Nothing Is Solid
Put your hand flat on a table. Feel the resistance. The solidity. The table pushes back against your palm and you experience that as contact between two solid surfaces.
No part of that description is accurate.
Your hand never touched the table. The atoms in your skin and the atoms in the table never made contact. What you are feeling is the electromagnetic repulsion between electron clouds: the electrons in your hand and the electrons in the table pushing back against each other across a gap that, at the atomic scale, is enormous. Matter is mostly empty space, and what we experience as solid is the force that keeps two mostly-empty things from passing through each other [1, 2].
The table is not there the way it feels like it is. Nothing is.
Solidity is not a property of matter. It is a property of the forces between matter, experienced by a nervous system that never evolved to notice the difference.
What an atom actually looks like
The standard model of an atom places the nucleus at the center and electrons in a cloud around it. If you scaled a hydrogen atom so that the nucleus was the size of a marble, the electron cloud would extend roughly a kilometer out [3]. Between the marble and the kilometer-wide cloud: nothing. No matter. Just the fields that structure the atom's behavior.
This is not empty in the way a room is empty. It is empty in the way that space is empty. And yet this emptiness is what everything is made of. Every object you have ever touched. Every surface you have ever walked on. The body doing the touching and the walking. All of it is this: nuclei separated by vast relative distances, held in relation by forces, with almost nothing in between.
The reason objects feel solid is not that matter is packed tightly together. It is that the electromagnetic force is strong enough to prevent matter from interpenetrating, and our nervous systems are calibrated to register that force as resistance, which we interpret as surface, which we call solid [2, 4].
Why this does not make things less real
The obvious response to this is that the solidity still works. The table holds the coffee cup. Your body does not pass through the floor. The forces are real even if the solidity is not what you thought it was.
This is correct, and it matters. The unreality of solidity is not an argument that the world is an illusion. It is a more specific claim: that the categories your nervous system imposes on physical reality, the most basic ones, solid and not solid, touching and not touching, here and there, are models the brain uses to navigate, not accurate descriptions of what is actually happening at the level where physics operates [4, 5].
The map works. The map is not the territory. Both of those things are true at once, and confusing them is the source of a consistent category error about what kind of thing the physical world is.
The structure underneath the solidity
What is actually there, underneath the experience of solidity, is fields and forces and the probabilistic behavior of particles [1, 3]. The electron cloud around an atom is not a fixed shell. It is a probability distribution: a description of where the electron is likely to be found if you look for it. The electron does not orbit the nucleus the way a planet orbits a star. It exists as a smeared-out possibility that collapses into a location only when measured.
This is not comfortable physics. It does not match the world of solid objects and clear surfaces that your nervous system presents to you. But it is what the experiments keep confirming, at every scale where we have been able to look carefully enough.
The world at the level of physics and the world at the level of experience are both real. They are descriptions of different layers of the same thing. The error is assuming that the experiential layer, the one with solid surfaces and touching hands, is the foundational one.
It is not. It is the useful one. That is different.
The point
Your hand on the table is a genuine experience. The resistance is real. The warmth is real. The texture is real. What is not real is the model underneath those experiences: the idea that two solid things are making contact at a surface.
What is actually happening is that two mostly-empty structures of fields and probabilities are influencing each other across a gap, and your nervous system is reporting that influence as the feeling of solid contact because that report is useful for navigating a world where you need to know when things will hold your weight and when they will not.
The world is stranger than the model. It always is. The model is what you have to live in. Understanding that the model is a model, and not the thing itself, is where the work begins.
Sources
- Feynman, R. P., Leighton, R. B., & Sands, M. (1963). The Feynman Lectures on Physics, Vol. II. Addison-Wesley. On electromagnetic forces, atomic structure, and the physical basis of what we experience as solidity.
- Close, F. (2009). Nothing: A Very Short Introduction. Oxford University Press. On the emptiness of matter and the forces that make empty matter behave as if it were solid.
- Ohanion, H. C. (1987). "What is spin?" American Journal of Physics 54(6): 500-505. On atomic scale structure and the relationship between quantum descriptions and classical experience.
- Eddington, A. S. (1928). The Nature of the Physical World. Cambridge University Press. The original account of the "two tables" problem: the solid table of experience and the mostly-empty table of physics.
- Heisenberg, W. (1958). Physics and Philosophy: The Revolution in Modern Science. Harper. On the gap between the quantum description of reality and the classical world of ordinary experience.