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Past Present and Future

  1. Aug 7, 2009 #1
    Do you buy into a block Universe theory? Is this theory still highly respected? What is the perferred interpretation of 'time' among most scientists?
     
  2. jcsd
  3. Aug 8, 2009 #2

    Highly respected? Only if you consider Special Relativity a Truth and not an approximation/useful model for predictions. The seeming quantum randomness(outcomes of scattering effects in same conditions) poses questions that cannot be addressed at this time and until some form of a TOE is on the table, every statement on determinism vs randomness is debatable. BTW, the only constant in physics is change, i keep my fingers crossed that this changes one day and we have a full TOE, but realistically this isn't going to happen in our lifetime.


    Funny as it may seem, fashion has long made its way into physics. But one notion remains unchanged - as far as our experience of reality goes, time is change, a more fundamental understanding of Time however, will require new insights. Most of the most revered physicists of our time, working on String Theory, appear to think, and claim that mathematical models require, that the notion of physical spacetime has to go. And if ST is true, it might be the biggest loss we've ever taken. In my personal opinion, this is what is considered 'everything'(all) and quite frankly i see it more as a dead-end than anything of practical use.
     
    Last edited: Aug 8, 2009
  4. Aug 8, 2009 #3

    apeiron

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    The block model of spacetime, like the many worlds approach to QM, are popular philosophical views within the physics community because the appear to be ontologies that arise in the simplest and most direct fashion from models that definitely work.

    So while outlandish in the extreme (and physicists are as prone to the wow boggle factor as others), they become the officially encouraged direction for going wow, that's cool, who would have thought reality could be like that.

    I don't like block worlds, or many worlds, as they are indeed projections from a myopic mechanical view of causality. So I prefer, for example, works like Prigogine's The End of Certainty or Coveny/Highfield's The Arrow of Time, over Julian Barbour's books for instance.

    So the message here is to make that distinction between models and their ontological interpretations. Everyone can agree that the models work (like GR, QM and Newtonian mechanics) but then derive a whole variety of interpretations.

    "Correct" interpretations would be expected to lead us towards even better, more general, theories. So the issue of interpretation is not simply a free choice. But still there is lattitude to explore the differing directions that appear to exist. Block universes are a logical outcome of taking one kind of ontic path. It has been around a while. So has it been fruitful in terms of advancing our modelling, is perhaps the question to ask?
     
  5. Aug 8, 2009 #4
    If the universe is based on fundamental building blocks, and time = change, wouldn't all the change in the universe follow the same fundamental rules, and thereby be consistent all through?
    Is it too crazy to think that there is no time, but rather only the rules that govern change?
     
  6. Aug 9, 2009 #5
    As I understand it, proponents of the block-universe see our universe as a static 4-dimensional block. How then do they explain our perception of passing through time, moving continually "forward"? I understand that entropy can explain an asymmetry in time, but see that as quite different to explaining time as flowing. Would proponents of the block-universe prefer to claim that time does not in fact flow, but rather that our brains impose that sensation upon us to make the world seem more intelligible?
     
  7. Aug 9, 2009 #6

    My opinion is that Time is not a fundamental property of reality but just a macroscopic appearance of things. I would say it’s only a macroscopic effect. It’s something that emerges only for big things, and i would say the same for Space. Sorry guys, it's very likely that string theorists have got this one right - the notion of physical space-time, as naively as we humans see it, has to go.
     
    Last edited: Aug 9, 2009
  8. Aug 9, 2009 #7
    But the block-universe is a macroscopic description. I don't see how that would address my question.
     
  9. Aug 9, 2009 #8
    No, I don't think it makes any sense. There could be better, more realistic bird's eye view models of our universe.

    I don't know. Maybe you can do a poll.

    My guess is that most scientists will tell you that time is an indexing parameter (eg., associating events with clock readouts).

    The ordinary meaning of the word time refers to the spatial configurations of sets of objects, and to changes in those spatial configurations. This is in line with the standard technical meaning of the term.
     
  10. Aug 9, 2009 #9
    Not crazy, just incoherent. If time=change, and there is change, then there is time. Change is just a term that refers to the incongruence of two or more pictures or perceptions of some set of objects.

    It seems clear enough to me that our universe is evolving, and that any given spatial configuration of it is transitory. The past doesn't exist except wrt records of it. The future doesn't exist except wrt projections of possibilities and probabilities based on records of the past.
     
