[SOLVED] Questions [Archive]

Richard H. Araujo

Jun13-04, 09:42 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 want to confirm some string theory bits of knowledge. A couple questions:\n\nIs it true that universe with a given energy level has the same physics as a\nuniverse with the inverse energy level? If so is this true for all energy\nlevels or only specific ones?\n\nString Theory predicts extra spacial and perhaps temporal dimensions, 9 or\n10 spacial and 1 or more time, correct? Inn regards to that is there\nanything that explains why the three spacial dimensions in our universe are\nextended while the others are collapsed? Is there something special about\nour three over the others that makes them more prone to being extended?\nAlso, what\'s keeping them extended for now?\n\nI had an idea after reading about String Theory for a while, just wanted to\nreview some info and see if my idea was original at all.\n\nRich\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>I want to confirm some string theory bits of knowledge. A couple questions:

Is it true that universe with a given energy level has the same physics as a
universe with the inverse energy level? If so is this true for all energy
levels or only specific ones?

String Theory predicts extra spacial and perhaps temporal dimensions, 9 or
10 spacial and 1 or more time, correct? Inn regards to that is there
anything that explains why the three spacial dimensions in our universe are
extended while the others are collapsed? Is there something special about
our three over the others that makes them more prone to being extended?
Also, what's keeping them extended for now?

I had an idea after reading about String Theory for a while, just wanted to
review some info and see if my idea was original at all.

Rich

Urs Schreiber

Jun16-04, 03:05 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 Sun, 13 Jun 2004, Richard H. Araujo wrote:\n\n> Is it true that universe with a given energy level has the same physics as a\n> universe with the inverse energy level? If so is this true for all energy\n> levels or only specific ones?\n\nPresumeably you are talking about T-duality. T-duality in its simplest\nform says that the physics of a compact dimension of radius R is the same\nis that of a compact dimension of radius 1/R (in appropriate units).\nSince inverse length defines an energy scale you can roughly rephrase that\nas you did above. Note that T-duality has a very simple reason: strings\ncan have momentum in the compact dimension, which goes as n/R. Or they can\nwind around the compact dimension, giving a tension enrgy proportional to\nwR. T-duality thus "just" exchanges winding modes for momentum modes.\nFormally that\'s pretty simple, but the heuristic picture is still\namazingly weird: The Fourier transform of the space of winding\nexcitationas becomes a spatial dimension.\n\n> String Theory predicts extra spacial and perhaps temporal dimensions, 9 or\n> 10 spacial and 1 or more time, correct?\n\nOne time dimension only.\n\nInn regards to that is there\n> anything that explains why the three spacial dimensions in our universe are\n> extended while the others are collapsed?\n\nThere are lots of ideas but this problem has not been solved yet. It is\nrelated to the general problem of finding phenomenologically realistic\nsolutions of string theory.\n\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 Sun, 13 Jun 2004, Richard H. Araujo wrote:

> Is it true that universe with a given energy level has the same physics as a
> universe with the inverse energy level? If so is this true for all energy
> levels or only specific ones?

Presumeably you are talking about T-duality. T-duality in its simplest
form says that the physics of a compact dimension of radius R is the same
is that of a compact dimension of radius 1/R (in appropriate units).
Since inverse length defines an energy scale you can roughly rephrase that
as you did above. Note that T-duality has a very simple reason: strings
can have momentum in the compact dimension, which goes as n/R. Or they can
wind around the compact dimension, giving a tension enrgy proportional to
wR. T-duality thus "just" exchanges winding modes for momentum modes.
Formally that's pretty simple, but the heuristic picture is still
amazingly weird: The Fourier transform of the space of winding
excitationas becomes a spatial dimension.

> String Theory predicts extra spacial and perhaps temporal dimensions, 9 or
> 10 spacial and 1 or more time, correct?

One time dimension only.

Inn regards to that is there
> anything that explains why the three spacial dimensions in our universe are
> extended while the others are collapsed?

