gravitons and photons [Archive]

alistair

Aug26-04, 12:15 PM

David K.

Oct9-04, 06:36 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>"alistair" <alistair@goforit64.fsnet.co.uk> wrote in message\nnews:861c1b21.0408260520.5af60906-100000@posting.google.com...\n\n> Does string theory say anything about how or whether gravitons can\n> interact with photons? They are both bosons so can they scatter off\n> one another for starters?\n>\n> [Moderator\'s note: Yes, string theory guarantees the principle of\n> equivalence. All mass and energy in the Universe is subject to gravity.\n> Photons carry nonzero energy, and therefore they interact with\n> gravitons. LM]\n\nThis has bothering me for a while (I am not a physicists): If mass can be\nconverted into energy (i.e., energy and mass are equivalent), how can photons\nhave zero rest mass while exchanging force between electrons? How can a photon\nexchange energy, and not have mass? The principle of equivalence states there\nis no discernable difference between inertial mass and gravitational mass, but\nit seems like there are two types of mass: "relativistic mass" and "rest\nmass." I think this has to do with inertial frames of reference, spacetime\ngeodesics and how the zero rest mass of a photon is still mass proportional to\nits frequency (nonzero energy?). If this requires too long of a reply (I\nrealize this is sci.physics.strings and not sci.physics.relativity), can I\nhave some URLs or names of books to read?\n\n[Moderator\'s note: The rest mass "m_0" of a photon is zero, but the rest\nmass is only relevant for expressing physics in the rest frame.\nThe rest frame of a photon does not exist - a photon moves by the speed\nof light, and therefore the Lorentz factor 1/sqrt(1-v^2/c^2) is infinite.\nOne must always observe the photon from another from, and then the ratio\nm_0 c^2/sqrt(1-v^2/c^2) - which is formally 0/0 - is a finite number that\nexpresses the total energy of your photon with respect to this frame.\nThis total energy E equals E=hf where f is the frequency and h is the\nPlanck\'s constant - and this total finite energy of objects is what\ndetermines both the inertial mass (resistance to acceleration) as well\nas the strength of the gravitational force (by the principle of\nequivalence). Photons move by the speed of light, which is certainly\nnot negligible compared to the speed of light, and therefore your\nnon-relativistic intuition fails completely. The kinetic energy is not\na small correction above the rest mass. Once again, the rest mass is\nzero, and the whole energy is kinetic - which does not mean that you can\nneglect it. LM]\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>"alistair" <alistair@goforit64.fsnet.co.uk> wrote in message
news:861c1b21.0408260520.5af60906-100000@posting.google.com...

> Does string theory say anything about how or whether gravitons can
> interact with photons? They are both bosons so can they scatter off
> one another for starters?
>
> [Moderator's note: Yes, string theory guarantees the principle of
> equivalence. All mass and energy in the Universe is subject to gravity.
> Photons carry nonzero energy, and therefore they interact with
> gravitons. LM]

This has bothering me for a while (I am not a physicists): If mass can be
converted into energy (i.e., energy and mass are equivalent), how can photons
have zero rest mass while exchanging force between electrons? How can a photon
exchange energy, and not have mass? The principle of equivalence states there
is no discernable difference between inertial mass and gravitational mass, but
it seems like there are two types of mass: "relativistic mass" and "rest
mass." I think this has to do with inertial frames of reference, spacetime
geodesics and how the zero rest mass of a photon is still mass proportional to
its frequency (nonzero energy?). If this requires too long of a reply (I
realize this is sci.physics.strings and not sci.physics.relativity), can I
have some URLs or names of books to read?

[Moderator's note: The rest mass "m_0" of a photon is zero, but the rest
mass is only relevant for expressing physics in the rest frame.
The rest frame of a photon does not exist - a photon moves by the speed
of light, and therefore the Lorentz factor 1/\sqrt(1-v^2/c^2) is infinite.
One must always observe the photon from another from, and then the ratio
m_0 c^2/\sqrt(1-v^2/c^2) - which is formally 0/0 - is a finite number that
expresses the total energy of your photon with respect to this frame.
This total energy E equals E=hf where f is the frequency and h is the
Planck's constant - and this total finite energy of objects is what
determines both the inertial mass (resistance to acceleration) as well
as the strength of the gravitational force (by the principle of
equivalence). Photons move by the speed of light, which is certainly
not negligible compared to the speed of light, and therefore your
non-relativistic intuition fails completely. The kinetic energy is not
a small correction above the rest mass. Once again, the rest mass is
zero, and the whole energy is kinetic - which does not mean that you can
neglect it. LM]