[Novice:] Speed of light [Archive]

Amin

Oct12-04, 07:45 AM

Urs Schreiber

Oct14-04, 03:06 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>On Tue, 12 Oct 2004, Amin wrote:\n\n> Is speed of light constant = c in strings theory?\n\nPerturbative string theory involves the propagation of relativistic\n1-dimensional objects on a pseudo-Riemannian manifold in a way that\nfollows the principles of special and general relativity.\n\nIn relativity, it might seem to be true but is a little too vague a\nstatement to be of much use that the speed of light is a constant. Since\nit is dimensionful, it is not perfectly clear what it would mean for it\nnot to be a constant. What is true, in ordinary relativity as well as in\nstring theory, is that no boost increases any speed to more than a maximal\nspeed which can be identified with that of massless waves/particles in\nvacuum, i.e. the "speed of light".\n\nThere have been discussions that the speed of light might in principle be\na variable, but as far as I can see statements like that only make sense\nwhen formulated in terms of dimensionless values, like the fine structure\nconstant. Apparent astrophysical evidence for the variation of the value\nof the fine structure constant over the ages has been discussed in the\npast.\n\nString theory in principle offers a natural framework for models in\nwhich coupling constants (like the fine structure constant) could vary\nover time. The reason is that in string theory all coupling constants are\nreally dynamical parameters that hang together for instance with size and\nshape of the compact dimensions or with the properties of various brane\nconfigurations, all of which have a dynamics.\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, 12 Oct 2004, Amin wrote:

> Is speed of light constant = c in strings theory?

Perturbative string theory involves the propagation of relativistic
1-dimensional objects on a pseudo-Riemannian manifold in a way that
follows the principles of special and general relativity.

In relativity, it might seem to be true but is a little too vague a
statement to be of much use that the speed of light is a constant. Since
it is dimensionful, it is not perfectly clear what it would mean for it
not to be a constant. What is true, in ordinary relativity as well as in
string theory, is that no boost increases any speed to more than a maximal
speed which can be identified with that of massless waves/particles in
vacuum, i.e. the "speed of light".

There have been discussions that the speed of light might in principle be
a variable, but as far as I can see statements like that only make sense
when formulated in terms of dimensionless values, like the fine structure
constant. Apparent astrophysical evidence for the variation of the value
of the fine structure constant over the ages has been discussed in the
past.

String theory in principle offers a natural framework for models in
which coupling constants (like the fine structure constant) could vary
over time. The reason is that in string theory all coupling constants are
really dynamical parameters that hang together for instance with size and
shape of the compact dimensions or with the properties of various brane
configurations, all of which have a dynamics.