View Full Version : [SOLVED] magnetic field splitting gamma photons in two
alistair
Dec4-04, 03:20 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>A magnetic field of 10^9 Tesla, around a neutron star, can cause a\ngamma photon to split into two lower energy photons.What is the\nunderlying reason for this? Presumably virtual photons from the\nmagnetic field initiate this process?\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>A magnetic field of 10^9 Tesla, around a neutron star, can cause a
\gamma photon to split into two lower energy photons.What is the
underlying reason for this? Presumably virtual photons from the
magnetic field initiate this process?
Igor Khavkine
Dec6-04, 07:17 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>On Sat, 04 Dec 2004 21:20:41 +0000, alistair wrote:\n\n> A magnetic field of 10^9 Tesla, around a neutron star, can cause a gamma\n> photon to split into two lower energy photons.What is the underlying\n> reason for this?\n\nIn the absence of external fields, this process is impossible. There are\ntwo lowest order diagrams that contribute. Both look like this:\n\n+~~~~~~~\n/|\n/ |\n~~~~~~~+ |\n\\ |\n\\|\n+~~~~~~~\n\nThe internal lines represent electrons. Fermion lines in a Feynman diagram\nmust be decorated with arrows indicating the flow of charge. Charge\nconjugation symmetry says that for any Feynman diagram with fermions,\nthere is another one with the same amplitude but with all arrows on the\nfermions reversed and multiplied by -1 for each fermion line. As you can\nsee, the internal triangle can be labeled with arrows going clockwise or\ncounterclockwise. The resulting two diagrams have the same amplitude which\ndiffers only by a minus sign, hence they cancel each other out when their\ncontributions are summed. The same thing happens to diagrams of all orders\ncontributing to this process.\n\nHowever, in the presence of an external field this symmetry is broken and\nthe above process is in general allowed. However, the amplitude is still\nvery small unless the external field is large.\n\n> Presumably virtual photons from the magnetic field initiate this process?\n\nAnd why do you presume so? One of the challenges a theoretical physicist\nfaces is coming up with different ways to perform the same calculation. To\neach method one can assign a different physical interpretation. This helps\nbuild intuition, because in different cases some calculation methods may\nbe easier to apply than others, correspondingly some physical\ninterpretations paint a clearer picture than others.\n\nTo help you expand your physical intuition, here\'s a challenge: come up\nwith a mechanism for the photon splitting process without invoking virtual\nphotons.\n\nI can see at least two ways of explaining this process, one involving\nvirtual photons and one not. However, as expected, in the end they are\nequivalent.\n\nIgor\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>On Sat, 04 Dec 2004 21:20:41 +0000, alistair wrote:
> A magnetic field of 10^9 Tesla, around a neutron star, can cause a \gamma
> photon to split into two lower energy photons.What is the underlying
> reason for this?
In the absence of external fields, this process is impossible. There are
two lowest order diagrams that contribute. Both look like this:
+~~~~~~~[/itex]
/|
/ |
~~~~~~~+ |
\ |
\|
[itex]+~~~~~~~
The internal lines represent electrons. Fermion lines in a Feynman diagram
must be decorated with arrows indicating the flow of charge. Charge
conjugation symmetry says that for any Feynman diagram with fermions,
there is another one with the same amplitude but with all arrows on the
fermions reversed and multiplied by -1 for each fermion line. As you can
see, the internal triangle can be labeled with arrows going clockwise or
counterclockwise. The resulting two diagrams have the same amplitude which
differs only by a minus sign, hence they cancel each other out when their
contributions are summed. The same thing happens to diagrams of all orders
contributing to this process.
However, in the presence of an external field this symmetry is broken and
the above process is in general allowed. However, the amplitude is still
very small unless the external field is large.
> Presumably virtual photons from the magnetic field initiate this process?
And why do you presume so? One of the challenges a theoretical physicist
faces is coming up with different ways to perform the same calculation. To
each method one can assign a different physical interpretation. This helps
build intuition, because in different cases some calculation methods may
be easier to apply than others, correspondingly some physical
interpretations paint a clearer picture than others.
To help you expand your physical intuition, here's a challenge: come up
with a mechanism for the photon splitting process without invoking virtual
photons.
I can see at least two ways of explaining this process, one involving
virtual photons and one not. However, as expected, in the end they are
equivalent.
