View Full Version : Asymptotic darkness
Yaakov K
Jun6-04, 02:04 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>Hi all,\n\nI\'ve been perusing arguments due to tom banks to the effect that if\nscattering at super-plankian energies is dominated by black hole\nproduction (banks calls this "asymptotic darkness"), then M-theory may\nadmit no background-independent formulation. Although I think it\'s\nvery premature to worry too much about such conclusions, I\'d still\nlike to know how asymptotic darkness may be wrong.\n\nAlso, if asymptotic darkness is correct, then the black hole\nentropy-area relation implies that a correct quantum theory of gravity\nmust be holographic and therefore allow no fundamental degrees of\nfreedom that are volume-extensive. Wouldn\'t this rule out loop quantum\ngravity since the nodes in LQG spin-networks represent quanta of\nvolume?\n\nYaakov.\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>Hi all,
I've been perusing arguments due to tom banks to the effect that if
scattering at super-plankian energies is dominated by black hole
production (banks calls this "asymptotic darkness"), then M-theory may
admit no background-independent formulation. Although I think it's
very premature to worry too much about such conclusions, I'd still
like to know how asymptotic darkness may be wrong.
Also, if asymptotic darkness is correct, then the black hole
entropy-area relation implies that a correct quantum theory of gravity
must be holographic and therefore allow no fundamental degrees of
freedom that are volume-extensive. Wouldn't this rule out loop quantum
gravity since the nodes in LQG spin-networks represent quanta of
volume?
Yaakov.
Lubos Motl
Jun6-04, 10:34 PM
<jabberwocky><div class="vbmenu_control"><a href="jabberwocky:;" onClick="newWindow=window.open('','usenetCode','toolbar=no, location=no,scrollbars=yes,resizable=yes,status=no ,width=650,height=400'); newWindow.document.write('<HTML><HEAD><TITLE>Usenet ASCII</TITLE></HEAD><BODY topmargin=0 leftmargin=0 BGCOLOR=#F1F1F1><table border=0 width=625><td bgcolor=midnightblue><font color=#F1F1F1>This Usenet message\'s original ASCII form: </font></td></tr><tr><td width=449><br><br><font face=courier><UL><PRE>On Sun, 6 Jun 2004, Yaakov K wrote:\n\n> I\'ve been perusing arguments due to tom banks to the effect that if ...\n\nGood that you read it. Many other physicists who are proposing potentially\nfar-reaching scenarios are getting a lot of attention (not always\njustified attention), but Tom Banks certainly deserves to be read because\nhe knows what he\'s doing although it may often sound weird to others.\n\n> scattering at super-plankian energies is dominated by black hole\n> production (banks calls this "asymptotic darkness"), then M-theory may\n> admit no background-independent formulation.\n\nFrankly, I have not understood the relation between the statements about\nthe asymptotic darkness on one side, and the existence of a\nbackground-independent formulation on the other side - probably because I\nhave not read enough of Tom\'s ideas. Concerning the latter, Tom has a very\noperational, experimental definition what he means by "one theory". He\nrequires that the physicists must be able to produce a large piece of the\nother "background" inside their Universe, otherwise these two backgrounds\nare "different theories". My personal definition is more mathematical, and\nit allows two vacua to be called "two states in the same theory" even if\nthe explicit experiment of producing one inside other is impossible - even\nif it is impossible "in principle" because of some arguments rooted in\nenergetics - as long as they follow from the same set of mathematical\nequations that joins these two vacua on the configuration space in any\ncontinuous fashion. Perhaps, I would call them the same theory even if\nthey\'re joined by the mathematical equations only - as two solutions of\nthe same constraints.\n\n> Although I think it\'s\n> very premature to worry too much about such conclusions, I\'d still\n> like to know how asymptotic darkness may be wrong.\n\nThere are many aspects of these statements. I personally understand and\nagree with some of them, don\'t understand others, and disagree with a\nthird group. It will be great if someone sends her or his opinion (for\nexample Tom!) ;-), or finds errors or loopholes in my statements below.\n\nAsymptotic darkness, my point of view\n\nFirst, I think that Tom\'s observations about the asymptotic darkness are\ntrue and potentially important. Physics at very low energies is described\nby the effective field theory, but physics at very high, trans-Planckian\nenergies is described by the same effective field theory, too, because it\nis dominated by production of large black holes that have very small\ncurvature at the horizon (well, I am not talking about the measurements of\nthe poor observers inside - or perhaps near the singularity - who might\nneed a better physical theory). In some sense, this statement is nothing\nelse than the usual insight that the Planck length is the shortest\ndistance scale that exists - if an appropriate definition of the word\n"exist" is chosen.\n\nWe sort of know that the asymptotic darkness must be true because when two\nobjects of total energy M.c^2 are closer than the Schwarzschild radius\n2GM/c^2, we expect a black hole to be created. This radius increases\nonce the masses grow above M_{planck}, and therefore it becomes *easier*\nto produce black holes at trans-Planckian energies; the colissions are\nbecoming increasingly classical and long-distance effects. A black hole is\nthen known to dominate over other objects entropically - because it has\nthe largest possible entropy that can be squeezed into a given volume -\nand therefore everything else becomes increasingly irrelevant. The\nproperties of large black holes are described by effective field theory\nbecause the curvatures etc. are small.