View Full Version : Are photons open or closed strings?
<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>In one of his talks, Robert Dijkgraf said that closed strings behave as\ngravitons at low energy, and that open strings manifest themselves as\nphotons or gluons. Half an hour later he said that Hawking radiation\nappears when two open strings recombine on the brane to a closed one which\ncan escape into space-time.\n\nThis is contradictory -- but maybe I confuse something or misunderstood\nthe statement. Are photons open or closed strings? Does this depend on the\nspecific version of string theory? In fact, I\'d like to have a sort of\nmental image of a photon in string theory. Is there a way to picture\nsomething that is precise enough to be helpful?\n\njon\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>In one of his talks, Robert Dijkgraf said that closed strings behave as
gravitons at low energy, and that open strings manifest themselves as
photons or gluons. Half an hour later he said that Hawking radiation
appears when two open strings recombine on the brane to a closed one which
can escape into space-time.
This is contradictory -- but maybe I confuse something or misunderstood
the statement. Are photons open or closed strings? Does this depend on the
specific version of string theory? In fact, I'd like to have a sort of
mental image of a photon in string theory. Is there a way to picture
something that is precise enough to be helpful?
jon
Lubos Motl
Jul20-04, 11:17 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>On Wed, 21 Jul 2004, Jon wrote:\n\n> In one of his talks, Robert Dijkgraf said that closed strings behave as\n> gravitons at low energy, and that open strings manifest themselves as...\n\nDear Jon,\n\nin the conventional heterotic string models, all known particles are\nclosed strings. Moreover, gravitons are closed strings in all models -\nbecause they are always responsible for the geometry of the whole\nspacetime - i.e. they cannot be confined.\n\nIn the new brane world scenarios, all other particles except for gravitons\ncan be open strings stretched between the branes. This is helpful e.g. in\nthe "old large dimensions" models where it explains the weakness of\ngravity - gravity is diluted in the large extra dimensions, but everything\nelse (such as photons) is concentrated on the brane.\n\nThere many other types of models where some particles arise from open\nstrings, some particles arise from singularities, and so on.\n\nThese different realizations of a photon are, of course, compatible with\nHawking radiation. Photons are always allowed to move anywhere in the 3+1\ndimensions we know; the only ambiguity is whether they are allowed to\nmove in the additional dimensions. Because they can move anywhere in the\nspace we know, they can also be emitted by a radiating black hole.\n\nIf you would like to have one mental picture of a photon and other\nparticles - be sure that you\'re not the only one. I would also love to\nhave a unique model describing Nature correctly. Unfortunately, string\ntheory is too rich as of today and we have many potential realizations of\nthe known physics. Gravitons are always closed strings, as long as there\nare any strings at all, but everything else can be both, depending on the\nmodel.\n\nBest wishes\nLubos\n___________________________________ ___________________________________________\nE-mail: lumo@matfyz.cz fax: +1-617/496-0110 Web: http://lumo.matfyz.cz/\neFax: +1-801/454-1858 work: +1-617/496-8199 home: +1-617/868-4487 (call)\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>On Wed, 21 Jul 2004, Jon wrote:
> In one of his talks, Robert Dijkgraf said that closed strings behave as
> gravitons at low energy, and that open strings manifest themselves as...
Dear Jon,
in the conventional heterotic string models, all known particles are
closed strings. Moreover, gravitons are closed strings in all models -
because they are always responsible for the geometry of the whole
spacetime - i.e. they cannot be confined.
In the new brane world scenarios, all other particles except for gravitons
can be open strings stretched between the branes. This is helpful e.g. in
the "old large dimensions" models where it explains the weakness of
gravity - gravity is diluted in the large extra dimensions, but everything
else (such as photons) is concentrated on the brane.
There many other types of models where some particles arise from open
strings, some particles arise from singularities, and so on.
These different realizations of a photon are, of course, compatible with
Hawking radiation. Photons are always allowed to move anywhere in the 3+1
dimensions we know; the only ambiguity is whether they are allowed to
move in the additional dimensions. Because they can move anywhere in the
space we know, they can also be emitted by a radiating black hole.
If you would like to have one mental picture of a photon and other
particles - be sure that you're not the only one. I would also love to
have a unique model describing Nature correctly. Unfortunately, string
theory is too rich as of today and we have many potential realizations of
the known physics. Gravitons are always closed strings, as long as there
are any strings at all, but everything else can be both, depending on the
model.
