Imi poate explica cineva fraza ,,What we need is
a new conserved quantity that has a direction in space, and such
a conservation law can only come from a symmetry that relates
to space.''
In contextul ,,The most fundamental laws of physics are conservation laws, and
Noether's theorem tells us that conservation laws are the way they
are because of symmetry. Time symmetry is responsible for conservation
of energy, but time is like a river with only two directions,
past and future. What's impossible about Lu's motion is the
abrupt reversal in the direction of his motion in space, but neither
time symmetry nor energy conservation tell us anything about directions
in space. When you put gas in your car, you don't have
to decide whether you want to buy north gas or south gas, east,
west, up or down gas. Energy has no direction.''
