Humans and their environment are all made of atoms.
Atoms are 99%+ empty.
Yet we cannot pass through solid matter (walls), but we can easily go through air and (less easily) through liquids (water).
What is the real reason for these differences ? Is it linked to the structure of the matter (but how would “empty” matter “block” us) ? Are there other forces (electromagnetism?) involved ?
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When people ask this question, people like to give answers involving the Pauli Exclusion Principle and fermions, and those answers can all be correct, but I think it over-complicates things. We can answer this question quite simply. First, if you try to walk through a wall you will feel a force preventing it from happening. Thus, there must be some force preventing it. Second, in the universe there are only four forces: gravity, electromagnetism, weak nuclear and strong nuclear. We know the last two aren’t responsible – the weak nuclear force is responsible for some forms of radioactive decay and the strong nuclear force is what binds nuclei together.
So, there’s gravity. But that’s only an attractive force. When you try to walk through a wall and bounce off, that’s a force pushing you away from the wall. So, the only one left is electromagnetism. So, you are correct in your answer, there is a force involved, and it’s the one you guessed.
How does electromagnetism stop up from going through solid objects? Because while atoms are electrically neutral, the positive charges (the protons) are all at the center of the atom, and the negative charges (electrons) form the shell of the atom. As you get really close to a solid surface, like a wall, the electrons in you are closer to the electrons on the wall than they are the protons. And since like charges repel, you are repelled by the electrons pushing off each other.
You forget that we can push through solid matter. A knife works great at it. When you "cut" something it works by a harder substance pushing the softer matter out of the way.
The same principle is true with liquid and gas. You, a more solid substance, pushing another substance out of the way as you move through it.
Others have already mentioned the physical principles as to why atoms repel other atoms to prevent simply phasing through substances.
You misunderstand how we "pass through" air and liquids. It’s not the atoms passing through each other, it’s us pushing those materials out of the way. That’s why there is resistance when you try to swim or wade through water. The net/ball pit analogy the other commenter gives is useful. I’ll also point out that you can "pass through" solid matter in the same way as air and liquids, you just require sufficient force to push it out of the way. Think of the Kool-Aid Man crashing through a wall. Why this happens is related to intermolecular forces, which increase as you go from gas to liquid to solid. The more that the individual molecules of a material are held tightly together, the more it resists you pushing through it, the more force you need to push through it.
I think you might just be asking about density and states of matter…?
We aren’t walking through air or liquids. We are pushing those molecules out of the way. If you jump into a pool of water, you can see that the water splashes up into the air because you displaced it. Because of the fluidity of water, or I guess, H2O molecules’ ability to form bonds with each other, the water (that didn’t splash out of the pool) can re-bond to each other and, I guess maybe they way you are seeing it as, would still appear as the original object, which is water. That’s just because water (air, etc) molecules aren’t constantly forming bonds with each other and aren’t just building a rigid bond to one molecule and stays attached to that molecule.
Solid mass forms their bonds pretty rigidly. They stay attached to the molecule they bonded to. You could ‘walk through a wall’ the same way you walk through water- you would probably just call it ‘breaking through the wall’ though, and the wall doesn’t have the physical properties to bend itself back into a straight wall, or re-form their bonds to their original form to rebuild the wall.
Gasses and liquids are just always forming and breaking bonds with other molecules in that gas or liquid so it isn’t just ‘one thing’. You could pour a cup of milk into a cup of water and it just becomes a cup of watered down milk. If you put a brick on a table, you don’t have this bricky-table mix that has become one solid object, it is still just a brick on a table.
You can ‘walk through water’, but you can’t walk through a sheet of ice, even though its the same ‘material’, if that makes sense.
Because the amount of energy you’d need is going to destroy the material. You can’t simply run that much energy in direct contact and expect the material to not react in any way. Electrical forces are long distance, it doesn’t matter how much space there is that you call empty.
You don’t go through anything. When you walk through Air, you push it away. But you are occupying a vacuum. If you disappear suddenly, the place where you stood will be temporarily a vacuum. The same goes for water.
You will not be able to push away a solid matter like a wall. But if you convert the wall into dust, you can perhaps push through it.
I think what you’re talking about is your molecules passing through another object’s molecules. Or the space in between them. The nuclear forces that hold your molecules together will prevent that from happening. If we can convert ourselves to a gas, we can permeate through some matter, but our bodies will not be bodies anymore.