Category Archives: String Theory

Sunday Egan

Greg Egan writes,

I wish we had a good word in English that meant only “the shattering majesty of reality”, so atheists could make it abundantly clear that they’re aware of this majesty, but don’t imagine that it’s due to anything that resembles a person in any way. But what atheists absolutely should not do is say “Well, I’m going to use the word ‘God’ to mean ‘the awesomeness of the universe’”. This is helpful for selling lots of tenth-rate pop-science books with “God” in their titles, and for winning the Templeton prize, but even when it’s not plain venal and dishonest it’s linguistically sloppy.

This is why I describe quantum mechanics as Loki playing dice with the Universe. Come on, Loki may be subtle, but he’s not malicious, right?

We can take this one step further. There is a model of the early Universe called string gas cosmology, in which the reason why the Cosmos has three dimensions is essentially the same as the reason why knots can exist in three dimensions but not more or less. (In 2D, there’s not enough “room” for a string to overlap itself, and in 4D or higher, there’s too much room, and a knotted loop can always “slip free”, returning to a simple circle.) I wonder if the Templeton Foundation will pay me for declaring that the Cosmos is the way it is because Aphrodite likes to get tied up in knots?

(Hah! And you thought I was going to quote a passage from Quarantine, didn’t you?)

Salvinorin A Acts on k-Opioid Receptors

Blogging on Peer-Reviewed ResearchReally, that’s about the size of it (although I do get a small kick from writing about psychedelic drugs immediately after wallowing in cultural heresies like multilingualism).

Salvia divinorum, which is scientist’s Latin for “diviner’s sage,” is a smokable plant which induces powerful but relatively short-lasting hallucinations. The main active ingredient, salvinorin A, acts on a class of nerve-cell input devices known as “κ-opioid receptors.” It’s a κ-opioid agonist, which is the opposite of antagonist — inducing activity, rather than suppressing it. Folks in the know had hypothesized that salvinorin A acted on the κ-opioid receptors, but Catherine B. Willmore-Fordham of Ohio Northern University and her colleagues were recently able to prove it. Of course, they had to work with rats, instead of people.

The paper, damnably, is locked behind a subscription wall, because Neuropharmacology is an Elsevier journal. (You did hear that Elsevier publishes a journal called Homeopathy, didn’t you? I guess they had to make up for the lost profits of not running arms fairs anymore.) Still, ye olde trusty webloggers will come through in a pinch:
Continue reading Salvinorin A Acts on k-Opioid Receptors

Superconductors via Superstrings

Blogging on Peer-Reviewed ResearchNature has an article about a nifty and relatively new application of ideas born out of string theory: to understand what happens in high-temperature superconductors! The story goes something like this.

Take a sample of some material which can conduct electricity, and apply two kinds of outside influence upon it. First, stick it in a magnetic field pointing in some direction, and second, apply a temperature gradient in a direction perpendicular to the magnetic field. In some substances, an electric field will appear, perpendicular to both the magnetic field and the temperature gradient. This is called the Nernst effect. It doesn’t happen very much with ordinary metals, but in semiconductors — like silicon or germanium — it can be quite noticeable. It also appears in some superconductors, like Y-Ba-Cu-O and CeCoIn5 to name but two.

Sean A. Hartnoll et al. have cooked up a theory to explain the Nernst effect and other behaviors seen in the cuprate superconductors, ceramic compounds containing copper. Looking at the situation near the phase transition, where a substance is “on the verge” of changing from insulator to superconductor, they developed a theory involving the magnetic field, call it [tex]B[/tex], and fluctuations in the material’s density, [tex]\rho[/tex]. Then they looked at this theory in the conceptual mirror known as the AdS/CFT correspondence. This connection between seemingly disparate ideas takes you from a “conformal field theory,” the sort of math involved with the superconductor problem (among other things), to a theory of gravity in a type of universe called anti-de Sitter space. In this mirror-world description, the perturbations in [tex]B[/tex] and [tex]\rho[/tex] become magnetic and electric charges of a black hole sitting in the AdS universe!
Continue reading Superconductors via Superstrings

Advanced String Theory Videos

If you’re looking for “higher dimensions of the spirit” or “quantum healing,” you’ve come to the wrong place.

Instead, we’ve got real science, for free. All you need is time! At the SciTalks blog, Jon Shock recommends several videos on advanced topics in string theory. The Theoretical Advanced Studies Institute in Elementary Particle Physics comes highly recommended; it’s got a whole slew of videos on the AdS/CFT correspondence.

