Theoretical physicists Joao Magueijo and Lee Smolin have proposed that time is not merely a backdrop against which the universe unfolds but a quantum variable that directly shapes cosmic expansion. Their work, developed across multiple preprints and peer-reviewed papers, treats time as conjugate to the cosmological constant, the mysterious factor driving the universe apart at an accelerating rate. If correct, this framework could bridge the long-standing divide between quantum mechanics and general relativity by placing time at the center of both.
How Atomic Clocks Define the Second
Every measurement in modern physics traces back to time. The International System of Units defines the second by counting exactly 9,192,631,770 oscillations of radiation corresponding to a specific transition in cesium-133 atoms. That number is not arbitrary; it was chosen because cesium atoms oscillate with extraordinary regularity, making them among the most reliable timekeepers available. Primary cesium fountain standards, maintained by national metrology institutes, realize this definition in practice and serve as the reference against which all other clocks are checked, from GPS satellites to laboratory lasers.
The precision matters far beyond specialized laboratories. Other SI units, including the meter and the ampere, ultimately depend on the stability of the second for their own definitions. The speed of light, for instance, fixes the meter as the distance light travels in a specific fraction of a second, so better timekeeping immediately sharpens our notion of length. Electrical units rely on frequency standards tied to the same cesium oscillation, anchoring everything from power grids to precision electronics. Strip away the second, and the entire measurement system collapses. That dependency is what makes time unique among physical quantities: it is not one variable among many but the foundation on which the rest are built.
Time as a Quantum Variable in Cosmology
While metrology treats time as a fixed, well-defined quantity, theoretical physics has long struggled with its deeper nature. In a preprint exploring a universe that “does not know the time,” Magueijo and Smolin argue that intuitive notions of a universal clock are often at odds with the way time appears in the equations of quantum gravity. Their proposal treats cosmological time as a quantum observable that does not commute with operators defining cosmological states, particularly the cosmological constant. In quantum mechanics, when two quantities do not commute, measuring one introduces uncertainty in the other. Applied to the cosmos, this means that a universe with a precisely known expansion rate cannot simultaneously have a sharply defined age.
A related paper by Magueijo and Smolin develops a quantum theory of the cosmological constant in which this parameter is promoted from a fixed background to a dynamical variable. In that framework, the cosmological constant becomes conjugate to a kind of “cosmic time,” much as energy is conjugate to time in ordinary quantum mechanics. A companion preprint by Stephon Alexander, Magueijo, and Smolin extends general relativity so that the cosmological constant is conjugate to the Chern-Simons invariant, a mathematical object drawn from the geometry of spacetime connections. The roots of this idea go back to a 1994 proposal by Smolin and Chopin Soo, who suggested the Chern-Simons invariant of the Ashtekar-Sen connection as a natural internal time coordinate for classical and quantum cosmology. In this line of thought, time is not an external parameter but a quantum degree of freedom intertwined with the dynamics of spacetime itself.
Why Physics Cannot Agree on “Now”
The difficulty runs deeper than competing equations. Humans experience time as a flowing sequence of moments, but physics offers no mechanism for that sensation. As a cosmology lecture from the University of Oregon notes, we do not perceive time with the same senses that reveal spatial distances and directions. Relativity dissolved the idea of a universal present tense: two observers moving at different speeds, or sitting in different gravitational fields, will disagree about which events are simultaneous. A philosophy-of-physics analysis in Zygon emphasizes that modern physics has abandoned any universally recognizable definition of “now,” replacing it with a four-dimensional spacetime in which all events simply exist.
One influential attempt to reconcile this block-universe picture with our experience of change came from Don Page and William Wootters in 1983. Their mechanism, published in Physical Review D, showed that apparent time evolution of a subsystem can emerge from correlations inside an overall stationary quantum state. In other words, a universe that is globally frozen in time can still contain clocks that appear to tick from the perspective of an observer embedded within it. The Page-Wootters mechanism treats time as relational and derived rather than fundamental: what matters is not an external clock but how one part of the universe changes relative to another. Magueijo and Smolin’s work builds on this tradition but pushes further. Rather than treating time as a mere illusion inside a static whole, they argue that time is a genuine quantum degree of freedom whose uncertainty is physically linked to the value of the cosmological constant, giving the flow of time a concrete role in cosmic expansion.
Entropy, Expansion, and the Arrow of Time
Even before quantum gravity entered the picture, physicists recognized that time has a preferred direction. Arthur Eddington proposed that time flows toward increasing entropy, or disorder. Because the second law of thermodynamics dictates that entropy in an isolated system can never decrease, time always increases. This thermodynamic arrow of time aligns with everyday experience: eggs break but do not reassemble, smoke disperses but does not spontaneously gather, and heat flows from hot objects to cold ones, not the reverse. Cosmology adds another arrow: the universe is expanding, and the early cosmos appears to have been in a remarkably low-entropy state compared with the vast, clumpy structures we see today.
Magueijo and Smolin’s approach suggests that the arrow of time might be tied not only to entropy but also to quantum fluctuations in the cosmological constant. If time and the cosmological constant are conjugate variables, then the history of the universe involves a trade-off between how sharply we can define its age and how precisely we can specify its acceleration. In such a picture, the growth of cosmic structure, the increase of entropy, and the quantum uncertainty in the vacuum energy could all be facets of a single underlying temporal dynamics. While this remains speculative, it hints at a synthesis in which the thermodynamic arrow, the cosmological arrow, and the quantum structure of spacetime are different expressions of the same deep asymmetry between past and future.
Preprints, Peer Review, and the Future of Time
The technical details of these proposals circulate first as preprints on arXiv, a repository maintained by a consortium of institutional member organizations that support its infrastructure. By posting their work there, theorists like Magueijo and Smolin invite rapid feedback from the global community before, during, and after formal peer review. Many landmark ideas in quantum gravity, including early discussions of time as an internal variable, appeared on arXiv years before their journal publication. This open circulation is particularly important for foundational questions, where progress often depends on cross-pollination between physics, mathematics, and philosophy rather than on incremental experimental results.
Keeping such a platform running requires more than institutional backing. Arxiv also depends on individual donations and ongoing technical support to remain free and widely accessible, and its maintainers publish detailed guidance for authors navigating submission, revision, and classification. The interplay between preprint culture and traditional journals shapes how radical ideas about time gain traction, face criticism, and evolve. As new generations of atomic clocks push the definition of the second to ever greater precision, and as quantum cosmology refines its treatment of time as a dynamical variable, this ecosystem of open dissemination and critical review will help determine which visions of cosmic time endure, and which fade into the past they seek to explain.
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*This article was researched with the help of AI, with human editors creating the final content.
