Hold a small magnet over a paperclip and let it jump up into your hand. In that trivial moment, you have just witnessed one of the deepest mysteries in physics. A magnet weighing a few grams overcomes the gravitational pull of the entire planet beneath it — six trillion trillion kilograms of Earth — without effort. The electromagnetic force in that little magnet is so overwhelmingly stronger than gravity that the contest is not even close. Just how not-close is almost impossible to picture: gravity is weaker than the strong nuclear force by a factor of ten thousand trillion trillion trillion — 10⁻⁴¹. Written out, that is a decimal point followed by forty zeros and a one. It is the largest unexplained number in physics, and it has a name: the hierarchy problem.
Conventional physics, operating in the three spatial dimensions we can see, has no explanation for it. Gravity is just weak, the textbooks effectively shrug. But “it just is” is not an answer a physicist can love. And in the last few decades, two very different lines of thinking have emerged that refuse to accept it — each by questioning something we normally take for granted about the structure of reality itself.
Randall-Sundrum: Gravity Is Not Weak, It Is Diluted
The first comes from the physicist Lisa Randall and her collaborator Raman Sundrum. Their proposal begins with a startling reframing: what if gravity only appears weak to us because we are seeing just a fraction of it?
Our entire observable universe — every star, every atom, every photon of light — is confined to a three-dimensional membrane. Randall calls it the brane. Think of it as an infinitely thin sheet, our isolated pocket of reality. But this brane is not all there is. It is suspended inside a larger, higher-dimensional space called the bulk — possibly infinite in extent, utterly invisible to us, because everything we are made of is stuck to the brane like a drawing on the surface of a soap bubble.
Here is the crucial move. The other three forces — electromagnetism, the strong force, the weak force — are trapped on the brane along with everything else. But gravity is special: in this model, gravity alone can escape the brane and spread out into the enormous volume of the bulk. When you measure gravity here, you are not measuring its true, full strength. You are measuring only the small fraction that remains on our membrane — the rest having leaked away into dimensions you cannot see.
Gravity is not weak. Its strength is simply diluted across higher dimensions we cannot perceive. The weakness is not a property. It is a geometric illusion.
The structure of the explanation is what matters. An anomaly that looked like a brute fact of nature — gravity is just absurdly weak, no reason given — dissolves into geometry. What appeared fundamental (the weakness of gravity) turns out to be emergent: a surface effect produced by a deeper structure. Randall keeps spacetime itself intact and fundamental, but reveals that one of its most puzzling features is an illusion generated by hidden architecture. And this is not idle speculation: the model predicts specific heavy particles — Kaluza-Klein gravitons — that would be signatures of the extra dimensions. Run 3 of the Large Hadron Collider at CERN is actively searching the energies where they might appear. As of 2026 they have not been found, and the model remains a beautiful, falsifiable, still-open idea.
Baron: The Deeper, More Unsettling Move
Randall questions how many dimensions reality has. The philosopher Sam Baron questions something more radical: whether spacetime is fundamental at all.
The setup is the great unfinished business of twentieth-century physics. General relativity describes gravity as the curvature of spacetime and triumphs at large scales. Quantum mechanics rules the microscopic world but has almost nothing to say about gravity. At the smallest scales — the Planck scale — general relativity breaks down and quantum mechanics takes over. The two most successful theories in the history of science flatly contradict each other, and in many attempts to reconcile them, spacetime simply dissolves.
For decades, the favoured escape has been emergence. Spacetime, the hope goes, is not fundamental — it emerges from a deeper quantum substrate, the way temperature emerges from the motion of molecules. Perhaps spacetime is a high-level description of some underlying quantum reality that has no space and no time in it at all. Baron’s objection is deceptively simple and, once seen, hard to unsee: every explanation of emergence we know how to give secretly relies on spacetime to do the explaining.
