View Full Version : Can the Cosmological constant go negative?
Serenus Zeitblom
May25-04, 04:58 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>Squark <fiis5d@yahoo.com> wrote in message news:<939044f.0405231017.41f7dde9-\n\n> 2) It is currently believed a transition from a universe\n> with non-negative cosmological constant to a negative\n> cosmological constant one is impossible.\n\nI don\'t think that this is right. See\nhttp://arxiv.org/abs/hep-th/0404220\nIt is true that they don\'t consider the case where the potential\ngoes negative, but it is also true that they claim that this\nis possible. They seem to think that going negative is not\n"generic" but they don\'t explain why they believe this.....\n\n> Apparently this is\n> so because classical gravity considerations imply the\n> resulting universe is a big crunch universe and it is not\n> clear whether the later makes sense in string theory.\n> Frankly, this whole idea is not clear to me since we\'re\n> living in a big bang universe, and if that makes sense, why\n> not big crunch? Possible there are additional arguments\n> against this kind of transitions which I am unaware of.\n\nA crunch very often --- though not always --- gives you a\nPenrose diagram that looks very much like the Penrose diagram\nof deSitter, and hence the same objections [as those raised\nby Susskind and others] apply to the\ncrunch in that case. But I have not seen anyone argue that\nthis argument rules out "a transition from a universe\nwith non-negative cosmological constant to a negative\ncosmological constant one". I guess it just means that\nmetastability of deS doesn\'t really solve those problems.\nIt\'s an interesting point.\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>Squark <fiis5d@yahoo.com> wrote in message news:<939044f.0405231017.41f7dde9-
> 2) It is currently believed a transition from a universe
> with non-negative cosmological constant to a negative
> cosmological constant one is impossible.
I don't think that this is right. See
http://arxiv.org/abs/http://www.arxiv.org/abs/hep-th/0404220
It is true that they don't consider the case where the potential
goes negative, but it is also true that they claim that this
is possible. They seem to think that going negative is not
"generic" but they don't explain why they believe this.....
> Apparently this is
> so because classical gravity considerations imply the
> resulting universe is a big crunch universe and it is not
> clear whether the later makes sense in string theory.
> Frankly, this whole idea is not clear to me since we're
> living in a big bang universe, and if that makes sense, why
> not big crunch? Possible there are additional arguments
> against this kind of transitions which I am unaware of.
A crunch very often --- though not always --- gives you a
Penrose diagram that looks very much like the Penrose diagram
of deSitter, and hence the same objections [as those raised
by Susskind and others] apply to the
crunch in that case. But I have not seen anyone argue that
this argument rules out "a transition from a universe
with non-negative cosmological constant to a negative
cosmological constant one". I guess it just means that
metastability of deS doesn't really solve those problems.
It's an interesting point.
Urs Schreiber
May25-04, 02:00 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 Tue, 25 May 2004, Serenus Zeitblom wrote:\n\n> Squark <fiis5d@yahoo.com> wrote in message news:<939044f.0405231017.41f7dde9-\n>\n> > 2) It is currently believed a transition from a universe\n> > with non-negative cosmological constant to a negative\n> > cosmological constant one is impossible.\n>\n> I don\'t think that this is right. See\n> http://arxiv.org/abs/hep-th/0404220\n> It is true that they don\'t consider the case where the potential\n> goes negative, but it is also true that they claim that this\n> is possible. They seem to think that going negative is not\n> "generic" but they don\'t explain why they believe this.....\n\nCorrect me if I am wrong (I am not even remotely an expert on landscaping)\nbut isn\'t the very point of metastable dS vacua that they decay into\nAdS vacua eventually? That\'s precisely why they are only metastable.\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, 25 May 2004, Serenus Zeitblom wrote:
> Squark <fiis5d@yahoo.com> wrote in message news:<939044f.0405231017.41f7dde9-
>
> > 2) It is currently believed a transition from a universe
> > with non-negative cosmological constant to a negative
> > cosmological constant one is impossible.
>
> I don't think that this is right. See
> http://arxiv.org/abs/http://www.arxiv.org/abs/hep-th/0404220
> It is true that they don't consider the case where the potential
> goes negative, but it is also true that they claim that this
> is possible. They seem to think that going negative is not
> "generic" but they don't explain why they believe this.....
Correct me if I am wrong (I am not even remotely an expert on landscaping)
but isn't the very point of metastable dS vacua that they decay into
AdS vacua eventually? That's precisely why they are only metastable.
Serenus Zeitblom
May26-04, 10:09 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 > Correct me if I am wrong (I am not even remotely an expert on landscaping)\n> but isn\'t the very point of metastable dS vacua that they decay into\n> AdS vacua eventually? That\'s precisely why they are only metastable.\n\nSee figures 1 and 2 of\nhttp://arxiv.org/abs/hep-th/0404220\nIf the effective potential for the radial dilaton\nremains positive, then there will be a runaway\nwhen the current deS phase either tunnels or\nfluctuates out, resulting in the explosive growth\nof the small dimensions; all dimensions will become\nequal, bringing democracy and destruction\nto the whole Universe, including Iraq. [Does anyone\nknow exactly how this disaster would manifest itself?\nIn rapidly varying "constants" no doubt, but how\nprecisely would we all be killed? I mean, which effect\nwould get us first?]\nIf the effective potential goes negative, which seems\nmore likely to you and me but not to the authors above, then\nwe get something like AdS, and only in this case\ndoes metastability lead to *something like* AdS\n[though presumably not AdS itself --- a Big Crunch\nis more likely.] Either way things don\'t look good.\nFor us I mean, not for 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>Urs Schreiber <Urs.Schreiber@uni-essen.de> wrote in message > Correct me if I am wrong (I am not even remotely an expert on landscaping)
> but isn't the very point of metastable dS vacua that they decay into
> AdS vacua eventually? That's precisely why they are only metastable.
See figures 1 and 2 of
http://arxiv.org/abs/http://www.arxiv.org/abs/hep-th/0404220
If the effective potential for the radial dilaton
remains positive, then there will be a runaway
when the current deS phase either tunnels or
fluctuates out, resulting in the explosive growth
of the small dimensions; all dimensions will become
equal, bringing democracy and destruction
to the whole Universe, including Iraq. [Does anyone
know exactly how this disaster would manifest itself?
In rapidly varying "constants" no doubt, but how
precisely would we all be killed? I mean, which effect
would get us first?]
If the effective potential goes negative, which seems
more likely to you and me but not to the authors above, then
we get something like AdS, and only in this case
does metastability lead to *something like* AdS
[though presumably not AdS itself --- a Big Crunch
is more likely.] Either way things don't look good.
For us I mean, not for string theory.
Urs Schreiber
May26-04, 11:49 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>"Serenus Zeitblom" <serenuszeitblomphd@yahoo.com> schrieb im Newsbeitrag\nnews:c7fd6c7a.0405260527.fe3e1ca-100000@posting.google.com...\n\n> See figures 1 and 2 of\n> http://arxiv.org/abs/hep-th/0404220\n\n[...]\n\n> If the effective potential goes negative, which seems\n> more likely to you and me\n\nTo be honest, I don\'t have any opinion on likeliness here. My general\nimpression is that way too little is known about the mechanisms that one\nwould like to study here. The discussion reminds me of some developments in\nquantum cosmology in the 80s-90s, where people would argue about having\nderived or having not derived the arrow of time and argue about if the\nuniverse is described by the "no boundary" or by the "tunneling" boundary\ncondition or something else. In retrospect I think it is fair to say that\nthese discussions, while philosophically very interesting, had very little\nexact physical underpinning. One could argue that something similar is\ntendentially true for the discussion that the above paper is part of. And\nthe authors do say so themselves in the introduction, where they mention for\ninstance that the use of the effective potential may well be just\ninsufficient.\n\n> but not to the authors above,\n\nMaybe I haven\'t read the paper carefully enough, but why exactly do the\nauthors say that the potential of Fig. 1 is "more generic" than that of Fig.\n2 (as in the paragraph right below Fig. 2)? At other places (in the\nintroduction and the conclusion) no reference to genericity is made, IIRC,\nbut it is stated that Fig. 1 is simply the case the authors decided to\nconcentrate on.\n\n> then\n> we get something like AdS, and only in this case\n> does metastability lead to *something like* AdS\n> [though presumably not AdS itself --- a Big Crunch\n> is more likely.]\n\nWhy is it more likely?\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>"Serenus Zeitblom" <serenuszeitblomphd@yahoo.com> schrieb im Newsbeitrag
news:c7fd6c7a.0405260527.fe3e1ca-100000@posting.google.com...
> See figures 1 and 2 of
> http://arxiv.org/abs/http://www.arxiv.org/abs/hep-th/0404220
[...]
