Time, the seemingly most fundamental feature of reality, is under scrutiny. Seconds tick by, days pass, and everything from planetary motion to human memory unfolds along a single, irreversible direction. We are born and we die, in exactly that order. Yet, for over a century, physics has struggled to define what time actually is. This struggle is not mere philosophical nitpicking but sits at the heart of some of the deepest problems in science.
Modern physics relies on several frameworks. Albert Einstein’s theory of general relativity describes the gravity and motion of large objects such as planets, while quantum mechanics governs the microcosmos of atoms and particles. On an even larger scale, the standard model of cosmology describes the universe’s birth and evolution. All these frameworks rely on time, yet they treat it in incompatible ways. When physicists attempt to combine these theories into a single framework, time often behaves unexpectedly, sometimes stretching, slowing, or disappearing entirely.
Einstein, Quantum Mechanics, and the Problem of Time
Einstein’s theory of relativity was the first major blow to our everyday intuition about time. He showed that time is not universal; it runs at different speeds depending on gravity and motion. Two observers moving relative to one another will disagree about which events happened simultaneously. Time became elastic, woven together with space into a four-dimensional fabric called spacetime.
Quantum mechanics made things even stranger. In quantum theory, time is not something the theory explains; it is simply assumed. The equations describe how systems evolve with respect to time, but time itself remains an external parameter, a background clock outside the theory. This mismatch becomes acute when physicists try to describe gravity at the quantum level, crucial for developing the much-coveted theory of everything. In many attempts to create such a theory, time vanishes from the fundamental equations altogether, leaving the universe appearing frozen.
This puzzle is known as the problem of time and remains a persistent obstacle to a unified theory of physics. Despite enormous progress in cosmology and particle physics, we still lack a clear explanation for why time flows at all.
Entropy and the Arrow of Time
When physicists try to explain the direction of time, they often turn to entropy. The second law of thermodynamics states that disorder tends to increase. A glass can fall and shatter, but the shards never spontaneously leap back together. This asymmetry between past and future is often identified with the arrow of time.
This idea has been enormously influential, explaining why many processes are irreversible, including why we remember the past but not the future. If the universe started in a state of low entropy and is getting messier as it evolves, that appears to explain why time moves forward. However, entropy does not fully solve the problem of time. The fundamental quantum mechanical equations do not distinguish between past and future. The arrow of time emerges only when considering large numbers of particles and statistical behavior.
The Information Revolution
Over the past few decades, a quiet but far-reaching revolution has taken place in physics. Information, once treated as an abstract bookkeeping tool, has increasingly been recognized as a physical quantity in its own right. While entropy measures how many microscopic states are possible, information measures how physical interactions limit and record those possibilities.
This shift emerged gradually, driven by puzzles at the intersection of thermodynamics, quantum mechanics, and gravity. One of the earliest cracks appeared in black hole physics. When Stephen Hawking showed that black holes emit thermal radiation, it raised the possibility that information about whatever falls into a black hole might be permanently lost as heat, conflicting with quantum mechanics, which demands that information be preserved.
Resolving this tension forced physicists to confront a deeper truth: Information is not optional.
If we want a full description of the universe that includes quantum mechanics, information cannot simply disappear without undermining the foundations of physics. This realization had profound consequences, making it clear that information has a thermodynamic cost. Erasing it dissipates energy, and storing it requires physical resources.
Time Arising from Information
Recently, researchers have extended this informational perspective to time itself. Rather than treating time as a fundamental background parameter, they propose that temporal order emerges from irreversible information imprinting. In this view, time is not something added to physics by hand. It arises because information is written in physical processes and cannot be globally unwritten again under the known laws of thermodynamics and quantum physics.
Every interaction writes information into the universe. These imprints accumulate, defining a natural ordering of events. Earlier states are those with fewer informational records, while later states have more. Quantum equations do not prefer a direction of time, but the process of information spreading does. Once information has spread out, there is no physical path back to a state in which it was localized.
Time, in this view, is the cumulative record of what has happened. Each interaction adds a new entry, and the arrow of time reflects the fact that this record only grows.
Implications and Observations
This accumulated imprint of information may have observable consequences. At galactic scales, the residual information imprint behaves like an additional gravitational component, shaping how galaxies rotate without invoking new particles. The unknown substance called dark matter was introduced to explain why galaxies and galaxy clusters rotate faster than their visible mass alone would allow. In the informational picture, this extra gravitational pull comes from the fact that spacetime itself has recorded a long history of interactions.
Testing this theory remains a challenge. Ideas about time are often accused of being philosophical rather than scientific. However, the informational approach makes concrete predictions and connects directly to systems we can observe, model, and in some cases, experimentally probe. Black holes provide a natural testing ground, as they suggest information is erased. In the informational framework, this conflict is resolved by recognizing that information is not destroyed but imprinted into spacetime before crossing the horizon.
As the black hole evaporates through Hawking radiation, the accumulated informational record does not vanish. Instead, it affects how radiation is emitted. Detecting such signs remains beyond current technology, but they provide a clear target for future theoretical and observational work.
Conclusion: A New Perspective on Time
Ideas about information do not replace relativity or quantum mechanics. In everyday conditions, informational time closely tracks the time measured by clocks. For most practical purposes, the familiar picture of time works extremely well. The difference appears in regimes where conventional descriptions struggle.
Near black hole horizons or during the earliest moments of the universe, the usual notion of time as a smooth, external coordinate becomes ambiguous. Informational time, by contrast, remains well-defined as long as interactions occur and information is irreversibly recorded.
This shift reframes the longstanding debate about time. The question is no longer whether time must be assumed as a fundamental ingredient of the universe, but whether it reflects a deeper underlying process. In this view, the arrow of time can emerge naturally from physical interactions that record information and cannot be undone. Time, then, is not a mysterious background parameter standing apart from physics. It is something the universe generates internally through its own dynamics.
Whether this framework turns out to be a final answer or a stepping stone remains to be seen. Like many ideas in fundamental physics, it will stand or fall based on how well it connects theory to observation. But it already suggests a striking change in perspective: The universe does not simply exist in time. Time is something the universe continuously writes into itself.
