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Does time exist apart from matter?

  1. Mar 30, 2009 #1
    Hello Physics Forums,

    Many of my google searches made in an attempt to understand relativity landed me on threads here, so I thought this would be a good place to get some clarification on a concept I recently read in the book God? by C. DeSalvo (my http://boulderchurch.net/viewtopic.php?t=362 [Broken] for the curious) which contains this paragraph:
    I'm wondering what people here, who understand relativity better than me (and probably the book's author), think of these statements.

    The paragraph and its implications confused me, because if photons *move* through space, then that implies a measure of time (from some perspective, at least). My understanding of relativity is that time is one of four coordinates of spacetime which describe the positions of bodies/events relative to a rest frame of reference. And so it doesn't seem sensible to assign time as an attribute of matter.

    I initially wrote it off as a result of the author's speculations about the point-of-view of photons (they don't experience space or time, etc.). However, even ignoring any "let's try to apply SR to the non-inertial reference frame of a photon' games, I'm not sure what time would mean in a universe without any massive particles.

    That is, if photons were the only particles in the universe, which would mean that there were no bodies moving below the speed of light and so no inertial frames of reference associated with any real thing, then would SR have anything to say about that universe?

    So, to conclude before I start rambling in my confusion, is the statement "Without matter or antimatter, time does not exist" sensible within the model of Einstein's theories of relativity?
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  3. Mar 30, 2009 #2
    I just noticed this recent thread which asks a similar question (though it quickly turns into a discussion on whether photons have mass):

    Does time exist without mass?
  4. Mar 30, 2009 #3
    That was my thread :)

    Maybe people (Dave) could answer the question of time existing without mass here... without bringing up a photon. If that's even possible?
  5. Mar 30, 2009 #4
    Hi Timmaay. Good idea. And maybe if it does come up, for the sake of simplicity in this thread we could assume a photon has no mass?

    I found another thread that deals with the same question (I know, I could have searched better before posting):

    Time can't exist without matter (mass) and motion

    (It contains an excellent post by Garth which doesn't exactly answer the question of whether time makes sense without a massive observer to measure it, but is definitely worth the read: https://www.physicsforums.com/showpost.php?p=1497521&postcount=16)
  6. Mar 31, 2009 #5
    I think time is fundamental and matter is a form of time, so in my mind time can exist apart from matter but matter cannot exist apart from time.
  7. Mar 31, 2009 #6
    No, I don't think so. Time and matter exist and are dependent on each other, I cannot believe Time to be independent of matter, but matter be dependent on time.
  8. Mar 31, 2009 #7
    My confusion is that other than a "photon with no mass" what could be used to measure time? I feel that if the only thing that can measure time besides a mass is a photon... then the odds of a photon having mass is more than it being the only thing able to measure time with out mass. Does my logic make sense there? Maybe if there was soomething else that could measure time besides a photon and mass...
    Don't say:
    Energy, because energy is basically equivelant to mass. Right?
    The wavelength of a photon, because that is dependent on a photon.
  9. Mar 31, 2009 #8
    The whole question of what is fundamental and what is emergent is interesting but a pointless exercise in speculation. No one knows what time nor space, for example, are.

    In FABRIC OF THE COSMOS, Brian Greene discusses some of the basic questions which have eluded us for centuries including the nature and relationships of space, time, mass,and so forth.
  10. Mar 31, 2009 #9
    I agree with you... kind of. I have asked a lot of questions so far because I haven't been convinced either way on a lot of topics (photon having mass). But not once has someone told me "With the information we currently have, this is the most likely answer." People have given me reasons on why I'm wrong that don't make any sense. I feel that with all the information we currently have people shouldn't saying this is true and this is not true. For all we know God could appear in the sky tommorrow and destroy everyone that isn't a mormon. We don't know.
  11. Mar 31, 2009 #10
    My confusion is along similar lines. In a universe in which only massless photons exist, time and space obviously *exist* as spacetime, but there would be no sublight particle in an inertial frame of reference to any photon to measure its movement. So it seems to me to be a variation of the old "if a tree falls in a forest with no listeners, does it make a sound?" But since it is possible to imagine an observer which would measure the movement of the photons through spacetime in such a universe, I think it does indeed make sense to speak of time existing without matter.