\n\nSmall coupling and inherently stringy effects\n\nWe usually say that string theory predicts a lot of physics beyond the\neffective field theory description. If we admit predictions such as very\nfine correlations of (amplitudes for) Hawking particles emitted by a small\nblack hole that we created (which is a calculation that most of us believe\nshould be possible in principle), no doubt, a full theory of quantum\ngravity is needed. String theory is the only known example; it answers\nthese questions via its S-matrix, and therefore we treat it seriously. On\nthe other hand, such fine correlations are hard to measure - the\nexperimentalists would tell us that the black hole has emitted thermal\nradiation, and that would be it. Semiclassical gravity is enough to make\nthese rough predictions of the experiments.\n\nIf we are looking at the experiments, we want much sharper predictions,\neffects that become qualitative, for example effects where the different\n(potential) theories differ qualitatively (yes/no) or by quantities of\norder 100% - such as some new particles, sharp enough resonances whose\nenergy can be measured, and so forth.\n\nI guess that this might be a variation of something that Tom has written\nsomewhere, but I would say that a *lot* of sharp predictions about new\nphysics beyond the effective field theory (or, equivalently, the need to\nenrich the effective field theory with a large number of new fields and\ninteractions whose structure would seem very arbitrary without the\nunderlying string theory) only exists if the string coupling, or a similar\nparameter, is *small*. A small string coupling is needed if the excited\nstring states are supposed to be long-lived, observable resonances. The\nsame string coupling is also able to separate various scales associated\nwith branes from each other. At string coupling of order one, the theory\nis essentially a boring low energy effective field theory whose structure\nis dictated by the spectrum of conserved charges.\n\nIn fact, M-theory in 11 infinitely large dimensions is boring, in a\nrelated sense. Is there a qualitative effect that distinguishes M-theory\nfrom "supergravity combined with common sense"? At low energies\n(relatively to the Planck length), SUGRA is more or less OK (and describes\nall pure states), and at higher energies, the graviton scattering produces\nSchwarzschild black holes. Well, there are also (large but compact)\nM2-branes and M5-branes (let\'s now treat them as if they don\'t exist in\nSUGRA, even though they exist as solutions; they carry new dynamics not\nderivable directly from SUGRA, such as the (2,0) theory), but they should\nalready exist a priori, otherwise we won\'t be able to produce them by\ncollisions of the graviton multiplets - a typical collission creates\nneutral black holes. M-theory has nothing such as excited stringy modes\nwith well-defined energies.\n\nString theory shows its "stringiness" only in the window of energies\nsomewhere in between the string scale and the Planck scale.\n\nYou ask how could one see that the asymptotic darkness is wrong, assuming\nthat it is wrong. Well, I am afraid that in the near future, the possible\nresolutions will have to have theoretical character. You will have to\nidentify some measurable high-energy quantities that are inherently\nstringy, and they will provide us with light in the realm that used to be\nthought of as asymptotic darkness.\n\n> Also, if asymptotic darkness is correct, then the black hole\n> entropy-area relation implies that a correct quantum theory of gravity\n> must be holographic and therefore allow no fundamental degrees of\n> freedom that are volume-extensive.\n\nWell, I am probably not the only one who believes that these statements\n(about holography) are in some sense correct regardless of the\nspeculations above.\n\n> Wouldn\'t this rule out loop quantum gravity since the nodes in LQG\n> spin-networks represent quanta of volume?\n\nI guess that Tom would agree that holography is one of the most important\nparadigms we have learned about quantum gravity - perhaps THE most\nimportant one - and that holography is another reason why loop quantum\ngravity (LQG) is wrong. LQG not only seems to violate holography, but it\ndoes so in a brutal way. In quantum gravity, there should be no\nvolume-extensive entropy. For example, we know that the black hole entropy\nscales with its surface area. If LQG wants to reproduce this result, its\nproponents must manually remove the interior of the black hole and count\nthe area entropy only (via Chern-Simons theory). If they don\'t do it (and\nif we assume that LQG is able to reproduce smooth space), the interior\nwould probably give them a volume-extensive entropy with Planckian density\neverywhere, even in vacuum. The entropy of vacuum should be zero; it is\nnecessary on rudimentary physical grounds - for example it is required by\nLorentz invariance, even an approximate one. Planckian entropy density\n(per volume) is the ultimate catastrophy because it leads to a Planckian\ntemperature, Lorentz symmetry breaking at the Planck scale (and everywhere\nbelow), and other fatal problems.\n\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[Posted for the 2nd time because of continuing problems with the FAS\nnewsserver. LM]\n</UL></PRE></font></td></tr></table></BODY><HTML>');"> <IMG SRC=/images/buttons/ip.gif BORDER=0 ALIGN=CENTER ALT="View this Usenet post in original ASCII form"> View this Usenet post in original ASCII form </a></div><P></jabberwocky>On Sun, 6 Jun 2004, Yaakov K wrote:
> I've been perusing arguments due to tom banks to the effect that if ...
