The Universe Contains More Than We See
Nov 9, 2026
By Sasha Alex Lessin, Ph.D. (Anthropology, UCLA)
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For thousands of years, people watched objects fall, stars move, lightning strike and magnets attract iron. They explained these events, sometimes by invoking gods, spirits or invisible agencies.
Modern physics replaced many of those explanations with mathematical descriptions of the forces that govern matter and energy. Yet its discoveries introduced mysteries as astonishing as anything earlier generations imagined. Why does gravity, which holds planets in orbit and binds galaxies together, appear so weak compared with the other fundamental interactions?
Could the universe contain extra spatial dimensions our senses cannot perceive? Might the particles we regard as fundamental arise from the vibrations of tiny strings? And could our familiar universe occupy only a small portion of a larger, multidimensional reality?
Three prominent theoretical physicists have brought these questions to public attention: Michio Kaku, Brian Greene and Lisa Randall. Kaku has explained the quest to unify the laws of physics. Greene has developed and popularized string theory and the mathematics of extra dimensions. Randall, a Harvard theoretical physicist, has investigated how extra dimensions might explain gravity’s weakness. Their research invites us to reconsider the boundaries of the physical universe without assuming that every mathematically possible world exists.
“Could our familiar universe occupy only a small portion of a larger, multidimensional reality?”
Four Fundamental Interactions Govern the Physical World
Modern physics describes four fundamental interactions: gravity, electromagnetism, the strong nuclear interaction and the weak nuclear interaction.
Gravity attracts matter, shapes planetary orbits and influences the evolution of stars and galaxies. Electromagnetism governs light, electricity, magnetism, chemical bonding and much of the behavior of matter we encounter in daily life.
The strong interaction binds quarks into protons and neutrons and, through its residual effects, holds atomic nuclei together. The weak interaction drives radioactive decay and the nuclear processes essential to stellar evolution.
These interactions differ enormously in strength and range. Comparing them requires care, because their effects depend on energy, distance and the particles involved.
Gravity
Gravity rules the motion of planets and galaxies, yet at the scale of elementary particles it is feeble. A small magnet can lift a steel paper clip against Earth’s pull. This familiar demonstration reveals a profound disparity.
Why should gravity be so much weaker than electromagnetism? One possibility holds that gravity differs at its root. Another suggests that our measurements reveal only part of its behavior because the universe has a structure we have yet to detect. This second possibility helped motivate Lisa Randall’s work on extra dimensions.
Michio Kaku: The Search for a Unified Theory
Michio Kaku has devoted much of his career as a science communicator to the possibility that the separate laws of physics belong to a deeper, unified framework.
In the nineteenth century, James Clerk Maxwell demonstrated that electricity and magnetism are two aspects of a single electromagnetic field. In the twentieth century, physicists developed the electroweak theory, which unites the electromagnetic and weak interactions in a common mathematical description. These successes suggested further unification might be possible, but gravity resisted reconciliation with quantum theory.
Einstein’s general relativity describes gravity as the curvature of spacetime. Matter and energy shape that curvature, and curved spacetime determines how objects move. Quantum mechanics, by contrast, describes microscopic phenomena through quantum states, probabilities and interactions.
General relativity and quantum mechanics have each passed demanding experimental tests in their own domains. Yet physicists have not yet established a complete, experimentally confirmed quantum theory of gravity.
Kaku Strings Us Along
Kaku championed string theory as one candidate for such a theory. Instead of describing every elementary particle as a dimensionless point, string theory proposes that the most fundamental objects may be tiny, extended strings. Observers see different vibrational states as different particles.
The analogy resembles a musical instrument: one string produces different notes depending on how it vibrates. The theory’s strings, though, are mathematical objects whose quantum behavior may generate the whole particle spectrum. A string’s spectrum can contain a massless spin-two state with the properties expected of a graviton, the hypothetical quantum carrier of gravity. In this way string theory bridges quantum mechanics and gravitation, and nature’s many apparent distinctions emerge from fewer underlying principles.
Such unification would still leave biology, psychology, and society to be explained at their own levels of organization. Fundamental laws constrain matter’s behavior, while complex systems demand their own accounts.
“One string produces different notes depending on how it vibrates.”
Brian Greene: Particles May Be String Vibrations
Brian Greene, a theoretical physicist at Columbia University, has helped readers without advanced mathematical training understand string theory. His book The Elegant Universe introduced the idea that familiar particles represent different vibrational patterns of fundamental strings.
In ordinary quantum field theory, electrons, quarks, photons and other particles are excitations of their corresponding fields. String theory replaces pointlike fundamental objects with strings whose vibrations may produce particles with different masses, spins and interactions. A single fundamental type of object might account for much of the particle-world diversity.
The catch: the relevant scales may lie far beyond the reach of present particle accelerators. Different mathematical configurations can also yield different low-energy universes, making unique predictions difficult.
Greene’s explanations also show how extra dimensions enter the mathematics. We experience three large spatial dimensions: length, width and height. Relativity adds time, forming four-dimensional spacetime. Superstring theories generally require ten spacetime dimensions, and M-theory requires eleven.
We miss the extra spatial dimensions because, in string theory, they curl up into structures too small for ordinary experiments to resolve. These hidden dimensions form intricate spaces whose shapes determine which particles exist, how strongly they interact and what physical laws emerge at accessible energies.
M-Theory: A Larger Framework
During the 1990s, physicists discovered mathematical relationships among several previously distinct string theories. These relationships suggested that the different theories might represent limiting cases of a single framework, M-theory.
M-theory involves eleven-dimensional spacetime and objects that extend across different numbers of spatial dimensions. Physicists call these objects branes, short for membranes. A string extends in one spatial dimension, a membrane in two, and higher-dimensional branes in more.
In some models, our observable universe forms a brane embedded in a higher-dimensional space called the bulk. Gravity can travel through the bulk while familiar matter and the other interactions remain confined to the brane. Because gravity behaves differently across dimensions, its apparent weakness in our world might reflect higher-dimensional geometry rather than a tiny gravitational interaction. In this picture, says Greene, the universe we observe sits inside a larger structure.
“The universe we observe sits inside a larger structure.”
Randall Explains Why Gravity Appears So Weak
Lisa Randall and Raman Sundrum published two influential papers in 1999 exploring how an extra spatial dimension could affect gravity. Their models involve a warped extra dimension.
In general relativity, spacetime geometry affects physical measurements, trajectories, and gravitational behavior. Randall and Sundrum investigated how a particular higher-dimensional geometry could generate dramatic differences between physical scales. In their original two-brane scenario, a warp factor produces an enormous hierarchy between the characteristic gravitational scale and the much smaller energy scale of familiar particle physics. Their second model showed that four-dimensional gravity can emerge even when the extra dimension extends without limit rather than curling up into a small circle. Together, these papers showed that gravity’s apparent weakness might have a geometrical explanation.
Instead of asking only why gravity has such a small coupling at accessible energies, physicists can ask whether that coupling emerges from the structure of a larger spacetime. The geometry affects how gravitational fields behave and how observers confined to an effectively four-dimensional world measure them.
Randall’s work established extra-dimensional gravity as a serious subject for theoretical investigation. It inspired proposals for departures from ordinary gravitational behavior and for new particle-like excitations of higher-dimensional fields. Experiments have yet to confirm the Randall–Sundrum models as descriptions of our universe. Still, their significance lies in demonstrating that gravity’s weakness could arise from geometry.
Does Gravity Leak Into Other Dimensions?
The phrase “gravity leaking into other dimensions” describes gravitational fields extending into dimensions that ordinary matter cannot reach in the same way. Gravitational theories involve mathematical relationships among spacetime curvature, field behavior, and the distribution of matter and energy. Different extra-dimensional models predict different physical effects: some involve large extra dimensions, others warped geometries, and still others additional fields or particles.
How Could Scientists Test the Idea?
Researchers have three main lines of attack:
- Measure gravitational attraction at tiny distances to see whether it departs from the behavior established theories expect.
- Search particle collisions for unexpected resonances, missing energy or other signatures particular models predict.
- Use astronomical observations to constrain theories involving additional gravitational fields or particles.
The Large Hadron Collider has searched for signs of extra dimensions, but no confirmed discovery has established that they exist. That absence still leaves many extra-dimensional models standing; it means scientific confidence must stay proportional to the evidence.
Dark Matter: Another Invisible Component of the Cosmos
Dark matter entered modern astrophysics because galaxies and galaxy clusters showed gravitational effects that visible matter alone could not explain within the standard cosmological framework. Stars orbit galaxies at speeds that imply a gravitational pull from more matter than astronomers can observe directly. Gravitational lensing, the bending of light by mass, provides further evidence of an unseen gravitational component. The large-scale distribution of galaxies and cosmic microwave background measurements also support the existence of substantial nonluminous matter.
The standard cosmological model attributes about 85 percent of the universe’s matter to dark matter. Because matter as a whole makes up less than a third of the cosmic energy budget, dark matter’s share of that total runs smaller, about 27 percent. Its microscopic identity remains unknown.
Randall has investigated whether dark matter has a richer structure than the simplest models assume. She explored the idea that a fraction of dark matter interacts with itself and forms a thin disk within our galaxy. Her approach models a principle: when researchers encounter something invisible, they need not assume it lacks structure. They can formulate models, derive predictions and compare those predictions with observations.
Could Dark Matter Affect Life on Earth?
In her book Dark Matter and the Dinosaurs, Randall explored a speculative connection between dark matter, the solar system’s motion through the Milky Way and disturbances in distant comet populations. She proposed that a dark-matter disk could influence the trajectories of objects in the outer solar system. Gravitational perturbations might send some of those objects toward the inner solar system, and one may have struck Earth 66 million years ago, ending the reign of the dinosaurs.
Our planet participates in a galaxy whose structure shapes its motion, even when much of that structure remains invisible.
