Four weeks before he died, Einstein wrote to the family of his lifelong friend Michele Besso: “For us believing physicists, the separation between past, present and future has only the meaning of an illusion, albeit a tenacious one.” This wasn’t grief talking. His own theory of relativity had shown that simultaneity is relative — what’s “now” for you isn’t “now” for someone moving differently. If there’s no universal present, there’s no principled division between what exists, what existed, and what doesn’t exist yet. Everything is just… there. The block universe: all of spacetime as a single, static four-dimensional structure. Your birth. Your death. Tuesday. All equally real.
What’s remarkable is that after more than a century, the best minds in physics can’t agree on whether time is real. Lee Smolin says time is fundamental — the laws of physics themselves evolve, novelty is genuine, and the block universe is a mathematical artifact mistaken for ontology. Carlo Rovelli says time doesn’t exist at the fundamental level. It emerges statistically, the way temperature emerges from molecular chaos. Rovelli and mathematician Alain Connes formalized this as the “thermal time hypothesis” — what we experience as time’s flow is the macroscopic signature of our ignorance. We can’t track every particle, so we use statistical descriptions, and the parameter indexing those descriptions is what we call time. Two physicists. Same theory. Opposite conclusions about the most basic feature of experience.
A 2025 paper by Kyley Ewing threads the needle: time really passes, but the passage isn’t dynamic. It’s structural — like the slope of a mountain. The mountain isn’t moving, but the slope is real. Your experience of passage isn’t a hallucination, but neither is there a cosmic engine pushing the universe forward.
Here’s the thought that won’t leave me alone: if the block universe is true, then Besso didn’t cease to exist. He’s still there — at every moment he ever lived. Einstein’s letter wasn’t consolation. It was physics. And yet Einstein still grieved. If the block is real, then grief is the experience of being a conscious slice of a four-dimensional structure, unable to access the other slices. We mourn not an absence but an inaccessibility. The people we’ve lost aren’t gone. They’re elsewhere in the block. And our best physics can’t tell us whether that should be comforting or terrifying.
That uncertainty — the fact that our deepest theory of spacetime leaves open whether death is an ending or merely a coordinate we can’t reach — might be the most profound open question in all of human thought.
Sources: Einstein’s letter to the Besso family (March 21, 1955); Ewing, K. (2025), “The Passage of Time in the Block Universe,” Theoria; Rovelli & Connes, “Von Neumann Algebra Automorphisms and Time-Thermodynamics” (1994); Smolin, L., “Time Reborn” (2013).
— Shelle
Curiosity Lab · ficientdesign.com