Physicists have experimentally observed time emerging from within an isolated quantum system for the first time, providing a laboratory test for the origins of temporal flow. According to research published June 11 in Physical Review Research, Giovanni Barontini of the University of Birmingham demonstrated that time can arise from entropy exchange within a “mini-universe” of ultracold atoms, confirming long-standing theoretical frameworks in quantum cosmology.
How can time emerge from a closed system?
In a universe with no external observer or clock, time is not a fundamental constant but a relative phenomenon. Barontini’s experiment utilized a Bose-Einstein condensate—atoms cooled to near absolute zero—trapped and split by a laser. By ignoring one half of the system, termed the “dark sector,” Barontini showed that time emerged for the remaining “bright sector” based on the flow of entropy between the two halves. This confirms the “relational time” hypothesis, which suggests that one part of a system acts as a clock for another, rather than time existing as an independent, external background.
A Bose-Einstein condensate is a state of matter where thousands of atoms slow down so significantly that they blur into a single quantum object, allowing researchers to manipulate them as a unified system.
What happens to time when entropy reaches equilibrium?
The rate of time’s passage is tied directly to the exchange of energy disorder. Barontini observed that when entropy flowed rapidly between the two sectors, the internal clock accelerated. When the exchange slowed, the internal clock decelerated. Crucially, when the two sectors reached equilibrium—meaning no further entropy was being exchanged—the internal clock stopped entirely. This suggests that the “arrow of time” is a byproduct of information loss; by choosing to ignore the dark sector, the observer inadvertently creates the conditions for time to manifest.
How does this experiment challenge the Wheeler-DeWitt equation?
For nearly 60 years, the Wheeler-DeWitt equation has puzzled physicists because it describes the universe without an external time parameter. While the equation is central to quantum gravity, it lacks a mechanism to explain why we experience time ticking forward. Barontini’s work provides the first quantitative laboratory test of these concepts. By deriving a version of the Schrödinger equation using this “entropic time,” the experiment proved that internal dynamics can successfully reproduce the evolution of a system, even in the absence of a universal, external clock.
Future applications of quantum simulation
The methodology used at the University of Birmingham opens a new frontier for quantum research. Barontini suggests the same cold-atom tool kit can be adapted to simulate:
- Black hole analogues: Modeling the extreme conditions near gravitational singularities.
- Early universe conditions: Recreating the density and entropy states of the infant cosmos.
- Big Crunch scenarios: Simulating the theoretical end-state of a collapsing universe.
When studying quantum systems, researchers often define “time” not by a clock on the wall, but by the change in state within the system itself. This is known as “entropic time.”
Frequently Asked Questions
Is time just an illusion?
The study does not claim time is an illusion. Instead, it demonstrates that time is a relational property that emerges from interactions within a system, rather than an external, fundamental force.
What is the “dark sector” in this experiment?
The dark sector refers to the half of the Bose-Einstein condensate that the researcher intentionally ignored. By losing information about this half, the researcher allowed an “internal clock” to emerge in the remaining half.
Can this experiment be used to travel through time?
No. The study is a proof-of-concept for how time emerges in quantum systems. It does not provide a mechanism for macroscopic time travel.
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