Whether time is a fundamental ingredient of reality or something that emerges from deeper, timeless physics is one of the biggest open questions in modern science. There is no consensus answer. General relativity treats time as a real, physical dimension woven into the fabric of the universe. Quantum mechanics treats it as a background clock that ticks independently of the system being studied. And the most ambitious attempts to unify these two theories suggest that time might not be fundamental at all, but instead a large-scale illusion arising from more primitive quantum relationships.
How Physics Currently Treats Time
The two pillars of modern physics handle time in fundamentally incompatible ways, which is part of why the question remains unresolved.
In general relativity, time is a physical thing. Einstein showed that space and time must be combined into a single four-dimensional object called spacetime, because the math only works when spatial and temporal coordinates get “mixed together.” Massive objects warp this fabric, which is why clocks tick slower near a planet’s surface than in orbit. Strikingly, when you solve Einstein’s equations for the shape of spacetime, the solution doesn’t change in time. It exists as a complete, timeless object, like a sculpture you could walk around. This is called the “block universe” view: past, present, and future all exist simultaneously, and what we experience as the flow of time is just our particular path through that block.
Quantum mechanics tells a different story. Here, time is not a dynamic part of the system. It’s an external parameter, a number on a clock sitting outside the experiment. Every other physical quantity in quantum mechanics, like position or momentum, gets promoted to a special mathematical object called an operator. Time does not. As the physicist John von Neumann noted as early as 1932, time corresponds to “an ordinary number-parameter, just as in classical mechanics.” The system evolves with respect to this background clock, but the clock itself is not part of the physics being described.
Why These Two Views Collide
The conflict between these treatments creates what physicists call the “problem of time.” In general relativity, time is flexible, warped by gravity, part of the dynamic universe. In quantum mechanics, time is rigid, external, and fixed. Trying to build a single framework that covers both, which you’d need for extreme scenarios like the interior of black holes or the first moments after the Big Bang, forces these two incompatible notions of time into direct confrontation.
This isn’t just a philosophical headache. It spawns at least eight distinct technical problems, including the “frozen formalism problem,” where the most natural way to quantize general relativity produces equations in which nothing changes at all. The universe, according to these equations, is static. Time disappears from the fundamental description entirely.
The Case for Time as Emergent
In almost all proposed theories of quantum gravity, spacetime is not part of the fundamental picture. It gets replaced by a framework that lacks at least some of the structure we associate with space and time. The everyday experience of minutes passing and clocks ticking would then be something that emerges at larger scales from a deeper, non-temporal reality, in the same way that temperature emerges from the collective motion of trillions of molecules even though no single molecule has a temperature.
Several specific mechanisms have been proposed for how this could work.
Time From Entanglement
The Page-Wootters mechanism, first proposed in the 1980s and refined with increasingly rigorous math since, suggests that time emerges from quantum entanglement. The idea is that the universe as a whole exists in a static, timeless state. But if you split it into two parts, say a “clock” and “everything else,” the entanglement between them creates correlations that look exactly like one system evolving in time relative to the other. A 2021 study published in Nature Communications showed that this mechanism produces not just quantum time evolution, but also the classical equations of motion we use in everyday physics. The authors concluded that “there is not a ‘quantum time’ possibly opposed to a ‘classical’ one; there is only one time, and it is a manifestation of entanglement.”
Time From Thermodynamics
Physicist Carlo Rovelli’s thermal time hypothesis takes a different angle. It starts from the frozen, timeless equations that emerge when you try to quantize gravity and asks: if the universe is fundamentally timeless, where does our experience of time come from? The answer, Rovelli proposes, is our ignorance. When we describe a physical system using statistical averages rather than tracking every microscopic detail (which is all we can ever do in practice), a flow that behaves exactly like time naturally appears. On this view, time is a macroscopic effect of not knowing the full microscopic state of the world.
The Holographic Approach
Work using a major theoretical tool called the AdS/CFT correspondence, which relates a theory with gravity to a theory without it on a lower-dimensional boundary, has shown that spacetime geometry can be built from patterns of quantum entanglement. When two quantum systems are maximally entangled, they generate a connected spacetime between them. Disentangle the systems, and the spacetime disconnects. Research in this framework has even shown that the thermodynamic arrow of time (the fact that entropy always increases toward the future) can be derived from the entanglement structure: when two quantum systems start uncorrelated, entropy can only increase, imposing a definite direction on time. In a highly correlated environment, that directionality breaks down.
Why Time Feels So Real
Even if time isn’t fundamental, it would still be “real” in every practical sense. Emergent properties can be qualitatively different from anything in the deeper theory they arise from. Water is wet even though no individual water molecule is wet. Similarly, time could flow, have a direction, and govern every aspect of our experience while being entirely absent from the most basic laws of physics. The emergent time we experience would depend on non-temporal structures underneath, but it would be autonomous enough to behave as its own distinct thing at the scales where we live.
The arrow of time, our sense that the past is fixed and the future is open, has a well-understood thermodynamic origin regardless of whether time itself is fundamental. Arthur Eddington coined the phrase “time’s arrow” to describe the connection between entropy and temporal direction: follow the arrow toward increasing randomness, and you’re pointing toward the future. As Eddington put it, “the introduction of randomness is the only thing which cannot be undone.” This one-way property of time has no analogue in space and is the only distinction between past and future that physics recognizes.
Can We Test Any of This?
For decades, the question of whether time is fundamental seemed purely philosophical. That’s beginning to change. A 2025 theoretical framework for emergent spacetime makes specific, falsifiable predictions that current and near-future instruments could check. The model predicts particular statistical signatures in the cosmic microwave background (the afterglow of the Big Bang), including a roughly 5% enhancement of the largest-scale temperature fluctuations and a specific pattern of non-Gaussian features that falls within the detection range of existing data from the Planck satellite.
The roadmap for 2025 to 2030 includes reanalyzing existing Planck and WMAP satellite data with improved statistical methods, using the planned LISA space mission to search for characteristic gravitational wave patterns, and looking for energy-dependent violations of the principle that all light travels at the same speed, which some emergent spacetime models predict. Finding correlated signatures across these independent channels would constitute strong evidence that spacetime, including time, emerges from something more fundamental.
No such evidence has been found yet. But the fact that the question has moved from “purely theoretical” to “testable within the next decade” marks a significant shift in how seriously physics takes the possibility that time is not a basic feature of reality.