Eli5 : If atoms are made of and separated by an incredible amount of empty space, why isn’t everything going through everything?
In: 456
Forces and sheer numbers. Specifically the electromagnetic force. Also, some things *do* go right through.
I’ll try to alternate back and forth between ELI5 and ELI20seekinganengineeringdegree
An atom has a very strong positive charge (the nucleus) focused on a very tiny concentration of mass.
That nucleus has a bunch of electrons orbiting around it, and they each have a negative charge. They’re attracted to the nucleus in the same way that a planet is attracted to the sun. It’s trying to fall into the sun, but it’s moving too fast sideways and its in a stable orbit of perpetually missing the sun.
Except there’s way more electrons than planets, and the orbits are not nicely behaved circles. They’re more like random spheres, toroids, and “[dumbbell](https://www.google.com/search?q=dumbbell+shaped+orbital&rlz=1C1GCEA_enCA1023CA1023&sxsrf=APwXEdcZEwGZZSlntHmQkqYGOhXO49HR-g%3A1685973144450&ei=mOh9ZLOJG9T3kPIPt6qA-AE&oq=dumbel+shap&gs_lcp=Cgxnd3Mtd2l6LXNlcnAQAxgBMgcIABCABBAKMgcIABCABBAKMgcIABCABBAKMgcIABCABBAKMgcIABCABBAKMgcIABCABBAKMgcIABCABBAKMgcIABCABBAKMgcIABCABBAKMgcIABCABBAKOgoIABBHENYEELADOgoIABCKBRCwAxBDOgcIIxCKBRAnOggIABCKBRCRAjoLCAAQgAQQsQMQgwE6EQguEIAEELEDEIMBEMcBENEDOgsILhCKBRCxAxCDAToECCMQJzoFCAAQgAQ6CwguEIMBELEDEIoFOggIABCABBCxAzoLCC4QgAQQsQMQgwE6DggAEIAEELEDEIMBEMkDOggIABCABBCSAzoICAAQigUQkgM6GgguEIAEELEDEIMBENQCEIsDEPADEKQDEKgDOhEILhCABBCxAxCDARDHARCvAToaCC4QgAQQsQMQgwEQ1AIQiwMQqAMQpAMQ8AM6CwguEIAEELEDENQCOggILhCABBCxAzoKCAAQgAQQsQMQCjoNCAAQgAQQsQMQgwEQCkoECEEYAFCSEFi9GWCOImgBcAF4AIABgwGIAcYIkgEDNy40mAEAoAEBuAECwAEByAEK&sclient=gws-wiz-serp)” shapes.
Anyways, the point is that the electrons move so much faster that it’s almost like they’re everywhere all at once.
Google [“drone racing”](https://www.google.com/search?q=drone+racing&rlz=1C1GCEA_enCA1023CA1023&sxsrf=APwXEdfzLopNo0kFU5xgu4QazGogtDMrhA%3A1685973628688&ei=fOp9ZKDWKbfykPIP3ZSkkAk&ved=0ahUKEwighPSZpaz_AhU3OUQIHV0KCZIQ4dUDCA8&uact=5&oq=drone+racing&gs_lcp=Cgxnd3Mtd2l6LXNlcnAQAzIICAAQigUQkQIyCwgAEIoFEMkDEJECMggIABCABBCSAzIOCC4QigUQxwEQ0QMQkQIyBQgAEIAEMgUIABCABDIFCAAQgAQyBQgAEIAEMgUIABCABDIFCAAQgAQ6CggAEEcQ1gQQsAM6DQgAEEcQ1gQQyQMQsAM6CwgAEIoFEJIDELADOgoIABCKBRCwAxBDOgcIABCKBRBDOgsILhCABBDHARDRA0oECEEYAFDVA1jzB2DmCGgBcAF4AIABrgGIAdwEkgEDMi4zmAEAoAEBwAEByAEK&sclient=gws-wiz-serp). The drones, like electrons, are “orbiting” around the track. Try telling yourself “it’s mostly empty space” as you walk across the track though, and you’ll quickly realize your fallacy.
To get to the “forces” part of it, the electromagnetic force is easily described as “opposites attract” and “like repels like”. If you have two atoms with full electron orbitals (e.g. two Neon atoms), and try to push them together, they *don’t like it*. Remember how I said that the electrons are like being everywhere at once? They kind of form a “shell” or “cloud” around the positive nucleus. That means that the nuclei are well guarded, and the atoms might as well be two balls with negative surface charges. The electron clouds repel each other, and don’t let them get close to each other. In fact, they’ll never touch.
The closer these atoms get, the stronger the force is, and this force is *insanely strong*. When a blacksmith hammers a glowing strip of iron with a hammer over an anvil, *nothing is actually “touching”*. The atoms in the head of that hammer are repelling the atoms in the metal so strongly as they get close together that they never actually “touch”.
Aside: When atoms form molecular bonds, they actually “bond” by sharing a pair (or 2, even 3 pairs) of electrons. Often each atom will provide one of the two electrons needed, and those electrons will form an orbital that encircles *both nuclei*. These electrons orbiting around (in what you might choose to think of as a ‘figure 8′) help keep the bonded atoms’ nuclei a stable distance apart. When two or more atoms bond to form a molecular structure, each atom has most of its electrons orbiting itself, and there will be a handful of electrons that orbit two or more atoms in the molecule, effectively forming an electron “shell” around the entire molecule. Because of this, the examples given above for atoms applies just the same to larger molecular structures as well.
In solids, atoms and molecules are bonded together through shared electron orbitals or ionic bonding, and they’re rigid with each other. If you want one more hilariously silly example of solids colliding, imagine two armies marching towards each other. Except they don’t carry shields and spears and march shoulder to shoulder. Instead, each soldier stands two meters apart from the next, and instead of soldiers, they’re all yo-yo masters doing all of their wildest, most violent tricks. Two armies of yo-yo masters marching towards each other. Both armies are “mostly empty space”. But there’s no way they’re getting through each other without some yo-yo on yo-yo interaction.
Then there’s light and other electromagnetic radiation, doing pesky EM radiation things.
Light is a photon, and while it carries energy, it’s not a charged particle itself. However they do kind of do weird things with the electromagnetic force, and this is where my knowledge and capability of explaining hits a rough patch.
The ratcheted down explanation starts with a science history lesson. Don’t sneeze because you’ll miss the whole lesson: For a long time, scientists couldn’t agree whether light was a wave or a particle. It very clearly exhibits properties of both. Turns out the answer is pretty much that photons wiggle as they zip through space and time. Yep. They wiggle. They act like particles shot out of a gun, except they wiggle and that wiggle also forms wave patterns making them behave like both a particle and a wave. There. Now you’ll actually know where the professor is going when they take 2-3 lectures to explain properties of light.
For pretty much all solids, there are particular wiggly patterns for photons that let them through. Essentially, the orbital patterns of the electrons in the solid need to be compatible with the wiggly pattern of the photos, otherwise they bump into each other and interact, often with the photons just being “absorbed” by the electrons, which speeds them and the atoms up, releasing energy as heat and/or re-emitting photons. I believe this depends on the composition, density, and crystal structure of the material. It’s what lets visible light pass through glass while not through an even thinner sheet of aluminum foil, and it’s what lets only red light pass through rubies and blue through sapphires.
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