Warp wrote:
>   I still don't quite get it. Well, I suppose I will have to submit to the
> fact that I have never understood it, and I still don't understand it.

Well, I'm certainly no Feynman, but you could say all the "gaps" you think 
are there are actually full of photons. The photons last only a very brief 
time. When the electrons from one atom are close enough to the other that 
the photon has time to go between, they interact.  That's really about all I 
understand of it also.  I'm not sure that anyone knows better the *why* of it.

-- 
Darren New, San Diego CA, USA (PST)
   Serving Suggestion:
     "Don't serve this any more. It's awful."

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Darren New <dne### [at] sanrrcom> wrote:
> Warp wrote:
> >   I still don't quite get it. Well, I suppose I will have to submit to the
> > fact that I have never understood it, and I still don't understand it.

> Well, I'm certainly no Feynman, but you could say all the "gaps" you think 
> are there are actually full of photons.

  Does that mean that the reason why objects can't pass through each other
is fundamentally electromagnetic?

  A photon is the basic unit (quantum) of electromagnetic radiation and
although it has no mass, it's also the force carrier of electromagnetic
force. But how exactly does this work in this situation? What forces are
acting what?

  Additionally, photons have a frequency. If the gaps are full of photons,
what produces them. what is the frequency of these photons and why?

> The photons last only a very brief time.

  Where do they disappear to, and why? Certainly their energy has to go
somewhere, it cannot simply disappear.

> When the electrons from one atom are close enough to the other that 
> the photon has time to go between, they interact.

  Why doesn't this happen with electrons orbiting the same atom?

  If the repulsive force of the photons produced by electrons is so strong
as to completely forbid two atoms from passing through each other, why are
the electrons in one atom exempt from this same repulsion force?

-- 
                                                          - Warp

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Note, again, this is all my layman understanding.

Warp wrote:
>   Does that mean that the reason why objects can't pass through each other
> is fundamentally electromagnetic?

Yes. There's only four forces: gravity, electomagnetic (aka electrostatic or 
quantum electrodynamic), the weak force (which I think is what holds the 
nucleus together) and the strong force (which I think is what holds the 
quarks in a proton or neutron together).  The QED force is photons 
interacting with electrons, and nothing else. So, basically, anything not 
gravity or "nuclear" is electromagnetic.

>   A photon is the basic unit (quantum) of electromagnetic radiation and
> although it has no mass, it's also the force carrier of electromagnetic
> force. But how exactly does this work in this situation? What forces are
> acting what?

Photons and electrons interact. It makes the electrons change which 
direction they're going.

>   Additionally, photons have a frequency. If the gaps are full of photons,
> what produces them. 

Quantum uncertainty, apparently. At this point, I'm not sure anyone knows 
the "why" of spontaneous photon generation. Basically, every possible 
combination of giving-off-photons and absorbing-photons is averaged together 
(with the appropriate math for "averaged") and the probability that 
something happens is based on that.

> what is the frequency of these photons and why?

There are apparently many frequencies. Altho, as I understand it, a photon 
doesn't have an actual frequency on its own. Every photon is identical. What 
gives a photon its frequency is the relative motion of the source and 
destination of the photon. Otherwise relativity wouldn't work.

>> The photons last only a very brief time.
> 
>   Where do they disappear to, and why? 

They get absorbed again. It's like saying the contact between billard balls 
lasts a very brief time.

> Certainly their energy has to go
> somewhere, it cannot simply disappear.

Yes, it is imparted to the electrons. Which is what's holding your ass up in 
spite of gravity. The photon pushes chair down and ass up, for a net change 
of zero. :-)

The emission of the photon from an electron causes that electron to have 
less energy. The absorption causes it to have more energy. Net result is zero.

Very often, photons will be emitted from an electron and almost instantly 
reabsorbed by the same electron. That's where the photons come from.

Read the first instance (i.e., the #10 negative energy) of this article:

http://listverse.com/2010/11/04/10-strange-things-about-the-universe/

Essentially, vacuum isn't empty. It's constantly full of random virtual 
particles that come into existence, last for a tiny amount of time, and then 
annihilate each other (being equal-and-opposite). Photons do this, and 
electrons do this, as far as anyone can tell from measurements. So at 10nm 
distance, the two plates have excluded enough random particle possibilities 
that there's an entire atmosphere of pressure on the outside more than there 
is between them, just as an example of how tiny is "tiny".

>> When the electrons from one atom are close enough to the other that 
>> the photon has time to go between, they interact.
> 
>   Why doesn't this happen with electrons orbiting the same atom?

It does. That's why all the electrons don't collapse onto the 
oppositely-charged nucleus. That is the source (I think) of the Pauli 
exclusion principle.

>   If the repulsive force of the photons produced by electrons is so strong
> as to completely forbid two atoms from passing through each other, why are
> the electrons in one atom exempt from this same repulsion force?

