RE: First collisions at the LHC with unprecedented Energy! (Ask a particle physisicist)
September 9, 2015 at 10:35 pm
(This post was last modified: September 9, 2015 at 10:56 pm by Alex K.)
That's not an easy question. I'll try to do the following - present several different aspects of it separately in the hopes of providing a clearer picture.
Maybe the cleanest approach is via Emmy Noether's theorem on conserved quantities. It states that any continuous symmetry in the laws of nature gives rise to a conserved physical quantity, and that vice versa this quantity determines how to perform the symmetry operation.
The relevant case for us is that the laws of nature do not seem to change over time, at least to a very good approximation. This means that formally moving back and forth in time is a symmetry of the laws of nature, just as rotation is a symmetry of a sphere. Noether's theorem states that there should be a conserved quantity associated with this symmetry. We call this quantity "Energy". The theorem makes sure that Energy is not lost over time and therefore Energy appears to us as if it were a substance flowing through space - if it is not lost in total, the reduction of energy in one place must correspond to the increase of energy elsewhere, in the case of the known laws of nature, neighboring patches of space (continuity equation). This creates the notion of a flow. Vice versa, by the same theorem, knowing the Energy of every configuration of particles and forces is sufficient to know what happens as time progresses, to know the dynamics.
Maybe the cleanest approach is via Emmy Noether's theorem on conserved quantities. It states that any continuous symmetry in the laws of nature gives rise to a conserved physical quantity, and that vice versa this quantity determines how to perform the symmetry operation.
The relevant case for us is that the laws of nature do not seem to change over time, at least to a very good approximation. This means that formally moving back and forth in time is a symmetry of the laws of nature, just as rotation is a symmetry of a sphere. Noether's theorem states that there should be a conserved quantity associated with this symmetry. We call this quantity "Energy". The theorem makes sure that Energy is not lost over time and therefore Energy appears to us as if it were a substance flowing through space - if it is not lost in total, the reduction of energy in one place must correspond to the increase of energy elsewhere, in the case of the known laws of nature, neighboring patches of space (continuity equation). This creates the notion of a flow. Vice versa, by the same theorem, knowing the Energy of every configuration of particles and forces is sufficient to know what happens as time progresses, to know the dynamics.
The fool hath said in his heart, There is a God. They are corrupt, they have done abominable works, there is none that doeth good.
Psalm 14, KJV revised edition