Good that you read it. Many other physicists who are proposing potentially
far-reaching scenarios are getting a lot of attention (not always
justified attention), but Tom Banks certainly deserves to be read because
he knows what he's doing although it may often sound weird to others.
> scattering at super-plankian energies is dominated by black hole
> production (banks calls this "asymptotic darkness"), then M-theory may
> admit no background-independent formulation.
Frankly, I have not understood the relation between the statements about
the asymptotic darkness on one side, and the existence of a
background-independent formulation on the other side - probably because I
have not read enough of Tom's ideas. Concerning the latter, Tom has a very
operational, experimental definition what he means by "one theory". He
requires that the physicists must be able to produce a large piece of the
other "background" inside their Universe, otherwise these two backgrounds
are "different theories". My personal definition is more mathematical, and
it allows two vacua to be called "two states in the same theory" even if
the explicit experiment of producing one inside other is impossible - even
if it is impossible "in principle" because of some arguments rooted in
energetics - as long as they follow from the same set of mathematical
equations that joins these two vacua on the configuration space in any
continuous fashion. Perhaps, I would call them the same theory even if
they're joined by the mathematical equations only - as two solutions of
the same constraints.
> Although I think it's
> very premature to worry too much about such conclusions, I'd still
> like to know how asymptotic darkness may be wrong.
There are many aspects of these statements. I personally understand and
agree with some of them, don't understand others, and disagree with a
third group. It will be great if someone sends her or his opinion (for
example Tom!) ;-), or finds errors or loopholes in my statements below.
Asymptotic darkness, my point of view
First, I think that Tom's observations about the asymptotic darkness are
true and potentially important. Physics at very low energies is described
by the effective field theory, but physics at very high, trans-Planckian
energies is described by the same effective field theory, too, because it
is dominated by production of large black holes that have very small
curvature at the horizon (well, I am not talking about the measurements of
the poor observers inside - or perhaps near the singularity - who might
need a better physical theory). In some sense, this statement is nothing
else than the usual insight that the Planck length is the shortest
distance scale that exists - if an appropriate definition of the word
"exist" is chosen.
We sort of know that the asymptotic darkness must be true because when two
objects of total energy M.c^2 are closer than the Schwarzschild radius
2GM/c^2, we expect a black hole to be created. This radius increases
once the masses grow above M_{planck}, and therefore it becomes *easier*
to produce black holes at trans-Planckian energies; the colissions are
becoming increasingly classical and long-distance effects. A black hole is
then known to dominate over other objects entropically - because it has
the largest possible entropy that can be squeezed into a given volume -
and therefore everything else becomes increasingly irrelevant. The
properties of large black holes are described by effective field theory
because the curvatures etc. are small.
Small coupling and inherently stringy effects
We usually say that string theory predicts a lot of physics beyond the
effective field theory description. If we admit predictions such as very
fine correlations of (amplitudes for) Hawking particles emitted by a small
black hole that we created (which is a calculation that most of us believe
should be possible in principle), no doubt, a full theory of quantum
gravity is needed. String theory is the only known example; it answers
these questions via its S-matrix, and therefore we treat it seriously. On
the other hand, such fine correlations are hard to measure - the
experimentalists would tell us that the black hole has emitted thermal
radiation, and that would be it. Semiclassical gravity is enough to make
these rough predictions of the experiments.
If we are looking at the experiments, we want much sharper predictions,
effects that become qualitative, for example effects where the different
(potential) theories differ qualitatively (yes/no) or by quantities of
order 100% - such as some new particles, sharp enough resonances whose
energy can be measured, and so forth.
I guess that this might be a variation of something that Tom has written
somewhere, but I would say that a *lot* of sharp predictions about new
physics beyond the effective field theory (or, equivalently, the need to
enrich the effective field theory with a large number of new fields and
interactions whose structure would seem very arbitrary without the
underlying string theory) only exists if the string coupling, or a similar
parameter, is *small*. A small string coupling is needed if the excited
string states are supposed to be long-lived, observable resonances. The
same string coupling is also able to separate various scales associated
with branes from each other. At string coupling of order one, the theory
is essentially a boring low energy effective field theory whose structure
is dictated by the spectrum of conserved charges.