> If the effective potential goes negative, which seems
> more likely to you and me
To be honest, I don't have any opinion on likeliness here. My general
impression is that way too little is known about the mechanisms that one
would like to study here. The discussion reminds me of some developments in
quantum cosmology in the 80s-90s, where people would argue about having
derived or having not derived the arrow of time and argue about if the
universe is described by the "no boundary" or by the "tunneling" boundary
condition or something else. In retrospect I think it is fair to say that
these discussions, while philosophically very interesting, had very little
exact physical underpinning. One could argue that something similar is
tendentially true for the discussion that the above paper is part of. And
the authors do say so themselves in the introduction, where they mention for
instance that the use of the effective potential may well be just
insufficient.
> but not to the authors above,
Maybe I haven't read the paper carefully enough, but why exactly do the
authors say that the potential of Fig. 1 is "more generic" than that of Fig.
2 (as in the paragraph right below Fig. 2)? At other places (in the
introduction and the conclusion) no reference to genericity is made, IIRC,
but it is stated that Fig. 1 is simply the case the authors decided to
concentrate on.
> then
> we get something like AdS, and only in this case
> does metastability lead to *something like* AdS
> [though presumably not AdS itself --- a Big Crunch
> is more likely.]
Why is it more likely?
Charlie Stromeyer Jr.
May26-04, 04:36 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>> Squark <fiis5d@yahoo.com> wrote in message news:<939044f.0405231017.41f7dde9-\n>\n> > 2) It is currently believed a transition from a universe\n> > with non-negative cosmological constant to a negative\n> > cosmological constant one is impossible.\n\nHi Squark. The latest astrophysical observations are compatible with\nthe idea of lambda remaining fairly constant. There is still a\npossibilty that the energy density could increase over time, but so\nfar there is no evidence for this. In either case, the next Big Crunch\nyou will see is when the New England Patriots win the SuperBowl for\nthe third time !-)\n\nSpeaking of the cosmological constant, do you know if there is\nanything additional to lambda or unusual with the structure of the\nEinstein tensor in dS scenarios?\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>> Squark <fiis5d@yahoo.com> wrote in message news:<939044f.0405231017.41f7dde9-
>
> > 2) It is currently believed a transition from a universe
> > with non-negative cosmological constant to a negative
> > cosmological constant one is impossible.
Hi Squark. The latest astrophysical observations are compatible with
the idea of \lambda remaining fairly constant. There is still a
possibilty that the energy density could increase over time, but so
far there is no evidence for this. In either case, the next Big Crunch
you will see is when the New England Patriots win the SuperBowl for
the third time !-)
Speaking of the cosmological constant, do you know if there is
anything additional to \lambda or unusual with the structure of the
Einstein tensor in dS scenarios?
Serenus Zeitblom
May27-04, 05:20 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:<2hjsj8FdobdvU1-100000@uni-berlin.de>...\n> "Serenus Zeitblom" <serenuszeitblomphd@yahoo.com> schrieb im Newsbeitrag\n> news:c7fd6c7a.0405260527.fe3e1ca-100000@posting.google.com...\n>\n> > See figures 1 and 2 of\n> > http://arxiv.org/abs/hep-th/0404220\n>\n> [...]\n>\n> > If the effective potential goes negative, which seems\n> > more likely to you and me\n>\n> To be honest, I don\'t have any opinion on likeliness here. My general\n> impression is that way too little is known about the mechanisms that one\n> would like to study here. The discussion reminds me of some developments in\n> quantum cosmology in the 80s-90s, where people would argue about having\n> derived or having not derived the arrow of time and argue about if the\n> universe is described by the "no boundary" or by the "tunneling" boundary\n> condition or something else. In retrospect I think it is fair to say that\n> these discussions, while philosophically very interesting, had very little\n> exact physical underpinning. One could argue that something similar is\n> tendentially true for the discussion that the above paper is part of. And\n> the authors do say so themselves in the introduction, where they mention for\n> instance that the use of the effective potential may well be just\n> insufficient.\n\nUrs, that is exactly the kind of thing that Peter Woit says about\nstring theory in general! It\'s no good saying that it is "premature"\nto consider such matters --- we have to try to answer these questions\nwith the resources we have, even though we know that we are unlikely\nto succeed right now. It\'s true, for example, that the efforts to\nget deSitter in string theory look pretty lame. But they look a\n*lot* less lame than just telling astrophysicists that we don\'t even\nknow whether it can be done at all. We *have* to get a believable\ncosmology out of string theory; otherwise people will just conclude\nthat string theory has failed to account for the observations, ie\nthey will conclude that it is wrong. It is one thing to tell\ncosmologists that at the moment we don\'t quite fully understand\nhow cosmology works in string theory, but we are working on it ---\nit is quite another thing to tell them that we aren\'t worried\nbecause it is "premature" to do so. The observational people just\nlaugh at that kind of talk.\n\nIsaac Newton didn\'t apply his mechanics to cosmology because\nhe didn\'t know that the universe is expanding --- he had no\ndata. We *do* have a massive amount of data now showing that\nthe universe is accelerating. We either address this problem\n*now* or the subject will die.\n\n\n>\n> > but not to the authors above,\n>\n> Maybe I haven\'t read the paper carefully enough, but why exactly do the\n> authors say that the potential of Fig. 1 is "more generic" than that of Fig.\n> 2 (as in the paragraph right below Fig. 2)? At other places (in the\n> introduction and the conclusion) no reference to genericity is made, IIRC,\n> but it is stated that Fig. 1 is simply the case the authors decided to\n> concentrate on.\n\nExcellent question! I have no idea.\n\n>\n> > then\n> > we get something like AdS, and only in this case\n> > does metastability lead to *something like* AdS\n> > [though presumably not AdS itself --- a Big Crunch\n> > is more likely.]\n>\n> Why is it more likely?\n\nThis is an old argument of Coleman and deLuccia. You can find it\nin http://arxiv.org/abs/hep-th/0211160.\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:<2hjsj8FdobdvU1-100000@uni-berlin.de>...
> "Serenus Zeitblom" <serenuszeitblomphd@yahoo.com> schrieb im Newsbeitrag
> news:c7fd6c7a.0405260527.fe3e1ca-100000@posting.google.com...
>
> > See figures 1 and 2 of
> > http://arxiv.org/abs/http://www.arxiv.org/abs/hep-th/0404220
>
> [...]
>
> > If the effective potential goes negative, which seems
> > more likely to you and me
>
> To be honest, I don't have any opinion on likeliness here. My general
> impression is that way too little is known about the mechanisms that one
> would like to study here. The discussion reminds me of some developments in
> quantum cosmology in the 80s-90s, where people would argue about having
> derived or having not derived the arrow of time and argue about if the
> universe is described by the "no boundary" or by the "tunneling" boundary
> condition or something else. In retrospect I think it is fair to say that
> these discussions, while philosophically very interesting, had very little
> exact physical underpinning. One could argue that something similar is
> tendentially true for the discussion that the above paper is part of. And
> the authors do say so themselves in the introduction, where they mention for
> instance that the use of the effective potential may well be just
> insufficient.
Urs, that is exactly the kind of thing that Peter Woit says about
string theory in general! It's no good saying that it is "premature"
to consider such matters --- we have to try to answer these questions
with the resources we have, even though we know that we are unlikely
to succeed right now. It's true, for example, that the efforts to
get deSitter in string theory look pretty lame. But they look a
*lot* less lame than just telling astrophysicists that we don't even
know whether it can be done at all. We *have* to get a believable
cosmology out of string theory; otherwise people will just conclude
that string theory has failed to account for the observations, ie
they will conclude that it is wrong. It is one thing to tell
cosmologists that at the moment we don't quite fully understand
how cosmology works in string theory, but we are working on it ---
it is quite another thing to tell them that we aren't worried
because it is "premature" to do so. The observational people just
laugh at that kind of talk.
Isaac Newton didn't apply his mechanics to cosmology because
he didn't know that the universe is expanding --- he had no
data. We *do* have a massive amount of data now showing that
the universe is accelerating. We either address this problem
*now* or the subject will die.
>
> > but not to the authors above,
>
> Maybe I haven't read the paper carefully enough, but why exactly do the
> authors say that the potential of Fig. 1 is "more generic" than that of Fig.
> 2 (as in the paragraph right below Fig. 2)? At other places (in the
> introduction and the conclusion) no reference to genericity is made, IIRC,
> but it is stated that Fig. 1 is simply the case the authors decided to
> concentrate on.
Excellent question! I have no idea.
>
> > then
> > we get something like AdS, and only in this case
> > does metastability lead to *something like* AdS
> > [though presumably not AdS itself --- a Big Crunch
> > is more likely.]
>
> Why is it more likely?
This is an old argument of Coleman and deLuccia. You can find it
in http://arxiv.org/abs/http://www.arxiv.org/abs/hep-th/0211160.
