View Full Version : upper/lower *theoretical* limits for photon wavelength
ensabah6@yahoo.com
May30-05, 01:27 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>i am wondering whether 1- there is a lower limit for short photon\nwavelength, or what would happen to the photon as it continually gets\nmore energetic. will it sponatenously become a electron-positron pair?\n\nalso, i wonder if thereis an upper limit for long wavelength photons.\nit\'s my understanding radio waves can have wavelengths in kilometers.\nis there a minimum energy a photon must have, or could it have a very\nvery low energy approaching zero?\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 am wondering whether 1- there is a lower limit for short photon
wavelength, or what would happen to the photon as it continually gets
more energetic. will it sponatenously become a electron-positron pair?
also, i wonder if thereis an upper limit for long wavelength photons.
it's my understanding radio waves can have wavelengths in kilometers.
is there a minimum energy a photon must have, or could it have a very
very low energy approaching zero?
mathman
May30-05, 03:31 PM
There is no limit (upper or lower) on photon wavelength.
Photons with energy >1.022 Mev may form electron-positron pairs in the presence of material - the higher the atomic number the better. In order to form such pairs in the absence of material, it takes two photons with enough energy - that's what happened right after the big bang. Conservation of momentum excludes the case of a single photon by itself.
Uncle Al
May31-05, 01:34 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>ensabah6@yahoo.com wrote:\n>\n> i am wondering whether 1- there is a lower limit for short photon\n> wavelength, or what would happen to the photon as it continually gets\n> more energetic. will it sponatenously become a electron-positron pair?\n\n1/Planck time for the highest photon frequency. Physics as currently\nformulated has no predictive power at higher local energies.\n\n> also, i wonder if thereis an upper limit for long wavelength photons.\n> it\'s my understanding radio waves can have wavelengths in kilometers.\n> is there a minimum energy a photon must have, or could it have a very\n> very low energy approaching zero?\n\nlambda/2=width of universe (not necessarily the observer\'s light cone)\nperhaps for the lowest frequency.\n\n--\nUncle Al\nhttp://www.mazepath.com/uncleal/\n(Toxic URL! Unsafe for children and most mammals)\nhttp://www.mazepath.com/uncleal/qz.pdf\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>ensabah6@yahoo.com wrote:
>
> i am wondering whether 1- there is a lower limit for short photon
> wavelength, or what would happen to the photon as it continually gets
> more energetic. will it sponatenously become a electron-positron pair?
1/Planck time for the highest photon frequency. Physics as currently
formulated has no predictive power at higher local energies.
> also, i wonder if thereis an upper limit for long wavelength photons.
> it's my understanding radio waves can have wavelengths in kilometers.
> is there a minimum energy a photon must have, or could it have a very
> very low energy approaching zero?
\lambda/2=width of universe (not necessarily the observer's light cone)
perhaps for the lowest frequency.
--
Uncle Al
http://www.mazepath.com/uncleal/
(Toxic URL! Unsafe for children and most mammals)
http://www.mazepath.com/uncleal/qz.pdf
Charles Francis
May31-05, 01:37 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>In message <1117427010.777559.120660@g47g2000cwa.googlegroups .com>,\nensabah6@yahoo.com writes\n>i am wondering whether 1- there is a lower limit for short photon\n>wavelength, or what would happen to the photon as it continually gets\n>more energetic. will it sponatenously become a electron-positron pair?\n\nConservation of energy-momentum means that a "real" (mass=0) photon\ncan\'t. Of course it can be absorbed by a charged particle and that can\nlead to particle creation.\n\n\n>\n>also, i wonder if thereis an upper limit for long wavelength photons.\n>it\'s my understanding radio waves can have wavelengths in kilometers.\n>is there a minimum energy a photon must have, or could it have a very\n>very low energy approaching zero?\n>\nThere is no bound on the number of photons at ever lower energies, a\nfact which used to cause "the infrared catastrophe" until it was\nunderstood.\n\n\nRegards\n\n--\nCharles Francis\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 message <1117427010.777559.120660@g47g2000cwa.googlegroups. com>,
ensabah6@yahoo.com writes
>i am wondering whether 1- there is a lower limit for short photon
>wavelength, or what would happen to the photon as it continually gets
>more energetic. will it sponatenously become a electron-positron pair?
Conservation of energy-momentum means that a "real" (mass=0) photon
can't. Of course it can be absorbed by a charged particle and that can
lead to particle creation.
>
>also, i wonder if thereis an upper limit for long wavelength photons.
>it's my understanding radio waves can have wavelengths in kilometers.
>is there a minimum energy a photon must have, or could it have a very
>very low energy approaching zero?
>
There is no bound on the number of photons at ever lower energies, a
fact which used to cause "the infrared catastrophe" until it was
understood.
Regards
--
Charles Francis
ensabah6@yahoo.com
May31-05, 11:07 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>what is "the infrared catastrophe" and how is it understood?\n\nis it possible that a sufficient number of extremely low energy photons\nis "dark matter"\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>what is "the infrared catastrophe" and how is it understood?
is it possible that a sufficient number of extremely low energy photons
is "dark matter"
mathman
May31-05, 04:11 PM
is it possible that a sufficient number of extremely low energy photons
is "dark matter"
No - the total energy of the photons in the universe is much too small to account for dark matter. Neutrinos are a slightly better candidate, but even here there is not enough and also if all neutrino galaxy formation wouldn't have taken place.
J. J. Lodder
Jun2-05, 12:27 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><ensabah6@yahoo.com> wrote:\n\n> i am wondering whether 1- there is a lower limit for short photon\n> wavelength, or what would happen to the photon as it continually gets\n> more energetic. will it sponatenously become a electron-positron pair?\n\nNo that would violate conservation laws.\n\n> also, i wonder if thereis an upper limit for long wavelength photons.\n> it\'s my understanding radio waves can have wavelengths in kilometers.\n> is there a minimum energy a photon must have, or could it have a very\n> very low energy approaching zero?\n\nSure, there are no photons with a wavelength that is\ngreater than the size of the universe,\n\nJan\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><ensabah6@yahoo.com> wrote:
> i am wondering whether 1- there is a lower limit for short photon
> wavelength, or what would happen to the photon as it continually gets
> more energetic. will it sponatenously become a electron-positron pair?
No that would violate conservation laws.
> also, i wonder if thereis an upper limit for long wavelength photons.
> it's my understanding radio waves can have wavelengths in kilometers.
> is there a minimum energy a photon must have, or could it have a very
> very low energy approaching zero?
Sure, there are no photons with a wavelength that is
greater than the size of the universe,
Jan
Ben Rudiak-Gould
Jun2-05, 12:44 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>ensabah6@yahoo.com wrote:\n> i am wondering whether 1- there is a lower limit for short photon\n> wavelength, or what would happen to the photon as it continually gets\n> more energetic. will it sponatenously become a electron-positron pair?\n\nLorentz invariance implies that this can\'t happen. Any photon has an\narbitrarily large wavelength with respect to some inertial frame, so there\'s\nno difference between the physics of low-energy and high-energy free photons.\n\nIt\'s possible that Lorentz invariance doesn\'t hold exactly in the real\nworld, but in terms of current accepted theory, the answer is a definite no.\n\n> also, i wonder if thereis an upper limit for long wavelength photons.\n> it\'s my understanding radio waves can have wavelengths in kilometers.\n> is there a minimum energy a photon must have, or could it have a very\n> very low energy approaching zero?\n\nThis is really two different questions. If the photon is not exactly\nmassless, then it does have a minimum energy, namely its mass. If the photon\nis massless (as theory says it is), then there is no minimum energy, again\nbecause of Lorentz invariance.\n\nWhether or not the photon is massless, there\'s no upper limit on wavelength.\nIn fact, in the case of a massive particle, the (spatial) wavelength can be\nexactly infinite, not just arbitrarily large. It\'s the inverse of the\nwavelength (called the wave number) that\'s constrained to be finite.\n\n-- Ben\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>ensabah6@yahoo.com wrote:
> i am wondering whether 1- there is a lower limit for short photon
> wavelength, or what would happen to the photon as it continually gets
> more energetic. will it sponatenously become a electron-positron pair?
Lorentz invariance implies that this can't happen. Any photon has an
arbitrarily large wavelength with respect to some inertial frame, so there's
no difference between the physics of low-energy and high-energy free photons.
It's possible that Lorentz invariance doesn't hold exactly in the real
world, but in terms of current accepted theory, the answer is a definite no.
> also, i wonder if thereis an upper limit for long wavelength photons.
> it's my understanding radio waves can have wavelengths in kilometers.
> is there a minimum energy a photon must have, or could it have a very
> very low energy approaching zero?
This is really two different questions. If the photon is not exactly
massless, then it does have a minimum energy, namely its mass. If the photon
is massless (as theory says it is), then there is no minimum energy, again
because of Lorentz invariance.
Whether or not the photon is massless, there's no upper limit on wavelength.
In fact, in the case of a massive particle, the (spatial) wavelength can be
exactly infinite, not just arbitrarily large. It's the inverse of the
wavelength (called the wave number) that's constrained to be finite.
-- Ben
Charles Francis
Jun3-05, 01:02 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>In message <1117550312.141429.96910@g44g2000cwa.googlegroups. com>,\nensabah6@yahoo.com writes\n>what is "the infrared catastrophe" and how is it understood?\n\nIt\'s a formula that goes to infinity in the limit of zero photon energy.\nIt is resolved by recognising that this formula can only appear inside\nan integral over a range of energies, and that when you do this it is\nfinite.\n>\n>is it possible that a sufficient number of extremely low energy photons\n>is "dark matter"\n>\nNo. The point is that there can be an indeterminate number of photons\nwith a low total energies\n\n\nRegards\n\n--\nCharles Francis\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 message <1117550312.141429.96910@g44g2000cwa.googlegroups.c om>,
ensabah6@yahoo.com writes
>what is "the infrared catastrophe" and how is it understood?
It's a formula that goes to infinity in the limit of zero photon energy.
It is resolved by recognising that this formula can only appear inside
an integral over a range of energies, and that when you do this it is
finite.
>
>is it possible that a sufficient number of extremely low energy photons
>is "dark matter"
>
No. The point is that there can be an indeterminate number of photons
with a low total energies
Regards
--
Charles Francis
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