Here's why:
* Concrete nouns refer to things that can be perceived by the senses (seen, touched, smelled, tasted, heard).
* Abstract nouns refer to ideas, concepts, qualities, or feelings.
While the universe is a vast and complex concept, it is a physical entity that exists in reality. We can observe and study it through telescopes, satellites, and other scientific tools.
Therefore, "universe" is a concrete noun because it refers to a tangible thing, even though it is extremely large and encompasses everything we know.