Urs Schreiber
May27-04, 10:40 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>"Serenus Zeitblom" <serenuszeitblomphd@yahoo.com> schrieb im Newsbeitrag\nnews:c7fd6c7a.0405270043.7bc35ce3-100000@posting.google.com...\n> Urs Schreiber <Urs.Schreiber@uni-essen.de> wrote in message\nnews:<2hjsj8FdobdvU1-100000@uni-berlin.de>...\n> > "Serenus Zeitblom" <serenuszeitblomphd@yahoo.com> schrieb im Newsbeitrag\n> > news:c7fd6c7a.0405260527.fe3e1ca-100000@posting.google.com...\n> >\n> > > See figures 1 and 2 of\n> > > http://arxiv.org/abs/hep-th/0404220\n> >\n> > [...]\n> >\n> > > If the effective potential goes negative, which seems\n> > > more likely to you and me\n> >\n> > To be honest, I don\'t have any opinion on likeliness here. My general\n> > impression is that way too little is known about the mechanisms that one\n> > would like to study here.\n>\n> Urs, that is exactly the kind of thing that Peter Woit says about\n> string theory in general!\n\nI don\'t think so. I am saying that it would have been premature for Newton\nto try to write the "Celestial Mechanics" or to try to prove the stability\nof the solar system, even though Newton had the full theory available\nalready. It takes a while to understand everything that is inside a theory.\n\nRecall that the KKLT paper crucially used some non-perturbative effects\nwhich weren\'t known a while before. So there has already been improvement in\nunderstanding the space of vacua. I said that my humble impression is that\nstill too little is known. But that will change as people keep studying this\nstuff.\n\n> It\'s no good saying that it is "premature"\n[...]\n> The observational people just laugh at that kind of talk.\n\nI\'d say that if anyone feels amused by the fact that quantum gravity isn\'t\nfully understood yet - let him laugh. (Of course I can imagine that it is\nmuch easier for a theorist to appreciate the progress that has already been\nmade than for an experimentalist.)\n\n> Isaac Newton didn\'t apply his mechanics to cosmology because\n> he didn\'t know that the universe is expanding --- he had no\n> data. We *do* have a massive amount of data now showing that\n> the universe is accelerating. We either address this problem\n> *now* or the subject will die.\n\nI am not sure that I understand your attitude. Surely everybody would like\nto know the answers to interesting open questions - but if we don\'t know yet\nwe don\'t know yet.\n\n> > Maybe I haven\'t read the paper carefully enough, but why exactly do the\n> > authors say that the potential of Fig. 1 is "more generic" than that of\nFig.\n> > 2 (as in the paragraph right below Fig. 2)? At other places (in the\n> > introduction and the conclusion) no reference to genericity is made,\nIIRC,\n> > but it is stated that Fig. 1 is simply the case the authors decided to\n> > concentrate on.\n>\n> Excellent question! I have no idea.\n\nHm. Isn\'t this the crucial point of that paper? Of course if we _assume_\nthat the potential for the internal volume modulus is as in figure 1 then it\nfollows automatically that the universe will spontaneously decompactify. So\nthe key point seems to be the question why Fig 2 is excluded. Does anyone\nelse have an idea?\n\n> >\n> > > then\n> > > we get something like AdS, and only in this case\n> > > does metastability lead to *something like* AdS\n> > > [though presumably not AdS itself --- a Big Crunch\n> > > is more likely.]\n> >\n> > Why is it more likely?\n>\n> This is an old argument of Coleman and deLuccia. You can find it\n> in http://arxiv.org/abs/hep-th/0211160.\n\nAh, there is this statment:\n"The Big Crunch singularity of the CDL solution is, I believe, an argument\nthat decays into spaces of negative cosmological constant do not occur in\nconsistent theories of quantum gravity." (T. Banks in hep-th/0211160)\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>"Serenus Zeitblom" <serenuszeitblomphd@yahoo.com> schrieb im Newsbeitrag
news:c7fd6c7a.0405270043.7bc35ce3-100000@posting.google.com...
> Urs Schreiber <Urs.Schreiber@uni-essen.de> wrote in message
news:<2hjsj8FdobdvU1-100000@uni-berlin.de>...
> > "Serenus Zeitblom" <serenuszeitblomphd@yahoo.com> schrieb im Newsbeitrag
> > news:c7fd6c7a.0405260527.fe3e1ca-100000@posting.google.com...
> >
> > > See figures 1 and 2 of
> > > http://arxiv.org/abs/http://www.arxiv.org/abs/hep-th/0404220
> >
> > [...]
> >
> > > If the effective potential goes negative, which seems
> > > more likely to you and me
> >
> > To be honest, I don't have any opinion on likeliness here. My general
> > impression is that way too little is known about the mechanisms that one
> > would like to study here.
>
> Urs, that is exactly the kind of thing that Peter Woit says about
> string theory in general!
I don't think so. I am saying that it would have been premature for Newton
to try to write the "Celestial Mechanics" or to try to prove the stability
of the solar system, even though Newton had the full theory available
already. It takes a while to understand everything that is inside a theory.
Recall that the KKLT paper crucially used some non-perturbative effects
which weren't known a while before. So there has already been improvement in
understanding the space of vacua. I said that my humble impression is that
still too little is known. But that will change as people keep studying this
stuff.
> It's no good saying that it is "premature"
[...]
> The observational people just laugh at that kind of talk.
I'd say that if anyone feels amused by the fact that quantum gravity isn't
fully understood yet - let him laugh. (Of course I can imagine that it is
much easier for a theorist to appreciate the progress that has already been
made than for an experimentalist.)
> Isaac Newton didn't apply his mechanics to cosmology because
> he didn't know that the universe is expanding --- he had no
> data. We *do* have a massive amount of data now showing that
> the universe is accelerating. We either address this problem
> *now* or the subject will die.
I am not sure that I understand your attitude. Surely everybody would like
to know the answers to interesting open questions - but if we don't know yet
we don't know yet.
> > Maybe I haven't read the paper carefully enough, but why exactly do the
> > authors say that the potential of Fig. 1 is "more generic" than that of
Fig.
> > 2 (as in the paragraph right below Fig. 2)? At other places (in the
> > introduction and the conclusion) no reference to genericity is made,
IIRC,
> > but it is stated that Fig. 1 is simply the case the authors decided to
> > concentrate on.
>
> Excellent question! I have no idea.
Hm. Isn't this the crucial point of that paper? Of course if we _assume_
that the potential for the internal volume modulus is as in figure 1 then it
follows automatically that the universe will spontaneously decompactify. So
the key point seems to be the question why Fig 2 is excluded. Does anyone
else have an idea?
> >
> > > then
> > > we get something like AdS, and only in this case
> > > does metastability lead to *something like* AdS
> > > [though presumably not AdS itself --- a Big Crunch
> > > is more likely.]
> >
> > Why is it more likely?
>
> This is an old argument of Coleman and deLuccia. You can find it
> in http://arxiv.org/abs/http://www.arxiv.org/abs/hep-th/0211160.
