Ask Symmetry - Why do objects feel solid?

A reader asked us, "If atoms are mostly empty space, then why does anything feel solid?" In this episode of Ask Symmetry, physicist James Beacham (post-doctoral researcher with the ATLAS Experiment group of The Ohio State University) helps explain the weirdness that appears at the atomic level.

[maltejohnsson]

Question is not actually answered in video; "what is Pauli Exclusion principle" that is, what is the forced involved that creates what we call the "Pauli Exclusion Principle"? Essentially, the question in the video is answered by referring to another, unexplained, word, so no actual explanation is given. How about expanding on it?

[jayarava]

Great. I learned something! One supplementary question that arises is how atoms form molecules at all if their electron clouds keep them apart. This is because some electron cloud configurations are more stable than others. Molecules allow atoms to create new, combined electron configurations that are more stable than atoms on their own.

Also the surface of any material is a cloud of electrons. This is why, for example, when you split a diamond in two you cannot simply push the halves backs together - where the split occurs the newly exposed surfaces are instantly surrounded by their own electron cloud.

Another question that emerges from this, then is, how do glues stick things together?

[stevefaure]

I still don't understand. Why isn't the universe then just a soup of quantum particles that cannot occupy the same space as another quantum particle? Why are there groups of things and other groups of things? Your explanation sounds like everything should be homogenized.

[jdzsf]

But is Pauli exclusion principle a force? It makes particles repel each other. So isn't it a force?

[KingSolomon]

I get that, cool, but my question is why does matter LOOK solid smh...

[DennisAllums]

Thank you, in very in-depth detail explained absolutely nothing. Read your title then rewatch your video..

[sweeneytodd]

And thus, the hologram that is the universe has “solidity”.

[jdzsf]

If particles are so close enough to each other that we have to consider Pauli exclusion principle for them, doesn't it mean that the solid in question is very very very compressed?

[thedom]

Tell that to the neutron stars and black holes :)

[cmiguel]

ok, if i dont touch the objects than means that they are...what? not solid?

[generalusearch]

I laid on my bed and felt into the bed. What I realized is that I and my bed are One. The more I feel it, the less solid it feels.

[austinguy]

Do the atoms become forced to occupy the same space in a black hole? Is it theoretically possible to force them to occupy the same cloud with enoguh force?

Another question, why do they LOOK solid?

[wood-eye]

No. Just no. The Pauli Exclusion Principle (PEP) is not a force. At 1:04 he says that you could bring two electrons together, but even in classical EM, that would require an infinite amount of energy. PEP might be relevant for neutron stars or brown dwarfs, but not for day to day objects here on Earth. You could argue that PEP is the reason why, in QM, the repulsive force component increases much faster (~12th power) than the attraction component (~6th power), but the interaction that gives rise to those forces is still electromagnetic. Also, PEP doesn't explain why air doesn't "feel solid".

[summertea]

Okay you stated why objects feel solid but what makes objects like wood, rock or metal solid?

[joebovovitch]

My answer to everything will be "because quantum mechanics doesnt allow it"

[rickryan]

No, no, no, no, no, no, no, No Dice.... ha! Great video! Keep 'em coming.

[Vindignatio]

Why do gazes not feel solid then? I'm not sure people were very satisfied with this answer.