A Simple Question
In April 2025, Nicola Bortolotti, a PhD student at the Enrico Fermi Museum in Rome, did something most physicists don't: he took an edge theory originally invented to explain "Schrödinger's cat" seriously, and asked a seemingly simple question —
If this theory is right, what happens to time itself?
The answer was published in November 2025 in *Physical Review Research*. Together with Catalina Curceanu, Lajos Diósi, Simone Manti, and Kristian Piscicchia, he demonstrated 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.
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 see why this matters, return to quantum mechanics' most awkward problem: the measurement problem.
The core equation of quantum mechanics — the Schrödinger equation — describes a quantum system's "wave function." A wave function 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 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 — Schrödinger's cat was invented to expose it.
Most physicists take a "don't ask, it works" attitude. But a small group of physicists weren't satisfied. They asked: what if collapse isn't an "interpretation" but a real physical process?
Spontaneous Collapse: Deleting the Observer
In the 1980s, physicists began exploring spontaneous collapse models. The core idea is simple: wave function collapse needs no observer, no measuring apparatus — it happens spontaneously, randomly, continuously.
These models make concrete, testable predictions that differ observably from standard quantum mechanics. They are not "interpretations" but "new physics."
Two of the best-known 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 make superposition unsustainable, and the wave function collapses spontaneously.
The CSL model (Continuous Spontaneous Localization): collapse happens continuously, like a faint "background noise" constantly pushing quantum systems toward localized states. This model originally 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." What if CSL's "unknown mechanism" is essentially gravity itself?
If collapse is related 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 crux: if collapse and gravity are connected, time cannot be perfectly stable.
Time Trembles
In general relativity, time is not an absolute background parameter — it is curved by gravitational fields (as GPS satellites must correct for daily). But that curvature is classical and deterministic.
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 that rate fluctuates too.
Time trembles.
Not a big 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 magnitude of this time uncertainty. In his own words: "The answer is clear, and surprisingly reassuring."
The uncertainty is many orders of magnitude smaller than the precision of existing atomic clocks. Curceanu emphasizes: "This uncertainty is many orders of magnitude smaller than anything we can measure now, so it has no practical impact on everyday timekeeping." Piscicchia adds: "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 worries. Time trembles, but so faintly that it remains "one of the most stable pillars."
So why care?
Why Something Unmeasurable Matters
There is a deep issue here: quantum mechanics and general relativity are each extremely precise in their own domains, but they treat time fundamentally differently.
In standard quantum mechanics, time is an external, classical parameter — a background clock, unaffected by the quantum system. In general relativity, time is part of spacetime, curved by mass and energy — dynamic, not background.
These two views are contradictory. Attempts to unify them — string theory, loop quantum gravity, asymptotic safety — have all hit fundamental difficulties and produced no testable predictions.
Bortolotti's work offers a different angle: instead of constructing a quantum gravity theory directly, ask what observable consequences follow if collapse is tied to gravity.
The consequence: time has 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 seek an interpretation; seek new physics. They assume collapse is a real physical process, then 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: don't answer the old question ("what is collapse?"), ask a new one ("if collapse is tied to gravity, what happens to time?") — and get concrete numbers.
The Actorship of Time
Imagine a stage. The play unfolds on it; the stage itself — floor, walls, lights — is a stable background you never notice.
Physics has always treated time as this stage. Bortolotti's work suggests a different picture: the stage itself trembles slightly. So faintly 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.
This means the stage is not background. The stage is part of the play.
The tremble 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 technological limit or measurement error — it is a limit imposed by the laws of physics themselves. 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 actually reading "the average of a tremble." 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