Dr. Shock on Extra Dimensions

Jonathan Shock has been working with the SciTalks people to make their site a repository of high-quality, informative physics material. At the SciTalks blag, Dr. Shock provides an introduction to the idea of “extra dimensions.” These aren’t woo-tastic flights of fancy like some “dimensions of the spirit,” but rather ideas we can explore with mathematical rigor in order to understand both their properties as abstract concepts and, perhaps, some features of the physical world.

We’re treated to a description of how to build a four-dimensional hypercube by shifting a cube at right angles to itself, along a fourth direction perpendicular to the cube’s three axes. That’s a hard idea to fit into a brain! However, by projecting the process down — essentially “casting shadows” of the higher-dimensional shapes — we can make a video of it.

As always, the math matters:
Continue reading Dr. Shock on Extra Dimensions

Overbye on Hunting the Higgs

Dennis Overbye has an article in today’s New York Times on the search for the Higgs boson, and naturally, I’ve got complaints about it. It’s a pretty good piece: Overbye can do solid work (he went a little overboard looking for journalistic “balance” in the Bogdanov Affair, but that was a while ago). Still, I wouldn’t be myself if I couldn’t gripe and grouse.

First, I’m definitely not alone in asking people to please stop saying “God particle.” Leon Lederman has a great deal to answer for after coining this term; I’ve never heard or seen physicists use it seriously, and it keeps inviting unwarranted metaphors. (Incidentally, there was once detected an “Oh-My-God Particle,” a cosmic-ray proton of astonishingly high energy; for recent developments in this ultra-high-energy regime, see here. Physicists joke about the term, but they don’t use it.)

Second, this part rubs me the wrong way:
Continue reading Overbye on Hunting the Higgs

Category Theory on the Wobosphere

Our seminar series might or might not be getting into category theory in the coming months. (We’re already drawing diagrams and showing that they commute; not everybody knows it yet!) To facilitate this process should we ever go in that direction, and to provide a general public service, I’m compiling a list of useful category-theory resources extant on the Wobosphere. My selection will be pedagogically oriented, rather than emphasizing the latest research; I’d like to collect reading material which could plausibly be presented to advanced undergraduate or beginning graduate students in, say, their first semester of encountering the subject. I’ll be both happy and eager to update this list with any beneficial suggestions the Gentle Readers have to offer.
Continue reading Category Theory on the Wobosphere

Video Physics Resources

I’ve mentioned both of these items before, but I figured I should bring them up explicitly. (A nasty stretch of PHP coding lies in my near future, and the need to procrastinate is becoming almost a physical pain.) First is Caltech’s series The Mechanical Universe (1985), which I first saw on PBS many years ago and is now available online for free. If you want a year’s worth of freshman physics, you can now get it in moving-picture form. Early episodes also cover some necessary math: derivatives, integrals and vectors. The videos require a free login before use.

Second in the video department is Barton Zwiebach’s String Theory for Pedestrians (2007). The content should be comprehensible to advanced undergrads. Summary:

In this 3-lecture series I will discuss the basics of string theory, some physical applications, and the outlook for the future. I will begin with the main concepts of the classical theory and the application to the study of cosmic superstrings. Then I will turn to the quantum theory and discuss applications to the investigation of hadronic spectra and the recently discovered quark-gluon plasma. I will conclude with a sketch of string models of particle physics and showing some avenues that may lead to a complete formulation of string theory.

Unfortunately, the CERN people haven’t yet figured out this neat “embedding video” thing. RealMedia is so, like, 2001 (and sucks besides). I was able to use Real Alternative to play the Zwiebach videos on Windows and MPlayer to watch them on Linux.
Continue reading Video Physics Resources

Polchinski on Smolin on Polchinski on Smolin

Over at Cosmic Variance, Sean Carroll has just posted a guest essay by Joe Polchinski replying to Lee Smolin’s response to Polchinski’s review of Smolin’s book. I managed to snag the first comment spot; I predict that Peter Woit will show up within ten. With any luck, the ensuing comments will contain much good talk about physics, though the signal-to-noise ratio is a perennial problem. (Even Sean admits that he doesn’t read every comment.)

