Jerzy Karczmarczuk
Apr27-04, 02:02 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>Patrick Van Esch wrote, commenting my own comment on classical Coulomb:\n\n>>It is well known that we have to go to\n>>the infra-red limit; the classical force will result from an infinite number\n>>of wee photons, with infinite wavelength... So, first of all, one should\n>>refrain from imagining a classical, macroscopical interaction as the exchange\n>>of virtual particles, unless one knows that one has to descend to a delicate\n>>coherent limit.\n>\n> This is true for bound states (I don\'t know much of that). But how do\n> you explain that the right potential (1/r) comes out of the single\n> tree diagram in scattering ? This means that the essence of the\n> Coulomb interaction is already present in this single exchange, no ?\n\nYes, sure, the Lagrangian starts with a \'classical\' stuff, which becomes the\nBorn term. But 1/r of the classical *final, physical result* concerning the\nlong range interaction between classical bodies is not the dynamics of ONE\nphoton, it is something resulting from the delicate interplay of infrared\nlimit and the Great Mystery of multiplicative renormalization, which **MUST**\npreserve the gauge symmetry, the fact that electromagnetic energy carriers\nhave mass zero!!\n\n\nMind you, when you say \'1/r\' you disregard the time dependence. Perfectly\nalright, the Coulomb potential is static. But if you use it as such in your\ncalculi, you *implicitly* (hm... for goodness sake, why "implicitly"...) you\nplace yourself already in the infrared limit, the "classical photons" exchanged\nbetween macroscopic bodies have infinite wavelength, and there is nothing to\nadd to it. Even doing relativistic, but CLASSICAL electrodynamics, you can\nLorenz-boost the Coulomb potential, but you will not, repeat NOT introduce\nany "photon frequencies". You will just produce a retarded potential.\n\n==================================== =====================\nIn order not to proliferate postings, a few words adressed to\n\nDavid/Ulmo, who wrote:\n\n> There are people who post on this board saying wavefunctions or\n> virtual particles aren\'t "real" but are instead a mathematcal device.\n> Well, you could say everything in every theory of physics is a\n> "mathematical device". All of our theories were invented by humans,\n> and are not the same thing as the real Universe. You could say all of\n> or theories is just a mathematical construct to get the predictions to\n> match up with observations, and all our theories are just convenient\n> ways of thiking about it, and all of our theories are obviously not\n> the real Universe, so how are wavefunctions or virtual particles less\n> "real" than anything else in physics?\n\nA personal confession first. I am not a physicist, but a computer scientist,\nand your questions are the same kind of existential horror, as found in my\nown milieu, where people discuss/yell/weep about the "computability of the\nUniverse". I recommend always Shakespeare "Much a do about nothing", or the\nDouglas Adams science fiction series as an additional literature, not because\nI want to show cynical or funny, but because we as humans are so hopelessly\nfar away of the True Mystery, that we should rather try to respond to the\nchallenge of "what is IMPORTANT, not what is "real".\n\nWhat is usable. What makes us progressing (from, say, the positivist perspec-\ntive). So, in order to target your specific issues:\n\n1. Virtual praticles are "not real", because they don\'t have serious mass, and\nbecause it is not possible to say whether one, or many, or infinite number\nof them have been produced; the process of their creation and absorption is\nnot described "physically" by any theory, they are irreducible events. And\nthose events are absolutely uncontrollable.\n\nIt requires an "act of faith" in order to see that a t-channel pole in the\nscattering amplitude has something resembling a "real particle" through the\nanalytic continuation to the s-channel propagators. But mathematics helps\nus here, and virtual particles offer a nice, intuitive picture. They become\n"real", as tool.\n\n2. Wave functions are "not real", because for those who consider *waves* as\nreal, there is no answer to the question: "waves of WHAT". You can\'t say\nwithout blinking "waves of probability" (or similar), since \'probability\'\nitself is an abstraction, a measure-theoretical concept.\n\nThey are "not real", because they are JUST A REPRESENTATION of quantum\nstates. You may transform them to a dual space (momenta) from the ordinary\nX space, and you get some other, mathematically equivalent form. So, they\ndescribe your *formalism*, not the "particle themselves". But since the\nformalism has some predictice power, we believe that wave functions somehow\nreflect the reality.\n\nNow, I will tell you what is "real", if you explain to me, a non-native\nEnglish speaker, the TRUE meaning of the expression "somehow reflect"...\n\n\nJerzy Karczmarczuk\n\n\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>Patrick Van Esch wrote, commenting my own comment on classical Coulomb:
>>It is well known that we have to go to
>>the infra-red limit; the classical force will result from an infinite number
>>of wee photons, with infinite wavelength... So, first of all, one should
>>refrain from imagining a classical, macroscopical interaction as the exchange
>>of virtual particles, unless one knows that one has to descend to a delicate
>>coherent limit.
