GF [00:00:06] A
mind of the brilliance of Edward Witten’s comes along in mathematical physics
about once every 50 years if we’re lucky. Since the late 1970s he’s been
preeminent among the physicists who are trying to understand the underlying
order of the universe. Or, as you might say, trying to discover the most
fundamental equations of physics. More than that, by studying the mathematical
qualities of nature, Witten became remarkably influential in pure mathematics.
The only physicist ever to have won the coveted Fields Medal which has much the
same stature in mathematics as a Nobel Prize has in physics.
GF [00:00:46] My
name is Graham Farmelo, author of “The universe speaks in numbers.” Witten is a
central figure in my book and he’s been helpful to me. Though he’s a reluctant
interviewee so I was pleased when he agreed to talk with me last August about
some aspects of his career and the relationship between mathematics and
physics. He was in a relaxed mood sitting on a sofa in his office at the
Institute for Advanced Study in Princeton wearing his tennis clothes. As usual, he speaks quietly so you’ll have to listen hard.
GF [00:01:20] He
uses quite a few technical terms too. But if you’re not familiar with them I
suggest that you just let them wash over you. The key thing is to get a sense
of Witten’s thinking about the big picture. He is worth it.
GF [00:01:32] He
gives us several illuminating insights into how he became interested in stateoftheart mathematics while remaining a physicist to his fingertips. I began by
asking him if he’d always been interested in mathematics and physics.
EW [00:01:47] When
I was a kid I was very interested in astronomy. It was the period of the space
race and everybody was interested in space. Then, when I was a little older, I was
exposed to calculus by my father. And for a while I was very interested in
math.
GF [00:02:02] You
said for a while, so did that lapse?
EW [00:02:04] Yes, it did lapse for a few years, and the reason it lapsed, I think, was that after
being exposed to calculus at the age of eleven it actually was quite a while
before I was shown anything that was really more advanced. So I wasn't really
aware that there was much more interesting more advanced math. Probably
not the only reason, but certainly one reason that my interest lapsed.
GF [00:02:22] Yeah.
Were you ever interested in any other subjects? I mean because you know you
came on to study history and things like that. Did that really interest you
comparably to math and physics?
EW [00:02:31] I
guess there was a period when I imagined doing journalism or history or
something but at about the age of 21 or 22 I realized that I wasn't going to
work out well in my case.
GF [00:02:42] After
studying modern languages he worked on George McGovern’s ill fated presidential
campaign and even studied economics for one semester before he finally turned
to physics.
GF [00:02:53] Apparently
he showed up at Princeton University wanting to do a Ph.D. in theoretical
physics and they wisely took him on after he made short work of some
preliminary exams. Boy did he learn quickly. One of the instructors tasked with
teaching him in the lab told me that within three weeks Witten’s questions on
the experiments went from basic to brilliant to Nobel level. As a postdoc at
Harvard, Witten became acquainted with several of the theorist pioneers of this
model including Steven Weinberg, Shelly Glashow, Howard Georgi, and Sydney
Coleman, who helped interest the young Witten in the mathematics of these new
theories.
EW [00:03:33] The
physicists I learned from most during those years were definitely Weinberg, Glashow, Georgi, and Coleman. And they were completely different. So Georgi and
Glashow were doing model building, basically weak interaction model building, elaborations on the Standard Model. I found it fascinating but it was a little
bit hard to find an entree there. If the
world had been a little bit different, I might have made my career doing things
like they were doing.
GF [00:04:01] Wow.
This was the first time I’d heard Witten say that he was at first expecting to
be like most other theorists and take his inspiration from the results of
experiments building socalled models of the real world. What, I wondered, led
him to change direction and become so mathematical.
EW [00:04:19] Let
me provide a little background for listeners. Up to and including the time I
was a graduate student, for 20, 25 years, there had been constant waves of new
discoveries in elementary particle physics: strange particles, muons, hadronic
resonances, parity violations, CP violation, scaling and deep inelastic
scattering, the Charm particle, and I’m forgetting a whole bunch. But that’s enough to give you the idea. So that was over a period of over 20 years. So even
after a lot of the big discoveries that was one every three years. Now, if
experimental surprises and discoveries had continued like that, which at the time
I think is what would have happened because it had been going on for a quarter century, then I would have
expected to be involved in model building, or grappling with it, like
colleagues such as Georgi and Glashow all were doing. Most notably, however, it
turned out that this period of constant surprise and turmoil was ending just
while I was a graduate and therefore later on I had no successful directions.
GF [00:05:20] Do
you remember being disappointed by that in any sense?
EW [00:05:23] Of
course I was, you never stop being disappointed.
GF [00:05:27] Oh
dear, oh it’s a hard life.
GF [00:05:31] You
were disappointed by the drawing up so to speak of the.
EW [00:05:33] There
have been important experimental discoveries since then. But the pace has not
been quite the same. Although they’ve been very important they’ve been a little
bit more abstract in what they teach us and definitely they’ve offered fewer
opportunities for model building than was the case in the 60s and 70s. I’d like
to just tell you a word or two about my interaction with the other physicists. There was Steve Weinberg and what I remember best from Weinberg. He was one of the
pioneers of a subject called current algebra which was an important part of
understanding the nuclear force. But he obviously thought most other physicists
didn't understand it properly and I was one of those. So whenever current
algebra was mentioned at a seminar or a discussion meeting he would always give
a short little speech explaining his understanding of it. In my case after
hearing those speeches the eight to 10 times [laughter] what Steve was telling
us.
EW [00:06:28] Then
there was Sidney Coleman. First of all Sidney was the only one who was
interested in strong coupling behavior of quantum field theories which is what
I’d become interested in as a graduate student with encouragement from my
advisor David Gross. So, he was really the only one I could interact with about
that. Others regarded strong coupling as a black box. So, maybe for your
listeners, I should explain that if you’re a student in physics they teach you
what to do when quantum effects are small, but no one tells you what to do when
quantum effects are big, there’s no general answer. It’s a smorgasbord of
different methods that work for different problems and a lot of problems that
are intractable. So, I'd become interested in that as a student but I was mostly
beating my head against a brick wall because it is usually intractable, and
Sydney was the only one of the professors at Harvard interested in such
matters. So, apart from interacting with him about that, also he exposed me to a
number of mathematical topics I wouldn’t have known about otherwise but that
eventually were important in my work which most physicists didn’t know about.
And certainly I didn’t know about.
GF [00:07:27] Yeah, can I ask were you consciously interested in advanced pure math at that time?
EW [00:07:32] Definitely
not
GF [00:07:32] You
were not?
EW [00:07:32] No,
most definitely not. I got dragged into math gradually because you see the
standard model had been discovered so the problems in physics were not exactly
the same as they had been before. But there were new problems that were opened
up by the standard model. For one thing there is new math that came into
understanding the standard model. Just when I was finishing graduate school
more or less Polyakov and others introduced the YangMills instanton which has
proved to be important in understanding physics. It’s also had a lot of
mathematical applications.
GF [00:08:02] You can think of instantons as fleeting events that occur in space and time on
the subatomic scale. These events are predicted by the theories of the
subatomic world known as gauge theories. A key moment in this story is Witten’s
first meeting with the great mathematician Michael Atiyah at the Massachusetts
Institute of Technology. They will become the leaders of the trend towards a
more mathematical approach to our understanding of the world.
EW [00:08:32] So
Polyakov and others had discovered the YangMills instanton and it was
important in physics and proved to have many other applications. And then
Atiyah was one of the mathematicians who discovered amazing mathematical
methods that could be used to solve the instanton equations. So he was
lecturing about that when he visited in Cambridge. I think in the spring of
1977, but I could be off by a few months, and I was extremely interested. And so we
talked about it a lot. I probably made more of an effort to understand the math
involved than most of the other physicists did. Anyway this interaction surely
led to my learning all kinds of math I’d never heard of before, complex manifolds, sheaf cohomology groups.
GF [00:09:16] This
was news to you at that time.
EW [00:09:18] Definitely.
So I might tell you at an even more basic level the AtiyahSinger index theorem
had been news to me a few months earlier when I heard about it from Sidney
Coleman.
GF [00:09:28] The
index theorem first proved by Michael Atiyah and his friend Isidore Singer
connects two branches of mathematics that had seemed unconnected. Calculus,
that’s the mathematics of changing quantities, and topology about the
properties of objects that don’t change when they’re stretched, twisted, or
deformed in some way, topology is now central to our understanding of
fundamental physics.
EW [00:09:51] Like
other physics graduate students of the period, I had no inkling of any 20th
century math, really. So, I’d never heard of the names Atiyah and Singer or of
the concept of the index or if the index theorem until Albert Schwarz showed
that it was relevant to understanding instantons. And even then that paper
didn’t make an immediate splash. If Coleman hadn’t pointed it out, I’m not sure
how long it would have been before I knew about it. And then there was
progress in understanding instanton equations by Atiyah among others. The first
actually was Richard Ward, Penrose’s doctoral student. So, I got interested in that but I was
interested in a sense in a narrow way which is what good would it be in
physics. And I learned the math or some of the math that the teacher was using.
But I was a little skeptical about the applicability for physics and I wasn’t
really wrong because the original program of Polyakov didn’t quite work out. The
details of the Instanton equations that were beautifully elucidated by the
mathematicians were not in practice that helpful for things you can actually do
as a physicist. So, to sort of summarize what happened in the long run, Atiyah’s
work and that of his colleagues made me learn a lot of math I’d never heard of
before which turned out to be very important later but not per se for the
original reasons.
GF [00:11:10] When
did you start to become convinced that math was really going to be interesting?
EW [00:11:14] Well that gradually happend in the
1980s I guess. So, for example one early episode which was in 1981 or two I was
trying to understand the properties of what's called the vacuum the quantum
ground state in supersymmetric field theories and it really had some behavior
that was hard to explain using standard physics ideas and since I couldn't
understand it I kept looking at simpler and simpler models and they all had the
same puzzle. So finally I got to what seemed like the simplest possible model
which you could ask the question and it still had a puzzling behavior. But at a
certain point, I think when I was in a swimming pool in Aspen Colorado, I
remembered Raoul Bott and actually Atiyah also had given some lectures to physicists a couple of years earlier in Cargesse, and they had tried to explain something
called Morse theory to us. I’m sure there are like me many other physicists
that have never heard of Morse theory or are familiar with any of the questions it
addresses or.
GF [00:12:11] Would you like to say what Morse theory is roughly speaking?
EW [00:12:14] Well
if you’ve got a rubber ball floating in space it’s got a lowest point, where
the elevation is lowest, it’s got a highest point where the elevation is
highest. So it’s got a maximum and a minimum. If you have a more complicated
surface like for example a rubber inner tube, it’ll have saddle points of height
function as well as a maximum and minimum. And Morse theory relates the maxima
and minima and the saddle points of a function such as height function to the
topology of a surface or topological manifold on which the function is defined.
GF [00:12:48] You
see that paper by Maxwell on that what he spoke about see in 1870.
EW [00:12:52] I’ve
not read that.
GF [00:12:53] Oh
I’ll show it to you later. It’s “On Hills and Dales,” gave it in Liverpool, very
thinly attended talk, erm, anyway.
EW [00:13:01] So
was he in fact describing the two dimensional version of Morse theory.
GF [00:13:04] I can’t
go into detail but the historians of Morse theory, they often refer to that. At a public meeting
incidentally in Liverpool.
EW [00:13:13] Actually
now you mentioned it, I heard the title of the Hills and Dales talk by Maxwell that had something
to do with the beginnings of topology. And topology was just barely beginning in roughly that period.
GF [00:13:23] But
this was useful in physics. Your Aspen swimming pool revelation...
EW [00:13:28] Well,
it shed a little bit of light on the vacuum state in super symmetric quantum
theories. So anyway I developed that further so you know at first that seemed
exceptional but eventually there were too many of these exceptions to
completely ignore.
GF [00:13:42] Am I
right in saying, not to put into your mouth, but it was the advent of String Theory post Michael
Greene and John Schwartz where these things started going front and center, is that
fair?
EW [00:13:50] After...
Following the first super string revolution as people call it which came to
fruition in 1984 with the work of Greene and Schwarz on the anomalies after that
the sort of math that Atiyah and others had used for the instaton equation was
suddenly actually useful. Because to understand string theory, complex
manifolds and index theory sheaf cohomology groups, all those funny things were
actually useful in doing basic things like constructing models of the elementary particles in string theory. I should give a slightly better explanation. In
physics there are the forces that we see for the elementary particles that
means basically everything except gravity. Then there's gravity which is so
weak that we only see it for macroscopic masses like the earth or the sun. Now
we describe gravity by Einstein's theory and then we describe the rest of it by
quantum field theory. It's difficult to combine the two together. Before 1984
you couldn't even make a halfway reasonable models for elementary particles
that included all the forces together with gravity. The advance that Greene and
Schwarz made with anomaly cancellation in 1984 made that possible. But to make
such models you needed to use a lot of the math that physicists had not used
previously but which was introduced by Atiyah and others when they solved the
instanton equations and you had to use complex manifolds, sheaf cohomology
groups and things that were totally alien to the education of a physics
graduate student back in the days when I'd been a student. So those things were
useful even at a basic level in making a model of the elementary particles with
gravity. And if you wanted to understand it more deeply you ended up using
still more maths. After string theory was developed enough that you could use
it in an interesting way to make models of particle physics it was clear that a
lot of previously unfamiliar math was important. I speak loosely when I say
previously unfamiliar because obviously it was familiar to some people. First
of all the to the mathematicians. Secondly in some areas like Penrose had used
some of it in his Twister theory. But broadly speaking unfamiliar to most physicists.
GF [00:15:46] So
we actually went very well in physics very very important for mathematicians in
mathematics a very important physicist they're working harmoniously alongside
each other. You go back to Leibnitz who used to talk about the pre
established harmony between math and physics. That was one of Einstein's
favorite phrases. Is there something you regard as a fact of life or is it
something you would regard as possibly can be explained one day will never be
explained. Do you have any comment at all on that relationship.
EW [00:16:09] Well, the intimate tie between math and physics seems to be a fact of life. I can't
imagine what it would mean to explain it. The world only seems to be based on
theories that involve interesting math and a lot of interesting math is at
least partly inspired by the role that it plays in physics. Not all of course.
GF [00:16:25] But
does it inspire you when you see a piece of math that's very relevant to
physics and vice versa when you're helping mathematicians. Does that motivate
you in some way to think you're on the right track.
EW [00:16:35] Well
when something turns out to be beautiful that does encourage you believe that
it's on the right track.
GF [00:16:39] Classic
Dirac. But he took it as he put it to almost a religion. But I sense you
are a little bit more skeptical, if
that's the right word or hard nosed about it I don't know.
EW [00:16:51] Having
discovered the Dirac equation, Dirac was entitled to commit its use to extremes, to put it that
way.
GF [00:16:58] Witten
has long been a leading pioneer of the string framework which seeks to give a
unified account of all the fundamental forces based on quantum mechanics and
special relativity. It describes the basic entities of nature in terms of tiny
pieces of string.
GF [00:17:14] Go
back to string theory. Do you see that as one among several candidates or the
preeminent candidate or what? I mean what do you see the status of that
framework in the landscape of mathematical physics.
EW [00:17:24] Id
say that string slash M theory is the only really interesting direction we have
for going beyond the established framework of physics by which I mean quantum
field theory at the quantum level and classical general relativity at the
macroscopic scale. So where where we've made progress that's been in the string
slash M theory framework where a lot of interesting things have been
discovered. I'd say that there's a lot of interesting things we don't
understand at all.
EW [00:17:48] But
you’ve never been tempted down the other route. The other options are not.
EW [00:17:52] I’m
not even sure what you would mean by other routes.
GF [00:17:54] Loop
quantum gravity?
EW [00:17:56] Those
are just words. There aren’t any other routes.
GF [00:17:58] Okay,
all right, fair enough.
GF [00:18:01] So there we have it. The preternaturally
cautious Witten says that if we want to discover a unified theory of all the
fundamental forces, string theory is the only interesting way forward that’s
arisen.
GF [00:18:17] Where
we are now strikes me as being quite an unusual time in particle physics
because so many of us were looking forward to the Large Hadron Collider, huge
energy available ,and finding the Higgs boson and maybe supersymmetry. And
yet it seems that we have gotten the Higgs particle just as we were hoping and
expecting. But nothing else that’s really stimulating. What are your views on where
we are now?
EW [00:18:39] My
generation grew up with a belief very very strong belief which by the way was
drummed into us by Steven Weinberg and by others. That when physics reached the
energy scale at which you can understand the weak interactions. You would not
only discover the mechanism of electroweak symmetry breaking but you’d learn what
fixes its energy scale as been relatively low compared to the scale of gravity.
That’s what ultimately makes gravity so weak in ordinary terms. So, it came as a
big surprise that we reached the energy scale to study the W and the Z and even
the Higgs particle without finding a bigger mechanism behind it. That’s an
extremely shocking development in the context of the thinking that I grew up
with.
EW [00:19:22] There
is another shock which also occurred during that 40 year period which possibly
should be comparative. This is the discovery that the acceleration of the
expansion of the universe. For decades physicists assumed that because of the
gravitational attraction of matter the expansion of the universe with be
slowing down and tried to measure it. It turned out that the expansion is
actually speeding up. We don't know this for sure it seems quite likely that
the results from the effects of Einstein's cosmological constant which is
incredibly small but nonzero. The two things the very very small but nonzero
cosmological constant and the scale of weak interactions the scale of
elementary particle masses which in human terms can seem like a lot of
energies. But it's very small compared to other energies in physics. The two
puzzles are analogous and they're both extremely bothersome. These two puzzles
although primarily the one about gravity which was discovered first are perhaps
the main motivation for discussions of a cosmic landscape of vacua. Which is an
idea that used to make me extremely uncomfortable and unhappy. I guess because
of the challenge it poses to trying to understand the universe and the possibly
unfortunate implications for our distant descendants tens of billions of years
from now. I guess I ultimately made my peace with it recognizing that the
universe hadn't been created for our convenience.
GF [00:20:43] So you come to terms with it.
EW [00:20:45] I've
come to terms with the landscape idea and the sense of not being upset about
it. As I was for many years.
GF [00:20:49] Really
upset?
EW [00:20:50] I
still would prefer to have a different explanation but it doesn't upset me
personally to the extent it used to.
GF [00:20:56] So
just to conclude what would you say the principal challenge is all down to
people looking at fundamental physics.
EW [00:21:01] I
think it's quite possible that new observations either in astronomy or
accelerators will turn up new and more down to earth challenges. But with what
we have now and also with my own personal inclinations it's hard to avoid
answering new terms of cosmic challenges. I actually believe that string slash
M theory is on the right track toward a more deeper explanation. But at a very
fundamental level it's not well understood. And I'm not even confident that we
have a good concept of what sort of thing is missing or where to find it. The
reason I'm not is that in hindsight it's clear that a view we might have given
in the 1980s was what was missing was too narrow. Instead of discovering what
we thought was missing instead we broadened the picture in the 90s in
unexpected directions. And having lived through that I feel it might happen
again.
EW [00:21:49] To
give you a slightly less cosmic answer if you ask me where I think is the most
likely direction for another major theoretical upheaval like happened in the
80s and then again in the 90s. I've come to believe that the whole it from qbit
stuff, the relation between geometry and entanglement, is the most interesting
direction.
GF [00:22:12] It
from bit that was a phrase coined by the late American theoretician John
Wheeler who guessed that the stuff of nature the "it" might
ultimately be built from the bits of information. Perhaps the theory of
information is showing us the best way forward in fundamental physics. Witten
is usually wary of making strong pronouncements about the future of his
subjects. So I was struck by his interest in this line of inquiry, now
extremely popular.
EW [00:22:39] I
feel that if in my active career there will be another real upheaval that's
where it's most likely to be coming [xxx]
EW [00:22:47] I
had a sense both in the early 80s and in the early 90s. I had a sense a couple
of years in advance of the big upheavals where they were most likely to come
from it and those two times did turn out to be right. Then for a long long time
I had no idea where another upheaval might come from. By the last few years
I've become convinced that it's most likely to be the it from qbit stuff of
which I have not been a pioneer now. But I was not one of the first to reach
the conclusion or a suspicion that I'm telling you right now. But anyway it's
the view I've come to.
GF [00:23:20] There's
a famous book about night thoughts of a quantum physics. are there night
thoughts of a string theorists is where you have a wonderful theory that's developing you know unable to test it. Does that ever bother you.
EW [00:23:31] Of
course it bothers us but we have to live with our existential condition. But
let's backtrack 34 years. So in the early 80s there were a lot of hints that
something important was happening in string theory but once Greene and Schwartz
discovered the anomaly cancellation and it became possible to make models of
elementary particle physics unified with gravity. From then I thought the
direction was clear. But some senior physicists rejected it completely on the
grounds that it would supposedly be untestable. Or even have cracked it would
be too hard to understand. My view at the time was that when we reached the
energies of the W, Z and the Higgs particle we'd get all kinds of fantastic new
clues.
EW [00:24:11] So.
I found it very very surprising that any colleagues would be so convinced that
you wouldn't be able to get important clues that would shed light on the
validity of a fundamental new theory that might in fact be valid. Now if you
analyze that 34 years later I'm tempted to say we were both a little bit wrong.
So the scale of clues that I thought would materialize from accelerators has
not come. In fact the most important clue possibly is that we've confirmed the
standard model without getting what we fully expected would come with him. And
as I told you earlier that might be a clue concerning the landscape. I think
the flaw in the thinking of the critics though is that while it's a shame that
the period of incredible turmoil and constant experiment and discovery that
existed until roughly when I started graduate school hasn't continued. I think
that the progress which has been made in physics since 1984 is much greater
than it would have been if the naysayers had been heeded and string theory
hadn't been done in that period.
GF [00:25:11] And it's had this bonus of benefiting mathematics as well.
EW [00:25:14] Mathematics
and by now even in other areas of physics because for example new ideas about
black hole of thermodynamics have influenced areas of condensed metaphysics* even in the study of quantum phase transitions, quantum chaos and really other
areas.
GF [00:25:31] Well
let's hope we all live to see some revolutionary triumph that was completely
unexpected that's the best one of all. Edward thank you very much indeed.
EW [00:25:38] Sure
thing.
GF [00:25:43] I’m
always struck by the precision with which Edward expresses himself and by his
avoidance of fuzzy philosophical talk. He's plainly fascinated by the closeness
of the relationship between fundamental physics and pure mathematics. He isn't
prepared to go further to say that their relationship is a fact of life. Yet no
one has done more to demonstrate that not only is mathematics unreasonably
effective in physics physics is unreasonably effective in mathematics.
GF [00:26:15] This
Witten said makes sense only if our modern theories are on the right track. One
last point. Amazingly Witten is sometimes underestimated by physicists who
characterize him as a mathematician, someone who has only a passing interest in
physics. This is quite wrong. When I talk with a great theoretician Steven
Weinberg he told me of his awe at Witten's physical intuition and elsewhere
said that Witten's got more mathematical muscles in his head than I like to
think about. You can find out more about Witten and his work in my book
"The universe speaks in numbers.

* Condensed matter physics. I am sure he says condensed matter physics. But really I think condensed metaphysics fits better.

* Condensed matter physics. I am sure he says condensed matter physics. But really I think condensed metaphysics fits better.
Not really important but the final EW comment actually appears to be by GF, a continuation of the previous paragraph.
ReplyDeleteThat's right of course, I fixed that. Thanks for pointing out.
DeleteWell...that last comment is labeled EW and it’s certainly not...
ReplyDelete��
This doesn't need to be published.
ReplyDeleteI didn't listen to all of the interview, but to react to your request about [xxx] in interview transcription (in some places there are a few words from what was already transcribed, I hope this makes some sort of sense):
12.14: rubber inner tube? (kind of makes sense)
12.53: thinly attended talk, erm, anyway
13.04: but that  historians of Morse theory  they
13.13: that hills and dales talk
13.42: started going front and centre
13.50: more maths (transcription has months, there are probably other places where similar incorrect transcription has occurred)
And two more where I couldn't completely fill in the gaps:
15.46: in his 
16.51: commit to his 
ksd,
DeleteThanks so much for this.
12:14 The "rubber inner tube" doesn't really make sense to me.
12:53 I changed that.
13:04 Yes! I'd never have figured that out.
13:13 What's hills and dales? Doesn't make any sense to me, help!
13:42 Okay. Is that a thing people say? Never heard this before.
13:50 I changed this
15:46 I don't know what this refers to, sorry, can you be more specific?
16:51 There still seems to be a word missing. What I hear is "was very entitled to commit to his strings, to put it that way" but that doesn't make any sense.
Regarding "Hills and Dales", I believe this must have been the title of the talk, at least he wrote a paper with that title. I added a reference for this.
DeleteA "rubber inner tube" is a donutshaped object that used to go inside an automobile tire. You may have to be fairly old to remember them ... they make tires differently now. Try googling it on "Google images".
DeletePeter,
DeleteThanks for clearing this up. I had no idea this is an actual word, sorry!
First [xxx] (in EW [00:09:51]): "Richard Ward, Penrose's doctoral student".
ReplyDeleteHere are a few mistakes that aren't tagged with [xxx]:
In the first paragraph, GF says "More than that..." not "Or on that..."
EW [00:04:19]: He says "even though I forgot [or left out?] a lot of the big discoveries", not "even after I'd ordered the big discoveries". Also in the same paragraph he says "which at the time I assumed would happen because it had been going on for a quarter century", not "which at the time I think what happened was even going on for a quarter century" (!).
EW [00:05:33]: Replace "General Steve Weinberg" with "There was Steve Weinberg" (and put a full stop between "physicists" and "There"). Also replace "discussion meaning" with "discussion meeting".
EW [00:06:28]: Get rid of the first full stop (the sentence doesn't end there) and replace "my advisor David Gross said" with "my advisor David Gross, so". Replace "they teach you what to do when quantum effects were small but no one tells you what to do when you don't have extra big there's no general answer" with "they teach you what to do when quantum effects are small, but no one tells you what to do when quantum effects are big, there's no general answer".
EW [00:07:32]: Replace "there is no math" with "there was new math".
GF [00:08:02]: The first word ("applications") belongs to the end of the previous paragraph and is spoken by EW not GF. Replace "Witness" with "Witten's".
EW [00:08:32]: Replace "could go on for a few months" with "but I could be off by a few months". Replace "cosmology" with "cohomology".
That's all I have for now (stopped listening at around the 10 minute mark). I will probably come back to this later...
Hi Jesse,
DeleteThanks so much. I had meanwhile made several of these changes already, but added the rest you point out. Esp the "doctoral student" I couldn't figure out!
If you come back, please make sure to reload the page.
Condensed metaphysics! Please don't change it!! 😄
DeleteHaha, I hadn't seen that. I actually thought you were saying the whole interview is "condensed metaphysics".
DeleteThank you for the transcription. I much prefer reading then listening to a talk or video.
ReplyDeleteHello Sabine,
ReplyDeleteI note on occasion you use a very dry/drol sense of humor, so when you said "I used an app called “Trint” which seems to works okay." in your opening paragraph I didn't know if you were just drawing attention to transcribing software making mistakes or if you meant to say 'seems to work okay' instead of 'seems to works okay'
CFT,
DeleteSorry, typo, I fixed that. Thanks for pointing out.
I gave a quick listen to some xxx you have marked and I got this:
ReplyDeletebut not [xxx] for the original reasons
but not per se for the original reasons
it still had a puzzling [xxx].
it still had a puzzling behaviour.
[xxx] say what morse
Would you like to say what morse
like for example a [xxx]
this could be  rubber interdune  but I am not sure about the second word.
Cheers!
Ugis
Thanks, Ugis, this is great!
DeleteWhere can I listen to it?
ReplyDeleteShippey,
DeleteYou can listen to it on this website. Or use the link in the first sentence of my blogpost.
from the transcript
ReplyDeleteEW [00:17:48] But you’ve never been tempted down the other route. The other options are not.
EW [00:17:52] I’m not even sure what you would mean by other routes.
GF [00:17:54] Loop quantum gravity?
EW [00:17:56] Those are just words. There aren’t any other routes.
Bee
do QG researchers typically only focus on strings and completely ignore LQG?
any idea why Witten is so antiLQG?
I don't know Witten, so, I am sorry, I do not know what his misgivings are about LQG. A lot of string theorists seem to think that LQG doesn't have a graviton propagator and hold that against the theory. What I find somewhat more perplexing though is that Witten doesn't seem to be aware of asymptotically safe gravity, or at least doesn't consider it to be viable for whatever reason.
Deletewhat if nature isn't super symmetric or is only 4 dimensional, it seems Witten is putting all his eggs on an unproven basket.
DeleteThanks for transcribing this!
ReplyDeleteAt 13:50 "sheaf cosmology groups" has got to be "sheaf cohomology groups", because the latter exist and the former don't.
