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

Quantum phenomena and the passage of time.

  1. Dec 30, 2007 #1
    From what I understand the future universe is qualitatively no different from the past universe.

    When someone experiences the present does not necessarily correlate with when another person experiences the present(e.g. stationary individual vs near-light speed traveling individual... for that matter... subquestion: what defines when one of these two individuals will/is experience/ing the present? is it a total unknown as I suspect?).

    Yet quantum phenomena, seem deterministic if looked after the fact. Say atomic decay, if you've a detector, and you analyze the results. There's a definite yes or no. Other phenomena can be linked to macroscopic objects in such a way that it triggers a macroscopic event. Again after the fact, it is seen as deterministic from our perspective... we couldn't remember what we remember if it were any different.

    Yet future quantum events are believed to be indeterministic by physicist.

    So what's the explanation for this. At which point does an event stop being in the future and is considered to be in the past? Especially given that different observers and time measuring apparatus can experience time different, and consider/experience themselves to be in the present at different times.
    Last edited: Dec 30, 2007
  2. jcsd
  3. Dec 30, 2007 #2
    I am not sure what you mean by "qualitatively". The same physical laws that govern the past also govern the future.

    The question you just asked is probably too philosophical for a physical answer, but I'll try anyway. Special relativity tells us that every inertial reference carries with it its own intrinsic clock that "ticks" at precisely the same rate throughout the IRF. Therefore, the so-called event of a person being in his own inertial reference DEFINES the present moment in that frame. The reason that this question is more philosophical than physical is because the concepts of the "present" and "experience" are ambiguously-defined in English. In physics, we try to avoid such terms or redefine them unambiguously. Thus, in the language and rigor of physics, your question becomes merely "What time is it in my inertial reference frame?" which is very well-defined by the oscillations of the caesium 133 atom.

    Again I think the problem could be the ambiguous English meaning of indeterministic. But for our purposes it means predictability. Saying that the past is predictable is a trivial, meaningless statement.

    I think you might want to read up on the role of inertial reference frames in special relativity. Also look up light-cones. Despite what it may seem, time and space and their relation are VERY WELL DEFINED by the Lorentz transformation. I think the problem is that you are trying to understand the mathematical models of special relativity and quantum mechanics with your linguistic faculties and fit them into your worldview without any math. That is impossible. To understand these things, you need to get a QM or an SR book and learn the math and do practice problems. After you get the math, the concepts all fall nicely into place.
    Last edited: Dec 30, 2007
  4. Dec 31, 2007 #3


    User Avatar
    Science Advisor
    Homework Helper

    quantum fenomenom are not deterministic in the ordinary sense. In QM, given initial conditions, only the PROBABILTY of a certain outcome is given. I would therefor call it pseudo-deterministic.
  5. Jan 1, 2008 #4
    Well my point is that is simply not the case when it comes to events that have passed or lie in the past.

    Look at the schrod cat, after the fact, after you open the box. The atom either decayed and killed it or it didn't, no more probabilities. Same with any experiment that does something like it. The results are not probabilities but deterministic facts when they are considered to be in the past. It is only when it comes to the future and present that we consider it to be a probability.

    Any quantum event tied to a macroscopic outcome, will after it takes place be definitive. The past doesn't change and it is set in stone.

    Now if we don't pull any arbitrary division of past/future and consider them qualitatively the same. I do not see why we can't use this to state that things like the decay of an atom while unpredictable to us, are deterministic. Same goes for any other quantum phenomena that fits under this.
  6. Jan 1, 2008 #5


    User Avatar
    Staff Emeritus
    Science Advisor
    Gold Member

    Consider the following: We set up 10 identical cat experiments last week. Yesterday we opened up all of the boxes simultaneously and found that they did not all have the same result. If I ask you today, to tell me what the outcome of the cat experiment performed over the course of last week was, what would you say?
  7. Jan 1, 2008 #6
    That simply it cannot change now. It is set in stone, some of the atoms decayed some didn't and that's it. There's no longer any probability that the outcome will be different, that a specific cat will die or live is set in stone.

