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Q & A: can things touch?

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Most recent answer: 02/28/2020
Q:
hi there, came across various videos of 'how you can't touch anything based on the premise that atoms don't touch, and everything is made up of atoms --> molecules, etc.However, how is it that you can throw a ball, clap, walk, despite the concept that atoms don't touch ?here is the video being referenced:https://www.youtube.com/watch?v=yE8rkG9Dw4s
- jack (age 14)
vancouver, bc, canada
A:

Although the guy in the video has heard all the fancy physics words, he doesn't really get the ideas. He sounds like some show-off kids I remember from junior high school.

The alleged "electrostatic repulsion" doesn't keep two ordinary uncharged objects apart. The net electrical force is a weak vanderWaals attraction.  Repulsion does come from the Pauli exclusion principle, as the video says. But that repulsion is zero until the wave functions from the electrons on the two objects start to overlap. So in fact the objects do "touch" in the only physical sense possible, having overlapping wave functions.

The core of the error of the video is to switch back and forth between quantum physics and classical cartoon pictures in an inconsistent way.

Mike W.


(published on 04/15/2017)

Follow-Up #1: things touching

Q:
Then what exactly would happen if they touched?And how would you make that happen?Would they meld together, pass through each other, fuse into something different?I'm just trying to imagine what the world would look like if things started passing through each other. Wouldn't everything just collapse?Sorry for bombarding you with questions
- David (age 28)
Copenhagen, Denmark
A:

Even in our familiar world, many things pass through each outher. For example, electromagnetc waves pass through many materials. That's why I can see the computer screen despite its glass cover.

Electron waves also routinely pass through other materials. That's how all the electronics in the computer work. 

Sometimes when waves overlap, they do fuse into something different, as you say. For example, when two H atoms approach their electrons can spread out, overlappingt, and form an H2 molecule,, giving off some energy either to neighbors or in the form of electromagnetic waves.

What keeps things from collapsing is the combination of two principles.

1) Quantum momentum-position uncertainty. Quantum momentum and position are both aspects of the same wave function, not separately specified classical quantities. States that are confined to small regions always have a large spread of momenta, and thus a lot of kinetic energy.

2) Fermi statistics. The most familiar ingredients of matter (electrons, protons, neutrons) are fermions, which means that at most one can exist in any particular quantum state. Piling more Fermions into a little region means that they have to find higher energy states to go to. 

Mike W.


(published on 10/20/2017)

Follow-Up #2: forces when things touch

Q:
So does this mean that if for example I attempt to push a box, there is some degeneracy pressure exerted where my hands are in contact? If so, how close do the nuclei need to be for degeneracy pressure to be exerted, and is electrostatic repulsion negligible in this case?
- Taylor (age 18)
Bedfordshire, United Kingdom
A:

The relevant nuclear distance is just a couple of typical atomic sizes, roughly 2 nm. The electron wave functions have to distort when the nuclei get that close, so there will be electrostatic force too, caused by the Pauli effect discussed at the top of the thread.

Mike W.


(published on 02/28/2020)

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