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

What size do particles start to get a quantum effect

  1. Aug 1, 2012 #1
    Im wondering at what size particles/object start to get a quantum effect? At what size does classical physics stop and at what size does quantum physics start?
     
  2. jcsd
  3. Aug 1, 2012 #2

    Drakkith

    User Avatar

    Staff: Mentor

    Well, as far as I understand we typically talk about quantum effects starting to dominate around the small-medium molecule scales. However, this really depends on what you are trying to figure out or discuss. The difference between two electron states in a large polymer probably requires quantum mechanics, but that polymers behavior in a material may or may not.

    Personally I would say that individual particles, atoms, and molecules generally require a quantum description, while large systems of these objects can be described by classical physics in most situations we deal with. I just don't think it's a clear cut between the two.
     
  4. Aug 1, 2012 #3
    when hbar starts looking a little less non-zero
    or more accurately speaking when the derivative of the de brodglie wavelength with respect to the coordinates stops being << 1
     
  5. Aug 2, 2012 #4

    tom.stoer

    User Avatar
    Science Advisor

    There are even macroscopic systems which show genuine quantum behavior like bose-einstein condensates, superconductors, superfluids, ...; even a single pair of entangled particles shows quantum behavior. There is no absolute size in terms of length scales or number of particles
     
  6. Aug 4, 2012 #5
    it is believed that over 1014 atoms begins macrorealism.


    quantum mechanics effects, actual experimental limit, 430 atoms:
    http://www.nature.com/ncomms/journal/v2/n4/full/ncomms1263.html

    ...PFNS10 and TPPF152 contain 430 atoms covalently bound in one single particle. This is ∼350% more than that in all previous experiments...
    ...in our experiment, the superposition consists of having all 430 atoms simultaneously 'in the left arm' and 'in the right arm' of our interferometer, that is, two possibilities that are macroscopically distinct. The path separation is about two orders of magnitude larger than the size of the molecules.....
     
  7. Aug 4, 2012 #6

    Vanadium 50

    User Avatar
    Staff Emeritus
    Science Advisor
    Education Advisor

    How long is a piece of string?

    There are quantum mechanical effects at all scales. Whether they are large enough that you care about them is a statement about what you care about, not anything physical.
     
  8. Aug 9, 2012 #7
    Thanks for all the replies, I understand know.
    thanks
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook