Anti-particles and Time

Most recent answer: 09/24/2013

Do anti-particles really go backward in time? If that's true, then is time's existence related to the matter to anti-matter ratio in the universe being greater than 1?
- Dylan (age 20)
Ithaca, NY, US

Anti-particles don't go backwards in time in the lab, only in Feynman diagrams.  In the lab they act just like regular particles.  For example at the Fermilab accelerator there were beams of proton and anti-protons being accelerated and being brought to collisions. 

However, you bring up an interesting point, 'why is there a matter/anti-matter asymmetery in the universe?'.   This is a very deep and fundamental question and is related to time reversal symmetry. The answer is 'We don't know'.  Andrei Sakharov a Russian physicist developed the necessary requirements for this asymmetry, one of which is that there must be some fundamental interaction that is not time invariant.   Newton's Laws for example are time invariant.  If you take a motion picture of some billiards bouncing around and play it backwards you can't tell which is the real one.  The electromagnetic and strong interactions are time invariant but subtle experiments show that the weak interaction is not.     Experimentalists and theorists are still working on this problem. 



(published on 09/24/2013)