Can we be the only unable to define Matter in universe? Something like antimatter. Universe is in permanent expansion as in the other hand Humans are in permanent absorption. Curiosity is insubordination in it's purest form (Nabokov said that). We exist only when observe. To be or not to be. Observation is fundamental skill of our nature. If it wasn't for that there would be something that could be called 'Entity of tranquility'. Everything else exist because we exist. And the all way round. We exist because everything else exist. Think of defined things as matter. Undefined ones as antimatter.A zebra is a zebra and she don't worry to know why she is a zebra. Same happens with rocks, trees, sky, sun, planets and universe and everything else which is not Human. Universe expansion vs Human absorption means Cosmos.