Ah, there is this statment:
"The Big Crunch singularity of the CDL solution is, I believe, an argument
that decays into spaces of negative cosmological constant do not occur in
consistent theories of quantum gravity." (T. Banks in http://www.arxiv.org/abs/hep-th/0211160)
Lubos Motl
May27-04, 11:12 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, 27 May 2004, Serenus Zeitblom wrote:\n\n> Urs, that is exactly the kind of thing that Peter Woit says about\n> string theory in general! It\'s no good saying that it is "premature"\n> to consider such matters --- we have to try to answer these questions\n> with the resources we have, even though we know that we are unlikely\n> to succeed right now.\n\nThere is some sense in which I agree, but one must be more careful and\nbalanced. There are obviously many examples from the history of physics in\nwhich people were asking premature questions. Einstein wanted to unify all\nforces and construct a unified field theory. Unfortunately he thought that\nelectromagnetism and gravity were the only forces, and nuclear\ninteractions (and even quantum mechanics) are emergent details that should\nnot be taken seriously and that will eventually be described by the\nunified theory for free.\n\nAlthough we are continuing his generalized dream, Kaluza-Klein ideas are\nthe only ideas that survived. All other specific proposals to unify\nelectromagnetism and gravity simply were premature, and I would also say\nmisguided. Today we know that the unification of gravity with the other\nforces was the hardest task, something that we had to wait for, and\nalthough string theory shows that it can be done - and it might be even\ndone in Nature - it simply does not seem to be an appropriate task for the\n1920s. It is likely that there are many examples of this sort.\n\nIt is always difficult to guess how the world would evolve had some\ndiscoveries been done in a different order. We see many illogical\nacausalities in the history of physics - B was often invented before A, so\nto say - but there are also many cases where the order could not have been\ndifferent. OK, let me now switch from this general philosophy to the\nmore particular question of string cosmology and related issues.\n\nI think it is premature to try to construct this major framework that\nwould explain the character of vacuum selection and very early cosmology\nin string theory, and it is wrong to study these questions separately from\nthe technical questions in string theory that work and that we can\ncalculate well. The reason is that we have very little data - that would\ngo beyond philosophy - about quantum cosmology. In other words, we have\nvery little data from cosmology (or no data at all) that would require us\nto go beyond classical physics. What we have are the semi-reliable\ntheoretical data - string theory results for many backgrounds and\nprocesses - and we should use them as much as we can.\n\nIt seems clear to me that the argument that the available cosmological\ndata should be described by a highly exotic and quantum theory - such as\nthe cannon of string theory tool - is strongly disfavored experimentally.\n\nIt seems also obvious to me that we have not yet found the universal rules\nof string theory that could be applied to extreme conditions, such as the\nvery Big Bang, or that could cover the whole "landscape", whatever its\nsize is. Let me say my favorite example. We have not found a formulation\nof M-theory on T^7 that would make the E_{7(7)}(Z) U-duality symmetry\nmanifest. This U-duality is an example of an idea that relates many\ndifferent points of the landscape, and moreover it might be the simplest\nidea of this sort because we are protected by 32 supercharges. So my\nbelief is that we will have to understand the nonperturbative structure of\nthe stringy arena using some new universal definition of string theory - a\ndefinition that is both non-perturbative (reaches the strongly coupled\nregions) as well as background-universal (reaches the geometries and\nnon-geometries that are different from the starting one), and only\nafterwards, we will be able to start answering the stringy cosmological\nquestions in a better context. Without this new tool, everything is just\nvague guesswork.\n\nIn my opinion, the research of string cosmology; stringy inflation; de\nSitter space in string theory; scattering in backgrounds with non-standard\ncausal diagrams; and all similar things that have essentially be started\nby the observation of accelerating Universe back in 1998 - has led to a\nvery small number of intriguing results. There is almost nothing\nnon-trivial and mathematically intriguing going on here; there is as much\noutput as much input we insert. It remains a combination of phenomenology\nand speculations where conjectures can rarely be clearly ruled out. There\nis simply no guarantee that a direct attack to string-theoretical\ncosmological questions will be as successful as the stringy explanations\nfor gravitatinoal S-matrix and various processes in highly supersymmetric\nbackgrounds that are not far from the flat (or AdS) space.\n\nIn general, we should study the questions that we have a chance to answer\n- questions where we have enough hints, enough data that require a unified\nexplanation - and it is simply not the case of string cosmology,\nespecially not string cosmology that neglects the truly new stringy\nphenomena such as U-dualities. And our proposed answers should be tested\nagainst the experimental data, even the general and qualitative ones - and\nin this respect it seems clear to me that the conjecture that the\navailable cosmological data require hugely exotic, quantum and stringy\nphenomena is essentially ruled out. Because they don\'t require\nstringy/quantum phenomena, they tell us almost nothing about the nature of\nquantum cosmology in string theory.\n\n> It\'s true, for example, that the efforts to\n> get deSitter in string theory look pretty lame. But they look a\n> *lot* less lame than just telling astrophysicists that we don\'t even\n> know whether it can be done at all.\n\nSomething like de Sitter space probably can be done, by arguments rooted\nin effective field theory that approximates string theory well. But it is\ntrue that we have essentially nothing new - beyond effective field theory\n- to tell astrophysicists about de Sitter space, and I don\'t care a single\nbit whether it sounds *lame* to anyone or not. For me it is much more\nimportant that it is *true*. Once again, we have found no reliable insight\nor prediction about the character of de Sitter space in string theory that\nwould go beyond general arguments and arguments rooted in effective field\ntheory.\n\nThe Standard Model has about 19 parameters that look free and have not\nbeen explained. If the purpose of science is to explain, I still think\nthat these are the next targets, and 19 is 19 times more than the number\nof cosmological constants, which for me implies that we should not spend\nmost of our time with debates about the cosmological constant because they\nturned out to be pretty fruitless. The cosmological constant seems very\ntiny, but there are many other numbers in Nature that look very small,\ntoo.\n\n> We *have* to get a believable\n> cosmology out of string theory; otherwise people will just conclude\n> that string theory has failed to account for the observations, ie\n> they will conclude that it is wrong.\n\nOnce again, I am not doing physics because I want the people to make some\npre-determined conclusions, which is what you propose. I am only studying\nphysical questions where the conclusion is not yet clear, and I want to\nfind out what the right conclusion - the truth - is. There is no guarantee\nthat there exists a believable purely stringy cosmology. I don\'t\nunderstand what it means to say that we "have to get it". If it does not\nexist, we even cannot get it in principle. Does the world end if one of\nour prejudices is wrong?\n\nSo far, string theory has never been successful in giving us new reliable\ninsights about cosmology, and if you ever built your arguments on the\nopposite, incorrect statement, then it is your problem - not something\nthat should determine what the people in string theory should work on.\n\n> It is one thing to tell cosmologists that at the moment we don\'t quite\n> fully understand how cosmology works in string theory, but we are\n> working on it --- it is quite another thing to tell them that we\n> aren\'t worried because it is "premature" to do so. The observational\n> people just laugh at that kind of talk.\n\nWell, if they laugh, then they are pretty stupid. Theorists have a harder\njob than to look in the telescope and say "I see a little green man". We\nshould try to get the right answers today or this year, but in reality, it\ncan take decades or fifty years to find the right answers. It took almost\n3 centuries to develop quantum field theory from Newton\'s discoveries -\neven though it was enough to make a field theoretical version of his\nequations of motion and quantize them, and even though they always had a\nlot of experiments.\n\nIf some of our fellow experimentalists think that it is easy to find the\nright explanation of cosmology in a quantum framework etc., they are free\nto change their field and try to compete with other theorists.\n\n> Isaac Newton didn\'t apply his mechanics to cosmology because\n> he didn\'t know that the universe is expanding --- he had no\n> data. We *do* have a massive amount of data now showing that\n> the universe is accelerating.\n\nI don\'t know what you mean by a massive amount of data. The Universe is\nhuge and it has many photons in it, and therefore we see many of their\nproperties very many times, but the data directly related to the\nacceleration are made of 1 number - the cosmological constant. There are\nseveral more important measurable numbers about cosmology - for example\nthe harmonics of the cosmic microwave background - but they are\nincreasingly far from the fundamental theory, and increasingly more\naffected by ordinary (even classical) physics.\n\nWhat I would call "massive amount of data" is something that gives us\nthousands of independent and non-trivial numbers so that one can look for\nnew patterns. For example, people knew a lot of particles that lie on the\nRegge trajectory - their masses and many other detailed patterns - so that\nVeneziano et al. could eventually construct "a" theory. It took several\nyears, and then it was realized that although this many data that agreed,\nother data disagreed and the theory was wrong as a description of the\nstrong force - a statement that was recently softened because of the\nAdS/CFT correspondece.\n\nBut the origin of the acceleration of the Universe? We have no data\nwhatsoever that could tell us what is the origin or structure of the\ncosmological constant. At a phenomenological level, we understood what\'s\ngoing on. But we depend on purely theoretical tools if we want to find the\nstringy origin of all these things.\n\n> We either address this problem\n> *now* or the subject will die.\n\nI don\'t think that string theory is (or should be) studied primarily as a\nphenomenological theory to explain current astronomical observations. I\ndon\'t think that this class of questions was ever a major reason why we\nstudied string theory, and I don\'t think that the famous and breath-taking\nresults of string theory were usually related to cosmology. The existing\nsuccesses of string cosmology, for example, could never justify big\nfunding, I believe. It is a totally uncertain issue whether string theory\nwill ever be as successful with cosmology as it has been with the graviton\nscattering, black hole entropy, dualities or mirror symmetry, for example.\nIf it will, great. If it won\'t, well, we must face this fact.\n\nAnyway, I find it clear that most of nontrivial quantum physics, the\nmajority of non-trivial patterns, relations, and very quantitative and\ntestable results of string theory are related to local, non-cosmological\nphysics describing phenomena where at least 3 dimensions are large enough\nand can be approximated by flat space. This theory is probably/hopefully\nincorporated into some bigger framework that admits cosmology and that we\ndon\'t know well as of today, but it seems perfectly plausible to me that\nthis "cosmological encapsulation" of string theory will be just a quite\nsimple set of mostly classical ideas that will occupy much less than 5% of\nthe string theory textbooks in 2100.\n\nMoreover, in 2007, most of us will probably (or possibly) return to\nparticle physics as the most important source of experimental data and\ninspiration. If there is new physics below a few TeV, you will see what it\nmeans "a lot of new data". If there is (almost) no new physics, we will\nhave to continue in our mostly theoretical enterprise.\n\n> > but it is stated that Fig. 1 is simply the case the authors decided to\n> > concentrate on.\n>\n> Excellent question! I have no idea.\n\nI agree, the measure of "genericity" is never quite defined in these\ncontexts.\n________________________________ ______________________________________________\nE-mail: lumo@matfyz.cz fax: +1-617/496-0110 Web: http://lumo.matfyz.cz/\neFax: +1-801/454-1858 work: +1-617/496-8199 home: +1-617/868-4487 (call)\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 Thu, 27 May 2004, Serenus Zeitblom wrote:
> Urs, that is exactly the kind of thing that Peter Woit says about
> string theory in general! It's no good saying that it is "premature"
> to consider such matters --- we have to try to answer these questions
> with the resources we have, even though we know that we are unlikely
> to succeed right now.
