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

It's Now or never -- Question about "universal" time

  1. Sep 12, 2014 #1
    I am not sure whether this is a 'relativity' query as it may not be concerned with the order of events nor simultaneity in the usual relativistic sense. So whether it remains, is moved, or is deleted I'll leave to the mercy of the Mentors. Very likely I've made a simple blunder or else the topic has already been done to death, in either case, please enlighten me... thanks!

    At any one moment in time the whole universe exists

    There cannot be a moment when the universe does not exist

    There cannot be a moment when the universe only partially exists.

    At any one moment in time the whole universe exists regardless of the relative time-frame of any object within it.

    Therefore the concept of a universal 'now' holds true regardless of relativistic concepts. So... there must be a fundamental and universal principle orchestrating the whole shebang... ???
  2. jcsd
  3. Sep 12, 2014 #2


    Staff: Mentor

    Hi, johniha, and welcome to PF!

    You're assuming that the concept of "any one moment in time" is meaningful. In relativity, it isn't. I realize that seems highly counterintuitive, but that's the way it is.
  4. Sep 12, 2014 #3


    User Avatar
    Science Advisor
    Gold Member

    If there is, then you neglected to mention one other attribute of this principle:

    It has the uncanny ability to remain illusive.

    So why bother speculating along these lines?
  5. Sep 12, 2014 #4


    User Avatar

    This counterintuitive problem is eliminated in (neo-)Lorentz Ether Theory (LET) which is equivalent to SR (in it's experimental effects on measurements). In this theory there is absolute time, space and simultaneity.

    The theory explains precisely why moving clocks run slower and lengths contract in classical terms. It does not require that time and space themselves are relative to the observer. In LET there is one and only one now in the Universe.
  6. Sep 12, 2014 #5


    User Avatar
    Science Advisor
    Gold Member

    Yes, and it's illusive. No one can identify the one and only state in which light propagates at c and in which time, space and simultaneity are absolute. So why bother?
  7. Sep 12, 2014 #6


    Staff: Mentor

    This is called "petitio principii" or "begging the question". Your premise "At any one moment in time the whole universe exists" contains the conclusion that there is a universal now.

  8. Sep 12, 2014 #7
    Plain language is inherently full of assumptions and causes no end of problems in science questions and answers. For example, someone is informed that there is "no absolute space and therefore no absolute motion, only relative motion".

    He may think about that and talk to himself "logically" saying that if two objects are in relative motion then at least one of them must be in absolute motion even if we can't determine or assign motionlessness to any particular object... because there are two objects in relative motion he could only assign motionlessness to at most only one of them. They both can't be motionless if in relative motion; they both might be in absolute motion, or only one of them... but at least one of them has to be in motion. So if relative motion is happening with two objects, that must mean that at least one of the motions must be "real motion" with respect to an absolute space.

    This has the appearance of a logical argument, like your idea about absolute time, but it also is full of dozens of assumptions in the clumsy plain language that need to be identified and examined...
  9. Sep 12, 2014 #8


    User Avatar

    Isn't that argument a little like the argument "I cannot see it, therefore it doesn't exist"?

    SR postulates that c is constant in all IRF. In order to explain such a strange phenomenon, SR concludes that space and time themselves must be frame dependent. The reason SR is forced to mess with space and time is the additional postulate that the speed of light is isotropic in all frames (and the implicit postulate that all clocks "measure time correctly").

    It has been since been pointed out by many physicists that these last postulates assume more than is necessary to explain the experimental results (in which the Lorentz transformations are validated). Furthermore, isotropy cannot be proved or disproved using these experimental results.

    In LET a mechanism is provided that explains why measurement of c is constant in all frames. Why should we abandon a physical mechanism to explain things when such a mechanism is viable? Why should we resort to an entirely different idea about time and space than the classical one when there is no need? Why should we abandon the notion that waves are an effect that occurs in some medium?

    To be clear I'm a novice in SR. However, it was only when I was shown how to account for the Lorentz transformations in classical physics with an aether (mechanistic physics) that I could say "It makes perfect sense". Perhaps this is because I was not indoctrinated through SR training to accept the mainstream interpretation of the physics of the Lorentz transform.
  10. Sep 12, 2014 #9


    Staff: Mentor

    Because we *observe*, experimentally, that ##c## is constant in all IRF. We didn't just make up the postulate from thin air.