    Anyway, I'm afraid the amount of speculation inherent to this thread is afoul of the Forum rules. Maybe it should be moved to the Philosophy board or some-such?

    The Brian Greene book that Naty recommended looks good. I've added it to my future-reading list. Thanks.
  12. Mar 31, 2009 #11
    Time and matter do exist, matter is the tool we use to measure time. I wrote "I think time is fundamental and matter is a form of time, so in my mind time can exist apart from matter but matter cannot exist apart from time." Think of space as the time separating matter we measure via the photon, "Can time exist apart from matter?" isn't that space?
  13. Mar 31, 2009 #12


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    That is an understandable attitude, but it's really a judgment call. The enterprise of quantum gravity is aimed at finding the fundamental microscopic elements from which (on a macroscopic scale) space, time, and matter emerge. The search for more fundamental descriptors, for a deeper mathematical model, seems to many people well worth pursuing.

    I wouldn't call it purely speculative either, since there are some tests already being performed and reported, and others being proposed (QG phenomenology is a growing field.)

    It's rather like the situation with the atomic theory of matter 150 years or so ago. Ideas were brewing that concerned a more fundamental description underlying solids, liquids, gasses. Much controversy and animosity ensued. Ludwig Boltzmann was attacked so bitterly that it undermined his health and morale. But eventually there were some clever insights leading to experimental ways of proving the existence of atoms and molecules. It hasn't been pointless. :biggrin:

    Cris, I would urge you to consider in what sense does time exist (in the context of relativity) with or without matter.

    You might have a look at several of the FQXi contest essays on the nature of time. You seem to come to this from a religious background so FQXi might be right down your alley! It is a non-religious offshoot funded by the Templeton Foundation (whose aims involve both science and religion.)

    FQXi set up a contest last year and managed to get some of the world's top experts on relativity and time (as well as many other people) to enter essays.

    Assuming you have limited time, I would look at those of Julian Barbour, Carlo Rovelli, and Claus Kiefer primarily.


    In GR the "coordinate time" is arbitrary and physically meaningless. It is not a measurable quantity, and can be replaced by any other version of coordinate time ad lib. More interestingly, each observer has his own idea of time. There is no way of saying whose clock is "right". No privileged observer and no privileged time.

    In cosmology, happily enough, there is a distinguished time, a kind of "universe standard time" defined with the help of the cosmic microwave background. Cosmology has become less abstract and more observational---more nuts and bolts. But you aren't asking about cosmology, you are specifically referring to the relativity context. (In some sense GR includes SR, it was a generalization that came 10 years later, so we can focus on GR.)

    To me, intuitively, the way it looks is that in GR there is no time. What there is instead is the gravitational field----a metric (a distance measure) that describes the evolving geometry of the whole spacetime trajectory, the whole process.

    The spacetime in GR can be threaded thru by many different observers, each of whom can have a clock and/or can observe external motions.
    (Julian Barbour in his essay explains why you don't really need a clock: all you need is to have some planets orbiting a star, some dynamical system to observe, a uniform timscale can be deduced from observed motion. I oversimplify but that's the general idea.)

    But no one observer is right. It is the whole spacetime trajectory that is right. More precisely, not the spacetime itself but its geometry, represented by a metric called the gravitational field.


    That's how it is in GR. Someone should correct me if I'm wrong. It's pretty abstract which is the bad news---so it's hard to grasp.

    The good news is that GR is a 1915 theory which is gradually being replaced by quantum GR. So we aren't permanently stuck with what vintage 1915 Einstein relativity tells us. There is hope of getting hold of some more fundamental handles.

    Rovelli's FQXi essay is about that.