There is some sense in which I agree, but one must be more careful and
balanced. There are obviously many examples from the history of physics in
which people were asking premature questions. Einstein wanted to unify all
forces and construct a unified field theory. Unfortunately he thought that
electromagnetism and gravity were the only forces, and nuclear
interactions (and even quantum mechanics) are emergent details that should
not be taken seriously and that will eventually be described by the
unified theory for free.
Although we are continuing his generalized dream, Kaluza-Klein ideas are
the only ideas that survived. All other specific proposals to unify
electromagnetism and gravity simply were premature, and I would also say
misguided. Today we know that the unification of gravity with the other
forces was the hardest task, something that we had to wait for, and
although string theory shows that it can be done - and it might be even
done in Nature - it simply does not seem to be an appropriate task for the
1920s. It is likely that there are many examples of this sort.
It is always difficult to guess how the world would evolve had some
discoveries been done in a different order. We see many illogical
acausalities in the history of physics - B was often invented before A, so
to say - but there are also many cases where the order could not have been
different. OK, let me now switch from this general philosophy to the
more particular question of string cosmology and related issues.
I think it is premature to try to construct this major framework that
would explain the character of vacuum selection and very early cosmology
in string theory, and it is wrong to study these questions separately from
the technical questions in string theory that work and that we can
calculate well. The reason is that we have very little data - that would
go beyond philosophy - about quantum cosmology. In other words, we have
very little data from cosmology (or no data at all) that would require us
to go beyond classical physics. What we have are the semi-reliable
theoretical data - string theory results for many backgrounds and
processes - and we should use them as much as we can.
It seems clear to me that the argument that the available cosmological
data should be described by a highly exotic and quantum theory - such as
the cannon of string theory tool - is strongly disfavored experimentally.
It seems also obvious to me that we have not yet found the universal rules
of string theory that could be applied to extreme conditions, such as the
very Big Bang, or that could cover the whole "landscape", whatever its
size is. Let me say my favorite example. We have not found a formulation
of M-theory on T^7 that would make the E_{7(7)}(Z) U-duality symmetry
manifest. This U-duality is an example of an idea that relates many
different points of the landscape, and moreover it might be the simplest
idea of this sort because we are protected by 32 supercharges. So my
belief is that we will have to understand the nonperturbative structure of
the stringy arena using some new universal definition of string theory - a
definition that is both non-perturbative (reaches the strongly coupled
regions) as well as background-universal (reaches the geometries and
non-geometries that are different from the starting one), and only
afterwards, we will be able to start answering the stringy cosmological
questions in a better context. Without this new tool, everything is just
vague guesswork.
In my opinion, the research of string cosmology; stringy inflation; de
Sitter space in string theory; scattering in backgrounds with non-standard
causal diagrams; and all similar things that have essentially be started
by the observation of accelerating Universe back in 1998 - has led to a
very small number of intriguing results. There is almost nothing
non-trivial and mathematically intriguing going on here; there is as much
output as much input we insert. It remains a combination of phenomenology
and speculations where conjectures can rarely be clearly ruled out. There
is simply no guarantee that a direct attack to string-theoretical
cosmological questions will be as successful as the stringy explanations
for gravitatinoal S-matrix and various processes in highly supersymmetric
backgrounds that are not far from the flat (or AdS) space.
In general, we should study the questions that we have a chance to answer
- questions where we have enough hints, enough data that require a unified
explanation - and it is simply not the case of string cosmology,
especially not string cosmology that neglects the truly new stringy
phenomena such as U-dualities. And our proposed answers should be tested
against the experimental data, even the general and qualitative ones - and
in this respect it seems clear to me that the conjecture that the
available cosmological data require hugely exotic, quantum and stringy
phenomena is essentially ruled out. Because they don't require
stringy/quantum phenomena, they tell us almost nothing about the nature of
quantum cosmology in string theory.
> It's true, for example, that the efforts to
> get deSitter in string theory look pretty lame. But they look a
> *lot* less lame than just telling astrophysicists that we don't even
> know whether it can be done at all.
Something like de Sitter space probably can be done, by arguments rooted
in effective field theory that approximates string theory well. But it is
true that we have essentially nothing new - beyond effective field theory
- to tell astrophysicists about de Sitter space, and I don't care a single
bit whether it sounds *lame* to anyone or not. For me it is much more
important that it is *true*. Once again, we have found no reliable insight
or prediction about the character of de Sitter space in string theory that
would go beyond general arguments and arguments rooted in effective field
theory.
The Standard Model has about 19 parameters that look free and have not
been explained. If the purpose of science is to explain, I still think
that these are the next targets, and 19 is 19 times more than the number
of cosmological constants, which for me implies that we should not spend
most of our time with debates about the cosmological constant because they
turned out to be pretty fruitless. The cosmological constant seems very
tiny, but there are many other numbers in Nature that look very small,
too.
> We *have* to get a believable
> cosmology out of string theory; otherwise people will just conclude
> that string theory has failed to account for the observations, ie
> they will conclude that it is wrong.
Once again, I am not doing physics because I want the people to make some
pre-determined conclusions, which is what you propose. I am only studying
physical questions where the conclusion is not yet clear, and I want to
find out what the right conclusion - the truth - is. There is no guarantee
that there exists a believable purely stringy cosmology. I don't
understand what it means to say that we "have to get it". If it does not
exist, we even cannot get it in principle. Does the world end if one of
our prejudices is wrong?
So far, string theory has never been successful in giving us new reliable
insights about cosmology, and if you ever built your arguments on the
opposite, incorrect statement, then it is your problem - not something
that should determine what the people in string theory should work on.
> It is one thing to tell cosmologists that at the moment we don't quite
> fully understand how cosmology works in string theory, but we are
> working on it --- it is quite another thing to tell them that we
> aren't worried because it is "premature" to do so. The observational
> people just laugh at that kind of talk.
Well, if they laugh, then they are pretty stupid. Theorists have a harder
job than to look in the telescope and say "I see a little green man". We
should try to get the right answers today or this year, but in reality, it
can take decades or fifty years to find the right answers. It took almost
3 centuries to develop quantum field theory from Newton's discoveries -
even though it was enough to make a field theoretical version of his
equations of motion and quantize them, and even though they always had a
lot of experiments.
If some of our fellow experimentalists think that it is easy to find the
right explanation of cosmology in a quantum framework etc., they are free
to change their field and try to compete with other theorists.
> Isaac Newton didn't apply his mechanics to cosmology because
> he didn't know that the universe is expanding --- he had no
> data. We *do* have a massive amount of data now showing that
> the universe is accelerating.
I don't know what you mean by a massive amount of data. The Universe is
huge and it has many photons in it, and therefore we see many of their
properties very many times, but the data directly related to the
acceleration are made of 1 number - the cosmological constant. There are
several more important measurable numbers about cosmology - for example
the harmonics of the cosmic microwave background - but they are
increasingly far from the fundamental theory, and increasingly more
affected by ordinary (even classical) physics.
What I would call "massive amount of data" is something that gives us
thousands of independent and non-trivial numbers so that one can look for
new patterns. For example, people knew a lot of particles that lie on the
Regge trajectory - their masses and many other detailed patterns - so that
Veneziano et al. could eventually construct "a" theory. It took several
years, and then it was realized that although this many data that agreed,
other data disagreed and the theory was wrong as a description of the
strong force - a statement that was recently softened because of the
AdS/CFT correspondece.
But the origin of the acceleration of the Universe? We have no data
whatsoever that could tell us what is the origin or structure of the
cosmological constant. At a phenomenological level, we understood what's
going on. But we depend on purely theoretical tools if we want to find the
stringy origin of all these things.
> We either address this problem
> *now* or the subject will die.
I don't think that string theory is (or should be) studied primarily as a
phenomenological theory to explain current astronomical observations. I
don't think that this class of questions was ever a major reason why we
studied string theory, and I don't think that the famous and breath-taking
results of string theory were usually related to cosmology. The existing
successes of string cosmology, for example, could never justify big
funding, I believe. It is a totally uncertain issue whether string theory
will ever be as successful with cosmology as it has been with the graviton
scattering, black hole entropy, dualities or mirror symmetry, for example.
If it will, great. If it won't, well, we must face this fact.
Anyway, I find it clear that most of nontrivial quantum physics, the
majority of non-trivial patterns, relations, and very quantitative and
testable results of string theory are related to local, non-cosmological
physics describing phenomena where at least 3 dimensions are large enough
and can be approximated by flat space. This theory is probably/hopefully
incorporated into some bigger framework that admits cosmology and that we
don't know well as of today, but it seems perfectly plausible to me that
this "cosmological encapsulation" of string theory will be just a quite
simple set of mostly classical ideas that will occupy much less than 5% of
the string theory textbooks in 2100.
Moreover, in 2007, most of us will probably (or possibly) return to
particle physics as the most important source of experimental data and
inspiration. If there is new physics below a few TeV, you will see what it
means "a lot of new data". If there is (almost) no new physics, we will
have to continue in our mostly theoretical enterprise.
> > but it is stated that Fig. 1 is simply the case the authors decided to
> > concentrate on.
>
> Excellent question! I have no idea.
I agree, the measure of "genericity" is never quite defined in these
contexts.
__{_______________________________________________ _____________________________}
E-mail: lumo@matfyz.cz fax: +1-617/496-0110 Web: http://lumo.matfyz.cz/
eFax: +1-801/454-1858 work: +1-617/496-8199 home: +1-617/868-4487 (call)
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
Serenus Zeitblom
May28-04, 05:54 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 > >\n\n\n> I\'d say that if anyone feels amused by the fact that quantum gravity isn\'t\n> fully understood yet - let him laugh. (Of course I can imagine that it is\n> much easier for a theorist to appreciate the progress that has already been\n> made than for an experimentalist.)\n\nAnecdotal evidence suggests that in some places young\npeople are being discouraged from working on string\ncosmology because it is "premature" to do so. Instead\nthey are being pushed to work on purely technical issues\nor even pure-mathematical issues associated with string\ntheory. I am very disturbed by this kind of thing. I\nthink that it is better to make a tiny contribution to\nsomething that is really important than a large contribution\nto some minor technical question. We don\'t need another\nduality. We do need a convincing account of what is going\nwrong with our understanding of gravity on large scales!\nSee\nhttp://preposterousuniverse.blogspot.com/\nto get some idea of the excitement among cosmologists. Surely\nstring theorists cannot just ignore this.\n\n> I am not sure that I understand your attitude. Surely everybody would like\n> to know the answers to interesting open questions - but if we don\'t know yet\n> we don\'t know yet.\n\nI guess the point is psychological. We don\'t like it when Peter\nWoit tells us we are wasting our time --- our retort is, "What\nwould you have us do instead?" Likewise we should not go about\ntelling string cosmologists that their work is "premature". If\nwe find it more exciting to work on the relationship between\nstring theory and number theory or twistorial categorification\nor whatever, that is fine by me --- but we should not discourage\nthe people who are trying to connect string theory with the most\nimportant observational physics of the last couple of decades......\nof course it\'s true that some of the landscapers have said some\nvery nutty things, but it is wrong to blame all string\ncosmologists for these excesses, they don\'t all come from Stanford...\n\n> > > Maybe I haven\'t read the paper carefully enough, but why exactly do the\n> > > authors say that the potential of Fig. 1 is "more generic" than that of\n> Fig.\n> > > 2 (as in the paragraph right below Fig. 2)? At other places (in the\n> > > introduction and the conclusion) no reference to genericity is made,\n> IIRC,\n> > > but it is stated that Fig. 1 is simply the case the authors decided to\n> > > concentrate on.\n> >\n> > Excellent question! I have no idea.\n>\n> Hm. Isn\'t this the crucial point of that paper? Of course if we _assume_\n> that the potential for the internal volume modulus is as in figure 1 then it\n> follows automatically that the universe will spontaneously decompactify. So\n> the key point seems to be the question why Fig 2 is excluded. Does anyone\n> else have an idea?\n\nMy guess is that they just found that they had more interesting things\nto say about the decompactification case, so they ignored the other\ncase! It\'s a standard move to substitute "generic" for "interesting"\nwhen writing papers....I may have been guilty of this sin myself.....\n\n\n>\n> > >\n> > > > then\n> > > > we get something like AdS, and only in this case\n> > > > does metastability lead to *something like* AdS\n> > > > [though presumably not AdS itself --- a Big Crunch\n> > > > is more likely.]\n> > >\n> > > Why is it more likely?\n> >\n> > This is an old argument of Coleman and deLuccia. You can find it\n> > in http://arxiv.org/abs/hep-th/0211160.\n>\n> Ah, there is this statment:\n> "The Big Crunch singularity of the CDL solution is, I believe, an argument\n> that decays into spaces of negative cosmological constant do not occur in\n> consistent theories of quantum gravity." (T. Banks in hep-th/0211160)\n\nNo, I don\'t think that Giddings and Myers are thinking along these\nlines. For one thing, Banks never really explains why he thinks that\na Big Crunch is so terrible! Though it\'s true I would rather be\ndecompactified than crunched, don\'t you agree? :)\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 > >
> I'd say that if anyone feels amused by the fact that quantum gravity isn't
> fully understood yet - let him laugh. (Of course I can imagine that it is
> much easier for a theorist to appreciate the progress that has already been
> made than for an experimentalist.)
Anecdotal evidence suggests that in some places young
people are being discouraged from working on string
cosmology because it is "premature" to do so. Instead
they are being pushed to work on purely technical issues
or even pure-mathematical issues associated with string
theory. I am very disturbed by this kind of thing. I
think that it is better to make a tiny contribution to
something that is really important than a large contribution
to some minor technical question. We don't need another
duality. We do need a convincing account of what is going
wrong with our understanding of gravity on large scales!
See
http://preposterousuniverse.blogspot.com/
to get some idea of the excitement among cosmologists. Surely
string theorists cannot just ignore this.
> I am not sure that I understand your attitude. Surely everybody would like
> to know the answers to interesting open questions - but if we don't know yet
> we don't know yet.
I guess the point is psychological. We don't like it when Peter
Woit tells us we are wasting our time --- our retort is, "What
would you have us do instead?" Likewise we should not go about
telling string cosmologists that their work is "premature". If
we find it more exciting to work on the relationship between
string theory and number theory or twistorial categorification
or whatever, that is fine by me --- but we should not discourage
the people who are trying to connect string theory with the most
important observational physics of the last couple of decades......
of course it's true that some of the landscapers have said some
very nutty things, but it is wrong to blame all string
cosmologists for these excesses, they don't all come from Stanford...
> > > Maybe I haven't read the paper carefully enough, but why exactly do the
> > > authors say that the potential of Fig. 1 is "more generic" than that of
> Fig.
> > > 2 (as in the paragraph right below Fig. 2)? At other places (in the
> > > introduction and the conclusion) no reference to genericity is made,
> IIRC,
> > > but it is stated that Fig. 1 is simply the case the authors decided to
> > > concentrate on.
> >
> > Excellent question! I have no idea.
>
> Hm. Isn't this the crucial point of that paper? Of course if we _assume_
> that the potential for the internal volume modulus is as in figure 1 then it
> follows automatically that the universe will spontaneously decompactify. So
> the key point seems to be the question why Fig 2 is excluded. Does anyone
> else have an idea?
My guess is that they just found that they had more interesting things
to say about the decompactification case, so they ignored the other
case! It's a standard move to substitute "generic" for "interesting"
when writing papers....I may have been guilty of this sin myself.....
>
> > >
> > > > then
> > > > we get something like AdS, and only in this case
> > > > does metastability lead to *something like* AdS
> > > > [though presumably not AdS itself --- a Big Crunch
> > > > is more likely.]
> > >
> > > Why is it more likely?
> >
> > This is an old argument of Coleman and deLuccia. You can find it
> > in http://arxiv.org/abs/http://www.arxiv.org/abs/hep-th/0211160.