>
> This is true for bound states (I don't know much of that). But how do
> you explain that the right potential (1/r) comes out of the single
> tree diagram in scattering ? This means that the essence of the
> Coulomb interaction is already present in this single exchange, no ?
Yes, sure, the Lagrangian starts with a 'classical' stuff, which becomes the
Born term. But 1/r of the classical *final, physical result* concerning the
long range interaction between classical bodies is not the dynamics of ONE
photon, it is something resulting from the delicate interplay of infrared
limit and the Great Mystery of multiplicative renormalization, which **MUST**
preserve the gauge symmetry, the fact that electromagnetic energy carriers
have mass zero!!
Mind you, when you say '1/r' you disregard the time dependence. Perfectly
alright, the Coulomb potential is static. But if you use it as such in your
calculi, you *implicitly* (hm... for goodness sake, why "implicitly"...) you
place yourself already in the infrared limit, the "classical photons" exchanged
between macroscopic bodies have infinite wavelength, and there is nothing to
add to it. Even doing relativistic, but CLASSICAL electrodynamics, you can
Lorenz-boost the Coulomb potential, but you will not, repeat NOT introduce
any "photon frequencies". You will just produce a retarded potential.
================================================== =======
In order not to proliferate postings, a few words adressed to
David/Ulmo, who wrote:
> There are people who post on this board saying wavefunctions or
> virtual particles aren't "real" but are instead a mathematcal device.
> Well, you could say everything in every theory of physics is a
> "mathematical device". All of our theories were invented by humans,
> and are not the same thing as the real Universe. You could say all of
> or theories is just a mathematical construct to get the predictions to
> match up with observations, and all our theories are just convenient
> ways of thiking about it, and all of our theories are obviously not
> the real Universe, so how are wavefunctions or virtual particles less
> "real" than anything else in physics?
A personal confession first. I am not a physicist, but a computer scientist,
and your questions are the same kind of existential horror, as found in my
own milieu, where people discuss/yell/weep about the "computability of the
Universe". I recommend always Shakespeare "Much a do about nothing", or the
Douglas Adams science fiction series as an additional literature, not because
I want to show cynical or funny, but because we as humans are so hopelessly
far away of the True Mystery, that we should rather try to respond to the
challenge of "what is IMPORTANT, not what is "real".
What is usable. What makes us progressing (from, say, the positivist perspec-
tive). So, in order to target your specific issues:
1. Virtual praticles are "not real", because they don't have serious mass, and
because it is not possible to say whether one, or many, or infinite number
of them have been produced; the process of their creation and absorption is
not described "physically" by any theory, they are irreducible events. And
those events are absolutely uncontrollable.
It requires an "act of faith" in order to see that a t-channel pole in the
scattering amplitude has something resembling a "real particle" through the
analytic continuation to the s-channel propagators. But mathematics helps
us here, and virtual particles offer a nice, intuitive picture. They become
"real", as tool.
2. Wave functions are "not real", because for those who consider *waves* as
real, there is no answer to the question: "waves of WHAT". You can't say
without blinking "waves of probability" (or similar), since 'probability'
itself is an abstraction, a measure-theoretical concept.
They are "not real", because they are JUST A REPRESENTATION of quantum
states. You may transform them to a dual space (momenta) from the ordinary
X space, and you get some other, mathematically equivalent form. So, they
describe your *formalism*, not the "particle themselves". But since the
formalism has some predictice power, we believe that wave functions somehow
reflect the reality.
