If atoms are 99.9% empty space, how do we interact with things?

Answer 1

Electrostatic interactions.

Take two magnets and set them up so they repel. Try to push them together. Its hard, isn't it?

Well, nuclei and electrons undergo a similar effect. If you try to push an electron next to an electron, they repel. Atoms are surrounded by an electron cloud, which repels other atoms. The electrons are held in place because they are attracted to the nucleus.

Or so the conventional explanation goes. Things are actually way more complex.

Answer 2

The first part of your statement is wrong, therefor your whole statement is wrong.

Atoms are not empty. They are filled with electronic wave functions. If you overlap two electronic wave functions, the electrostatic term in the Schroedinger Equation will lead to an enormous interaction energy term. This energy term is equivalent to a classical potential which will either push the atoms apart (that's how we interact with things) or lead to a chemical reaction which binds the two atoms into a molecule with lower energy than the two atoms had when they were separated.

I believe the details of this process are being discussed in QM I for physicists and probably introductory chemistry for the chemists.

The naive notion that the atom is 99.9% empty comes from nuclear physics and is meant to qualitatively describe the smallness of the nucleus. But if one puts too much faith in this oversimplified statement, one will be off by many orders of magnitude for any realistic nuclear size. Since the nucleus is much smaller than 10% of the atom, the volume filling factor is more in the order of 10e-9 than 1e-3. Of course, this is all highly dependent on how one probes the "empty space". If one happens to use radiation for which the particular nucleus has a large cross section, all these numbers would change by many orders of magnitude, yet again.

The best way to escape the problem is to learn a little bit of quantum mechanics and accept that the nuclear problem is too complicated to summarize in a single statement.

Answer 3

If you imagine two large circular roadways, in a “figure eight” configuration, then any vehicle on the roadway that happens to approach any coming from the other direction will “interact” with it.

If you imagine the figure eight in three dimensions, as in two spheres that are next to each other, then the same principle applies.

The rate at which the atomic particles proceed is so high that collisions are constant. This only addresses material interaction.

Then you must consider field energies and their interactions. Electrons oppose particles of same charge [other electrons]. So, the outer particles of atoms repulse outer particles of other atoms. Atoms do not like to touch. Their field energies oppose.

The why of this is a totally different discussion, The fact is, like charges repel like charges. At the atomic level, there is very little interaction of particles.

So, the empty space remains empty. The particles of nearby atoms do not intrude on the emptiness of other atoms. The field charges cause the atoms to rebound from one another, and the binding of the atoms to other atoms in the molecules of the proteins that make up the structure of YOU allow you to perceive the “interaction” you refer to. Your electrons oppose other electrons, these electrons are tied to atomic structures within the matrix of the tissues that represent the organic “you”, and you “interact”.

Again, the why and how of this is a totally different discussion, the complexity of which blushes your question.

Bottom line: Electrons oppose. The outer shell of all atoms is electrons. This opposition causes all atoms to refuse sharing of the inner void within their electron shields, except when that sharing forms relaxing molecular combinations. In all other cases, this opposition results in the tactile sensation of touch, and prevents the mixing of your electrons with those of any object you touch [except, when that object is the object of love. In that instance, the electrons may cooperate ].

We interact when the electron shields of our atoms impinge on the electron shields of the objects that surround us.

Answer 4

The electron shells that surround atoms will not interpenetrate. Electrons as particles are tiny things, but in orbit around an atom they exist as a wave function that forms a continuous shell around the nucleus. So even though an uncharged particle can pass right through an atom, we can't pass through walls because our electron shells are blocked by the wall's electron shells.