[SOLVED] Penrose's critique of string theory

Lubos Motl

<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 Sat, 31 Jul 2004, Daniel wrote:\n\n> Roger Penrose offered a lecture on string theory title "Fashion,\n> Faith, and Fantasy in Theoretical Physics".\n\nLet me first say that Roger Penrose has done a large number of\ncontributions to physics and thinking and many of them are being intensely\nused and studied especially by string theorists - for example twistors;\ncausal diagrams; pp-wave limits of geometries; cosmic censorship, and so\non.\n\nWe all admire his talent and his precious insights. I am pretty sure that\nif he decided to study current physics seriously - instead of thinking\n(like an overly speculative fan of physics) about gravitational collapses\nof the wavefunction in the brain and instead of giving shallow lectures\ninspired by science like this one, he might become a tough competitor for\nsome of the current leaders of theoretical physics, including Edward\nWitten.\n\n> [RP] apparently is critical of string theory, and prefers loop quantum\n> gravity.\n\nWell, Roger Penrose anticipated the emergence of spin networks in quantum\ngravity, which eventually occurred in loop quantum gravity. On the other\nhand, although his insights are valuable for string theorists, none of\nthem is truly string-theoretical.\n\n> polemic aside, what are his criticisms of string theory, how has\n> string theorists responded, including edward witten and lubos motl,\n\nHonestly, I find it inappropriate to appear in the same sentence as Edward\nWitten who has done more than me for science by several orders of\nmagnitude, but let me assume that your point was different. It would be\ngreat if Edward Witten responded, too.\n\n> and why does he think LQG is preferable?\n\nIt may be a good idea to ask him, and of course, he will be always welcome\nif he appears on this newsgroup. ;-) If you ask me and you want to know\nwhat I really think, the real reason behind this preference may be that he\nmight be viewed as a grandfather of loop quantum gravity, but he has not\ncontributed much to string theory.\n\n> the reason i am posting is that roger penrose is one of the world\'s\n> most preeminent physcist, easily on par in prestige with edward witten\n> and stephen hawking, and i am curious as to whether penrose offers new\n> or original criticisms from string theory and whether there are new or\n> original counter-arguments from string theorists.\n\nAs far as the contents of the criticism goes, I\'ve heard about a few\nlectures by Penrose about these issues. One lecture, two years ago or so\n(Hawkingfest?), was dedicated to singularities. He pointed out that the\nmoduli spaces of manifolds (such as the Calabi-Yau manifolds) have\nsingularities in them, and therefore - he argued - string theory was in\ntrouble. Such a statement showed that, sadly, Penrose had no idea what was\nreally going on in string theory. String theory has marvelously resolved a\nlarge class of timelike singularities (e.g. of the conifold) and all\npotential problems arising from such singularities were shown to be\nregular due to branes and their associated physics. See "The Elegant\nUniverse" (chapters 11,13, for example) to learn why it is exactly string\ntheory that wins near the singularities where all other theories lose.\n\nPenrose\'s criticism - at least this aspect of it - is therefore rather\noriginal and different from other criticisms - but it does not seem to be\nwell-informed.\n\n> String theory has had a kind of tulip-mania fad or craze and now seems\n> to be in decline.\n\nWell, we\'ve heard such things since the middle 1980s at least. It is\ncertainly a longer-lasting fad than any other fad in the history of\nhumankind. ;-) String theory has had its revolutions and its declines\n(and it may be more fair to talk about a decline today, at least if we\ncompare the present with the middle 1990s or middle 1980s), but it remains\nthe only real contender for a conceptual framework that goes beyond\nquantum field theory and classical GR. Most string theorists are also too\nnice - perhaps except for me - and therefore they won\'t comment on\ndeclines of Roger Penrose although there would certainly be a lot of stuff\nto discuss.\n\n> But it is also a kind of religious faith for some of\n> those who have invested a lot of effort in understanding it.\n\nThat\'s right. So was relativity and other important breakthroughs in\nscience.\n\n> so there are some diehard believers who will give you elaborate\n> specious arguments why it is impossible that any of the newer\n> approaches to quantizing gravity can work\n\nIt would be more interesting scientifically if Roger Penrose could take,\nfor example, my 25 kilobyte long (devastating) review of Rovelli\'s new\nbook (to appear) which is also an analysis of the whole field of LQG and\nif he showed which arguments against this "newer approach" may have a\nloophole. Instead, Penrose seems to believe that he can influence the\ndirection where physics goes without any arguments. I am not sure whether\nthe overlap between science and religion is *that* far-reaching.\n\n> and it lives in a kind of fantasy realm, making no testable\n> predictions and ungoverned by experimental evidence, so the\n> researchers indulge in untrammelled mathematical inventiveness\n\nOn the other hand, this statement is not original at all. String theory is\nthe most conservative extension of the successfully tested principles of\nmodern physics, and all its features are - at least qualitatively - very\nphysical and realistic. It is a rich theory but all of its different\nphenomena will remain to be highly interesting and important mathematical\nsubjects to study.\n\n> finally such an embarrassing richness of possibilities has emerged\n> that the distinct variations of the theory have been estimated by its\n> insiders (Susskind, Douglas) at ten-to-the-100 different base states\n> and things like the Anthropic Principle, a latterday Hand of God, are\n> being invoked in a desperate effort to find the right one.\n> So it has gotten bogged down in its own fecundity.\n\nWe have discussed these questions a lot on this board. If the number of\npossibilities to create a Universe - including working cosmology - in the\ncorrect theory *is* that huge, we will have to live with this fact. String\ntheorists don\'t agree yet whether the usage of the Anthropic Reasoning\nwill be necessary. Many of us hate it. But it is a logical possibility. At\nany rate, as long as theoretical physics exists as a field, the scholars\nin it will study something. Because they have no new experiments, they\nmust study more or less pure theory. String theory remains the most\npromising game in town, perhaps the only game in town. This might\nhypothetically change - but only if someone found something equally (or\nmore) interesting. It cannot change by political speaches without\nscientific content, even if the speaker is as famous as Roger Penrose.\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</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 Sat, 31 Jul 2004, Daniel wrote:

