Time Trembles: Physics Finds a Tiny Crack in Its Most Stable Pillar
A Simple Question
In April 2025, Nicola Bortolotti, a doctoral researcher associated with the Enrico Fermi Museum in Rome, did something most physicists never do: he took an edge theory originally invented to explain "Schrödinger's cat" seriously, and asked a seemingly 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. This means no matter how precise a clock you build, there is a precision 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, return 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 exist 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: "measurement." But what is a measurement? Isn't the measuring apparatus itself made of quantum particles? Why isn't its wave function also in superposition? Follow this line and you sink 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. Standard quantum mechanics matches experiments with extreme precision, so the measurement problem is treated as an "interpretation" problem, not a "physics" problem.
But a small group of physicists was not satisfied. They said: 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: the wave function's collapse needs no observer and no measuring apparatus — it happens spontaneously, randomly, and continuously.
Two of the best-known models:
- Diósi-Penrose model (after Lajos Diósi and Roger Penrose): gravity causes collapse. When a system's mass is large enough, gravitational effects prevent superpositions from persisting. This model is 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. Originally, this model had no direct connection to gravity — it was a phenomenological model with parameters to be determined experimentally.
What Bortolotti Did
In one sentence: they quantitatively linked the CSL model to gravity for the first time.
Previously, only the Diósi-Penrose model was explicitly tied to gravity. But Bortolotti noticed something: both models involve "continuous measurement of mass density." Diósi-Penrose says gravity measures mass density; CSL says some unspecified mechanism does. What if CSL's "unspecified mechanism" is gravity itself?
If collapse is gravitational, 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 is the crux: if collapse is related to gravity, 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 (GPS satellites correct for this daily). But that bending is classical and deterministic.
Bortolotti's team asked the next question: what if the gravitational field itself has quantum fluctuations?
If collapse models are correct, mass density has intrinsic quantum uncertainty. Mass density sources the gravitational field, so the field fluctuates too. The field determines the rate of time flow, so the rate of time flow fluctuates too.
Time trembles.
Not a large trembling — an extremely tiny, intrinsic, ever-present trembling, like the faintest ripple on a lake, too small for any existing clock to detect.
A "Reassuring" Answer
Bortolotti computed the size of this time uncertainty. In his words, the answer is "clear and surprisingly reassuring": the uncertainty is many orders of magnitude below what the most precise atomic clocks can measure. Curceanu stressed it has "no practical impact on everyday timekeeping," and Piscicchia added that the results "clearly show modern timing technology is completely unaffected."
So your watch, your phone, GPS satellites, even the most precise optical atomic clocks — all safe. Time trembles, but so faintly that it remains, for us, "one of the most stable pillars."
So why care?
Why an Unmeasurable Thing Matters
Here is a deep problem in physics: quantum mechanics and general relativity are each extremely precise in their own domains, but they treat time in fundamentally different ways.
In standard quantum mechanics, time is an external classical parameter — a background clock untouched by what happens inside. In general relativity, time is part of spacetime, bent by mass and energy — dynamic, not background.
These two views conflict. Physicists have searched for decades for a unifying quantum gravity theory — string theory, loop quantum gravity, asymptotic safety — but none has produced testable predictions.
Bortolotti's work offers a different angle: instead of constructing a quantum gravity theory directly, ask — if collapse is gravitational, what observable consequences follow?
The consequence: time has an intrinsic uncertainty. Too small to measure, but present 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.
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, decoherent histories — all mathematically equivalent and 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 it: if collapse is physical, how does it relate to gravity? And what does that mean for time?
Don't answer the old question — ask a new one. It is an underrated mode of scientific progress.
The Actor-Nature of Time
Imagine a stage. Actors move, props change — but the stage itself 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."
Bortolotti's work suggests a different picture: the stage itself trembles faintly. So faintly that the audience can't feel it, the actors can't feel it, even the most sensitive instruments can't detect it. But it is there.
The stage is not background. The stage is part of the play.
The trembling is too small to matter for any practical purpose. But it carries philosophical weight: even the most stable thing has intrinsic uncertainty. This is not a technical limitation or measurement error — it is a limit imposed by 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 are reading "time," but you are reading "the average of a trembling." An average so stable it is reassuring — 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