why symmetry is neccesary in physics
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why symmetry is neccesary in physics
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Let's take the obvious symmetry :
Space is symmetrical -
In the days when physics was "classical" , scientists believed that the laws of physics are unchanged regardless of left or right - This seems like common sense!
In physics terminology this is called P symmetry - P stands for Parity.
All classical physics phenomena have no preference for any particular orientation or direction, P symmetry holds.
Then we have the C symmetry - C stands for charge. The effect of this would be that if charges were swapped (negative to positive and vice versa) then the laws of physics would be the same.
Then we have the T symmetry - T for time which says that physics is invariant for time direction - say if you had a movie of two billiard balls bouncing off each other, you could not tell if it was playing forwards or backwards - both are equally valid under Newtonian mechanics.
Thus it was thought at the turn of the century that the laws of physics obeyed C P and T symmetries
Once physics evolved and the atom was smashed, it was fond that this is not true - experiments in the late 50s showed that certain particles behaved differently as if there was a preferred "handedness" - Think of it as assuming that there are equal numbers of right and left-handed people, and suddenly finding that right-handed is a huge majority.
Thus the P symmetry by itself does not hold.
There are certain kinds of behaviors among particles called "weak interactions" for which C symmetry is also broken.
Some posited that perhaps CP would be preserved, but even that does not.
Time, while being symmetric in theory is not, given thermodynamics and at the quantum level too.
So eventually it has been proved that the combined CPT symmetry holds - In other words, take this universe, swap every particle for an anti-particle, take the mirror image, and reverse the direction of time and the laws of physics will be exactly as they are here.
That's one sense of the word "symmetry".
The other is about symmetry in mathematical models. For example - the standard model, which expounds a kind of hierarchy into which all known particles fit is symmetrical - there are some particles that are observed and some that "ought" to be there on account of symmetry : We have electrons in plenty, and the math says there ought to be a positive equivalent with the same mass - the positron. A lot of particles have been hunted for and found, based on the fact that their symmetric twins exist. The higgs boson is one such too.
Ultimately super-symmetry, a theory, says that all detected sub atomic particles are different views of the same fundamental thing. Suppose you had a pyramid shape - you could cast a variety of shapes of shadow on the floor by rotating it. Super symmetry says something similar (though the sense of rotation there is not spatial, but a rotation in n-dimensional values mathematically). It says all particles are "projections" of the same underlying particle.