Of Particular Significance

Author: Matt Strassler

You’re making it quite clear that you’re devoted to doing exactly what I find problematic: misleading and confusing people about the status of string unification by refusing to distinguish between two completely different technical issues.

So I stand accused by Peter Woit, in his latest comments on Tuesday’s post.

Dear readers, you are now the jury, and I stand by your opinion.  I do not want to mislead you — indeed, the purpose of this website is to be a reliable, trustworthy source of information about high-energy physics for the public —  and if I have misled you, I will correct the error.

If you look at Tuesday’s post, you will notice that at the start I stated (abridged here, but you can look back at the full text)

————–

String theory has several applications, and you need to keep them straight. Let me mention two.

  1. Application number 1: this is the one you’ve heard about. String theory is a candidate (and only a candidate) for a “theory of everything” — …[which] really means is “a theory of all of nature’s particles, forces and space-time”.
  2. Application number 2: String theory can serve as a tool. You can use its mathematics, and/or the physical insights that you can gain by thinking about and calculating how strings behave, to solve or partially solve problems in other subjects. (Here’s an example.)

———–

I carefully distinguished these two things, because the first is highly controversial, and the second — well, it should be much less controversial.   And also because I don’t work on the first, and I work occasionally on the second, when it proves helpful to the physics I’m interested in.  String theory sits in my toolbox, ready for use if needed.

Then I went on to mention that if string theory in its vanilla form were true in Application Number 1, then you would be able to make predictions for how particles would scatter that are characteristic of their being strings — although no one in the next century or maybe millenium is likely to be able to carry out such experiments.  Now, I thought this was also non-controversial, and made it as an off-hand comment; but Woit complains that this is highly misleading, and also that I’m misleading you on purpose.

He’s wrong that I’m misleading you on purpose, but he’s right that there is a risk of being misled and that the situation is indeed complicated.  So I added a note at the end of the post emphasizing the importance of the qualifier “in its vanilla form”, and that there’s no guarantee at all that string theory, even if it were true, wouldn’t be in ginger passionfruit soybean flavor, in which case the predictions would be different.  Apparently this wasn’t enough for Woit; I am still accused.

Personally, I have never thought string theory was likely to predict the particles and forces of nature in a unique way.  I am not surprised there’s a huge landscape of possibilities; I’m only surprised it seems so… conventional.  In my opinion, any sufficiently complicated quantum field theory or quantum gravity theory will likely have a landscape.    And so, in this sense, string theory is very unlikely to ever make predictions for exactly what particles and fields we will find in nature… these details will likely depend on the early history of the universe and on accidents of history that we are not going to learn about from the theory itself.  On this point, most high-energy physicists seem to be agreed right now.

Question for readers: Do you feel misled, by what I wrote Tuesday, into thinking that I believe that string theory currently makes, or is likely to make, unique and specific predictions about nature? 

If you do, then I screwed up, and I’ll correct the error.

Now I’d like to ask you another question.

In his comments to Tuesday’s post, Woit said that his “short-hand claim `string theory makes no predictions‘ is obviously a simplification of a very complicated situation, one that has been exploited for decades by string theorists making bogus claims for predictions.” [boldface mine]

Question: When Woit says “string theory makes no predictions“, and “string theorists making bogus claims for predictions“, do you think he means only Application Number 1, which is what he called “string unification”?

Or do you think he means Application Number 2 as well?  Am I, because I have string theory in my toolbox and I use it occasionally, accused by Woit of being a “string theorist making bogus claims for predictions”?  Or am I not, in fact, accused?

In particular, let me requote the accusation he levels at me:

“…misleading and confusing people about the status of string unification by refusing to distinguish between two completely different technical issues.

Question: Is Woit, in your opinion, “misleading and confusing people about the status of string theory as a whole by failing to distinguish between two completely different applications of the theory“?

Picture of POSTED BY Matt Strassler

POSTED BY Matt Strassler

ON September 19, 2013

Over the weekend, someone said to me, breathlessly, that they’d read that “Results from the Large Hadron Collider [LHC] have blown string theory out of the water.”

Good Heavens! I replied. Who fed you that line of rubbish?!

Well, I’m not sure how this silliness got started, but it’s completely wrong. Just in case some of you or your friends have heard the same thing, let me explain why it’s wrong.

First, a distinction — one that is rarely made, especially by the more rabid bloggers, both those who are string lovers and those that are string haters. [Both types mystify me.] String theory has several applications, and you need to keep them straight. Let me mention two.

  1. Application number 1: this is the one you’ve heard about. String theory is a candidate (and only a candidate) for a “theory of everything” — a silly term, if you ask me, for what it really means is “a theory of all of nature’s particles, forces and space-time”. It’s not a theory of genetics or a theory of cooking or a theory of how to write a good blog post. But it’s still a pretty cool thing. This is the theory (i.e. a set of consistent equations and methods that describes relativistic quantum strings) that’s supposed to explain quantum gravity and all of particle physics, and if it succeeded, that would be fantastic.
  2. Application number 2: String theory can serve as a tool. You can use its mathematics, and/or the physical insights that you can gain by thinking about and calculating how strings behave, to solve or partially solve problems in other subjects. (Here’s an example.) These subjects include quantum field theory and advanced mathematics, and if you work in these areas, you may really not care much about application number 1. Even if application number 1 were ruled out by data, we’d still continue to use string theory as a tool. Consider this: if you grew up learning that a hammer was a religious idol to be worshipped, and later you decided you didn’t believe that anymore, would you throw out all your hammers? No. They’re still useful even if you don’t worship them.

