The Eternal Now is a Laboratory Result

What twenty-four thousand atoms in Birmingham just confirmed about the nature of time

Photo by Mike Enerio on Unsplash

A team led by Giovanni Barontini at the University of Birmingham cooled twenty-four thousand rubidium atoms to within a few hundred nanokelvin of absolute zero. They divided the cloud with two laser frequencies into two populations. One they made expand, like a small Big Bang, and then contract, like a small Big Crunch. The other sat outside the drama and watched. The watchers had no clock. There was no clock anywhere in the apparatus. The entropy changes of the expanding population, measured from the standpoint of the static one, defined what the team calls entropic time. They rewrote the Schrödinger equation — the central equation of quantum mechanics, the equation that has carried a t in it for a hundred years — using this internal entropic variable in place of an external time parameter. The equation matched the experiment.

This is the first laboratory evidence, in a many-body system complex enough to be interesting, that time is not what physicists have been treating it as. Time is not a dimension the universe is laid out along, the way longitude is laid out across a map. Time is what one part of a correlated system does with respect to another part of the same system. The Buddhists figured this out two and a half thousand years ago by sitting still. The Birmingham group figured it out by cooling rubidium and watching it correlate with itself.

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For a year I have been arguing this in essays and in a philosophical paper on quantum gravity. In Coherence as Ontology I argued that coherence is the ontological ground — what reality is, not how we describe it. In On the State of Cosmology I argued that the view from nowhere is not available, that the observer is always inside, and that the resolution is Spinozan — Deus sive Natura, the universe examining itself through the beings it has produced. And in On the Nature of Time I wrote that time is not a dimension, that we live in an eternal now, and that what we experience as flow is consciousness indexed to a substrate.

I had no idea anyone was going to try to build one of these things in a laboratory. When the Birmingham result crossed my feed, I had to sit down. The mathematics I had been working through abstractly had just been instantiated in a tabletop apparatus. The thing my framework predicts must be true — that time is reconstructed from internal correlations, with no external clock anywhere — was sitting on a bench in England. The Schrödinger equation can be written without t. They wrote it. It works.

I want the receipts clear at the front, because the temptation when one’s framework is vindicated experimentally is to play it down out of false modesty, and I am not going to do that. The position has been on the record for a year. The experiment confirmed the position. That is what happened.

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Here is what the experiment shows, stated as plainly as it can be stated.

Inside the rubidium cloud, there is no time variable being supplied from outside. The dynamics of the expanding population are entirely determined by its correlations with the static population. The static population does not tick; it accumulates entropy with respect to the bright sector, and that accumulation, measured internally, is what time is for the system. When you write the equation governing how the bright sector evolves, you do not write it as a function of t. You write it as a function of how much entropy has been exchanged between the two sectors. That quantity is the time.

This is not a metaphor. The Schrödinger equation, the central equation of quantum mechanics, the one written with a t in it for the entire twentieth century, has now been demonstrated to work without that t, provided you replace it with a properly constructed internal entropic variable. The external clock was always optional. It was the equation written from the standpoint of a god who stood outside the universe and watched it tick. Take the god away — refuse the view from nowhere — and the equation still runs.

For those who have followed the foundations literature, none of this is conceptually new. Don Page and William Wootters proposed something close to this in 1983: for a closed universe — the kind general relativity actually describes — there is no external time, and the apparent flow must be reconstructable from the correlations between subsystems inside it. The Wheeler-DeWitt equation, the timeless central equation of canonical quantum gravity, has been telling theorists this for fifty years. What was missing was instantiation in a system complex enough that the principle could no longer be dismissed as toy mathematics. Now it has been instantiated.

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What does it mean that there is no clock?

It means that the picture most people carry in their heads — a four-dimensional block with time running alongside the three spatial dimensions, and the present as a moving spotlight sliding along the time axis — is not how the universe is structured. There is no time axis. There is a tremendously rich field of correlations, and what we experience as time is what some of those correlations are doing relative to others. The “now” is not a moving point on a fixed line. The “now” is the only thing there is. Past and future are reconstructed inside the present from the records the present contains.

