Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

I Relativity and eternalism

  1. May 26, 2017 #1
    Eternalism is the view that many moments of time exists and each of these moment are equally privileged/unprivileged.
    I am trying to back up this view with SR, so I remember watching Brian Greene's documentary "the B-series of time" or something, where he used the spacetime loaf to illustrate how it is possible for an observer in the distant galaxy to 'see to our future' by moving towards the earths and 'see to the past' when he moves away relative to the earth(and this is all that is needed to be prove eternalism).

    My understanding of this prophecy fairy tale is a mere disagreement on simultaneity, time dilation for that moving observer makes him sees an event later what he would've seen at rest. But I can't see how 'seeing to the future' is possible. And how will I justify this mathematically? Lorentz transformation allows the calculation for the time interval between two events for different frame of references, what choice of coordinates and initial conditions will I need to adopt to prove that one can see 'the future' earlier than his original reference frame?
  2. jcsd
  3. May 26, 2017 #2


    User Avatar
    Science Advisor
    Gold Member
    2017 Award

    You can't prove this by construction. Special Relativity is science, not esoterics!
  4. May 26, 2017 #3
    Well, I think SR&GR are both self consistent theory and gives far more detailed explanation of how the behaviour of spacetime than metaphysical ideas.
  5. May 26, 2017 #4
    Even though, I'm more attracted to the physics now than finishing my philosophy assignment. Please give us some hints on how to approach this interpretation
  6. May 26, 2017 #5


    User Avatar
    Science Advisor

    A popular (probably the most popular) interpretation of SR is what Greene talked about - the block universe (or B theory of time, which I think is what you were aiming at). But it's just an interpretation of the maths. You aren't required to adopt it and you can choose to stick with an (undetectable) absolute frame (the A theory of time).

    By changing your state of motion (or just deciding to use a different simultaneity convention) you can change what you call "now" at locations other than your own. It doesn't change what you actually see because what you see is the past - when light now reaching you left whatever you're looking at. Since it's impossible to see anything "now" until light gets here, what you choose to call "now" turns out to be just a matter of book keeping, not physics (although there are physical limits to what you can sensibly call now). And since it's just book keeping you can't use it to make an argument about the physical world.

    As I recall, @PeterDonis wrote an insight on the topic. You might want to look that up.
  7. May 26, 2017 #6
    Thanks for your reply! I am still a bit confused by how exactly motion changes the labelling of the 'now'? Is it because with relative motion to initial/rest position, one can reach the information/photons earlier or later than rest position? If so, does the distance between the observer and the event have a great effect on the labelling of 'now'?

    My argument in supporting eternalism isn't exactly built on SR, rather, I am arguing that 'existence' is a local property, just like the observations we make and 'now' we choose. In that sense, with some reasoning, I established 'being observable' ≡ 'existence'. Then it follows, if one can see what he considers to be the future in his current reference frame, within lesser amount of time providing that he moves towards the event, then I can conclude future exists. My argument is probably more to do with the ontology of existence, but I still wish to learn the mathematics of this phenomena:-)
  8. May 26, 2017 #7


    User Avatar

    Staff: Mentor

    Thread closed temporarily for Moderation...
  9. May 26, 2017 #8


    User Avatar

    Staff: Mentor

    Sort of. Labelling two spatially separated events as both happening "now" is a special case of saying that the two events happened "at the same time". (If I say "There is a car driving by right now", I'm basically saying that the event "car drives by" is happening at the same time that I am speaking).

    However, if you Google for "Einstein train simultaneity" you will find the classic thought experiment that shows that simultaneity, the notion of two spatially separated things happening at the same time, depends on the motion of the observer. If you and and I are moving relative to one another then in general the things that are simultaneous for you will not be simultaneous for me, and vice versa.

    Understanding this thought experiment and letting go of the deeply ingrained idea of absolute simultaneity might be the single most important step in understanding special relativity.
    Last edited: May 26, 2017
  10. May 26, 2017 #9


    User Avatar

    Staff: Mentor

    That is not something that physics, as an empirical science, can help you with.
    there is no mathematics in "existence" and "eternity"; relativity is a mathematical concept to describe what we can measure. There are some pretty good pointers in the previous posts in this thread and we have even more Insight articles on related subjects, search for the Author of "Blockworld" or keywords like "universe", "spacetime" or similar

    If you want to get scientific recommendations on the subject, please tell us in a new thread and in more detail on which level you stand and what you want to learn or investigate. But please, do that in a new thread. This thread will remain closed.
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook