Talk:Invariant (physics)

Invariance depends on scalar invariances?
If we take a "purely geometric object" like a vector that is written in some Cartesian coordinate system and transform it another Cartesian system, it is common to regard the vector as "invariant" even though all its coordinates may change. There are scalar quantities (such as length and direction cosines) that are associated with a coordinate representation of a vector. Whether the vector written in another coordinate system is "equivalent" to the vector written in the first system is tested by comparing the equality of these various scalar quantites.

Does the definition of "invariance" used by physicists include the above type of "invariance", which is based on an "equivalence relation" more complicated than the simple equality of a scalar? If so, is the "invariance" of a geometric object always defined in terms of invariances of some associated scalar quantities?

It always irritates me to read articles on physics that remark how wonderful it is that particular equations "keep the same form" under particular coordinate transformations. But they never define what "keep the same form" means. Is it supposed to mean that each symbol in the equation is an "invariant" of the coordinate transformation?

Tashiro (talk) 05:19, 20 August 2009 (UTC)

Added the following, to clear up a perhaps not so obvious linquistical idiosyncracy.
Note: In variance, does not imply not varying, it pertains to a condition where there is no variation of the system under observation, and the only applicable condition, is the instantaneous condition. Invariance pertains to now. Now(+1), to a condition where all variations are solely due the internal variables, with no external aspects imparting nor removing energy (Newton´s law of motion: a system in motion continues in motion, unless an external force imparts or removes energy). That condition is met by using de parcial derivative function, ∂f(internal)xf(external) and presuming/setting f(external)=constant, leading to ∂f(external)=1 using the chain rule. Obviously, this is a model used solely for calculations, and not a reality. Reality is, that at all and every instance, energy is both removed and added to any system in observation. — Preceding unsigned comment added by 201.209.217.235 (talk) 15:41, 11 February 2013 (UTC)

Intro paragraph
The introductory paragraph is a bit messed up. — Preceding unsigned comment added by Hwfr (talk • contribs) 04:41, 13 August 2015 (UTC)
 * More precise, you might as well go ahead and improve it (but add a citation). Or add it here ... prokaryotes (talk) 05:48, 13 August 2015 (UTC)

A better primary example than Polaris?
Perhaps we could find a better example than Polaris. This maps a 2D star chart onto a singularity at the North Pole, which may be a different coordinate system issue, than the one we are describing. Also for careful observers the star Polaris is about 3/4 degree off center from the pole: declination +89° 15′ 38.1″, so it is not really invariant, and it gets worse, especially with precession of the equinoxes. Invariance has to do with the laws of physics being independent of the coordinate systems we humans impose on the map, to study them. Physical law arises independently from these coordinates, based on symmetries, which via Noether, lead to conservation laws. Perhaps a better example would be invariance with translation, or rotation? — Preceding unsigned comment added by Cwfmd (talk • contribs) 13:41, 30 June 2016 (UTC)


 * I agree, the Polaris example is confusing as it is hard to tell which physical law (if any) is behind it. Does Polaris know where our N pole is and adjusts its position, or does it not really care about us? Ponor (talk) 11:10, 24 July 2020 (UTC)

Merge with Invariant (mathematics)
This page describes the same exact concept as Invariant (mathematics). While invariants carry a special importance in physics, that should be described on that page, not given its own page. It's possible in the future that there might be enough content about invariants as they relate to physics to justify their own page, but we aren't at that point yet.

All the best, Ramzuiv (talk) 04:15, 3 December 2019 (UTC)
 * I think this article should be kept, maybe even renamed to Invariance (physics) as a broader term. Invariance is very important in physics, it should not be lost in the much broader and less readable Invariant (mathematics) article. Ponor (talk) 14:37, 24 July 2020 (UTC)
 * Closed, with no merge, given the uncontested objection and no support. Klbrain (talk) 21:02, 30 October 2020 (UTC)