How Close Do Molecules Get When Two Objects Are Touching?

[PhanthomJay]

How close before "touching"?

If I slowly lower a book to a table from a height of say 1 m, it is at some point, 0.5m away, then 0.4 m away, etc., until ultimately it rests on the table and I let it lie there. Now i understand (correctly?) that the book is not actually touching the table, there is some sort of photon exchange, but the molecules/electrons of the book never actually 'touch' the molecules/electrons of the table. So my question is, just exactly how close to the book molecules/particles get to the book molecules/particles of the table. Is the answer

a.) The Planck Length
b.) A silly fraction of a nanometer
c.) 0
d.) none of the above

I expect the answer is (d), but I'd like an explanation. (I'm not talking about Zeno's paradox). Thanks!

 

[DaveC426913]

there is some sort of photon exchange, but the molecules/electrons of the book never actually 'touch' the molecules/electrons of the table.

It's not a photon exchange, it's an electrical repulsion between electrons in the book and electrons in the table.

As for what the distance is, that is, of course not a simple answer. First, let's pretend the book and table are perfectly flat down at the molecular level. This is pretty much impossible, since neither book not table are single elements and crystaline in structure (think about the giant cellulose molecules that make up the paper fibres in the book and table).

But let's say both are a perfectly flat layer of one homogenous element.

Ultimately, the distance comes down to the atomic substance in the outermost layers of the molecules of the book/table (hydrogen? carbon?), more specifically, the replusive factor of the outermost electron shell in that particular element.

So,

d.ii) The sum total of the electrorepulsivity between the outer electron shells of the atoms in the surface of the book and the atoms in the surface of the table.



All that being said, note that, whenever we talk about proximity of macroscopic objects, we are always talking about the electroreplusive interaction between their outer orbitals. The boundaries of a macroscopic object are defined by its electron shells.

This means that it's kind of meaningless to talk about when they're "really" touching versus when they're "just" interacting electrically.

Simply, any two obejcts are "really" touching when their electro-repulsivity is enough to offset the force pushing them together.

So,

c.) 0 - They're really touching, in any meaningful sense of the word.

 

[PhanthomJay]

Dave, thanks very much for your excellent response. One more question...when an object passes thru space moving from one point to another, does it traverse through a "Planck Length" of space while doing so, or is the motion actually in a series of 'quantum jumps' as it's moving, rather than a continuous smooth motion through all 'points' in that space of movement, if that makes sense.

 

[DaveC426913]

Dave, thanks very much for your excellent response. One more question...when an object passes thru space moving from one point to another, does it traverse through a "Planck Length" of space while doing so, or is the motion actually in a series of 'quantum jumps' as it's moving, rather than a continuous smooth motion through all 'points' in that space of movement, if that makes sense.

There is no reason to think that space is quantized like that, but we don't know. Or at least, I don't.

 

[granpa]

http://en.wikipedia.org/wiki/Pauli_exclusion_principle#Stability_of_matter

It has been shown that the Pauli exclusion principle is responsible for the fact
that ordinary bulk matter is stable and occupies volume.
This suggestion was first made in 1931 by Paul Ehrenfest, who pointed out
that the electrons of each atom cannot all fall into the lowest-energy orbital
and must occupy successively larger shells.
Atoms therefore occupy a volume and cannot be squeezed too closely together.

A more rigorous proof was provided in 1967 by Freeman Dyson and Andrew Lenard,
who considered the balance of attractive (electron-nuclear) and repulsive (electron-electron and nuclear-nuclear) forces
and showed that ordinary matter would collapse and occupy a much smaller volume without the Pauli principle.
The consequence of the Pauli principle here is that electrons of the same spin
are kept apart by a repulsive exchange interaction[/color],
which is a short-range effect complemented by the long-range electrostatic or coulombic force.
This effect is therefore partly responsible for the everyday observation in the macroscopic world
that two solid objects cannot be in the same place in the same time.[/color]

However, Dyson and Lenard did not consider the extreme magnetic or gravitational forces which occur in some astronomical objects.
In 1995, Elliott Lieb and coworkers showed that the Pauli principle still leads to stability
in intense magnetic fields such as in neutron stars, although at a much higher density than in ordinary matter.
It is a consequence of General Relativity that in sufficiently intense gravitational fields, matter collapses to form a black hole.

http://en.wikipedia.org/wiki/Exchange_interaction

 

[PhanthomJay]

There is no reason to think that space is quantized like that, but we don't know. Or at least, I don't.

Ok, Thank you!

 

[PhanthomJay]

http://en.wikipedia.org/wiki/Pauli_exclusion_principle#Stability_of_matter

Thanks for the reference. Truthfully, I can understand little from Wiki. It starts off complexly and proceeds to the more complex, even in the most basic applications of Physics, in my opinion.

 

[inflector]

Truthfully, I can understand little from Wiki. It starts off complexly and proceeds to the more complex, even in the most basic applications of Physics, in my opinion.

I find wikipedia to be almost useless for learning physics. It always assumes you know the subject matter. The definitions are probably accurate but seem to be built for those who already know the subject matter.

Unfortunately, knowing the material doesn't qualify one as a good writer or teacher.

I love wikipedia but the physics explanations are lacking unless you are already a physicist, IMHO.

 

[DaveC426913]

Thanks for the reference. Truthfully, I can understand little from Wiki. It starts off complexly and proceeds to the more complex, even in the most basic applications of Physics, in my opinion.

I found it a fascinating read, but I have yet to divine its relevance to the thread. I'm pretty sure there's a PF rule somewhere prohibiting the posting of a link without an explanatory comment.

I find wikipedia to be almost useless for learning physics. It always assumes you know the subject matter. The definitions are probably accurate but seem to be built for those who already know the subject matter.

Unfortunately, knowing the material doesn't qualify one as a good writer or teacher.

I love wikipedia but the physics explanations are lacking unless you are already a physicist, IMHO.

That's because Wiki isn't a learning tool. It's a reference tool, like an encyclopedia, which is why it's divided into discrete, manageable chunks.

If you want to learn Physics, https://www.amazon.com/books"&tag=pfamazon01-20.