Best wishes
Lubos
__{_______________________________________________ _____________________________}
E-mail: lumo@matfyz.cz fax: +1-617/496-0110 Web: http://lumo.matfyz.cz/
eFax: +1-801/454-1858 work: +1-617/496-8199 home: +1-617/868-4487 (call)
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
<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>Dear Lubos,\n\nto keep the discussion concrete, I\'d like to focus on photons only.\nSince there are many options, and all seem to have some truth, let us take one.\nI am not interested (for the moment) in electrons or gravitons - just photons.\n\nLet us take the version where photons are strings between branes, for example.\nHow do we have to imagine the motion of a photon? When a photon moves in a\nlight beam, how does the string (and the branes) move?\n\nIn simple terms, is the string perpendicular to the motion, or along it?\n\n\njon\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>Dear Lubos,
to keep the discussion concrete, I'd like to focus on photons only.
Since there are many options, and all seem to have some truth, let us take one.
I am not interested (for the moment) in electrons or gravitons - just photons.
Let us take the version where photons are strings between branes, for example.
How do we have to imagine the motion of a photon? When a photon moves in a
light beam, how does the string (and the branes) move?
In simple terms, is the string perpendicular to the motion, or along it?
jon
Lubos Motl
Jul21-04, 09:34 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>On Wed, 21 Jul 2004 pdkgpznxenvlya@mailinator.com wrote:\n\n> Let us take the version where photons are strings between branes, for example.\n> How do we have to imagine the motion of a photon? When a photon moves in a\n> light beam, how does the string (and the branes) move?\n>\n> In simple terms, is the string perpendicular to the motion, or along it?\n\nDear Jon, not only photons in braneworld scenarios, but *all* strings\neverywhere in string theory always oscillate in all dimensions (which\nusually means "all ten of dimensions") regardless of the motion of the\nresulting photon. It would not be a critical string theory (critical means\n"with the right number of spacetime dimensions, and therefore canceling\nconformal anomaly") if the generic points on the string were moving in a\nlimited number of dimensions.\n\nThe only confined points can be the endpoints. In your case, the endpoints\nare restrictd to oscillate within the worldvolume of the branes - which\nincludes the familiar 3+1 dimensions, and perhaps (but not necessarily)\na subset of the additional dimensions. But within the worldvolume of the\nbranes, again, even the endpoints are oscillating in *all* directions,\nregardless of the motion of the center of mass (of your photon).\n\nAnother question is how the strings and their endpoints move in classical\nstring theory, which is essentially equivalent to the time evolution of\nthe "zero modes", especially in a particular classical solution. Yes, if\nyou consider a physical, transversely polarized photon (e.g.\nx-polarization in a z-moving photon), the classical mode on the string\nthat is excited is the x-mode, which adds sinusoidal oscillations to the\nstring that are directed in the x-direction, and are therefore\nperpendicular to the direction of motion. So the classical, average shape\nof the string vibrates in this x-direction only - and this would be true\nboth for closed-string-photons and open-string-photons. But don\'t forget\nthat quantum mechanics implies that the string and everything else has\nnonzero oscillations in all conceivable directions. Because of the\nuncertainty principle, you cannot have a vanishing coordinate as well as\nthe same component of the velocity of a point along the string.\n_________________________________________ _____________________________________\nE-mail: lumo@matfyz.cz fax: +1-617/496-0110 Web: http://lumo.matfyz.cz/\neFax: +1-801/454-1858 work: +1-617/496-8199 home: +1-617/868-4487 (call)\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>On Wed, 21 Jul 2004 pdkgpznxenvlya@mailinator.com wrote:
> Let us take the version where photons are strings between branes, for example.
> How do we have to imagine the motion of a photon? When a photon moves in a
> light beam, how does the string (and the branes) move?
>
> In simple terms, is the string perpendicular to the motion, or along it?
Dear Jon, not only photons in braneworld scenarios, but *all* strings
everywhere in string theory always oscillate in all dimensions (which
usually means "all ten of dimensions") regardless of the motion of the
resulting photon. It would not be a critical string theory (critical means
"with the right number of spacetime dimensions, and therefore canceling
conformal anomaly") if the generic points on the string were moving in a
limited number of dimensions.