Because they're also exchanging photons with the protons. The protons have 
an opposite charge, which means they basically move in the opposite 
direction (of how an electron would move) when they absorb or emit a photon, 
and this causes the electrons to move closer to the proton instead of 
farther away. So the electrons are pushing each other apart, but the protons 
are pulling them closer, so the more protons, the more electrons it'll hold 
onto. Then you can look at the periodic table and see how the "holes" and 
"overages" of ionic behavior follow.

Alternately, and I might be misunderstanding/misremembering this, one of the 
"nuclear" forces (strong or weak) might be involved here. Oh, OK, according 
to wikipedia, the strong force holds protons to other protons (i.e., holds 
the nucleus together) *and* holds quarks together. Weird. The weak force 
apparently deals with neutrinos, beta decay, and other stuff I understand 
nothing about. :-)

Basically, the nuclear forces work on essentially the same principle, except 
they have different particles, different likelihoods of interaction, etc.

-- 
Darren New, San Diego CA, USA (PST)
   Serving Suggestion:
     "Don't serve this any more. It's awful."

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Darren New <dne### [at] sanrrcom> wrote:
> >   If the repulsive force of the photons produced by electrons is so strong
> > as to completely forbid two atoms from passing through each other, why are
> > the electrons in one atom exempt from this same repulsion force?

> Because they're also exchanging photons with the protons. The protons have 
> an opposite charge, which means they basically move in the opposite 
> direction (of how an electron would move) when they absorb or emit a photon, 
> and this causes the electrons to move closer to the proton instead of 
> farther away. So the electrons are pushing each other apart, but the protons 
> are pulling them closer, so the more protons, the more electrons it'll hold 
> onto. Then you can look at the periodic table and see how the "holes" and 
> "overages" of ionic behavior follow.

  So this is the reason why when you shoot a lone neutron towards an object,
it will (usually) go right through as if there was nothing there (except in
the odd cases where it just happens to collide with a nucleus, as there are
quite many of them there, in which case it's deviated or even reflected),
because neutrons are electromagnetically neutral and thus don't interact
with the electrons and protons? Moreso with neutrinos, which are like
neutrons but a lot smaller (so a lot less chances of colliding with
something in there).

  Btw, I don't remember now what happens if you shoot a lone proton towards
an object. As it's electrically charged, it ought to interact with the
object immediately, if I understand correctly. But what happens?

-- 
                                                          - Warp

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Warp wrote:
>   So this is the reason why when you shoot a lone neutron towards an object,
> it will (usually) go right through as if there was nothing there (except in
> the odd cases where it just happens to collide with a nucleus, as there are
> quite many of them there, in which case it's deviated or even reflected),
> because neutrons are electromagnetically neutral and thus don't interact
> with the electrons and protons? 

That's my understanding of the basics of it, yes. "Charge" is basically the 
probability that any given photon will be emitted or absorbed by another 
particle. A charge of "1" (plus or minus) means you have about one chance in 
137 of a particular photon interacting with a particular electron at any 
particular instant they meet.  Nobody knows where that number comes from.

> Moreso with neutrinos, which are like
> neutrons but a lot smaller (so a lot less chances of colliding with
> something in there).

That I don't know about.

>   Btw, I don't remember now what happens if you shoot a lone proton towards
> an object. As it's electrically charged, it ought to interact with the
> object immediately, if I understand correctly. But what happens?

Yes, but it's so much bigger than an electron that it can knock an electron 
out of orbit (i.e., it can affect an electron with so many photons that the 
electron's attraction to the electron's associated nucleus is basically 
overwhelmed) without losing much of its own momentum. So it tends to go 
quite some way if it's moving quickly, but with the charge it tends to stop 
quickly once it slows down (compared to neutrons), in part because it'll 
pick up an electron of its own, turn into a hydrogen atom, and now be much 
closer to the size of other atoms instead of the size of a nucleus.

In other words, yes, it interacts with (mostly) the electrons and possibly 
the protons if it happens to get close, but mostly by smashing through the 
substance you're shooting them at if they're going fast.  Electrons, on the 
other hand, will run into other electrons and stop quickly, no matter how 
fast they're going, because each interaction will on average result in two 
electrons with half the momentum (and shooting off a bunch of photons in the 
process, which is where you get x-ray machines and CRTs and such). A proton 
is some 2000x as heavy, so it can go a lot farther before it stops.

That's why gamma radiation (high-energy photons) takes thick lead to stop, 
x-rays (slightly less energetic) takes thin lead to stop, beta radiation 
(high-energy electrons) takes a few millimeters of lighter metal to stop, 
and alpha radiation (basically helium nuclei) takes like a piece of paper to 
stop.

-- 
Darren New, San Diego CA, USA (PST)
   Serving Suggestion:
     "Don't serve this any more. It's awful."

