## Non-physicist: nothing is actually "moving"?

<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 was wondering if the string theory says that photons are actualy\nwaves in the space-time fabric.\n\nAlso I would like to know if their is a theory that says, instead of\nhaving many tiny strings, space-time itself would be The String and\nwhat appeared to be tiny strings would be ripples (interference?)in\nthe space-time fabric.\n\nI\'m not really a physicist so I might not make sense.\nThank you.\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">&nbsp;&nbsp;View this Usenet post in original ASCII form </a></div><P></jabberwocky>I was wondering if the string theory says that photons are actualy
waves in the space-time fabric.

Also I would like to know if their is a theory that says, instead of
having many tiny strings, space-time itself would be The String and
what appeared to be tiny strings would be ripples (interference?)in
the space-time fabric.

I'm not really a physicist so I might not make sense.
Thank you.



On Fri, 8 Oct 2004, unifieur wrote: > I was wondering if the string theory says that photons are actualy > waves in the space-time fabric. Photons have been quanta of electromagnetic waves since they were first proposed in the early 20th century. Theodor Kaluza made a shocking suggestion back in 1919 when he proposed that the electromagnetic waves are actually ripples on the shape of spacetime in the 5th dimension. This "Kaluza-Klein theory" was the first serious proposal to unify gravity and electromagnetism. This KK theory has become a part of string theory. In some cases (in some spacetimes that solve the constraints of string theory), the electromagnetism can be interpreted as curvature of spacetime (including an extra, hidden, small dimension). In all cases, electromagnetism and gravity are unified into something like a "generalized geometry". Moreover, a photon, much like a graviton, can be interpreted as a string moving in space and vibrating in a certain way. Gravitons are always closed strings (circle-shaped loops) while photons can be both closed strings as well as open strings (in the braneworlds). > Also I would like to know if their is a theory that says, instead of > having many tiny strings, space-time itself would be The String and > what appeared to be tiny strings would be ripples (interference?)in > the space-time fabric. Actually, there is one proposal that sort of matches your - otherwise a bit confusing - remark. Some authors have proposed that the whole Universe started, a very short time after the big bang, as a single string. No four-dimensional spacetime really existed at that moment; the Universe could have been interpreted using two-dimensional theory describing two dimensions of stringy worldsheets (one spatial dimension, one time). Moreover, in some sense, the spacetime is always made of strings $- it$ is a condensate of strings organized in a very specific fashion. See my new blog - http://motls.blogspot.com/ - for related texts. __{____________________________________________________________________ ________} E-mail: lumo@matfyz.cz fax: $+1-617/496-0110$ Web: http://lumo.matfyz.cz/ eFax: $+1-801/454-1858$ work: $+1-617/384-9488$ home: $+1-617/868-4487$ (call) ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ ^^^^^^^



Lubos Motl wrote in message news:... > This KK theory has become a part of string theory. In some cases (in some > spacetimes that solve the constraints of string theory), the > electromagnetism can be interpreted as curvature of spacetime (including > an extra, hidden, small dimension). In all cases, electromagnetism and > gravity are unified into something like a "generalized geometry". How is it known that the extra dimension is small? L.M.: In the models without branes, the dimensions must be small, otherwise we would already have seen them: they must be smaller than $10^{-18}$ meters because we have probed Nature up to these small distances, and everything is consistent with theories based on 3+1 dimensions, and inconsistent with theories in other dimensions. In the braneworld models, we may be attached to a brane, and only gravity can propagate to the extra dimensions. These extra dimensions, transverse to the branes, may be much larger, but they must still be smaller than 10 microns because we've checked that the gravitational $1/r^2$ force holds up to 10 microns, and an extra dimension would modify this formula. There are many other ways how to argue that the dimensions should be rather small, but these are the basic two.

## Non-physicist: nothing is actually "moving"?

 Quote by Patrick Powers How is it known that the extra dimension is small?
Read The Elegant Universe. Greene explains that the theory is only mathematically coherent if only four dimensions expand. I don't want to give false information as it's been a while sine I read the book, so just go read it yourself. = )

- Alisa

 This KK theory has become a part of string theory. In some cases (in some spacetimes that solve the constraints of string theory), the electromagnetism can be interpreted as curvature of spacetime (including an extra, hidden, small dimension). In all cases, electromagnetism and gravity are unified into something like a "generalized geometry". Moreover, a photon, much like a graviton, can be interpreted as a string moving in space and vibrating in a certain way. Gravitons are always closed strings (circle-shaped loops) while photons can be both closed strings as well as open strings (in the braneworlds).
I suppose this question can't be answered yet but I'll ask it anyway. If both gravity and electromagnetism can be viewed as spacetime curvature, and if both can also be viewed as strings, which creates which? Is the string a product of spacetime curvature or visa versa? And if the string is fundamental, wouldn't that imply that spacetime itself is secondary to energy? That is, space and time are products of particles, not fundamental aspects of the universe but rather dirived from quantum mechanical computations?