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Jake1

Why objects are solid

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My high school physics teacher told us that solid objects don't pass through each other because their electrons exchange virtual photons and repel each other as part of the electric force. But with my rudimentary understanding of quantum mechanics, it's not the electrons' charges that repel each other. It's the fact that electrons are fermions and fermions can't occupy the same quantum state (hence the Pauli exclusion principle), and thus electrons cannot occupy other electrons' orbitals. Is that correct? And does the negative charge on electrons have anything to do with the solidity of objects, or is that not a contributing factor at all?

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The Pauli exclusion principle doesn't really come into play, since you aren't trying to put any of the fermions into identical quantum states. A beam of electrons can pass through a thin sheet of material — they are not rejected even though they are fermions. If this mechanism were involved, when you brought two atoms together, the interaction between the electrons and nuclei would just shift the existing energy states, similar to what happens when you form a molecule.

 

The sign of the charge doesn't matter; it's an arbitrary designation. What we call + and - are by convention so we can all communicate.

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Yes,the negative charge on electrons are responsible for the solidity of objects.

Its the sharing of electrons by atoms that hold molecules together.

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No, I know that objects are held together because of the charges on electrons and protons. I'm talking about why objects can't pass through other objects. Is that because the electrons of object A are repelling the electrons in object B with virtual photons? I definitely remember Benjamin Schumacher explaining that his hand can't pass through a table because of the properties of Fermions, not because the electrons in his hand are repelled by the electrons in the table due to their charge.

 

Or did I misunderstand Schumacher and he meant that his hand is solid due to the Pauli exclusion principle, but the interaction between his hand and the desk is still due to electrons' charges repelling each other?

Edited by Jake1

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At the more fundamental level, I would give a thumbs up for Pauli's exclusion principle. The exclusion principle and electron 'spin' is the current way we describe how fermions (eg. 'fuzzy' electrons fill atomic orbitals) and give structural composition to things. In my opinion it is the half-spin nature of fermions and the defence of their spatial volume that best demonstrates this feature. If you are simply talking electrical repulsion from the merging of two atom's electron clouds, then you would also have to explain why attraction can also be caused in say ionic bonding. smile.png

Edited by Implicate Order

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Both amorphous (e.g., glass sheet) and crystalline (e.g., aluminum foil) solids are held together rigidly by electrostatic forces between atoms or molecules (see Van der Walls force), whenever the heat energy that vibrates atoms/molecules provides little force to break the electrostatic bonds. Adding energy in the form of heat (e.g., a torch flame) or impact (a hammer impact) can break the bonds and cause the solid to melt (from a flame) or deform and/or break (from an impact). Also, either an amorphous or crystalline sold can be altered by a strong gravity field, for example that of a black hole, neutron star, or massive planet.

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the inter molecular attraction is high and the space between two molecules is very low so they cannot pass through each other

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the inter molecular attraction is high and the space between two molecules is very low so they cannot pass through each other

 

The empty space in an atom or molecule is quite large compared to the size of the nucleus/nuclei.

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The empty space in an atom or molecule is quite large compared to the size of the nucleus/nuclei.

yaa thats true but sill the space between two molecules is much much much lower then gases and liquid which stops it to flow

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yaa thats true but sill the space between two molecules is much much much lower then gases and liquid which stops it to flow

 

 

Gases yes, liquids not so much (water, for example, is less dense as a solid), and this has nothing to do with the question.

 

I will point out that atoms having a finite size that's much larger than the nucleus does rely on the PEP, and that could be how it gets into the conversation. But a chunk of graphite will not fall through ice, so the whole "identical energy states" argument would seem to not apply here — you don't have to worry about electrons in a carbon atom and a water molecule having the same energy state.

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The Pauli exclusion principle only comes into play when all lowest orbitals are filled. And this only happens at extremely high densities.

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I will point out that atoms having a finite size that's much larger than the nucleus does rely on the PEP, and that could be how it gets into the conversation. But a chunk of graphite will not fall through ice, so the whole "identical energy states" argument would seem to not apply here — you don't have to worry about electrons in a carbon atom and a water molecule having the same energy state.

 

Nice reasoning swansont. I concede and I dropped an olive in your martini. :))

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Yeah, I understand basic chemistry, so most of this is stuff I already knew. I should have phrased my question, "What do our nerve endings detect when we touch other objects?" The answer seems to be that we are feeling the repulsion of our electrons by the virtual photons emitted by the other object's electrons, correct?

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