Space is physically real in the sense that it can bend, ripple, and carry energy, but a growing body of theoretical work in physics suggests it may not be fundamental. Instead, space could be an emergent phenomenon, something that arises from deeper ingredients like quantum entanglement and information. The question “is space real or an illusion?” turns out to be less of a binary and more of a layered puzzle that has occupied physicists and philosophers for over three centuries, and the answers keep getting stranger.
The 300-Year-Old Argument That Still Has Not Been Settled
The modern version of this debate traces back to Isaac Newton and Gottfried Wilhelm Leibniz. Newton proposed that space is absolute: a rigid, three-dimensional Euclidean container that exists independently of any matter inside it. Objects move through this container, and their “true” motion is defined relative to space itself. Leibniz flatly denied that space has any mind-independent reality, arguing instead that space is nothing more than the set of spatial relations between objects. Remove all the objects, and you have not left behind empty space. You have left behind nothing.1Stanford Encyclopedia of Philosophy. Absolute and Relational Space and Motion: Classical Theories
This was not a minor philosophical quibble. If Newton was right, space is a thing with its own existence, like a stage on which physics plays out. If Leibniz was right, space is a convenient fiction we use to describe relationships between real objects. The argument lingered unresolved through the centuries, with most working physicists treating space as Newton’s fixed stage. Then Einstein arrived and broke the stage.
Einstein Made Space Into Something Physical
General relativity did something neither Newton nor Leibniz anticipated: it turned spacetime into a dynamic participant in physics. In Einstein’s framework, mass and energy tell spacetime how to curve, and curved spacetime tells matter how to move. Space is no longer a passive background. It stretches, warps, and carries gravitational waves that we have now detected directly. In that sense, general relativity made space more real than Newton imagined: it is not just a container, it is a physical entity with its own behavior.
But this created a new puzzle. If spacetime is dynamic rather than fixed, then the background itself is part of the physics. Physicists call this property “background independence,” and it is widely considered one of general relativity’s most important lessons. The theory does not posit a fixed spacetime background the way Newtonian mechanics does; instead, the geometry of spacetime is determined by the matter and energy it contains.2Studies in History and Philosophy of Modern Physics. Background independence: Lessons for further decades of dispute Researchers working on quantum gravity see this as a feature that any successor theory should preserve: whatever replaces general relativity should not smuggle in a fixed background through the back door.
The Frothy Bottom of Reality
General relativity describes space as smooth and continuous, but quantum mechanics suggests that smoothness has limits. More than 65 years ago, physicist John Wheeler argued that quantum uncertainties in the metric of spacetime would become enormous at the Planck scale, around 10⁻³⁵ meters. At that scale, spacetime geometry and even its topology would fluctuate wildly, creating what Wheeler called “spacetime foam.”3Reports on Progress in Physics. Spacetime foam: a review
If Wheeler was right, the smooth space you walk through is something like the surface of an ocean viewed from an airplane. From far away, it looks flat and featureless. Zoom in close enough, and it is a roiling mess of waves and foam. The smoothness of everyday space would then be an approximation that works at the scales humans inhabit but breaks down at the tiniest scales physics can describe. Nobody has directly observed spacetime foam, but its existence would imply that smooth, continuous space is not the final word.
The Universe as a Hologram
One of the most provocative ideas to emerge from theoretical physics in the past three decades is the holographic principle. It originated from studies of black holes and the realization that the maximum amount of information a region of space can contain scales not with its volume but with its surface area. That is deeply counterintuitive. If you had a room full of hard drives, you would expect the storage capacity to depend on how many drives you could fit inside. The holographic principle says the real limit is set by the walls of the room, not its interior.
