relative vs Absolute

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  • #32
    Morbert
    Registered Users, Registered Users 2 Posts: 3,457 ✭✭✭Morbert


    roosh wrote: »
    Defining relative motion isn't the issue, the question is how could relative motion possibly occur in a universe where objects exist as worldlines extended in 4D spacetime, where those worldlines don't move and the points on the worldlines don't move.

    If you imagine two chopsticks lying on the desk in front of you, lying at angles to each other - they represent the worldlines of two objects extended in 4D spacetime - how can they give rise to what we observe as relative motion?

    I would probably say that physics is the attempt to describe the laws of the physical world we observer, which would imply conscious observers.

    I don't doubt that the universe will continue to exist when I die, but the sort of world that is going to be left to our descendents is still a universe in which there are conscious observers.

    Physical theories are descriptions independent of conscious observers.


  • #33
    citrus burst
    Registered Users, Registered Users 2 Posts: 147 ✭✭citrus burst


    roosh wrote: »
    The contention is that, for any given observer, all of their measurement occur in their own present moment; in the parlance of SR (as it is popularly categorised in programmes such as NOVAs the Fabric of the Cosmos), every observer makes their own observation in their own "now slice", or what their co-ordinate reference frame would classify as "now". This is true for relativity as it is for presentism.
    So in other words you can't really.
    roosh wrote: »
    "The present moment" is nothing more complicated than the moment in which your experience occurs. This would be circular reasoning except that it isn't solely reasoning on which it is based, it is derived from experience.
    This is just a hand waving argument with not much merit behind it.
    roosh wrote: »
    The experience you are having as you read this is occurring in the present moment, "your present moment" if necessary. It's what is meant when we say "now".
    But how long is now?
    roosh wrote: »
    The problem is one of misinterpretation I think. It's not so much that you would technically be dead when the distant observer sees you brushing your teeth, it's that you would be clinically dead. What the distant observer sees is just an image of you brushing your teeth. It's like seeing a photograph of a "past" event.
    No you would be dead (assuming you are far enough away), in all sense of the word, kaput.

    Technically speaking everything we see is a photograph of a past event.

    roosh wrote: »
    You might be thinking of light from distant events reaching you, in your present moment. In this case, the image that you see is from an event that did happen "in the past". It must necessarily have happened "before now" if light from the event is reaching you now, given the finite speed of light
    If there is any distance between two events, they occurred in the past. Even if they are part of your so called present moment.


    roosh wrote: »
    Entropy could be used to explain an ever changing present moment; they are essentially one and the same thing.
    You still need time for entropy.
    roosh wrote: »
    I don't see how assuming time is more favourable to dropping the assumption that time exists.
    It provides an existence free definition of the universe, along with mass, length, charge etc.
    roosh wrote: »
    It doesn't have a duration, per se. It lasts as long as there is existence.
    Then what happens?
    roosh wrote: »
    The issue is that "time as a measurable quantity" is just an assumption; when we examine it, we can see that time isn't actually a measurable quantity; that is, time is not the object of measurement, it is the abstract system of measurement. We would still retain a concept of time, we would just see it for what it isn't. There would still be clocks, just no physical time.
    If that was the case we could justify that all measurable quantities in the universe are redundant.

    I take it you have no problems with mass or length? How are these measured?


  • #34
    thecornflake
    Registered Users, Registered Users 2 Posts: 784 ✭✭✭thecornflake


    roosh wrote: »
    What everyone experiences in the present moment can be different; someone in France would have a different experience to what you are experiencing right now.

    In other words, someone in Paris is experiencing something right now, and you are experiencing something different right now; if you drop the assumptions that your past and/or future exist then the simultaneity of those two events must be absolute.


    We don't even have to assume an overlap; all you have to do is acknowledge that your experience occurs in the present moment; if you drop the assumptions that your past and/or future exist, then only your present moment exists and simultaneity must be absolute.


    I don't immediately see the necessity of this.


    Any experience you or I have of the universe, that is, the entirety of our experience, occurs in what we call "the present moment".

