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

Causality, the law of cause and effect

  1. Aug 3, 2003 #1

    Causality, the law of cause and effect, is the most general law used to describe the (physical) reality. The common conviction was that causality holds everywhere, at all time and in all cases.

    Since modern physcics and quantum mecahnics, this concept of reality has been altered in a fundamental way, although it only applies to the sub atomic world.

    The fundamental question is however, if we can realy proof that an underlying material reality, not only just shows up to be acausal and indeterministic due to the way we observe it (which also means interference with the thing we want to observe) but can proof also that the material reality in nature is acausal and indeterministic.

    My argument would be that there is no experiment that can be performed, that could ever proof that. We only "proof" by way of our mathematical and physics models of reality, that the approach of indeterminism and probability, makes sense for practical purposes.

    So, this would mean we would not all by all have to give up the idea that nature is deterministic and causal everywhere and at all time.

    But same as in some macroscopic events, which we also think of as deterministic in nature, we will in all practical cases deal with it in a probabilistic and indeterministic way. Like for instance weather forecast, has to deal with the fact that the weather system is so complex, that we can only use indeterministic and probabilistic models. But this does not claim that the airmolecules itself would not act deterministic and causal.

    Although my argument is only a point from philosophical perspective, and would not change the way we deal with it in experiment, I think that the current argument that a wave function itself is indeterministic in nature, is an unprovable assertion. In fact same unprovable as the opposite, that this wave function is deterministic.
    The point is of course that there is no experiment that could show the difference. This means that both interpretations are both unprovable.

    My argument for still holding on to causality in all these cases, as a general outlook and perspective on reality, is because we have no reason to assume, and neither can proof, that the material reality at the quantum level is with respect to causality in any way different as the macroscopic reality.

    But the dominating viewpoint in physics seems to be, to interpret quantum events as indeterministic and acausal in nature.

    Is that justified?
    Last edited by a moderator: Feb 5, 2013
  2. jcsd
  3. Aug 3, 2003 #2
    I believe that it might be best to make a slight distinction in the wording, quantum events are not indeterministic, or acausal, they instead do rely on what happened before, but what happened before can only influence the probabilities of what is about to happen.

    For instance, lets say a gamma ray leaves a radioactive isotope with a specific amount of energy, such that it has a 50% chance of pentrating a lead wall that is a meter from it. Now if we add more energy to that gamma ray, it increases the probability that the gamma ray can pentatrate the lead wall. Although the gamma ray could still act in an acausal manner by not penetrating the wall, it is more likely to act in a causal manner and penetrate the wall. Thus in the quantum world, the cause does not ensure the effect, but it makes the effect more likely.

    Now, if millions of gamma rays left this radioactive isotope and headed towards the wall and we added energy to all of them so that they had a 75% chance of penetrating the wall, we would see a classic cause and effect situation set up as the probabilities ballance out. You would now see the cause and effect situation where adding energy to increase the liklihood that the rays would penetrate and thus more did. So microworld indeterminancy is determinant in the larger world.
  4. Aug 4, 2003 #3

    Thanks for the response.

    Do you conceive of it that a certain threshold value must be reached, before effects come visible?

    And aa what was my main question, do you conceive that nature at all levels still is strictly deterministc and causal, and that no phenomena in fact proofs otherwise?

    This in itself does not contradict the fact that there are threshold values. For instance, a wind consists of moving molecules, and when strong enough, can cause for instance the lifting of a body.
    But this requires a certain magnitude of the force of the wind, before this effect is observable.
  5. Aug 4, 2003 #4
    Causation as a Folk Science

    Causation as a Folk Science

    Here is an articale that argues exactly against the common point of view of causality.

    http://philsci-archive.pitt.edu/archive/00001214/" [Broken]

    And here is more related stuff on http://philsci-archive.pitt.edu/view/subjects/determinism-indeterminism.html" [Broken]
    Last edited by a moderator: May 1, 2017
  6. Aug 7, 2003 #5
    I can't see why nature can't be deterministic and probabilistic at the same time.

