Answer by TKoL for Is something physical if and only if we can perceive it (directly or indirectly) with our bodily senses?

Can something be physical even if there is no known or conceivable way of perceiving it, directly or indirectly, with our senses?

There could be completely undetectable physical things - we just wouldn't know about them.

The closest thing to undetectable that we do know about is dark matter - it's only mostly undetectable, it has mass so it affects gravity.

There could be undetectable parts of physics that don't interact with the particles that make up our every day life and don't have mass, that would be maybe 100% undetectable. There might be analytical ways to infer their existence, but there's no guarantee.