    You know, I think you may be on something here.


  • #35
    roosh
    Registered Users, Registered Users 2 Posts: 2,554 ✭✭✭roosh


    Morbert wrote: »
    That was never a contention.
    The contention has been that if the assumptions of past and future are dropped then presentism is the only remaining conclusion. It's been your contention that presentism necessitates a dynamical cause, I just accepted it.


    Morbert wrote: »
    And that is false. Presentism is true if and only if the past and future do not exist. Thus, if you want to argue that presentism is true, then you must establish that the past and future do not exist, or are at the very least can be assumed not to exist by Occam's razor.
    Again, the contention isn't necessarily that presentism is true, it's that it is the only possible conclusion of the assumptions of past and future are dropped; this is true because "not-presentism" is only a possible conclusion if the assumptions of past and future are made; if they're not made i.e. if they're dropped, then the conclusion of "not-presentism" cannot be reached; that would leave presentism as the only possible conclusion.

    Morbert wrote: »
    I meant ontologically. I.e. What exists according to b) is what exists according to a) plus a Newtonian spacetime. Thus, we can indeed disregard b) based on Occam's razor.
    If we're justified in making the assumptions of past and future for one, then we're justified in making them for the other; but we don't necessarily need b) to be a realistic possibility, it's just helpful for highlighting that more than just the assumption of past and future is required to arrive at the conclusion of Minkowski spacetime.


    Morbert wrote: »
    And that contention is not true, because not assuming x is not the same as assuming x is false. If we don't assume spacetime, then either a) or c) is true. We cannot conclude either.
    Again, that not assuming x is not the same as assuming x is false is not in contention, indeed, it is applied to demonstrate that presentism is the only option left when the assumptions of past and future are dropped.

    It is a feature of circular reasoning that if the conclusion, X, requires the assumption X, and the assumption X is dropped, then conclusion X is not an option; that is, conclusion X is only an option with the assumption X.

    When you say that either a) or c) are left as possibilities, when the assumptions of past and future are dropped, what you are, in effect, saying is that, "we can always take the assumptions up again "; because only by making the assumptions of past and future can those conclusions be reached.


    Morbert wrote: »
    See? Nobody is arguing against what you say above. I have never said spacetime can be concluded without making assumptions. I am saying what applies to c) also applies to a). Both positions are ontological positions that hinge on assumptions.
    ...
    No, because then we are in vague territory, where it boils down to whether or not you "like" an undetected dynamical cause, or a kinematic spacetime structure.
    This is true. I guess it could come down to the number of assumptions required by both and indeed the logical consequences of both.

    As has been the topic of discussion in the thread on absolute motion, a block universe is one in which relative motion is not an objective reality but would be entirely dependent on the consciousness of an observer and their capacity for memory; it is a universe in which only a smidgen of relative motion would ever be observed by the 3D manifestation of any observer; and it is a universe in which experience of the 3D world would be limited to a single moment of time, or a single point on an observers worldline, without ever going beyond that; given that all points are fixed on an observers worldline and there is no transition to later moments.

    Being manifest in the 3D world, whatever time any of us sees on the clock right now is what our experience of the 3D world should be limited to, because as the 3D manifestation of a fixed point on a wordline, which does not transition to the next moment, that is all we should experience.


  • #36
    roosh
    Registered Users, Registered Users 2 Posts: 2,554 ✭✭✭roosh


    Morbert wrote: »
    Physical theories are descriptions independent of conscious observers.
    It would seem that, from the discussion on absolute motion, that relative motion is dependent on the consciousness of observers.


    With regard to presentism, it wouldn't really matter, because the present moment would not be dependent on a conscious observer; if it is all that exists then it is as much Jupiter's present moment as it is ours.


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  • #37
    roosh
    Registered Users, Registered Users 2 Posts: 2,554 ✭✭✭roosh


    citrus burst wrote: »
    So in other words you can't really.
    I'm not entirely sure what it is that you're looking for.

