What if it’s just a concept that exists inside your mind?
Time has puzzled scientists for many decades. Does it
meaningfully exist apart from our experience of it as everything moves toward
the disintegration of entropy along its irrefutable arrow? You can’t put the
“spilled milk” of the weirdness of time back in the jug.
In new research published in the American Physical Society's
peer-reviewed journal Physical Review A, scientists from Italy (led by
Alessandro Coppo) try to translate one theory of time into real life—or, at
least, closer to it. The theory is called Page and Wootters mechanism, and
Coppo has studied it for years. It’s a quantum mechanics idea that dates back
to 1983.
While general relativity (in the classical physics model)
lets time be a variable—like the perception-dependent difference between time
on Earth and time in space in stories like Interstellar—quantum physics
requires it to be nailed down. That means instead of a dependent variable
(something defined by an external property, like local gravity or an object’s
distance from Earth), time must be independent, and there must be some way to
measure it as such.
This may seem counterintuitive. After all, quantum mechanics
is considered the newer version of things—the one that destabilizes the
foundation of physics in order to be reconciled with the classical model. But
time has a unique role in quantum systems. After all, everything in a
particular time, defined in some objective way, is knitted together through
quantum interactions until it forms a capture of the entire universe (if you
zoom out enough).
In their paper, Coppo and his coauthors turn the Page and
Wootters approach into a real concept for a clock. Within quantum physics, a
clock isn’t much like the one you wear on your wrist or hang in your
office—it’s anything that has a predictable and uniform behavior that can be
used as a measurement. (For example, this 2021 Quanta article lists
increasingly stinky garbage as a kind of clock!)
New Scientist explains that Page and Wootters wondered if
our world is so quantumly entangled within itself that any visible passing of
time is a symptom of entanglement. They also suggested that we ourselves are
implicated in that entanglement just by seeing the passage of time—because
someone outside of the entangled system would see it standing still. The
“clock,” therefore, is the item within the entangled system that shows time
passing.
It’s easy to see why this theory has stayed mostly abstract
for over 40 years. To turn it into something with measurements based in real
life observation, scientists took iconic physics equations and restricted them
to conditions that match the Page and Wootters scenario. They considered two
systems that are entangled but do not interact, where one system is a harmonic
oscillator—like a quartz timing in a watch, or a pendulum.
Their solution may prove to be consistent within classical
and quantum mechanics, because when enough particles are placed into each
quantum system—when it reaches the threshold called “macroscopic,” based on
mass—the systems align with classical physics as well.
That‘s a big deal—if our entire, very macroscopic world fits
into this definition of time based on entanglement, it means everything around
us is entangled. Things would need to be entangled almost by definition in
order to be part of our observable world. And it would mean that anything we
see where time passes (no matter how far away it is) is linked with us in a
vital way.