View Full Version : Is Pauli's repulsive force fundamental?
Pedro Tamirez
Sep6-04, 04:47 AM
<jabberwocky><div class="vbmenu_control"><a href="jabberwocky:;" onClick="newWindow=window.open('','usenetCode','toolbar=no, location=no,scrollbars=yes,resizable=yes,status=no ,width=650,height=400'); newWindow.document.write('<HTML><HEAD><TITLE>Usenet ASCII</TITLE></HEAD><BODY topmargin=0 leftmargin=0 BGCOLOR=#F1F1F1><table border=0 width=625><td bgcolor=midnightblue><font color=#F1F1F1>This Usenet message\'s original ASCII form: </font></td></tr><tr><td width=449><br><br><font face=courier><UL><PRE>\nHello physics world out there,\n\nI am a bit confused about how many fundamental forces exist. Everybody\nkeeps on saying that there are four fundamental forces: gravity,\nstrong, weak and electromagnetic. (I don\'t want to start any\ndiscussion about possible unifications or additional exotic forces.)\nBut then there is this strange repulsive force, caused by the Pauli\nexclusion principle, that two fermions with the same quantum numbers\ncannot be brought together infinitely close. A repulsive force keeps\nthem seperated.\n\nNow my question is: How does this _new_ force tie in with the other\nfour. As no one talks of 5 fundamental forces, it somehow must be\nrelated to the others? Or is it a fundamental force?\n\nI hope someone can help me to understand this.\nThanks!\n\nPedro\n</UL></PRE></font></td></tr></table></BODY><HTML>');"> <IMG SRC=/images/buttons/ip.gif BORDER=0 ALIGN=CENTER ALT="View this Usenet post in original ASCII form"> View this Usenet post in original ASCII form </a></div><P></jabberwocky>Hello physics world out there,
I am a bit confused about how many fundamental forces exist. Everybody
keeps on saying that there are four fundamental forces: gravity,
strong, weak and electromagnetic. (I don't want to start any
discussion about possible unifications or additional exotic forces.)
But then there is this strange repulsive force, caused by the Pauli
exclusion principle, that two fermions with the same quantum numbers
cannot be brought together infinitely close. A repulsive force keeps
them seperated.
Now my question is: How does this _new_ force tie in with the other
four. As no one talks of 5 fundamental forces, it somehow must be
related to the others? Or is it a fundamental force?
I hope someone can help me to understand this.
Thanks!
Pedro
Roland Franzius
Sep7-04, 05:23 AM
<jabberwocky><div class="vbmenu_control"><a href="jabberwocky:;" onClick="newWindow=window.open('','usenetCode','toolbar=no, location=no,scrollbars=yes,resizable=yes,status=no ,width=650,height=400'); newWindow.document.write('<HTML><HEAD><TITLE>Usenet ASCII</TITLE></HEAD><BODY topmargin=0 leftmargin=0 BGCOLOR=#F1F1F1><table border=0 width=625><td bgcolor=midnightblue><font color=#F1F1F1>This Usenet message\'s original ASCII form: </font></td></tr><tr><td width=449><br><br><font face=courier><UL><PRE>\nPedro Tamirez wrote:\n> Hello physics world out there,\n>\n> I am a bit confused about how many fundamental forces exist. Everybody\n> keeps on saying that there are four fundamental forces: gravity,\n> strong, weak and electromagnetic. (I don\'t want to start any\n> discussion about possible unifications or additional exotic forces.)\n> But then there is this strange repulsive force, caused by the Pauli\n> exclusion principle, that two fermions with the same quantum numbers\n> cannot be brought together infinitely close. A repulsive force keeps\n> them seperated.\n>\n> Now my question is: How does this _new_ force tie in with the other\n> four. As no one talks of 5 fundamental forces, it somehow must be\n> related to the others? Or is it a fundamental force?\n\nThe so called repulsive exchange force of a fermion pair is a matrix\nelement of the normal two particle potential (typically of coulomb type\nor something derived from it like the mean field in a thermodynamic many\nparticle enviroment).\n\nThe exchange energy displays a energy difference between the spatially\nsymmetric case (spin 0 singulett of the relativ coordinate reduced\nsystem) and the spatial antisymmetic case (spin 1 triplett). Let U(x-y)\nbe the two particle potential and psi_k(x) a base of one particle wave\nfunctions. Then the two particle exchange energy is defined to be\n\nV_ex ~ - I ( 1/4 + s_1 . s_2)\n\nwhere s_k are the two particles spin operators, "." is the natural\ncontraction of vectors and I is an integral over flipped wave function\narguments in the product wave functions taken as a base for the full\ntensor product space L^2(R^6)\n\nI = int_R^3 dx^3x int_R^3 d^3y\nphi_1(x) phi_1^*(y) U(x-y) phi_2(y) phi_2^*(x)\n\nThis term arises as a mixed product in the evaluation of the total\npotential two particle energy taken in a antisymmetrized state\n\nint_R^3 dx^3x int_R^3 d^3y\n|phi_1(x) phi_2^(y)- phi_1(y) phi_2^(x)|^2 U(x-y)\n\nThe absolute squares of the summands are the "classical" energies, the\ncross terms with unpaired complex conjugates are responsible for the\nfermionic exchange energy of identical particles.\n\n--\n\nRoland Franzius\n</UL></PRE></font></td></tr></table></BODY><HTML>');"> <IMG SRC=/images/buttons/ip.gif BORDER=0 ALIGN=CENTER ALT="View this Usenet post in original ASCII form"> View this Usenet post in original ASCII form </a></div><P></jabberwocky>Pedro Tamirez wrote:
> Hello physics world out there,
>
> I am a bit confused about how many fundamental forces exist. Everybody
> keeps on saying that there are four fundamental forces: gravity,
> strong, weak and electromagnetic. (I don't want to start any
> discussion about possible unifications or additional exotic forces.)
> But then there is this strange repulsive force, caused by the Pauli
> exclusion principle, that two fermions with the same quantum numbers
> cannot be brought together infinitely close. A repulsive force keeps
> them seperated.
>
> Now my question is: How does this _new_ force tie in with the other
> four. As no one talks of 5 fundamental forces, it somehow must be
> related to the others? Or is it a fundamental force?
The so called repulsive exchange force of a fermion pair is a matrix
element of the normal two particle potential (typically of coulomb type
or something derived from it like the mean field in a thermodynamic many
particle enviroment).
The exchange energy displays a energy difference between the spatially
symmetric case (spin singulett of the relativ coordinate reduced
system) and the spatial antisymmetic case (spin 1 triplett). Let U(x-y)
be the two particle potential and \psi_k(x) a base of one particle wave
functions. Then the two particle exchange energy is defined to be
V_{ex} ~ - I ( 1/4 + s_1 . s_2)
where s_k are the two particles spin operators, "." is the natural
contraction of vectors and I is an integral over flipped wave function
arguments in the product wave functions taken as a base for the full
tensor product space L^2(R^6)I = \int_R^3 dx^3x \int_R^3 d^{3y}\phi_1(x) \phi_1^*(y) U(x-y) \phi_2(y) \phi_2^*(x)
This term arises as a mixed product in the evaluation of the total
potential two particle energy taken in a antisymmetrized state
\int_R^3 dx^3x \int_R^3 d^{3y}|\phi_1(x) \phi_2^(y)- \phi_1(y) \phi_2^(x)|^2 U(x-y)
The absolute squares of the summands are the "classical" energies, the
cross terms with unpaired complex conjugates are responsible for the
fermionic exchange energy of identical particles.
--
Roland Franzius
Alf P. Steinbach
Sep7-04, 05:57 AM
<jabberwocky><div class="vbmenu_control"><a href="jabberwocky:;" onClick="newWindow=window.open('','usenetCode','toolbar=no, location=no,scrollbars=yes,resizable=yes,status=no ,width=650,height=400'); newWindow.document.write('<HTML><HEAD><TITLE>Usenet ASCII</TITLE></HEAD><BODY topmargin=0 leftmargin=0 BGCOLOR=#F1F1F1><table border=0 width=625><td bgcolor=midnightblue><font color=#F1F1F1>This Usenet message\'s original ASCII form: </font></td></tr><tr><td width=449><br><br><font face=courier><UL><PRE>\n* Roland Franzius:\n>\n> Pedro Tamirez wrote:\n> > Hello physics world out there,\n> >\n> > I am a bit confused about how many fundamental forces exist. Everybody\n> > keeps on saying that there are four fundamental forces: gravity,\n> > strong, weak and electromagnetic. (I don\'t want to start any\n> > discussion about possible unifications or additional exotic forces.)\n> > But then there is this strange repulsive force, caused by the Pauli\n> > exclusion principle, that two fermions with the same quantum numbers\n> > cannot be brought together infinitely close. A repulsive force keeps\n> > them seperated.\n> >\n> > Now my question is: How does this _new_ force tie in with the other\n> > four. As no one talks of 5 fundamental forces, it somehow must be\n> > related to the others? Or is it a fundamental force?\n\nThe trick to keeping 4 fundamental forces is to deny that other forces\nsuch e.g. inflation force, are "forces". Unfortunately that denial also\nincludes denying that gravity is a "force". So then we\'re down to 3... :o)\n\n\n> The so called repulsive exchange force of a fermion pair is a matrix\n> element of the normal two particle potential (typically of coulomb type\n> or something derived from it like the mean field in a thermodynamic many\n> particle enviroment).\n\nAs far as I\'m concerned -- I\'m not a scientist -- that\'s mumbo-jumbo.\n\nI once sent this very question to the SciAm "experts" answer-providing\nservice, but no reply.\n\nSo, is the force involved one of the 4 forces, or a combination of them?\n\nYes or no, please.\n\nIf yes, which?\n\n--\nA: Because it messes up the order in which people normally read text.\nQ: Why is it such a bad thing?\nA: Top-posting.\nQ: What is the most annoying thing on usenet and in e-mail?\n</UL></PRE></font></td></tr></table></BODY><HTML>');"> <IMG SRC=/images/buttons/ip.gif BORDER=0 ALIGN=CENTER ALT="View this Usenet post in original ASCII form"> View this Usenet post in original ASCII form </a></div><P></jabberwocky>* Roland Franzius:
>
> Pedro Tamirez wrote:
> > Hello physics world out there,
> >
> > I am a bit confused about how many fundamental forces exist. Everybody
> > keeps on saying that there are four fundamental forces: gravity,
> > strong, weak and electromagnetic. (I don't want to start any
> > discussion about possible unifications or additional exotic forces.)
> > But then there is this strange repulsive force, caused by the Pauli
> > exclusion principle, that two fermions with the same quantum numbers
> > cannot be brought together infinitely close. A repulsive force keeps
> > them seperated.
> >
> > Now my question is: How does this _new_ force tie in with the other
> > four. As no one talks of 5 fundamental forces, it somehow must be
> > related to the others? Or is it a fundamental force?
The trick to keeping 4 fundamental forces is to deny that other forces
such e.g. inflation force, are "forces". Unfortunately that denial also
includes denying that gravity is a "force". So then we're down to 3... :o)
> The so called repulsive exchange force of a fermion pair is a matrix
> element of the normal two particle potential (typically of coulomb type
> or something derived from it like the mean field in a thermodynamic many
> particle enviroment).
As far as I'm concerned -- I'm not a scientist -- that's mumbo-jumbo.
I once sent this very question to the SciAm "experts" answer-providing
service, but no reply.
So, is the force involved one of the 4 forces, or a combination of them?
Yes or no, please.
If yes, which?
--
A: Because it messes up the order in which people normally read text.
Q: Why is it such a bad thing?
A: Top-posting.