> Roger Penrose offered a lecture on string theory title "Fashion,
> Faith, and Fantasy in Theoretical Physics".

Let me first say that Roger Penrose has done a large number of
contributions to physics and thinking and many of them are being intensely
used and studied especially by string theorists - for example twistors;
causal diagrams; pp-wave limits of geometries; cosmic censorship, and so
on.

We all admire his talent and his precious insights. I am pretty sure that
if he decided to study current physics seriously - instead of thinking
(like an overly speculative fan of physics) about gravitational collapses
of the wavefunction in the brain and instead of giving shallow lectures
inspired by science like this one, he might become a tough competitor for
some of the current leaders of theoretical physics, including Edward
Witten.

> [RP] apparently is critical of string theory, and prefers loop quantum
> gravity.

Well, Roger Penrose anticipated the emergence of spin networks in quantum
gravity, which eventually occurred in loop quantum gravity. On the other
hand, although his insights are valuable for string theorists, none of
them is truly string-theoretical.

> polemic aside, what are his criticisms of string theory, how has
> string theorists responded, including edward witten and lubos motl,

Honestly, I find it inappropriate to appear in the same sentence as Edward
Witten who has done more than me for science by several orders of
magnitude, but let me assume that your point was different. It would be
great if Edward Witten responded, too.

> and why does he think LQG is preferable?

It may be a good idea to ask him, and of course, he will be always welcome
if he appears on this newsgroup. ;-) If you ask me and you want to know
what I really think, the real reason behind this preference may be that he
might be viewed as a grandfather of loop quantum gravity, but he has not
contributed much to string theory.

> the reason i am posting is that roger penrose is one of the world's
> most preeminent physcist, easily on par in prestige with edward witten
> and stephen hawking, and i am curious as to whether penrose offers new
> or original criticisms from string theory and whether there are new or
> original counter-arguments from string theorists.

