We take time for granted.
Every second that passes feels like a step toward the future—morning turns to night, old photos gather dust, and spilled coffee never jumps back into the cup. Time is a one-way street. Or is it?
A groundbreaking study from researchers at the University of Surrey suggests that the laws of physics don’t care which way time moves.
The equations governing motion—whether it’s a swinging pendulum, a planet orbiting a star, or even the chaotic swirl of cream in your coffee—work just as well forward as they do backward.
In theory, time could be flowing in reverse, and we’d never notice.
If this sounds like science fiction, you’re not alone.
Our entire existence is built on the assumption that time progresses forward. But if physics itself doesn’t demand this, what does?
And what happens if we challenge our understanding of time?
The Physics of Time
For centuries, physicists have struggled to explain why time flows in only one direction. Newton’s laws of motion—the foundation of classical mechanics—make no distinction between past and future.
If you were to watch a video of a planet orbiting a star and then play it backward, the motion would still make perfect sense from a physics standpoint.
Even in quantum mechanics, the rules remain indifferent. .
Schrödinger’s equation, which describes the behavior of particles at the smallest scales, doesn’t enforce a direction for time either.
So, if neither classical nor quantum mechanics dictate time’s forward motion, why does everything seem to march toward the future?
The answer, at least according to conventional thinking, lies in thermodynamics—the study of heat and energy flow.
The second law of thermodynamics states that the total entropy (disorder) of a closed system always increases.
A shattered glass doesn’t spontaneously reassemble, and a hot cup of coffee inevitably cools down.
This principle gives us the perception that time moves forward.
But what if this isn’t the whole story?
What If Time Has No Preferred Direction?
Physics tells us that time could move in either direction. So why don’t we experience time running backward?
One explanation comes from Markovian dynamics, which describes processes where each step depends on the previous one—like a line of dominoes falling.
Once a sequence begins, it’s difficult to reverse.
But here’s where things get even more mind-bending: some physicists propose that time’s forward motion is merely an effect of the expanding universe.
After the Big Bang, the universe began expanding outward, stretching space itself.
As it expands, matter clumps together, stars form, galaxies evolve, and the world we know emerges.
In this view, time is tied to this cosmic expansion—but what if the universe contracts one day? Would time start running backward?
This idea leads to an even stranger possibility: a parallel universe where time moves in reverse.
Are We the Ones Moving Backward?
Some physicists propose that the Big Bang didn’t create just one universe—but two, each experiencing time in opposite directions.
In one, time moves forward (as we perceive it). In the other, time moves the other way.
From the perspective of a being in that universe, their “future” is our past, and vice versa.
If you could somehow observe their world, it might look like a movie being rewound—except, for them, it would feel normal. And here’s the real kicker: from their perspective, we’d be the ones experiencing time in reverse.
This mind-bending idea doesn’t just exist on the fringes of theoretical physics.
It’s supported by mathematical models suggesting that time’s direction isn’t an absolute property of reality, but rather an emergent phenomenon tied to cosmic conditions.
What Does This Mean for Time Travel?
If time isn’t strictly one-directional, does this mean time travel is possible? Maybe.
Scientists have long theorized about closed timelike curves (CTCs)—loops in spacetime that could, in theory, allow an object to travel backward in time.
Some physicists believe that wormholes—hypothetical tunnels in spacetime—could provide a shortcut between different points in time.
However, practical time travel faces enormous obstacles. The biggest challenge? Preventing paradoxes.
If you went back in time and changed something—like preventing your grandparents from meeting—would you erase your own existence?
This classic paradox, known as the grandfather paradox, suggests that time travel might be limited by the very nature of cause and effect.
What If We’re Already Experiencing Time Wrong?
There’s another way to think about time: maybe we’re experiencing it incorrectly.
Some physicists propose that time doesn’t actually “flow” at all. Instead, everything that has ever happened and will ever happen already exists in a four-dimensional structure known as the block universe.
In this view, the past, present, and future all coexist—our perception of time moving forward is just an illusion caused by how our brains process information.
If this is true, then the future already exists—we just haven’t experienced it yet.
The Future of Time Science
While time reversal remains a thought experiment, advances in physics could one day reveal whether time is truly as rigid as we think.
Scientists are experimenting with quantum mechanics, gravitational waves, and space-time distortions to uncover whether time travel, reverse causality, or even alternative timelines are possible.
If future research confirms that time can run backward under certain conditions, it could revolutionize computing, physics, and even our understanding of reality itself.
For now, time remains an enigma. But one thing is certain: our perception of time may be far from the ultimate truth.