Q: What is the most annoying thing on usenet and in e-mail?
chris h fleming
Sep8-04, 06:15 AM
<jabberwocky><div class="vbmenu_control"><a href="jabberwocky:;" onClick="newWindow=window.open('','usenetCode','toolbar=no, location=no,scrollbars=yes,resizable=yes,status=no ,width=650,height=400'); newWindow.document.write('<HTML><HEAD><TITLE>Usenet ASCII</TITLE></HEAD><BODY topmargin=0 leftmargin=0 BGCOLOR=#F1F1F1><table border=0 width=625><td bgcolor=midnightblue><font color=#F1F1F1>This Usenet message\'s original ASCII form: </font></td></tr><tr><td width=449><br><br><font face=courier><UL><PRE>\nalfps@start.no (Alf P. Steinbach) wrote in message news:<413d836a.363819140@news.individual.net>...\n > I once sent this very question to the SciAm "experts" answer-providing\n> service, but no reply.\n>\n> So, is the force involved one of the 4 forces, or a combination of them?\n>\n> Yes or no, please.\n>\n> If yes, which?\n\nThe Pauli Exclusion Principle is an innate property of fermions.\n\nIn QM it is related to the fact that fermions must have antisymmetric\nwave functions. In Relativistic QFT where spin and PEP more naturally\ncome out, it is implied from anticommutators. Those two explainations\nare what you would probably call mumbo jumbo again.\n\nI wouldn\'t say that PEP is a force, because the two\nparticles/antiparticles cannot have the same spin and momentum - it is\nnot that they are flexibly being resisted from having the same states.\n\nSometimes though PEP is thought of as providing a force as with a\nmassive star formed out of degenerate matter. The degeneracy pressure\nof the electrons could be keeping the star from collapse. I am\nassuming this is where the confusion lies. So in this situation what\nis preventing the collapse is the electrons\' inability to become any\nmore compact. (There is more to think about here) Now if you keep on\nsquishing PEP will not give in, but the electrons and protons will\nmerge to make neutrons. Does that make sense now? I think to say PEP\nis a force is like to say there is a force that prevents dogs from\nturning into cats.\n\nAlso I would agree that Gravity is not a force in the usual sense. It\nhas mass in the coupling constant and can be transformed away (LIF).\n</UL></PRE></font></td></tr></table></BODY><HTML>');"> <IMG SRC=/images/buttons/ip.gif BORDER=0 ALIGN=CENTER ALT="View this Usenet post in original ASCII form"> View this Usenet post in original ASCII form </a></div><P></jabberwocky>alfps@start.no (Alf P. Steinbach) wrote in message news:<413d836a.363819140@news.individual.net>...
> I once sent this very question to the SciAm "experts" answer-providing
> service, but no reply.
>
> So, is the force involved one of the 4 forces, or a combination of them?
>
> Yes or no, please.
>
> If yes, which?
The Pauli Exclusion Principle is an innate property of fermions.
In QM it is related to the fact that fermions must have antisymmetric
wave functions. In Relativistic QFT where spin and PEP more naturally
come out, it is implied from anticommutators. Those two explainations
are what you would probably call mumbo jumbo again.
I wouldn't say that PEP is a force, because the two
particles/antiparticles cannot have the same spin and momentum - it is
not that they are flexibly being resisted from having the same states.
Sometimes though PEP is thought of as providing a force as with a
massive star formed out of degenerate matter. The degeneracy pressure
of the electrons could be keeping the star from collapse. I am
assuming this is where the confusion lies. So in this situation what
is preventing the collapse is the electrons' inability to become any
more compact. (There is more to think about here) Now if you keep on
squishing PEP will not give in, but the electrons and protons will
merge to make neutrons. Does that make sense now? I think to say PEP
is a force is like to say there is a force that prevents dogs from
turning into cats.
Also I would agree that Gravity is not a force in the usual sense. It
has mass in the coupling constant and can be transformed away (LIF).
<jabberwocky><div class="vbmenu_control"><a href="jabberwocky:;" onClick="newWindow=window.open('','usenetCode','toolbar=no, location=no,scrollbars=yes,resizable=yes,status=no ,width=650,height=400'); newWindow.document.write('<HTML><HEAD><TITLE>Usenet ASCII</TITLE></HEAD><BODY topmargin=0 leftmargin=0 BGCOLOR=#F1F1F1><table border=0 width=625><td bgcolor=midnightblue><font color=#F1F1F1>This Usenet message\'s original ASCII form: </font></td></tr><tr><td width=449><br><br><font face=courier><UL><PRE>\n\nalfps@start.no (Alf P. Steinbach) wrote in message news:<413d836a.363819140@news.individual.net>...\n > * Roland Franzius:\n> >\n> > Pedro Tamirez wrote:\n> > > Hello physics world out there,\n> > >\n> > > I am a bit confused about how many fundamental forces exist. Everybody\n> > > keeps on saying that there are four fundamental forces: gravity,\n> > > strong, weak and electromagnetic. (I don\'t want to start any\n> > > discussion about possible unifications or additional exotic forces.)\n> > > But then there is this strange repulsive force, caused by the Pauli\n> > > exclusion principle, that two fermions with the same quantum numbers\n> > > cannot be brought together infinitely close. A repulsive force keeps\n> > > them seperated.\n> > >\n> > > Now my question is: How does this _new_ force tie in with the other\n> > > four. As no one talks of 5 fundamental forces, it somehow must be\n> > > related to the others? Or is it a fundamental force?\n>\n> The trick to keeping 4 fundamental forces is to deny that other forces\n> such e.g. inflation force, are "forces". Unfortunately that denial also\n> includes denying that gravity is a "force". So then we\'re down to 3... :o)\n>\n>\n> > The so called repulsive exchange force of a fermion pair is a matrix\n> > element of the normal two particle potential (typically of coulomb type\n> > or something derived from it like the mean field in a thermodynamic many\n> > particle enviroment).\n>\n> As far as I\'m concerned -- I\'m not a scientist -- that\'s mumbo-jumbo.\n>\n> I once sent this very question to the SciAm "experts" answer-providing\n> service, but no reply.\n>\n> So, is the force involved one of the 4 forces, or a combination of them?\n>\n> Yes or no, please.\n>\n> If yes, which?\n\n\nThe OP\'s question was whether the force was fundamental. The answer\nwould have to be no, since it can be derived from other underlying\nfactors -- namely the antisymmetric part of the wavefunction under\nexchange of particles. This is the same reason that Van der Waals\nforces are not considered fundamental, because they are the residual\neffects of electrostatic forces between individual atoms and\nmolecules.\n</UL></PRE></font></td></tr></table></BODY><HTML>');"> <IMG SRC=/images/buttons/ip.gif BORDER=0 ALIGN=CENTER ALT="View this Usenet post in original ASCII form"> View this Usenet post in original ASCII form </a></div><P></jabberwocky>alfps@start.no (Alf P. Steinbach) wrote in message news:<413d836a.363819140@news.individual.net>...
> * Roland Franzius:
> >
> > Pedro Tamirez wrote:
> > > Hello physics world out there,
> > >
> > > I am a bit confused about how many fundamental forces exist. Everybody
> > > keeps on saying that there are four fundamental forces: gravity,
> > > strong, weak and electromagnetic. (I don't want to start any
> > > discussion about possible unifications or additional exotic forces.)
> > > But then there is this strange repulsive force, caused by the Pauli
> > > exclusion principle, that two fermions with the same quantum numbers
> > > cannot be brought together infinitely close. A repulsive force keeps
> > > them seperated.
> > >
> > > Now my question is: How does this _new_ force tie in with the other
> > > four. As no one talks of 5 fundamental forces, it somehow must be
> > > related to the others? Or is it a fundamental force?
>
> The trick to keeping 4 fundamental forces is to deny that other forces
> such e.g. inflation force, are "forces". Unfortunately that denial also
> includes denying that gravity is a "force". So then we're down to 3... :o)
>
>
> > The so called repulsive exchange force of a fermion pair is a matrix
> > element of the normal two particle potential (typically of coulomb type
> > or something derived from it like the mean field in a thermodynamic many
> > particle enviroment).
>
> As far as I'm concerned -- I'm not a scientist -- that's mumbo-jumbo.
>
> I once sent this very question to the SciAm "experts" answer-providing
> service, but no reply.
>
> So, is the force involved one of the 4 forces, or a combination of them?
>
> Yes or no, please.
>
> If yes, which?
The OP's question was whether the force was fundamental. The answer
would have to be no, since it can be derived from other underlying
factors -- namely the antisymmetric part of the wavefunction under
exchange of particles. This is the same reason that Van der Waals
forces are not considered fundamental, because they are the residual
effects of electrostatic forces between individual atoms and
molecules.
Franz Heymann
Sep9-04, 05:18 AM
<jabberwocky><div class="vbmenu_control"><a href="jabberwocky:;" onClick="newWindow=window.open('','usenetCode','toolbar=no, location=no,scrollbars=yes,resizable=yes,status=no ,width=650,height=400'); newWindow.document.write('<HTML><HEAD><TITLE>Usenet ASCII</TITLE></HEAD><BODY topmargin=0 leftmargin=0 BGCOLOR=#F1F1F1><table border=0 width=625><td bgcolor=midnightblue><font color=#F1F1F1>This Usenet message\'s original ASCII form: </font></td></tr><tr><td width=449><br><br><font face=courier><UL><PRE>\n"Pedro Tamirez" <ptamirez@yahoo.co.uk> wrote in message\nnews:11d563b8.0409040632.6ebf80f9@posting .google.com...\n>\n> Hello physics world out there,\n>\n> I am a bit confused about how many fundamental forces exist.\nEverybody\n> keeps on saying that there are four fundamental forces: gravity,\n> strong, weak and electromagnetic. (I don\'t want to start any\n> discussion about possible unifications or additional exotic forces.)\n> But then there is this strange repulsive force, caused by the Pauli\n> exclusion principle, that two fermions with the same quantum numbers\n> cannot be brought together infinitely close. A repulsive force keeps\n> them seperated.\n>\n> Now my question is: How does this _new_ force tie in with the other\n> four. As no one talks of 5 fundamental forces, it somehow must be\n> related to the others? Or is it a fundamental force?\n>\nTHere are no forces involved in the Exclusion Principle. It simply\nsays that in a system consisting of many identical Fermions, the\nresultant wavefunction of the system must be such that it changes sign\nif any two of the particles are interchanged. From that it may be\ndeduced that the particles must arrange themselves such that no two of\nthem have the same quantum numbers.\n\nFranz\n\n\n</UL></PRE></font></td></tr></table></BODY><HTML>');"> <IMG SRC=/images/buttons/ip.gif BORDER=0 ALIGN=CENTER ALT="View this Usenet post in original ASCII form"> View this Usenet post in original ASCII form </a></div><P></jabberwocky>"Pedro Tamirez" <ptamirez@yahoo.co.uk> wrote in message
news:11d563b8.0409040632.6ebf80f9@posting.google.c om...
>
> Hello physics world out there,
>
> I am a bit confused about how many fundamental forces exist.
Everybody
> keeps on saying that there are four fundamental forces: gravity,
> strong, weak and electromagnetic. (I don't want to start any
> discussion about possible unifications or additional exotic forces.)
> But then there is this strange repulsive force, caused by the Pauli
> exclusion principle, that two fermions with the same quantum numbers
> cannot be brought together infinitely close. A repulsive force keeps
> them seperated.
>
> Now my question is: How does this _new_ force tie in with the other
> four. As no one talks of 5 fundamental forces, it somehow must be
> related to the others? Or is it a fundamental force?
>
THere are no forces involved in the Exclusion Principle. It simply
says that in a system consisting of many identical Fermions, the
resultant wavefunction of the system must be such that it changes sign
if any two of the particles are interchanged. From that it may be
deduced that the particles must arrange themselves such that no two of
them have the same quantum numbers.
Franz
<jabberwocky><div class="vbmenu_control"><a href="jabberwocky:;" onClick="newWindow=window.open('','usenetCode','toolbar=no, location=no,scrollbars=yes,resizable=yes,status=no ,width=650,height=400'); newWindow.document.write('<HTML><HEAD><TITLE>Usenet ASCII</TITLE></HEAD><BODY topmargin=0 leftmargin=0 BGCOLOR=#F1F1F1><table border=0 width=625><td bgcolor=midnightblue><font color=#F1F1F1>This Usenet message\'s original ASCII form: </font></td></tr><tr><td width=449><br><br><font face=courier><UL><PRE>No, the repulsive force caused by the exclusion principle is not a\nfundamental force.\nBy example, in atomic physic, if you compute the coulombian interaction by\nusing the spin-orbital approximation,\n\nfor a two electrons system, you obtain two parts\n\n<F_k(1)F_j(2)| 1/r_{12} |F_k(1)F_j(2)> n_k n_j -> this is\nthe coulombian interaction\n\n- <F_k(1)F_j(2)| 1/r_{12} |F_k(2)F_j(1)> ( n^{+}_k . n^{+}_j + n^{-}_k .\nn^{-}_j ) -> this is the exchange energie.\n\nwith r_{12} = || r_2 - r_1||,\nFk an orbital,\nn_k the total number of electron in orbital\nand n^{+}_k and n^{-}_k the number of electron with, respectively a spin\nup or down in the kth orbital\n\nIn the two case you compute matrix elements of the coulombian potential, and\nyou do not have to invoke the fifth force.\n\n\n"Pedro Tamirez" <ptamirez@yahoo.co.uk> a écrit dans le message de\nnews:11d563b8.0409040632.6ebf80f9@posting.goog le.com...\n>\n> Hello physics world out there,\n>\n> I am a bit confused about how many fundamental forces exist. Everybody\n> keeps on saying that there are four fundamental forces: gravity,\n> strong, weak and electromagnetic. (I don\'t want to start any\n> discussion about possible unifications or additional exotic forces.)\n> But then there is this strange repulsive force, caused by the Pauli\n> exclusion principle, that two fermions with the same quantum numbers\n> cannot be brought together infinitely close. A repulsive force keeps\n> them seperated.\n>\n> Now my question is: How does this _new_ force tie in with the other\n> four. As no one talks of 5 fundamental forces, it somehow must be\n> related to the others? Or is it a fundamental force?\n>\n> I hope someone can help me to understand this.\n> Thanks!\n>\n> Pedro\n\n</UL></PRE></font></td></tr></table></BODY><HTML>');"> <IMG SRC=/images/buttons/ip.gif BORDER=0 ALIGN=CENTER ALT="View this Usenet post in original ASCII form"> View this Usenet post in original ASCII form </a></div><P></jabberwocky>No, the repulsive force caused by the exclusion principle is not a
fundamental force.