    Which we also observe, experimentally. If you don't like this postulate, take it up with Nature. :wink:

    No. First of all, we don't assume that all clocks measure time correctly; some clocks do it better than others. Second, we don't postulate that clocks measure time correctly; we postulate that "time" is what clocks measure. In other words, we have a theoretical model in which "time" appears, and we link this model to what we actually observe by linking the "time" in the model to the observations we make of clocks. This has to be done for any physical theory.

    Really? Why not? Can't we just observe light moving in different directions?

    Because this "mechanism" is inherently unobservable.

    Because there still is a need. Nobody actually observes this "absolute time" or "absolute space"; the "different idea about time and space" is about the time and space we actually *observe*.

    Because we can't observe the medium, even in principle.
  11. Sep 12, 2014 #10


    Staff: Mentor

    I don't know why you would equate "why bother" with "does not exist". "Why bother" means that it does not matter if it exists or not, it doesn't affect anything measurable.
  12. Sep 12, 2014 #11
    Thank you guys.

    Well it certainly is from my perspective, and I refuse to believe anyone who tells me that the universe is not out there, and not out there at this moment!

    Would it be better to say that there is a different universe for each point in space-time, with neighboring points having fairly similar universes? (Not that points could have universes of course)
  13. Sep 12, 2014 #12


    Staff: Mentor

    You might spend some time thinking about what "at this moment" means experimentally and why you think that the universe must not only be "out there" but must be "out there" specifically "at this moment" which is a distinct concept. How would one prove it experimentally?
  14. Sep 12, 2014 #13


    Staff: Mentor

    Really? Suppose you and I are on opposite sides of Earth. The information you are getting from me is, at best, about 70 milliseconds old. The information you are getting from the Moon at the same instant (meaning, that arrives at your eyes and other sensory apparatus at the same event) is about 1.25 seconds old. The information you are getting from the Sun at the same instant is about 500 seconds old. And from Jupiter, about 45 minutes old. And from Alpha Centauri, about 4.3 years old. And from the Andromeda Galaxy, about 2 million years old. And...

    Your brain presents to you the illusion that all of these objects exist in a "now", even though the information you get from them is never fully up to date; there is always some delay. Before relativity was discovered, we could tell ourselves that the delay didn't matter, that there was still a single "now" despite the delay, because *something* in the universe could connect things without the delay (perhaps gravity, which according to Newton's theory acted instantaneously).

    But now we know that the delay is fundamental: *all* information transfer in the universe is limited to the speed of light. There is *no* way around it. And that means there is no way around the fact that the "now" that you are so sure is "out there" is an illusion. That doesn't mean the universe doesn't exist; it means that the simple deduction you think you are drawing from your immediate perceptions is in fact a huge leap, which your perceptions by themselves do not justify. The only thing your immediate perceptions justify is belief in the existence of someone on the other side of the Earth 70 milliseconds ago, or the Moon 1.25 seconds ago, or the Sun 500 seconds ago, etc. But these, put all together, do not form a single "now". (What they form, in relativity, is called your past light cone.)

    No; that just compounds the problem, because you would have to explain why there are all these different universes, instead of just all these different "nows". It's much simpler just to admit that "now" is a construction, that it's relative.
  15. Sep 12, 2014 #14
    I'm far from sure what "this moment" means and was hoping for some straightforward pointers, but instead I'm getting elusive 'Zen' type responses :bugeye:, without anyone actually closing the door on the question. The implication being that the question isn't totally without merit, but so far as experimental physics is concerned answers remain elusive?
  16. Sep 12, 2014 #15
    OK belay my previous post... you've been at some pains to address my misapprehension Peter, thank you, I shall try to absorb...
  17. Sep 12, 2014 #16
    OK, you've dumbed it down enough for me... I think I got it... thank you all! - Our intuitive understandings do not correspond to the physical reality of the world. It's safe to say there is a universe out there, but my everyday understanding of what "this moment" is simply isn't up to the job, according to SR....

    ...nonetheless I cannot resist a peek at LET.
  18. Sep 12, 2014 #17


    User Avatar

    I am not contradicting that postulate; the two-way speed of light is supported by hard evidence. It is not that postulate that is unnecessary. It's the others (isotropy of c and that clocks measure "real time" regardless of motion) that force us to an explanation in which time and space themselves are only relative things.

    The postulate that moving clocks measure "actual time" is unnecessary to explain the Lorentz transformations, as is the postulate that the speed of light is the same in all directions.

    You cannot prove the isotropy of c with experiments.

    That moving clocks measure actual time is a definition of time in SR. That definition is unnecessary to explain the LTs.

    Experiments are easily explained using wave physics in absolute space and time. In LET, moving clocks are demonstrated to tick slower than those at rest in the ether. The Lorentz transformation for time as measured by clocks is a direct consequence of a simple analysis of waves in a medium.