Igor
alistair@goforit64.fsnet.co.uk
Dec7-04, 08:06 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\nIgor Khavkine wrote in message:\n\n>To help you expand your physical intuition, here\'s a >challenge: come\nup\n>with a mechanism for the photon splitting process without >invoking\nvirtual\n>photons.\n\nMagnetic field lines could split the gamma photon in two.\nIn the presence of a strong magnetic field are some of the higher\norder Feynman diagrams favoured over the others? And are there more\nvirtual photons emitted by a stronger magnetic field, or the same\nnumber with more energy?\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 Khavkine wrote in message:
>To help you expand your physical intuition, here's a >challenge: come
up
>with a mechanism for the photon splitting process without >invoking
virtual
>photons.
Magnetic field lines could split the \gamma photon in two.
In the presence of a strong magnetic field are some of the higher
order Feynman diagrams favoured over the others? And are there more
virtual photons emitted by a stronger magnetic field, or the same
number with more energy?
greywolf42
Dec7-04, 11:11 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>Igor Khavkine <k_igor_k@lycos.com> wrote in message\nnews:pan.2004.12.06.04.04.56.712847@lycos .com...\n> On Sat, 04 Dec 2004 21:20:41 +0000, alistair wrote:\n>\n> > A magnetic field of 10^9 Tesla, around a neutron star, can cause a gamma\n> > photon to split into two lower energy photons.What is the underlying\n> > reason for this?\n>\n> In the absence of external fields, this process is impossible.\n\nI\'d consider a field of a billion Tesla to be an external field.\n\n> There are\n> two lowest order diagrams that contribute. Both look like this:\n>\n> +~~~~~~~\n> /|\n> / |\n> ~~~~~~~+ |\n> \\ |\n> \\|\n> +~~~~~~~\n>\n> The internal lines represent electrons. Fermion lines in a Feynman diagram\n> must be decorated with arrows indicating the flow of charge. Charge\n> conjugation symmetry says that for any Feynman diagram with fermions,\n> there is another one with the same amplitude but with all arrows on the\n> fermions reversed and multiplied by -1 for each fermion line. As you can\n> see, the internal triangle can be labeled with arrows going clockwise or\n> counterclockwise. The resulting two diagrams have the same amplitude which\n> differs only by a minus sign, hence they cancel each other out when their\n> contributions are summed. The same thing happens to diagrams of all orders\n> contributing to this process.\n>\n> However, in the presence of an external field this symmetry is broken and\n> the above process is in general allowed. However, the amplitude is still\n> very small unless the external field is large.\n\nHow large a magnetic field do you need, if 10^9 Tesla is not sufficient?\n\n> > Presumably virtual photons from the magnetic field initiate this\n> > process?\n>\n> And why do you presume so? One of the challenges a theoretical physicist\n> faces is coming up with different ways to perform the same calculation. To\n> each method one can assign a different physical interpretation. This helps\n> build intuition, because in different cases some calculation methods may\n> be easier to apply than others, correspondingly some physical\n> interpretations paint a clearer picture than others.\n>\n> To help you expand your physical intuition, here\'s a challenge: come up\n> with a mechanism for the photon splitting process without invoking virtual\n> photons.\n>\n> I can see at least two ways of explaining this process, one involving\n> virtual photons and one not. However, as expected, in the end they are\n> equivalent.\n\nBut which one is really what happens? How do you determine this? Or are\nyou simply using virtual photons (and the not-virtual-photon method) as\nmathematical placeholders?\n\n--\ngreywolf42\nubi dubium ibi libertas\n{remove planet for return 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 Khavkine <k_{igor_k}@lycos.com> wrote in message
news:pan.2004.12.06.04.04.56.712847@lycos.com...
> On Sat, 04 Dec 2004 21:20:41 +0000, alistair wrote:
>
> > A magnetic field of 10^9 Tesla, around a neutron star, can cause a \gamma
> > photon to split into two lower energy photons.What is the underlying
> > reason for this?
>
> In the absence of external fields, this process is impossible.
I'd consider a field of a billion Tesla to be an external field.
> There are
> two lowest order diagrams that contribute. Both look like this:
>
> +~~~~~~~
> /|
> / |
> ~~~~~~~+ |
> \ |
> \|
> +~~~~~~~
>
> The internal lines represent electrons. Fermion lines in a Feynman diagram
> must be decorated with arrows indicating the flow of charge. Charge
> conjugation symmetry says that for any Feynman diagram with fermions,
> there is another one with the same amplitude but with all arrows on the
> fermions reversed and multiplied by -1 for each fermion line. As you can
> see, the internal triangle can be labeled with arrows going clockwise or
> counterclockwise. The resulting two diagrams have the same amplitude which
> differs only by a minus sign, hence they cancel each other out when their
> contributions are summed. The same thing happens to diagrams of all orders
> contributing to this process.
>
> However, in the presence of an external field this symmetry is broken and
> the above process is in general allowed. However, the amplitude is still
> very small unless the external field is large.
How large a magnetic field do you need, if 10^9 Tesla is not sufficient?
> > Presumably virtual photons from the magnetic field initiate this
> > process?
>
> And why do you presume so? One of the challenges a theoretical physicist
> faces is coming up with different ways to perform the same calculation. To
> each method one can assign a different physical interpretation. This helps
> build intuition, because in different cases some calculation methods may
> be easier to apply than others, correspondingly some physical
> interpretations paint a clearer picture than others.
>
> To help you expand your physical intuition, here's a challenge: come up
> with a mechanism for the photon splitting process without invoking virtual
> photons.
>
> I can see at least two ways of explaining this process, one involving
> virtual photons and one not. However, as expected, in the end they are
> equivalent.
But which one is really what happens? How do you determine this? Or are
you simply using virtual photons (and the not-virtual-photon method) as
mathematical placeholders?
--
greywolf42
ubi dubium ibi libertas
{remove planet for return e-mail}
alistair@goforit64.fsnet.co.uk
Dec7-04, 11:12 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>Igor Khavkine wrote in message:\n\n>To help you expand your physical intuition, here\'s a >challenge: come\nup\n>with a mechanism for the photon splitting process without >invoking\nvirtual\n>photons.\n\n\n>Magnetic field lines could split the gamma photon in two.\n>In the presence of a strong magnetic field are some of the >higher\n>order Feynman diagrams favoured over the others? And >are there more\n>virtual photons emitted by a stronger magnetic field, or the >same\n>number with more energy?\n\n\nAnd I\'d also like to ask:\ncan a virtual photon be split in two by\na magnetic field?\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 Khavkine wrote in message:
>To help you expand your physical intuition, here's a >challenge: come
up
>with a mechanism for the photon splitting process without >invoking
virtual
>photons.
>Magnetic field lines could split the \gamma photon in two.
>In the presence of a strong magnetic field are some of the >higher
>order Feynman diagrams favoured over the others? And >are there more
>virtual photons emitted by a stronger magnetic field, or the >same
>number with more energy?
And I'd also like to ask:
can a virtual photon be split in two by
a magnetic field?
Igor Khavkine
Dec8-04, 06:53 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>On Tue, 07 Dec 2004 14:06:15 +0000, alistair wrote:\n> Igor Khavkine wrote in message:\n>\n>>To help you expand your physical intuition, here\'s a >challenge: come\n> up\n>>with a mechanism for the photon splitting process without >invoking\n> virtual\n>>photons.\n>\n> Magnetic field lines could split the gamma photon in two.\n\nAnd how exactly do you bring in "magnetic field lines" into a QED\ncalculation? There is a well known rule of English style: don\'t mix\nmetaphors. There is a similar rule in theoretical physics: don\'t mix\nillustrative concepts from different problems.\n\n> In the presence\n> of a strong magnetic field are some of the higher order Feynman diagrams\n> favoured over the others?\n\nYes. Which ones and why?\n\n> And are there more virtual photons emitted by a\n> stronger magnetic field, or the same number with more energy?\n\nIn general, the intensity of a magnetic or electric field in a QED state\nis related to the number of photons not their frequency. But remember, no\nvirtual photons this time.\n\nIgor\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>On Tue, 07 Dec 2004 14:06:15 +0000, alistair wrote:
> Igor Khavkine wrote in message:
>
>>To help you expand your physical intuition, here's a >challenge: come
> up
>>with a mechanism for the photon splitting process without >invoking
> virtual
>>photons.
>
> Magnetic field lines could split the \gamma photon in two.
And how exactly do you bring in "magnetic field lines" into a QED
calculation? There is a well known rule of English style: don't mix
metaphors. There is a similar rule in theoretical physics: don't mix
illustrative concepts from different problems.
> In the presence
> of a strong magnetic field are some of the higher order Feynman diagrams
> favoured over the others?
Yes. Which ones and why?