    Unlike with the future we can't say: Could it've been different? Hypothetically in some what if? yeah it could've, realistically no!.
  8. Jan 2, 2008 #7


    User Avatar
    Staff Emeritus
    Science Advisor
    Gold Member

    The point of science, however, is not to look at something that happened and say, "Well, that's what happened." The point of science is to say "If you do <blah1>, then what you will get is <blah2>."
  9. Jan 2, 2008 #8


    User Avatar
    Science Advisor
    Homework Helper

    solidon: There is a difference between determinism and "the past does not change".
  10. Jan 2, 2008 #9
    Well, yes there is. But the basis for taking it into account when dealing with our reality is quantum phenomena. If for example things like the decay of an atom are such that they will decay at a set specific moment and at no other time with 100% probability, then at least that type of event should be considered deterministic.
  11. Jan 2, 2008 #10


    User Avatar
    Science Advisor
    Homework Helper

    You have then re-defined the term "deterministic", you can never say when a speficic nucleus will decay, only the probabilty per unit time that it will do it. The decay of a nucleus is probabilistic, not deterministic. Determinism is that you given a certain circumstance, you can calculate when and what outcome you will get. But you cant NEVER determine when a specific nucleus will decay (determinism). But WHEN it has decayed, ofcorse we see the result in our detector. But we can never calculate WHEN before it has decayed, only the probabilty for decay per unit time.

    What is a decay of an atom?
  12. Jan 2, 2008 #11
    Let me re-word my point. If the future is to be taken as no different than the past... Then minus our subjective experience, we should consider the present moment and upcoming moments the same as if they were in the past already. If the future equals the past and as such it does not change, it's basically saying it is fixed in stone and deterministic.

    That is, if what we consider 'now, and the 'future' are the same, as the past, regardless of our ability to predict. The fact that a specific atom will decay at a precise and determined point and the moment It will do so, is unchangeable, unalterable, and predetermined, fixed in stone... again unless there's something to differentiate the future/present from the past.
  13. Jan 2, 2008 #12


    User Avatar
    Science Advisor
    Homework Helper

    The laws of physics are unchangable as we think today.

    I still dont get your point, you only seem to have many missconceptions.
  14. Jan 2, 2008 #13
    Again the problem is, the caesium atom gets out of sync with other caesium atoms given differing velocities, in other words some will be running later or faster than others. IOW, some of the ticks will seem to be in the past others in the future relative to each other. And you can't say one's more valid or presentish than the other.

    My point is that under the not so outrageous assumption that the future and the past are the same qualitatively. The future is as set in stone and immutable as the past is. Under this view, the probabilities are but illusions.

    The only way out is to assume that either a.) the past changes and is probabilistic("I've heard this one..."), b.) there's something that makes the future different from the past.
    Last edited: Jan 2, 2008
  15. Jan 2, 2008 #14


    User Avatar
    Science Advisor
    Homework Helper

    "Under this view, the probabilities are but illusions."

    1. The future is different from the past in some aspectsm but in other aspects the same as the past. The laws of physics are assumed to be same today as yesterday as tomorrow. But this does not impy that the world is static, it is very easy to show that the world is dynamic (that configurations of matter and energy is chaning).

    2. You cant DETERMINE the future in 100%, since the smallest entity of our world (the elementary particles) are probabalistic. Hence we can not, on the very smallest scale of our world, determine its future configuration from the present configuration and the past configuration.

    3. Of course WHEN a nucleus has decayed it is written in stone. The future WILL be written in stone, but is not written in stone today, we can not know 100% how the future will be.

    Now I have of course not included the action of living beeings, because then we must include the concept of free will etc. Lets hold our self to 1kg of radioactive Uran for example, as our world. You can never determine WHICH U-nucleus that will decay the within the next 10min, hence you can not determine its configuration, since the mechanism that governs the decay of U-nuclei is not deterministic. This mechanism (the law of physics is however hold to time-independent).

    It so easy, grasp it.
  16. Jan 2, 2008 #15
    Chaotic nonlinear complex systems are pretty much unpredictable to us even when they are of a completely deterministic nature. There are VIABLE hypothetical theories in development that put determinism back on the table by putting it at a more fundamental level than quantum phenomena. Yes they're unproven, and as of today the evidence is still in favor of uncertainty/randomness having knocked determinism, it just remains to be seen if it will remain that way.

    1. A deterministic future is pretty much indistinguishable from a nondeterministic future except when it comes to experiments and theories probing reality at its deepest. If our present moments where nothing more than subjective, and we were actually in the past from another's perspective, we couldn't even tell.

    2. Present evidence does point to it being random, but it could turn out to be deterministic after further evidence pops up... again even if it were deterministic, if the processes are complex enough it might remain unpredictable anyway.

    3. That there are things written and things yet to be written. Implies there is something special about the present... yet clocks go out of sync. Which clock's ticks represent the present when they're each experiencing the passage of time at a different rate? It also implies that the future is qualitatively different from both the past and the present.