Now, I will tell you what is "real", if you explain to me, a non-native
English speaker, the TRUE meaning of the expression "somehow reflect"...
Jerzy Karczmarczuk
>>It is well known that we have to go to
>>the infra-red limit; the classical force will result from an infinite number
>>of wee photons, with infinite wavelength... So, first of all, one should
>>refrain from imagining a classical, macroscopical interaction as the exchange
>>of virtual particles, unless one knows that one has to descend to a delicate
>>coherent limit.
>
> This is true for bound states (I don't know much of that). But how do
> you explain that the right potential (1/r) comes out of the single
> tree diagram in scattering ? This means that the essence of the
> Coulomb interaction is already present in this single exchange, no ?
Yes, sure, the Lagrangian starts with a 'classical' stuff, which becomes the
Born term. But 1/r of the classical *final, physical result* concerning the
long range interaction between classical bodies is not the dynamics of ONE
photon, it is something resulting from the delicate interplay of infrared
limit and the Great Mystery of multiplicative renormalization, which **MUST**
preserve the gauge symmetry, the fact that electromagnetic energy carriers
have mass zero!!
Mind you, when you say '1/r' you disregard the time dependence. Perfectly
alright, the Coulomb potential is static. But if you use it as such in your
calculi, you *implicitly* (hm... for goodness sake, why "implicitly"...) you
place yourself already in the infrared limit, the "classical photons" exchanged
between macroscopic bodies have infinite wavelength, and there is nothing to
add to it. Even doing relativistic, but CLASSICAL electrodynamics, you can
Lorenz-boost the Coulomb potential, but you will not, repeat NOT introduce
any "photon frequencies". You will just produce a retarded potential.
================================================== =======
In order not to proliferate postings, a few words adressed to
David/Ulmo, who wrote:
> There are people who post on this board saying wavefunctions or
> virtual particles aren't "real" but are instead a mathematcal device.
> Well, you could say everything in every theory of physics is a
> "mathematical device". All of our theories were invented by humans,
> and are not the same thing as the real Universe. You could say all of
> or theories is just a mathematical construct to get the predictions to
> match up with observations, and all our theories are just convenient
> ways of thiking about it, and all of our theories are obviously not
> the real Universe, so how are wavefunctions or virtual particles less
> "real" than anything else in physics?
A personal confession first. I am not a physicist, but a computer scientist,
and your questions are the same kind of existential horror, as found in my
own milieu, where people discuss/yell/weep about the "computability of the
Universe". I recommend always Shakespeare "Much a do about nothing", or the
Douglas Adams science fiction series as an additional literature, not because
I want to show cynical or funny, but because we as humans are so hopelessly
far away of the True Mystery, that we should rather try to respond to the
challenge of "what is IMPORTANT, not what is "real".
What is usable. What makes us progressing (from, say, the positivist perspec-
tive). So, in order to target your specific issues:
1. Virtual praticles are "not real", because they don't have serious mass, and
because it is not possible to say whether one, or many, or infinite number
of them have been produced; the process of their creation and absorption is
not described "physically" by any theory, they are irreducible events. And
those events are absolutely uncontrollable.
It requires an "act of faith" in order to see that a t-channel pole in the
scattering amplitude has something resembling a "real particle" through the
analytic continuation to the s-channel propagators. But mathematics helps
us here, and virtual particles offer a nice, intuitive picture. They become
"real", as tool.
2. Wave functions are "not real", because for those who consider *waves* as
real, there is no answer to the question: "waves of WHAT". You can't say
without blinking "waves of probability" (or similar), since 'probability'
itself is an abstraction, a measure-theoretical concept.
They are "not real", because they are JUST A REPRESENTATION of quantum
states. You may transform them to a dual space (momenta) from the ordinary
X space, and you get some other, mathematically equivalent form. So, they
describe your *formalism*, not the "particle themselves". But since the
formalism has some predictice power, we believe that wave functions somehow
reflect the reality.
Now, I will tell you what is "real", if you explain to me, a non-native
English speaker, the TRUE meaning of the expression "somehow reflect"...
Jerzy Karczmarczuk