Charles Francis
Apr7-04, 08:32 AM
<jabberwocky><div class="vbmenu_control"><a href="jabberwocky:;" onClick="newWindow=window.open('','usenetCode','toolbar=no, location=no,scrollbars=yes,resize=yes,status=no,wi dth=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\nIn article <7inbc.13962$vo5.423583@bgtnsc05-news.ops.worldnet.att.net>,\nCalvin Ritchie <DonRitchie870@csWebmail.com> writes\n>Charles Francis wrote:\n>\n>>I don\'t know quite how you work this out. There are four photon\n>>polarisation states, not just two. The time like and longitudinal states\n>>must always have the same amplitude, and may be considered as a\n>>lightlike states, but although cross sections for this state are zero\n>>and some treatments discard it, it is responsible for the Coulomb force,\n>>and if it is discarded it becomes impossible to model the classical em\n>>field.\n>\n>This thread seems to be merging with the one titled J=1, spin=0, Massless\n>fields. If you haven\'t been following that, you might be particularly\n>interested in the message I posted this afternoon (2 April \'04) which has a\n>u.r.l. to a 2003 paper in Journal of Physics. A on this which gives concise\n>equations for \'little group\' transformations.\n> In playing around with such things, particularly the various reps. of\n>sl(2,C)Xsl(2,C), I easily found (before seeing that paper) that elements of\n>Wigner\'s little group transform both +/-1 helicity 4-vectors into the\n>(1,0,0,1), and that those same elements annihilate (1,0,0,1).\n\nYes, this is true. The amplitude of lightlike states is indeterminate.\nThis is a gauge invariance. I like to split gauge invariance into\ndifferent causes. This one is a true physical invariance, the lightlike\nstates have to be there because you can transform the transverse states\ninto them but you cannot give an amplitude for them. Other gauge\ninvariances are simply mathematical and have no such metaphysical\ninterpretation.\n\n> Apparently, this is one of those things that "everyone knows", so it\'s\n>missed (and messed) in many texts.\n\nI get worried about these things that "everyone knows". In my own\ndoctorate in the eighties I found I had to rederive several things that\n"everyone knew" in the fifties, but everyone had forgotten by the\neighties. Sometimes something that everyone knows, like the\nnon-existence of gravitons, become so forgotten that after a bit\neveryone thinks they know that it isn\'t true.\n\n> All of this is rather new to me, and I\'d really appreciate hearing from\n>an "old hand" what it all might mean.\n>\n\nI will write fuller response in the other thread.\n\n\nRegards\n\n--\nCharles Francis\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>In article <7inbc.13962$vo5.423583@bgtnsc05-news.ops.worldnet.att.net>,
Calvin Ritchie <DonRitchie870@csWebmail.com> writes
>Charles Francis wrote:
>
>>I don't know quite how you work this out. There are four photon
>>polarisation states, not just two. The time like and longitudinal states
>>must always have the same amplitude, and may be considered as a
>>lightlike states, but although cross sections for this state are zero
>>and some treatments discard it, it is responsible for the Coulomb force,
>>and if it is discarded it becomes impossible to model the classical em
>>field.
>
>This thread seems to be merging with the one titled J=1, spin=0, Massless
>fields. If you haven't been following that, you might be particularly
>interested in the message I posted this afternoon (2 April '04) which has a
>u.r.l. to a 2003 paper in Journal of Physics. A on this which gives concise
>equations for 'little group' transformations.
> In playing around with such things, particularly the various reps. of
>sl(2,C)Xsl(2,C), I easily found (before seeing that paper) that elements of
>Wigner's little group transform both +/-1 helicity 4-vectors into the
>(1,0,0,1), and that those same elements annihilate (1,0,0,1).
Yes, this is true. The amplitude of lightlike states is indeterminate.
This is a gauge invariance. I like to split gauge invariance into
different causes. This one is a true physical invariance, the lightlike
states have to be there because you can transform the transverse states
into them but you cannot give an amplitude for them. Other gauge
invariances are simply mathematical and have no such metaphysical
interpretation.
> Apparently, this is one of those things that "everyone knows", so it's
>missed (and messed) in many texts.
I get worried about these things that "everyone knows". In my own
doctorate in the eighties I found I had to rederive several things that
"everyone knew" in the fifties, but everyone had forgotten by the
eighties. Sometimes something that everyone knows, like the
non-existence of gravitons, become so forgotten that after a bit
everyone thinks they know that it isn't true.
> All of this is rather new to me, and I'd really appreciate hearing from
>an "old hand" what it all might mean.
>
I will write fuller response in the other thread.
Regards
--
Charles Francis
Calvin Ritchie <DonRitchie870@csWebmail.com> writes
>Charles Francis wrote:
>
>>I don't know quite how you work this out. There are four photon
>>polarisation states, not just two. The time like and longitudinal states
>>must always have the same amplitude, and may be considered as a
>>lightlike states, but although cross sections for this state are zero
>>and some treatments discard it, it is responsible for the Coulomb force,
>>and if it is discarded it becomes impossible to model the classical em
>>field.
>
>This thread seems to be merging with the one titled J=1, spin=0, Massless
>fields. If you haven't been following that, you might be particularly
>interested in the message I posted this afternoon (2 April '04) which has a
>u.r.l. to a 2003 paper in Journal of Physics. A on this which gives concise
>equations for 'little group' transformations.
> In playing around with such things, particularly the various reps. of
>sl(2,C)Xsl(2,C), I easily found (before seeing that paper) that elements of
>Wigner's little group transform both +/-1 helicity 4-vectors into the
>(1,0,0,1), and that those same elements annihilate (1,0,0,1).
Yes, this is true. The amplitude of lightlike states is indeterminate.
This is a gauge invariance. I like to split gauge invariance into
different causes. This one is a true physical invariance, the lightlike
states have to be there because you can transform the transverse states
into them but you cannot give an amplitude for them. Other gauge
invariances are simply mathematical and have no such metaphysical
interpretation.
> Apparently, this is one of those things that "everyone knows", so it's
>missed (and messed) in many texts.
I get worried about these things that "everyone knows". In my own
doctorate in the eighties I found I had to rederive several things that
"everyone knew" in the fifties, but everyone had forgotten by the
eighties. Sometimes something that everyone knows, like the
non-existence of gravitons, become so forgotten that after a bit
everyone thinks they know that it isn't true.
> All of this is rather new to me, and I'd really appreciate hearing from
>an "old hand" what it all might mean.
>
I will write fuller response in the other thread.
Regards
--
Charles Francis