    I can make a similar argument to yours. SR assumes some things that you cannot detect so why believe that it is the correct interpretation of nature?

    You can attempt to measure the one-way speed with a ruler and clocks, but you have to choose a convention for clock synchronization to measure one-way velocity. There are many choices. Einstein's choice implicitly assumes that the speed of light is isotropic. That choice is not required to explain experimental results.

    I would agree that the absolute frame is undetectable in the context of the Lorentz transformations. Beyond that, who knows?

    I think you will agree that isotropy of the speed of light is undetectable if you study some papers on the subject of clock synchronization.

    You can define "space" as what is measured by similar rods in any frame and "time" as what is measured by a similar clocks in any frame regardless of motion, and assert that time and space are frame dependent i.e. relative. You can apply Minkowsky space and all the things that have already been done using the concept of relativity. That's perfectly correct in terms of results. You can do the same thing in LET.

    What is lacking in SR is a physical theory of why "space' and "time" (as defined above) behave the way they do. This view that time and space are not absolute is forced by the "extra" postulates of SR.

    On the other hand, it is easily demonstrated with a simple application of classical physics to waves in a medium that moving clocks tick slower and consequently that length is measured as contracted in a frame moving with respect to the medium. That the speed of light is an upper bound is obvious for waves in a isotropic medium from classical physics. In LET nothing can travel faster. Tachyons are impossible.

    In SR you cannot observe the one-way speed of light, even in principle. SR assumes that c is isotropic.

    There is nothing that you can observe "directly" in principle. All you ever get to do is measure quantities and infer or theorize what is actually there. These "things that you observe" have the same level of reality as ether.

    In LET, waves in the ether is "all" that is observable. Light and matter are waves. Because we are waves we cannot directly perceive the ether but we can measure it's properties by seeing how the waves behave.

    In summary, SR is forced to assume that actual time and space are relative by certain postulates that cannot be demonstrated.

    SR deprives light waves and matter waves of a medium in which to propagate. All the other types of waves that we study in physics are the result of changes in a medium.

    Many physicists have also pointed out that motion cannot be entirely relative because we can detect absolute rotation using the Sagnac effect (laser gyros). Also, acceleration is absolute.
    Last edited by a moderator: Sep 13, 2014
  19. Sep 12, 2014 #18


    User Avatar
    Gold Member

    Well, no, that's not quite right. Our "common sense" / "intuition", and so forth DO correspond to an EXTREMELY limited range of things in the universe. Things that are close to us and are not moving at relativistic speeds, are a of macro size, and ... and ... and ...

    We evolve with survival mechanisms that require our ability to make sound judgments based on an awareness of the world the including those constrictions without being aware of, or even NEEDING to be aware of, their existence. They just don't matter to how individuals have survived since living beings came into existence on this planet.

    Consequently, when you start to study cosmology (the very large) and quantum mechanics (the very small) and black holes (the very heavy/dense) you are going to have moments when your brain just flat out says NO WAY !!!

    Consequently, to be successful in such studies you have to be willing to suspend disbelief long enough to work things out with mathematics, NOT English language, and see that your initial disbelief was wrong.
  20. Sep 12, 2014 #19
    When I consider that I only exist in the current 'now' - the future has no existence, neither does the past - my existence is limited to an infinitesimal wave of time, likewise the rest of the universe has no temporally sustained existence... that idea is very much at odds with the way I view the world which is more 'me passing through a landscape were objects are fairly permanent temporal fixtures'... So it seems to me my mind has embellished reality. It has created a world distinctly different to the actual reality
  21. Sep 12, 2014 #20


    User Avatar

    While I agree with what you are saying about experience being limited, this does not imply that we should not employ our experience to explain things when we can.

    SR is not intuitive. In fact it is so counter-intuitive that complicated explanations are required for untrained people to "get it". That people keep popping up with apparent paradoxes illustrates the difficulty of the concepts.

    In the LET interpretation, we do not need the counter-intuitive concepts that space, time and simultaneity are just relative to explain nature. So why adopt them, as in SR?

    With the lack of any "reasonable" interpretation in Quantum Mechanics, it seems that most physicist have abandoned any attempt to try. Thus it's become popular to say that the equations are physics and leave any deeper explanation as impossible or unnecessary.

    Now, the idea that understanding nature is impossible because of some limitation of our imaginations has become common. I have to agree with Einstein and not accept that as true and instead believe that our understanding is as yet far from complete.
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Similar Discussions: It's Now or never -- Question about "universal" time