BUT: today we are talking about Application Number 1: string theory as a candidate theory of all particles, etc. (more…)

Picture of POSTED BY Matt Strassler

POSTED BY Matt Strassler

ON September 17, 2013

I attended a conference this past week celebrating two great physicists (Steve Shenker and Renata Kallosh) whom I got to know pretty well during the early part of my career. Unlike most of the conferences I’ve attended in recent years, there were no talks at all about the Large Hadron Collider; the community of speakers was largely drawn from experts on quantum field theory, quantum gravity, string theory and cosmology.

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Any one of the talks would require an extensive article, especially since the required background material isn’t currently explained on this website. So rather than get bogged down in details, I thought I’d try to give you more of the general flavor — reflective, perhaps, of the tenor of the field at the moment. I’ll cover a couple of the talks later, if time permits (though I’m a bit under the gun at the moment…)

If you like to put labels on people, you’d probably call most of the speakers “string theorists.” This is a useful label if you’re in a hurry and not very interested, or if you want to abuse people, but not so useful if you want to actually understand their research. Indeed, out of about 21 talks, there were 3 on string theory.  That said, many of the speakers have in the past done some research in string theory, and many of the talks owe a debt to lessons that have been learned from string theory.

So what were the talks about?  What are these people actually doing? (more…)

Picture of POSTED BY Matt Strassler

POSTED BY Matt Strassler

ON September 16, 2013

This week I’m at Stanford University, where I went to graduate school, attending a conference celebrating the illustrious careers of two great physicists, Renata Kallosh and Steve Shenker.

KalloshenkerColorPhotosBWBackground

Kallosh is one of the world’s experts on black holes, supersymmetry,  cosmic inflation (that period, still conjectural but gaining acceptance, during which the universe is suspected to have expanded at an unbelievable rapid rate), and “quantization” (i.e., on how to define quantum field theories and quantum gravity theories so that they actually make mathematical sense — which is not easy to do correctly). Much of her work concerns supersymmetry and its application to quantum gravity and to superstring theory. Her technical expertise and her inventiveness are legendary, as is her friendly enthusiasm. I’ve known her since I was a graduate student; she was one of a number of famous scientists from the former Soviet Union who came to the United States around 1988-1989.  Aside from just interacting with her within Stanford’s small community of theoretical physics students, postdocs and faculty, I also attended two courses that she taught on advanced topics, one on supersymmetry and one on quantization.

Shenker is famous for a number of papers that significantly changed our understanding of quantum field theory, quantum gravity and string theory. His fame derives in part from his ability to extract deep insights about physics from just a few mathematical clues — often ones that only he recognizes as being clues in the first place. Shenker was a faculty member at Rutgers when I was a postdoctoral researcher there in the mid-90s. (He later moved to Stanford.)  I cannot count the profound lessons that I learned during those years from him (and the other Rutgers faculty), both at our daily group lunch, and in the lounge where several of the faculty and other postdocs would regularly gather in the mornings. And I was even fortunate enough to write a paper (on black holes and their entropy) together with him and another then-postdoc, Dan Kabat. Aside from his down-to-earth no-nonsense style, and his strong support of young people and their ideas, one thing I remember well about Shenker is that it was perilous to say anything interesting to him while walking back from lunch on a bitterly cold day. He would stop and think… and the rest of us would freeze.

In the wider world of the public, and especially the blogosphere, Kallosh and Shenker would probably be labelled as “string theorists.” Such terminology would be somewhat crude, for it would fail to capture the range and depth of their careers. Appropriately, the talks at the conference so far have ranged widely, including general attempts to make some sense of quantum gravity,  discussion of the information-loss problem of black holes (the so-called “firewall” problem), unexpected subtleties in how quantum field theory works (yes, we are still learning!), new ways of thinking about the physics of electrical conductors and insulators, and advances in our understanding of cosmic inflation. And there were even a couple of talks on string theory.  (That said, the long shadow of string theory, and its direct and indirect influence on many other subfields, can be palpably felt at this conference.  More on that subject another day.)

Since I’ve been so busy with Large Hadron Collider physics in recent years, and haven’t been following these subfields closely, it’s been a very educational conference for me.  I’ll describe some of the talks later in the week.

Picture of POSTED BY Matt Strassler

POSTED BY Matt Strassler

ON September 11, 2013

This week I’m in California, at a conference celebrating two famous professors, from whom I learned an enormous amount when I was a graduate student and postdoctoral researcher. More on this later in the week.

Today, I just want to let you know I have completed the core of my naturalness article, which I began writing a couple of weeks ago. (more…)

Picture of POSTED BY Matt Strassler

POSTED BY Matt Strassler

ON September 9, 2013

Done: All three parts of my lecture for a general audience on String Theory are up now…

Beyond the Hype: The Weird World of String Theory (Science on Tap, Seattle, WA, September 25, 2006). Though a few years old, this talk is still very topical; it covers the history, development, context and impact of string theory from its earliest beginnings to the (then) present.

Be forewarned: although the audio is pretty good, this was an amateur video taken by one of the organizers of the talk, and because the place was small and totally packed with people, it’s not great quality… but good enough to follow, I think, so I’ve posted it.

  1. Part 1 (10 mins.): String theory’s beginnings in hadron physics and the early attempts to use it as a theory of quantum gravity.
  2. Part 2 (10 mins.): String theory was shown to be a mathematically consistent candidate for a theory of all of quantum gravity and particle physics, and became a really popular idea.
  3. Part 3 (9 mins.): How string theory evolved through the major technical and conceptual advances of the 1990s.

By the way, if you’re interested in other talks I’ve given for a general audience, you can check out my video clips, which include a recent hour-long talk on the Quest for the Higgs Boson.

Picture of POSTED BY Matt Strassler

POSTED BY Matt Strassler

ON September 6, 2013

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