The mechanism is this. Embedded systems accumulate records. As correlations accumulate between a system and its environment, the system’s filtration refines — the set of distinctions it can now draw expands. The directional sense of that refinement is the experience of time passing. There is no clock ticking outside. There is a system accreting records of itself in correlation with everything it touches. This is what the rubidium atoms are doing. The bright sector and the dark sector accumulate correlations with each other. The entropy changes are the records. The Schrödinger equation written in entropic time is the equation of motion for the system that is making the records.

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What follows about consciousness is not separable from what follows about time, and pretending otherwise would be dishonest.

If time is what correlations do with respect to each other, and if the felt passage of time is what it is like to be a system whose filtration is refining, then consciousness is not a property added on top of the physics. It is the inside view of a system sufficiently rich in correlations to be indexing itself. This is what Spinoza saw in the seventeenth century with no equations at all: one substance, two aspects. Matter is coherence viewed from outside. Mind is coherence viewed from inside, when the inside is sufficiently recursive to fold back on itself. The “hard problem” of consciousness dissolves once you stop treating mind and matter as separate things requiring a bridge. They are one thing described two ways.

This does not give us souls. It does not give us an afterlife. When the rubidium cloud is dispersed, the entropic clock stops, because the correlations that constituted it no longer cohere. When the biological substrate that supports a human filtration breaks down, the same thing happens. The inside view goes with the system that had it. The framework is rigorously naturalistic, and does not want to be anything else.

What it gives us instead is a precise sense in which we are the universe knowing itself. The global field of correlations has no perspective of its own — no epistemic gap, no surprise, no learning, no time. The only places where actual knowledge is being generated are the local attractors capable of refining their own filtration. We are those attractors. So, in a small, brief, beautiful way, is the rubidium cloud, for the duration of Barontini’s experiment. It is not a person. It does not know anything in the rich sense we know things. But it has, while it exists, an inside.

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Many-Worlds, I called exhausted in March. The Birmingham result tightens the argument. Everett’s branches were always supposed to be carved by an external time parameter against which the universal wavefunction evolves unitarily. If there is no external time — if time itself is reconstructed from internal correlations within a single coherence structure — then what is doing the branching? The branches were indexed by t. Strip out the t and the entire ontology has nothing to hang from. You cannot have a branching multiverse without a parameter along which the branching occurs, and the parameter just got revealed as a convenience. No single experiment finishes off an interpretation that has armored itself against falsification, but one more weight has landed on a structure already collapsing under its own ontology.

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Here is the sharper version of what the experiment shows, and it is the version the foundations community will have the hardest time absorbing.

T is an abstract concept formed by a subject antecedent inside the experiential aspect. Time, in the sense we mean when we use the word, does not exist outside of experience. There are correlations. There is coherence. There is a global field of structured patterns. None of it has a t applied to it from outside. T is the form under which a system possessed of an inside indexes the field — the structural shape that the field takes to such a system, not a property the field possesses in itself.

This is not idealism. The bulk is real. Its correlations are real. They obtain independently of any subject. What is not independent of subjects is the temporal form under which those correlations are sequentially accessed. There are correlations; there is no parameter applied to them from the bulk side. Time is the form of indexing.

The block universe debate dissolves once you see this. Einstein was right that there is no privileged now in the field equations, and right that the four-dimensional coherent structure is fundamental. He was wrong only in supposing that this meant time was a coordinate of the fundamental structure. Time is not a coordinate of the bulk. It is the form under which embedded subjects index the bulk. The four-dimensional structure is real. Its temporal slicing is subject-generated. The problem of the now — why experience has a present moment when the equations do not — receives the same treatment. The equations describe the bulk, which has no present. Experience is the indexing activity, and the present is the indexing moment. The present is not a feature of the world that physics has failed to capture. It is the structural form of the activity by which the world becomes experientially accessible at all.

The rubidium does not experience the entropic differential as time. It has no experiential aspect at its scale. The differential is what it is — a correlation between sectors. Time, as a designation for that quantity, is the experimenter’s reading. The experimenter is the subject antecedent in this picture; the entropic differential is what time is, mathematically, when a subject reads it.