Hi John,
DeleteThanks for pointing out. I had fixed this in a few places, but must have missed it in other. The "cohomology" generally came out as cosmology. And sometimes it was sheep cosmology :o) Oh, and Witten usually was a "witness".
sheaf cohomology was the most important chunk. Here some tiny pieces:
Delete But nothing else that’s really [xxx]. > … really stimulating
 which possibly should be [xxx]. > … should be comparative.
Thanks, I made these changes!
DeleteInteresting, that Witten was shocked that no supersymmetry was found at the LHC. I was so deeply impressed at the time by Alain Connes' derivation of the Standard Model, which doesn't require supersymmetry, that I wrote in Sept. 2010:
Delete"What will not be found: Supersymmetric particles (and I would bet a fortune one that)."
Yes. I'm shocked Witten was shocked.
DeleteWe've known all along the Standard Model does not require supersymmetry. What has Connes to do with that?
I would have been shocked if supersymmetry had been discovered, since I used string theory to prove that supersymmetry will not be discovered at the LHC.
DeleteConnes said:
Delete"This prediction (mass of the Higgs particle) was based on the hypothesis of the 'big desert', namely that there will be no new physics up to the uniﬁcation
scale, besides the Standard Model coupled to gravity. Thus it was a bit like trying to see a ﬂy in a cup of tea by looking at the earth from another planetary system. But very strangely the model also predicted the correct mass of the top quark, and a surprising number of mechanisms such as the Higgs and the see saw mechanisms."
Moreover, he wrote:
"The noncommutative approach predicts all the fermionic and bosonic spectrum of the standard model, and the correct representations. One can also take as a prediction that there are no other particles to be discovered, except for the three scalar ﬁelds: the Higgs ﬁeld, the singlet ﬁeld and the dilaton ﬁeld."
Except that his prediction for the Higgs mass was wrong. In any case, we have all known since the invention of supersymmetry that the standard model does not require supersymmetry.
DeleteHis prediction was actually right, he only mistakenly neglected a term.
DeleteThe important point of his derivation is that the spectral action applies to the GUT scale and it contains no supersymmetry. He then "runs it down" to the SM energy scale. This is all extremely minimalistic and not the kind of Rube Goldberg machine supersymmetric people prefer.
"Except that his prediction for the Higgs mass was wrong."
DeleteThat was already corrected here: https://arxiv.org/abs/1208.1030
Sure, experiment falsified an earlier (2007!) noncommutative Standard Model, but progress has been made in more recent years, pointing to physics beyond the Standard Model while staying compatible with experiment. It is a small group of mathematical/theoretical physicists working on this, but definitely worth taking a look at if you ask me ;)
DeleteThanks for the transcript!
If you predict a measurement after it's been made it's not a prediction.
DeleteBut it just corrected an earlier calculation. The math was already there, he didn't change the formalism after the discovery of the Higgs! Look, Sabine, if you find any fault with Connes' math, let us know. But otherwise, the intellectually honest position would be to remain in silence. I'm fed up with the same rubbish argument (i.e. 'he corrected the prediction after the measurement'), especially comming from people who aren't even acquainted with the relevant math (operator algebra, spin manifolds, spectral triples, etc).
DeleteOf course it's not. But the interesting thing is that the scalar field they used to correct the wrong initial prediction was already there in the original papers, i.e., *before* the measurement, they simply ignored its contribution for the wrong reasons. Anyway, it's not my intent to enter into the semantics of what is and what is not a correct prediction, but just to point out that the story is more interesting than a mere wrong prediction.
DeleteI read several of Connes' papers. I will not claim that I understood them, but I understood enough to know that he did not just correct a mistake. He did, as a matter of fact, correct the prediction after the measurement, regardless of how much you dislike that.
DeleteYes, but what he did is not the usual "make the mass bigger" that susy advocates do whenever experiment shows no superpartners. He did, as a matter of fact, correct the prediction after the measurement but by taking into account elements that were already predicted by his model and which he neglected in his initial calculation, regardless of how much you dislike that.
DeleteI'd like to be precise at this point: in 2012 Ali Chamseddine and Alain Connes did not "correct the prediction after the measurement", but merely found a natural extension of the Standard Model formulated in the same formalism of noncommutative geometry that "restores the consistency of the noncommutative geometric model with the low Higgs mass" (last phrase in the abstract of their arXiv:1208.1030, and confirmed by others)
DeleteIt's not even a retrodiction, because there's a new parameter that has to be adjusted (value depends on the unification scale) to get 125 GeV  the constant n, introduced on page 3, also see figure 2 on page 9. What changed is that such a Higgs mass was actually inconsistent with their simpler model ("invalidating the positivity of the coupling at unification which is an essential prediction of the spectral action", page 2), but is consistent with the expanded model.
Deletealeazk,
DeleteYou are wrong in thinking that I dislike that. What I dislike are false statements, like the ones you have made. I suggest you stop doing it.
Walter,
DeleteWell, if you want to say that they argued it's no longer a prediction, fine with me. In any case, the statement that Connes' prediction for the Higgs mas was right is incorrect. The only reason I can think of that Markus would make such a statement is that he was hoping no one here would know any better.
Fwiw, the only correct prediction of the Higgs mass that I know of is that by Wetterich et al, which no one seems to pay any attention to. Why is that, I ask you? Is it that asymptotically safe gravity isn't pretty enough because it doesn't unify three forces into one unified force?
"The only reason I can think of that Markus would make such a statement is that he was hoping no one here would know any better."
DeleteNo, I am just trying to rephrase what Connes said:
https://www.youtube.com/embed/4RzeY0ZF4kI?start=360
"I am just trying to rephrase what Connes said"
DeleteOkay, thanks. That certainly explains it.
@Mitchell Thanks for that hint. That figure 2 looks more like a "Higgs mass landscape" than a Higgs mass prediction :)
Delete@Sabine I agree, no prediction here it now seems to me.