In fact, M-theory in 11 infinitely large dimensions is boring, in a
related sense. Is there a qualitative effect that distinguishes M-theory
from "supergravity combined with common sense"? At low energies
(relatively to the Planck length), SUGRA is more or less OK (and describes
all pure states), and at higher energies, the graviton scattering produces
Schwarzschild black holes. Well, there are also (large but compact)
M2-branes and M5-branes (let's now treat them as if they don't exist in
SUGRA, even though they exist as solutions; they carry new dynamics not
derivable directly from SUGRA, such as the (2,0) theory), but they should
already exist a priori, otherwise we won't be able to produce them by
collisions of the graviton multiplets - a typical collission creates
neutral black holes. M-theory has nothing such as excited stringy modes
with well-defined energies.
String theory shows its "stringiness" only in the window of energies
somewhere in between the string scale and the Planck scale.
You ask how could one see that the asymptotic darkness is wrong, assuming
that it is wrong. Well, I am afraid that in the near future, the possible
resolutions will have to have theoretical character. You will have to
identify some measurable high-energy quantities that are inherently
stringy, and they will provide us with light in the realm that used to be
thought of as asymptotic darkness.
> Also, if asymptotic darkness is correct, then the black hole
> entropy-area relation implies that a correct quantum theory of gravity
> must be holographic and therefore allow no fundamental degrees of
> freedom that are volume-extensive.
Well, I am probably not the only one who believes that these statements
(about holography) are in some sense correct regardless of the
speculations above.
> Wouldn't this rule out loop quantum gravity since the nodes in LQG
> spin-networks represent quanta of volume?
I guess that Tom would agree that holography is one of the most important
paradigms we have learned about quantum gravity - perhaps THE most
important one - and that holography is another reason why loop quantum
gravity (LQG) is wrong. LQG not only seems to violate holography, but it
does so in a brutal way. In quantum gravity, there should be no
volume-extensive entropy. For example, we know that the black hole entropy
scales with its surface area. If LQG wants to reproduce this result, its
proponents must manually remove the interior of the black hole and count
the area entropy only (via Chern-Simons theory). If they don't do it (and
if we assume that LQG is able to reproduce smooth space), the interior
would probably give them a volume-extensive entropy with Planckian density
everywhere, even in vacuum. The entropy of vacuum should be zero; it is
necessary on rudimentary physical grounds - for example it is required by
Lorentz invariance, even an approximate one. Planckian entropy density
(per volume) is the ultimate catastrophy because it leads to a Planckian
temperature, Lorentz symmetry breaking at the Planck scale (and everywhere
below), and other fatal problems.
__{_______________________________________________ _____________________________}
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)
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
[Posted for the 2nd time because of continuing problems with the FAS
newsserver. LM]
<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>Lubos Motl <motl@feynman.harvard.edu> wrote in message news:<20040607043432.X2574@mail.kolej.mff.cuni.cz> ...\n> ...\n> In fact, M-theory in 11 infinitely large dimensions is boring, in a\n> related sense. Is there a qualitative effect that distinguishes M-theory\n> from "supergravity combined with common sense"? At low energies\n> (relatively to the Planck length), SUGRA is more or less OK (and describes\n> all pure states), and at higher energies, the graviton scattering produces\n> Schwarzschild black holes. Well, there are also (large but compact)\n> M2-branes and M5-branes (let\'s now treat them as if they don\'t exist in\n> SUGRA, even though they exist as solutions; they carry new dynamics not\n> derivable directly from SUGRA, such as the (2,0) theory), but they should\n> already exist a priori, otherwise we won\'t be able to produce them by\n> collisions of the graviton multiplets - a typical collission creates\n> neutral black holes.\n\nThis is only true if you believe in cosmic censorship. Otherways\nnaked singularities may form, the output of which cannot computed\nin any effective field theory. However, it is claimed in the\n"TASI Lectures on Black Holes in String Theory" (hep-th/0008241)\npage 36 that cosmic censorship is violated due to the\nGregory-Laflamme instability. Naked singularities appears while\nneutral black strings decay into black holes. The question is\nwhether it is possible to construct such black strings if they\ndidn\'t exist in the first place. Intuitively it seems to me it\nshould be possible, via some kind of cylindrically symmetric\ngravitational collapse for instance. It appears to me a\nmacroscopic black-string would live for a long time before\ndecaying since it is stable in the effective field theory.\n\nBest regards,\nSquark.\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>Lubos Motl <motl@feynman.harvard.edu> wrote in message news:<20040607043432.X2574@mail.kolej.mff.cuni.cz>...
> ...