    Have you ever made an observation when it wasn't the present moment; has anyone ever made an observation when it wasn't the present moment; is it even theoretically possible to observe something when it isn't the present moment?
    citrus burst wrote: »
    This is just a hand waving argument with not much merit behind it.
    It might be just the manner in which you are thinking about it. "The present moment", or "now" is simply a label which we apply to our experience; it's how we label the "moment" in which our experience occurs.

    citrus burst wrote: »
    But how long is now?
    I think you might be thinking in terms of "what length of 'time' is 'now'?" I think length only applies to spatial dimensions, particularly if time doesn't exist.
    citrus burst wrote: »
    No you would be dead (assuming you are far enough away), in all sense of the word, kaput.
    That's what I meant by "clinically".
    citrus burst wrote: »
    Technically speaking everything we see is a photograph of a past event.
    Indeed, but just as with a photograph, we only ever observe them in the present moment.

    citrus burst wrote: »
    If there is any distance between two events, they occurred in the past. Even if they are part of your so called present moment.
    I don't think we are in disagreement here; essentially, once the light from an event, which is separated in space, reaches you, that event - from whence the light was emitted - is necessarily in the past. We observe the image in our present moment, but that image is like a photograph of a past event.

    citrus burst wrote: »
    You still need time for entropy.
    I don't see why; entropy would still occur in a timeless universe.

    citrus burst wrote: »
    It provides an existence free definition of the universe, along with mass, length, charge etc.
    I don't see how it does, or how presentism doesn't. If only the present moment exist, then this is true for jupiter as it is for any conscious observer.

    citrus burst wrote: »
    Then what happens?
    Nothing happens when existence ceases; if it ever ceases. If it were to cease then there would be nothing, and therefore no "happening".
    citrus burst wrote: »
    If that was the case we could justify that all measurable quantities in the universe are redundant.
    That assumes that time is a measurable property.
    citrus burst wrote: »
    I take it you have no problems with mass or length? How are these measured?
    I'm not 100% on the measurement of mass, off the top of my head, but, to give a very crude example, the spatial dimensions of object A are measurable by placing another spatially extended object, B, beside it and then the spatial dimensions of A are expressed in terms of B; where B is taken as a standard unit in which the spatial dimensions of all objects are expressed, for the purposes of comparison.

    We don't measure time in the same way and we don't observe any objects as being temporally extended; we only ever view objects in a single moment.


  • #38
    Morbert
    Registered Users, Registered Users 2 Posts: 3,457 ✭✭✭Morbert


    roosh wrote: »
    The contention has been that if the assumptions of past and future are dropped then presentism is the only remaining conclusion. It's been your contention that presentism necessitates a dynamical cause, I just accepted it.

    Again, the contention isn't necessarily that presentism is true, it's that it is the only possible conclusion of the assumptions of past and future are dropped; this is true because "not-presentism" is only a possible conclusion if the assumptions of past and future are made; if they're not made i.e. if they're dropped, then the conclusion of "not-presentism" cannot be reached; that would leave presentism as the only possible conclusion.

    And again, yes, I agree. That is your contention. And again, I say it is false. If assumptions about the existence of past and future are dropped, presentism is not "the only possibly conclusion". Instead, presentism can not be concluded any more or less than Minkowski spacetime can be concluded.
    If we're justified in making the assumptions of past and future for one, then we're justified in making them for the other; but we don't necessarily need b) to be a realistic possibility, it's just helpful for highlighting that more than just the assumption of past and future is required to arrive at the conclusion of Minkowski spacetime.

    I don't understand this paragraph. But I also feel the above is a somewhat irrelevant point. If its only purpose is to argue that Minkowski spacetime is not merely the existence of past and future then sure.
    Again, that not assuming x is not the same as assuming x is false is not in contention, indeed, it is applied to demonstrate that presentism is the only option left when the assumptions of past and future are dropped.

