How to detect antimatter in an alien without touching it

[Soff]

Suppose you are going to meet an alien from another planet. How can you make sure that the alien is not build of antimatter without touching it?

My teacher told me that I have to compare the rate of the C-P violated processes. I didn't understand this point.

 

[da_willem]

Throw something at him ;)

 

[mjsd]

if CP is a good symmetry between particles and anti-particles, then CP violation means that reaction rates between set of particles will be different from those rates generated by a set of anti-particles. so by observing the rate of CP violating processes generated by these aliens you can tell (in principle, not sure this is practical) whether they are made of anti-matter.

 

[interested_learner]

Your teacher was referring to a joke that Feynman had in his famous lectures. Go to the library and look up Feynman's lectures on Physics Volume one pages 52-10 to 52-11.