> And are there more virtual photons emitted by a
> stronger magnetic field, or the same number with more energy?
In general, the intensity of a magnetic or electric field in a QED state
is related to the number of photons not their frequency. But remember, no
virtual photons this time.
Igor
Igor Khavkine
Dec8-04, 06:54 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>On Tue, 07 Dec 2004 17:12:43 +0000, alistair wrote:\n\n> Igor Khavkine wrote in message:\n>\n> > To help you expand your physical intuition, here\'s a\n> > challenge: come up with a mechanism for the photon splitting\n> > process without invoking virtual photons.\n\n> And I\'d also like to ask:\n> can a virtual photon be split in two by a magnetic field?\n\nI don\'t think you are trying to meet my challenge very hard. :-)\n\nOnce again, I could say something about the fallacy of deriving observable\nconsequences from a concept whose existence is at best tenuous. But that\'s\nalready been said.\n\nSince what you mean by "virtual photon" is somewhat different from what\nthe term actually stands for, I think you are the only person who can\nanswer this question to your satisfaction. So, can a virtual photon be\nsplit in two by a magnetic field?\n\nIgor\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>On Tue, 07 Dec 2004 17:12:43 +0000, alistair wrote:
> Igor Khavkine wrote in message:
>
> > To help you expand your physical intuition, here's a
> > challenge: come up with a mechanism for the photon splitting
> > process without invoking virtual photons.
> And I'd also like to ask:
> can a virtual photon be split in two by a magnetic field?
I don't think you are trying to meet my challenge very hard. :-)
Once again, I could say something about the fallacy of deriving observable
consequences from a concept whose existence is at best tenuous. But that's
already been said.
Since what you mean by "virtual photon" is somewhat different from what
the term actually stands for, I think you are the only person who can
answer this question to your satisfaction. So, can a virtual photon be
split in two by a magnetic field?
Igor
Frank Hellmann
Dec8-04, 06:54 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>Igor Khavkine wrote:\n> On Sat, 04 Dec 2004 21:20:41 +0000, alistair wrote:\n>\n> However, in the presence of an external field this symmetry is broken\nand\n> the above process is in general allowed. However, the amplitude is\nstill\n> very small unless the external field is large.\n>\n\nThe electromagnetic field is mediated by photons. This would mean that\nsome interaction with other present matter presumably creating said\nmagnetic field would create the required asymetry?\n\nThis is really a more gneral question, the whole Feynman graph\nformalism doesn\'t seem to allow for much in terms of external fields.\nHow would you calculate this?\nThe presence fo a background field implies broken Lorentz symmetry. In\nparticular the strong magnetic field could always be transformed away\nthrough a Lorentz transformation, as our theory is covariant it should\nstill describe the splitting of the photon though, I guess we would\nneed to use a form of the Feynman notation that breaks covariance?\n\nPresumably the presence of an external field implies the presence of\nother free photons which could interact with the diagram in several\nways:\n\nxooo+---+ooox\n| |\noooo+ |\n| |\noooo+---+oooo\n\nFor example, where the x lines denote a photon which we interpretate as\nthe external field photon. This would then not enter in a completely\ncovariant manner. Your argument on cancellations still would apply\nthough, wouldn\'t it?\n\nc\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>Igor Khavkine wrote:
> On Sat, 04 Dec 2004 21:20:41 +0000, alistair wrote:
>
> However, in the presence of an external field this symmetry is broken
and
> the above process is in general allowed. However, the amplitude is
still
> very small unless the external field is large.
>
The electromagnetic field is mediated by photons. This would mean that
some interaction with other present matter presumably creating said
magnetic field would create the required asymetry?
This is really a more gneral question, the whole Feynman graph
formalism doesn't seem to allow for much in terms of external fields.
How would you calculate this?
The presence fo a background field implies broken Lorentz symmetry. In
particular the strong magnetic field could always be transformed away
through a Lorentz transformation, as our theory is covariant it should
still describe the splitting of the photon though, I guess we would
need to use a form of the Feynman notation that breaks covariance?
Presumably the presence of an external field implies the presence of
other free photons which could interact with the diagram in several
ways:
xooo+---+ooox
| |oooo+ || |
oooo+---+oooo
For example, where the x lines denote a photon which we interpretate as
the external field photon. This would then not enter in a completely
covariant manner. Your argument on cancellations still would apply
though, wouldn't it?
c
Frank.
