10 Theories About What Exists in the 4th Dimension

Added: 2026-05-17

[00:00:00]All right, let's go. Number 10, the Tesseract. In 1884, a British school teacher and theologian named Edwin Abbott Abbott published a slim novela called Flatland, in which a two-dimensional square encounters a sphere passing through its world. The sphere appears as a circle that materializes from nothing, expands, then shrinks, and vanishes. Abbott wasn't writing fantasy. He was illustrating a precise mathematical principle that has haunted geometers ever since. Beings confined to fewer dimensions cannot perceive higher ones. They can only witness the shadow left behind. That principle gave mathematicians the conceptual tools to describe something genuinely strange. A tesseract is the four-dimensional analog of a cube. Where a cube has six square faces, 12 edges, and eight corners. A tesseract has eight cubic cells, 24 square faces, 32 edges, and 16 vertices. The rules are consistent, rigorous, and provable. In 1888, mathematician Charles Hinton formalized the geometry and coined the word tesseract in his book, A New Era of Thought, giving the object its name and its place in scientific literature. What makes the tesseract so deeply unsettling is the gap between knowing and seeing.

[00:01:09]Mathematicians can describe it with complete precision. Computer models can render its three-dimensional shadow rotating on a screen, a shape called a Schlaggel diagram, a cube within a cube connected by warping edges. But no human mind can genuinely visualize the object itself. You can follow the logic. You cannot picture the reality. Salvador Deli understood the peculiar horror of this. In his 1954 painting Corpus Hyper Cubis, he depicted Christ crucified on an unfolded tesseract. Eight cubes arranged in a cross, the three-dimensional skin of a four-dimensional object spread flat like a dissected form. It was not an accident that Deli chose that shape for a painting about transcendence. The tesseract is not a speculation or a hypothesis. It is mathematically certain. The fourth spatial dimension follows every rule geometry demands.

[00:01:57]Equations describe it without contradiction. The dimensional scaling that gives a square four edges in a cube 12 gives a tesseract 32 and every number checks out. The problem is not the mathematics. The problem is us. Our brains evolved in three spatial dimensions. Perceiving three, navigating three. The testact exists in a space our cognition simply was not built to enter.

[00:02:20]We have built a perfect mathematical cage for something we cannot see. And the bars are made of numbers we cannot argue with. The tesseract is not a mystery in the sense of being unknown.

[00:02:29]It is a mystery in the deeper sense, fully described, entirely real by every mathematical standard and completely beyond human perception. That gap between description and experience is where the fourth dimension begins.

[00:02:42]Number nine, time is the fourth dimension. In 1905, a 26-year-old patent clerk in Baron published a paper that quietly dismantled the architecture of the universe. Albert Einstein's special theory of relativity did not merely correct Newtonian mechanics. It revealed that space and time were not separate independent structures as every physicist before him had assumed. They were woven together into a single four-dimensional fabric. The universe was not three dimensions moving through time. It was four dimensions, unified, inseparable, and stranger than anyone had imagined. The mathematician Herman Mancowski formalized Einstein's insight in a landmark lecture in 1908, declaring that henceforth space by itself and time by itself were doomed to fade into mere shadows and only a union of the two would preserve independent reality. This four-dimensional structure became known as spacetime. And it was not a metaphor.

[00:03:33]It was the actual geometry of the universe with time entering the equations as a genuine fourth coordinate distinct from the three spatial ones but mathematically bound to them in ways that produce measurable testable astonishing consequences. Those consequences are not theoretical curiosities. Every GPS satellite orbiting Earth must account for the effects of relativistic spacetime.

[00:03:55]Clocks aboard those satellites moving fast and sitting higher in Earth's gravitational field run at a different rate than clocks on the ground. Without continuous corrections based on Einstein's equations, GPS systems would accumulate positional errors of approximately 10 kilometers every single day. The four-dimensional geometry of spaceime is not a philosophical abstraction. It is encoded into the infrastructure of modern navigation. In 1971, the halflake heating experiment flew atomic clocks around the world on commercial aircraft and measured the exact time dilation Einstein's equations predicted. The clocks disagreed with stationary ones by precisely the calculated amount. The first direct detection of ripples in this four-dimensional fabric came on September 14th, 2015 when the LIGO Observatory registered gravitational waves produced by two black holes merging 1.3 billion lighty years away.