> In fact, M-theory in 11 infinitely large dimensions is boring, in a
> related sense. Is there a qualitative effect that distinguishes M-theory
> from "supergravity combined with common sense"? At low energies
> (relatively to the Planck length), SUGRA is more or less OK (and describes
> all pure states), and at higher energies, the graviton scattering produces
> Schwarzschild black holes. Well, there are also (large but compact)
> M2-branes and M5-branes (let's now treat them as if they don't exist in
> SUGRA, even though they exist as solutions; they carry new dynamics not
> derivable directly from SUGRA, such as the (2,0) theory), but they should
> already exist a priori, otherwise we won't be able to produce them by
> collisions of the graviton multiplets - a typical collission creates
> neutral black holes.
This is only true if you believe in cosmic censorship. Otherways
naked singularities may form, the output of which cannot computed
in any effective field theory. However, it is claimed in the
"TASI Lectures on Black Holes in String Theory" (http://www.arxiv.org/abs/hep-th/0008241)
page 36 that cosmic censorship is violated due to the
Gregory-Laflamme instability. Naked singularities appears while
neutral black strings decay into black holes. The question is
whether it is possible to construct such black strings if they
didn't exist in the first place. Intuitively it seems to me it
should be possible, via some kind of cylindrically symmetric
gravitational collapse for instance. It appears to me a
macroscopic black-string would live for a long time before
decaying since it is stable in the effective field theory.
Best regards,
Squark.
Lubos Motl
Jun7-04, 08:05 PM
<jabberwocky><div class="vbmenu_control"><a href="jabberwocky:;" onClick="newWindow=window.open('','usenetCode','toolbar=no, location=no,scrollbars=yes,resizable=yes,status=no ,width=650,height=400'); newWindow.document.write('<HTML><HEAD><TITLE>Usenet ASCII</TITLE></HEAD><BODY topmargin=0 leftmargin=0 BGCOLOR=#F1F1F1><table border=0 width=625><td bgcolor=midnightblue><font color=#F1F1F1>This Usenet message\'s original ASCII form: </font></td></tr><tr><td width=449><br><br><font face=courier><UL><PRE>On Mon, 7 Jun 2004, Squark wrote:\n\n> This is only true if you believe in cosmic censorship. Otherways\n> naked singularities may form, the output of which cannot computed\n> in any effective field theory.\n\nWhile it is true that I believe that cosmic censorship is true at least in\nsome moral sense (and the counterexamples don\'t seem generic or convincing\nso far), it seems that in 11 dimensions it is more than just a belief.\nIt is rather a consequence of supersymmetry, is not it?\n\n> However, it is claimed in the\n> "TASI Lectures on Black Holes in String Theory" (hep-th/0008241)\n> page 36 that cosmic censorship is violated due to the\n> Gregory-Laflamme instability.\n\nNot really, Amanda does not claim that. She writes "Let us now consider\nthe possibility that this decay violates cosmic censorship." Finally she\nonly says that it is difficult to argue that the violation does not occur\nwhich is different than the statement that it is easy to prove that the\nviolation does occur. ;-) Moreover she is not talking about M-theory in\n11D, as far as I see.\n\n> Naked singularities appears while\n> neutral black strings decay into black holes. The question is\n> whether it is possible to construct such black strings if they\n> didn\'t exist in the first place. Intuitively it seems to me it\n> should be possible, via some kind of cylindrically symmetric\n> gravitational collapse for instance. It appears to me a\n> macroscopic black-string would live for a long time before\n> decaying since it is stable in the effective field theory.\n\nThat might be a good point to analyze in detail...\n\nAll the best\nLubos\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 Mon, 7 Jun 2004, Squark wrote:
> This is only true if you believe in cosmic censorship. Otherways
> naked singularities may form, the output of which cannot computed
> in any effective field theory.
While it is true that I believe that cosmic censorship is true at least in
some moral sense (and the counterexamples don't seem generic or convincing
so far), it seems that in 11 dimensions it is more than just a belief.
It is rather a consequence of supersymmetry, is not it?
> However, it is claimed in the
> "TASI Lectures on Black Holes in String Theory" (http://www.arxiv.org/abs/hep-th/0008241)
> page 36 that cosmic censorship is violated due to the
> Gregory-Laflamme instability.
Not really, Amanda does not claim that. She writes "Let us now consider
the possibility that this decay violates cosmic censorship." Finally she
only says that it is difficult to argue that the violation does not occur
which is different than the statement that it is easy to prove that the
violation does occur. ;-) Moreover she is not talking about M-theory in
11D, as far as I see.
> Naked singularities appears while
> neutral black strings decay into black holes. The question is
> whether it is possible to construct such black strings if they
> didn't exist in the first place. Intuitively it seems to me it
> should be possible, via some kind of cylindrically symmetric
> gravitational collapse for instance. It appears to me a
> macroscopic black-string would live for a long time before
> decaying since it is stable in the effective field theory.
That might be a good point to analyze in detail...
All the best
Lubos
__{_______________________________________________ _____________________________}
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)
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
<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>Lubos Motl <motl@feynman.harvard.edu> wrote in message news:<Pine.LNX.4.31.0406071955280.22339-100000@feynman.harvard.edu>...\n\n> While it is true that I believe that cosmic censorship is true at least in\n> some moral sense (and the counterexamples don\'t seem generic or convincing\n> so far), it seems that in 11 dimensions it is more than just a belief.\n> It is rather a consequence of supersymmetry, is not it?\n\nI don\'t know, is it? How does cosmic censorship follow from SUSY in 11D?\n\n[Moderator\'s note: The most general argument is that supersymmetry\nguarantees that the mass is greater than the charge, in appropriate\nunits: M > |Z|, i.e. M + Z > 0, M - Z > 0, which follows from the\nfact that M+Z and M-Z can be written as positively-semidefinite bilinear\nexpressions constructed from the SUSY generators. All states in\na supersymmetric theory automatically satisfy the BPS bound, and\ntherefore "superextremal" black holes can\'t exist in a supersymmetric\ntheory. Of course, this is a general argument, and one would have to\nstudy the precise context - and the precise proposed creation of naked\nsingularities - in detail. I think that if one thinks about it,\nthe production of known types of naked singularities in 11 large\ndimensions will be excluded. LM]\n\n> Not really, Amanda does not claim that. She writes "Let us now consider\n> the possibility that this decay violates cosmic censorship." Finally she\n> only says that it is difficult to argue that the violation does not occur\n> which is different than the statement that it is easy to prove that the\n> violation does occur. ;-)\n\nNeveretheless she is inclined to think it does, and so are\nthe authors of the original paper "Black String and Black\np-Branes are Unstable" (hep-th/9301052). Apparently the\ninstability occurs classically as well (at least on the\ninfinitesimal level, i.e. there are destabilizing modes).\nIt is then should be possible to test cosmic censorship\nin this case via a numerical simulation. I wonder whether\nanyone has tried that?\n\n[Moderator\'s note: There has been a large activity initiated by\nGary Horowitz et al., and an even larger amount of papers that\nHorowitz\'s statements about the censorship violation are not\nconfirmed numerically. Instead, black holes form and the cosmic\ncensorship hypothesis is upheld in the context of AdS/CFT.\nFor example, see\n\nhttp://arxiv.org/abs/hep-th/0402109\nhttp://arxiv.org/abs/gr-qc/0403078\nhttp://arxiv.org/abs/hep-th/0403198\n\nThis overwhelming counter-evidence convinced Horowitz et al. to find\na problem in their original construction, and therefore\n"the question whether censorship is violated in AdS remains\nopen". See the paper below... LM]\n\nhttp://arxiv.org/abs/gr-qc/0405050\n\n> Moreover she is not talking about M-theory in\n> 11D, as far as I see.\n\nApparently not, since the original paper also\nconcentrates on D <= 10. However, it appears to me that\nif black strings decay into black holes in type IIA SUGRA\nat D = 10, black membranes decay into black strings\n(at least) in D = 11.\n\nAnother issue regarding potentially purely quantum\ngravitational phenomena in 11D is topology change\n(including "macroscopic" topology change). It seems to me\nthere are grounds to believe such proccesses are possible\nin string theory, at least because it\'s possible for the\ntopology of the compactified dimensions in CY\ncompactifications. I don\'t know whether additional\nevidence of topology change is known? It is however\nunobvious what kind of proccesses can lead to topology\nchange with high probability.\n\n[Moderator\'s note: Macroscopic topology change will probably\nalways be unlikely, nevertheless the topology change in\nthe microscopic context is a fact that can be showed in the\nCalabi-Yau context, secured by SUSY and mirror symmetry,\nand by locality it implies that topology change is allowed\nin general. LM]\n\nBest regards,\nSquark.\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>Lubos Motl <motl@feynman.harvard.edu> wrote in message news:<Pine.LNX.4.31.0406071955280.22339-100000@feynman.harvard.edu>...
> While it is true that I believe that cosmic censorship is true at least in
> some moral sense (and the counterexamples don't seem generic or convincing
> so far), it seems that in 11 dimensions it is more than just a belief.
> It is rather a consequence of supersymmetry, is not it?
I don't know, is it? How does cosmic censorship follow from SUSY in 11D?