    Also this month a new book came out called Approaches to Quantum Gravity: Towards a New Understanding of Space, Time, and Matter. Cambridge University Press.
    Mainly for professional researchers, campus libraries, not general public. But it's a sign of what to expect. More books of that sort. "Approaches" is the work of some 20 worldclass experts in the different mathematical systems that are trying to replace General Relativity with something more fundamental--that will work at small scale and not develop singularities. And matter may turn out to arise from the same stuff as geometry, particle fields just a different aspect or facet of what underlies spacetime geometry.
    You can read the table of contents and view sample pages of "Approaches" at the Cambridge Press website. But more accessible (and affordable) books will be coming out, I expect, on these same topics.

    I would agree that time cannot be measured without matter. I don't think the question has been settled of in what sense does time exist. I suppose that it does not exist in any fundamental sense and that the question we will be asking in the next few years is what deeper reality underlies the gravitational field---underlies geometry and matter. How shall this deeper reality be math-modeled? How shall it be simulated in computer?

    For a taste of initial work along the computer simulation lines, look at Jan Ambjorn and Renate Loll's article in the Scientific American. The link is in my signature, in small print at the bottom of the post. It is a beautiful and very readable account of how they simulate small quantum universes (coming into and going out of existence) and study them in the computer.

    They have a chapter in the new "Approaches" book, but their SciAm article is more illustrated and accessible. Renate Loll writes extremely well.
  14. Mar 31, 2009 #13
    Thank you, Marcus, for taking the time to reply and for the suggested resources. I'd never heard of FQXi before. I just read Julian Barbour's "Nature of Time" essay. It's very readable, but I'll have to read it again before I feel I understand much of it. I seem to constantly conflate "the measure or standard of time" with "the nature or ontology of time." That might be the root of most of my (and others') confusion regarding Time.

    That consideration is exactly what lead me to make my original posting :). The best picture I can come up with is in my previous post (#10). I don't know if you had a chance to read that before writing your post, but I'd be interested in any response you might have to it.
  15. Mar 31, 2009 #14
    I agree completely...I never intended to imply otherwise....
    I should have instead posted something like "... its pointless to speculate here and now on this forum because the theoretical and experimental work has not been done yet...." in other words, unless something revolutionary happened last night, nobody knows right now...

    And I'd also agree for those who like to believe a photon really has some mass to go work and try prove that if you like...I can't imagine anybody encouraged Einstein to think about what light looks light when you catch up to it when he started at age 16....based on what we know it's rather hopeless, but that has never stopped the most brilliant...

    Also its worth while keeping in mind that as we make progress from Newtonian physics to special to general relativity and next maybe quantum gravity we get more complete formulations and accurate insights...which usually simplify to the prior theories....right now general relativity may be the best we have but there are solid reasons to believe it's neither complete nor entirely accurate...
  16. Apr 1, 2009 #15


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    Naty, now I understand what you were saying much better, or think I do at least.
    It's probably useless for us here and now to speculate on our own, as you say. But we can link up with the the main directions of thought about these questions (even though abstract and difficult) in the mainstream scientific world.

    I mentioned that new book of Oriti's called Approaches. Actually it has 20-some authors each contributing to separate chapters, and then there are discussions among the authors. They represent several different approaches and come at the problems differently.

    The book just went on sale at Amazon.co.uk. Not yet available at the USA amazon.
    Both amazon.co and the publisher Cambridge let you read Carlo Rovelli's chapter in the book free, as a sample. It is chapter 1.
    But this chapter is already available free on arxiv.org!

    I will get a link, and find the part where he talks about Time. It is written in completely non-math style and I think it will connect solidly with what Cris is asking.

    I can't think of anybody better qualified to give an overview of what's going on in this area. For instance he is the guy that the organizers of Strings 2008 invited to give a talk on LQG to the main annual string conference. A new understanding of space and time is basically what quantum gravity is about---what is it that underlies the geometry of space and time?
    That's the real question the QG research community addresses---it is not just about apples falling :biggrin:.

    And the current attempt could all be wrong, as everybody realizes, but at least you have a few hundred people working on it. So I will get that link, and paste in a few sample paragraphs.
  17. Apr 1, 2009 #16


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    It's 8 pages of non-mathematical overview.
    and here's a sample excerpt.

    He is talking about the gradual progressive weakening of the concept of time. From classical mechanics, to special rel, to general rel, and finally to quantum GR...