There are lots of ideas but this problem has not been solved yet. It is
related to the general problem of finding phenomenologically realistic
solutions of string theory.

xahrx

Jun17-04, 09:16 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>Urs Schreiber <Urs.Schreiber@uni-essen.de> wrote in message news:<Pine.LNX.4.31.0406161457510.1966-100000@feynman.harvard.edu>...\n\n> There are lots of ideas but this problem has not been solved yet. It is\n> related to the general problem of finding phenomenologically realistic\n> solutions of string theory.\n\nI was wondering about this. It seems some scientists are working on\nthe idea that the extra spacial dimensions present in String Theory\ncould explain things like the behavior of gravity over distance. I\'m\nwondering if it\'s possible that it wasn\'t, and won\'t always be the\ncase within the life of our universe that there will only be three\nextended spacial dimensions. Is it possible that very early in the\nexpansion of our universe that four or more dimensions were extended\nand that as the universe ages and cools down further that the current\nthree extended dimensions might collpase? Might this explain/be\nrelated to the four matter forces and how they diverged from one\nanother, cosmic expansion and a few other things? As the energy level\nof the universe goes higher as you move into the past the forces\nconverge, might this be because the increased energy of the universe\nalso forces the extension of the extra dimensions, and that it\'s the\nbehavior of the forces in the presence of more spacial dimensions that\ncauses them to converge into one unifed force?\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:<Pine.LNX.4.31.0406161457510.1966-100000@feynman.harvard.edu>...

> There are lots of ideas but this problem has not been solved yet. It is
> related to the general problem of finding phenomenologically realistic
> solutions of string theory.

I was wondering about this. It seems some scientists are working on
the idea that the extra spacial dimensions present in String Theory
could explain things like the behavior of gravity over distance. I'm
wondering if it's possible that it wasn't, and won't always be the
case within the life of our universe that there will only be three
extended spacial dimensions. Is it possible that very early in the
expansion of our universe that four or more dimensions were extended
and that as the universe ages and cools down further that the current
three extended dimensions might collpase? Might this explain/be
related to the four matter forces and how they diverged from one
another, cosmic expansion and a few other things? As the energy level
of the universe goes higher as you move into the past the forces
converge, might this be because the increased energy of the universe
also forces the extension of the extra dimensions, and that it's the
behavior of the forces in the presence of more spacial dimensions that
causes them to converge into one unifed force?

Urs Schreiber

Jun17-04, 09:26 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, 17 Jun 2004, xahrx wrote:\n\n> Urs Schreiber <Urs.Schreiber@uni-essen.de> wrote in message news:<Pine.LNX.4.31.0406161457510.1966-100000@feynman.harvard.edu>...\n>\n> > There are lots of ideas but this problem has not been solved yet. It is\n> > related to the general problem of finding phenomenologically realistic\n> > solutions of string theory.\n>\n> I was wondering about this. It seems some scientists are working on\n> the idea that the extra spacial dimensions present in String Theory\n> could explain things like the behavior of gravity over distance.\n\nMore precisely, the presence of curled up extra dimensions would imply\nthat on very short distance scales the gravitational force would scale\ndifferently than we are used to. But note that gravity as such is not a\nconsequence of the extra dimensions in string theory, but of the existence\nof closed strings.\n\n> I\'m\n> wondering if it\'s possible that it wasn\'t, and won\'t always be the\n> case within the life of our universe that there will only be three\n> extended spacial dimensions. Is it possible that very early in the\n> expansion of our universe that four or more dimensions were extended\n> and that as the universe ages and cools down further that the current\n> three extended dimensions might collpase?\n\n\nYes, that\'s possible. One can make a couple of educated guesses, but so\nfar no complete string cosmology is known, so that these quetions cannot\nbe fully answered for the time being. But there is lots of literature\nconcerned with questions of this type. For instance, look up the\n"Brandenberger-Vafa mechanism", e.g. hep-th/0204099 .\n\n\n> Might this explain/be\n> related to the four matter forces and how they diverged from one\n\nThe _shape_ of the compactified dimensions may have to do with the gauge\nforces that we see, but that we live in 4 large dimensions and that there\nare four fundamental forces is a numerical coincidence.\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, 17 Jun 2004, xahrx wrote:

> Urs Schreiber <Urs.Schreiber@uni-essen.de> wrote in message news:<Pine.LNX.4.31.0406161457510.1966-100000@feynman.harvard.edu>...
>
> > There are lots of ideas but this problem has not been solved yet. It is
> > related to the general problem of finding phenomenologically realistic
> > solutions of string theory.
>
> I was wondering about this. It seems some scientists are working on
> the idea that the extra spacial dimensions present in String Theory
> could explain things like the behavior of gravity over distance.

More precisely, the presence of curled up extra dimensions would imply
that on very short distance scales the gravitational force would scale
differently than we are used to. But note that gravity as such is not a
consequence of the extra dimensions in string theory, but of the existence
of closed strings.

> I'm
> wondering if it's possible that it wasn't, and won't always be the
> case within the life of our universe that there will only be three
> extended spacial dimensions. Is it possible that very early in the
> expansion of our universe that four or more dimensions were extended
> and that as the universe ages and cools down further that the current
> three extended dimensions might collpase?

Yes, that's possible. One can make a couple of educated guesses, but so
far no complete string cosmology is known, so that these quetions cannot
be fully answered for the time being. But there is lots of literature
concerned with questions of this type. For instance, look up the
"Brandenberger-Vafa mechanism", e.g. http://www.arxiv.org/abs/hep-th/0204099 .

> Might this explain/be
> related to the four matter forces and how they diverged from one

The _shape_ of the compactified dimensions may have to do with the gauge
forces that we see, but that we live in 4 large dimensions and that there
are four fundamental forces is a numerical coincidence.

xahrx

Jun17-04, 02:16 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>Urs Schreiber <Urs.Schreiber@uni-essen.de> wrote in message news:<Pine.LNX.4.31.0406170918510.3488-100000@feynman.harvard.edu>...\n\n> The _shape_ of the compactified dimensions may have to do with the gauge\n> forces that we see, but that we live in 4 large dimensions and that there\n> are four fundamental forces is a numerical coincidence.\n\nThanks for the quick response and the references. I\'m gonna do some\nreading. As for the above I\'d need to clarify. I didn\'t mean to\nimply a relationship between the number of extended dimensions and the\nnumber of forces, but that the break down of the forces from one to\nfour might be the result of the collapse of the extra dimensions.\nThat\'s to say how the forces split out is a direct consequence of\ndimensions collapsing over time, and further that dimensional collapse\nmight be the result of falling levels of energy. So right after the\nbang you\'ve perhaps got all dimensions extended, all forces unified.\nThe universe cools, some dimensions quickly collapse and it\'s this\ncollapse that causes the splitting of gauge forces. And now that I\nthink about it I\'ve read some people imply there might be extra gauge\nforces that we just don\'t know of right now because we can\'t measure\nthem. Perhaps the behavior if not the number of the forces is\ndetermined by how many and which dimensions are extended. Maybe\nbecause of scaling as you say in the case of gravity, or some other\nreason.\n\nLike you say there\'s no way to know right now I guess. Just an idea I\nwas messing with.\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:<Pine.LNX.4.31.0406170918510.3488-100000@feynman.harvard.edu>...

> The _shape_ of the compactified dimensions may have to do with the gauge
> forces that we see, but that we live in 4 large dimensions and that there
> are four fundamental forces is a numerical coincidence.

Thanks for the quick response and the references. I'm gonna do some
reading. As for the above I'd need to clarify. I didn't mean to
imply a relationship between the number of extended dimensions and the
number of forces, but that the break down of the forces from one to
four might be the result of the collapse of the extra dimensions.
That's to say how the forces split out is a direct consequence of
dimensions collapsing over time, and further that dimensional collapse
might be the result of falling levels of energy. So right after the
bang you've perhaps got all dimensions extended, all forces unified.
The universe cools, some dimensions quickly collapse and it's this
collapse that causes the splitting of gauge forces. And now that I
think about it I've read some people imply there might be extra gauge
forces that we just don't know of right now because we can't measure
them. Perhaps the behavior if not the number of the forces is
determined by how many and which dimensions are extended. Maybe
because of scaling as you say in the case of gravity, or some other
reason.

Like you say there's no way to know right now I guess. Just an idea I
was messing with.