Out of all the forces shaping our daily lives, time exerts the most profound influence.
It moves relentlessly from past to present to future, and no matter how much we wish otherwise, it never flows in reverse.
But what if everything we assume about time is wrong?
According to fundamental physics, the universe’s behavior shouldn’t change whether time moves forward or backward.
And now, physicists suggest that gravity isn’t strong enough to dictate a universal forward-moving direction for time.
So, does time actually exist?
Or is it just a construct of human perception?
Why Things Move Forward
The concept of the arrow of time is why young people grow old and why you can’t unscramble an egg.
In daily life, time is unidirectional, always moving forward. But if we take a step back and view the universe as a whole, something strange happens.
The laws of physics are time-reversible.
In other words, they work just as well whether time runs forward or backward.
“Whether through Newton’s gravitation, Maxwell’s electrodynamics, Einstein’s relativity, or quantum mechanics, all the equations that best describe our universe work perfectly if time flows forward or backward,” explains Lee Billings in Scientific American.
One striking example of this is planetary orbits.
“Whether time runs forwards or backwards, planetary orbits follow the exact same paths.
The only difference is the direction of the orbit,” Brendan Cole wrote earlier this year.
This raises an unsettling question: If the universe doesn’t require time to move forward, then why does it?
The One Law That Breaks Time Symmetry
The only physical law that seems to distinguish past from future is the second law of thermodynamics. ‘
This states that as time passes, entropy (or disorder) in a system always increases.
Think back to that scrambled egg.
Once mixed, it’s impossible to put the yolk and whites back into a perfect, unbroken shell.
This increasing disorder is why time appears to move in only one direction.
Physicists, somewhat reluctantly, have settled on the second law of thermodynamics as the best explanation for the arrow of time.
But that still leaves one major problem—for entropy to increase, the universe must have started in a highly ordered state.
Why would that be the case?
Some researchers propose a radical answer: there may be parallel universes where time runs backward, sideways, or even in completely unknown directions.
What If Gravity Isn’t Controlling Time at All?
Many physicists believe that time’s forward motion emerges when gravity forces particles to interact on a large scale.
This transition point, where particles shift from being governed by quantum mechanics to classical physics, is called decoherence.
A widely accepted theory, the Wheeler-DeWitt equation, predicts when this shift happens due to gravity’s influence.
But now, researchers are questioning this assumption.
Physicists Dmitry Podolsky of Harvard University and Robert Lanza of Astellas Global Regenerative Medicine decided to test whether gravity is really responsible for time’s arrow.
Their findings were shocking.
Gravity Might Be Too Weak to Create Time’s Arrow
When Podolsky and Lanza ran calculations using the Wheeler-DeWitt equation, they found something surprising: gravity’s effects emerge far too slowly to explain the forward movement of time.
In other words, if gravity were the main force creating the arrow of time, it should be happening much more gradually—or not at all.
This means that something else must be responsible for the unidirectional flow of time.
Lanza explains:
“Our paper shows that time doesn’t just exist ‘out there’ ticking away from past to future, but rather is an emergent property that depends on the observer’s ability to preserve information about experienced events.”
This radical idea suggests that time is subjective—created by the observer rather than being an inherent property of the universe.
Does the Observer Create Time?
Einstein’s special theory of relativity already showed that time is relative—meaning that two observers moving at different speeds will experience time at different rates.
But Lanza and Podolsky take this even further.
“Our paper argues that the observer actually creates time,” Lanza told Wired.
This proposal is, understandably, controversial. UC Berkeley physicist Yasunori Nomura, who was not involved in the study, has criticized their model.
He argues that Lanza and Podolsky fail to account for the fabric of spacetime itself.
“The answer depends on whether the concept of time can be defined mathematically without including observers in the system,” Nomura says.
In other words, if we need an observer for time to exist, then what happens to time in an empty universe?
Are We Missing Something Bigger?
If gravity isn’t responsible for the arrow of time, then what is?
Some physicists speculate that dark energy—the mysterious force accelerating the universe’s expansion—might play a role.
This idea remains highly speculative, but one thing is certain: we are nowhere near fully understanding time.
While Podolsky and Lanza’s work challenges the idea that time is fundamental, the debate is far from over.
Whether time is an illusion, a byproduct of entropy, or something even stranger, scientists will continue searching for answers.
For now, the next time you check your watch or count the seconds ticking by, remember—time might not be what you think it is.