“Our planet participates in a galaxy whose structure shapes its motion, even when much of that structure remains invisible.”
The Human Body, Gravity and the Question of Portals
Gravity, electromagnetism, and nuclear interactions all act on the human body; its atoms, molecules, tissues, and organs operate within the physical universe. Some theoretical models propose extra spatial dimensions or undiscovered particles and interactions. Imagine microscopic portals near the occiput, the region at the back of the skull, connecting the body to those extra dimensions.
Human bodies function on Earth because biological systems evolved under Earth’s gravity and because molecular interactions support metabolism, sensation, movement and reproduction. Gravity contributes to body weight, circulation, balance, posture and the mechanical demands on muscles and bones. Yet the body’s ordinary functioning requires no mechanism that strengthens gravity to match the other interactions. Gravity’s weakness forms part of the environment in which life developed.
Can the Fundamental Forces Be Unified?
Maxwell’s electromagnetic theory demonstrated that different-looking phenomena can arise from a single mathematical structure. The electroweak theory provided another major advance. The Standard Model describes the electromagnetic, weak, and strong interactions through quantum field theory, but it lacks a complete quantum description of gravity. String theory attempts to close this gap with extended fundamental objects, and M-theory suggests that the various string descriptions belong to a larger mathematical structure.
Geometry may account for the observed relationships among fundamental physical scales. To succeed, any such theory must explain established observations and produce predictions that distinguish it from competing models.
The search continues because the open questions run deep:
- What is spacetime at the smallest scales?
- Does spacetime emerge from something deeper?
- Why do particles possess their observed masses and interactions?
- Why does our universe exhibit the particular physical constants scientists measure?
- Why is gravity so weak compared with the other interactions at accessible energies?
These questions connect the smallest known physical scales with the largest structures in the cosmos.
From Invisible Dimensions to Human Cooperation
The history of physics shows how intellectual cooperation can transform understanding. Maxwell built on earlier discoveries about electricity and magnetism. Einstein developed relativity on mathematical and experimental foundations other scientists laid. Quantum theory emerged through the contributions of many researchers, often working across national and institutional boundaries. Modern particle physics depends on international collaborations, shared instruments, competing hypotheses and independent verification.
Science thus offers a model of partnership: individuals contribute distinct skills to a common investigation, challenge one another’s assumptions and refine their explanations through evidence. Competition can stimulate discovery, but the enduring results depend on collective testing and criticism.
The work of Kaku, Greene and Randall illustrates this pattern. Their theories concern phenomena no human can observe with unaided senses. They use mathematics to investigate possibilities beyond ordinary perception, yet their explanations remain accountable to the observable universe.
A society can encourage creative speculation without treating every speculation as established truth. It can recognize intellectual differences without requiring domination by a single authority. And it can value cooperation without demanding that all participants agree.
“A society can value cooperation without demanding that all participants agree.”
The Universe May Be Larger Than Our Senses Reveal
We live in a world that appears to possess three spatial dimensions. We experience gravity as the force that gives us weight, makes objects fall and keeps the Moon in orbit around Earth. Yet atoms contain quantum fields and particles that behave radically differently from familiar objects. Spacetime curves. Light behaves as both a wave and a stream of quanta. Most of the matter astronomers infer emits no detectable light. Some mathematically consistent theories describe dimensions beyond those we experience.
The question is which possibilities describe the universe we inhabit. Kaku’s pursuit of unification, Greene’s investigations of strings and extra dimensions, and Randall’s warped-spacetime models show how scientists can explore seemingly impossible ideas while staying committed to mathematical rigor.
Future experiments may reveal new dimensions. Gravity may have a deeper structure that current theories only partly describe. Researchers may discover particles or interactions that transform our understanding of dark matter. Science stays open to all these outcomes, and today’s theories will give way to better explanations as evidence arrives.
The universe remains open to investigation. The most productive response to its mysteries is neither unquestioning belief nor automatic dismissal. It is sustained curiosity, rigorous inquiry and cooperation in the search for evidence.
Source broadcast: Exploration, KPFA/Pacifica Radio, November 7, 2017.
References
- Randall, Lisa, and Raman Sundrum. (1999). “A Large Mass Hierarchy from a Small Extra Dimension.” Physical Review Letters, 83, 3370–3373.
- Randall, Lisa, and Raman Sundrum. (1999). “An Alternative to Compactification.” Physical Review Letters, 83, 4690–4693.
- Greene, Brian. (1999). The Elegant Universe: Superstrings, Hidden Dimensions, and the Quest for the Ultimate Theory.
- Randall, Lisa. (2005). Warped Passages: Unraveling the Mysteries of the Universe’s Hidden Dimensions.
- Randall, Lisa. (2015). Dark Matter and the Dinosaurs.
- Kaku, Michio. (2021). The God Equation: The Quest for a Theory of Everything.
- Kaku, Michio. Exploration, KPFA/Pacifica Radio, November 7, 2017. Radio broadcast.
- WIRED. Lisa Randall: Atoms Make Up Only 5 Percent of Our Universe. Video.
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