[00:04:47]Those waves were literal distortions in the geometry of spaceime, compressions and expansions of the four-dimensional structure passing through Earth at the speed of light. General relativity, Einstein's 1915 completion of his earlier work had predicted them exactly.

[00:05:02]If time is a genuine fourth dimension, then past and future moments are not events that happen and disappear. They are coordinates in a four-dimensional structure as fixed and as real as points in space. The present moment may be nothing more than our position moving through a geometry that already, fully, and permanently contains every moment that has ever happened or ever will.

[00:05:21]Whether that interpretation is correct is one of the deepest open questions in physics and we will return to it. Number eight, higher dimensional beings. Apply the logic of flatland to our own reality and the implications become genuinely disturbing. Abbott's two-dimensional square could not perceive the sphere passing through its world as a sphere.

[00:05:38]It perceived only the cross-section, a circle appearing from nothing, growing and vanishing. If a being with four spatial dimensions were to pass through our three-dimensional world, we would face exactly the same limitation. We would not see a four-dimensional entity.

[00:05:52]We would see a three-dimensional cross-section of one. An object that materializes without warning, shifts its shape as different parts of its four-dimensional body, intersect our space, and then disappears. The mathematics of this are consistent and precise. A four-dimensional hypersphere passing through three-dimensional space would appear to an observer as a sphere growing from a single point, expanding to a maximum size, then shrinking back to a point, and vanishing. No violation of physics. No special mechanism required, just geometry. Charles Howard Hinton explored these implications rigorously in his 1904 book, The Fourth Dimension, concluding that a four-dimensional being would have capabilities that would appear to any three-dimensional observer completely inexplicable. Physicist Miokaku has returned to this framework in his popular science work, noting that such a being would perceive our entire three-dimensional world simultaneously, including the interiors of sealed rooms, the insides of living bodies, and the contents of locked containers. What makes this more than philosophical speculation is the framework modern physics provides for it. String theory describes fundamental objects called brains, membranes of various dimensions embedded in a higher dimensional space.

[00:07:01]A three-dimensional brain can intersect our own three-dimensional space, producing effects that appear in our world without a visible cause. The object would not be invisible in the traditional sense. It would be present in a spatial direction we simply cannot look. Physicists call that additional direction the bulk. And within it, higher dimensional structures can exist, move, and interact with our space in ways that would produce exactly the kind of anomalous sourceless phenomena humans have reported throughout recorded history. The boundary between a higherdimensional being and what earlier cultures called a supernatural entity is mathematically non-existent. A four-dimensional being could appear inside a sealed room, see through walls, remove objects from locked containers, and vanish without trace. Not through any violation of physics, but through perfect compliance with the physics that include spatial dimensions we cannot access. The descriptions of divine appearances across ancient texts appearing from nothing, shifting form, departing without physical egress, match precisely what four-dimensional geometry would produce. What happens when the observation period ends is a question this framework raises but cannot answer.

[00:08:07]A four-dimensional being watching our world would have complete information.

[00:08:11]Perceiving us from an angle we cannot detect or defend against. Whether that possibility is unsettling or profound depends entirely on what such a being might want. Number seven, Kuza Klein theory and the hidden dimensions. In 1919, a relatively obscure German mathematician named Theodore Kuza did something that stopped Albert Einstein in his tracks. Kuza added a single extra spatial dimension to Einstein's equations of general relativity and discovered something that should not have been possible. When he worked through the mathematics of a five-dimensional universe, collapsing one dimension back down to four, two of the four fundamental forces of nature fell out of the same equation. Gravity and electromagnetism, forces that physicists had treated as entirely unrelated, were revealed as aspects of the same geometric structure. Einstein sat on the paper for 2 years before publishing it in 1921, troubled by how right it seemed. The obvious problem was immediate. If a fourth spatial dimension exists, where is it? Why can't we move through it, detect it, or measure it?