>
> Ah, there is this statment:
> "The Big Crunch singularity of the CDL solution is, I believe, an argument
> that decays into spaces of negative cosmological constant do not occur in
> consistent theories of quantum gravity." (T. Banks in http://www.arxiv.org/abs/hep-th/0211160)
No, I don't think that Giddings and Myers are thinking along these
lines. For one thing, Banks never really explains why he thinks that
a Big Crunch is so terrible! Though it's true I would rather be
decompactified than crunched, don't you agree? :)
Urs Schreiber
May28-04, 11:35 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>"Serenus Zeitblom" <serenuszeitblomphd@yahoo.com> schrieb im Newsbeitrag\nnews:c7fd6c7a.0405280148.526ab0dc-100000@posting.google.com...\n> Urs Schreiber <Urs.Schreiber@uni-essen.de> wrote in message > >\n\n> Anecdotal evidence suggests that in some places young\n> people are being discouraged from working on string\n> cosmology because it is "premature" to do so. Instead\n> they are being pushed to work on purely technical issues\n> or even pure-mathematical issues associated with string\n> theory.\n\nWhat is it that initiated the KKLT big bang of landscape discussion? Wasn\'t\nit the availablity of new non-perturbative effects resulting from purely\ntechnical and pure-mathematical studies? (I really mean this as a question.)\n\n> We don\'t need another duality.\n\nDon\'t let that know those who criticise that too little about\nnon-perturbative string theory is known! ;-)\n\n> We do need a convincing account of what is going\n> wrong with our understanding of gravity on large scales!\n> See\n> http://preposterousuniverse.blogspot.com/\n> to get some idea of the excitement among cosmologists. Surely\n> string theorists cannot just ignore this.\n\nHey, nobody is trying to stop you to work on string cosmology! :-)\n\nIn fact, maybe while the present CC is hard, the past one may be more\naccesible:\n\nWhat is the status of understanding _inflation_ (and/or the Higgs mechanism\nmaybe) in string theory/string cosmology?\n\n>From what I have heard the models using <inflaton=D\\bar D-tachyon> look\ngood. Apparently tachyon inflation nicely solves the problem why the\ninflaton is excited in the first place, thus ready to do a slow roll:\n\n>From what I understand while the brane approaches the anti-brane, the\ntachyon potential evolves from a parabolic form at far seperation to the\nmexican hat form as the branes come close. Hence it is natural that the\ntachyon sits in the middle of the hat at the beginning.\n\nIs that about right? How do such inflationary models go along with\ntachyon=Higgs approaches? Is there some canonical picture emerging?\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>"Serenus Zeitblom" <serenuszeitblomphd@yahoo.com> schrieb im Newsbeitrag
news:c7fd6c7a.0405280148.526ab0dc-100000@posting.google.com...
> Urs Schreiber <Urs.Schreiber@uni-essen.de> wrote in message > >
> Anecdotal evidence suggests that in some places young
> people are being discouraged from working on string
> cosmology because it is "premature" to do so. Instead
> they are being pushed to work on purely technical issues
> or even pure-mathematical issues associated with string
> theory.
What is it that initiated the KKLT big bang of landscape discussion? Wasn't
it the availablity of new non-perturbative effects resulting from purely
technical and pure-mathematical studies? (I really mean this as a question.)
> We don't need another duality.
Don't let that know those who criticise that too little about
non-perturbative string theory is known! ;-)
> We do need a convincing account of what is going
> wrong with our understanding of gravity on large scales!
> See
> http://preposterousuniverse.blogspot.com/
> to get some idea of the excitement among cosmologists. Surely
> string theorists cannot just ignore this.
Hey, nobody is trying to stop you to work on string cosmology! :-)
In fact, maybe while the present CC is hard, the past one may be more
accesible:
What is the status of understanding _inflation_ (and/or the Higgs mechanism
maybe) in string theory/string cosmology?
>From what I have heard the models using <inflaton=D\bar D-tachyon> look
good. Apparently tachyon inflation nicely solves the problem why the
inflaton is excited in the first place, thus ready to do a slow roll:
>From what I understand while the brane approaches the anti-brane, the
tachyon potential evolves from a parabolic form at far seperation to the
mexican hat form as the branes come close. Hence it is natural that the
tachyon sits in the middle of the hat at the beginning.
Is that about right? How do such inflationary models go along with
tachyon=Higgs approaches? Is there some canonical picture emerging?
Lubos Motl
May28-04, 02:00 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 Fri, 28 May 2004, Serenus Zeitblom wrote:\n\n> Anecdotal evidence suggests that in some places young\n> people are being discouraged from working on string\n> cosmology because it is "premature" to do so.\n\nI think that it is absolutely desirable: they *should* be discouraged\nbecause string cosmology is a very speculative and premature subject. Many\nsenior physicists cannot resist to say something about their (usually\nidiosyncratic) understanding of string cosmology, but most of these people\nhave done a lot of technical, well-defined work in physics, and acquired\nexpertise that gives them the "moral right" to promote their opinions\nabout the "big" questions on the boundary with philosophy, and (often)\nspend their credit by spreading crazily sounding speculations.\n\nIt would be un-pedagogical if a young person, who is not really\nexperienced in "real" physics calculations and "routine", would be led to\nthis speculative field. Moreover, even if the young person wrote\nsomething that is comparably reasonable to the stringy cosmological papers\nof his more senior colleagues, it is very likely that she or he would\n*not* be considered equally seriously. We might think that it\'s unfair,\nbut nevertheless it is quite natural not to take too seriously a new\nperson in the field who immediately wants to solve the biggest questions.\n\nIt is the responsibility of every good advisor to encourage his or her\nstudents to work on a topic where the actual calculations matter more than\nsome philosophical prejudices. It is very easy to switch from hard data to\nphilosophizing, but it would be much more difficult to move in the\nopposite direction. Well, if a young person has a lot of big visions and\nideas to say, she or he will say them anyway.\n\nOf course, if a young person discovers something great in string\ncosmology, I will be excited and grateful. But it would be a very bad idea\nto establish a whole school of young people writing not-terribly-good\nand not-quite-technical articles on string cosmology. This is what I would\ncertainly view as physics going down the hill.\n\n> Instead they are being pushed to work on purely technical issues or\n> even pure-mathematical issues associated with string theory.\n\nI could not disagree more.\n\n> I am very disturbed by this kind of thing. I\n> think that it is better to make a tiny contribution to\n> something that is really important than a large contribution\n> to some minor technical question. We don\'t need another\n> duality.\n\nPerhaps, we don\'t need to find another flux vacuum - or not even a new\nclass of vacua. We already have 10^307 of them, as Mike Douglas counted\nhere in Santa Barbara yesterday ;-), and they are even grouped to many\ndifferent classes. But another *duality* (or a relation between various\nconcepts and phenomena that used to be thought of as independent) is\nsomething that we will *always* need because this is what makes most\nprogress in physics - and dualities, including T-duality, S-duality,\nmirror symmetry, AdS/CFT correspondence, Matrix theory description of\nM-theory, and so on, are the great examples what physics is able to do.\n\nThe goal of theoretical physics is to explain ever larger classes of\nphenomena in terms of ever more compact, more predictive sets of ideas and\nequations. In a generalized sense, theoretical physics is a search for\ndualities and their applications.\n\n> We do need a convincing account of what is going\n> wrong with our understanding of gravity on large scales!\n\nThis sentence *assumes* that something is wrong with our understanding of\ngravity on large scales, which itself is nothing more than a possibility.\nWe know almost for sure that according to effective field theory or string\ntheory on the simple background that we know and love, *nothing* is wrong\nabout the usual description of gravity at long distance scales. The goal\nof physics is not to prove some assumptions that have been determined\npreviously and cannot be questioned; the goal of physics is to find the\nright answers that are *not* known at the beginning - and the question\nwhether something is wrong with our very IR picture of gravity is\ncertainly an open question.\n\n> I guess the point is psychological. We don\'t like it when Peter\n> Woit tells us we are wasting our time --- our retort is, "What\n> would you have us do instead?" Likewise we should not go about\n> telling string cosmologists that their work is "premature".\n\nSorry, but Peter Woit can think and write whatever he wants about string\ntheory; others can assign his opinion as much importance as they find\nreasonable; and all of us can think and write anything we believe to be\ncorrect about string cosmology. I believe that this freedom is one of the\nbasic human rights, and it is certainly one of the necessary assumptions\nfor science to work.\n\n> If we find it more exciting to work on the relationship between string\n> theory and number theory or twistorial categorification or whatever,\n> that is fine by me --- but we should not discourage the people who are\n> trying to connect string theory with the most important observational\n> physics of the last couple of decades......\n\nI apologize but I reserve the right for me as well as for my colleagues to\nencourage others to work on things that I/we find interesting, convincing,\nand promising, and discourage my colleagues from things that I/we find\nless interesting, less convincing, and less promising. Others are doing\nthe same thing, either by explicit statements, or by their interest in\nvarious papers. By the way, twistors have very little to do with\ncategories.\n\nFor example, the twistorial look at physical phenomena is potentially very\nnew and it might be important, and because we now know about new relations\nbetween twistors and rather physical gauge theories, we should study this\nold new approach until we\'re really stuck. In my opinion, it is more\nlikely that the full understanding of string cosmology will be found by\ngeneralizing this twistor approach, rather than by direct philosophical\nattack on the cosmological questions, an attack without any new powerful\nideas and mathematical tools, an attack that could have been done decades\nago - which is, as far as I understand, what you are proposing.\n\n> of course it\'s true that some of the landscapers have said some\n> very nutty things, but it is wrong to blame all string\n> cosmologists for these excesses, they don\'t all come from Stanford...\n\nI don\'t know what you exactly want to say because at this moment, Stanford\nis almost undoubtedly *the* center and the leading institution of string\ncosmology. Which string cosmology are you talking about if you want to\nexclude Stanford?\n\n> My guess is that they just found that they had more interesting things\n> to say about the decompactification case, so they ignored the other\n> case! It\'s a standard move to substitute "generic" for "interesting"\n> when writing papers....I may have been guilty of this sin myself.....\n\nWell, "generic" and "interesting" are very different, independent words -\nand if there is a correlation between them, I would guess that this\ncorrelation is negative.\n\n> No, I don\'t think that Giddings and Myers are thinking along these\n> lines. For one thing, Banks never really explains why he thinks that\n> a Big Crunch is so terrible! Though it\'s true I would rather be\n> decompactified than crunched, don\'t you agree? :)\n\nBig Crunch is a big disaster, indeed. It is a singularity in which our\neffective theories as well as the concept of S-matrix and similar notions\nbreaks down, and Big Crunch is also a phenomenon that forced Raphael\nBousso to reformulate the entropy bounds because huge entropy seems to be\nsqueezed into an arbitrarily small volume. Big Crunch spacetimes are not\nstable states of anything, and Tom Banks is explaining that Big Crunch is\na disaster that invalidates various scenarios that claim that tunnelling\nto AdS spaces will occur. Moreover, Tom might believe that Big Crunch\ncannot occur at all in the full theory of quantum cosmology which - I\nthink - is about as legitimate guess about the eventual form of quantum\ncosmology as the opposite guess. Or do you have some experimental evidence\nthat one of these statements is incorrect? ;-)\n_______________________________________________ _______________________________\nE-mail: lumo@matfyz.cz fax: +1-617/496-0110 Web: http://lumo.matfyz.cz/\neFax: +1-801/454-1858 work: +1-617/496-8199 home: +1-617/868-4487 (call)\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 Fri, 28 May 2004, Serenus Zeitblom wrote:
> Anecdotal evidence suggests that in some places young
> people are being discouraged from working on string
> cosmology because it is "premature" to do so.
