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Are there any theories about why causality appears?

  1. Aug 10, 2007 #1
    I have a question, but I am not sure how to express it.

    I have been thinking about the idea of the universe as a four-dimensional object, with time as just another dimension. I have also been thinking about David Deutsch's idea of the universe as a sequence of quantized slices or slides.

    People usually think of causality as an active phenomenon - one thing causes another to happen.

    But both these analogies seem to question the necessity of causality. Why should one "slice/slide" of the universe have any relation to the one before it or after it? Why should a four-dimensional universe have a kind of continuity and relatedness in its contents across the time dimension?

    When we drop a ball from a tower, the ball hits the ground. But viewed four-dimensionally, the ball in the future was already on the ground. If the past and future are both physically real, then there is no necessity in having a relation between them. The ball you dropped could have fallen up, or disappeared, or turned into a pot of geraniums.

    This is kind of backing into the question of why physical causal laws exist - the physical causal laws describe the apparently already-existing relation between things in temporal sequences. But why is there any relation at all? There doesn't seem to be any need for there to be.

    If time is really just a dimension, and there is no "meta-time" as Deutsch puts it, then causality is not really an 'active' force that causes things to be the way they are - it is more like a kind of tautological description of the way things happen to be. But the way things happen to be LOOKS very 'causal', and just happens to be easily describable by 'laws' of connections across time.

    Are there any theories about why causality appears? Or is it possibly even an illusion? That is, we are in a "slice/slide" of the universe, the past or future sequence might be an illusion and not exist. Or am I missing something???

  2. jcsd
  3. Aug 10, 2007 #2
    The existence of the four-manifold does not alter the fact that certain laws are observed to be true when comparing points on it, and this would be violated if the ball is also a germanium. Similarly, if the one end of the four-manifold has a low-entropy state compared to the other, then that defines an arrow of time, and we can deduce that balls will statistically only fall down (toward planets) as we move toward that other end of the manifold. (Read up perhaps on block-universe philosophy, or arrow-of-time pop-sci.)

    You'd be justified to say "causality" is an artificial interpretation imposed by humans, whereas physics basically says only whether two events are "correlated" (which is a time-symmetric relation).
  4. Aug 11, 2007 #3
    all the possible 'slides' exist- slides with complex ordered structre that are complex enough to contain intelligent states of information correspond more often to the output's of possible causal algorithms- because algorithms produce complexity more cheaply than any random/chaotic/noisy sets of states- so complex states are more likely to be part of causal sets and thus complex observers are going to observe a causal timelike structure to their world
  5. Aug 11, 2007 #4


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    Can a universe exist without observers? Who knows? Such a universe will never have any observational consequence to us. Hence, the question is moot.
  6. Aug 11, 2007 #5
    cesiumfrog - yes, but why are events correlated in this way?
  7. Aug 11, 2007 #6
    setAI - if I understand you right, I believe I was wondering the same thing.

    What if the relationship between the 'slides' we see is just a coincidence about us (like a kind of anthropic principle)? Maybe the sequence of events is different than we see it, but we see it in a particular way because of the kind of observers we are.

    So maybe falling balls turn into pots of geraniums as well as balls on the ground, but we only see the balls on the ground because the geranium pots would be part of a different network of connections, seen by different (chaotic-like?) observers.

    Now I may really be not knowing what I am talking about... but 'slides' of spacetime kind of like fragmented files on a computer. Each slide has a kind of 'index note' about which other slide it connects to, but that is not necessarily the slide it is adjacent to physically.

    Or is this crazy?
  8. Aug 12, 2007 #7


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    Slides do not objectively portray reality, even if you mix them up. Just another trick pony.
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