[00:09:13]Swedish physicist Oscar Klene answered that question in 1926 with a proposal that has shaped theoretical physics ever since. Klein suggested the extra dimension was not absent, but compactified, curled up so tightly on itself that it existed at a scale of approximately 10 to the power of - 33 cm. The plank length far below anything any instrument could ever probe. The combined framework became known as Kuza Klein theory and it introduced a concept that would eventually define modern theoretical physics. The idea that the universe contains extra dimensions too small to detect with current technology.

[00:09:47]That idea did not remain exotic. String theory, the leading candidate for a unified theory of all physical forces requires 10 spatial dimensions to be mathematically consistent. M theory, the framework that unified the five competing string theories in 1995 through the work of Edward Whitten requires 11. In both cases, the extra dimensions are compactified using exactly the mechanism Klein proposed.

[00:10:12]They are there. They are simply curled up too small to observe. The Large Hadron Collider at CERN was designed in part to look for evidence of these dimensions through the production of microscopic black holes that would signal gravitational leakage into the bulk. No such signal has been confirmed.

[00:10:28]Experiments have tested the behavior of gravity down to scales of approximately 50 micrometers, searching for deviations that would indicate it was leaking into extra dimensions. None have been found.

[00:10:38]But the absence of detection is not the same as absence. Kuza Klein theory makes a prediction so elegant it is difficult to dismiss. The reason two apparently unrelated forces share the same mathematical structure is that they are the same force viewed from different dimensional angles. That prediction has never been falsified. It simply hasn't been confirmed. The extra dimensions may not be absent from our universe. They may simply be curled up too tightly for anything we have ever built to unfold them, waiting at scales where our physics ends and something stranger begins. Number six, dark matter as a fourthdimensional phenomenon. Something is holding galaxies together that has no right to be there. In the 1970s, astronomer Vera Rubin and her colleague Kent Ford made a discovery that violated every expectation of Newtonian and Einsteinian gravity. Stars at the outer edges of spiral galaxies were orbiting their galactic centers far too fast. By every known gravitational law, they should have been flung into intergalactic space long ago. Instead, they held their orbits as if constrained by an invisible mass, something that provided gravitational force without emitting, absorbing, or reflecting a single photon of light. Physicists named it dark matter and it has refused to reveal itself ever since. Dark matter is estimated to constitute approximately 27% of the total energy content of the universe. More than 5 times the ordinary matter that makes up every star, planet and human being. It does not interact with the electromagnetic force. It is invisible across the entire spectrum from radio waves to gamma rays. It passes through ordinary matter without detectable interaction. Every direct detection experiment from deep underground laboratories to the detectors at the Large Hadron Collider has returned the same answer. Nothing.

[00:12:19]Whatever dark matter is, it is not a particle from the standard model of physics. As of 2025, no confirmed direct detection has been made. One of the most serious theoretical proposals currently under investigation reframes the question entirely. Rather than searching for a new particle within our universe, some physicists suggest dark matter may be ordinary matter existing on a parallel brain, a three-dimensional surface separated from our own in the higher dimensional bulk predicted by the Randall Sundrum models developed by Lisa Randall and Ramen Sunundrum at Harvard in 1999. In this framework, the matter on the neighboring brain interacts with ours through only one force, gravity, which unlike all other forces can propagate through extra dimensions. We feel its weight. We cannot see it, touch it, or detect it by any other means. The implications of this model are genuinely strange. If dark matter is matter on a parallel brain, then every galaxy in the observable universe has a twin. A dark counterpart of comparable mass occupying the same three-dimensional coordinates, but separated from us by a distance measured not in light years, but in the direction of a spatial dimension we cannot access. The gravitational entanglement between these two layers of reality would be real, measurable, and permanent. We are already feeling the gravitational pull of another universe.

[00:13:35]We just cannot see it. Could every galaxy be double? A visible version we can observe and a dark twin we can only feel separated from us by a dimension we cannot cross. The mathematics permit it.

[00:13:46]The observations are consistent with it and no experiment we have built can yet rule it out. Number five, the quantum realm and higher dimensional probability. In 1927, Verer Heisenberg published a paper that has disturbed physicists in every subsequent generation. At the quantum scale, particles do not have definite positions or velocities until the moment they are measured. Before measurement, they exist as probability waves smeared across multiple possible states simultaneously.