When a physicist says spacetime “emerges from” a deeper layer, the phrase emerges from already smuggles in time. When they say the substrate “gives rise to” spacetime, that is a causal claim, and causation requires temporal order. When they describe the substrate as an arrangement of quantum fields, arrangement requires space. Every tool we have for explaining emergence is built out of the very spacetime we are trying to explain. We need spacetime to explain how spacetime emerges — and that is circular in a bad way. If the circularity is genuine, the emergence project cannot succeed on its own terms, and we are left with a radical conclusion: spacetime, as Einstein described it — that four-dimensional fabric weaving space and time into one structure — may not fundamentally exist.
The Question Underneath Both
Place the two ideas side by side and a single question comes into focus — the one that organises this whole approach to physics. What is actually fundamental, and what only appears to be?
Randall takes an observable anomaly — gravity’s weakness — and dissolves it by positing a deeper geometric structure. This is the classic and powerful move of physics: explain the surprising surface by uncovering the hidden depth. Baron then turns the same move on physics itself and asks the vertiginous follow-up. If surface features emerge from deeper structure, and that structure emerges from something deeper still — at what point do we hit something that does not presuppose space and time to describe? And if the answer is “never,” then perhaps space and time are not where the explanation bottoms out. Perhaps they are near the top.
What It Means
“Fundamental” is doing more work than we usually notice. We move through a world of apparently solid foundations — three dimensions, forces with fixed strengths, space and time as the fixed stage on which everything happens. Both of these ideas suggest the stage itself may be a prop. Randall shows that a quantity we treat as a fundamental constant — gravity’s strength — could be a geometric accident of dimensions we cannot see. Baron shows that the stage itself — spacetime — might not be fundamental at all. The lesson is methodological: be suspicious of anything called fundamental until you have asked what it might be emergent from.
Randall and Baron are not really opponents. They are the same instinct at two depths — explain the surface anomaly through hidden structure — with Baron applying it one level down, to spacetime itself. And when a serious philosopher and a serious physicist independently arrive at “the thing that is fundamental is not a thing in space and time,” they are standing where contemplatives and metaphysicians have stood for millennia. This rhymes exactly with the argument that the immaterial is the real substrate of the world: if what is truly fundamental is not a thing in space but something that generates space, that is structurally the pantheist and Schopenhauerian intuition — the Will as the thing-in-itself, beyond space and time. Physics, approached at its foundations, keeps arriving at the doorstep of metaphysics. That is not a defeat. It is the point.
Flight Log — Dispatch from Altitude
Every instrument in my cockpit shows me an emergent reality, not a fundamental one. The attitude indicator shows a little aircraft on an artificial horizon — but there is no little aircraft and no line in the sky. It is a representation, generated from gyroscopes sensing forces I cannot feel. The altimeter shows a number in feet — but the aircraft does not know what a foot is; the instrument is inferring height from air pressure, which is itself a statistic over countless molecules. Everything I navigate by is a high-level display emerging from a deeper layer I never directly see.
And here is the thing every instrument pilot learns, sometimes the hard way: the display can be real and useful and trustworthy — and also not be the underlying thing itself. When I fly into cloud and lose all outside reference, my inner ear lies to me. My bodily sense of “which way is up” — which feels utterly fundamental — turns out to be an emergent guess that can be catastrophically wrong. I have to trust the instruments precisely because the thing that feels most fundamental, my own sense of space and orientation, is revealed to be a construction.
This is why Randall and Baron do not unsettle me the way they unsettle some people. I spend my working life acting on the knowledge that the world I directly perceive — up and down, level and turning — is an emergent display, not the bedrock. Randall says gravity’s strength is a display generated by hidden dimensions. Baron says space and time themselves may be a display generated by something deeper. A pilot’s instinct says: of course they might be. The thing that feels most solid is usually the thing most worth questioning.
At 38,000 feet in solid cloud, I am a living demonstration of the thesis. My sense of space is emergent and fallible. The instruments reach past it toward something more fundamental. Physics is now saying the same about the universe. What feels fundamental may be the display. The real foundation is in the layer beneath — and we are still learning to read those instruments.