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.(adsbygoogle = window.adsbygoogle || []).push({});

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 beobserved(quantitatively described and remembered).

(b) a specific real or imaginedactionhas 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 beobservedagain.

(d) observations (a) and (c) must becompared(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 anabsenceof causality.

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

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# Symmetry and Causality: are the two connected?

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