By example, in atomic physic, if you compute the coulombian interaction by
using the spin-orbital approximation,
for a two electrons system, you obtain two parts
<F_k(1)F_j(2)| 1/r_{12} |F_k(1)F_j(2)> n_k n_j -> this is
the coulombian interaction
- <F_k(1)F_j(2)| 1/r_{12} |F_k(2)F_j(1)> ( n^{+}_k . n^{+}_j + n^{-}_k .n^{-}_j ) -> this is the exchange energie.
with r_{12} = || r_2 - r_1||,
Fk an orbital,
n_k the total number of electron in orbital
and n^{+}_k and n^{-}_k the number of electron with, respectively a spin
up or down in the kth orbital
In the two case you compute matrix elements of the coulombian potential, and
you do not have to invoke the fifth force.
"Pedro Tamirez" <ptamirez@yahoo.co.uk> a écrit dans le message de
news:11d563b8.0409040632.6ebf80f9@posting.google.c om...
>
> Hello physics world out there,
>
> I am a bit confused about how many fundamental forces exist. Everybody
> keeps on saying that there are four fundamental forces: gravity,
> strong, weak and electromagnetic. (I don't want to start any
> discussion about possible unifications or additional exotic forces.)
> But then there is this strange repulsive force, caused by the Pauli
> exclusion principle, that two fermions with the same quantum numbers
> cannot be brought together infinitely close. A repulsive force keeps
> them seperated.
>
> Now my question is: How does this _new_ force tie in with the other
> four. As no one talks of 5 fundamental forces, it somehow must be
> related to the others? Or is it a fundamental force?
>
> I hope someone can help me to understand this.
> Thanks!
>
> Pedro
<jabberwocky><div class="vbmenu_control"><a href="jabberwocky:;" onClick="newWindow=window.open('','usenetCode','toolbar=no, location=no,scrollbars=yes,resizable=yes,status=no ,width=650,height=400'); newWindow.document.write('<HTML><HEAD><TITLE>Usenet ASCII</TITLE></HEAD><BODY topmargin=0 leftmargin=0 BGCOLOR=#F1F1F1><table border=0 width=625><td bgcolor=midnightblue><font color=#F1F1F1>This Usenet message\'s original ASCII form: </font></td></tr><tr><td width=449><br><br><font face=courier><UL><PRE>Pedro Tamirez wrote:\n\n>\n> Hello physics world out there,\n>\n> I am a bit confused about how many fundamental forces exist. Everybody\n> keeps on saying that there are four fundamental forces: gravity,\n> strong, weak and electromagnetic. (I don\'t want to start any\n> discussion about possible unifications or additional exotic forces.)\n> But then there is this strange repulsive force, caused by the Pauli\n> exclusion principle, that two fermions with the same quantum numbers\n> cannot be brought together infinitely close. A repulsive force keeps\n> them seperated.\n>\n> Now my question is: How does this _new_ force tie in with the other\n> four. As no one talks of 5 fundamental forces, it somehow must be\n> related to the others? Or is it a fundamental force?\n>\n> I hope someone can help me to understand this.\n> Thanks!\n\nI think you are playing a word game. The Pauli principle was put in by hand\ninto quantum mechanics, so it that sense you could consider this law as\nfundamental (i.e. it does not follow from other laws). Whether or not you\ncall it a "force", who cares?\n\nThe four fundamental forces all exists at a classical level, but the Pauli\nprinciple is a quantum effect. If you want to call this effect a force, go\nright ahead, the world won\'t change a bit.\n\nbest,\nJeroen\n\n</UL></PRE></font></td></tr></table></BODY><HTML>');"> <IMG SRC=/images/buttons/ip.gif BORDER=0 ALIGN=CENTER ALT="View this Usenet post in original ASCII form"> View this Usenet post in original ASCII form </a></div><P></jabberwocky>Pedro Tamirez wrote:
>
> Hello physics world out there,
>
> I am a bit confused about how many fundamental forces exist. Everybody
> keeps on saying that there are four fundamental forces: gravity,
> strong, weak and electromagnetic. (I don't want to start any
> discussion about possible unifications or additional exotic forces.)
> But then there is this strange repulsive force, caused by the Pauli
> exclusion principle, that two fermions with the same quantum numbers
> cannot be brought together infinitely close. A repulsive force keeps
> them seperated.
>
> Now my question is: How does this _new_ force tie in with the other
> four. As no one talks of 5 fundamental forces, it somehow must be
> related to the others? Or is it a fundamental force?
>
> I hope someone can help me to understand this.
> Thanks!
I think you are playing a word game. The Pauli principle was put in by hand
into quantum mechanics, so it that sense you could consider this law as
fundamental (i.e. it does not follow from other laws). Whether or not you
call it a "force", who cares?
The four fundamental forces all exists at a classical level, but the Pauli
principle is a quantum effect. If you want to call this effect a force, go
right ahead, the world won't change a bit.
best,
Jeroen
Rufus Anton
Sep9-04, 04:02 PM
<jabberwocky><div class="vbmenu_control"><a href="jabberwocky:;" onClick="newWindow=window.open('','usenetCode','toolbar=no, location=no,scrollbars=yes,resizable=yes,status=no ,width=650,height=400'); newWindow.document.write('<HTML><HEAD><TITLE>Usenet ASCII</TITLE></HEAD><BODY topmargin=0 leftmargin=0 BGCOLOR=#F1F1F1><table border=0 width=625><td bgcolor=midnightblue><font color=#F1F1F1>This Usenet message\'s original ASCII form: </font></td></tr><tr><td width=449><br><br><font face=courier><UL><PRE>> Now my question is: How does this _new_ force tie in with the other\n> four. As no one talks of 5 fundamental forces, it somehow must be\n> related to the others? Or is it a fundamental force?\n\nNo, it is not a fundamental force. It is already implicit in the spin\ndependence of the fundamental interactions. If you evaluate the\nFeynman diagrams for gauge boson exchange between two particles of\nnon-zero spin, the answer will be spin dependent. It is this\nspin-dependence at the microscopic level that can give rise to\nmacroscopic effects relative to the case of spinless particles. It\ndoes not matter whether or not you choose to describe this as "an\nadditional force". At the fundamental level we count the number of\ndifferent forces as the number of different gauge bosons that mediate\nsuch forces.\n\n</UL></PRE></font></td></tr></table></BODY><HTML>');"> <IMG SRC=/images/buttons/ip.gif BORDER=0 ALIGN=CENTER ALT="View this Usenet post in original ASCII form"> View this Usenet post in original ASCII form </a></div><P></jabberwocky>> Now my question is: How does this _new_ force tie in with the other
> four. As no one talks of 5 fundamental forces, it somehow must be
> related to the others? Or is it a fundamental force?
No, it is not a fundamental force. It is already implicit in the spin
dependence of the fundamental interactions. If you evaluate the
Feynman diagrams for gauge boson exchange between two particles of
non-zero spin, the answer will be spin dependent. It is this
spin-dependence at the microscopic level that can give rise to
macroscopic effects relative to the case of spinless particles. It
does not matter whether or not you choose to describe this as "an
additional force". At the fundamental level we count the number of
different forces as the number of different gauge bosons that mediate
such forces.
Frank Hellmann
Sep9-04, 04:03 PM
<jabberwocky><div class="vbmenu_control"><a href="jabberwocky:;" onClick="newWindow=window.open('','usenetCode','toolbar=no, location=no,scrollbars=yes,resizable=yes,status=no ,width=650,height=400'); newWindow.document.write('<HTML><HEAD><TITLE>Usenet ASCII</TITLE></HEAD><BODY topmargin=0 leftmargin=0 BGCOLOR=#F1F1F1><table border=0 width=625><td bgcolor=midnightblue><font color=#F1F1F1>This Usenet message\'s original ASCII form: </font></td></tr><tr><td width=449><br><br><font face=courier><UL><PRE>alfps@start.no (Alf P. Steinbach) wrote in message news:<413d836a.363819140@news.individual.net>...\n >\n> > The so called repulsive exchange force of a fermion pair is a matrix\n> > element of the normal two particle potential (typically of coulomb type\n> > or something derived from it like the mean field in a thermodynamic many\n> > particle enviroment).\n>\n> As far as I\'m concerned -- I\'m not a scientist -- that\'s mumbo-jumbo.\n>\n\nWell put this way: It\'s not a fundamental force because fundamentally\nit appears in the way described above and not as a force. It\'s in the\nmechanic structure of the theory.\nBasically the argument is this: Every other force can be turned of in\na thought experiment without changing the mechanics of the theory. Not\nso the "Pauli-force" It is in the mechanics via the Spin-Statistics\nTheorem.\nIncidently Gravity in the classical theory isn\'t strictly a\nfundamental force either. It is an apparent forcelike centrifugal\nforces. Fundamental is that space time is curvedby matter. Again you\ncan\'t remove the force without changing the mechanics. (At least in\nGR)\n\n---\nfrank\n\n</UL></PRE></font></td></tr></table></BODY><HTML>');"> <IMG SRC=/images/buttons/ip.gif BORDER=0 ALIGN=CENTER ALT="View this Usenet post in original ASCII form"> View this Usenet post in original ASCII form </a></div><P></jabberwocky>alfps@start.no (Alf P. Steinbach) wrote in message news:<413d836a.363819140@news.individual.net>...
>
> > The so called repulsive exchange force of a fermion pair is a matrix
> > element of the normal two particle potential (typically of coulomb type
> > or something derived from it like the mean field in a thermodynamic many
> > particle enviroment).
>
> As far as I'm concerned -- I'm not a scientist -- that's mumbo-jumbo.
>
Well put this way: It's not a fundamental force because fundamentally
it appears in the way described above and not as a force. It's in the
mechanic structure of the theory.
Basically the argument is this: Every other force can be turned of in
a thought experiment without changing the mechanics of the theory. Not
so the "Pauli-force" It is in the mechanics via the Spin-Statistics
Theorem.
Incidently Gravity in the classical theory isn't strictly a
fundamental force either. It is an apparent forcelike centrifugal
forces. Fundamental is that space time is curvedby matter. Again you
can't remove the force without changing the mechanics. (At least in
GR)
---
frank
<jabberwocky><div class="vbmenu_control"><a href="jabberwocky:;" onClick="newWindow=window.open('','usenetCode','toolbar=no, location=no,scrollbars=yes,resizable=yes,status=no ,width=650,height=400'); newWindow.document.write('<HTML><HEAD><TITLE>Usenet ASCII</TITLE></HEAD><BODY topmargin=0 leftmargin=0 BGCOLOR=#F1F1F1><table border=0 width=625><td bgcolor=midnightblue><font color=#F1F1F1>This Usenet message\'s original ASCII form: </font></td></tr><tr><td width=449><br><br><font face=courier><UL><PRE>Igor wrote:\n\n>\n>\n> alfps@start.no (Alf P. Steinbach) wrote in message\n> news:<413d836a.363819140@news.individual.net>...\n >> * Roland Franzius:\n>> >\n>> > Pedro Tamirez wrote:\n>> > > Hello physics world out there,\n>> > >\n>> > > I am a bit confused about how many fundamental forces exist.\n>> > > Everybody keeps on saying that there are four fundamental forces:\n>> > > gravity, strong, weak and electromagnetic. (I don\'t want to start any\n>> > > discussion about possible unifications or additional exotic forces.)\n>> > > But then there is this strange repulsive force, caused by the Pauli\n>> > > exclusion principle, that two fermions with the same quantum numbers\n>> > > cannot be brought together infinitely close. A repulsive force keeps\n>> > > them seperated.\n>> > >\n>> > > Now my question is: How does this _new_ force tie in with the other\n>> > > four. As no one talks of 5 fundamental forces, it somehow must be\n>> > > related to the others? Or is it a fundamental force?\n>>\n>> The trick to keeping 4 fundamental forces is to deny that other forces\n>> such e.g. inflation force, are "forces". Unfortunately that denial also\n>> includes denying that gravity is a "force". So then we\'re down to 3...\n>> :o)\n>>\n>>\n>> > The so called repulsive exchange force of a fermion pair is a matrix\n>> > element of the normal two particle potential (typically of coulomb type\n>> > or something derived from it like the mean field in a thermodynamic\n>> > many particle enviroment).\n>>\n>> As far as I\'m concerned -- I\'m not a scientist -- that\'s mumbo-jumbo.\n>>\n>> I once sent this very question to the SciAm "experts" answer-providing\n>> service, but no reply.\n>>\n>> So, is the force involved one of the 4 forces, or a combination of them?\n>>\n>> Yes or no, please.\n>>\n>> If yes, which?\n>\n>\n> The OP\'s question was whether the force was fundamental. The answer\n> would have to be no, since it can be derived from other underlying\n> factors -- namely the antisymmetric part of the wavefunction under\n\nWhy is the wavefunction anti-symmetric?: to obey the Pauli exclusion\nprinciple. So the anti-symmetry is put in by hand, in other words, it is\nfundamental. It can not be derived from anything else.\n\nbest,\nJeroen\n\n</UL></PRE></font></td></tr></table></BODY><HTML>');"> <IMG SRC=/images/buttons/ip.gif BORDER=0 ALIGN=CENTER ALT="View this Usenet post in original ASCII form"> View this Usenet post in original ASCII form </a></div><P></jabberwocky>Igor wrote:
>
>
> alfps@start.no (Alf P. Steinbach) wrote in message
> news:<413d836a.363819140@news.individual.net>...
>> * Roland Franzius:
>> >
>> > Pedro Tamirez wrote:
>> > > Hello physics world out there,
>> > >
>> > > I am a bit confused about how many fundamental forces exist.
>> > > Everybody keeps on saying that there are four fundamental forces:
>> > > gravity, strong, weak and electromagnetic. (I don't want to start any
>> > > discussion about possible unifications or additional exotic forces.)
>> > > But then there is this strange repulsive force, caused by the Pauli
>> > > exclusion principle, that two fermions with the same quantum numbers
>> > > cannot be brought together infinitely close. A repulsive force keeps
>> > > them seperated.
>> > >
>> > > Now my question is: How does this _new_ force tie in with the other
>> > > four. As no one talks of 5 fundamental forces, it somehow must be
>> > > related to the others? Or is it a fundamental force?
>>
>> The trick to keeping 4 fundamental forces is to deny that other forces
>> such e.g. inflation force, are "forces". Unfortunately that denial also
>> includes denying that gravity is a "force". So then we're down to 3...
>> :o)
>>
>>
>> > The so called repulsive exchange force of a fermion pair is a matrix
>> > element of the normal two particle potential (typically of coulomb type
>> > or something derived from it like the mean field in a thermodynamic
>> > many particle enviroment).
>>
>> As far as I'm concerned -- I'm not a scientist -- that's mumbo-jumbo.
>>
>> I once sent this very question to the SciAm "experts" answer-providing
>> service, but no reply.
>>
>> So, is the force involved one of the 4 forces, or a combination of them?
>>
>> Yes or no, please.
>>
>> If yes, which?
>
>
> The OP's question was whether the force was fundamental. The answer
> would have to be no, since it can be derived from other underlying
> factors -- namely the antisymmetric part of the wavefunction under
Why is the wavefunction anti-symmetric?: to obey the Pauli exclusion
principle. So the anti-symmetry is put in by hand, in other words, it is
fundamental. It can not be derived from anything else.
best,
Jeroen
Alf P. Steinbach
Sep9-04, 04:04 PM
<jabberwocky><div class="vbmenu_control"><a href="jabberwocky:;" onClick="newWindow=window.open('','usenetCode','toolbar=no, location=no,scrollbars=yes,resizable=yes,status=no ,width=650,height=400'); newWindow.document.write('<HTML><HEAD><TITLE>Usenet ASCII</TITLE></HEAD><BODY topmargin=0 leftmargin=0 BGCOLOR=#F1F1F1><table border=0 width=625><td bgcolor=midnightblue><font color=#F1F1F1>This Usenet message\'s original ASCII form: </font></td></tr><tr><td width=449><br><br><font face=courier><UL><PRE>* chris h fleming:\n>\n> alfps@start.no (Alf P. Steinbach) wrote in message news:<413d836a.363819140@news.individual.net>...\n > > I once sent this very question to the SciAm "experts" answer-providing\n> > service, but no reply.\n> >\n> > So, is the force involved one of the 4 forces, or a combination of them?\n> >\n> > Yes or no, please.\n> >\n> > If yes, which?\n>\n> The Pauli Exclusion Principle is an innate property of fermions.\n>\n> In QM it is related to the fact that fermions must have antisymmetric\n> wave functions. In Relativistic QFT where spin and PEP more naturally\n> come out, it is implied from anticommutators. Those two explainations\n> are what you would probably call mumbo jumbo again.\n>\n> I wouldn\'t say that PEP is a force, because the two\n> particles/antiparticles cannot have the same spin and momentum - it is\n> not that they are flexibly being resisted from having the same states.\n>\n> Sometimes though PEP is thought of as providing a force as with a\n> massive star formed out of degenerate matter. The degeneracy pressure\n> of the electrons could be keeping the star from collapse. I am\n> assuming this is where the confusion lies. So in this situation what\n> is preventing the collapse is the electrons\' inability to become any\n> more compact. (There is more to think about here)\n\nSo, what is the force that cancels the inward pressure: is the force involved\none of the 4 forces, or a combination of them?\n\nYet again: yes or no, please.\n\nIf yes, which?\n\n\n\n> Now if you keep on\n> squishing PEP will not give in, but the electrons and protons will\n> merge to make neutrons. Does that make sense now?\n\nThat has always made sense.\n\nThe question raised is: what is the force that until some threshold is reached\ncancels the inward pressure?\n\nIt\'s perfectly okay if that turns out to be some interaction of other\nforces, and that was part of the question -- but, is this force composed\n(solely) of one or more of the 4 fundamental forces, and if so which one(s)?\n\n\n\n> I think to say PEP\n> is a force is like to say there is a force that prevents dogs from\n> turning into cats.\n\nThe analogy is extremely misleading and I must wonder why.\n\nRe lack of technical foundation: you cannot apply enough pressure to a dog and\nturn it into a cat, so there is no similarity whatsoever.\n\nRe emotional appeal: there is nothing ridiculous about the _question_.\n\n\n\n> Also I would agree that Gravity is not a force in the usual sense. It\n> has mass in the coupling constant and can be transformed away (LIF).\n\nGoodie, just 3 fundamental forces, then. :-)\n\n--\nA: Because it messes up the order in which people normally read text.\nQ: Why is it such a bad thing?\nA: Top-posting.\nQ: What is the most annoying thing on usenet and in e-mail?\n\n</UL></PRE></font></td></tr></table></BODY><HTML>');"> <IMG SRC=/images/buttons/ip.gif BORDER=0 ALIGN=CENTER ALT="View this Usenet post in original ASCII form"> View this Usenet post in original ASCII form </a></div><P></jabberwocky>* chris h fleming:
>
> alfps@start.no (Alf P. Steinbach) wrote in message news:<413d836a.363819140@news.individual.net>...
> > I once sent this very question to the SciAm "experts" answer-providing
> > service, but no reply.
> >
> > So, is the force involved one of the 4 forces, or a combination of them?
> >
> > Yes or no, please.
> >
> > If yes, which?
>
> The Pauli Exclusion Principle is an innate property of fermions.
>
> In QM it is related to the fact that fermions must have antisymmetric
> wave functions. In Relativistic QFT where spin and PEP more naturally
> come out, it is implied from anticommutators. Those two explainations
> are what you would probably call mumbo jumbo again.
>
> I wouldn't say that PEP is a force, because the two
> particles/antiparticles cannot have the same spin and momentum - it is
> not that they are flexibly being resisted from having the same states.
>
> Sometimes though PEP is thought of as providing a force as with a
> massive star formed out of degenerate matter. The degeneracy pressure
> of the electrons could be keeping the star from collapse. I am
> assuming this is where the confusion lies. So in this situation what
> is preventing the collapse is the electrons' inability to become any
> more compact. (There is more to think about here)
So, what is the force that cancels the inward pressure: is the force involved
one of the 4 forces, or a combination of them?
Yet again: yes or no, please.
If yes, which?
> Now if you keep on
> squishing PEP will not give in, but the electrons and protons will
> merge to make neutrons. Does that make sense now?
That has always made sense.
The question raised is: what is the force that until some threshold is reached
cancels the inward pressure?
It's perfectly okay if that turns out to be some interaction of other
forces, and that was part of the question -- but, is this force composed
(solely) of one or more of the 4 fundamental forces, and if so which one(s)?
> I think to say PEP
> is a force is like to say there is a force that prevents dogs from
> turning into cats.
The analogy is extremely misleading and I must wonder why.
Re lack of technical foundation: you cannot apply enough pressure to a dog and
turn it into a cat, so there is no similarity whatsoever.
Re emotional appeal: there is nothing ridiculous about the _question_.
> Also I would agree that Gravity is not a force in the usual sense. It
> has mass in the coupling constant and can be transformed away (LIF).
Goodie, just 3 fundamental forces, then. :-)
--
A: Because it messes up the order in which people normally read text.
Q: Why is it such a bad thing?
A: Top-posting.
Q: What is the most annoying thing on usenet and in e-mail?
Alf P. Steinbach
Sep9-04, 04:06 PM
<jabberwocky><div class="vbmenu_control"><a href="jabberwocky:;" onClick="newWindow=window.open('','usenetCode','toolbar=no, location=no,scrollbars=yes,resizable=yes,status=no ,width=650,height=400'); newWindow.document.write('<HTML><HEAD><TITLE>Usenet ASCII</TITLE></HEAD><BODY topmargin=0 leftmargin=0 BGCOLOR=#F1F1F1><table border=0 width=625><td bgcolor=midnightblue><font color=#F1F1F1>This Usenet message\'s original ASCII form: </font></td></tr><tr><td width=449><br><br><font face=courier><UL><PRE>* Igor:\n>\n>\n> alfps@start.no (Alf P. Steinbach) wrote in message news:<413d836a.363819140@news.individual.net>...\n > > * Roland Franzius:\n> > >\n> > > Pedro Tamirez wrote:\n> > > > Hello physics world out there,\n> > > >\n> > > > I am a bit confused about how many fundamental forces exist. Everybody\n> > > > keeps on saying that there are four fundamental forces: gravity,\n> > > > strong, weak and electromagnetic. (I don\'t want to start any\n> > > > discussion about possible unifications or additional exotic forces.)\n> > > > But then there is this strange repulsive force, caused by the Pauli\n> > > > exclusion principle, that two fermions with the same quantum numbers\n> > > > cannot be brought together infinitely close. A repulsive force keeps\n> > > > them seperated.\n> > > >\n> > > > Now my question is: How does this _new_ force tie in with the other\n> > > > four. As no one talks of 5 fundamental forces, it somehow must be\n> > > > related to the others? Or is it a fundamental force?\n> >\n> > The trick to keeping 4 fundamental forces is to deny that other forces\n> > such e.g. inflation force, are "forces". Unfortunately that denial also\n> > includes denying that gravity is a "force". So then we\'re down to 3... :o)\n> >\n> >\n> > > The so called repulsive exchange force of a fermion pair is a matrix\n> > > element of the normal two particle potential (typically of coulomb type\n> > > or something derived from it like the mean field in a thermodynamic many\n> > > particle enviroment).\n> >\n> > As far as I\'m concerned -- I\'m not a scientist -- that\'s mumbo-jumbo.\n> >\n> > I once sent this very question to the SciAm "experts" answer-providing\n> > service, but no reply.\n> >\n> > So, is the force involved one of the 4 forces, or a combination of them?\n> >\n> > Yes or no, please.\n> >\n> > If yes, which?\n>\n>\n> The OP\'s question was whether the force was fundamental. The answer\n> would have to be no, since it can be derived from other underlying\n> factors -- namely the antisymmetric part of the wavefunction under\n> exchange of particles.\n\nSo which of the 4 fundamental forces are those carrier particles for?\n\n\n> This is the same reason that Van der Waals\n> forces are not considered fundamental, because they are the residual\n> effects of electrostatic forces between individual atoms and\n> molecules.\n\nAre you saying Pauli exlusion principle somehow generates eletrostatic\nforces?\n\n--\nA: Because it messes up the order in which people normally read text.\nQ: Why is it such a bad thing?\nA: Top-posting.\nQ: What is the most annoying thing on usenet and in e-mail?\n\n</UL></PRE></font></td></tr></table></BODY><HTML>');"> <IMG SRC=/images/buttons/ip.gif BORDER=0 ALIGN=CENTER ALT="View this Usenet post in original ASCII form"> View this Usenet post in original ASCII form </a></div><P></jabberwocky>* Igor:
>
>
> alfps@start.no (Alf P. Steinbach) wrote in message news:<413d836a.363819140@news.individual.net>...
> > * Roland Franzius:
> > >
> > > Pedro Tamirez wrote:
> > > > Hello physics world out there,
> > > >
> > > > I am a bit confused about how many fundamental forces exist. Everybody
> > > > keeps on saying that there are four fundamental forces: gravity,
> > > > strong, weak and electromagnetic. (I don't want to start any
> > > > discussion about possible unifications or additional exotic forces.)
> > > > But then there is this strange repulsive force, caused by the Pauli
> > > > exclusion principle, that two fermions with the same quantum numbers
> > > > cannot be brought together infinitely close. A repulsive force keeps
> > > > them seperated.
> > > >
> > > > Now my question is: How does this _new_ force tie in with the other
> > > > four. As no one talks of 5 fundamental forces, it somehow must be
> > > > related to the others? Or is it a fundamental force?
> >
> > The trick to keeping 4 fundamental forces is to deny that other forces
> > such e.g. inflation force, are "forces". Unfortunately that denial also
> > includes denying that gravity is a "force". So then we're down to 3... :o)
> >
> >
> > > The so called repulsive exchange force of a fermion pair is a matrix
> > > element of the normal two particle potential (typically of coulomb type
> > > or something derived from it like the mean field in a thermodynamic many
> > > particle enviroment).
> >
> > As far as I'm concerned -- I'm not a scientist -- that's mumbo-jumbo.
> >
> > I once sent this very question to the SciAm "experts" answer-providing
> > service, but no reply.
> >
> > So, is the force involved one of the 4 forces, or a combination of them?
> >
> > Yes or no, please.
> >
> > If yes, which?
>
>
> The OP's question was whether the force was fundamental. The answer
> would have to be no, since it can be derived from other underlying
> factors -- namely the antisymmetric part of the wavefunction under
> exchange of particles.
So which of the 4 fundamental forces are those carrier particles for?
> This is the same reason that Van der Waals
> forces are not considered fundamental, because they are the residual
> effects of electrostatic forces between individual atoms and
> molecules.
Are you saying Pauli exlusion principle somehow generates eletrostatic
forces?
--
A: Because it messes up the order in which people normally read text.
Q: Why is it such a bad thing?
A: Top-posting.
Q: What is the most annoying thing on usenet and in e-mail?
Gerard Westendorp
Sep9-04, 04:06 PM
<jabberwocky><div class="vbmenu_control"><a href="jabberwocky:;" onClick="newWindow=window.open('','usenetCode','toolbar=no, location=no,scrollbars=yes,resizable=yes,status=no ,width=650,height=400'); newWindow.document.write('<HTML><HEAD><TITLE>Usenet ASCII</TITLE></HEAD><BODY topmargin=0 leftmargin=0 BGCOLOR=#F1F1F1><table border=0 width=625><td bgcolor=midnightblue><font color=#F1F1F1>This Usenet message\'s original ASCII form: </font></td></tr><tr><td width=449><br><br><font face=courier><UL><PRE>Pedro Tamirez wrote:\n\n> Hello physics world out there,\n>\n> I am a bit confused about how many fundamental forces exist. Everybody\n> keeps on saying that there are four fundamental forces: gravity,\n> strong, weak and electromagnetic. (I don\'t want to start any\n> discussion about possible unifications or additional exotic forces.)\n> But then there is this strange repulsive force, caused by the Pauli\n> exclusion principle, that two fermions with the same quantum numbers\n> cannot be brought together infinitely close. A repulsive force keeps\n> them seperated.\n>\n> Now my question is: How does this _new_ force tie in with the other\n> four. As no one talks of 5 fundamental forces, it somehow must be\n> related to the others? Or is it a fundamental force?\n\n\nIts amazing that matter does not implode under the electric force\nbetween electrons and nuclei. In classical mechanics, the thing\nstopping this would have to be a force, acting on the electrons,\nwhich would be little balls in classical physics.\n\nBut in quantum field theory, electrons are not little balls, but\nexcitations of the electron field. This is pretty hard to visualize.\nIn QFT, the definition of a force is different. In the path\nintegral picture of Feynman, forces are diagrams with\nforce-carrying particles interconnecting other particles. Each\nfundamental force has a fundamental force carrying particle.\nPauli exclusion is caused by the fact that you have to sum all\npossible diagrams. This is a different thing, although the\nnet effect on the electrons behavior is very similar.\n\n\nGerard\n\n</UL></PRE></font></td></tr></table></BODY><HTML>');"> <IMG SRC=/images/buttons/ip.gif BORDER=0 ALIGN=CENTER ALT="View this Usenet post in original ASCII form"> View this Usenet post in original ASCII form </a></div><P></jabberwocky>Pedro Tamirez wrote:
> Hello physics world out there,
>
> I am a bit confused about how many fundamental forces exist. Everybody
> keeps on saying that there are four fundamental forces: gravity,
> strong, weak and electromagnetic. (I don't want to start any
> discussion about possible unifications or additional exotic forces.)
> But then there is this strange repulsive force, caused by the Pauli
> exclusion principle, that two fermions with the same quantum numbers
> cannot be brought together infinitely close. A repulsive force keeps
> them seperated.
>
> Now my question is: How does this _new_ force tie in with the other
> four. As no one talks of 5 fundamental forces, it somehow must be
> related to the others? Or is it a fundamental force?
Its amazing that matter does not implode under the electric force
between electrons and nuclei. In classical mechanics, the thing
stopping this would have to be a force, acting on the electrons,
which would be little balls in classical physics.
But in quantum field theory, electrons are not little balls, but
excitations of the electron field. This is pretty hard to visualize.
In QFT, the definition of a force is different. In the path
integral picture of Feynman, forces are diagrams with
force-carrying particles interconnecting other particles. Each
fundamental force has a fundamental force carrying particle.
Pauli exclusion is caused by the fact that you have to sum all
possible diagrams. This is a different thing, although the
net effect on the electrons behavior is very similar.
Gerard
Frank Hellmann
Sep10-04, 05:25 AM
<jabberwocky><div class="vbmenu_control"><a href="jabberwocky:;" onClick="newWindow=window.open('','usenetCode','toolbar=no, location=no,scrollbars=yes,resizable=yes,status=no ,width=650,height=400'); newWindow.document.write('<HTML><HEAD><TITLE>Usenet ASCII</TITLE></HEAD><BODY topmargin=0 leftmargin=0 BGCOLOR=#F1F1F1><table border=0 width=625><td bgcolor=midnightblue><font color=#F1F1F1>This Usenet message\'s original ASCII form: </font></td></tr><tr><td width=449><br><br><font face=courier><UL><PRE>\n\nJeroen <wijnhout@science.uva.nl> wrote in message news:<chmrjb\\$lmh\\$1@info.science.uva.nl>...\n> Igor wrote:\n>\n> Why is the wavefunction anti-symmetric?: to obey the Pauli exclusion\n> principle. So the anti-symmetry is put in by hand, in other words, it is\n> fundamental. It can not be derived from anything else.\n>\n\nFirst of all google for the Spin Statistics Theorem, if you are to\nhave Spin N/2 particles they neccesarily behave as fermions.\nSecondly, people would tend to agree that it\'s fundamental, but\ndisagree that it\'s a force as it is in the kinematic set up of the\ntheory instead of the dynamic behaviour.\n\n\n---\nfrank\n</UL></PRE></font></td></tr></table></BODY><HTML>');"> <IMG SRC=/images/buttons/ip.gif BORDER=0 ALIGN=CENTER ALT="View this Usenet post in original ASCII form"> View this Usenet post in original ASCII form </a></div><P></jabberwocky>Jeroen <wijnhout@science.uva.nl> wrote in message news:<chmrjb$lmh$1@info.science.uva.nl>...
> Igor wrote:
>
> Why is the wavefunction anti-symmetric?: to obey the Pauli exclusion
> principle. So the anti-symmetry is put in by hand, in other words, it is
> fundamental. It can not be derived from anything else.
>
First of all google for the Spin Statistics Theorem, if you are to
have Spin N/2 particles they neccesarily behave as fermions.
Secondly, people would tend to agree that it's fundamental, but
disagree that it's a force as it is in the kinematic set up of the
theory instead of the dynamic behaviour.
---
frank
Alf P. Steinbach
Sep12-04, 03:23 AM
<jabberwocky><div class="vbmenu_control"><a href="jabberwocky:;" onClick="newWindow=window.open('','usenetCode','toolbar=no, location=no,scrollbars=yes,resizable=yes,status=no ,width=650,height=400'); newWindow.document.write('<HTML><HEAD><TITLE>Usenet ASCII</TITLE></HEAD><BODY topmargin=0 leftmargin=0 BGCOLOR=#F1F1F1><table border=0 width=625><td bgcolor=midnightblue><font color=#F1F1F1>This Usenet message\'s original ASCII form: </font></td></tr><tr><td width=449><br><br><font face=courier><UL><PRE>* Gerard Westendorp:\n> Pedro Tamirez wrote:\n>\n> > Hello physics world out there,\n> >\n> > I am a bit confused about how many fundamental forces exist. Everybody\n> > keeps on saying that there are four fundamental forces: gravity,\n> > strong, weak and electromagnetic. (I don\'t want to start any\n> > discussion about possible unifications or additional exotic forces.)\n> > But then there is this strange repulsive force, caused by the Pauli\n> > exclusion principle, that two fermions with the same quantum numbers\n> > cannot be brought together infinitely close. A repulsive force keeps\n> > them seperated.\n> >\n> > Now my question is: How does this _new_ force tie in with the other\n> > four. As no one talks of 5 fundamental forces, it somehow must be\n> > related to the others? Or is it a fundamental force?\n>\n>\n> Its amazing that matter does not implode under the electric force\n> between electrons and nuclei. In classical mechanics, the thing\n> stopping this would have to be a force, acting on the electrons,\n> which would be little balls in classical physics.\n>\n> But in quantum field theory, electrons are not little balls, but\n> excitations of the electron field. This is pretty hard to visualize.\n> In QFT, the definition of a force is different. In the path\n> integral picture of Feynman, forces are diagrams with\n> force-carrying particles interconnecting other particles. Each\n> fundamental force has a fundamental force carrying particle.\n> Pauli exclusion is caused by the fact that you have to sum all\n> possible diagrams. This is a different thing, although the\n> net effect on the electrons behavior is very similar.\n\nI think this is the best explanation so far.\n\nIn essence, the definition of "force" adopted is not that it acts like\na force, i.e. induces acceleration, but that it _in a certain theory_ causes\nacceleration in a certain way, by exchange of messenger particles.\n\nThis is not uncommon in my own field of expertise (programming), where\nordinary words are very often redefined to mean quite different things\nin different contexts, and, of course, depending on the relevant standard\nand programming language and so on: this allows for very lively discussions\nand also for side-stepping thorny issues and contradictions.\n\nI suggest a new more general term is required, e.g. "acceleration-inducer".\n\nThen the question becomes: how many fundamental acceleration-inducers\nare there, disregarding arguments that gravity does not induce\nacceleration (since I still hurt a little in my sitting area after\ndrainage of an abscess I have direct evidence here & now that gravity\ndoes induce a downward acceleration of my body)?\n\n--\nA: Because it messes up the order in which people normally read text.\nQ: Why is it such a bad thing?\nA: Top-posting.\nQ: What is the most annoying thing on usenet and in e-mail?\n\n</UL></PRE></font></td></tr></table></BODY><HTML>');"> <IMG SRC=/images/buttons/ip.gif BORDER=0 ALIGN=CENTER ALT="View this Usenet post in original ASCII form"> View this Usenet post in original ASCII form </a></div><P></jabberwocky>* Gerard Westendorp:
> Pedro Tamirez wrote:
>
> > Hello physics world out there,
> >
> > I am a bit confused about how many fundamental forces exist. Everybody
> > keeps on saying that there are four fundamental forces: gravity,
> > strong, weak and electromagnetic. (I don't want to start any
> > discussion about possible unifications or additional exotic forces.)
> > But then there is this strange repulsive force, caused by the Pauli
> > exclusion principle, that two fermions with the same quantum numbers
> > cannot be brought together infinitely close. A repulsive force keeps
> > them seperated.
> >
> > Now my question is: How does this _new_ force tie in with the other
> > four. As no one talks of 5 fundamental forces, it somehow must be
> > related to the others? Or is it a fundamental force?
>
>
> Its amazing that matter does not implode under the electric force
> between electrons and nuclei. In classical mechanics, the thing
> stopping this would have to be a force, acting on the electrons,
> which would be little balls in classical physics.
>
> But in quantum field theory, electrons are not little balls, but
> excitations of the electron field. This is pretty hard to visualize.
> In QFT, the definition of a force is different. In the path
> integral picture of Feynman, forces are diagrams with
> force-carrying particles interconnecting other particles. Each
> fundamental force has a fundamental force carrying particle.
> Pauli exclusion is caused by the fact that you have to sum all
> possible diagrams. This is a different thing, although the
> net effect on the electrons behavior is very similar.
I think this is the best explanation so far.
In essence, the definition of "force" adopted is not that it acts like
a force, i.e. induces acceleration, but that it _in a certain theory_ causes
acceleration in a certain way, by exchange of messenger particles.
This is not uncommon in my own field of expertise (programming), where
ordinary words are very often redefined to mean quite different things
in different contexts, and, of course, depending on the relevant standard
and programming language and so on: this allows for very lively discussions
and also for side-stepping thorny issues and contradictions.
I suggest a new more general term is required, e.g. "acceleration-inducer".
Then the question becomes: how many fundamental acceleration-inducers
are there, disregarding arguments that gravity does not induce
acceleration (since I still hurt a little in my sitting area after
drainage of an abscess I have direct evidence here & now that gravity
does induce a downward acceleration of my body)?
--
A: Because it messes up the order in which people normally read text.
Q: Why is it such a bad thing?
A: Top-posting.
Q: What is the most annoying thing on usenet and in e-mail?
Hendrik van Hees
Sep14-04, 01:14 PM
<jabberwocky><div class="vbmenu_control"><a href="jabberwocky:;" onClick="newWindow=window.open('','usenetCode','toolbar=no, location=no,scrollbars=yes,resizable=yes,status=no ,width=650,height=400'); newWindow.document.write('<HTML><HEAD><TITLE>Usenet ASCII</TITLE></HEAD><BODY topmargin=0 leftmargin=0 BGCOLOR=#F1F1F1><table border=0 width=625><td bgcolor=midnightblue><font color=#F1F1F1>This Usenet message\'s original ASCII form: </font></td></tr><tr><td width=449><br><br><font face=courier><UL><PRE>\nFrank Hellmann wrote:\n\n>\n>\n> Jeroen <wijnhout@science.uva.nl> wrote in message\n> news:<chmrjb\\$lmh\\$1@info.science.uva.nl>...\n>> Igor wrote:\n>>\n>> Why is the wavefunction anti-symmetric?: to obey the Pauli exclusion\n>> principle. So the anti-symmetry is put in by hand, in other words, it\n>> is fundamental. It can not be derived from anything else.\n>>\n>\n> First of all google for the Spin Statistics Theorem, if you are to\n> have Spin N/2 particles they neccesarily behave as fermions.\n> Secondly, people would tend to agree that it\'s fundamental, but\n> disagree that it\'s a force as it is in the kinematic set up of the\n> theory instead of the dynamic behaviour.\n\nPauli blocking is no force.\n\nTo my understanding the most logical line of arguments is as follows:\n\n(1) Laidlav/de Witt: In theories where space has >=3 dimensions,\nelementary particles must bei either bosons or fermions\n\nM. G. G. Laidlaw, C. M. DeWitt, Feynman Functional Integrals for Systems\nof Indistinguishable Particles, Phys. Rev. D 3 (1970) 1375, URL\nhttp://link.aps.org/abstract/PRD/v3/i6/p1375\n\n(2) In a local, microcausal relativistic quantum field theory with\nstable ground state (hamiltonian bounded from below) particles with\ninteger spin (helicity) are necessarily bosons, particles with\nhalf-integer spin (helicity) are necessarily fermions. Vgl. z.B.\n\nWeinberg, Quantum Theory of Fields, Vol. I\n\n--\nHendrik van Hees Cyclotron Institute\nPhone: +1 979/845-1411 Texas A&M University\nFax: +1 979/845-1899 Cyclotron Institute, MS-3366\nhttp://theory.gsi.de/~vanhees/ College Station, TX 77843-3366\n</UL></PRE></font></td></tr></table></BODY><HTML>');"> <IMG SRC=/images/buttons/ip.gif BORDER=0 ALIGN=CENTER ALT="View this Usenet post in original ASCII form"> View this Usenet post in original ASCII form </a></div><P></jabberwocky>Frank Hellmann wrote:
>
>
> Jeroen <wijnhout@science.uva.nl> wrote in message
> news:<chmrjb$lmh$1@info.science.uva.nl>...
>> Igor wrote:
>>
>> Why is the wavefunction anti-symmetric?: to obey the Pauli exclusion
>> principle. So the anti-symmetry is put in by hand, in other words, it
>> is fundamental. It can not be derived from anything else.
>>
>
> First of all google for the Spin Statistics Theorem, if you are to
> have Spin N/2 particles they neccesarily behave as fermions.
> Secondly, people would tend to agree that it's fundamental, but
> disagree that it's a force as it is in the kinematic set up of the
> theory instead of the dynamic behaviour.
Pauli blocking is no force.
To my understanding the most logical line of arguments is as follows:
(1) Laidlav/de Witt: In theories where space has >=3 dimensions,
elementary particles must bei either bosons or fermions
M. G. G. Laidlaw, C. M. DeWitt, Feynman Functional Integrals for Systems
of Indistinguishable Particles, Phys. Rev. D 3 (1970) 1375, URL
http://link.aps.org/abstract/PRD/v3/i6/p1375
(2) In a local, microcausal relativistic quantum field theory with
stable ground state (hamiltonian bounded from below) particles with
integer spin (helicity) are necessarily bosons, particles with
half-integer spin (helicity) are necessarily fermions. Vgl. z.B.
Weinberg, Quantum Theory of Fields, Vol. I
--
Hendrik van Hees Cyclotron Institute
Phone: +1 979/845-1411 Texas A&M University
Fax: +1 979/845-1899 Cyclotron Institute, MS-3366
http://theory.gsi.de/~vanhees/ College Station, TX 77843-3366
chris h fleming
Sep14-04, 01:15 PM
<jabberwocky><div class="vbmenu_control"><a href="jabberwocky:;" onClick="newWindow=window.open('','usenetCode','toolbar=no, location=no,scrollbars=yes,resizable=yes,status=no ,width=650,height=400'); newWindow.document.write('<HTML><HEAD><TITLE>Usenet ASCII</TITLE></HEAD><BODY topmargin=0 leftmargin=0 BGCOLOR=#F1F1F1><table border=0 width=625><td bgcolor=midnightblue><font color=#F1F1F1>This Usenet message\'s original ASCII form: </font></td></tr><tr><td width=449><br><br><font face=courier><UL><PRE>\nalfps@start.no (Alf P. Steinbach) wrote in message news:<413ef8a5.459365812@news.individual.net>...\n > * chris h fleming:\n> > alfps@start.no (Alf P. Steinbach) wrote in message news:<413d836a.363819140@news.individual.net>...\n > > Sometimes though PEP is thought of as providing a force as with a\n> > massive star formed out of degenerate matter. The degeneracy pressure\n> > of the electrons could be keeping the star from collapse. I am\n> > assuming this is where the confusion lies. So in this situation what\n> > is preventing the collapse is the electrons\' inability to become any\n> > more compact. (There is more to think about here)\n>\n> So, what is the force that cancels the inward pressure: is the force involved\n> one of the 4 forces, or a combination of them?\n>\n> Yet again: yes or no, please.\n>\n> If yes, which?\n>\n> > Now if you keep on\n> > squishing PEP will not give in, but the electrons and protons will\n> > merge to make neutrons. Does that make sense now?\n>\n> That has always made sense.\n>\n> The question raised is: what is the force that until some threshold is reached\n> cancels the inward pressure?\n>\n> It\'s perfectly okay if that turns out to be some interaction of other\n> forces, and that was part of the question -- but, is this force composed\n> (solely) of one or more of the 4 fundamental forces, and if so which one(s)?\n\nIt\'s just pressure. And pressure is not a fundamental force.\n\nThe pressure is directly a result of the momenta of the electrons.\nThey are in high momentum states because the low momentum states are\nall taken - because there isn\'t enough volume and PEP.\n\nThe more massive the particle, the more degeneracy pressure you can\nget. Degenerate electron stars collapse to degenerate neutron stars.\n\nThis makes PEP a force no more than any other gas pressure. The\ndifference between this degenerate gas pressure and a regular gas\npressure is that the degenerate gas pressure is a QM effect and will\nnot go away in the limit to zero temperature.\n\nConsider squeezing a container with an ideal gas in it. An ideal gas\nhas no interactions by definition/construction. You decrease the\nvolume and the pressure will go up. Eventually the pressure will\nresist your squeezing. Same thing with the degenerate matter stars.\n\n> > I think to say PEP\n> > is a force is like to say there is a force that prevents dogs from\n> > turning into cats.\n>\n> The analogy is extremely misleading and I must wonder why.\n>\n> Re lack of technical foundation: you cannot apply enough pressure to a dog and\n> turn it into a cat, so there is no similarity whatsoever.\n>\n> Re emotional appeal: there is nothing ridiculous about the _question_.\n\nThink about it some more. You CAN\'T apply enough pressure to put the\nelectrons in the same state. There is nothing you can do to turn a dog\ninto a cat and there is nothing you can do to put electrons in the\nsame state.\n</UL></PRE></font></td></tr></table></BODY><HTML>');"> <IMG SRC=/images/buttons/ip.gif BORDER=0 ALIGN=CENTER ALT="View this Usenet post in original ASCII form"> View this Usenet post in original ASCII form </a></div><P></jabberwocky>alfps@start.no (Alf P. Steinbach) wrote in message news:<413ef8a5.459365812@news.individual.net>...
> * chris h fleming:
> > alfps@start.no (Alf P. Steinbach) wrote in message news:<413d836a.363819140@news.individual.net>...
> > Sometimes though PEP is thought of as providing a force as with a
> > massive star formed out of degenerate matter. The degeneracy pressure
> > of the electrons could be keeping the star from collapse. I am
> > assuming this is where the confusion lies. So in this situation what
> > is preventing the collapse is the electrons' inability to become any
> > more compact. (There is more to think about here)
>
> So, what is the force that cancels the inward pressure: is the force involved
> one of the 4 forces, or a combination of them?
>
> Yet again: yes or no, please.
>
> If yes, which?
>
> > Now if you keep on
> > squishing PEP will not give in, but the electrons and protons will
> > merge to make neutrons. Does that make sense now?
>
> That has always made sense.
>
> The question raised is: what is the force that until some threshold is reached
> cancels the inward pressure?
>
> It's perfectly okay if that turns out to be some interaction of other
> forces, and that was part of the question -- but, is this force composed
> (solely) of one or more of the 4 fundamental forces, and if so which one(s)?
It's just pressure. And pressure is not a fundamental force.
The pressure is directly a result of the momenta of the electrons.
They are in high momentum states because the low momentum states are
all taken - because there isn't enough volume and PEP.
The more massive the particle, the more degeneracy pressure you can
get. Degenerate electron stars collapse to degenerate neutron stars.
This makes PEP a force no more than any other gas pressure. The
difference between this degenerate gas pressure and a regular gas
pressure is that the degenerate gas pressure is a QM effect and will
not go away in the limit to zero temperature.
Consider squeezing a container with an ideal gas in it. An ideal gas
has no interactions by definition/construction. You decrease the
volume and the pressure will go up. Eventually the pressure will
resist your squeezing. Same thing with the degenerate matter stars.
> > I think to say PEP
> > is a force is like to say there is a force that prevents dogs from
> > turning into cats.
>
> The analogy is extremely misleading and I must wonder why.
>
> Re lack of technical foundation: you cannot apply enough pressure to a dog and
> turn it into a cat, so there is no similarity whatsoever.
>
> Re emotional appeal: there is nothing ridiculous about the _question_.
Think about it some more. You CAN'T apply enough pressure to put the
electrons in the same state. There is nothing you can do to turn a dog
into a cat and there is nothing you can do to put electrons in the
same state.
Frank Hellmann
Sep14-04, 01:15 PM
<jabberwocky><div class="vbmenu_control"><a href="jabberwocky:;" onClick="newWindow=window.open('','usenetCode','toolbar=no, location=no,scrollbars=yes,resizable=yes,status=no ,width=650,height=400'); newWindow.document.write('<HTML><HEAD><TITLE>Usenet ASCII</TITLE></HEAD><BODY topmargin=0 leftmargin=0 BGCOLOR=#F1F1F1><table border=0 width=625><td bgcolor=midnightblue><font color=#F1F1F1>This Usenet message\'s original ASCII form: </font></td></tr><tr><td width=449><br><br><font face=courier><UL><PRE>\n\nalfps@start.no (Alf P. Steinbach) wrote in message news:<413ef8a5.459365812@news.individual.net>...\n \n> So, what is the force that cancels the inward pressure: is the force involved\n> one of the 4 forces, or a combination of them?\n>\n> Yet again: yes or no, please.\n>\n> If yes, which?\n>\n\nIn special relativity, what is the force that prevents me from\naccelarating a particle to more then c?\nThere is no force, it\'s the kinematic framework of the theory, and not\nthe dynamic content. On the statistical level the distinction get\'s\nblurred and the kinematic property can be described by a force,\nfundamentally it isn\'t.\n\nIt\'s similar for gravity, in GR it is not a "fundamental" force, just\nas the centrifugal force isn\'t.\nHowever, the whole notion of force is somewhat questionable when we\ndvelve deep into the core of physics. It makes sense in the Newtonian\ncase, where it enters explicitly in F=ma and where we can think of it\nas a macroscopic entity we have an intuition of, but once every\npossible "left hand side" becomes part of the theory itself it becomes\ncritical whether something is dynamical or kinematic. It has long been\na matter of contention (and ultimately irrelevant IMO, since we are\ntalking about our words instead of our physics) whether the coulomb\npotential of a point charge is kinematic or dynamic.\n\n---\nfrank\n</UL></PRE></font></td></tr></table></BODY><HTML>');"> <IMG SRC=/images/buttons/ip.gif BORDER=0 ALIGN=CENTER ALT="View this Usenet post in original ASCII form"> View this Usenet post in original ASCII form </a></div><P></jabberwocky>alfps@start.no (Alf P. Steinbach) wrote in message news:<413ef8a5.459365812@news.individual.net>...
