m theory [Archive] - Physics Forums

alistair

Apr30-04, 09:37 AM

Mikael Djurfeldt

Apr30-04, 03:12 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>alistair wrote:\n\n> M theory says that the force of gravity is weak compared to the force\n> of electricity because gravity "leaks" into a brane.\n> Isn\'t this the same as saying that in four dimensional space-time,\n> the force of gravity is weaker than the force of electricity because\n> there are negative gravitons - gravitons which cancel the effects of\n> normal gravitons - as well as positive gravitons.\n> In fact if M theory is right couldn\'t negative gravitons come from a\n> brane\n> into four dimensional space-time instead of normal gravitons leaking\n> into the brane.\n\nIt is a little audacious for me to reply, because I\'m a novice and have\njust started learning a little simplified string theory, but here\'s my\ntake anyway:\n\n1. Gravitons do not "leak" into a brane. The case is rather that they\nare unconstrained by branes, so the situation could better be\ndescribed as gravitons leaking out of a brane.\n\nThe reason is that while some particles are open strings, which have\ntheir endpoints attached to one or two branes, gravitons are closed\nstrings, which are not attached, and thus free to move about.\n\n(The idea is that we are living *in* a brane.)\n\n2. I know too little to say whether string theory could provide anything\nlike a "negative graviton", but I\'d anyway like to point out that\nstring theorists are not free to pick and choose and compose a\nsuitable set of particles. For example, the lowest state of\nexcitation of a closed string in bosonic string theory is a tachyon,\nand the next set of states is a "positive" graviton, the Kalb-Ramond\nB-field and the dilaton --- whether you\nlike it or not. It\'s simply the result of the quantization of a\nclassical relativistic string with the added requirement of Lorentz\ninvariance, and nothing more. The graviton is not there "by design".\n\nI hope experts will correct me where I\'m wrong.\n\nBest regards,\nM\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 wrote:

> M theory says that the force of gravity is weak compared to the force
> of electricity because gravity "leaks" into a brane.
> Isn't this the same as saying that in four dimensional space-time,
> the force of gravity is weaker than the force of electricity because
> there are negative gravitons - gravitons which cancel the effects of
> normal gravitons - as well as positive gravitons.
> In fact if M theory is right couldn't negative gravitons come from a
> brane
> into four dimensional space-time instead of normal gravitons leaking
> into the brane.

It is a little audacious for me to reply, because I'm a novice and have
just started learning a little simplified string theory, but here's my
take anyway:

1. Gravitons do not "leak" into a brane. The case is rather that they
are unconstrained by branes, so the situation could better be
described as gravitons leaking out of a brane.

The reason is that while some particles are open strings, which have
their endpoints attached to one or two branes, gravitons are closed
strings, which are not attached, and thus free to move about.

(The idea is that we are living *in* a brane.)

2. I know too little to say whether string theory could provide anything
like a "negative graviton", but I'd anyway like to point out that
string theorists are not free to pick and choose and compose a
suitable set of particles. For example, the lowest state of
excitation of a closed string in bosonic string theory is a tachyon,
and the next set of states is a "positive" graviton, the Kalb-Ramond
B-field and the dilaton --- whether you
like it or not. It's simply the result of the quantization of a
classical relativistic string with the added requirement of Lorentz
invariance, and nothing more. The graviton is not there "by design".

I hope experts will correct me where I'm wrong.

Best regards,
M