    If you compare a sub-atomic event to the roll of a dice. When you make a measurement, you throw the dice. That doesn't mean that the dice isn't deterministic while it's being rolled.
  7. Aug 7, 2003 #6


    User Avatar
    Gold Member

    i think it is hard for us humans to think that our world isnt detreministic because we ourselves determinstic predetermined, and thus cant comprehend indeterminism.
  8. Aug 7, 2003 #7
    Isn't the alternative unthinkable? If it were indeterministic how can there then be any laws of nature at all, or anything else for that matter. It would be too weird if nature was only "slightly deterministic" or "deterministic enough to create the universe". :)
  9. Aug 7, 2003 #8
    Our uncertainty and Nature's determinism.

    My current personal opinion is that nature is deterministic, but that there are just too many variables in an event for us to track down and determine their physical consequences.

    For example, imagine a set of dice being tossed on a flat surface. There are many variables that will determine the outcome of the toss such as the orientation of the dice before toss, gravitational pull, the manner in which they are tossed, etc. We do not know what all the variables are, so we just know a probability of how they will affect the outcome. The variables, of course, affect the outcome in a way based on their different properties.

    Just because we don't know what the variables are does not mean that they dont exist.

    My main point is that Nature is not bound by the Uncertainty Principle, but we are.
    Last edited: Aug 9, 2003
  10. Aug 30, 2003 #9

    So, isn't anybody going to reply.
  11. Aug 30, 2003 #10
    Your wrong...

    I think it's up in the air at this point. Modern physics has strayed so far from the classical standpoint that we only can theorize about the true nature of reality. I prefer a unifying viewpoint, so I believe the universe is interconnected (no ftl hidden variables; Bell's Theorem). As to what all the implications of that are, I don't know. Quantum events appear to be truly random, that is to say, probablilistic, but I still think macro events are determined.
  12. Aug 30, 2003 #11


    User Avatar
    Staff Emeritus
    Science Advisor
    Gold Member

    I'm fond of the hypothesis that "position" & "momentum" are the wrong way to interpret the universe; they are only approximations. They work great on large scales, but not on small scales, and we've inserted indeterminacy into our theories in an attempt to preserve the position/momentum view.
  13. Aug 31, 2003 #12


    User Avatar
    Science Advisor

    Greetings !

    heusdens, what's with this thread ?

    I mean no offense, but this sounds like one of those
    ridiculous no evidence for God/lack of God threads.
    It's simple really: "If it walk like a duck...".

    You say that: "...we have no reason to assume, and
    neither can proof, that the material reality at the
    quantum level is with respect to causality in any way
    different as the macroscopic reality."

    Well, first of all it's just wrong. If a photon from
    a distant quasar or supernova splits its WF on its
    way to Earth due to some space-time distortion then
    repeating the double slit experiment without a detector
    will give us an interference pattern, but adding a detector
    aimed at one of the possible directions will allow us to
    collapse the WF of a photon and decide which path it took
    "just now" despite the fact that it existed before our Sun
    was even formed.

    Second, what exactly do you mean when you talk about proof ?
    I can invalidate ANY proof to ANYTHING you could ever tell
    me if I wish to, because there's apparently no absolute proof.
    But, there are certain levels of proof which we consider

    For example, if we can collapse a WF in the past or at
    different locations instantly (for us) then we either have
    to assume that causality is wrong or that we are dealing
    with something that can communicate instantly between any
    incredibly "distant" space-time coordinates.

    This evidence or any other for that matter can never make
    us absolutely certain of something but it can certainly
    show us what's more and what is less likely, occasionaly,
    like in this case, even if that conclusion is in violation
    of our basic premises about the Universe.

    Live long and prosper.
  14. Sep 4, 2003 #13
    I don't see why indeterminacy couldn't remain, even in the absence of a "position/momentum" view.

    However, I do see how Relativity (completely independent of quantum indeterminacy) would lose much of it's creditability (and eventually be completely replaced) if it could be proven that position and momentum don't really exist.

    I think you should start a thread about this idea, Hurkyl.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook