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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On 11/4/2010 3:25 PM, Darren New wrote:
> http://www.youtube.com/watch?v=wMFPe-DwULM
>

Microsoft hosts seven Messenger Lectures of Dr. Richard Feynman on their 
Project Tuva site.  The lectures were filmed at Cornell University in 
1964.  They are well worth the six to seven hours that it takes to view 
them all.  You'll need Silverlight...

http://research.microsoft.com/apps/tools/tuva/


-- Kyle

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Kyle <no### [at] spamhere> wrote:
> You'll need Silverlight...

  How typical of Microsoft to take some scientific lectures which could
benefit our understanding of the universe... and offer them only if you
have a proprietary software of theirs.

-- 
                                                          - Warp

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http://www.youtube.com/watch?v=WAwDvbIfkos

Why don't trains fall off the rails?

-- 
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:
> http://www.youtube.com/watch?v=WAwDvbIfkos

> Why don't trains fall off the rails?

  I certainly didn't know that, and it's once again one of those really
simple yet marvelous shows of human engineering ingenuity. Quite often
problems have the simplest solutions, but it's really difficult for
someone to come up with it, even though it sounds so simple afterwards.

-- 
                                                          - Warp

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Darren New <dne### [at] sanrrcom> wrote:
> http://listverse.com/2010/11/04/10-strange-things-about-the-universe/

  There seems to be an error or discrepancy with the description of the
Kerr black hole in that page. The image shows the Kerr black hole having
three surfaces: The ergosphere, the outer event horizon and the inner
event horizon. The text also talks about these three.

  However, if you look at the wikipedia article:

http://en.wikipedia.org/wiki/Kerr_metric#Important_surfaces

there are only two surfaces: The ergosphere and the event horizon. What
the article at listverse.com calls "outer event horizon" seems to actually
be the ergosphere, and the description seems to confirm that. It seems
that (assuming the wikipedia article is accurate) the author thought
that the ergosphere and the "outer horizon" are two different surfaces,
rather than just being two names for the same thing.

-- 
                                                          - Warp

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Warp wrote:
>   There seems to be an error or discrepancy 

I think you're right. But then, what do you expect from "top 10 lists"? :-)

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

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