It's indeed not the best way to frame it as a "prediction" or "retrodiction" or whatever of a *single value* for the mass. What the model gives is a certain range of possible mass values that are compatible with the model. But the model is tight enough that this range is bounded from both sides and, therefore, there are values which are incompatible with the model and that would falsify it if observed. And, indeed, in their first model, the range of compatible values was 160 to 180 GeV. That model was, of course, falsified by the observation of the value being 125 GeV. Now, they came back to their calculations and realized that they ignored the full contribution of a scalar field that was already predicted by the spectral action (one must realize that the spectral action and some other theorems, severely constraint the field content of the model, one cannot add just whatever field one desires.) With the full contribution of this field (which involves a minimal extension of the SM) now being taken into account, the range of mass values (for the Higgs field) compatible with the model now contains the observed value.
Delete"Is it that asymptotically safe gravity isn't pretty enough because it doesn't unify three forces into one unified force?"
DeleteAs you have argued before, the quest for unification per se is not completely justified in terms of *directly* looking for the answer of a well posed problem (which is defined as a contradiction between different parts of our current knowledge.) But, one could argue that unification (of all forces, gravity included) can give clues to the resolution of an actual problem, quantuam gravity, since it would imply that at that energy scale things are much more subtle than the mere quantization of gravity alone. Now, you could say, why overcomplicating it in that way? We don't know if unification is correct, you are just adding an additional, illmotivated, and potentially superfluous thing to the original problem. That would be true if the proposed unification involves currently unobserved features (sure, it may be falsifiable, but we could add pretty much any thing to the problem if we follow that logic.) And this is indeed the case with many of the popular unifications. But, what makes Connes' model interesting, is that it's pretty much a fully geometrical *reformulation* of the SM, without any additional and controversial hypothesis (with the exception, perhaps, of that additional field, but it's a minimal extension, i.e., no new spacetime dimensions or an arbitrary amount of new unobserved particles.) That is, the "unification" is practically already here, with the currently observed data. That's really a very interesting discovery that is not getting the deserved attention. And, unlike what you tacitly suggest in your comparisom with asymptotically safe gravity, Connes' model is actually a marginal research area, with only Connes himself, and collaborators, and a small group in the Netherlands working on it (as far as I know.)
"... the only correct prediction of the Higgs mass that I know of is that by Wetterich et al, which no one seems to pay any attention to."
DeleteAt least I did so early on and was pretty impressed by their prediction. But as in the case of the noncommutative standard model, no low energy supersymmetry is required. So why was Witten so shocked? Would there be a problem if supersymmetry was broken at very high energies instead?
MarkusM,
DeleteNo, it would not be a problem for string theory if supersymmetry was broken at much higher energies. I explained this here.
It it a problem for gaugecoupling unification, if that's something you believe in.
Yes, why was Witten shocked? I can only guess that he actually believed in naturalness arguments. Someone should tell him to read my book ;o)
@11:50 ...But at a certain point, I think when I was in a swimming pool in Aspen Colorado, I remembered [xxx]. and actually Atiyah...
ReplyDeletexxx is Raoul Bott a HungarianAmerican mathematician who worked with Atiyah.
Miguel,
DeleteThanks so much, you are awesome!
Around 15 minutes I think he's saying "Secondly in some areas like Penrose had used some of it in his twistor theory."
ReplyDeleteyes, now I also can hear it.
DeleteIn “Road to Reality” there is the chapter “33.9 Twistor sheaf cohomology”  it is about gluing of patches …
It is unbelievable, that only with the right (predictive) model we can see/hear what someone or nature is telling us all the time.
Witten developed what has been called the twistorstring minirevolution. Twistor theory is CP^3 with the isometry group SU(2,2). The projective twistor space CP^3 ~ SU(2,2)/SO(4,1)×U(1) with is isotopy group SO(4,1). This connects with the Maldecena AdS/CFT and Mtheory.
DeleteIf you want to read a really great paper by Witten that does not lean on string theory that heavily I suggest Three Dimensional Gravity Revisited, or a title of that sort. It is almost poetry in my opinion on how Witten links results of analysis and topology with physical theory.
Theoretical physics has a lot of structure developed, which runs from twistor theory to supersymmetry and string to unification based on group theory to attempts to make forms of general relativity quantizable in a direct setting  LQG or dynamic triangles etc. We have no general anchor for this. There is a sort of crisis here, which in one sense is a wonderful thing to be facing.
Lawrence,
DeleteThis Witten paper is indeed impressive how he juggles with the various mathematical structures. It would take me some time to understand most of the details and to grasp what you already can sense as almost poetry.
It is impressive, but on the other hand, it is also very restrictive since the EinsteinHilbert action lives in D=2+1 and needs Λ<0. We live in D=3+1 with Λ>0. Also, the CFT in AdS/CFT is restricted to D=2.
(And the conformal algebra in D = 2 has an infinitedimensional extension, the Virasoro algebra, unlike in D=3 or D=4 where it has finitely many generators.)
One fascinating application of CFT are continuous/(second order) phase transitions, where scale invariance is actually taking place. Already 1970 Polyakov conjectured not only scale but more general conformal invariance [1]. Recently [2, 3] the additional symmetry in the special conformal transformation was used to calculate critical exponents in D=3.
Renormalization group and lattice methods work together to explore the ‘“kink” on the boundary of the region allowed by the constraints of crossing symmetry and unitarity.’ [3].
The transition to BoseEinstein condensate (BEC) and the superfluid transition of helium belong to the same universality class. Both are in O(N) with N=2. Phases in statistical field theory are characterized by the symmetry G of the free energy and the symmetry H of the ground state. The free energy, aka Wilsonian effective action represents the struggle between energy E and entropy S in F=ETS (F=log Z).
I find it fascination that a second order phase transition washes away all memory of the underlaying details, whether it is He or rubidium87 atoms. Kind of a major information loss.