As far as the contents of the criticism goes, I've heard about a few
lectures by Penrose about these issues. One lecture, two years ago or so
(Hawkingfest?), was dedicated to singularities. He pointed out that the
moduli spaces of manifolds (such as the Calabi-Yau manifolds) have
singularities in them, and therefore [itex]- he[/itex] argued - string theory was in
trouble. Such a statement showed that, sadly, Penrose had no idea what was
really going on in string theory. String theory has marvelously resolved a
large class of timelike singularities (e.g. of the conifold) and all
potential problems arising from such singularities were shown to be
regular due to branes and their associated physics. See "The Elegant
Universe" (chapters 11,13, for example) to learn why it is exactly string
theory that wins near the singularities where all other theories lose.

Penrose's criticism [itex]- at[/itex] least this aspect of [itex]it -[/itex] is therefore rather
original and different from other criticisms - but it does not seem to be
well-informed.

> String theory has had a kind of tulip-mania fad or craze and now seems
> to be in decline.

Well, we've heard such things since the middle 1980s at least. It is
certainly a longer-lasting fad than any other fad in the history of
humankind. ;-) String theory has had its revolutions and its declines
(and it may be more fair to talk about a decline today, at least if we
compare the present with the middle 1990s or middle 1980s), but it remains
the only real contender for a conceptual framework that goes beyond
quantum field theory and classical GR. Most string theorists are also too
nice - perhaps except for [itex]me -[/itex] and therefore they won't comment on
declines of Roger Penrose although there would certainly be a lot of stuff
to discuss.

> But it is also a kind of religious faith for some of
> those who have invested a lot of effort in understanding it.

That's right. So was relativity and other important breakthroughs in
science.

> so there are some diehard believers who will give you elaborate
> specious arguments why it is impossible that any of the newer
> approaches to quantizing gravity can work

It would be more interesting scientifically if Roger Penrose could take,
for example, my 25 kilobyte long (devastating) review of Rovelli's new
book (to appear) which is also an analysis of the whole field of LQG and
if he showed which arguments against this "newer approach" may have a
loophole. Instead, Penrose seems to believe that he can influence the
direction where physics goes without any arguments. I am not sure whether
the overlap between science and religion is *that* far-reaching.

> and it lives in a kind of fantasy realm, making no testable
> predictions and ungoverned by experimental evidence, so the
> researchers indulge in untrammelled mathematical inventiveness

On the other hand, this statement is not original at all. String theory is
the most conservative extension of the successfully tested principles of
modern physics, and all its features are [itex]- at[/itex] least qualitatively - very
physical and realistic. It is a rich theory but all of its different
phenomena will remain to be highly interesting and important mathematical
subjects to study.

> finally such an embarrassing richness of possibilities has emerged
> that the distinct variations of the theory have been estimated by its
> insiders (Susskind, Douglas) at ten-to-the-100 different base states
> and things like the Anthropic Principle, a latterday Hand of God, are
> being invoked in a desperate effort to find the right one.
> So it has gotten bogged down in its own fecundity.

We have discussed these questions a lot on this board. If the number of
possibilities to create a Universe - including working cosmology - in the
correct theory *is* that huge, we will have to live with this fact. String
theorists don't agree yet whether the usage of the Anthropic Reasoning
will be necessary. Many of us hate it. But it is a logical possibility. At
any rate, as long as theoretical physics exists as a field, the scholars
in it will study something. Because they have no new experiments, they
must study more or less pure theory. String theory remains the most
promising game in town, perhaps the only game in town. This might
hypothetically change - but only if someone found something equally (or
more) interesting. It cannot change by political speaches without
scientific content, even if the speaker is as famous as Roger Penrose.

