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

Quantum Mechanics versus Determinism

  1. Mar 27, 2010 #1
    As you might know, determinism basically says that the universe is not random, and it is impossible to have a completely random event.

    So there are arguments against this stance that lie in quantum mechanics: they say that quantum mechanics describes a probabilistic and random set of rules that particles follow.

    Maybe I don't understand quantum mechanics very well, but I have to ask for some arguments for and against this randomness in QM, or perhaps an explanation of this. Also, if you have any input on arguments for or against anything determinism-related, I would like to hear.
  2. jcsd
  3. Mar 27, 2010 #2
    No, quantum mechanics in no way implies that the universe is not deterministic, it implies that it's impossible to find out what is going to happen, which one can interpret as that.

    We have the Copenhagen interpretation, which says it is not deterministic, there is the many worlds interpretation, which implies it is, I am personally a big fan of the 'shut up and calculate' interpretation, or 'no interpretation to it at all'.

    It's just a mathematical model, and from its axioms effectively comes what's often called an 'undecidability problem'. Take another example of one of those, the halting problem, simplifiedly said: if you have a random computer program, there is no way to know in advance if it will produce a value after some time, or go on forever.

    If it will do or not is quite deterministic, however, it is impossible to find out if it will in advance.

    All Quantum Mechanics says is that's it's impossible to find out what's going to happen in advance, that doesn't mean it isn't fixed.
  4. Mar 27, 2010 #3
    True randomness is so counter intuitive, and by default it lacks an explanation and process.
    Take any event in the universe and remove the reason and process, and you have randomness, so I ask you, why and how could the universe function like this?

    Mind you, probabilistic does not mean random, it just means there's too many variables to count them all.
    Sort of like the weather.

    But in any case, if there truly are events without explanation then we can never understand them, and they can pop up anywhere, so science fails and we might as well give up now.
  5. Mar 27, 2010 #4
    A lot of things are counter intuïtive for people, says little about their likeliness to occur.

    Human intuïtion is a bad tool for investigation of the world around us.
  6. Mar 27, 2010 #5
    I like to think about it this way...determinism says that for each cause there is a unique effect that follows so that if you could know what is happening at a given time you could in principle predict the future with absolute certainty. Quantum mechanics is interpreted as saying that for each cause there are many different possible effects. The best you can do is talk about which outcome is most probable in any given quantum senario. Despite what some people say, the probability that appears in quantum physics isn't like the probability that appears in classical statistical physics. In statistical physics, probability is introduced because the system being studied is too complex to analyze all the causes individually. In quantum physics, the probability is a fundamental aspect of the theory. I've also never like the "shut up and calculate" view that avoids thinking about what quantum mechanics "means". People who hold that view have contented themselves with describing the universe, but don't seem to care about understanding the universe.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook