Why does time only move forward?

How do we know that white light contains every colour? Why does time only move forward? Why aren't birds electrocuted by power lines? How do aeroplanes manage to stay airbourne? Why can't different species reproduce? How do X-Rays work? Why do antibiotics work against bacteria, but not viruses? Lester Kiewit and Dr Chris have the answers... Like this podcast? Please help us by supporting the Naked Scientists