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let us suppose the gedanken experiment

a man isolated into a room he ask if he is made of matter oder of antimatter

could he set some experiments to see if he is made of matter or if he is made of anti matter instead ??

is it possible to have an universe similar to ours but 'inverted' in the sense that this new universe would be made of anti-atoms ?

is there any physical way to decide it ?

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Im a newbie , but I think measuring inverse directed spin ? – mick Oct 22 '12 at 13:13
I Guess I am wrong about this spin thing. – mick Oct 23 '12 at 20:21

2 Answers 2

up vote 3 down vote accepted

To do this, the man needs to build a particle accelerator and measure Kaon decays, or some other process involving higher quark flavors. Everything else is CP invariant, so he wouldn't know for sure.

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Being the egocentrics, we typically define matter to be the stuff we are made of, and antimatter to be the stuff we are not. So from a semantic point of view, the man will always conclude that he is made of matter.

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