    It's easy to grasp yeah, but you have to assume that a.) the present exists and is not an illusion, b.) the present and the future have different qualities from each other and from the past. c.) a law or means for the qualitative transition from past to present to future exists, and seeing as the so-called rate at which times passes can change quite easily for any object and is infact different for objects going at different velocities... some way to reconcile the time based discrepancies.

    Again perceptually there's no way to tell the difference.
  17. Jan 2, 2008 #16


    User Avatar
    Science Advisor
    Homework Helper

    But there is no such thing as hidden variables in QM, this has been proven by Bells inequality etc. Search for old threads about this if you like.

    We can neither rely on that in the future, one might find that QM just a ver very complex deterministic system, but we a living today and are discussing about the facts that we know of today.

    That clocks go out of sync is just that their machinery is not working good, it is difference bewteen time itself and our clocks..

    Of course one must make a lot of assumptions, also you must make a lot of assumptions. The meaning of philosophy is to find out which paradigms are consistent and seems to fit our experience of the world.

    The assumption a) everybody (at least that have common sense and are trained philosophers) have.

    Assumption b) follows from a)

    Assumption c) is one of the basic assumptions in physics, and since looking out in space is a form of looking back into the past, one can test this assumption in some manner.

    I still dont have a clue what you want to say/ask in this thread. Just draw a time-event diagram.
  18. Jan 2, 2008 #17
    From what I understand a.) there are loopholes in the experiment that may allow them to exist., b.) bell doesn't rule out non-local hidden variables, iirc, c.) I recently read an article about rotational non-symmetric math/algebra or something like that in a recent newscientist(from a few months back) and how they could re-introduce determinism back, iirc.
    Well, I'm taking this from the aspect of time and its passage. Why are we experiencing the present? Is there any qualitative split between past and future? There have been many scientists that have asked about it. Here's a link to two abstracts from two articles of the special edition of sciam dealing with it that I read some time ago.(I have it on pdf if you want the particular article... that is if it's not against the rules here.):


    A paragraph from the article to show what I mean

    Not really, it's due to time dilation. Time actually runs slower. Going at near light speed you could get to the edge of the galaxy within your lifetime, even to the edge of the visible universe. For you only a few decades would have passed, while outside countless centuries would have passed. Time goes slower for you. There was an experiment on earth when the clocks differed by minuscule fractions of a second after one was flown around and the other left on the ground, or something... it showed the effects of dilation. It probably occurs at everyday speeds too, only it's likely minuscule fractions of an atto-second(dunno, haven't done calculations.)

    Well as someone that believes in the multiverse, and seeing as for each instant there are nearly an infinity of alternative paths, I simply believe that it's likely the reason why this specific path out of all the infinite alternatives is the one we're stuck experiencing is because it is the only path which we can be experiencing(others are experiencing the alternate paths).

    To be more specific I believe that the universe is information. Just as information itself(patterns in the brain.) and the complex relationships between elements, appears to be capable of generating qualia and consciousness. It's not a stretch for me to believe that relationships that exists between abstract information(for example, two subsequent frames in a film are fundamentally related to each others, even if they were never put on said film... not only that but such frames exists abstractly outside of time as mathematical entities, as binary numbers for example. The same applies for two subsequent instances in a hyper-realistic matrix like simulation, they exist abstractly outside of time as binary numbers... and again so do the relationships. ), somehow generates time itself... after all such as stated already have qualia, and consciousness under their belt.

    What I'm saying in this thread is that just as free will is considered an illusion by many, maybe the 'specialness' of the present is another one too. Maybe nothing is being written in the present, maybe its all just already set as firmly in stone as the past is to us, and we're only under the illusion that there's choice. Maybe the people of the past really only had the illusion of choice, and their fate was as firmly in stone as it seems now from the so-called 'present, that is before they even experienced it, from the very beginning.
    Last edited by a moderator: Apr 23, 2017
  19. Jan 3, 2008 #18


    User Avatar
    Science Advisor
    Homework Helper

    yes there are some loop holes.

    I did not know you was referring to time dilation when you talked about clocks go out of sync.

    Then we just move over to relativistic QM, where time is an observable, not a parameter.

    I cant really see your argument that the past is not written by reffering to quantum fenomenon. What you really is discussing is the special relativity.
  20. Jan 3, 2008 #19
    Well I found one of the articles over here:
    http://urgrue.org/lib/mysterious-flow.html" [Broken]

    It seems complete from what I saw.

    Here are a few select quotes from it:

    Last edited by a moderator: May 3, 2017
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook