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

Parity Conservation Means?

  1. Oct 26, 2008 #1
    Parity Conservation Means???

    Hello all, What is Mean By Parity Conservation?.Dont tell That When Parity Of L.H.S and R.H.S Become Equal.I want to Know the Concept Behind It.Please help
  2. jcsd
  3. Oct 27, 2008 #2


    User Avatar
    Science Advisor
    Homework Helper

    Re: Parity Conservation Means???

    Here are some basic info:


    Your question is perhaps "why should things be parity conserving"?
    That question is (in principle) the same as "why should angular momentum be conserved?"

    Both quantites are related to the coordinate transformation which you impose on your system. e.g angular momentum conservation is due to the fact that it doesen't matter from wich angle you perform your measurements on a system -> you can rotate as you wish.
    Parity is if you see your experiment in a mirror, the results should not matter if you are the man looking at the mirror or if you are the mirror image looking at the man

    [forget about philosophical considerations how an image in a mirror can see anything and so on;-) ]

    One major thing in phyics is symmetries. Symmetry gives you a conserved quantitiy. Nature shouldn't care which coordinate system you impose on it.

    But there are processes which violoates parity! The weak interaction is an example of that.
  4. Nov 2, 2008 #3


    User Avatar
    Science Advisor

    Re: Parity Conservation Means???

    Let me take malawi_glenn's explanation one step further, if I may.

    Imagine you are watching a movie of a ball that's spinning clockwise bounce off a wall and go in some direction. Now imagine watching another movie of a similar event, but now the ball is spinning counterclockwise, and it bounces off in the opposite direction (to conserve angular momentum).

    QUESTION: How do you know if the second movie you saw was a "real event", or just the first movie, with the camera recording through a mirror?

    There's no way to know: both scenarios would give you exactly the same movie!

    **UNLESS** parity is not conserved. For example, if the "wall" the ball bounced off of was a W-boson, the movie with the clockwise-rotating ball would NEVER happen in the real world, so now you would KNOW for sure that it was not a "real event".

    Of course, my example is a little silly since clearly quantum helicity and spinning balls are not the same thing, but this is just to give you an intuition, not to be taken too seriously. The point is that if parity was conserved, the mirror world and the "real" world would both exist. If parity was violated, then only one of these worlds would exist. The other would only be an illusion.

    Hope that helps.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook