1. Limited time only! Sign up for a free 30min personal tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Symmetry and Causality: are the two connected?

  1. Oct 16, 2011 #1
    I've been reading an <URL=http://www.nybooks.com/articles/archives/2011/oct/27/symmetry-key-natures-secrets/> article </URL> by Steven Weinberg on symmetry, written for laymen, in the New York Review of Books. Weinberg describes as simply as he can how symmetry lies at the heart of the Standard Model and of physics beyond this model. I know also that there are folk, like Renate Loll, who use causality as a criterium in their attempts to clarify the structure (if any) of the spacetime arena against which physics is set. Both symmetry and causality are central topics in modern physics.

    In attempting to clarify my understanding of symmetry I have come to wonder if 'Symmetry' is not just a synonym for 'absence of causality'. Is this just an obvious piece of trivia? Perhaps there are contributers to this forum who can enlighten me.

    My take on symmetry is this:

    Symmetry is a property that physical objects, paintings, images as well as more abstract constructs like mathematical expressions and the laws of physics, may all possess. For familiar objects like vases or geometrical circles only a glance is needed to ‘spot’ symmetry. In more abstract situations establishing symmetry may need more than just a glance. Much more. It is a devised process of real or imagined action that could change one’s perception of something. Or, as Weinberg puts it, change one's point of view.

    To establish a symmetry for something (say a circle) it has:

    (a) to be observed (quantitatively described and remembered).

    (b) a specific real or imagined action has to happen (for example the observer and item could move relative to one another and/or the item may be transformed in some stipulated way).

    (c) the item has to be observed again.

    (d) observations (a) and (c) must be compared (perhaps by some specified mutual mapping process).

    If (d) shows no change, the item is said to be symmetric under the specified action.

    I conclude that symmetry tells one which specific actions are inconsequential for a given situation. More simply, it reveals restrictions on or an absence of causality.

    Would a universe symmetric in all imaginable ways not be causal?
  2. jcsd
  3. Oct 21, 2011 #2
    From what you've said

    symmetry means an absence of causality

    and therefore, a universe symmetric in all known ways, lacks causality.

    fair enough, but that really only suggests that anything 'we' have done thus far, has not affected it.
    That does not really suggest that a 'creator' did not cause - and create the universe. By definition, a 'creator' has done something we cannot, which has affected the universe, and therefore is not symmetric, having causality.

    When I picture symmetry, one of those infinitely zooming out videos of fractals pop into my head - picture an atom, the proton and electron are symmetric, then we zoom out to see how a system of atoms is symmetric, and then molecules, and so forth... until we get to the entire universe - and to zoom out again and compare it would require another universe - incomprehensible... unless our universe is the electron of another universe! lol and then we have the infinite zooming seen with fractals. But thats all just nonsense really.
  4. Oct 22, 2011 #3
    Thanks for your reply, elegysix --- I'd begun to wonder if anybody was going to comment on what may well be a trivial conclusion for physicists.

    Yes, I agree that such possible nonsense could also have theological implications, but by posting in this Forum (rather than say in the Philosophy Forum) I was seeking technical comments, perhaps an operational evidence-based definition of causality (if such a definition is possible), which could have similarities with my take on symmetry in post #1. My dictionary defines causality as universal operation of cause and effect as a belief, which does support your take on my (here slightly edited) final question:

    Would a universe symmetric in all imaginable ways be not causal?

    Could be a question better not answered, for fear it makes Somebody cross.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook