Block Time, Many Worlds, and the Persistence of Ordinariness

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Block Time, Many Worlds, and Why Tomorrow Resembles Yesterday - Mostly

If we combine two ideas that are often kept in separate conceptual boxes - the block universe of eternalism, and the Everettian “many worlds” account of quantum uncertainty - a question naturally follows. If the universe is a fixed four-dimensional whole, and if quantum events constantly branch reality into a plurality of decoherent futures, why doesn’t the world look, at the large scale, like a riot of amplified randomness?

Why does the past, looking backwards from here, present itself as overwhelmingly law-governed and almost pedestrian in its Newtonian-style determinism? And if that is what the past looks like, shouldn’t we expect the future, in almost all respects, to have the same look and feel despite its underlying quantum indeterminacy?

On the surface, this seems like a tension. “Many worlds” is habitually sold with a kind of metaphysical euphoria: infinite branching, limitless divergence, cosmic roulette. Yet our lived-history has never felt like roulette.

Most days contain no miracles, no macroscopic quantum surprises, no sudden turn of events caused by a radioactive atom choosing left rather than right. The planets keep their appointments; bridges don’t randomly fail because of a quantum coin-flip; people mostly continue being the sorts of people they were last week. Looking back, the macro-past seems more like a classical trajectory with occasional noise than like a random walk whose steps were decided by quantum dice.

The first thing to say is that, in Everett, the deep story is deterministic anyway - just not in the way we are used to. The universal wavefunction evolves unitarily: nothing “collapses”. There is no fundamental stochastic law picking a single outcome. The branching is not indeterminism in the global dynamics; it is the proliferation of effectively non-interfering sectors. What feels like chance from inside a branch is not a God’s-eye randomness but a self-location problem: which decohered continuation will I find myself in? From 'outside', the entire branching structure is fixed; from within, one experiences merely uncertainty about one’s address inside it.

That already blunts the popular intuition that “many worlds” ought to generate a future that is macroscopically erratic. Branching is constant, but meaningful divergence is not. Most quantum events do not amplify into macroscopic differences; they thermalise, cancel, or remain trapped in degrees of freedom that never climb the ladder of scale. Decoherence does not inject chaos into the classical world; it does almost the opposite. It explains why quasi-classical “pointer states” are stable, why macroscopic objects persist, why a chair remains a chair, why the classical description becomes such a good effective theory for large aggregates. The world looks classical because, for most practical purposes, it is.

It is worth stating an underappreciated symmetry here: what we now call “the past” was once, from some deeper-past vantage point, the future. The difference between “past” and “future” is not that one is ontologically settled while the other is metaphysically open; it is that we are embedded - instance by instance - at particular locations in the block.

In a block universe, every event is future-ward relative to earlier slices and past-ward relative to later ones. So if the world’s quantum branching had a natural tendency to erupt into large-scale caprice, we would already see that eruption when we look backwards - because the macro-history we inhabit has already run the gauntlet of being “the future” for countless earlier observers. The fact that it still reads, at human scale, as orderly is evidence that the branching is mostly hidden by the same structural constraints that will hide it tomorrow.

There is also the brute constraint of low-entropy initial conditions — the Past Hypothesis in its various guises. The universe’s special beginning does not merely explain the arrow of time; it also massively limits which macroscopic histories carry significant weight.

Wild, spectacularly diverging macroscopic histories exist as mathematical possibilities inside the universal wavefunction, but most of them are thin as mist in Born measure. The block is thick where the classical narrative is thick: regularities, stable structures, robust thermodynamic flows. The “tree” branches constantly, but almost all of the branch weight is clustered in futures that differ only in microscopic details and wash out at human scales.

So the rephrased answer is this: the reason the past looks largely deterministic is not that quantum randomness never happened, but that it almost never mattered at the scale we care about.

The macro-world is an emergent attractor: it is what you get when you coarse-grain a quantum substrate under decoherence and thermodynamics. And if that is what happened in the past, then in a block universe the future is not poised to suddenly become a carnival of amplified quantum accidents. The future block is “already there” in the same sense the past is already there - with branching built in, but with most branches differing only in trivial microscopic ways.

None of this denies that amplification can happen - it can: evolutionary contingency, threshold phenomena in neurobiology, chaotic systems near bifurcation points, rare catastrophic events. But even there, the range of viable macrostates is narrow, selection effects prune hard, and the world remains governed by constraints and regularities rather than by caprice. 

Everett does not imply a future that is wildly branching in any humanly vivid way.

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