Have you ever watched a movie where someone just strolls through a solid wall as if it were a curtain? Characters like Vision from Avengers or Harry Potter running through Platform 9¾ make it look so easy. Sadly, in real life, trying that trick would just give you a sore nose and a whole lot of explaining to do at the emergency room.
But here’s the puzzle: if atoms—the building blocks of everything—are mostly empty space, why does solid matter feel so… solid? Why can’t we just glide through walls like in the movies?
The answer lies in two key principles of physics that hold our universe together: electrostatic repulsion and the Pauli exclusion principle. Together, these invisible forces are what keep you from walking through walls, and they explain why the world doesn’t collapse into one big cosmic mush.
Atoms Are Mostly Empty—So What’s Stopping Us?
Every object you see—your phone, your hand, the wall in front of you—is made of atoms. And most of an an atom is, surprisingly, empty space.
Imagine scaling an atom up to the size of a football stadium. The dense nucleus, made of protons and neutrons, would be like a tiny marble sitting on the 50-yard line. The electrons, which carry negative charges, would be buzzing far away near the stands. Everything else? Empty void.
So why can’t your hand slip through a wall the same way a cloud drifts past another?
Read more: Physicists Finally Catch ‘Free-Range’ Atoms in Action—Confirming A 100-Year-Old Quantum Theory
The Quantum Twist: Electrons Don’t Orbit Like Planets
You might have learned in school that electrons orbit the nucleus like planets around the sun. But quantum mechanics flips that idea on its head.
Electrons don’t follow neat paths. Instead, they live in probability clouds—blurry zones where the electron is most likely to be found. Think of it like a hazy mist wrapping the nucleus instead of a tidy orbit.
This cloud isn’t just decoration—it’s negatively charged. And since like charges repel, when the atoms in your hand approach the atoms in a wall, their electron clouds push back.
Force Field Alert: Electrostatic Repulsion
That pushback is called electrostatic repulsion (or electromagnetic repulsion). It’s the same principle you feel when you try to push two magnets together at the same pole—they refuse to meet.
When you lean on a wall, your atoms and the wall’s atoms are exchanging electromagnetic forces through their electrons. These forces stop the two sets of atoms from merging, creating the sensation of solidity.
Without this repulsion, everything would collapse like a cosmic pancake.
The Pauli Exclusion Principle: Nature’s “No Sharing” Rule
As if electrostatic repulsion weren’t enough, nature throws in a second rule: the Pauli exclusion principle.
This principle says that no two particles called fermions (like electrons) can occupy the same quantum state at the same time. In plain English: two electrons can’t share the same spot in space under the same conditions—ever.
So when the electron clouds of your hand and the wall start to overlap, Pauli’s rule steps in and says, “Nope, not happening.” This restriction is non-negotiable. Without it, atoms wouldn’t just bump into each other—they’d collapse into a dense mess.
Why We Feel Solids as Solid
Together, electrostatic repulsion and Pauli exclusion form an invisible armor around every object. They prevent atoms from stacking on top of each other and give matter its rigidity.
Even in liquids and gases, where atoms have more wiggle room, these principles still apply. They just stop atoms from overlapping completely, allowing fluid motion instead of total fusion.
So the next time you put your coffee mug on a desk without it sinking through, thank these two principles for holding your world together.
Read more: After Half a Century, Scientists Finally Catch The Elusive ‘Ghost Particles’
Could Quantum Tunneling Let Us Walk Through Walls?
Okay, so we can’t walk through walls in the classical sense. But quantum mechanics loves to throw curveballs, and here’s one: quantum tunneling.
Particles like electrons behave as both particles and waves. When a wave hits a barrier, classical physics says it should bounce back. But in the quantum world, the wave doesn’t just stop—it fades inside the barrier, like an echo disappearing in the distance.
If the barrier is thin enough, the wave might even peek out the other side, meaning the particle has a small chance of appearing there. This process is called quantum tunneling.
This isn’t sci-fi. Tunneling makes technologies like scanning tunneling microscopes and nuclear fusion in stars possible.
So, Could You Tunnel Through a Wall?
Theoretically, yes. Practically? Absolutely not. The probability of every atom in your body tunneling through a wall simultaneously is beyond minuscule—about 1 in 10^(10^30). That’s a one followed by billions of billions of zeros.
Even if you waited longer than the lifetime of the universe, your chances wouldn’t improve much. As physicist Steven Rolston says, “It’s about as close to zero as you can get, but it’s not zero.”
So if you’re planning to ghost through your front door, you might want to grab a snack—you’ll be waiting forever.
Read more: Strange New Quantum ‘Species’ Discovered in Lab—And It’s Unlike Anything Seen Before
The Big Picture: Why This Question Matters
At first glance, asking “Why can’t we walk through walls?” might seem like a playful, even absurd question—something you’d ask in a science-fiction forum or a late-night conversation with friends. But peel back the layers, and you’ll find this question touches on the very fabric of reality.
It’s not just about walls. It’s about why the universe works the way it does. It’s about what keeps matter stable, why stars shine instead of collapsing into dark voids, and why life—our life—can exist at all.
If the laws of physics were even slightly different—if electrons didn’t repel each other or if Pauli’s rule didn’t forbid overlapping states—the world would be unrecognizable. Atoms could stack on top of each other without limit, and everything around us would compress into an unimaginably dense lump. Planets wouldn’t hold their shape. Your desk wouldn’t exist as a desk—it might not exist at all.
In other words, the simple fact that you can’t walk through a wall is not an inconvenience; it’s a feature of a universe that values order over chaos. These invisible principles—electrostatic repulsion and the Pauli exclusion principle—are the guardians of structure. They’re the unsung rules that allow complexity to flourish, from the delicate lattice of crystals to the spiral arms of galaxies.