Extended to cosmology, the holographic principle suggests that the four-dimensional universe we experience, three spatial dimensions plus time, could be described as a holographic projection of information encoded on a two-dimensional boundary.4PubMed. How an emergent cosmology of a nonlocally unified, meaningfully in-formed and holographically manifested Universe can underpin and frame the biological embodiment of quantum entanglement If that sounds like it implies space is “not real,” it is more accurate to say that the spatial dimensions you perceive would be a higher-level description of something fundamentally lower-dimensional. The three-dimensional room you sit in would be real in the way a temperature is real: genuinely meaningful and measurable, but not itself a fundamental ingredient of nature.
The mathematical backbone of this idea comes from the AdS/CFT correspondence, a precise relationship between a gravitational theory in a curved spacetime and a quantum theory living on its boundary with one fewer dimension. Recent work has pushed this further, arguing that for the holographic correspondence to function, spacetime must be seen as emergent from a more fundamental structure whose basic ingredients are quantum correlations alone.5Nuclear Physics B. A note on the AdS/CFT correspondence and the nature of spacetime in quantum gravity
Building Space From Entanglement
If space is emergent, what does it emerge from? One increasingly influential answer is quantum entanglement, the phenomenon in which particles become correlated so that measuring one instantly constrains what you will find about the other, regardless of the distance between them. In 2013, physicists Juan Maldacena and Leonard Susskind proposed a striking conjecture known as ER=EPR: that the geometric connection between two regions of spacetime (an Einstein-Rosen bridge, or wormhole) is fundamentally the same thing as quantum entanglement between particles in those regions. Recent work has formalized this idea algebraically, associating spacetime connectivity and disconnectivity directly with the structure of entanglement in a quantum gravity system.6Journal of High Energy Physics. Algebraic ER=EPR and complexity transfer
The practical toolkit for exploring how entanglement builds geometry comes from tensor networks, mathematical structures borrowed from quantum information theory. A tensor network organizes quantum information in layers, and physicists have shown that these layers can reproduce the geometric properties of curved spacetimes. One recent study demonstrated that a particular type of tensor network, applied to a critical quantum system, naturally produces the geometry of de Sitter space, which is the type of expanding spacetime that describes our universe.7arXiv. Emergent de Sitter Space and Non-Unitary Tensor Networks from Non-Hermitian Quantum Criticality In this picture, each layer of the network corresponds to a time-slice of an expanding universe, with the causal structure of spacetime emerging from the way the network’s tensors are connected.8Nature Communications. Overlapping qubits from non-isometric maps and de Sitter tensor networks
Other work has modeled the holographic relationship between a one-dimensional critical spin system and a two-dimensional bulk theory, and found that gravitational forces emerge naturally from the entanglement structure.9Physical Review X. Emergent Holographic Forces from Tensor Networks and Criticality The implication is striking: the geometry of space, and even the force of gravity, may be consequences of how quantum information is organized rather than features built into the fabric of reality from the start.
Gravity as an Information Effect
Physicist Erik Verlinde pushed this line of reasoning into provocative territory in 2011 by arguing that gravity itself is not a fundamental force but an entropic effect, a statistical tendency arising from information. Starting from general assumptions and a holographic setup, Verlinde showed that Newton’s law of gravitation arises naturally and, in his words, “unavoidably” in a theory where space is emergent. The relativistic version of the argument leads directly to the Einstein field equations.10arXiv. On the Origin of Gravity and the Laws of Newton
Verlinde’s approach treats gravity the way we treat temperature or pressure: not as a fundamental microscopic force, but as a macroscopic description of deeper microscopic behavior. Just as the pressure of a gas emerges from the collective jostling of trillions of molecules rather than from a “pressure force” written into the laws of physics, gravity would emerge from changes in the information associated with the positions of matter. This remains controversial, and not all physicists are convinced the derivation holds up under scrutiny. But the fact that it reproduces both Newtonian gravity and general relativity from informational principles keeps the idea alive.