[00:14:13]This is not a limitation of our instruments. It is the actual condition of reality at the smallest scales. And the mathematical structure required to describe it is not three-dimensional. It is something far larger and far stranger. The quantum wave function describing a single particle requires three dimensions. Two entangled particles require six. 10 particles require 30. For any system of n particles, the wave function inhabits a mathematical space of three n dimensions. A structure called Hilbert space which grows without practical limit as the number of particles increases. The universe contains approximately 10 to the power of 80 particles. The mathematical space required to fully describe their quantum states has a dimensionality that dwarfs any number in ordinary comprehension.

[00:14:58]The question physicists cannot agree on is whether Hilbert space is a mathematical tool or a physical reality.

[00:15:04]In 1957, physicist Hugh Everett proposed what became known as the many worlds interpretation of quantum mechanics. In Everett's framework, every quantum event that can produce multiple outcomes produces all of them with reality branching into a new configuration at each measurement. Those branches are not metaphors. They are proposed as physically real coexisting in the higher dimensional wave function. The universe that appears singular and three-dimensional from our vantage point may be at the level of the full quantum description an incomprehensibly highdimensional structure containing every possible outcome of every quantum event that has ever occurred. Physicist Alan Asp and his team confirmed quantum entanglement experimentally in 1982, demonstrating that particles could affect each other instantaneously regardless of distance. a result Einstein had called spooky action at a distance and had spent years trying to disprove. The holographic principle developed by Gerard Tuft in 1993 and extended by Leonard Suskin in 1995 adds another layer. It proposes that the maximum information content of any region of space is proportional not to its volume but to its surface area. The interior is redundant. Everything happening in three-dimensional space can be encoded on the two-dimensional boundary surrounding it, suggesting the three-dimensional volume we inhabit is itself a kind of projection from a lower dimensional surface read out into apparent depth along what would function as a fourth dimension. Every quantum measurement you have ever witnessed may be a three-dimensional shadow of an event occurring in a space of incomprehensibly many dimensions. And the reality you experience may be the projected surface of something your mathematics can describe, but your senses will never reach. Number four, the multiverse and parallel brains. In 1995, physicist Edward Whitten stood before an audience at the University of Southern California and announced that the five competing versions of string theory were not five separate theories.

[00:16:59]They were five different perspectives on a single deeper framework. He called it M theory and it required 11 dimensions, 10 spatial and one temporal to be mathematically consistent. Six or seven of those spatial dimensions were compactified in the Kuza Klein sense, curled up below detectability. But the remaining dimensions allowed for something extraordinary. Large three-dimensional membranes called brains floating through a higher dimensional space called the bulk. Our universe in this framework is one such brain. And it is not alone. In 2001, cosmologists Paul Steinhard of Princeton and Neil Trock of Cambridge published a paper in science proposing the eerotic universe model. In their framework, the Big Bang was not a spontaneous creation event. It was a collision. Two parallel three-dimensional brains separated from each other by a tiny distance in the fourth spatial dimension drifted slowly together through the bulk and collided.

[00:17:52]The energy of that collision released into both brains simultaneously manifested in ours as the Big Bang. An explosion of heat, matter, and expanding space generated not from nothing but from contact with a neighboring universe separated from us by a gap in a dimension we cannot see. In this model, the Big Bang may not be unique. Brains can drift together and collide cyclically. Our universe may have been born many times. What makes this model particularly unsettling is the nature of the separation. The gap between our brain and its neighbors need not be vast. In some formulations, it could be as small as a millimeter in the extra dimension. An unimaginable proximity given that crossing it is physically impossible for anything governed by the standard model of physics. All electromagnetic, strong, and weak forces are confined to our brain. Gravity alone penetrates the bulk, which is why we might detect neighboring brains through their gravitational influence, but never directly observe them. A parallel universe could be a millimeter away in the fourth spatial dimension, and we would have no means of reaching it or seeing it, only of feeling its gravitational presence. Stephven Hawkings final scientific paper published in the journal of high energy physics in 2018 co-authored with Thomas Herthog proposed a mechanism for what they called a smooth multiverse drawing on higher dimensional physics to constrain the range of universes that could emerge from a quantum big bang.

