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Is the real world deterministic?

  1. Aug 21, 2009 #1
    Do you know of any theory or evidence that shows the real world is (or is not) deterministic?
    By "deterministic" I mean: If we give exactly the same initial conditions to any system in the world, does it evolve to the same state?
  2. jcsd
  3. Aug 21, 2009 #2
    This belongs in the philosophy forum! :smile: No such evidence could exist. See the problem of induction for starters.

    What we do know from quantum mechanics is that basic elements of a deterministic reality cannot be described in terms of a relativistic space-time framework. It's up to you to make your assumptions though. Standard quantum mechanics assumes that space-time is real and nature is not deterministic. Many disagree. Standard practice historically in science has been to assume determinism, and this assumption may even be required for scientific progress. There are tons of arguments over the issue.

    While physics, such as QM, sheds light on the issue and limits the possibilities, determinism in nature can never be proven or disproven. It's a metaphysical issue.
  4. Aug 21, 2009 #3
    Could you please explain this more? Is there any work done on this by a physicist? (Actually I do physics and I'm not a philosopher!)

  5. Aug 21, 2009 #4
    Apparently you are a philosopher :smile:. Physics can't answer this question. There are no possible experiments.

    For a philosophy primer on the issue, see: http://plato.stanford.edu/entries/determinism-causal/. My apologies for the 35 page encyclopedia entry. Sometimes that's as concise as philosophy can get.
  6. Aug 21, 2009 #5
    Well, I would say there IS an imaginary experiment. And that is to prepare two absolutely identical systems which are known to have a random nature and monitor their evolution. The two systems should be the same in an infinite accuracy. I am not sure if it is possible! but it is the simplest plan.
  7. Aug 21, 2009 #6
    1) How do you know that something has a random nature before you've disproven determinism? If something is deterministic then it is not random.
    2) How do you prove your observed correlations apply to all the other systems you didn't test?
    3) How do you know the correlation between your systems wasn't due to both systems randomly changing in the same way? What if both systems switched from having a red appearance to having a blue appearance? How could you tell if there were a cause or not?
    4) How do you know that one of your systems isn't composed of atoms that decay after exactly 10 years while the other is composed of atoms that do not decay?

    These are some of the questions you have to ask. There is a deep history of philosophy regarding this question, with thousands of years thinkers developing the issue in one continuous dialogue. Welcome to the conversation :smile:.
    Last edited: Aug 21, 2009
  8. Aug 21, 2009 #7
    Suppose you have two identical atoms of uranium-238. Will they both emit an alpha particle at the same instant?

    Let's do another imaginary experiment. You are driving your car along a busy street. How long would you dare to close your eyes while driving? While you are driving, you are constantly making corrections for thousands of conditions you encounter along your route.

    Imagine the probability of the particles and photons aligning themselves out of the chaos 13.7 billion years ago in just the right way to determine all the corrections you make while driving. Now consider that it doesn't just happen for you but for all drivers on earth over and over again. Rarely do we see a better example of Ockham's razor rejecting a theory.
  9. Aug 21, 2009 #8
    Hey skeptic, what did you mean with the driving analogy? I think I need an explanation of that one.

    As for the quote above... do you want me to assume determinism or not before I answer? It's either, "duh; identical objects behave the same way," or "duh; atomic decay is inherently random." Not sure which you're going for, but either way it doesn't seem very enlightening for deciding determinism!
  10. Aug 22, 2009 #9
    It would be reasonable to suppose that if we are living in a purely deterministic universe(a sort of matrix style simulation), our simulators would have wanted more control over the course of how everything plays out in the simulation. So they would probably leave loopholes in this deterministic universe, like quantum indeterminacy, through which they could impose invisible 'corrections'.
    Last edited: Aug 22, 2009
  11. Aug 22, 2009 #10
    Actually kote, in my post when I referred to U238 atoms, I wasn't referring to your post but to somy's post #5. The fact that you also mentioned decaying atoms was just coincidence. somy mentioned an experiment of two identical systems and I was trying to point out even with identical systems the results may not be identical.

    I suppose to a deist the creation of a deterministic universe such that even billions of years later matter interacts in such a way as to suggest meaning (e.g. driving to the store to get a loaf of bread) is not incredible, but to me it is. If we live in a deterministic universe, one in such that if we knew the exact positions and momenta of all the particles of the universe we could predict the future to the end of time, then the act of driving a car is pretty incredible. Not only must the driver react to various unrelated evens, he must also obey various non-physical laws. To believe in determinism means believing that all the driver's reactions were somehow encoded in the positions and momenta of the particles 13.7 billion years ago that are only now coming together to create a car and driver seemingly reacting to various phenomena.
  12. Aug 22, 2009 #11
    Good point. Well, our brain is very complex, but in the case of determinism (as you mentioned by knowing the exact initial states of all the matter) our brain would always decide the same.
    Also you mentioned a very interesting thing about the spontaneous decay. My quick argument is that: we don't know the complete state of the matter. i.e. we know that the position, momentum, spin, ... would determine the state of the matter. But whether it is a complete one or not is unclear. (You might be familiar with the discovery of new nuclear states).
    So, the ambiguity is in 2 facts:
    1- We don't know the complete state of the matter.
    2- We are unable to construct two exactly similar systems to test their evolution.
  13. Aug 22, 2009 #12
    Is the real world deterministic? Probably not.

