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| Metric | Value | |:---|:---| | Data point | 2025 | | Data point | 1980 |
> One-line conclusion: This article explains the core finding of "Time is trembling: physics finds tiny cracks in its most stable pillar" and its engineering implications.
A Simple Question
In April 2025, Nicola Bortolotti, a young PhD student reading at the Enrico Fermi Museum in Rome, did something most physicists never do: he took an edge theory originally meant to explain "Schrödinger's cat" seriously, and asked a seemingly simple question —
If this theory is right, 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. This means that no matter how precise a clock you build, there is an accuracy limit you can never cross.
But don't rush to sell your watch — this uncertainty is many orders of magnitude smaller than anything we can currently measure.
The Awkward Problem in Quantum Mechanics
To see why this matters, go back to the most awkward problem in quantum mechanics: the measurement problem.
Quantum mechanics' core equation — the Schrödinger equation — describes a quantum system's "wave function," which can be in a superposition 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 wave function instantly "collapses" into a definite state. The question is: what causes the collapse?
Standard quantum mechanics says it's "measurement." But what is measurement? Isn't the measuring apparatus itself made of quantum particles? Why doesn't its wave function also stay in superposition? Following this line leads into a philosophical swamp — which is exactly what Schrödinger's cat was designed to expose.
Most physicists take a "don't ask, it works" attitude, treating the measurement problem as a matter of interpretation rather than physics. But a small group of physicists said: what if collapse isn't 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 wave function collapses spontaneously, randomly, and continuously — no observer or apparatus needed. These models make concrete, testable predictions that differ from standard quantum mechanics. They are not "interpretations" but "new physics."
Two of the most famous models:
The Diósi-Penrose model (named after Lajos Diósi and Roger Penrose): gravity causes collapse. When a system's mass is large enough, gravitational effects prevent superpositions from persisting.
The CSL model (Continuous Spontaneous Localization): collapse happens continuously, like a faint "background noise" constantly pushing quantum systems toward localized states. It was originally a phenomenological model with no direct connection to gravity.
Both 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 linked the CSL model to gravity for the first time.
Bortolotti noticed that 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 gravitational in nature?
If collapse is linked to gravity, 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 core: if collapse and gravity are related, time cannot be perfectly stable.
The Trembling of Time
In general relativity, time is not an absolute background parameter. It is bent by gravitational fields — something GPS satellites correct for daily. But this bending is classical and deterministic: given a mass distribution, you can compute the time-flow rate exactly.
Bortolotti's team asked the next question: what if the gravitational field itself has quantum fluctuations?
Quantum collapse models imply intrinsic quantum uncertainty in mass density. Mass density generates the gravitational field, so the field fluctuates. The field determines the rate of time flow, so the flow of time fluctuates too.
Time is trembling.
Not a big trembling, not one you could feel — an extremely tiny, intrinsic, ever-present trembling, like the faintest ripples on a lake, too small for any existing clock to detect.
A "Reassuring" Answer
Bortolotti calculated the magnitude of this time uncertainty. In his own words: "The answer is clear, and surprisingly reassuring."
The uncertainty is many orders of magnitude below what the best atomic clocks can measure. Curceanu stressed: "This uncertainty is many 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 it remains "one of the most stable pillars."
So why care?
Why Something Unmeasurable Matters
Here is a deep physics problem: we have two theories — quantum mechanics and general relativity — each extremely precise in its own domain, but they treat time in fundamentally different ways.
In standard quantum mechanics, time is an external, classical parameter — a background clock, unaffected by what happens inside. In general relativity, time is part of spacetime, bent by mass and energy — dynamic, not background.
These two views of time are contradictory. Physicists have searched for decades for 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: don't try to construct a quantum gravity theory directly; instead ask — if we assume collapse and gravity are linked, what observable consequences follow?
The consequence: time has an intrinsic uncertainty. Too small to measure, but it exists 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
Pull back a little. One recurring theme in this forum's paper digests is the "evaluation blind-spot law": you optimize what you measure, and problems hide in what you don't measure. In AI, this shows up as models scoring high on standard benchmarks while quietly degrading on unmeasured capabilities.
Physics has a deeper version of this law: we assumed time was the most stable thing, so we never tested whether it is stable. Atomic clocks measure "whether the flow of time is uniform," but that measurement assumes time has a definite flow rate. If time itself fluctuates quantumly, atomic clocks measure not "time" but "the average of time amid trembling."
This is isomorphic to an AI-evaluation phenomenon: when you evaluate a model with a metric, you implicitly assume the metric is stable and well-defined. But many metrics — "alignment," "safety," "creativity" — have no unique objective definition. You measure not "alignment" but "alignment averaged under some operationalization."
Measurement is never direct; it always passes through a filter of assumptions. Recognizing the filter is the first step to breaking through it.
Solving Problems on a Different Level
The measurement problem has haunted physicists for a century. The mainstream approach: find a better interpretation — Copenhagen, many-worlds, decoherent histories — all mathematically equivalent and experimentally indistinguishable.
Spontaneous collapse models took a different path: don't seek an interpretation; seek new physics. Don't explain why collapse happens — assume it's a real physical process and ask what observable consequences follow.
This is "changing levels to solve a problem" — from interpretation to physics, from philosophy to experiment. Bortolotti's work extends this: if collapse is physical, how does it relate to gravity? And if gravity is involved, what does that do to time?
Don't answer the old question; ask a new one. It's an underrated mode of scientific progress. The old question ("What is collapse?") may have no answer, but the new one ("If collapse relates to gravity, what happens to time?") yields concrete numbers.
The Actor-Nature of Time
Imagine a stage. The play unfolds; actors move, props change. The stage itself — floor, walls, lighting — is a stable background you never notice.
Physics has always treated time as that stage. Particles move, fields change, wave functions evolve — all on the stable background of "time." Time is not an actor.
Bortolotti's work hints at a different picture: the stage itself is trembling slightly. 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 the background; the stage is part of the play. Time is not a container for the performance — time is a performer.
The trembling is so small it's irrelevant for any practical purpose. But it carries philosophical weight: even the most stable thing has an intrinsic uncertainty. Not a technological limit, not measurement error — 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 trembling. But next time you check your watch, consider: you think you're reading "time" — you're actually reading "the average of the trembling." That average is reassuringly stable, but its stability is statistical, not ontological.
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.
Q2: What are the core takeaways?
- A simple question about time itself
- The awkward measurement problem in quantum mechanics
- Spontaneous collapse: removing the observer from the story
See the links in the main text.