  11. Aug 10, 2009 #10

    It does, but in a wider sense. The problem again is our intuition and its pre-conceived ideas of time ad space. This is a problem that has been plaguing physics for the last 100 years. Forcing our own preconceived notions of this weird reality on its true nature is rather impossible. It's not a coincidence that the ontological questions are the hardest in physics.
    The idea of Now is pretty central to how we view the universe, it's our intuitive starting point, a deeply rooted assumption that this is a correct approach to understand the true nature of reality. But is this assumption correct? It appears that it's not, SR posits that every moment in the universe is as real as any other, regardless which frame of reference is selected.

    Here is Einstein's opinion on Block Universe:

    "Once Einstein said that the problem of Now worried him seriously. He explained that the experience of the Now means something special for man, something essentially different from the past and the future, but that this important difference does not and cannot occur within physics. That this experience cannot be grasped by science seemed to him a matter for painful but inevitable resignation. I remarked that all that occurs objectively can be described in science; on the one hand the temporal sequence of events is described in physics; and on the other hand, the peculiarities of man’s experiences with respect to time, including his different attitude towards past, present and future, can be described and (in principle) explained in psychology. But Einstein thought that these scientific descriptions cannot possibly satisfy our human needs; that there is something essential about the Now which is just outside the realm of science."


    Physics hasn't been able to find any physical mechanism that could separate one moment from all the others and in the community it's referred to as "the problem of time". It appears we are left with 2 options:

    1. Either the flow of time is a psychological phenomenon(as Einstein appears to believe in the quote "The distinction between past, present, and future is only a stubbornly persistent illusion" - a kind of - the only real thing that exists is the wholeness of all nows in the universe, or

    2. Science is unable to grasp the fundamental nature of time, that the human mind takes so easily for granted.

    I tend to side with the first option because:

    a. Our human intuition and predjudices have been proven time and again to be wrong when applied to the fundamental nature of reality.

    b. QM does not in any way confirm our preconceived classical idea of flow of time(and of space - tentatively speaking because of the different interpretations).

    c. Hints from ST point to a space-time that is not essential to its maths. It can be removed without any change to its mathematical predictions.

    d. It has become obvious during the last 100 years, that it's the classical world as we perceive it, that is "flawed", not the world as it is.
     
    Last edited: Aug 10, 2009
  12. Aug 10, 2009 #11
    Incoherent?
    The problem as I see it is that there can't be such a thing as time, and thus there is no need for the term.
    We don't know why things are capable of moving, or why the universe has motion at all, but I would say the reason for that has to lie in the way the universe is built.
    I have seen people say that the universe moves because it has a time dimension, this is what I was trying to refute.
    I think time is just a model we have placed on the universe to explain our subjective experience of it.

    Physically I believe the fundamental mechanisms in the quantum world, along with the momentum created from the big bang perhaps created motion in the universe. But not a time dimension.
     
  13. Aug 10, 2009 #12

    ConradDJ

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    This is a bugaboo of mine, so please excuse the mini-dissertation (rant) –

    I have the impression that the block universe view is widely-held among physicists, though many would welcome a well-developed alternative. It’s hard to be comfortable with the notion that time is a “psychological” phenomenon, which just side-steps a very difficult issue, treating it as if it has nothing to do with physics.

    For me the big problem with the block universe idea is that it encourages us to imagine spacetime as if it were a vast 4-dimensional space, where the past still exists “back there in time,” and the future already exists, in the other direction. I assume most physicists realize that the geometry and topology of spacetime in Special Relativity are completely different from that of a 4-space. But this gets lost in the translation to non-physicists, who’ve often been told that “time is just another dimension of space.”

    In fact, the spacetime structure of SR guarantees that for any set of communicating observers, there is a common past that can be known, and a common future that’s unknowable. The big difference from classical physics is that we used to think there’s a single instant Now that cleanly divides the past from the future, everywhere in the universe at once. SR tells us that the Now of any given observer is essentially local to that observer. I share the present moment with the people and things around me, but if I’m talking with someone on Mars, his Now is 6 minutes in the future, for me, and my Now is 6 minutes in his future.