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Darren New <dne### [at] sanrrcom> writes:

> Note, again, this is all my layman understanding.
>
> Warp wrote:
>>   Does that mean that the reason why objects can't pass through each other
>> is fundamentally electromagnetic?
>
> Yes. There's only four forces: gravity, electomagnetic (aka

Freeman Dyson say no:

"A seminal work by Dyson came in 1966 when, together with Andrew Lenard
and independently of Elliott H. Lieb and Walter Thirring, he proved
rigorously that the exclusion principle plays the main role in the
stability of bulk matter.[13] Hence, it is not the electromagnetic
repulsion between electrons and nuclei that is responsible for two wood
blocks that are left on top of each other not coalescing into a single
piece, but rather it is the exclusion principle applied to electrons and
protons that generates the classical macroscopic normal force. In
condensed matter physics"

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

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Neeum Zawan wrote:
> Darren New <dne### [at] sanrrcom> writes:
> 
>> Note, again, this is all my layman understanding.
>>
>> Warp wrote:
>>>   Does that mean that the reason why objects can't pass through each other
>>> is fundamentally electromagnetic?
>> Yes. There's only four forces: gravity, electomagnetic (aka
> 
> Freeman Dyson say no:
> 
> "A seminal work by Dyson came in 1966 when, together with Andrew Lenard
> and independently of Elliott H. Lieb and Walter Thirring, he proved
> rigorously that the exclusion principle plays the main role in the
> stability of bulk matter.[13] Hence, it is not the electromagnetic
> repulsion between electrons and nuclei that is responsible for two wood
> blocks that are left on top of each other not coalescing into a single
> piece, but rather it is the exclusion principle applied to electrons and
> protons that generates the classical macroscopic normal force. In
> condensed matter physics"

 From what I understand, the exclusion principle is a result of the quantum 
electrodynamic theory, which is what used to be called "electromagnetic 
theory" before it was quantum.  I.e., it's the same math going on, with 
photons interacting with electrons and etc.  Clearly I'm not capable of 
talking about it at this level. :-)

-- 
Darren New, San Diego CA, USA (PST)
   Serving Suggestion:
     "Don't serve this any more. It's awful."

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Darren New <dne### [at] sanrrcom> writes:

>> "A seminal work by Dyson came in 1966 when, together with Andrew Lenard
>> and independently of Elliott H. Lieb and Walter Thirring, he proved
>> rigorously that the exclusion principle plays the main role in the
>> stability of bulk matter.[13] Hence, it is not the electromagnetic
>> repulsion between electrons and nuclei that is responsible for two wood
>> blocks that are left on top of each other not coalescing into a single
>> piece, but rather it is the exclusion principle applied to electrons and
>> protons that generates the classical macroscopic normal force. In
>> condensed matter physics"
>
> From what I understand, the exclusion principle is a result of the
> quantum electrodynamic theory, which is what used to be called
> "electromagnetic theory" before it was quantum.  I.e., it's the same
> math going on, with photons interacting with electrons and etc.  Clearly
> I'm not capable of talking about it at this level. :-)

Could be - I never studied QED. However, it's not plain old
electromagnetics. What Dyson showed was that the electromagnetic
interactions between/among nuclei and electrons is not sufficient to
explain the volume of matter - it would be smaller without the exclusion
principle. 

One aspect that keeps particles apart is the exchange interaction, which
is purely due to quantum mechanics (i.e. not, AFAIK, related to
electromagnetics). This was one of those oddities of the quantum world
in undergrad quantum mechanics - that two such particles would prefer to
stay apart even though there is no actual force interaction between them
(even for uncharged particles). 

IANAP

kkk

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Neeum Zawan wrote:
> Could be - I never studied QED. However, it's not plain old
> electromagnetics. 

OK. I don't know the difference between QED and electromagnetics. I thought 
"electromagnetic" was the pre-quantum formulation of electrical and magnetic 
field interactions, i.e., the interaction of electrons with photons.

 > What Dyson showed was that the electromagnetic
> interactions between/among nuclei and electrons is not sufficient to
> explain the volume of matter - it would be smaller without the exclusion
> principle. 

That seems obvious to me. :-) Clearly I'm not educated enough to understand 
why that's surprising.

> One aspect that keeps particles apart is the exchange interaction, which
> is purely due to quantum mechanics (i.e. not, AFAIK, related to
> electromagnetics). This was one of those oddities of the quantum world
> in undergrad quantum mechanics - that two such particles would prefer to
> stay apart even though there is no actual force interaction between them
> (even for uncharged particles). 

I understand the math of why they try to stay apart. I'll have to re-read 
the bit that talks about that and see if I can understand what leads to the 
math.

-- 
Darren New, San Diego CA, USA (PST)
   Serving Suggestion:
     "Don't serve this any more. It's awful."

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Neeum Zawan wrote:
> stay apart even though there is no actual force interaction between them

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

"""
The consequence of the Pauli principle here is that electrons of the same 
spin are kept apart by a repulsive exchange interaction, 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.
"""

Sounds like it's both, holding your butt up. :-)

-- 
Darren New, San Diego CA, USA (PST)
   Serving Suggestion:
     "Don't serve this any more. It's awful."

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