[Moderator's note: The most general argument is that supersymmetry
guarantees that the mass is greater than the charge, in appropriate
units: M > |Z|, i.e. M + Z > 0, M - Z > 0, which follows from the
fact that M+Z and M-Z can be written as positively-semidefinite bilinear
expressions constructed from the SUSY generators. All states in
a supersymmetric theory automatically satisfy the BPS bound, and
therefore "superextremal" black holes can't exist in a supersymmetric
theory. Of course, this is a general argument, and one would have to
study the precise context - and the precise proposed creation of naked
singularities - in detail. I think that if one thinks about it,
the production of known types of naked singularities in 11 large
dimensions will be excluded. LM]
> Not really, Amanda does not claim that. She writes "Let us now consider
> the possibility that this decay violates cosmic censorship." Finally she
> only says that it is difficult to argue that the violation does not occur
> which is different than the statement that it is easy to prove that the
> violation does occur. ;-)
Neveretheless she is inclined to think it does, and so are
the authors of the original paper "Black String and Black
p-Branes are Unstable" (http://www.arxiv.org/abs/hep-th/9301052). Apparently the
instability occurs classically as well (at least on the
infinitesimal level, i.e. there are destabilizing modes).
It is then should be possible to test cosmic censorship
in this case via a numerical simulation. I wonder whether
anyone has tried that?
[Moderator's note: There has been a large activity initiated by
Gary Horowitz et al., and an even larger amount of papers that
Horowitz's statements about the censorship violation are not
confirmed numerically. Instead, black holes form and the cosmic
censorship hypothesis is upheld in the context of AdS/CFT.
For example, see
http://arxiv.org/abs/http://www.arxiv.org/abs/hep-th/0402109
http://arxiv.org/abs/http://www.arxiv.org/abs/gr-qc/0403078
http://arxiv.org/abs/http://www.arxiv.org/abs/hep-th/0403198
This overwhelming counter-evidence convinced Horowitz et al. to find
a problem in their original construction, and therefore
"the question whether censorship is violated in AdS remains
open". See the paper below... LM]
http://arxiv.org/abs/http://www.arxiv.org/abs/gr-qc/0405050
> Moreover she is not talking about M-theory in
> 11D, as far as I see.
Apparently not, since the original paper also
concentrates on D <= 10. However, it appears to me that
if black strings decay into black holes in type IIA SUGRA
at D = 10, black membranes decay into black strings
(at least) in D = 11.
Another issue regarding potentially purely quantum
gravitational phenomena in 11D is topology change
(including "macroscopic" topology change). It seems to me
there are grounds to believe such proccesses are possible
in string theory, at least because it's possible for the
topology of the compactified dimensions in CY
compactifications. I don't know whether additional
evidence of topology change is known? It is however
unobvious what kind of proccesses can lead to topology
change with high probability.
[Moderator's note: Macroscopic topology change will probably
always be unlikely, nevertheless the topology change in
the microscopic context is a fact that can be showed in the
Calabi-Yau context, secured by SUSY and mirror symmetry,
and by locality it implies that topology change is allowed
in general. LM]
Best regards,
Squark.
<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.0406080855.2eea90ff-100000@posting.google.com>...\n> Lubos Motl <motl@feynman.harvard.edu> wrote in message news:<Pine.LNX.4.31.0406071955280.22339-100000@feynman.harvard.edu>...\n> [Moderator\'s note: The most general argument is that supersymmetry\n> guarantees that the mass is greater than the charge, in appropriate\n> units: M > |Z|, i.e. M + Z > 0, M - Z > 0, which follows from the\n> fact that M+Z and M-Z can be written as positively-semidefinite bilinear\n> expressions constructed from the SUSY generators. All states in\n> a supersymmetric theory automatically satisfy the BPS bound, and\n> therefore "superextremal" black holes can\'t exist in a supersymmetric\n> theory. Of course, this is a general argument, and one would have to\n> study the precise context - and the precise proposed creation of naked\n> singularities - in detail. I think that if one thinks about it,\n> the production of known types of naked singularities in 11 large\n> dimensions will be excluded. LM]\n\nHowever, I don\'t see why any naked singularity has to have to form\nof a "superextremal" black-hole.\n\n> [Moderator\'s note: There has been a large activity initiated by\n> Gary Horowitz et al., and an even larger amount of papers that\n> Horowitz\'s statements about the censorship violation are not\n> confirmed numerically. Instead, black holes form and the cosmic\n> censorship hypothesis is upheld in the context of AdS/CFT.\n> For example, see\n>\n> http://arxiv.org/abs/hep-th/0402109\n> http://arxiv.org/abs/gr-qc/0403078\n> http://arxiv.org/abs/hep-th/0403198\n>\n> This overwhelming counter-evidence convinced Horowitz et al. to find\n> a problem in their original construction, and therefore\n> "the question whether censorship is violated in AdS remains\n> open". See the paper below... LM]\n\nOK, this is a quite different scenario than the\nGregory-Laflamme one. It is possible that in\nasymptotically flat spacetime cosmic censorship\nholds somehow, but it is difficult to imagine how\ncan it be salvaged for R^n x S^1 topology, say\nwith near-cylindrically-symmetric gravitational\ncollapse warped around the S^1 (n > 3).\n\n> [Moderator\'s note: Macroscopic topology change will probably\n> always be unlikely, nevertheless the topology change in\n> the microscopic context is a fact that can be showed in the\n> Calabi-Yau context, secured by SUSY and mirror symmetry,\n> and by locality it implies that topology change is allowed\n> in general. LM]\n\nIt is however far from understood what the general\ncase entails. For instance, can small compact bubbles\n"clip away" from spacetime and what would happen\nwith them afterwards? Can small wormholes form\nbetween distant locations?\n\nBest regards,\nSquark.\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.0406080855.2eea90ff-100000@posting.google.com>...
