Question: There are two worlds we live in. When one world appears, the other disappears. In one world, you are all alone. In the other, there are a lot of people and things. Which one is real?
Answer: This riddle describes the contrast between the dream world and the waking world.
In the dream world, you are technically "alone" because all the characters and scenery are projections of your own subconscious mind. In the waking world, you interact with external entities and a shared environment.
From a conventional perspective, the waking world is considered "real" because it follows consistent physical laws and is shared and verifiable by others. However, from a philosophical standpoint, the only thing that is undeniably "real" in both worlds is the observer (you)—the consciousness that experiences both dreaming and waking.