Lubos Motl
Dec15-04, 11:19 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>The new google interface reduced the intensity of posting considerable, so\nwe should perhaps stimulate it. Let me start a thread about\nlandskepticism.\n\nhttp://motls.blogspot.com/2004/12/landskepticism.html\n\nTom Banks, my (former) PhD advisor, has submitted a new paper\n\n* hep-th/0412129\n\nTom argues that the landscape is not a well-established feature of string\ntheory. In a conceptual paper which does not bother you with too many\nequations (the Wheeler-DeWitt equation being an exception), he argues that\n\n* one must distinguish the 1PI and the Wilsonian effective actions\nmore carefully: the 1PI action describes the whole field content, and you\nget the same action regardless of the point around which you expand\n* on the other hand, the Wilsonian effective action contains the\nlow-energy degrees of freedom that depend on the point in the\nconfiguration space - and this is the type of the effective action that\none obtains in string theory\n* Tom re-uses his statements that one cannot think about the bubble of\nanother vacuum (such as a de Sitter bubble) as an excitation of the\noriginal vacuum, and interprets the Guth-Farhi results in this fashion -\none cannot verify the existence of a dS bubble inside the bottle because\nthe external observer sees that it is surrounded by a black hole\n\nIf I understand well, Tom does not propose new arguments that the numerous\nKKLT-like vacua don\'t exist. Instead, he says that they cannot be\neffectively used as vacua of the same theory, i.e. they cannot be combined\ninto a big multiverse, and therefore there is no cosmological mechanism\nthat would connect them and create a realistic ensemble of the Universes.\n\nI would agree that this "disconnected feature" of the vacua prevents us\nfrom making a scientific claim about the probability measure of different\nones. He argues that the "democratic" measure on the space of vacua is\nunjustified, and a more precise measure cannot be defined - and I agree\nwith these statements. On the other hand, if the large number of stringy\nvacua exist (just imagine that!), we may perhaps be living in either of\nthem, regardless of the existence of cosmological solutions (such as the\neternal inflation) that interpolate between them. Of course that I tend to\nagree that even in this case, the full rules of string theory are more\nlikely to pick some "special" vacua rather than the numerous ones, but we\ndon\'t have any proof either way. In order to kill the current versions of\nthe landscape idea completely, one would have to find a general enough and\nserious problem with the construction of the KKLT-like vacua.\n\nNima Arkani-Hamed, who has been converted to a landscape supporter much\nlike many other people have been converted to Christianity ;-) (but\notherwise he studies it much more scientifically than other landscapers!),\nargues very correctly that the anthropic idea is either colossally correct\nor colossally wrong. It is a bifurcation point that can direct physics in\nthe next 10 years in vastly different directions, and one cannot decide\nwhich answer is correct by cheap attacks.\n________________________________________ ______________________________________\nE-mail: lumo@matfyz.cz fax: +1-617/496-0110 Web: http://lumo.matfyz.cz/\neFax: +1-801/454-1858 work: +1-617/384-9488 home: +1-617/868-4487 (call)\nWebs: http://schwinger.harvard.edu/~motl/ http://motls.blogspot.com/\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>The new google interface reduced the intensity of posting considerable, so
we should perhaps stimulate it. Let me start a thread about
landskepticism.
http://motls.blogspot.com/2004/12/landskepticism.html
Tom Banks, my (former) PhD advisor, has submitted a new paper
* http://www.arxiv.org/abs/hep-th/0412129
Tom argues that the landscape is not a well-established feature of string
theory. In a conceptual paper which does not bother you with too many
equations (the Wheeler-DeWitt equation being an exception), he argues that
* one must distinguish the 1PI and the Wilsonian effective actions
more carefully: the 1PI action describes the whole field content, and you
get the same action regardless of the point around which you expand
* on the other hand, the Wilsonian effective action contains the
low-energy degrees of freedom that depend on the point in the
configuration space - and this is the type of the effective action that
one obtains in string theory
* Tom re-uses his statements that one cannot think about the bubble of
another vacuum (such as a de Sitter bubble) as an excitation of the
original vacuum, and interprets the Guth-Farhi results in this fashion -
one cannot verify the existence of a dS bubble inside the bottle because
the external observer sees that it is surrounded by a black hole
If I understand well, Tom does not propose new arguments that the numerous
KKLT-like vacua don't exist. Instead, he says that they cannot be
effectively used as vacua of the same theory, i.e. they cannot be combined
into a big multiverse, and therefore there is no cosmological mechanism
that would connect them and create a realistic ensemble of the Universes.
I would agree that this "disconnected feature" of the vacua prevents us
from making a scientific claim about the probability measure of different
ones. He argues that the "democratic" measure on the space of vacua is
unjustified, and a more precise measure cannot be defined - and I agree
with these statements. On the other hand, if the large number of stringy
vacua exist (just imagine that!), we may perhaps be living in either of
them, regardless of the existence of cosmological solutions (such as the
eternal inflation) that interpolate between them. Of course that I tend to
agree that even in this case, the full rules of string theory are more
likely to pick some "special" vacua rather than the numerous ones, but we
don't have any proof either way. In order to kill the current versions of
the landscape idea completely, one would have to find a general enough and
serious problem with the construction of the KKLT-like vacua.
Nima Arkani-Hamed, who has been converted to a landscape supporter much
like many other people have been converted to Christianity ;-) (but
otherwise he studies it much more scientifically than other landscapers!),
argues very correctly that the anthropic idea is either colossally correct
or colossally wrong. It is a bifurcation point that can direct physics in
the next 10 years in vastly different directions, and one cannot decide
which answer is correct by cheap attacks.
__{_______________________________________________ _____________________________}
E-mail: lumo@matfyz.cz fax: +1-617/496-0110 Web: http://lumo.matfyz.cz/
eFax: +1-801/454-1858 work: +1-617/384-9488 home: +1-617/868-4487 (call)
Webs: http://schwinger.harvard.edu/~motl/ http://motls.blogspot.com/
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
we should perhaps stimulate it. Let me start a thread about
landskepticism.
http://motls.blogspot.com/2004/12/landskepticism.html
Tom Banks, my (former) PhD advisor, has submitted a new paper
* http://www.arxiv.org/abs/hep-th/0412129
Tom argues that the landscape is not a well-established feature of string
theory. In a conceptual paper which does not bother you with too many
equations (the Wheeler-DeWitt equation being an exception), he argues that
* one must distinguish the 1PI and the Wilsonian effective actions
more carefully: the 1PI action describes the whole field content, and you
get the same action regardless of the point around which you expand
* on the other hand, the Wilsonian effective action contains the
low-energy degrees of freedom that depend on the point in the
configuration space - and this is the type of the effective action that
one obtains in string theory
* Tom re-uses his statements that one cannot think about the bubble of
another vacuum (such as a de Sitter bubble) as an excitation of the
original vacuum, and interprets the Guth-Farhi results in this fashion -
one cannot verify the existence of a dS bubble inside the bottle because
the external observer sees that it is surrounded by a black hole
If I understand well, Tom does not propose new arguments that the numerous
KKLT-like vacua don't exist. Instead, he says that they cannot be
effectively used as vacua of the same theory, i.e. they cannot be combined
into a big multiverse, and therefore there is no cosmological mechanism
that would connect them and create a realistic ensemble of the Universes.
I would agree that this "disconnected feature" of the vacua prevents us
from making a scientific claim about the probability measure of different
ones. He argues that the "democratic" measure on the space of vacua is
unjustified, and a more precise measure cannot be defined - and I agree
with these statements. On the other hand, if the large number of stringy
vacua exist (just imagine that!), we may perhaps be living in either of
them, regardless of the existence of cosmological solutions (such as the
eternal inflation) that interpolate between them. Of course that I tend to
agree that even in this case, the full rules of string theory are more
likely to pick some "special" vacua rather than the numerous ones, but we
don't have any proof either way. In order to kill the current versions of
the landscape idea completely, one would have to find a general enough and
serious problem with the construction of the KKLT-like vacua.
Nima Arkani-Hamed, who has been converted to a landscape supporter much
like many other people have been converted to Christianity ;-) (but
otherwise he studies it much more scientifically than other landscapers!),
argues very correctly that the anthropic idea is either colossally correct
or colossally wrong. It is a bifurcation point that can direct physics in
the next 10 years in vastly different directions, and one cannot decide
which answer is correct by cheap attacks.
__{_______________________________________________ _____________________________}
E-mail: lumo@matfyz.cz fax: +1-617/496-0110 Web: http://lumo.matfyz.cz/
eFax: +1-801/454-1858 work: +1-617/384-9488 home: +1-617/868-4487 (call)
Webs: http://schwinger.harvard.edu/~motl/ http://motls.blogspot.com/
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ ^^^^^^^^^^^^^^^^^^^^^^^^^^^^