Igor Khavkine
Dec9-04, 11:33 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\nOn Tue, 07 Dec 2004 17:11:00 +0000, greywolf42 wrote:\n\n> Igor Khavkine <k_igor_k@lycos.com> wrote in message\n> news:pan.2004.12.06.04.04.56.712847@lycos.com...\n >> On Sat, 04 Dec 2004 21:20:41 +0000, alistair wrote:\n>>\n>> > A magnetic field of 10^9 Tesla, around a neutron star, can cause a\n>> > gamma photon to split into two lower energy photons.What is the\n>> > underlying reason for this?\n>>\n>> In the absence of external fields, this process is impossible.\n>\n> I\'d consider a field of a billion Tesla to be an external field.\n\nI was merely explaining why this process would be unusual under normal\ncircumstances.\n\n>> However, in the presence of an external field this symmetry is broken\n>> and the above process is in general allowed. However, the amplitude is\n>> still very small unless the external field is large.\n>\n> How large a magnetic field do you need, if 10^9 Tesla is not sufficient?\n\nA Google search lets one dig up one of the early references:\n\nPhoton Splitting in a Strong Magnetic Field\nS. L. Adler, J. N. Bahcall*, C. G. Callan, and M. N. Rosenbluth\nPhys. Rev. Lett, v.25, p.1061\n\nThere, the critical field is given as B_c = m^2/e ~ 4.41e13 Gauss ~\n4e9 Tesla, where m is the mass of the electron and e is the elementary\nelectric charge (he is probably using some sort or relativistic or natural\nunits).\n\n>> I can see at least two ways of explaining this process, one involving\n>> virtual photons and one not. However, as expected, in the end they are\n>> equivalent.\n>\n> But which one is really what happens? How do you determine this? Or are\n> you simply using virtual photons (and the not-virtual-photon method) as\n> mathematical placeholders?\n\nWords are words. If I calculate an experimental prediction in two\ndifferent ways and then describe each calculation in words to you. If each\ncalculation was done correctly they should give the same result which can\nbe tested by experiment. So which of the explanations describes what\n"really happens"?\n\nIgor\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>On Tue, 07 Dec 2004 17:11:00 +0000, greywolf42 wrote:
> Igor Khavkine <k_{igor_k}@lycos.com> wrote in message
> news:pan.2004.12.06.04.04.56.712847@lycos.com...
>> On Sat, 04 Dec 2004 21:20:41 +0000, alistair wrote:
>>
>> > A magnetic field of 10^9 Tesla, around a neutron star, can cause a
>> > \gamma photon to split into two lower energy photons.What is the
>> > underlying reason for this?
>>
>> In the absence of external fields, this process is impossible.
>
> I'd consider a field of a billion Tesla to be an external field.
I was merely explaining why this process would be unusual under normal
circumstances.
>> However, in the presence of an external field this symmetry is broken
>> and the above process is in general allowed. However, the amplitude is
>> still very small unless the external field is large.
>
> How large a magnetic field do you need, if 10^9 Tesla is not sufficient?
A Google search lets one dig up one of the early references:
Photon Splitting in a Strong Magnetic Field
S. L. Adler, J. N. Bahcall*, C. G. Callan, and M. N. Rosenbluth
Phys. Rev. Lett, v.25, p.1061
There, the critical field is given as B_c = m^2/e ~ 4.41e13 Gauss ~
4e9 Tesla, where m is the mass of the electron and e is the elementary
electric charge (he is probably using some sort or relativistic or natural
units).
>> I can see at least two ways of explaining this process, one involving
>> virtual photons and one not. However, as expected, in the end they are
>> equivalent.
>
> But which one is really what happens? How do you determine this? Or are
> you simply using virtual photons (and the not-virtual-photon method) as
> mathematical placeholders?
Words are words. If I calculate an experimental prediction in two
different ways and then describe each calculation in words to you. If each
calculation was done correctly they should give the same result which can
be tested by experiment. So which of the explanations describes what
"really happens"?