    This criss-cross structure is built into spacetime, but it’s hard to grasp intuitively. So we tend to substitute the 4-dimensional block universe picture. And then we say “the present moment is an illusion”...? But come on – if the Now you live in is an illusion — the Now you share with all the people around you, the Now which is all you’ve ever experienced – what basis do you have for assuming anything isn’t illusory?

    SR certainly doesn’t prove there is no Now, for any given observer. But it challenges us to think about the present moment in a new way, and think about how the local present times of different observers are physically connected in their interaction. For me, this line of thought heads directly toward QM, because the present moment – if it means anything in physics – means the moment in which new facts come into being.

    Classical physics had no use for this idea, since it was certain that every fact is causally determined by prior fact. But given all the evidence of QM, you have to work very hard to avoid the conclusion that new facts come into being all around us, all the time. And again, in QM this happens for each observer in actual interactions with things, not in some cosmic Now of universal Becoming.

    So I think there’s something really new we can learn about time, from SR and QM. I’m guessing physics will eventually tell us how this Now each of us lives in actually works – i.e. how there get to be new facts in the world, in the network of real-time interaction. Whereas the block universe view – the world as a vast body of fact, where everything is just given and nothing ever happens or evolves – just seems to me like a way of avoiding and covering over the most interesting issues.
     
  14. Aug 10, 2009 #13
    Wavejumper - you seem to be arguing that the experience of a present moment and time flowing from past to present to future is purely psychological. Isn't that the same as what I said in my original question: "...time does not in fact flow, but rather that our brains impose that sensation upon us to make the world seem more intelligible"?

    I don't see why you call this a macroscopic effect.
     
  15. Aug 10, 2009 #14
    Oops, I didn't immediately notice that you said that earlier.



    Time as a concept is close to non-existent in the quantum realm and at the planck scale it completely disappears. This fact alone is worthy of philosophical consideration.
     
    Last edited: Aug 10, 2009
  16. Aug 10, 2009 #15
    The word, time, has objective referents wrt both technical and ordinary language usage.

    Time, as an indexing tool (clocks, calenders, etc.), is an essential part of sorting things out and communicating what's observed. The deep question of the origin of the universe, the beginning of motion, is objectively unanswerable.

    I agree with you that saying that time is why things move doesn't tell us anything. It's just saying that there's motion because there's motion.

    Time, by itself, doesn't explain anything. As a tool, an indexing or ordering parameter, it helps us to communicate our sensory experience as unambiguously as possible. As a term which refers to the general motion or changes that we observe, it's just a synonym for those terms.

    There's no way to objectively, scientifically, know how or exactly when our universe began -- or even if it had a beginning. The 'time dimension' just refers to the motions of the objects that we observe, their changing configurations.

    But of course you're free to speculate. :smile:

    The assumption is that there are some fundamental dynamics governing the evolution of our universe, along with emergent scale-specific organizing principles. This is what basic physical scientific research is about. It's what scientists are trying to discover, formalize, and demonstrate in increasingly more precise and comprehensive ways.
     
  17. Aug 11, 2009 #16
    Okay then I agree with you with no objections ;)
     
  18. Aug 11, 2009 #17
    Thought this deserved attention:

    "The only reason for time is so that everything doesn't happen at once."

    I get the idea Einstein was thinking past, present, and future are merely figments of our imagination, constructs built by our brains(through evolution/god) so that everything doesn’t seem to happen at once.
     
  19. Aug 12, 2009 #18

    ConradDJ

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    Hmm. Can you explain to me how evolution works, given that time is a figment of our imagination?
     
  20. Aug 14, 2009 #19
    It seems to me the present state for each observer is what exists. Past states and future states do not exist. Past states are just previous present states that are conceptualized in a current present state (thoughts and recall of 'past' observed events). Too, it might be said that future states are just conceptualized current present states (thoughts or predictions about events that have have not been observed yet). So, if this is true, then the present state of the observed 'now' which can include thoughts of previous and anticipated events, which is subjective, is what exists. Nothing more. This seems to lead one down a path of questioning what is 'reality' and if the essence behind this notion is only conceptual.
     
  21. Aug 14, 2009 #20
    I'm not sure what you mean by 'time'. As I type this, it's 5:46 PM. That's a time coordinate. If you mean the dimension, then that's true. By the inherent nature of the English languge, it's grammatically correct to say there is no time dimension. It does not exist.
     
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