Last week I explored the idea of time irreversibility in the universe. Our laws of physics are invariant over a T-transformation; whatever a particle does is not affected by whether it is moving forwards or backwards in time. Yet why do we still see an obvious ‘arrow of time’ in real life?
…which of the symmetries hold at all? The universe is a curious place and cosmologists endeavour to contain this curiosity into one theory. Or maybe two, if they’re unlucky.
If there’s anything that physicists love, it’s obeying laws.