Time May Tremble: Physicists Find Tiny Cracks in Physics' Most Stable Pillar

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One-line takeaway: This article analyzes the core finding and implications of "time trembling": quantum collapse models imply a fundamental limit on clock precision.

A Simple Question

In April 2025, Nicola Bortolotti, a PhD researcher at the Enrico Fermi Museum in Rome, did something most physicists never do: he took a fringe theory originally introduced to explain "Schrödinger's cat" seriously, and asked a deceptively simple question—

If this theory is correct, what happens to time itself?

The answer appeared in November 2025 in *Physical Review Research*. Together with Catalina Curceanu, Lajos Diósi, Simone Manti, and Kristian Piscicchia, he showed that if quantum collapse models are correct, time itself has a tiny, intrinsic uncertainty. No matter how precise a clock you build, there is a precision limit you can never cross.

Don't rush to sell your watch, though—this uncertainty is many orders of magnitude smaller than anything we can currently measure.

The Awkward Problem in Quantum Mechanics

To understand why this matters, return to quantum mechanics' most embarrassing problem: the measurement problem.

Quantum mechanics' core equation—the Schrödinger equation—describes a system's wavefunction, which can exist in superpositions of multiple states: an electron can be here and there at once; a cat can be alive and dead at once. But when we "measure," the wavefunction instantly "collapses" into a definite state.

The question: what causes the collapse?

Standard quantum mechanics says "measurement" causes it. But what is a measurement? Isn't the measuring apparatus itself made of quantum particles? Why isn't its wavefunction also in superposition? Following this line of questioning leads to a philosophical quagmire—the very quagmire Schrödinger's cat was designed to expose.

Most physicists take a "don't ask, it works" attitude. Standard quantum mechanics matches experiments with extreme precision, so the measurement problem is treated as an interpretation issue, not a physics issue. Interpretations (Copenhagen, many-worlds, decoherence histories) are mathematically equivalent and experimentally indistinguishable.

But a small group of physicists is unsatisfied. They say: what if collapse is not an "interpretation" but a real physical process?

Spontaneous Collapse: Deleting the Observer from the Story

In the 1980s, physicists began exploring spontaneous collapse models. The core idea is simple: wavefunction collapse needs no observer, no measuring apparatus—it happens spontaneously, randomly, and continuously.

This sounds like replacing the "observer" with "magic," but it isn't. These models make concrete, testable predictions that differ observably from standard quantum mechanics. They are not "interpretations"—they are "new physics."

Two of the most famous models:

Diósi-Penrose model (named for Lajos Diósi and Roger Penrose): gravity causes collapse. When a system's mass is large enough, gravitational effects prevent superpositions from persisting, and the wavefunction spontaneously collapses. This model was tied to gravity from the start.

CSL model (Continuous Spontaneous Localization): collapse happens continuously, like a faint "background noise" constantly pushing quantum systems toward localized states. This model was originally unrelated to gravity—a phenomenological model with parameters determined by experiment.

Both models explain why macroscopic objects don't appear in superposition—spontaneous collapse destroys it. But their mechanisms differ: one relies on gravity, the other on "some unidentified noise."

What Bortolotti Did

In one sentence: they quantitatively connected the CSL model to gravity for the first time.

Previously only the Diósi-Penrose model was explicitly tied to gravity—its core premise is that gravity causes collapse. CSL was an independent framework.

But Bortolotti noticed something: both models involve "continuous measurement of mass density." Diósi-Penrose says gravity measures mass density; CSL says some unidentified mechanism does. What if CSL's "unidentified mechanism" is itself gravitational in nature?

If collapse is gravity-related, then quantum fluctuations of the gravitational field affect the collapse process. And fluctuations of the gravitational field affect spacetime itself—including the flow of time.

That's the crux: if collapse is linked to gravity, time cannot be perfectly stable.

The Trembling of Time

In general relativity, time is not an absolute background parameter. It is curved by gravitational fields—GPS satellites correct for this daily. Time runs slower in strong fields, faster in weak ones. But in general relativity, this curvature is classical and deterministic: given a mass distribution, the rate of time is exactly computable.

Bortolotti's team asked the next step: what if the gravitational field itself has quantum fluctuations?

Quantum collapse models (if correct) imply intrinsic quantum uncertainty in mass density. Mass density generates the gravitational field, so the field fluctuates too. The field determines the rate of time, so the rate of time fluctuates too.

Time trembles.

Not a large tremble, not one you could feel—an extremely tiny, intrinsic, ever-present tremble, like the faintest ripple on a lake, too small for any existing clock to detect.

A "Reassuring" Answer

Bortolotti calculated the size of this time uncertainty. His conclusion, in his own words: "the answer is sharp and surprisingly reassuring."

