Symmetry
In physics a symmetry is a change you can make to a system that leaves its behaviour unaltered. Running an experiment tomorrow instead of today, or in another room, or facing a different direction, should give the same result, and each of those is a symmetry of the laws involved. Symmetries can also be internal, having nothing to do with space or time, such as relabelling the charges of particles in a way the equations do not notice. When a symmetry holds only in the underlying equations and not in the state a system settles into, physicists call it spontaneously broken.
Why it matters
Modern theories are built by first choosing the symmetries the laws must respect, which fixes most of the equations before any measurement is taken.
Also written: symmetries
Where it comes up
Read about Symmetry on Wikipedia
Sources
- Symmetry (physics) English Wikipedia
- Symmetry and Symmetry Breaking Stanford Encyclopedia of Philosophy
