What is reality? Every great answer, from Kant to Heisenberg to Gödel, turns out to be a map of where knowledge ends. That hasn’t stopped science from speculating about what lies past the edge.

The sparest account science has to offer is Hugh Everett’s Many Worlds Interpretation, in which all possibilities exist. It is simple because it adds nothing to the Schrödinger equation. Every mathematically allowed quantum state corresponds to a real, physical outcome. There are no “unrealized” possibilities.

Science’s most baroque account has to be string theory, where reality is the “bulk,” a higher-dimensional space (five dimensions in the braneworld models, ten in full string theory, eleven in M-theory) inside which float lower-dimensional universes called “branes.” Strictly, these two theories aren’t rivals: Many Worlds interprets quantum mechanics, while string theory tries to marry it to gravity. But that’s why they can be stacked.

The bulk is not to be confused with the Block Universe that falls out of Einstein’s relativity. For Einstein, the universe is a fixed, four-dimensional “block” in which past, present, and future all coexist. Time is a dimension of the block, like space, though it keeps a mathematical signature of its own.

Combine the Block Universe with the Many Worlds and you get a deterministic, static, higher-dimensional structure. The wave function of the universal state (Ψ) evolves continuously and deterministically according to the Schrödinger equation. Every possible history forms its own 4D block, continually branching as quantum interactions decohere.

What these models have in common is the Monad (from the Greek monas, “unity” or “one”). Whether it’s the Block, the Bulk, or the Many Worlds, there is a unity that holds them together even as they are internally estranged, their parts unable to communicate with one another.

For Pythagoras, one of the progenitors of science, the Monad is the origin of existence because it generates all numbers. Add 1 to any number and you get the next, so everything in the cosmos is built out of iterations of the Monad.

For Leibniz, the monads are the ultimate constituents of reality: simple, indivisible, and famously “windowless.” Nothing passes in or out. Each monad mirrors the whole universe, but only from its own point of view. Change the point of view and you change the universe that is mirrored.

For us, the Monad is a quantum superposition of all possibilities in the Bulk, the Block, or the Many Worlds. Zooming in from that cosmic scale to the conscious observer, where we stand inside the monad of our skull selects which branch we find ourselves on, and so what we experience of this surprising thing: Now.

The delicate precision of being here now, alive as a biological being powered by this grotesque and joyous force of life that must kill to eat, makes your Monad mine. Self and other, each an iridescent wing of the human mind. That is why language is possible among all the possibilities. Our common language “decoheres” a shared experience within the Many Worlds.

And therein, our identity as nomads: Each of us a windowless monad, sealed in a skull, yet migrating with every choice from branch to branch of the Many Worlds – and from mind to mind with every sentence.