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Quantum physics, randomness and its influence on the arrow of time

  1. Aug 4, 2010 #1
    Hi, I have a question which I've been pondering over and would like to have an anwser to. I'm not schooled in physics so I may be using bad terminology which you're welcome to point out of course.

    Anyway my question mainly has to do with the randomness in quantum physics.

    I know that the observer effect in quantum physics means that you cannot have exact certainty over all parameters of a certain particle. Trying to measure it means you're interfering with the normal behaviour of the particle. I also assume that the observer effect is broader than just deliberate measuring (e.g. by a human). The particle we're talking about could simply bump by chance into another particle that happens to be nearby, without the presence of an actual observer, and this would also introduce randomness in the particle's behaviour.

    The main question I have has to do with the cause and effect of randomness and its impact on events as they unfold in time...

    Say we turn the clock of time back to 1000 years AD (any date would do basically) and have it resume ticking at that date without interfering ourselves in any way with this timeline... would history play itself out exactly the way it did the first time? Or would the inherent uncertainty/randomness in quantum mechanics mean that there would be tiny differences which would pile up and up until the outcome of historical events would become measurably different (which I assume would lead to ever bigger and bigger differences compared to the original timeline, but with a minute chance that the randomness would nonetheless produce an identical outcome after all)?

    Basically I think my question is, formulated in a more abstract manner, whether the randomness has some form of determination... i.e. if particle A bumps into particle B in a specific manner then will this event always influence particle A in way X1 and particle B in way Y1? Since the events on the starting date are already preconfigured would the collision of these particles always play out the same, and in turn have the exact same influence on the particles they interact with in their now altered state and so on... so that we end up with exactly the same events in both timelines? Or is the randomness truly indetermined for every event, so that the exact same collision of particle A with particle B could now lead to an influence on A of X2 and on particle B of Y2, i.e. an outcome that may be different from X1 and Y1 and thus capable of introducing ever more differences as events continue (in a way that becomes very noticeable in our physical world as the new timeline unfolds)?

    PS in a related manner...where does the randomness come from? Does it require contact with other particles (or with forces or something?) (which I'd assume) or is there simply an inherent randomness in every particle itself even if it is travelling unopposed?

    I'm very interested in your insights on this matter!
  2. jcsd
  3. Aug 4, 2010 #2
    For randomness we require the deterministic causal sequence to be broken.

    This might happen if the dynamical system passes through a singularity for example, or perhaps the microscopic dynamics transition between different dimensions or degrees of freedom, which might allow for randomness in the new degrees of freedom at the boundary points.

    But we don't have such a detailed underlying mathematical model of QM to say whether it is truly random or not, it just appears that way.

    If not we have determinism and everything that happens is already decided.
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