system
Given the following post, respond as if you're commenting on Reddit:
human
What is exotic matter?
gpt
There is a lot about physics that is frustratingly constraining, or elusive. Lightspeed is a rock-solid constraint on things moving in the universe and so far there has not been a truly effective method actually proposed to break through that barrier.

But, the properties of quantum mechanics lead to the discovery of a lot of weird stuff underlying the basic fundamental nature of reality, and it comes down to a list of basically 16 particles. There are ways that this list could be extended, if for instance there existed particles that don't interact with the same set of forces as act on these. Arguably this is what dark matter likely is.

But what if you really wanted to bend the rules?

That's where exotic matter comes in. You build a ring out of it, and then you can start ripping a hole in spacetime because its properties work against the fundamental nature of reality in specific, scientifically consistent if essentially impossible, ways. For instance, in the Xeelee novels by Stephen Baxter, the first wormholes are developed by somehow creating an exotic material that somehow was composed of negative energy (in the opposite way that normal matter is composed of positive, existing energy). To make such matter involves a number of things that just don't make sense. But, give a sci-fi writer a little broken physics and they'll build a world out of it with a wave of their hand.

Of course, with such an unhelpfully generic name exotic matter may well mean different things. You might argue that short lived particles resulting from collisions in particle accelerators or cosmic ray strikes are exotic, in the sense that they are novel and rare.