> So, what is the force that cancels the inward pressure: is the force involved
> one of the 4 forces, or a combination of them?
>
> Yet again: yes or no, please.
>
> If yes, which?
>
In special relativity, what is the force that prevents me from
accelarating a particle to more then c?
There is no force, it's the kinematic framework of the theory, and not
the dynamic content. On the statistical level the distinction get's
blurred and the kinematic property can be described by a force,
fundamentally it isn't.
It's similar for gravity, in GR it is not a "fundamental" force, just
as the centrifugal force isn't.
However, the whole notion of force is somewhat questionable when we
dvelve deep into the core of physics. It makes sense in the Newtonian
case, where it enters explicitly in F=ma and where we can think of it
as a macroscopic entity we have an intuition of, but once every
possible "left hand side" becomes part of the theory itself it becomes
critical whether something is dynamical or kinematic. It has long been
a matter of contention (and ultimately irrelevant IMO, since we are
talking about our words instead of our physics) whether the coulomb
potential of a point charge is kinematic or dynamic.
---
frank
<jabberwocky><div class="vbmenu_control"><a href="jabberwocky:;" onClick="newWindow=window.open('','usenetCode','toolbar=no, location=no,scrollbars=yes,resizable=yes,status=no ,width=650,height=400'); newWindow.document.write('<HTML><HEAD><TITLE>Usenet ASCII</TITLE></HEAD><BODY topmargin=0 leftmargin=0 BGCOLOR=#F1F1F1><table border=0 width=625><td bgcolor=midnightblue><font color=#F1F1F1>This Usenet message\'s original ASCII form: </font></td></tr><tr><td width=449><br><br><font face=courier><UL><PRE>\nFrank Hellmann wrote:\n\n>\n>\n> Jeroen <wijnhout@science.uva.nl> wrote in message\n> news:<chmrjb\\$lmh\\$1@info.science.uva.nl>...\n>> Igor wrote:\n>>\n>> Why is the wavefunction anti-symmetric?: to obey the Pauli exclusion\n>> principle. So the anti-symmetry is put in by hand, in other words, it is\n>> fundamental. It can not be derived from anything else.\n>>\n>\n> First of all google for the Spin Statistics Theorem, if you are to\n\nI know the Spin Statistics Theorem, not from Google but from actual\nQFT books ;-)\n\n> have Spin N/2 particles they neccesarily behave as fermions.\n\nSure, within QFT this is true.\n\n> Secondly, people would tend to agree that it\'s fundamental, but\n> disagree that it\'s a force as it is in the kinematic set up of the\n> theory instead of the dynamic behaviour.\n\nMy point was: it is fundamental (here we agree), if you want to _call_ it\na force, be my guest, it doesn\'t change anything (here we can\'t disagree,\ncan we?).\n\nbest,\nJeroen\n\n</UL></PRE></font></td></tr></table></BODY><HTML>');"> <IMG SRC=/images/buttons/ip.gif BORDER=0 ALIGN=CENTER ALT="View this Usenet post in original ASCII form"> View this Usenet post in original ASCII form </a></div><P></jabberwocky>Frank Hellmann wrote:
>
>
> Jeroen <wijnhout@science.uva.nl> wrote in message
> news:<chmrjb$lmh$1@info.science.uva.nl>...
>> Igor wrote:
>>
>> Why is the wavefunction anti-symmetric?: to obey the Pauli exclusion
>> principle. So the anti-symmetry is put in by hand, in other words, it is
>> fundamental. It can not be derived from anything else.
>>
>
> First of all google for the Spin Statistics Theorem, if you are to
I know the Spin Statistics Theorem, not from Google but from actual
QFT books ;-)
> have Spin N/2 particles they neccesarily behave as fermions.
Sure, within QFT this is true.
> Secondly, people would tend to agree that it's fundamental, but
> disagree that it's a force as it is in the kinematic set up of the
> theory instead of the dynamic behaviour.
My point was: it is fundamental (here we agree), if you want to _call_ it
a force, be my guest, it doesn't change anything (here we can't disagree,
can we?).
best,
Jeroen
Gerard Westendorp
Sep17-04, 06:32 AM
<jabberwocky><div class="vbmenu_control"><a href="jabberwocky:;" onClick="newWindow=window.open('','usenetCode','toolbar=no, location=no,scrollbars=yes,resizable=yes,status=no ,width=650,height=400'); newWindow.document.write('<HTML><HEAD><TITLE>Usenet ASCII</TITLE></HEAD><BODY topmargin=0 leftmargin=0 BGCOLOR=#F1F1F1><table border=0 width=625><td bgcolor=midnightblue><font color=#F1F1F1>This Usenet message\'s original ASCII form: </font></td></tr><tr><td width=449><br><br><font face=courier><UL><PRE>\nAlf P. Steinbach wrote:\n\n[..]\n\n\n> I suggest a new more general term is required, e.g. "acceleration-inducer".\n>\n> Then the question becomes: how many fundamental acceleration-inducers\n> are there,\n\n\nPauli exclusion can influence the acceleration of particles, as fas as I\ncan see this is true.\n\nAnother feature "ordinary" fundamental forces have is field energy.\nElectromagnetism does not only push electric charges, it can also\ncarry energy by itself, in the form of EM-radiation. Static fields\nalso contain local energy.\n\nThis does not seem to be true for "Pauli force".\n\nIf you combine quantum mechanics with the classical notion\nof acceleration (ie think of a localized particle whose\nspeed changes with time), you will run into some weird\nstuff. Pauli exclusion is weird, but it is so ubiquitous.\nWhat about the quantum Zeno effect, the Casimir effect..\n\nGerard\n</UL></PRE></font></td></tr></table></BODY><HTML>');"> <IMG SRC=/images/buttons/ip.gif BORDER=0 ALIGN=CENTER ALT="View this Usenet post in original ASCII form"> View this Usenet post in original ASCII form </a></div><P></jabberwocky>Alf P. Steinbach wrote:
[..]
> I suggest a new more general term is required, e.g. "acceleration-inducer".
>
> Then the question becomes: how many fundamental acceleration-inducers
> are there,
Pauli exclusion can influence the acceleration of particles, as fas as I
can see this is true.
Another feature "ordinary" fundamental forces have is field energy.
Electromagnetism does not only push electric charges, it can also
carry energy by itself, in the form of EM-radiation. Static fields
also contain local energy.
This does not seem to be true for "Pauli force".
If you combine quantum mechanics with the classical notion
of acceleration (ie think of a localized particle whose
speed changes with time), you will run into some weird
stuff. Pauli exclusion is weird, but it is so ubiquitous.
What about the quantum Zeno effect, the Casimir effect..
Gerard
<jabberwocky><div class="vbmenu_control"><a href="jabberwocky:;" onClick="newWindow=window.open('','usenetCode','toolbar=no, location=no,scrollbars=yes,resizable=yes,status=no ,width=650,height=400'); newWindow.document.write('<HTML><HEAD><TITLE>Usenet ASCII</TITLE></HEAD><BODY topmargin=0 leftmargin=0 BGCOLOR=#F1F1F1><table border=0 width=625><td bgcolor=midnightblue><font color=#F1F1F1>This Usenet message\'s original ASCII form: </font></td></tr><tr><td width=449><br><br><font face=courier><UL><PRE>\n\n> THere are no forces involved in the Exclusion Principle.\n\nWell, some authors call it an \'effective force\'.\n\nBTW: how is the notion \'force\' defined? Isn\'t that just a classical\nnotion with no consistent meaning in quantum mechanics?\n\nRegards,\nMark\n</UL></PRE></font></td></tr></table></BODY><HTML>');"> <IMG SRC=/images/buttons/ip.gif BORDER=0 ALIGN=CENTER ALT="View this Usenet post in original ASCII form"> View this Usenet post in original ASCII form </a></div><P></jabberwocky>THere are no forces involved in the Exclusion Principle.
Well, some authors call it an 'effective force'.
BTW: how is the notion 'force' defined? Isn't that just a classical
notion with no consistent meaning in quantum mechanics?
Regards,
Mark
Cedric Beny
Sep19-04, 07:56 AM
<jabberwocky><div class="vbmenu_control"><a href="jabberwocky:;" onClick="newWindow=window.open('','usenetCode','toolbar=no, location=no,scrollbars=yes,resizable=yes,status=no ,width=650,height=400'); newWindow.document.write('<HTML><HEAD><TITLE>Usenet ASCII</TITLE></HEAD><BODY topmargin=0 leftmargin=0 BGCOLOR=#F1F1F1><table border=0 width=625><td bgcolor=midnightblue><font color=#F1F1F1>This Usenet message\'s original ASCII form: </font></td></tr><tr><td width=449><br><br><font face=courier><UL><PRE>\n\nptamirez@yahoo.co.uk (Pedro Tamirez) wrote in message news:<11d563b8.0409040632.6ebf80f9@posting.google. com>...\n> I am a bit confused about how many fundamental forces exist. Everybody\n> keeps on saying that there are four fundamental forces:\n(snip)\n> But then there is this strange repulsive force, caused by the Pauli\n> exclusion principle, that two fermions with the same quantum numbers\n> cannot be brought together infinitely close. A repulsive force keeps\n> them seperated.\n\nBecause we are used to classical mechanics, we picture particles as\nindividual objects each with a definite positions. When we translate\nthe notion of particles to quantum mechanics we first keep this\nintuitive view, because that\'s all we have to start with. But then\nexperiments tell us that this is wrong and that the actual\nconfiguration space of fermions (or bosons) is much smaller than the\none we would have if each particles had an individuality as is the\ncase for macroscopic objects.\nSo the fact is that a state of tightly packed fermions does not exist.\nThis is the exclusion principle. The very idea of such a state comes\nfrom the classical concept of a particle and had to be removed from\nthe naive first attempt at constructing a quantum many body theory.\nThis illustrates how the process of quantization consists in trying to\nguess the quantum theory underlying macroscopic phenomenon. One lacks\ninformation and the result of such a process is at best an\napproximation that has to be corrected by experiments.\nNow if one directly starts from the right configuration (Hilbert)\nspace of the theory, one doesn\'t have to mention any exclusion\nprinciple or resulting \'force\'.\n\nCedric\n</UL></PRE></font></td></tr></table></BODY><HTML>');"> <IMG SRC=/images/buttons/ip.gif BORDER=0 ALIGN=CENTER ALT="View this Usenet post in original ASCII form"> View this Usenet post in original ASCII form </a></div><P></jabberwocky>ptamirez@yahoo.co.uk (Pedro Tamirez) wrote in message news:<11d563b8.0409040632.6ebf80f9@posting.google.com>...
> I am a bit confused about how many fundamental forces exist. Everybody
> keeps on saying that there are four fundamental forces:
(snip)
> But then there is this strange repulsive force, caused by the Pauli
> exclusion principle, that two fermions with the same quantum numbers
> cannot be brought together infinitely close. A repulsive force keeps
> them seperated.
Because we are used to classical mechanics, we picture particles as
individual objects each with a definite positions. When we translate
the notion of particles to quantum mechanics we first keep this
intuitive view, because that's all we have to start with. But then
experiments tell us that this is wrong and that the actual
configuration space of fermions (or bosons) is much smaller than the
one we would have if each particles had an individuality as is the
case for macroscopic objects.
So the fact is that a state of tightly packed fermions does not exist.
This is the exclusion principle. The very idea of such a state comes
from the classical concept of a particle and had to be removed from
the naive first attempt at constructing a quantum many body theory.
This illustrates how the process of quantization consists in trying to
guess the quantum theory underlying macroscopic phenomenon. One lacks
information and the result of such a process is at best an
approximation that has to be corrected by experiments.
Now if one directly starts from the right configuration (Hilbert)
space of the theory, one doesn't have to mention any exclusion
principle or resulting 'force'.