[00:19:10]Even in his final work, Hawking returned to the framework of extra dimensions as the key to understanding why our universe has the properties it does. If the eperotic model is correct, the big bang, the defining creation event of everything we know, was caused by our three-dimensional universe colliding with another universe separated from us only by a distance in the fourth spatial dimension. And that neighbor may still be out there drifting, waiting for the next collision to begin everything again. Number three, the holographic universe. In 1997, theoretical physicist Juan Maldisena published a paper that would become by citation count the most referenced paper in the history of high energy physics, accumulating over 25,000 citations as of 2025. Its central claim was so counterintuitive that even physicists took years to absorb its full implications. Maldina demonstrated that a complete theory of gravity operating in a three-dimensional space is mathematically equivalent to a quantum theory with no gravity operating on the two-dimensional surface surrounding that space. The two descriptions are not approximations of each other. They are identical. They describe the same physical reality from different dimensional perspectives. The foundations for this had been laid decades earlier. In 1972, physicist Jacob Beaconstein showed that the entropy of a black hole, the measure of its internal information content, is proportional not to its volume, but to the area of its event horizon, its surface. This was the first serious hint that volume might be redundant, that the information needed to describe everything inside a region of space could be encoded on its boundary. Gerard at Huft formalized this into the holographic principle in 1993 and Leonard Suskin extended and popularized it in 1995. Maldecina's paper 2 years later provided the most rigorous mathematical proof that the principle actually worked in a specific well-defined physical context. In 2017, physicists at the University of Southampton published a paper in physical review letters, arguing that analysis of the cosmic microwave background, the faint thermal afterglow of the early universe showed as much statistical support for a holographic description of the big bang as for the standard inflationary model. Between 2012 and 2016, FELAB operated an instrument called the hometer, specifically designed to detect quantum holographic noise in the fabric of spaceime. fluctuations that would indicate our reality was being read out from a two-dimensional surface at the plank scale. The results were inconclusive but refine the experimental constraint significantly. If the holographic principle is correct, the three dimensions we experience, length, width, and height are emergent properties of information encoded on a two-dimensional boundary. The fourth dimension, depth into the bulk, is the direction from which our reality is being projected. We do not live in a three-dimensional universe that happens to exist inside a larger four-dimensional space. We live in a three-dimensional projection being generated by a two-dimensional surface we will never reach in a direction we will never be able to look. Every object, every person, every galaxy would be at the most fundamental level of physical description, a pattern on a surface. The fourth dimension is not a place beyond our reality. It is the direction from which our reality is being generated. And everything you have ever seen, touched, or known, is a shadow cast from a surface you will never reach. Number two, wormholes and fourthdimensional shortcuts. In 1935, Albert Einstein and his colleague Nathan Rosen were not trying to discover time travel or interstellar shortcuts. They were trying to fix an annoyance. The mathematics of general relativity produced a solution describing a black hole that seemed in the equations to connect through to a mirror region of spaceime. Einstein and Rosen treated it as a mathematical curiosity, a bridge between two sheets of space-time geometry that appeared in the algebra, but almost certainly had no physical meaning. They published it as a theoretical note and moved on. Decades later, physicists realized they had accidentally written the blueprint for a tunnel through the fourth dimension.

[00:23:09]Physicist John Wheeler named these structures wormholes in 1957. And the concept remained largely a theoretical amusement until 1988 when Kip Thorne of Caltech and his colleagues published a rigorous analysis in physical review letters examining whether a traversible wormhole, one that a person or signal could actually pass through, was permitted by known physics. Their conclusion was carefully worded but significant. Traversible wormholes were not ruled out. They would require exotic matter with negative energy density to hold them open against gravitational collapse. And such matter had never been confirmed to exist. But the Casmir effect, a measurable quantum phenomenon first observed experimentally in 1997, demonstrates that negative energy density is physically possible in small quantities confined between closely space conducting plates. The physics does not forbid it. A wormhole is not a tunnel through space in the ordinary sense. It is a fold in four-dimensional spaceime. A geometric configuration in which two distant locations in our three-dimensional universe are connected through the fourth dimension. The way two points on a flat sheet of paper can be made adjacent by folding the paper in a third dimension. The shortcut does not exist in the three spatial dimensions we navigate. It exists in the fourth. To travel through a wormhole would be to leave three-dimensional space entirely, pass through a geometry that has no location in our universe, and re-enter at a point that might be billions of light years away. The journey would take no time at all from the traveler's perspective because the path through the fourth dimension is shorter than any path through three-dimensional space. In November 2022, researchers at Caltech published a paper in nature describing a quantum simulation of a wormhole performed using Google's Sycamore quantum processor. Using nine cubits to represent a simplified gravitational system, they simulated the passage of quantum information through an Einstein Rosen bridge, demonstrating that the dynamics of the system were consistent with traversal through a wormhole geometry. The experiment did not create a physical wormhole. It simulated the physics of one in a quantum system and the results match the theoretical predictions precisely. The fourth dimension is not merely a space where things might exist. It is a space through which things might travel.

