Is symmetry fundamental to forces? #physics #science

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7 ай бұрын

It turns out that our universe also has symmetries. A symmetry of the universe is the transformation that doesn’t affect the laws of physics. To understand, consider an empty universe. If we throw a ball, it moves in a straight line at a constant speed. Repeating this experiment elsewhere in the universe yields the same result: the ball behaves identically. This suggests that the universe exhibits translational symmetry, meaning the laws of physics remain unchanged regardless of location.
Similarly, the universe is also symmetric under rotations. Orienting ourselves differently does not affect the ball's motion. Additionally, it is also symmetric through time. Performing the experiment at different times yields the same outcome, as the laws of physics do not change over time.
These symmetries impose constraints on the behavior of objects. In our empty universe, translational symmetry implies that once the ball is thrown, it must conserve its motion because the laws of physics are the same everywhere. This explains why it moves in a straight line at a constant speed. Likewise, rotational symmetry dictates that if an object rotates, it will continue rotating to preserve symmetry.
Every symmetry in the universe corresponds to a conserved quantity. Translational symmetry corresponds to conservation of momentum. Rotational symmetry corresponds to conservation of angular momentum. Time symmetry corresponds to conservation of energy. This principle is known as Noether's theorem, which links symmetries to conservation laws.
The symmetry we already talked about are all global symmetries, as they transform physical systems in a way that is always the same everywhere. On the contrary, gauge symmetry is a local symmetry under gauge transformation, which is allowed to affect different points of spacetime differently, while the conservation of a certain quantity is still respected. Gauge symmetry is extremely successful in providing a fundamental theory that unifies all non gravitational forces of our universe: electromagnetic force, weak force and strong force.