One Universe, One Reality, Until Now

Before there was talk of multiverses, there was a much simpler picture of reality. For most of human history, the sky was a dome, the stars were lanterns, and the world was whatever lay just beyond the horizon. Even when science began to peel back those ideas, the basic assumption stayed the same. There was one universe, one continuous fabric of space and time, and everything that existed was contained within it.

In the early twentieth century, that picture began to strain. Quantum mechanics arrived with its strange probabilities and superpositions, suggesting that at the smallest scales, reality did not behave like a solid, single track, but like a set of overlapping possibilities. At the same time, general relativity reshaped our understanding of gravity and showed that space and time themselves could bend, stretch, and expand.

As these theories developed, physicists started to notice that our universe looked suspiciously fine tuned. The values of physical constants, from the strength of gravity to the charge of the electron, seemed to sit in narrow ranges that allowed galaxies, stars, planets, and eventually life to emerge. Change them slightly and the cosmos becomes a place where nothing complex ever forms.

This raised uncomfortable questions. Was this fine tuning a lucky accident, an illusion, or a clue? Some scientists and philosophers proposed an answer that would have sounded like myth in any other era. Perhaps there was not just one universe, but many. Perhaps our cosmos was one bubble in a much larger structure, and the reason our constants were life friendly was that we happened to be in the kind of bubble where observers can exist.

Long before the term "multiverse" became popular, older stories were already playing with similar intuitions. Religious and mystical traditions spoke of layered worlds, higher planes, hidden realms running alongside the visible one. These were not scientific models, but they reflected a recurring human instinct. The feeling that what we see is not all that there is, and that other versions of reality might be unfolding just out of reach.