[00:25:18]Folding the geometry of our universe into shortcuts that make the distances between stars irrelevant and the mathematics say it is not impossible.

[00:25:25]Number one, you already exist in four dimensions. The most radical theory about what exists in the fourth dimension is not a theory about strange objects, parallel universes, or hidden brains. It is a theory about you. It follows directly from the same equations that gave us GPS satellites, gravitational waves, and the confirmed geometry of spaceime. It has been taken seriously by Roger Penrose, Brian Green, and Julian Barber, among the most rigorous physicists of the modern era.

[00:25:51]And if it is correct, then the question of what exists in the fourth dimension has only one answer. Everything.

[00:25:57]including every moment of your life, past and future, existing simultaneously, permanently, and completely in a four-dimensional structure that has no past and no future because it contains all of time at once.

[00:26:10]The argument follows from a specific consequence of special relativity called the relativity of simultaneity. Einstein demonstrated in 1905 that two observers moving at different velocities will disagree about which events in the universe are happening. Right now, there is no universal present moment. What is simultaneous for one observer is sequential for another depending entirely on their relative motion.

[00:26:32]Herman Minkowski formalizing this in 1908 concluded that the universe must therefore be understood as a static four-dimensional object with time as its fourth coordinate and the flow of time as an illusion produced by our movement through it. Physicist Julian Barber extended this to its logical conclusion in his 1999 book, The End of Time, arguing that the universe does not evolve through time. It simply is a four-dimensional structure containing every moment that has ever occurred or ever will with no privilege present, no genuine before or after, only position within a geometry that is already entirely and unchangeably complete. This interpretation is not fringe speculation. It is the literal reading of the mathematics taken seriously by mainstream physicists who have spent careers working with the equations.

[00:27:18]Brian Green described it in the fabric of the cosmos. In 2004, Roger Penrose has engaged with it in the road to reality and elsewhere. The philosophical name for it is eternalism. And in the framework of eternalism, the fourth dimension does not contain exotic objects from outside our universe. It contains every person who has ever lived, preserved at every moment of their existence, as fixed and permanent as a mountain range. Your childhood is not gone. It is a coordinate in four-dimensional spacetime as real as any point in space, unchangeable and present in the geometry of the universe.

[00:27:52]The moment of your birth exists, the moment of your death exists already. A fixed point in spacetime, whether or not you have reached it yet in your subjective experience of moving through the fourth coordinate. If the block universe is the correct interpretation of relativistic spacetime, then free will in the classical sense is geometrically impossible. Every decision you believe you are making is already a fixed point in four-dimensional spaceime as predetermined as the location of a star. Every conversation, every choice, every moment of joy or grief in every human life that has ever been lived is frozen into the structure of the universe, permanently present, permanently real, and permanently beyond any possibility of change. The dead are not gone. They are coordinates. The future is not unwritten. It is already written in a geometry your consciousness has not yet reached. The most terrifying theory about what exists in the fourth dimension is not that it contains parallel universes, higher dimensional beings or tunnels through space. It is that it contains you, every version of you, every moment you have lived and every moment you have yet to live permanently, simultaneously, and unchangeably. You have never moved through time. Time has always been complete. And somewhere in the fourth dimension, you are still there. If you want to see more videos like this, click the video on screen now and make sure to subscribe.