Igor
Igor Khavkine
Dec13-04, 10:38 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>or corporation executives; and so forth. Most individuals\nare not in a position to secure themselves against these threats to\nmore [than] a very limited extent. The individual\'s search for\nsecurity is therefore frustrated, which leads to a sense of\npowerlessness.\n\n68. It may be objected that primitive man is physically less secure\nthan modern man, as is shown by his shorter life expectancy; hence\nmodern man suffers from less, not more than the amount of insecurity\nthat is normal for human beings. but psychological security does not\nclosely correspond with physical security. What makes us FEEL secure\nis not so much objective security as a sense of confidence in our\nability to take care of ourselves. Primitive man, threatened by a\nfierce animal or by hunger, can fight in self-defense or travel in\nsearch of food. He has no certainty of success in these efforts, but\nhe is by no means helpless against the things that threaten him. The\nmodern individual on the ot\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>or corporation executives; and so forth. Most individuals
are not in a position to secure themselves against these threats to
more [than] a very limited extent. The individual's search for
security is therefore frustrated, which leads to a sense of
powerlessness.
68. It may be objected that primitive man is physically less secure
than modern man, as is shown by his shorter life expectancy; hence
modern man suffers from less, not more than the amount of insecurity
that is normal for human beings. but psychological security does not
closely correspond with physical security. What makes us FEEL secure
is not so much objective security as a sense of confidence in our
ability to take care of ourselves. Primitive man, threatened by a
fierce animal or by hunger, can fight in self-defense or travel in
search of food. He has no certainty of success in these efforts, but
he is by no means helpless against the things that threaten him. The
modern individual on the ot
Igor Khavkine
Dec13-04, 11:04 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>of life and work were apparent by 1900, when\nsome 76 percent of the 2,805,346 inhabitants of Massachusetts were\nclassified as urbanites. Much violent or irregular behavior which had\nbeen tolerable in a casual, independent society was no longer\nacceptable in the more formalized, cooperative atmosphere of the later\nperiod. . .The move to the cities had, in short, produced a more\ntractable, more socialized, more \'civilized\' generation than its\npredecessors."\n\n17. (Paragraph 117) Apologists for the system are fond of citing cases\nin which elections have been decided by one or two votes, but such\ncases are rare.\n\n18. (Paragraph 119) "Today, in technologically advanced lands, men\nlive very similar lives in spite of geographical, religious and\npolitical differences. The daily lives of a Christian bank clerk in\nChicago, a Buddhist bank clerk in Tokyo, a Communist bank clerk in\nMoscow are far more alike than the life any one of them is like that\nof any single man who lived a thousand years ago. These similarities\nare the result of a common technology. . ." L. Sprague de Camp, "The\nAncient Engineers," Ballentine edition, page 17.\n\nThe lives of the three bank clerks are not IDENTICAL. Ideology does\nhave SOME effect. But all technological societies, in order to\nsurvive, must evolve along APPROXIMATELY the same trajectory.\n\n19. (Paragraph 123) Just think an irresponsible genetic engineer might\ncreate a lot of terrorists.\n\n20. (Paragraph 124) For a further example of undesirable consequences\nof medical progress, suppose a reliable cure for cancer is discovered.\nEven if the treatment is too expensive to be available to any but the\nelite, it will greatly reduce their incentive to stop the escape of\ncarcinogens into the environment.\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>of life and work were apparent by 1900, when
some 76 percent of the 2,805,346 inhabitants of Massachusetts were
classified as urbanites. Much violent or irregular behavior which had
been tolerable in a casual, independent society was no longer
acceptable in the more formalized, cooperative atmosphere of the later
period. . .The move to the cities had, in short, produced a more
tractable, more socialized, more 'civilized' generation than its
predecessors."
17. (Paragraph 117) Apologists for the system are fond of citing cases
in which elections have been decided by one or two votes, but such
cases are rare.
18. (Paragraph 119) "Today, in technologically advanced lands, men
live very similar lives in spite of geographical, religious and
political differences. The daily lives of a Christian bank clerk in
Chicago, a Buddhist bank clerk in Tokyo, a Communist bank clerk in
Moscow are far more alike than the life any one of them is like that
of any single man who lived a thousand years ago. These similarities
are the result of a common technology. . ." L. Sprague de Camp, "The
Ancient Engineers," Ballentine edition, page 17.
The lives of the three bank clerks are not IDENTICAL. Ideology does
have SOME effect. But all technological societies, in order to
survive, must evolve along APPROXIMATELY the same trajectory.
19. (Paragraph 123) Just think an irresponsible genetic engineer might
create a lot of terrorists.
20. (Paragraph 124) For a further example of undesirable consequences
of medical progress, suppose a reliable cure for cancer is discovered.
Even if the treatment is too expensive to be available to any but the
elite, it will greatly reduce their incentive to stop the escape of
carcinogens into the environment.
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