    Presentism is not the only option left precisely because not assuming x is not the same as assuming x is false.
    It is a feature of circular reasoning that if the conclusion, X, requires the assumption X, and the assumption X is dropped, then conclusion X is not an option; that is, conclusion X is only an option with the assumption X.

    When you say that either a) or c) are left as possibilities, when the assumptions of past and future are dropped, what you are, in effect, saying is that, "we can always take the assumptions up again "; because only by making the assumptions of past and future can those conclusions be reached.

    Yes, we can always, at a later stage, assume/suppose the past and future exist and, by doing so, reject b). Similarly, we can also always assume/suppose the past and future don't exist and, by doing so, reject a).
    This is true. I guess it could come down to the number of assumptions required by both and indeed the logical consequences of both.

    As has been the topic of discussion in the thread on absolute motion, a block universe is one in which relative motion is not an objective reality but would be entirely dependent on the consciousness of an observer and their capacity for memory; it is a universe in which only a smidgen of relative motion would ever be observed by the 3D manifestation of any observer; and it is a universe in which experience of the 3D world would be limited to a single moment of time, or a single point on an observers worldline, without ever going beyond that; given that all points are fixed on an observers worldline and there is no transition to later moments.

    Being manifest in the 3D world, whatever time any of us sees on the clock right now is what our experience of the 3D world should be limited to, because as the 3D manifestation of a fixed point on a wordline, which does not transition to the next moment, that is all we should experience.

    If you want to resurrect that old philosophy thread on the philosophy forum, that's fine. But for know I am going to assume the contention initially raised in this thread has been settled: I.e. Insisting spacetime is real requires an ontological assumption, independent of empirical evidence. Similarly, insisting presentism is real requires an ontological assumption, independent of empirical evidence.


  • #39
    roosh
    Registered Users, Registered Users 2 Posts: 2,554 ✭✭✭roosh


    Morbert wrote: »
    And again, yes, I agree. That is your contention. And again, I say it is false. If assumptions about the existence of past and future are dropped, presentism is not "the only possibly conclusion". Instead, presentism can not be concluded any more or less than Minkowski spacetime can be concluded.
    If the assumptions of past and future are not made, then presentism is the only possible conclusion, but it would require an additional assumption, as you point out. In the absence of all of those assumptions I think we are left with "shut up and calculate".

    Morbert wrote: »
    I don't understand this paragraph. But I also feel the above is a somewhat irrelevant point. If its only purpose is to argue that Minkowski spacetime is not merely the existence of past and future then sure.
    The point was to highlight that Minkowski spacetime, perhaps, requires more assumptions than dynamical relativity.

    Morbert wrote: »
    Presentism is not the only option left precisely because not assuming x is not the same as assuming x is false.
    In essence, presentism is simply the absence of past and future. Since the conclusion of "not-presentism" requires the assumptions of past and future, then dropping the assumptions of past and future leaves only presentism. However, as you point out, the conclusion of a presentist universe requires a further assumption.

    Morbert wrote: »
    Yes, we can always, at a later stage, assume/suppose the past and future exist and, by doing so, reject b). Similarly, we can also always assume/suppose the past and future don't exist and, by doing so, reject a).
    We don't need to assume that past and future don't exist; without the assumptions of past and future, presentism is the only conclusion which can be reached; as you've pointed out though, it would require an additional assumption.


    Morbert wrote: »
    If you want to resurrect that old philosophy thread on the philosophy forum, that's fine. But for know I am going to assume the contention initially raised in this thread has been settled: I.e. Insisting spacetime is real requires an ontological assumption, independent of empirical evidence. Similarly, insisting presentism is real requires an ontological assumption, independent of empirical evidence.
    As ever, thanks for the reasoned discussion. I think it's fair to say that it is settled, alright. The point I was trying to make wasn't as strong as I initially thought. The question of which assumption is more reasonable would be a different discussion and not one I'd be too concerned about getting into hear, particularly in the physics forum, unless anyone else were to raise it.

    On the other point though, I would be interested to hear the thoughts of those who are more scientifically inclined, so I might start a thread in the physics forum.


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