if atoms are mostly empty space, then is the vacuum of space the same kind of emptiness? Or are they different?

Question

Also, how can atoms be solid and opaque if they are mostly nothingness?

In: Physics

Answer 1

When you get down to the size of atoms, concepts like “space with matter in it” and “empty space” kind of break down. We can sort of measure the “sizes” of electrons, and atomic nuclei, but it’s also valid to think of them as single points in space that have certain properties, and whose charges affect a certain area of space.

Two solid objects don’t pass through each other because of repulsion between the electrons in both objects.* It’s got nothing to do with objects that exist in 3 dimensions hitting each other physically. We do “collide” particles in particle accelerators, but it’s more accurate to say that we shoot them close enough that they interact through fundamental forces. All basic collisions that we imagine, like a billiard ball hitting another, are Electromagnetic interactions.

Light, likewise, does/doesn’t pass through something because of how the atoms in the material interact with the photons (or light waves) hitting it. A pane of glass allows light to pass through it without changing its frequency (color) or scattering it because of its crystal structure – it doesn’t have less “stuff” than an opaque sheet of paper. Atoms in glass may absorb and re-emit that light a bunch of times, but it’s transparent to us because the light coming out still has mostly the same information as the light that went in. The paper just reflects (or absorbs and re-emits at a different frequency) most of the light hitting it, destroying whatever information the light had.

So…. the idea of matter as stuff that exists in otherwise empty space is really something we perceive at our scale, and not really something fundamental about existence. Matter and energy aren’t fundamentally different either, and most of the mass of your body comes from the energy holding your atoms together. Crazy, huh?

*To push the electron clouds of the atoms in your skin into the electron clouds of the atoms in the floor you stand on would require the kind of force that creates neutron stars. On the other end, neutrinos stream through earth and your body by the trillions all the time, affecting nothing because they have no EM charge and just don’t interact with your atoms.