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

Probabilistic quantum world and deterministic macro world?

  1. Aug 10, 2010 #1

    I have a question about the current interpretation of the laws of nature which, according to what I have understood, says that the laws of quantum world are pure probabilistic but the laws of the macro world are deterministic. Logically, I would think that probabilism at the quantum level would affect the macro level in such a way that it also would be probabilistic, at least to a certain extent.

    However, accepting that nature does not care much whether I think it is logical or not, I also accept that I may have a wrong view of it, and that the macro world may actually be completely deterministic, even though the quantum world is completely probabilistic.

    My question is: Are there some results in the current science that somehow explains how the probabilistic nature of the quantum world does not affect the macro world and it's laws? I have thought a lot about this lately, but I have not found any good answers to this question. Could this e.g. have something to do with the speed of the electron, i.e. that before the macro world (and the laws thereof) is able to "detect" it's position and being influenced by it, it has been in almost all positions around the kernel, and hence where it was at which time before this detection is not affecting the macro world?

    I hope you understand my question!
    Thanks in advance!

  2. jcsd
  3. Aug 10, 2010 #2
    I think your sources might just have not been specific enough for you. The macroscopic world is deterministic in that if I drop my cup of coffee, I know that it will fall according to newton's law with negligible probabilities and errors.

    Technically, the macroscopic world is not deterministic for just the reasons you are thinking. I think the best example is the formation of galaxies and galaxy clusters: according to our current theories, those are due to random quantum mechanical fluctuations soon after the big-bang.
  4. Aug 10, 2010 #3
    Thanks for your reply! I think that sounds sensible. :smile:

    I think it is rather misleading that many "Newtonians" (in lack of a better word) are calling the macro world "deterministic" then. In my definition, "determinism" means that the future can only happen in one specific way, i.e. that there are no future possibillities. This is certainly wrong (at least according to what current science predicts), even if no elephants will appear out of the blue or no coffee cups will ever fall upwards. :smile:
  5. May 1, 2012 #4
    Uncertainty principle says that the product of the multiplication of the imprecision with which we know a particle position and the imprecision with which we know its momentum will be greater than some value given by quantum theory, by some set amount which is determined by the nature of the universe. The more accurately we know one, the less accurately we will know the other. This goes for numerous complementary properties of particles (not just momentum and position). The planck constant figures into this limiting factor.

    It is not just light that has a wave nature. All particles have a dual particle/wave duality, even buckyball particles (as many as 60 atoms in one them). The behave light light in the slit experiment (form an interference pattern). Same for electrons. Matter does self-interact just as light does. De Broglie was able to describe the wavelength of a particle as the planck constant H divided by the momentum of an object. For human being, our debroglie wave length is 10E-37 meters (smaller than the Planck constant), so it is very small (a proton is 10E-15 meters). We are not going to be interfering or interactingg with each other going through doorways in a quantum sense. This wavelength begins to take on importance when you work with fast moving very small particles. At small scales these properties begin to have an actual influence. At large macro scales, it is present, but just negligible. It fades into the background noise.

    Part of the uncertainty comes from the wave nature of particles. You cannot say precisely exactly "where" a wave is, where its center is. It is spread out. You have to look the full wave packet, all of the different wavelengths to see the particle nature of a particle. But in doing that you remove the momentum nature of the particle. The very nature of matter stops precise measurement because the particle cease to have pure particle properties at the sub atomic level.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook