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Let us suppose this gedanken experiment:

A man isolated into a room asks if he is made of matter or antimatter.

Could he set some experiments to see if he is made of matter or antimatter instead?

Is it possible to have a 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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  • $\begingroup$ Im a newbie , but I think measuring inverse directed spin ? $\endgroup$
    – mick
    Commented Oct 22, 2012 at 13:13
  • $\begingroup$ I Guess I am wrong about this spin thing. $\endgroup$
    – mick
    Commented Oct 23, 2012 at 20:21

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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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  • $\begingroup$ Well maybe make something that is opposite to the type of matter(matter or antimatter) and test their properties. Also make sure the two different types of matters do not touch each other or there will be an explosion. After this you can probably check whether there is matter or antimatter. $\endgroup$
    – Roghan Arun
    Commented May 18, 2020 at 14:57
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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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