The only confined points can be the endpoints. In your case, the endpoints
are restrictd to oscillate within the worldvolume of the branes - which
includes the familiar 3+1 dimensions, and perhaps (but not necessarily)
a subset of the additional dimensions. But within the worldvolume of the
branes, again, even the endpoints are oscillating in *all* directions,
regardless of the motion of the center of mass (of your photon).
Another question is how the strings and their endpoints move in classical
string theory, which is essentially equivalent to the time evolution of
the "zero modes", especially in a particular classical solution. Yes, if
you consider a physical, transversely polarized photon (e.g.
x-polarization in a z-moving photon), the classical mode on the string
that is excited is the x-mode, which adds sinusoidal oscillations to the
string that are directed in the x-direction, and are therefore
perpendicular to the direction of motion. So the classical, average shape
of the string vibrates in this x-direction only - and this would be true
both for closed-string-photons and open-string-photons. But don't forget
that quantum mechanics implies that the string and everything else has
nonzero oscillations in all conceivable directions. Because of the
uncertainty principle, you cannot have a vanishing coordinate as well as
the same component of the velocity of a point along the string.
__{_______________________________________________ _____________________________}
E-mail: lumo@matfyz.cz fax: +1-617/496-0110 Web: http://lumo.matfyz.cz/
eFax: +1-801/454-1858 work: +1-617/496-8199 home: +1-617/868-4487 (call)
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
Thomas Dent
Jul22-04, 12:21 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>Jon <pdkgpznxenvlya@mailinator.com> wrote\n\n(...)\n\n> Are photons open or closed strings?\n\n(...)\n\n>\n> jon\n\n\nI believe that the answer to this question is, for a string theorist, "Yes".\n\nFor a non-string-theorist, "No".\n\nUnfortunately, one cannot be more precise at present.\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>Jon <pdkgpznxenvlya@mailinator.com> wrote
(...)
> Are photons open or closed strings?
(...)
>
> jon
I believe that the answer to this question is, for a string theorist, "Yes".
For a non-string-theorist, "No".
Unfortunately, one cannot be more precise at present.
Urs Schreiber
Jul22-04, 12:23 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>On Thu, 22 Jul 2004, Thomas Dent wrote:\n\n> Jon <pdkgpznxenvlya@mailinator.com> wrote\n\n> > Are photons open or closed strings?\n\n> I believe that the answer to this question is, for a string theorist, "Yes".\n\nAs Lubos has pointed out, the U(1) need not come from the open string\nsector. But in recent times, with intersecting barne models etc, this is\nmaybe the case which is receiving more attention.\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 Thu, 22 Jul 2004, Thomas Dent wrote:
> Jon <pdkgpznxenvlya@mailinator.com> wrote
> > Are photons open or closed strings?
> I believe that the answer to this question is, for a string theorist, "Yes".
As Lubos has pointed out, the U(1) need not come from the open string
sector. But in recent times, with intersecting barne models etc, this is
maybe the case which is receiving more attention.
<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>This is getting interesting.\n\n> Another question is how the strings and their endpoints move in classical\n> string theory, which is essentially equivalent to the time evolution of\n> the "zero modes", especially in a particular classical solution. Yes, if\n> you consider a physical, transversely polarized photon (e.g.\n> x-polarization in a z-moving photon), the classical mode on the string\n> that is excited is the x-mode, which adds sinusoidal oscillations to the\n> string that are directed in the x-direction, and are therefore\n> perpendicular to the direction of motion. So the classical, average shape\n> of the string vibrates in this x-direction only - and this would be true\n> both for closed-string-photons and open-string-photons. But don\'t forget\n> that quantum mechanics implies that the string and everything else has\n> nonzero oscillations in all conceivable directions. Because of the\n> uncertainty principle, you cannot have a vanishing coordinate as well as\n> the same component of the velocity of a point along the string.\n\nCan one say the following:\n\nIn classical string theory, one can imagine\na photon in a beam along the z direction, polarized in the x direction,\nas a string somehow moving along z, and oscillating in x direction.\nThe tails of the string "oscillate wildly" and are barely noticeable\n(at usual low energy).\nIn x and y direction there is some fuzzyness, to agree with the uncertainty\nprinciple. The same in z direction.\n\nIf that is correctly rendered, what happens during interference of a\nphoton going through a double split?\nWhat exactly happens when the photon is "split" and\nwhen it interferes where the two "parts" come back together?\n\n\n\njon\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>This is getting interesting.