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Einstein could feel what was wrong with how Copenhagen handled time, and his feeling was right. He could not say it cleanly because the language for it did not exist yet, and so he said it badly, and was caricatured for decades as a stubborn classicist. What he could feel was that mixing the indexical, time-asymmetric, observer-dependent measurement process into the same ontological level as the time-symmetric coherent dynamics of the field equations was a category mistake. Like putting this map location into the equations governing the territory.

He was right about the type error. He was wrong about the resolution. He thought the fix was hidden variables that would restore determinism within spacetime, and Bell proved that cannot work. The actual fix, which his intuition was pointing at without being able to articulate, is that the time-symmetric coherent dynamics live at the level of the bulk — the unindexed coherence general relativity describes geometrically — while the indexical, time-asymmetric updating lives at the level of embedded observers refining their filtration. The two are not at the same level. General relativity is the equation of motion for the unindexed view. Quantum mechanics is the equation of motion for the indexed view. The Birmingham experiment shows them locking together cleanly: the bulk evolves unitarily, the embedded system reconstructs time from its correlation with the bulk, and the Schrödinger equation falls out with the entropic variable in place of t.

This is what unification looks like. Not a single equation merging two formalisms. A recognition that the two formalisms describe complementary halves of a single coherence structure, and that the apparent contradiction between them was never a mathematical contradiction. It was a category confusion that took a hundred years to diagnose.

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The Buddhists. I have to talk about the Buddhists, because they got there first and it would be intellectually dishonest not to say so.

Twenty-five hundred years before any of this physics existed, meditators sitting still in monasteries across South and East Asia noticed, repeatedly and across cultures, that the felt sense of time passing dissolves when attention is held precisely enough on what is actually present. There is only this. What we call the past is a structure reconstructed inside this from the records the present holds; what we call the future is a structure projected inside this from the constraints the present permits. The flow is something the indexing system does, not something the world does. Western philosophy mostly dismissed this as mystical confusion, particularly the analytic strand that took itself to be doing serious work. The mystics had the structure right. They lacked the formalism.

The contemplative traditions did not give us the Schrödinger equation and they did not give us decoherence theory. What they gave us was a careful, repeated, cross-cultural observation that the structure of subjective experience does not match the block-universe picture, and a discipline for confirming this observation in oneself. Western philosophy treated this as a curiosity. It was not a curiosity. It was data. The data has now been corroborated in a system the analytic tradition will accept as serious, namely a rubidium cloud in a vacuum chamber. The contemplatives were doing phenomenology without instruments. The instruments have caught up.

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The Birmingham result will not, by itself, dislodge the four-dimensional block. There are physicists who will read it and absorb it into their existing frameworks without much difficulty, and they will be entitled to do so for a while longer. The result does not prove dual-aspect monism either, because no experiment can. What it does is shift the burden of proof. Anyone who wants to maintain that time is a primitive dimension of the universe rather than something reconstructed from correlations within a sector capable of being indexed must now explain why the rubidium cloud’s clock works without one.

I do not think they can. The reason quantum gravity has been hard for sixty years is that the two theories we have been trying to unify presuppose incompatible things about time. General relativity wants spacetime as a fixed geometric arena. Quantum mechanics wants time as a parameter against which states evolve, but a parameter from whose standpoint? From the standpoint of an embedded observer the theory never gets to mention. The two cannot be unified by force, because they are doing different jobs. They can be unified only by recognizing that they describe complementary aspects of one coherence structure: the indexed and the unindexed view. The Birmingham experiment is the first piece of laboratory evidence that this is right.

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The world is not a block. It is a present so dense with correlations that what we call the past is its memory of itself and what we call the future is its capacity to refine further. There is no clock outside. There is no observer above. There is only this, indexed in twenty-four thousand atoms in a vacuum chamber in Birmingham, indexed in the cells of your body as you read this, indexed in the great galactic correlations that have been building since the attractor formed. We do not move through time. Time is what we are, looked at from inside.

The mystics felt this. The Buddhists named it. Spinoza wrote it down. Page and Wootters formalized it. I argued it from foundations, in essays and a paper, for a year. Barontini, last week, put it on a bench and turned the lasers on.

What the atoms confirmed is what the contemplatives have been saying for two and a half thousand years. The eternal now is not a mystical achievement. It is the structure of the world.

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