It is a question of when all the light from all around impinges upon our senses. To us it is real, but the light from various sources from reflections off glass close by to the furthest reaches of the cosmos has different ages. The light we see from the sun is what the sun was like 8 and 1/2 minutes ago. Since then the real sun has changed and is not in the sky where we see it due to the time lag. It is the same for the rest of the cosmos. We see galaxies as they were millions of years ago. We don't know what they look like today and have no way of telling due to the limit of the velocity of light. The cosmos we see is real, but it is as it was when the light left and the time it took to reach us. This varies by distance. Further, as some of the cosmos is moving toward us and some moving away, the light is blue or red shifted. In the world of sound where we can hear pitch change as something moves past us, we get a sense of this change.
Other hints of the reality come in the form of meteorites that fall from the sky to earth. These are real enough and can be physically measured. Yes indeed, the cosmos we see at night is real, but there are catches.