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Past attempts to reconcile quantum theory with relativity have led to the “problem of time,” where time behaves differently in each regime.A new study suggests that in a “geometric clock,” time may flow as we expect in curved regimes, but wind down in flatter ones.This is yet another mind-bending take on time that shows that the concept is much more complex than the simple tick-tock of a physical clock.
For most of us, time is an intuitive concept. Sixty seconds in a minute, 1,440 minutes in a day, 28,835 days in an average lifetime. But as science has progressed from water clocks to atomic clocks, we’ve gained a more nuanced understanding of time. Within the framework of General Relativity, for example, time is a dynamic dimension woven through space-time. That means time is relative, since it’s warped by mass and energy. In quantum physics, however, time is more of a constant and external backdrop to changes in a system (mathematically speaking, it’s a parameter rather than an operator).
In 1967, American theoretical physicists John Wheeler and Bryce DeWitt created what’s regarded as the first attempt to reconcile these two theories. Known as the Wheeler-Dewitt equation, it essentially contains no time variable at all, forming what’s known today as “the problem of time.”
“There were no great mysteries except at the interface between gravitation and quantum theory,” Wheeler (who also coined the term “black hole”) said in an interview in 1996. “It’s one thing to have an equation, another thing to solve it, and so another thing to interpret the solution […]. That’s a continuing enterprise.”
The latest attempt to understand that solution comes from Anderson Gama Fernandes de Freitas of the Universidade Federal de Itajubá in Brazil. In a paper published in the journal Classical and Quantum Gravity, Fernandes de Freitas argues that the phenomenon of time might be intrinsically tied to the geometry of space itself. He introduces a “geometric clock”—a mathematical construct derived from the curvature properties of three-dimensional spatial slices—that determines whether time can function as a meaningful ordering parameter. When space is intensely curved, as in the conditions immediately following the Big Bang, this clock is rigid and the universe evolves just as standard physics predicts. But as the universe expands and flattens, the curvature weakens, and Fernandes de Freitas’ geometric clock winds down with it, meaning time itself gradually loses its operational meaning.
“The analysis of solvable sectors demonstrates that this geometric notion of time naturally reproduces standard results in strongly curved regimes, such as the early [u]niverse, while predicting a smooth weakening of temporal ordering in weakly curved or asymptotically flat regions,” Fernandes de Freitas wrote. “This behavior offers a coherent interpretation of why time-based descriptions are effective in some regimes and cease to be meaningful in others.”
Fernandes de Freitas’ theory argues that time is neither “fundamental nor universally available.” Crucially, this mathematical theory moves the philosophical question of time into the more concrete realm, developing testable predictions. However, the author points out that his theory was only tested on simplified cosmological models. It’ll take more than that to unify the two greatest scientific theories of the modern age—a quest that’s perplexed the greatest scientific minds in history, Wheeler included.
“We still haven’t got a full insight into what the solutions mean and how to speak about them,” Wheeler said in the 1996 interview. “It’s strange that the two greatest developments of theoretical physics—quantum theory and relativity—should take so long to come into a union.”
Darren lives in Portland, has a cat, and writes/edits about sci-fi and how our world works. You can find his previous stuff at Gizmodo and Paste if you look hard enough.