__{____________________________________________________________________ ________}
E-mail: lumo@matfyz.cz fax: [itex]+1-617/496-0110[/itex] Web: http://lumo.matfyz.cz/
eFax: [itex]+1-801/454-1858[/itex] work: [itex]+1-617/496-8199[/itex] home: [itex]+1-617/868-4487[/itex] (call)
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ ^^^^^^^

Daniel

<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>Roger Penrose offered a lecture on string theory title "Fashion,\nFaith, and Fantasy in Theoretical Physics".\n\nI have not heard his lecture, nor am i acquainted with his latest\nwork, Road to Reality: A Complete Guide to the Physical Universe by\nRoger Penrose, which apparently is not yet available in the US, but he\napparently is critical of string theory, and prefers loop quantum\ngravity.\n\npolemic aside, what are his criticisms of string theory, how has\nstring theorists responded, including edward witten and lubos motl,\nand why does he think LQG is preferable?\n\nthe reason i am posting is that roger penrose is one of the world\'s\nmost preeminent physcist, easily on par in prestige with edward witten\nand stephen hawking, and i am curious as to whether penrose offers new\nor original criticisms from string theory and whether there are new or\noriginal counter-arguments from string theorists.\n\n\nFASHION, FAITH AND FANTASY IN THEORETICAL PHYSICS\n\nand it is at the Dublin concert hall at 8PM on Friday 23 July\n\nString theory has had a kind of tulip-mania fad or craze and now seems\nto be in decline. But it is also a kind of religious faith for some of\nthose who have invested a lot of effort in understanding it.\n\nso there are some diehard believers who will give you elaborate\nspecious arguments why it is impossible that any of the newer\napproaches to quantizing gravity can work\n\nand it lives in a kind of fantasy realm, making no testable\npredictions and ungoverned by experimental evidence, so the\nresearchers indulge in untrammelled mathematical inventiveness\n\nfinally such an embarrassing richness of possibilities has emerged\nthat the distinct variations of the theory have been estimated by its\ninsiders (Susskind, Douglas) at ten-to-the-100 different base states\nand things like the Anthropic Principle, a latterday Hand of God, are\nbeing invoked in a desperate effort to find the right one.\nSo it has gotten bogged down in its own fecundity.\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>Roger Penrose offered a lecture on string theory title "Fashion,
Faith, and Fantasy in Theoretical Physics".

I have not heard his lecture, nor am i acquainted with his latest
work, Road to Reality: A Complete Guide to the Physical Universe by
Roger Penrose, which apparently is not yet available in the US, but he
apparently is critical of string theory, and prefers loop quantum
gravity.

polemic aside, what are his criticisms of string theory, how has
string theorists responded, including edward witten and lubos motl,
and why does he think LQG is preferable?

the reason i am posting is that roger penrose is one of the world's
most preeminent physcist, easily on par in prestige with edward witten
and stephen hawking, and i am curious as to whether penrose offers new
or original criticisms from string theory and whether there are new or
original counter-arguments from string theorists.

FASHION, FAITH AND FANTASY IN THEORETICAL PHYSICS

and it is at the Dublin concert hall at 8PM on Friday 23 July

String theory has had a kind of tulip-mania fad or craze and now seems
to be in decline. But it is also a kind of religious faith for some of
those who have invested a lot of effort in understanding it.

so there are some diehard believers who will give you elaborate
specious arguments why it is impossible that any of the newer
approaches to quantizing gravity can work

and it lives in a kind of fantasy realm, making no testable
predictions and ungoverned by experimental evidence, so the
researchers indulge in untrammelled mathematical inventiveness

finally such an embarrassing richness of possibilities has emerged
that the distinct variations of the theory have been estimated by its
insiders (Susskind, Douglas) at ten-to-the-100 different base states
and things like the Anthropic Principle, a latterday Hand of God, are
being invoked in a desperate effort to find the right one.
So it has gotten bogged down in its own fecundity.

alistair

<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>Daniel:\n\n>Roger Penrose.. is critical of string theory\n\nI think he mentioned in a newspaper article\nthe other day that it would be nice to have some experimental evidence\nfor string theory.I\'m sure even string theorists would agree with\nthis!\nStephen Hawking says that it is the existence of the dualities in\nstring theory that make him believe string theorists could be on to\nsomething.\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>Daniel:

>Roger Penrose.. is critical of string theory

I think he mentioned in a newspaper article
the other day that it would be nice to have some experimental evidence
for string theory.I'm sure even string theorists would agree with
this!
Stephen Hawking says that it is the existence of the dualities in
string theory that make him believe string theorists could be on to
something.

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