(I should have added here also the link where Sabine talks in her book about decoupling, effective field theories, i.e. the renormalisation group)
You said “There is a sort of crisis here, which in one sense is a wonderful thing to be facing.”
Yes, indeed, it is and I guess we have to rethink sentences like “information is never lost” not only at the horizon of forming and evaporating black holes, a topological transition.
ceterum censeo:
Our universe is not evolving exclusive unitarily – so far, we ignored the measurement problem.
And (observer independent triggered) measurements are the source for random flukes all the time.
The variable “time” in QM is just used to calculate probability amplitudes and this of course must be unitary.
And we already know how Fermions and Bosons evolve on a curved nonquantized spacetime.
This separation of QM “time” immediately makes it plausible why virtual particles are, well, virtual, way off massshell and entanglement simply is nonlocal.
This all has to do with why it is that cyclic imaginary time is connected to temperature, besides being just an analytic continuation …
Whether this separated QM “time” also has some connection with the second “time” variable in AdS, i.e. SO(2,2) would in principle be an interesting question, but I for now (and for reasons of limited time ;) just want to understand the world we are living in.

[1] A. M. Polyakov, “Conformal symmetry of critical fluctuations" (pdf)
At 12:14:
ReplyDelete"...example a [xxx], it’ll have saddle..." definitely sounds like "rubber inner tube" to my English ears.
In the earlier sentence he talks of a rubber ball, so I guess he's contrasting a rubber ball with a rubber inner tube (presumably it's a topology thing about a torus versus a sphere).
Bee,
ReplyDeleteWitten states he was 11 when he learned calculus. Is this common for physics professors and how old were you when you learned it?
This is what I make out:
ReplyDelete12:14 rubber inner tube
13:42 not to put words into your mouth
16:51 Having discovered the Dirac equation Dirac was entitled to commit its use to extremes, let's put it that way.
Thanks, I have added this.
DeleteThanks for this report from the enemy, i.e. those day dreaming, 'headtheclouds' string theorists with their infinity of unfalsifiable possibilities. :)
ReplyDeleteEW [00:16:35] ...doesn't hurt you believe, sounds like ...does encourage you to believe.
EW [00:25:14] ...have influenced areas of condensed metaphysics, sounds more like ...have influenced areas of condensed matter physics, to my ear at least.
But who knows, maybe Ted is suggesting that mathematics has somehow bolstered the assertions of the monotheisticly inclined dispensations, ...or something. :)
I liked the 'areas of condensed metaphysics' at 00:25:14,
ReplyDeleteguess it means more vonventional condensec matter physics
Without listening:
ReplyDeleteEW [00:17:24] ... scale. So where [where] we've made progress that's been in the string slash M theory framework ...
(probably doubled)
GF [00:15:46] ... Is there something you regard as a fact of life or is it something you would regard as possibly can be explained one day [word missing here?] will never be explained. ...
ReplyDeleteI have read a fair number of Witten's papers. They are long, but they are very approachable. He presents these advanced concepts in a clear and concise way.
ReplyDeleteHe points to something I have been pondering. He states:
EW [00:21:01] ... I actually believe that string slash M theory is on the right track toward a more deeper explanation. But at a very fundamental level it's not well understood. And I'm not even confident that we have a good concept of what sort of thing is missing or where to find it.
The connection between string types, with S. T and other transformations, is on the boundary of somethings else. The most general Mtheory is missing. Will that clear things up or will we end up with a far more ponderous and never ending or closing set of problems? Who knows.
In other words :
ReplyDeleteEW : " I know nothing, I come from Barcelona "
Is Edward Witten a hero that hurts science?
ReplyDeleteWhy even bother with Witten and co ? He may have an IQ of 190 or so, but since he's been barking up the wrong tree and will continue doing so till his final breath, what he says is a complete waste of time.
ReplyDeleteI noticed there are few more xxx remaining, so I checked those out. I got:
ReplyDeletesome of it [xxx] > some of it in (his) Twistor theory.  can not make out if there is "his" in between, and name of theory found through hearing+Googling. :)
The last one is really tough ... Tried to reduce speed of the audio by 10, 20, 30 and 50 percent and listen to it, but could not make sense.
GF 2:53 Sydney <— Sidney
ReplyDeleteEW 6:28 Sydney <— Sidney
GF 13:42 Greene <— Green & Schwartz <— Schwarz
EW 13:50 Greene <— Green (2 occurrences)
EW 23:31 Greene <— Green & Schwartz <— Schwarz
Hi Sabine, !
ReplyDeleteJust getting to this (been busy)
Thanks for the transcript. I didn't have much trouble figuring out the'xxx's. Nice program anyway.
Witten, what a wonderful mind.
 always a pleasure to to
read/hear.
If you'll permit me; a brief remark to the ,'peanut gallery'.
@ Dennis,  regardless frames
of reference (age, generation,
etc.)
How about this;
YOU go ahead and win
a Fields Award.
... and,
we'll let you piss
on any tree you want.
 you don't even have to bark.
. smartass.
Also, @ Adrian
 indeed, a topological
dimensional reference. (difference between a sphere and torus) basic, you can twist a torus any way you want and the surface equations stay the same.
( not to get all 'CallabiYau'
on ya ;)

also, 'hills and dales',
ReplyDelete part of 'first generation'
topology (c. 1870 ?)
 really cool.
Thanks again, Sabine.
Ich hoffe du hast einen
Guten Tag.
 Love Your Work.
Could it be that the 126 GeV prediction of Shaposhnikov & Wetterich for the Higgs mass arxiv.org/abs/0912.0208 (computed with a 173 GeV top quark mass)* gets more attention with the last measurements of a 171 GeV top quark mass reported by CMS & ATLAS from LHC data at 13 TeV https://twitter.com/bardot_cedric/status/1126494790110142464...?
ReplyDelete*Shaposhnikov & Wetterich mention a former pretty correct Higgs mass prediction (with different hypothesis) by Frogatt & Nielsen https://arxiv.org/abs/hepph/9511371.