The uncertainty is many orders of magnitude smaller than what today's most precise atomic clocks can measure. Curceanu emphasized: "This uncertainty is orders of magnitude smaller than anything we can currently measure, so it has no practical effect on everyday timekeeping." Piscicchia added: "Our results clearly show that modern timing technology is completely unaffected."

So your watch, your phone, GPS satellites, even the most precise optical atomic clocks—no need to worry. Time trembles, but so faintly that for us it remains "one of the most stable pillars."

So why care?

Why Something Unmeasurable Matters

There is a deep physics problem here: we have two theories—quantum mechanics and general relativity—each extremely precise in its domain, but they treat time in fundamentally different ways.

In standard quantum mechanics, time is an external, classical parameter—unaffected by quantum systems, a background clock ticking along regardless of what happens inside.

In general relativity, time is part of spacetime, curved by mass and energy—dynamic, not a background.

These two views of time are contradictory. Physicists have spent decades seeking a unified quantum gravity theory—string theory, loop quantum gravity, asymptotic safety—but none has produced testable predictions.

Bortolotti's work offers a different angle: rather than constructing a quantum gravity theory directly, ask—if we assume collapse is gravity-related, what observable consequences follow?

The consequence: time has an intrinsic uncertainty. Too small to measure, but real in principle. Time is not a classical background parameter but a physical quantity with quantum structure.

Time is not the stage; time is an actor.

A Cross-Domain Analogy

The article draws an analogy to AI evaluation: the "evaluation blind spot law"—you optimize what you measure, and problems hide in what you don't measure. AI models score highly on standard benchmarks while quietly degrading on unmeasured capabilities.

Physics has a deeper version: we assumed time was the most stable thing, so we never tested whether it is stable. Atomic clocks measure "whether the rate of time is uniform," but that measurement assumes time itself has a definite rate. If time has quantum fluctuations, atomic clocks measure not "time" but "the average of trembling time."

This is isomorphic to a phenomenon in AI evaluation: when you measure a model with some metric, you implicitly assume the metric is stable and well-defined. But many metrics—"alignment," "safety," "creativity"—have intrinsic ambiguity. You measure not "alignment" but "alignment averaged over some operationalization."

Measurement is never direct; it always passes through a filter of assumptions. Recognizing the filter is the first step to breakthrough.

Solving Problems on a Different Level

The measurement problem has troubled physicists for a century. The mainstream approach: find a better interpretation—Copenhagen, many-worlds, decoherence—all mathematically equivalent, experimentally indistinguishable.

Spontaneous collapse models took a different path: don't find an interpretation, find new physics. They don't explain why collapse happens; they assume collapse is a real physical process and ask what observable consequences follow.

This is "solving the problem on a different level"—from interpretation to physics, from philosophy to experiment. Bortolotti's work extends this: if collapse is physical, what is its relation to gravity? If gravity-related, how does it affect time?

Don't answer old questions—ask new ones. Old questions ("what is collapse?") may have no answer, but new questions ("if collapse is gravity-related, what happens to time?") yield concrete numbers.

The Actorhood of Time

Picture a stage. A play is on; actors move, props change. The stage itself—floor, walls, lights—is a stable background you ignore.

In physics, time has always been that stage. Particles move, fields change, wavefunctions evolve—all on the stable background of "time." Time is not affected by the performance; time is not an actor.

Bortolotti's work suggests a different picture: the stage itself trembles slightly. Not the props, not the actors—the floor itself sways gently. So gently that the audience can't feel it, the actors can't feel it, even the most sensitive instruments can't feel it. But it's there.

The stage is not a background. The stage is part of the play. Time is not a container for performance—time is an actor.

The tremble is too small to matter for any practical purpose. But it carries philosophical weight: the most stable things have intrinsic uncertainty. This is not a technical limitation or measurement error—it is a limit built into physical law itself. Time trembles because quantum mechanics and gravity are connected at the deepest level.

You won't be late because of this tremble. But next time you check your watch, consider: you think you're reading "time," but you're reading "the average of the trembling." An average reassuringly stable—but statistically stable, not ontologically stable.

Even the most reliable pillar has its grain.

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Paper: Bortolotti, N., Curceanu, C., Diósi, L., Manti, S., & Piscicchia, K. (2025). Fundamental limits on clock precision from spacetime uncertainty in quantum collapse models. *Physical Review Research*, 7, 043166. arXiv:2504.06109. DOI: 10.1103/PhysRevResearch.7.043166

FAQ

Q1: Who is this content for?

Practitioners, researchers, and students interested in AI, machine learning, and deep learning, as well as readers curious about quantum foundations and quantum gravity.

Q2: What are the key takeaways?

• If quantum collapse models are correct and gravity-related, time has an intrinsic quantum uncertainty.
• This uncertainty is orders of magnitude below current atomic-clock precision, so practical timekeeping is unaffected.
• The work demonstrates a strategy for quantum gravity: derive testable consequences from collapse-plus-gravity assumptions rather than building full unified theories.

See the links in the original topic for details.