In other words, in terms of science, is there a category that has both antimatter and matter in it?
"Matter" (in particle physics)
Or more specifically: "massive particles", to exclude photons, which are neither matter nor antimatter.
What about Z bosons? They are massive particles, but do not belong to "matter" or "antimatter" as they are their own antiparticles.
What about mesons? They are not their own antiparticles (neutral pion as exception), but there is no clear way to call some "matter" and some "antimatter".
This is a perfect example of how the term "matter" is not clearly defined.
If we are using the definition of matter to be something of mass and volume, then isn't antimatter actually matter by this definition?
I would say that you could use the term matter to refer to fundamental and composite particles that bind together to form structures of finite volume and mass. In such a case, yes, antimatter would fit this definition.
It's important not to get the idea that 'antimatter' has negative mass. It just has other aspects to it which are the opposite 'sign' to 'normal matter'. The two forms of matter will still anihilate each other when they get close enough and produce a lot of energy (EM).
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