    In classical GR, indeed, the notion of time differs strongly from the one used in the special-
    relativistic context. Before special relativity, one assumed that there is a universal physical variable t, measured by clocks, such that all physical phenomena can be described in terms of evolution equations in the independent variable t.

    In special relativity, this notion of time is weakened. Clocks do not measure a universal time variable, but only the proper time elapsed along inertial tra jectories. If we fix a Lorentz frame, nevertheless, we can still describe all physical phenomena in terms of evolution equations in the independent variable x0, even though this description hides the covariance of the system.

    In general relativity, when we describe the dynamics of the gravitational field (not to be confused with the dynamics of matter in a given gravitational field), there is no external time variable that can play the role of observable independent evolution variable. The field equations are written in terms of an evolution parameter, which is the time coordinate x0, but this coordinate, does not correspond to anything directly observable. The proper time τ along spacetime trajectories cannot be used as an independent variable either, as τ is a complicated non-local function of the gravitational field itself.

    Therefore, properly speaking, GR does not admit a description as a system evolving in terms of an observable time variable. This does not mean that GR lacks predictivity. Simply put, what GR predicts are relations between (partial) observables, which in general cannot be represented as the evolution of dependent variables on a preferred independent time variable.

    This weakening of the notion of time in classical GR is rarely emphasized: After all, in classical GR we may disregard the full dynamical structure of the theory and consider only individual solutions of its equations of motion. A single solution of the GR equations of motion determines “a spacetime”, where a notion of proper time is associated to each timelike worldline.

    But in the quantum context a single solution of the dynamical equation is like a single “trajectory” of a quantum particle: in quantum theory there are no physical individual trajectories: there are only transition probabilities between observable eigenvalues. Therefore in quantum gravity it is likely to be impossible to describe the world in terms of a spacetime, in the same sense in which the motion of a quantum electron cannot be described in terms of a single trajectory.

    Last edited: Apr 1, 2009
  18. Apr 1, 2009 #17
    Thanks for the link, marcus. I've also downloaded the pdf of his entry to the FQXi contest, which also argues for "fogetting time" in any theory of quantum gravity. I'll give them both a read sometime today.
  19. Apr 1, 2009 #18


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    Go for it! The FQXi essay has math parts including a part towards the end which I don't understand. You just have to get what you can out of it and not worry.
    The link I just posted is to a completely math-free essay written in 2006 as an overview chapter for Oriti's book.
    I'd say, given limited time, the thing to do is read that excerpt I posted and around the excerpt, to get context. Then, if you want, ask questions.

    The essay in Approaches is broad, only a certain amount (mainly that excerpt) is about time which is your focus topic. I'd love to pursue just that with you.

    The good thing about that excerpt is that it gives an historical sketch. Rovelli is both a leading researcher and an expert in history/philosophy of physics. He has a book out on the origins of Greek science and is teaching a course in history. The concepts used in physics change! To really understand requires historical perspective. So this little excerpt about the gradual change in the time concept is, in my view, unusually helpful.

    I'd welcome follow-up on just that passage---staying focused on the concept of time. So don't let me swamp you with links :biggrin: stay choosy.
  20. Apr 3, 2009 #19
    Marcus...GREAT REFERENCE>>> WOW...lots to consider there...THANK YOU....
  21. Apr 5, 2009 #20
    Good idea to focus on the excerpt you posted. Otherwise my ignorance will take us in too many directions at once.

    In that excerpt I don't quite understand the distinction between SR and GR. Particularly, what does he mean by an "observable" time variable?

    My biggest problem at this point in my physics career is my limited knowledge of the mathematics involved. I need to spend some time with some text books before I return to this topic in the future.

    But in regards to my original question, at least if I limit it to the context of SR, I'm satisfied for now with my own answer that SR can only be applied to a universe when there is a (real or imagined) inertial frame of reference from which to apply it.

    From another thread on time, ZapperZ said:
    Which is a good point. My original question (and the passage in the book I read) could have just as easily been about whether space exists without matter.

    Thanks for all of the pointers, marcus. I'll be back around here once I know some math :)
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