Cedric
<jabberwocky><div class="vbmenu_control"><a href="jabberwocky:;" onClick="newWindow=window.open('','usenetCode','toolbar=no, location=no,scrollbars=yes,resizable=yes,status=no ,width=650,height=400'); newWindow.document.write('<HTML><HEAD><TITLE>Usenet ASCII</TITLE></HEAD><BODY topmargin=0 leftmargin=0 BGCOLOR=#F1F1F1><table border=0 width=625><td bgcolor=midnightblue><font color=#F1F1F1>This Usenet message\'s original ASCII form: </font></td></tr><tr><td width=449><br><br><font face=courier><UL><PRE>\n\nMark wrote:\n> > THere are no forces involved in the Exclusion Principle.\n>\n> Well, some authors call it an \'effective force\'.\n\nYou could imagine other QM results as "forces", like in ol\' dual slit\ninterference you could argue that some "force" is keeping particles\naway from the pattern nodes in the same way as the pauli exclusion\narises from a probability pattern with a node resulting from the\ninterference of wavefunctions during the exchange of identical\nparticles of a particular spin.\n\n> BTW: how is the notion \'force\' defined? Isn\'t that just a classical\n> notion with no consistent meaning in quantum mechanics?\n\nAs another poster wrote, I think standard model forces are simply more\nor less defined by the force-particle carrying fields and their\nassociated symmetry groups, whose dynamics and kinematics can be\nwritten in the classical lagrangian style. Gravitation looks\ntheoretically similar but since there is no unification of classical\ngravity and QM, you probably would run into trouble with the\n"consistent meaning" if you want to include gravity as a force in the\nquestion..\n\n/BW\n</UL></PRE></font></td></tr></table></BODY><HTML>');"> <IMG SRC=/images/buttons/ip.gif BORDER=0 ALIGN=CENTER ALT="View this Usenet post in original ASCII form"> View this Usenet post in original ASCII form </a></div><P></jabberwocky>Mark wrote:
> > THere are no forces involved in the Exclusion Principle.
>
> Well, some authors call it an 'effective force'.
You could imagine other QM results as "forces", like in ol' dual slit
interference you could argue that some "force" is keeping particles
away from the pattern nodes in the same way as the pauli exclusion
arises from a probability pattern with a node resulting from the
interference of wavefunctions during the exchange of identical
particles of a particular spin.
> BTW: how is the notion 'force' defined? Isn't that just a classical
> notion with no consistent meaning in quantum mechanics?
As another poster wrote, I think standard model forces are simply more
or less defined by the force-particle carrying fields and their
associated symmetry groups, whose dynamics and kinematics can be
written in the classical lagrangian style. Gravitation looks
theoretically similar but since there is no unification of classical
gravity and QM, you probably would run into trouble with the
"consistent meaning" if you want to include gravity as a force in the
question..
/BW
alistair
Sep19-04, 11:38 AM
<jabberwocky><div class="vbmenu_control"><a href="jabberwocky:;" onClick="newWindow=window.open('','usenetCode','toolbar=no, location=no,scrollbars=yes,resizable=yes,status=no ,width=650,height=400'); newWindow.document.write('<HTML><HEAD><TITLE>Usenet ASCII</TITLE></HEAD><BODY topmargin=0 leftmargin=0 BGCOLOR=#F1F1F1><table border=0 width=625><td bgcolor=midnightblue><font color=#F1F1F1>This Usenet message\'s original ASCII form: </font></td></tr><tr><td width=449><br><br><font face=courier><UL><PRE>\n\nCedric Beny wrote in message:\n\n>Because we are used to classical mechanics, we picture particles as\n>individual objects each with a definite positions. When we translate\n>the notion of particles to quantum mechanics we first keep this\n>intuitive view, because that\'s all we have to start with. But then\n>experiments tell us that this is wrong\n\nExperiments do not tell us the particle picture is wrong - most\nphysicists choose to interpret results this way.Bohm\'s pilot wave\nversion of qm gives predictions that match standard qm and the theory\nallows electrons and photons to be particles.\n</UL></PRE></font></td></tr></table></BODY><HTML>');"> <IMG SRC=/images/buttons/ip.gif BORDER=0 ALIGN=CENTER ALT="View this Usenet post in original ASCII form"> View this Usenet post in original ASCII form </a></div><P></jabberwocky>Cedric Beny wrote in message:
>Because we are used to classical mechanics, we picture particles as
>individual objects each with a definite positions. When we translate
>the notion of particles to quantum mechanics we first keep this
>intuitive view, because that's all we have to start with. But then
>experiments tell us that this is wrong
Experiments do not tell us the particle picture is wrong - most
physicists choose to interpret results this way.Bohm's pilot wave
version of qm gives predictions that match standard qm and the theory
allows electrons and photons to be particles.
Enquirer
Sep19-04, 11:38 AM
<jabberwocky><div class="vbmenu_control"><a href="jabberwocky:;" onClick="newWindow=window.open('','usenetCode','toolbar=no, location=no,scrollbars=yes,resizable=yes,status=no ,width=650,height=400'); newWindow.document.write('<HTML><HEAD><TITLE>Usenet ASCII</TITLE></HEAD><BODY topmargin=0 leftmargin=0 BGCOLOR=#F1F1F1><table border=0 width=625><td bgcolor=midnightblue><font color=#F1F1F1>This Usenet message\'s original ASCII form: </font></td></tr><tr><td width=449><br><br><font face=courier><UL><PRE>\n\nalfps@start.no (Alf P. Steinbach) wrote in message news:<41413827.606694515@news.individual.net>...\n > * Gerard Westendorp:\n> > Pedro Tamirez wrote:\n> >\n> > > Hello physics world out there,\n> > >\n> > > I am a bit confused about how many fundamental forces exist. Everybody\n> > > keeps on saying that there are four fundamental forces: gravity,\n> > > strong, weak and electromagnetic. (I don\'t want to start any\n> > > discussion about possible unifications or additional exotic forces.)\n> > > But then there is this strange repulsive force, caused by the Pauli\n> > > exclusion principle, that two fermions with the same quantum numbers\n> > > cannot be brought together infinitely close. A repulsive force keeps\n> > > them seperated.\n> > >\n> > > Now my question is: How does this _new_ force tie in with the other\n> > > four. As no one talks of 5 fundamental forces, it somehow must be\n> > > related to the others? Or is it a fundamental force?\n> >\n> >\n> > Its amazing that matter does not implode under the electric force\n> > between electrons and nuclei. In classical mechanics, the thing\n> > stopping this would have to be a force, acting on the electrons,\n> > which would be little balls in classical physics.\n> >\n> > But in quantum field theory, electrons are not little balls, but\n> > excitations of the electron field. This is pretty hard to visualize.\n> > In QFT, the definition of a force is different. In the path\n> > integral picture of Feynman, forces are diagrams with\n> > force-carrying particles interconnecting other particles. Each\n> > fundamental force has a fundamental force carrying particle.\n> > Pauli exclusion is caused by the fact that you have to sum all\n> > possible diagrams. This is a different thing, although the\n> > net effect on the electrons behavior is very similar.\n>\n> I think this is the best explanation so far.\n>\n> In essence, the definition of "force" adopted is not that it acts like\n> a force, i.e. induces acceleration, but that it _in a certain theory_ causes\n> acceleration in a certain way, by exchange of messenger particles.\n>\n> This is not uncommon in my own field of expertise (programming), where\n> ordinary words are very often redefined to mean quite different things\n> in different contexts, and, of course, depending on the relevant standard\n> and programming language and so on: this allows for very lively discussions\n> and also for side-stepping thorny issues and contradictions.\n>\n> I suggest a new more general term is required, e.g. "acceleration-inducer".\n>\n> Then the question becomes: how many fundamental acceleration-inducers\n> are there, disregarding arguments that gravity does not induce\n> acceleration (since I still hurt a little in my sitting area after\n> drainage of an abscess I have direct evidence here & now that gravity\n> does induce a downward acceleration of my body)?\n\nI too agree that there it depends upon what you call a force and\nstrictly speaking its not a force but just a kinematical requirement.\nBut just to add...PEP can even lead to an effective *attraction*\nbetween two fermions in some situations. Check American Journal of\nPhysics 71 (12), page 1223. The article also deals with the question\nraised in somewhat more detail than usual text-books.\n</UL></PRE></font></td></tr></table></BODY><HTML>');"> <IMG SRC=/images/buttons/ip.gif BORDER=0 ALIGN=CENTER ALT="View this Usenet post in original ASCII form"> View this Usenet post in original ASCII form </a></div><P></jabberwocky>alfps@start.no (Alf P. Steinbach) wrote in message news:<41413827.606694515@news.individual.net>...
> * Gerard Westendorp:
> > Pedro Tamirez wrote:
> >
> > > Hello physics world out there,
> > >
> > > I am a bit confused about how many fundamental forces exist. Everybody
> > > keeps on saying that there are four fundamental forces: gravity,
> > > strong, weak and electromagnetic. (I don't want to start any
> > > discussion about possible unifications or additional exotic forces.)
> > > But then there is this strange repulsive force, caused by the Pauli
> > > exclusion principle, that two fermions with the same quantum numbers
> > > cannot be brought together infinitely close. A repulsive force keeps
> > > them seperated.
> > >
> > > Now my question is: How does this _new_ force tie in with the other
> > > four. As no one talks of 5 fundamental forces, it somehow must be
> > > related to the others? Or is it a fundamental force?
> >
> >
> > Its amazing that matter does not implode under the electric force
> > between electrons and nuclei. In classical mechanics, the thing
> > stopping this would have to be a force, acting on the electrons,
> > which would be little balls in classical physics.
> >
> > But in quantum field theory, electrons are not little balls, but
> > excitations of the electron field. This is pretty hard to visualize.
> > In QFT, the definition of a force is different. In the path
> > integral picture of Feynman, forces are diagrams with
> > force-carrying particles interconnecting other particles. Each
> > fundamental force has a fundamental force carrying particle.
> > Pauli exclusion is caused by the fact that you have to sum all
> > possible diagrams. This is a different thing, although the
> > net effect on the electrons behavior is very similar.
>
> I think this is the best explanation so far.
>
> In essence, the definition of "force" adopted is not that it acts like
> a force, i.e. induces acceleration, but that it _in a certain theory_ causes
> acceleration in a certain way, by exchange of messenger particles.
>
> This is not uncommon in my own field of expertise (programming), where
> ordinary words are very often redefined to mean quite different things
> in different contexts, and, of course, depending on the relevant standard
> and programming language and so on: this allows for very lively discussions
> and also for side-stepping thorny issues and contradictions.
>
> I suggest a new more general term is required, e.g. "acceleration-inducer".
>
> Then the question becomes: how many fundamental acceleration-inducers
> are there, disregarding arguments that gravity does not induce
> acceleration (since I still hurt a little in my sitting area after
> drainage of an abscess I have direct evidence here & now that gravity
> does induce a downward acceleration of my body)?
I too agree that there it depends upon what you call a force and
strictly speaking its not a force but just a kinematical requirement.
But just to add...PEP can even lead to an effective *attraction*
between two fermions in some situations. Check American Journal of
Physics 71 (12), page 1223. The article also deals with the question
raised in somewhat more detail than usual text-books.
<jabberwocky><div class="vbmenu_control"><a href="jabberwocky:;" onClick="newWindow=window.open('','usenetCode','toolbar=no, location=no,scrollbars=yes,resizable=yes,status=no ,width=650,height=400'); newWindow.document.write('<HTML><HEAD><TITLE>Usenet ASCII</TITLE></HEAD><BODY topmargin=0 leftmargin=0 BGCOLOR=#F1F1F1><table border=0 width=625><td bgcolor=midnightblue><font color=#F1F1F1>This Usenet message\'s original ASCII form: </font></td></tr><tr><td width=449><br><br><font face=courier><UL><PRE>\nalistair wrote:\n\n> Experiments do not tell us the particle picture is wrong - most\n> physicists choose to interpret results this way.Bohm\'s pilot wave\n> version of qm gives predictions that match standard qm and the theory\n> allows electrons and photons to be particles.\n\nI am not familiar with Bohm\'s interpretation but I would bet that\nBohm\'s particles come out of a re-intepretations of the theory and do\nnot have much in common with the pre-quantization particles. Am I\nwrong?\n\nCedric\n</UL></PRE></font></td></tr></table></BODY><HTML>');"> <IMG SRC=/images/buttons/ip.gif BORDER=0 ALIGN=CENTER ALT="View this Usenet post in original ASCII form"> View this Usenet post in original ASCII form </a></div><P></jabberwocky>alistair wrote:
> Experiments do not tell us the particle picture is wrong - most
> physicists choose to interpret results this way.Bohm's pilot wave
> version of qm gives predictions that match standard qm and the theory
> allows electrons and photons to be particles.
I am not familiar with Bohm's interpretation but I would bet that
Bohm's particles come out of a re-intepretations of the theory and do
not have much in common with the pre-quantization particles. Am I
wrong?
Cedric
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