Discrete Threads of Space in Loop Quantum Gravity
A parallel approach to quantum gravity, loop quantum gravity, builds space from the ground up using entirely different mathematical machinery. In this framework, quantum states of geometry are represented by spin networks: graphs whose edges carry quantum numbers representing discrete chunks of area. An edge of the network carries a half-integer spin value that represents a basic quantum of area.11Classical and Quantum Gravity. Area propagator and boosted spin networks in loop quantum gravity
This is a radically different picture from general relativity’s smooth geometry. Space is not infinitely divisible. It has a smallest possible area and a smallest possible volume, much as energy comes in discrete packets in ordinary quantum mechanics. The smooth space of everyday experience would then be something like a fabric that looks continuous from a distance but is actually woven from discrete threads. Loop quantum gravity and the entanglement-based approaches are not yet unified into a single theory, but both point in the same direction: smooth, continuous space is an approximation, not the ground truth.
How Your Brain Constructs Space
Whether or not physics eventually settles on space being emergent, there is a separate and well-established sense in which the space you experience is constructed rather than directly perceived. Your brain does not have a window onto the external world. It sits inside a dark skull and builds a spatial model from fragmentary sensory signals: visual parallax, vestibular feedback from your inner ear, proprioceptive signals from your joints and muscles, even auditory cues.
The neural hardware for this construction is remarkably specific. Grid cells in the entorhinal cortex fire in regular hexagonal patterns as an animal moves through space, effectively creating an internal coordinate system. These cells combine self-motion information with environmental landmarks to track location in what researchers describe as allocentric, or world-centered, coordinates. The regular structure of grid cell firing fields encodes the relative structure of space and supports goal-directed navigation.12PubMed Central. From A to Z: a potential role for grid cells in spatial navigation
The philosophical implications here run deeper than neuroscience. The philosopher Immanuel Kant argued in the 18th century that space is not something we perceive in the world but a form that the mind imposes on experience. We cannot perceive anything non-spatially, Kant claimed, because spatiality is the framework the mind uses to organize sensory data in the first place. Modern predictive processing theories in cognitive science echo this Kantian picture, emphasizing the brain’s top-down generation of percepts: you do not passively receive a spatial world, you actively generate one based on internal models and then check it against incoming signals.13PubMed Central. The Predictive Processing Paradigm Has Roots in Kant
So even if physicists never prove that space is emergent, the space you actually experience is already a mental construction. The question is whether there is also a physical construction story underneath it.
Looking for Evidence
The biggest criticism of emergent-spacetime proposals is that they are hard to test. If the interesting quantum structure of space only shows up at the Planck scale, no conceivable experiment can probe it directly. But there are indirect strategies.
One approach uses gamma-ray bursts, the most energetic events in the observable universe. If spacetime has a granular microstructure, photons of different energies traveling across billions of light-years should arrive at slightly different times, because the quantum structure would affect high-energy photons more than low-energy ones. Algorithms like DisCan have been developed specifically to search for this energy-dependent dispersion in gamma-ray burst data, and some analyses have suggested that photon dispersion effects consistent with certain quantum gravity models might be detectable in sufficiently bright bursts.14arXiv. An Algorithm for Detecting Quantum-Gravity Photon Dispersion in Gamma-Ray Bursts: DISCAN So far, conclusive evidence has not appeared, but the sensitivity of gamma-ray observatories continues to improve.
A complementary strategy comes from condensed matter physics. Researchers have shown that certain laboratory systems, such as Bose-Einstein condensates, can serve as analogue models of curved spacetime. Low-energy excitations in these condensates obey wave equations that couple to an “effective metric” with the same mathematical structure as a curved spacetime in general relativity.15Classical and Quantum Gravity. Analogue gravity from Bose-Einstein condensates These analogue systems cannot prove that our spacetime is emergent, but they provide concrete demonstrations that spacetime-like geometry can emerge from a non-gravitational substrate. The fact that the phenomenon works in the lab makes the theoretical proposals feel less speculative.
