New research says time only exists where space is curved enough to support it, implying that our expanding universe is slowly losing its grip on time itself.
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.”