I think that it is absolutely desirable: they *should* be discouraged
because string cosmology is a very speculative and premature subject. Many
senior physicists cannot resist to say something about their (usually
idiosyncratic) understanding of string cosmology, but most of these people
have done a lot of technical, well-defined work in physics, and acquired
expertise that gives them the "moral right" to promote their opinions
about the "big" questions on the boundary with philosophy, and (often)
spend their credit by spreading crazily sounding speculations.
It would be un-pedagogical if a young person, who is not really
experienced in "real" physics calculations and "routine", would be led to
this speculative field. Moreover, even if the young person wrote
something that is comparably reasonable to the stringy cosmological papers
of his more senior colleagues, it is very likely that she or he would
*not* be considered equally seriously. We might think that it's unfair,
but nevertheless it is quite natural not to take too seriously a new
person in the field who immediately wants to solve the biggest questions.
It is the responsibility of every good advisor to encourage his or her
students to work on a topic where the actual calculations matter more than
some philosophical prejudices. It is very easy to switch from hard data to
philosophizing, but it would be much more difficult to move in the
opposite direction. Well, if a young person has a lot of big visions and
ideas to say, she or he will say them anyway.
Of course, if a young person discovers something great in string
cosmology, I will be excited and grateful. But it would be a very bad idea
to establish a whole school of young people writing not-terribly-good
and not-quite-technical articles on string cosmology. This is what I would
certainly view as physics going down the hill.
> Instead they are being pushed to work on purely technical issues or
> even pure-mathematical issues associated with string theory.
I could not disagree more.
> I am very disturbed by this kind of thing. I
> think that it is better to make a tiny contribution to
> something that is really important than a large contribution
> to some minor technical question. We don't need another
> duality.
Perhaps, we don't need to find another flux vacuum - or not even a new
class of vacua. We already have 10^307 of them, as Mike Douglas counted
here in Santa Barbara yesterday ;-), and they are even grouped to many
different classes. But another *duality* (or a relation between various
concepts and phenomena that used to be thought of as independent) is
something that we will *always* need because this is what makes most
progress in physics - and dualities, including T-duality, S-duality,
mirror symmetry, AdS/CFT correspondence, Matrix theory description of
M-theory, and so on, are the great examples what physics is able to do.
The goal of theoretical physics is to explain ever larger classes of
phenomena in terms of ever more compact, more predictive sets of ideas and
equations. In a generalized sense, theoretical physics is a search for
dualities and their applications.
> We do need a convincing account of what is going
> wrong with our understanding of gravity on large scales!
This sentence *assumes* that something is wrong with our understanding of
gravity on large scales, which itself is nothing more than a possibility.
We know almost for sure that according to effective field theory or string
theory on the simple background that we know and love, *nothing* is wrong
about the usual description of gravity at long distance scales. The goal
of physics is not to prove some assumptions that have been determined
previously and cannot be questioned; the goal of physics is to find the
right answers that are *not* known at the beginning - and the question
whether something is wrong with our very IR picture of gravity is
certainly an open question.
> I guess the point is psychological. We don't like it when Peter
> Woit tells us we are wasting our time --- our retort is, "What
> would you have us do instead?" Likewise we should not go about
> telling string cosmologists that their work is "premature".
Sorry, but Peter Woit can think and write whatever he wants about string
theory; others can assign his opinion as much importance as they find
reasonable; and all of us can think and write anything we believe to be
correct about string cosmology. I believe that this freedom is one of the
basic human rights, and it is certainly one of the necessary assumptions
for science to work.
> If we find it more exciting to work on the relationship between string
> theory and number theory or twistorial categorification or whatever,
> that is fine by me --- but we should not discourage the people who are
> trying to connect string theory with the most important observational
> physics of the last couple of decades......
I apologize but I reserve the right for me as well as for my colleagues to
encourage others to work on things that I/we find interesting, convincing,
and promising, and discourage my colleagues from things that I/we find
less interesting, less convincing, and less promising. Others are doing
the same thing, either by explicit statements, or by their interest in
various papers. By the way, twistors have very little to do with
categories.
For example, the twistorial look at physical phenomena is potentially very
new and it might be important, and because we now know about new relations
between twistors and rather physical gauge theories, we should study this
old new approach until we're really stuck. In my opinion, it is more
likely that the full understanding of string cosmology will be found by
generalizing this twistor approach, rather than by direct philosophical
attack on the cosmological questions, an attack without any new powerful
ideas and mathematical tools, an attack that could have been done decades
ago - which is, as far as I understand, what you are proposing.
> of course it's true that some of the landscapers have said some
> very nutty things, but it is wrong to blame all string
> cosmologists for these excesses, they don't all come from Stanford...
I don't know what you exactly want to say because at this moment, Stanford
is almost undoubtedly *the* center and the leading institution of string
cosmology. Which string cosmology are you talking about if you want to
exclude Stanford?
> My guess is that they just found that they had more interesting things
> to say about the decompactification case, so they ignored the other
> case! It's a standard move to substitute "generic" for "interesting"
> when writing papers....I may have been guilty of this sin myself.....
Well, "generic" and "interesting" are very different, independent words -
and if there is a correlation between them, I would guess that this
correlation is negative.
> No, I don't think that Giddings and Myers are thinking along these
> lines. For one thing, Banks never really explains why he thinks that
> a Big Crunch is so terrible! Though it's true I would rather be
> decompactified than crunched, don't you agree? :)
Big Crunch is a big disaster, indeed. It is a singularity in which our
effective theories as well as the concept of S-matrix and similar notions
breaks down, and Big Crunch is also a phenomenon that forced Raphael
Bousso to reformulate the entropy bounds because huge entropy seems to be
squeezed into an arbitrarily small volume. Big Crunch spacetimes are not
stable states of anything, and Tom Banks is explaining that Big Crunch is
a disaster that invalidates various scenarios that claim that tunnelling
to AdS spaces will occur. Moreover, Tom might believe that Big Crunch
cannot occur at all in the full theory of quantum cosmology which - I
think - is about as legitimate guess about the eventual form of quantum
cosmology as the opposite guess. Or do you have some experimental evidence
that one of these statements is incorrect? ;-)
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SERENUS ZEITBLOM said:
Apparently this is
> so because classical gravity considerations imply the
> resulting universe is a big crunch universe and it is not
> clear whether the later makes sense in string theory
According to stephen Hawking if the universe oscillates between big bangs and big crunches black holes become larger than the universe itself after a finite number of oscillations! There are the theories which attempt to overcome this problem by saying
that dark energy tears the black holes to pieces just before a crunch.So crunches are not ruled out.
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