Things are observable either directly or indirectly. Direct observation of a thing is made with the senses, with sight for example. The moon can be directly observed. Indirect observation of a thing can be made by observing the effect it has on a directly observable thing. Electrons or x-rays, which can only be observed indirectly, produce observable effects on a phosphor screen or photographic film.

The existence of a thing is verified by observing it. Anything that cannot be directly or indirectly observed is a hypothetical thing whose existence is supposed or imagined.

The universe itself cannot be directly observed. Only a portion of what is out there can be directly observed. As for indirect observation, the universe does not seem to produce effects on the things that can be directly observed. Since the universe itself cannot be directly or indirectly observed, it seems to be a hypothetical thing.

Nonetheless, the universe is not considered to be hypothetical. Physical properties (such as density and entropy) and histories (such as Big Bang or Steady State) attributed to the universe presume that the universe physically exists. What justifies the idea that the universe has physical existence?