    Interesting, I wonder if you could calculate P(deterministic)
  14. Aug 22, 2009 #13
    Hi all !!,

    seems to me there are two distinct determinisms here... one is cause and effect, the other is global pre-determinism...

    Regarding cause and effect, imho, based on the fact that everything must obey F=ma or any synonymous/derived equation, true randomness originating from any/all scales, must be determined since it exists in an evolving environment. So, I believe that true randomness exits but is 'determined' at its root level.

    Regarding pre-determinism, imho in any universe/multi-universe situation, any process having its origin other than a 'decisional' source, falls under the cause-effect category and is determined.

    All other processes are products of 'sub routines' that are not effected by the F=ma equivalents thus being able to generate outcomes that are not determined but nevertheless imperatively having to return to the on-going, ever evolving deterministic main stream in order to materialise/actuate.



    Now, it is also my belief that through insight, human intelligence, intellect, and freewill reach far more deeper in the QM well than any equation or description ever formulated or written down by these same human attributes...
    Last edited: Aug 22, 2009
  15. Aug 23, 2009 #14
    Light bulbs, sex, internal combustion engines, radios, cd players, plumbing, the solar system, the space shuttle, the tides, Las Vegas, etc. Our existence and comfort is based on the predictability of various processes and natural phenomena.

    The archetypal experimental demonstration of determinism that anybody can do is to drop a small pebble into a smooth pool of water. The disturbance (wavefront) propagates away from its point(s) of origin. This is the fundamental dynamic of any and all disturbances in any and all media. It defines in a general and visualizable way what is meant by determinism.

    Here's more evidence of determinism that can be extrapolated to relate to the underlying nature of our world:

    Because the world of our experience offers so many examples (so much evidence) of determinism, it therefore makes sense to assume that the deeper reality is also deterministic.

    Anyway, what's the alternative?
    Last edited by a moderator: Sep 25, 2014
  16. Aug 23, 2009 #15

    One hundred million trillion universes, one of which happens to just 'look like' it's deterministic, but is entirely random and is due only to the fact that there are 100 trillion trillion 'irregular', weak and inappropriate universes. In personal plan, this hypothesis doesn't make more sense than seeing Darth Vader make raspberry jam in Nairobi, Kenya, but cannot be excluded completely.
  17. Aug 23, 2009 #16
    An alternative is a fine grained randomness which produces an effectively deterministic coarse grained world. We can measure the changes in the entropy of a system very well with this kind of model.

    In terms of our existence and comfort, I would say I'm not at all comfortable with being a programmed automaton with no free will. When scientists talk about strict determinism, there are possible social consequences. The ax murderer should not be punished because his behavior was predetermined and inevitable. Defense lawyers would love to have you as an expert witness. It doesn't take much imagination to see the psycho-social consequences of placing the prestige of science behind what is in fact a metaphysical idea.

    A science based on experiment and cause/effect models would also need to re-think its basic philosophy. We do not manipulate experimental variables by choice. We can only realize one possible outcome and the 'choices' are not choices at all. In statistics, we cannot prove causality. We can only establish associations. Under strict determinism, we only have associations with probability 1. The reduces cause/effect to mere correlations and we know mere correlations should not be confused with causality (even with R^2=1). I could given many examples.

    EDIT: Also the very important concept of time dependent covariance is invalid since cov(x,y)=corr(x,y)/sd(x)sd(y). It's obvious that if there's no time dependent variation, then the standard deviations both equal are zero.
    Last edited: Aug 23, 2009
  18. Aug 23, 2009 #17
    Bell's theorem, derived in his seminal 1964 paper titled On the Einstein Podolsky Rosen paradox[3] has been called "the most profound in science".

    "Bell's theorem implies that if quantum mechanics is correct, the universe is not locally deterministic."

    Multiple researchers have performed equivalent experiments using different methods. It appears most of these experiments produce results which agree with the predictions of quantum mechanics,[1] thus refuting the notion that local-hidden-variable theories can account for QM or supporting the notion that QM involves some degree of nonlocality...After all current experimentation it seems these experiments uphold prima facie support for quantum mechanics' predictions of non-locality.[1]

  19. Aug 23, 2009 #18
    Locally deterministic is entirely different than deterministic. All this means is the world can't be deterministic in one way we thought it might be.
  20. Aug 24, 2009 #19

    If determinism is true, God should be put on trial for all evil that has ever happened. Occam's razor however says that it's much more likely that our God would resemble something like a team of simulators sitting in front of a quantum computer. I assume they wouldn't mind being tried by a virtual court, in a virtual world and being handed out virtual sentences. I think we are f***ed as far as real justice goes.
  21. Aug 24, 2009 #20
    Those who believe that their 'wills' are 'free' might miss some important opportunities to engineer their environments so as to maximize the probability that they'll make the choices that will help them progress toward their goals.

    We punish behaviors that we want to minimize or erradicate. It doesn't matter if the behavior was strictly determined or not. If it's deemed a threat to the desired social order, then it's punished. If it's deemed beneficial, then it's rewarded. If our wills are free, then why is operant conditioning so effective?

    Believing that Nature is operating at the most fundamental level with some "fine-grained randomness", or that the murderers that we execute could have behaved any differently than they did given the circumstances (including their internal and external histories) won't obviate our efforts to control and direct behavior. Indeed, for those who believe that Nature is fundamentally random, then what's the point ... of anything -- and the defense attorney could then argue that the murderer's actions were the result of unpredictable spontaneous quantum brain farts.

    Many of the attitudes codified in our laws haven't caught up with what modern science is teaching us.
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