> Lubos Motl <motl@feynman.harvard.edu> wrote in message news:<Pine.LNX.4.31.0406071955280.22339-100000@feynman.harvard.edu>...
> [Moderator's note: The most general argument is that supersymmetry
> guarantees that the mass is greater than the charge, in appropriate
> units: M > |Z|, i.e. M + Z > 0, M - Z > 0, which follows from the
> fact that M+Z and M-Z can be written as positively-semidefinite bilinear
> expressions constructed from the SUSY generators. All states in
> a supersymmetric theory automatically satisfy the BPS bound, and
> therefore "superextremal" black holes can't exist in a supersymmetric
> theory. Of course, this is a general argument, and one would have to
> study the precise context - and the precise proposed creation of naked
> singularities - in detail. I think that if one thinks about it,
> the production of known types of naked singularities in 11 large
> dimensions will be excluded. LM]
However, I don't see why any naked singularity has to have to form
of a "superextremal" black-hole.
> [Moderator's note: There has been a large activity initiated by
> Gary Horowitz et al., and an even larger amount of papers that
> Horowitz's statements about the censorship violation are not
> confirmed numerically. Instead, black holes form and the cosmic
> censorship hypothesis is upheld in the context of AdS/CFT.
> For example, see
>
> http://arxiv.org/abs/http://www.arxiv.org/abs/hep-th/0402109
> http://arxiv.org/abs/http://www.arxiv.org/abs/gr-qc/0403078
> http://arxiv.org/abs/http://www.arxiv.org/abs/hep-th/0403198
>
> This overwhelming counter-evidence convinced Horowitz et al. to find
> a problem in their original construction, and therefore
> "the question whether censorship is violated in AdS remains
> open". See the paper below... LM]
OK, this is a quite different scenario than the
Gregory-Laflamme one. It is possible that in
asymptotically flat spacetime cosmic censorship
holds somehow, but it is difficult to imagine how
can it be salvaged for R^n x S^1 topology, say
with near-cylindrically-symmetric gravitational
collapse warped around the S^1 (n > 3).
> [Moderator's note: Macroscopic topology change will probably
> always be unlikely, nevertheless the topology change in
> the microscopic context is a fact that can be showed in the
> Calabi-Yau context, secured by SUSY and mirror symmetry,
> and by locality it implies that topology change is allowed
> in general. LM]
It is however far from understood what the general
case entails. For instance, can small compact bubbles
"clip away" from spacetime and what would happen
with them afterwards? Can small wormholes form
between distant locations?
Best regards,
Squark.
Charlie Stromeyer Jr.
Jun9-04, 02:50 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:\n\n> This is only true if you believe in cosmic censorship. Otherways\n> naked singularities may form, the output of which cannot computed\n> in any effective field theory. However, it is claimed in the\n> "TASI Lectures on Black Holes in String Theory" (hep-th/0008241)\n> page 36 that cosmic censorship is violated due to the\n> Gregory-Laflamme instability.\n\nThere is new evidence for the entropy argument for GL instability:\n\nhttp://arxiv.org/abs/hep-th/0405045\n\nHowever, the author explains some reasons esp. in the Conclusion and\nNote Added sections about why this issue still remains unclear. If\nquantum gravity might be involved as the author suggests then I would\nalso expect that the spectra of black holes in dS should be\nnon-trivially related to the gravitational quasinormal modes of the\nblack hole, but so far this has not yet been established.\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:
> This is only true if you believe in cosmic censorship. Otherways
> naked singularities may form, the output of which cannot computed
> in any effective field theory. However, it is claimed in the
> "TASI Lectures on Black Holes in String Theory" (http://www.arxiv.org/abs/hep-th/0008241)
> page 36 that cosmic censorship is violated due to the
> Gregory-Laflamme instability.
There is new evidence for the entropy argument for GL instability:
http://arxiv.org/abs/http://www.arxiv.org/abs/hep-th/0405045
However, the author explains some reasons esp. in the Conclusion and
Note Added sections about why this issue still remains unclear. If
quantum gravity might be involved as the author suggests then I would
also expect that the spectra of black holes in dS should be
non-trivially related to the gravitational quasinormal modes of the
black hole, but so far this has not yet been established.
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