> Another question is how the strings and their endpoints move in classical
> string theory, which is essentially equivalent to the time evolution of
> the "zero modes", especially in a particular classical solution. Yes, if
> you consider a physical, transversely polarized photon (e.g.
> x-polarization in a z-moving photon), the classical mode on the string
> that is excited is the x-mode, which adds sinusoidal oscillations to the
> string that are directed in the x-direction, and are therefore
> perpendicular to the direction of motion. So the classical, average shape
> of the string vibrates in this x-direction only - and this would be true
> both for closed-string-photons and open-string-photons. But don't forget
> that quantum mechanics implies that the string and everything else has
> nonzero oscillations in all conceivable directions. Because of the
> uncertainty principle, you cannot have a vanishing coordinate as well as
> the same component of the velocity of a point along the string.
Can one say the following:
In classical string theory, one can imagine
a photon in a beam along the z direction, polarized in the x direction,
as a string somehow moving along z, and oscillating in x direction.
The tails of the string "oscillate wildly" and are barely noticeable
(at usual low energy).
In x and y direction there is some fuzzyness, to agree with the uncertainty
principle. The same in z direction.
If that is correctly rendered, what happens during interference of a
photon going through a double split?
What exactly happens when the photon is "split" and
when it interferes where the two "parts" come back together?
jon
Lubos Motl
Jul24-04, 01:04 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 Thu, 22 Jul 2004 pdkgpznxenvlya@mailinator.com wrote:\n\n> Can one say the following:\n>\n> In classical string theory, one can imagine\n> a photon in a beam along the z direction, polarized in the x direction,\n> as a string somehow moving along z, and oscillating in x direction.\n> The tails of the string "oscillate wildly" and are barely noticeable\n> (at usual low energy).\n\nYes, it is roughly correct, I think.\n\n> In x and y direction there is some fuzzyness, to agree with the uncertainty\n> principle. The same in z direction.\n\nYou would have to specify what exactly is fuzzy. Some quantities are\nfuzzy, some quantities are not.\n\n> If that is correctly rendered, what happens during interference of a\n> photon going through a double split?\n> What exactly happens when the photon is "split" and\n> when it interferes where the two "parts" come back together?\n\nI don\'t know why this question is related to the previous question on the\nlink between polarization and the direction of oscillation.\n\nNevertheless interference experiments in string theory work just like\ninterference in previous quantum theories. The internal structure of the\nparticle involves a string, but the external behavior is virtually\nunchanged. The photon (a vibrating string) has a wavefunction (for its\ncenter-of-mass degrees of freedom), and this wavefunction behaves just\nlike in quantum mechanics before string theory.\n\nIf you discover that a car has a motor inside, it does not change the\nrules how it moves on the roads.\n__________________________________________ ____________________________________\nE-mail: lumo@matfyz.cz fax: +1-617/496-0110 Web: http://lumo.matfyz.cz/\neFax: +1-801/454-1858 work: +1-617/496-8199 home: +1-617/868-4487 (call)\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>On Thu, 22 Jul 2004 pdkgpznxenvlya@mailinator.com wrote:
> Can one say the following:
>
> In classical string theory, one can imagine
> a photon in a beam along the z direction, polarized in the x direction,
> as a string somehow moving along z, and oscillating in x direction.
> The tails of the string "oscillate wildly" and are barely noticeable
> (at usual low energy).
Yes, it is roughly correct, I think.
> In x and y direction there is some fuzzyness, to agree with the uncertainty
> principle. The same in z direction.
You would have to specify what exactly is fuzzy. Some quantities are
fuzzy, some quantities are not.
> If that is correctly rendered, what happens during interference of a
> photon going through a double split?
> What exactly happens when the photon is "split" and
> when it interferes where the two "parts" come back together?
I don't know why this question is related to the previous question on the
link between polarization and the direction of oscillation.
Nevertheless interference experiments in string theory work just like
interference in previous quantum theories. The internal structure of the
particle involves a string, but the external behavior is virtually
unchanged. The photon (a vibrating string) has a wavefunction (for its
center-of-mass degrees of freedom), and this wavefunction behaves just
like in quantum mechanics before string theory.
If you discover that a car has a motor inside, it does not change the
rules how it moves on the roads.
__{_______________________________________________ _____________________________}
E-mail: lumo@matfyz.cz fax: +1-617/496-0110 Web: http://lumo.matfyz.cz/
eFax: +1-801/454-1858 work: +1-617/496-8199 home: +1-617/868-4487 (call)
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
<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>Jon <pdkgpznxenvlya@mailinator.com> wrote\n\n> Are photons open or closed strings?\n\nThe answer is morally speaking, both. Because there is in general no\nun-ambiguous notion whether a given degree of freedom arises from\nan open or closed string.\n\nThe important point is that generically, various models are not\njust different "machines" to achieve gauge symmetry (or chiral\nfermions, or other things for that matter) - they are just different\ndescriptions, or parametrizations of _one and the same thing_.\nBecause of duality, certain constructions (say of gauge symmetry)\ncan be equivalent to each other, in the sense that there is no\npossible physical measurement that would allow to distinguish between\nthem.\n\nFor example, in heterotic string language, a gauge boson in four\ndimensions may arise in a certain Calabi-Yau compactification; this\nis a closed string formulation. This theory is generically dual\nto a type II string compactification with D-branes, where gauge\nsymmetry arises via open strings stretched between the D-branes\n(there are explicitly known examples for such dualities). These theories\nbeing dual to each other, there is no physical distinction\nbetween the two representations of the gauge field.\n\nThe same logic applies to all sorts of intersecting brane constructions,\nflux compactifications, type II string-, M-, F-theory constructions\non various manifolds. Generically, these "different" constructions\nare just different ways to represent or parametrize the same physics\n(though it is often so that one parametrization is better suited\nfor describing the same physics than another one, depending on the\nregion of parameter space one is considering). In general there\nis no unambiguous notion of what the underlying background geometry,\nor string theory is; these notions are not well defined, except in\ncertain weak coupling limits (where there exist formulations\nin terms of string world-sheets, and thus in terms of perturbation theory).\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>Jon <pdkgpznxenvlya@mailinator.com> wrote
> Are photons open or closed strings?
The answer is morally speaking, both. Because there is in general no
un-ambiguous notion whether a given degree of freedom arises from
an open or closed string.
The important point is that generically, various models are not
just different "machines" to achieve gauge symmetry (or chiral
fermions, or other things for that matter) - they are just different
descriptions, or parametrizations of _one and the same thing_.
Because of duality, certain constructions (say of gauge symmetry)
can be equivalent to each other, in the sense that there is no
possible physical measurement that would allow to distinguish between
them.
For example, in heterotic string language, a gauge boson in four
dimensions may arise in a certain Calabi-Yau compactification; this
is a closed string formulation. This theory is generically dual
to a type II string compactification with D-branes, where gauge
symmetry arises via open strings stretched between the D-branes
(there are explicitly known examples for such dualities). These theories
being dual to each other, there is no physical distinction
between the two representations of the gauge field.
The same logic applies to all sorts of intersecting brane constructions,
flux compactifications, type II string-, M-, F-theory constructions
on various manifolds. Generically, these "different" constructions
are just different ways to represent or parametrize the same physics
(though it is often so that one parametrization is better suited
for describing the same physics than another one, depending on the
region of parameter space one is considering). In general there
is no unambiguous notion of what the underlying background geometry,
or string theory is; these notions are not well defined, except in
certain weak coupling limits (where there exist formulations
in terms of string world-sheets, and thus in terms of perturbation theory).
<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>Lubos Motl <motl@feynman.harvard.edu> wrote in message news:>\n\n> I don\'t know why this question is related to the previous question on the\n> link between polarization and the direction of oscillation.\n>\n> Nevertheless interference experiments in string theory work just like\n> interference in previous quantum theories. The internal structure of the\n> particle involves a string, but the external behavior is virtually\n> unchanged. The photon (a vibrating string) has a wavefunction (for its\n> center-of-mass degrees of freedom), and this wavefunction behaves just\n> like in quantum mechanics before string theory.\n\nMy question was wether the string model allows a visualization of\ninterference.This is indeed an additional question.\nI had the -- possibly naive -- idea that the usual quantum\nmechanical description of light might be only an "unsharp" image of a\nvibrating and oscillating string. In that case, string theory would\nhelp to provide a "mental image" for photons that might be useful even\nin simple quantum theory. (And possibly the same for matter\nwave functions.) Is there a chance for this to be true?\n\njon\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>Lubos Motl <motl@feynman.harvard.edu> wrote in message news:>
> I don't know why this question is related to the previous question on the
> link between polarization and the direction of oscillation.
>
> Nevertheless interference experiments in string theory work just like
> interference in previous quantum theories. The internal structure of the
> particle involves a string, but the external behavior is virtually
> unchanged. The photon (a vibrating string) has a wavefunction (for its
> center-of-mass degrees of freedom), and this wavefunction behaves just
> like in quantum mechanics before string theory.
My question was wether the string model allows a visualization of
interference.This is indeed an additional question.
I had the -- possibly naive -- idea that the usual quantum
mechanical description of light might be only an "unsharp" image of a
vibrating and oscillating string. In that case, string theory would
help to provide a "mental image" for photons that might be useful even
in simple quantum theory. (And possibly the same for matter
wave functions.) Is there a chance for this to be true?
jon
<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>I see that the answer to the question really depends on many details.\nWhat is the answer with the following conditions:\nthe usual low-energy viewpoint we have in everyday life is assumed,\nthe ususal smaller than one coupling constant for electrodynamics,\nflat background, and usual perturbation theory?\nAre photons open strings in this case?\n\njon\n\n\n"R.X." <redlum.xohp@wanadoo.fr> wrote in message news:<7b5bf479.0407232354.450baef0-100000@posting.google.com>...\n\n> Jon <pdkgpznxenvlya@mailinator.com> wrote\n>\n> > Are photons open or closed strings?\n>\n> The answer is morally speaking, both.\n\n[...]\n\n> In general there\n> is no unambiguous notion of what the underlying background geometry,\n> or string theory is; these notions are not well defined, except in\n> certain weak coupling limits (where there exist formulations\n> in terms of string world-sheets, and thus in terms of perturbation theory).\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>I see that the answer to the question really depends on many details.
What is the answer with the following conditions:
the usual low-energy viewpoint we have in everyday life is assumed,
the ususal smaller than one coupling constant for electrodynamics,
flat background, and usual perturbation theory?
Are photons open strings in this case?
jon
"R.X." <redlum.xohp@wanadoo.fr> wrote in message news:<7b5bf479.0407232354.450baef0-100000@posting.google.com>...
> Jon <pdkgpznxenvlya@mailinator.com> wrote
>
> > Are photons open or closed strings?
>
> The answer is morally speaking, both.
[...]
> In general there
> is no unambiguous notion of what the underlying background geometry,
> or string theory is; these notions are not well defined, except in
> certain weak coupling limits (where there exist formulations
> in terms of string world-sheets, and thus in terms of perturbation theory).
Urs Schreiber
Jul26-04, 03:16 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><pdkgpznxenvlya@mailinator.com> schrieb im Newsbeitrag\nnews:828cb1da.0407251250.24204b12-100000@posting.google.com...\n\n> My question was wether the string model allows a visualization of\n> interference.This is indeed an additional question.\n> I had the -- possibly naive -- idea that the usual quantum\n> mechanical description of light might be only an "unsharp" image of a\n> vibrating and oscillating string.\n\nNo, this is not the case. The center of mass of any string is a point and is\ndescribed by a "wavefunction" whose wave-like character has nothing to do\nwith the oscillations of the string. String theory does not "explain"\nquantum mechanics, but takes it for granted.\n\nFor more on how to understand states of string at an elementary level see\n\nhttp://groups.google.de/groups?selm=3E973BB4.273CFACD%40uni-essen.de\n\nand\n\nhttp://golem.ph.utexas.edu/string/archives/000334.html .\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><pdkgpznxenvlya@mailinator.com> schrieb im Newsbeitrag
news:828cb1da.0407251250.24204b12-100000@posting.google.com...
> My question was wether the string model allows a visualization of
> interference.This is indeed an additional question.
> I had the -- possibly naive -- idea that the usual quantum
> mechanical description of light might be only an "unsharp" image of a
> vibrating and oscillating string.
No, this is not the case. The center of mass of any string is a point and is
described by a "wavefunction" whose wave-like character has nothing to do
with the oscillations of the string. String theory does not "explain"
quantum mechanics, but takes it for granted.
For more on how to understand states of string at an elementary level see
http://groups.google.de/groups?selm=3E973BB4.273CFACD%40uni-essen.de
and
http://golem.ph.utexas.edu/string/archives/000334.html .
<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><pdkgpznxenvlya@mailinator.com> wrote in message news:<828cb1da.0407252146.17d8bd03-100000@posting.google.com>...\n\n> What is the answer with the following conditions:\n> the usual low-energy viewpoint we have in everyday life is assumed,\n> the ususal smaller than one coupling constant for electrodynamics,\n> flat background, and usual perturbation theory?\n> Are photons open strings in this case?\n>\nYes and no - there are both open and closed string models for describing\nU(1) gauge symmetry, at weak coupling.\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><pdkgpznxenvlya@mailinator.com> wrote in message news:<828cb1da.0407252146.17d8bd03-100000@posting.google.com>...
> What is the answer with the following conditions:
> the usual low-energy viewpoint we have in everyday life is assumed,
> the ususal smaller than one coupling constant for electrodynamics,
> flat background, and usual perturbation theory?
> Are photons open strings in this case?
>
Yes and no - there are both open and closed string models for describing
U(1) gauge symmetry, at weak coupling.
arivero
Jul27-04, 12:07 AM
If you discover that a car has a motor inside, it does not change the
rules how it moves on the roads.
Hmm hmm comparisions are always dangereus. Suppose for instance a single vertical engine and a car on a ice skating floor. The car will turn to preserve angular momentum.
<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>Urs Schreiber <Urs.Schreiber@uni-essen.de> wrote in message news:<2mjsulFnhqslU1-100000@uni-berlin.de>...\n> <pdkgpznxenvlya@mailinator.com> wrote\n>\n> > My question was wether the string model allows a visualization of\n> > interference.This is indeed an additional question.\n> > I had the -- possibly naive -- idea that the usual quantum\n> > mechanical description of light might be only an "unsharp" image of a\n> > vibrating and oscillating string.\n>\n> No, this is not the case. The center of mass of any string is a point and is\n> described by a "wavefunction" whose wave-like character has nothing to do\n> with the oscillations of the string. String theory does not "explain"\n> quantum mechanics, but takes it for granted.\n\nThe question was simply how a single string representing a photon,\nwhich we represented in a given way (see previous posts) in\nfree space, looks when the photon passes a double slit.\nOne must be able to answer this in string theory.\n\nIf in free space a photon looks like an short oscillating wavetrain with\nfuzzy ends, there must be a picture about how the state looks when the photon\npasses a double slit. The diffference between the situations\nis simply that the potential is not zero.\n\nThe ability of string theory to provide a model for a free photon\nimplies that it is also able to provide an image for a double slit\nsituation. I just am looking for that image. I think\nit would interest many others as well!\n\njon\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>Urs Schreiber <Urs.Schreiber@uni-essen.de> wrote in message news:<2mjsulFnhqslU1-100000@uni-berlin.de>...
> <pdkgpznxenvlya@mailinator.com> wrote
>
> > My question was wether the string model allows a visualization of
> > interference.This is indeed an additional question.
> > I had the -- possibly naive -- idea that the usual quantum
> > mechanical description of light might be only an "unsharp" image of a
> > vibrating and oscillating string.
>
> No, this is not the case. The center of mass of any string is a point and is
> described by a "wavefunction" whose wave-like character has nothing to do
> with the oscillations of the string. String theory does not "explain"
> quantum mechanics, but takes it for granted.
The question was simply how a single string representing a photon,
which we represented in a given way (see previous posts) in
free space, looks when the photon passes a double slit.
One must be able to answer this in string theory.
If in free space a photon looks like an short oscillating wavetrain with
fuzzy ends, there must be a picture about how the state looks when the photon
passes a double slit. The diffference between the situations
is simply that the potential is not zero.
The ability of string theory to provide a model for a free photon
implies that it is also able to provide an image for a double slit
situation. I just am looking for that image. I think
it would interest many others as well!
jon
Urs Schreiber
Jul28-04, 04:07 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><pdkgpznxenvlya@mailinator.com> schrieb im Newsbeitrag\nnews:828cb1da.0407272116.2a825508-100000@posting.google.com...\n\n> The question was simply how a single string representing a photon,\n> which we represented in a given way (see previous posts) in\n> free space, looks when the photon passes a double slit.\n> One must be able to answer this in string theory.\n\nLet me say it again: The internal oscillation of the string is what makes it\nlook like a photon, a graviton, an electron, etc. This oscillation is not\nthe same as the oscillations of any wavefunction. In the everyday limit like\nthat of double slit experiments only the center-of-mass motion of the string\nis observed and it behaves just like any other point particle. It is\ndescribed by a wavefunction which may exhibit self-interference.\n\n[Moderator\'s note: Further disucssion of the basics of quantum mechanics\nare off-topic for sci.physics.strings and should be taken to some other\nnewsgroup. -usc]\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><pdkgpznxenvlya@mailinator.com> schrieb im Newsbeitrag
news:828cb1da.0407272116.2a825508-100000@posting.google.com...
> The question was simply how a single string representing a photon,
> which we represented in a given way (see previous posts) in
> free space, looks when the photon passes a double slit.
> One must be able to answer this in string theory.
Let me say it again: The internal oscillation of the string is what makes it
look like a photon, a graviton, an electron, etc. This oscillation is not
the same as the oscillations of any wavefunction. In the everyday limit like
that of double slit experiments only the center-of-mass motion of the string
is observed and it behaves just like any other point particle. It is
described by a wavefunction which may exhibit self-interference.
[Moderator's note: Further disucssion of the basics of quantum mechanics
are off-topic for sci.physics.strings and should be taken to some other
newsgroup. -usc]
<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>Perhaps one should also say here, that\nthere are actually two situations here,\none classical and one quantum. First,\nclassically speaking, I don\'t think that\nyou can claim that a string is a "photon".\nIn this classical case you can just talk\nabout a string flying about and depending\non whether or not the slit is emanating a\nforce field, or if the only force the slit\ncan place on the string is a contact force\nyou just describe the situation classically\nand that\'s it.\nNow, in the quantum situation, you have\nwavefunctions over the possible confi-\ngurations that a string may have, i.e.,\nhow it\'s layed out in space. Now some of\nthese states or wavefunctions are simul-\ntaneously eigenstates of the Mass, and Spin\noperators and the states with the mass and\nspin of a photon, are "photon states" .\nNow, I suppose that one may begin with\none of these photon states, with momentum\ndirected toward a slit arrangement and\nattempt to see what the time evolution is.\nI have not attempted this, but I guess that\nthe model one uses for say a single slit\nis more complicated than the one for a single\nparticle. What\'s its form? I don\'t know.\nMind you, I\'m not even touching the more\ncomplex issue that there may be particle\ncreation when the (I hate to use this language)\nstring collides with the slit. And I hate to use\nthe language because there\'s not one string in\nsome sense, just probabilities for the string\nto have different configurations. But I figure\nthis already arises in the analogous case in\nordinary QM.\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>Perhaps one should also say here, that
there are actually two situations here,
one classical and one quantum. First,
classically speaking, I don't think that
you can claim that a string is a "photon".
In this classical case you can just talk
about a string flying about and depending
on whether or not the slit is emanating a
force field, or if the only force the slit
can place on the string is a contact force
you just describe the situation classically
and that's it.
Now, in the quantum situation, you have
wavefunctions over the possible confi-
gurations that a string may have, i.e.,
how it's layed out in space. Now some of
these states or wavefunctions are simul-
taneously eigenstates of the Mass, and Spin
operators and the states with the mass and
spin of a photon, are "photon states" .
Now, I suppose that one may begin with
one of these photon states, with momentum
directed toward a slit arrangement and
attempt to see what the time evolution is.
I have not attempted this, but I guess that
the model one uses for say a single slit
is more complicated than the one for a single
particle. What's its form? I don't know.
Mind you, I'm not even touching the more
complex issue that there may be particle
creation when the (I hate to use this language)
string collides with the slit. And I hate to use
the language because there's not one string in
some sense, just probabilities for the string
to have different configurations. But I figure
this already arises in the analogous case in
ordinary QM.
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