The Trouble With de Sitter Space
Most of the mathematical success stories in emergent spacetime, particularly the AdS/CFT correspondence, apply to anti-de Sitter spacetimes: universes with negative cosmological constant. Our universe, however, has a positive cosmological constant and is best described by de Sitter space, which is expanding and has cosmological horizons. Extending holographic ideas to de Sitter space has been notoriously difficult, and this is where some of the most active research is happening right now.
Holographic complexity, a measure of how computationally difficult it is to reconstruct the interior of a spacetime from boundary information, behaves very differently in de Sitter space compared to anti-de Sitter space. In geometries with black hole horizons, certain complexity measures grow steadily over time, but in de Sitter space the behavior is more exotic. Some proposals predict that complexity can grow indefinitely in de Sitter static patches, while others find it diverges after a finite time.16Physical Review D. Complexity equals anything can grow forever in de Sitter space Other analyses find that geodesics of finite length in de Sitter flow geometries only exist for short durations and do not show the late-time linear growth seen in black hole geometries.17Journal of High Energy Physics. Holographic complexity and de Sitter space
Recent work on Carroll geometry, a mathematical framework that emerges when the speed of light is taken to zero, has made progress connecting de Sitter holography to established results in anti-de Sitter holography.18Physics Letters B. Carroll geometry meets de Sitter space via holography Whether these approaches will eventually produce a complete holographic dictionary for our expanding universe is an open question. Until they do, the claim that “space is emergent” rests on mathematical frameworks that work beautifully in toy-model universes but have not been fully extended to the one we actually live in.
What Philosophers Make of All This
Philosophers of physics have not been sitting on the sidelines. The question of whether spacetime is fundamental or emergent has generated its own subfield. One influential position, ontic structural realism, argues that what is real about spacetime is not its points or substance but its relational structure. In a sense, this updates Leibniz for the quantum age: space is not a thing, but neither is it nothing. It is a pattern of relations, and the pattern is what is real.
Even this moderate position runs into technical difficulties, particularly around how to distinguish individual spacetime points if the structure is all that exists. Some philosophers have defended a monistic version of structural realism, while others argue for a dualistic version that treats both structure and some minimal notion of individuality as real.19Roczniki Filozoficzne. Moderate Ontic Structural Realism about the Nature of Spacetime: Monistic and Dualistic Approaches A more radical version, radical ontic structural realism, dispenses with objects entirely and argues that the world is nothing but structure, a position that has recently been reframed as a form of “existence monism.”20Synthese. Radical ontic structural realism as a structuralist existence monism
These positions matter because they shape what physicists mean when they say space “is” or “isn’t” real. If structural realism is correct, the question “is space real?” has a surprisingly nuanced answer: the spatial structure you interact with every day is perfectly real, but it is made of relationships rather than substance. There is no invisible container holding things apart. There are things, and the distances between them, and the distances are what space is.
The Problem of Time
If space can be emergent, what about time? In classical general relativity, space and time are woven together into spacetime, so if one is emergent the other probably is too. But this creates a deep conceptual problem. All of standard physics describes how things evolve in time. If time itself is not fundamental, how do you write equations of motion? Motion through what?
This is known as the “problem of time” in quantum gravity, and it has been explored using simplified toy models of relational particle mechanics. In these models, there is no external clock ticking. Instead, semiclassical time emerges from the relationships between the components of the system itself, one part of the universe effectively serves as a clock for the rest.21Classical and Quantum Gravity. Emergent semiclassical time in quantum gravity: I. Mechanical models The experienced flow of time, in this picture, is not built into the fundamental laws but emerges from them the way temperature emerges from molecular motion. You would never catch a single molecule being “hot.” Likewise, you might never catch a fundamental degree of freedom being “in the future.” Time would be a macroscopic description of something that does not exist at the most basic level.
The problem of time is arguably even harder than the problem of space, because while we can imagine different spatial geometries fairly easily, imagining physics without any notion of change or sequence pushes against something that feels more than scientific. It feels existential. Yet the theoretical arrows keep pointing in this direction, and any satisfying resolution to the puzzle of space will almost certainly have to resolve the puzzle of time along with it.