I would like to skim past several details of the physics and pull out for special consideration a passage of Polchinski’s which concerns, ironically, what happens when you think in text instead of physics:

This process of translation of an idea from words to calculation will be familiar to any theoretical physicist. It is often the hardest part of a problem, and the point where the greatest creativity enters. Many word-ideas die quickly at this point, or are transmuted or sharpened. Had you applied it to your word-ideas, you would probably have quickly recognized their falsehood. Further, over-reliance on the imprecise language of words is surely correlated with the tendency to confuse scientific arguments with sociological ones.

Polchinski is speaking about the standards one must maintain while doing science, but similar concerns apply to the process of explaining science. Of course, the latter process is one ingredient in the former, but we often think of “popularizing” (or vulgarisation if we want to be Gallic) as a distinct enterprise from communicating with fellow researchers and educating the next round of students. John Armstrong’s recent post on this topic addresses the same question from the opposite direction: according to Polchinski, going from words to equations is the hard part of getting work done, while Armstrong points out that when “vulgarizing” the science, that’s the very step we omit!

Armstrong amplified his point in the comments here at Sunclipse:

Roger Penrose noted specifically in his introduction to The Road To Reality that modern physics is no longer accessible to anyone — specialists included — except through the mathematics. We understand quantum field theory as well as we do because we understand the mathematics. To avoid the mathematics in its entirely [sic] cuts the legs out from under any popularization of physics, and risks becoming The Tao of Physics or The Dancing Wu Li Masters.

Continue reading Polchinski on Smolin on Polchinski on Smolin

A Quarter of Everything

I have just two quibbles with this New Yorker article on the Large Hadron Collider to which Scott Aaronson directed my attention. First, throughout her informative story, Elizabeth Kolbert consistently abbreviates “Large Hadron Collider” as “L.H.C.” I’ve yet to see anybody in the physics community use the periods when they write “LHC.” Is this some official policy which we, the project’s website and the rest of the Internet just are too lazy to follow? Or are these strange little dots the product of a New Yorker in-house style guide demanding their presence based on some holier-than-Sinai rule about tiny ink specks? If the latter is the case, the foolish prescriptivist responsible needs an introduction to my friend the clue-by-four.

My second and marginally more serious complaint involves the following passage from page five:
Continue reading A Quarter of Everything

Press Release from AdS/CFT Territory

The good folks at Princeton have been beavering away at the esoteric, abstrusely mathematical yet infinitely tantalizing relationships between string theories and gauge theories. The latter are the rather well-respected mathematical descriptions of how the bits and pieces of atomic nuclei interact; the former is what you get when you look at the dawn of time, the centers of black holes and the other places where our understanding throws up its hands, and you jump in with both feet. Or, at least that’s what string theory was, back in 1997 or so.

Today, we’ve come to recognize that physics has a strange property: ideas you invent in one place pop their heads up where you never expected. Thus, supersymmetry — a mathematical concept invented in the 1970s to make string theory look a little more like the real world — branched off to become its own field of inquiry. In trying to figure out the implications of supersymmetry, Ed Witten and company invented supersymmetric quantum mechanics, which (among other things) gives you a wickedly delightful insight into all the problems professors use to torture their undergraduate physics students in Quantum Mechanics I.

The journey from string theory to SUSY QM leaves behind the essential “stringiness” of the original theory, but over the past several years, we’ve seen a whole slew of results which suggest that the math invented to quantize gravity, break the hearts of black holes and hold the Big Bang in our hands is also applicable to other, more accessible situations. Does this mean that string theory is the right path to quantizing gravity and all the rest? No, not necessarily. Does it mean that we can get our teeth into the equations and use experiments to see if at least some of our ideas work? Yes. Is knowing about this arena of activity a key part of understanding what physicists are doing today? Again, the answer is yes.

You can really hear the writer stretching for metaphors in the ScienceDaily story based on Princeton’s press release: “Between the two road sections lay a seemingly unbridgeable mathematical gulf”, etc. If you look at the paper which provoked this release, or even its abstract, you can appreciate why the press office’s language gets so tortured:

In two remarkable recent papers the planar perturbative expansion was proposed for the universal function of the coupling appearing in the dimensions of high-spin operators of the N=4 super Yang-Mills theory. We study numerically the integral equation derived by Beisert, Eden, and Staudacher, which resums the perturbative series. In a confirmation of the anti–de Sitter-space/conformal-field-theory (AdS/CFT) correspondence, we find a smooth function whose two leading terms at strong coupling match the results obtained for the semiclassical folded string spinning in AdS5. We also make a numerical prediction for the third term in the strong coupling series.

Clear as a kegger in a mud pit.

The press release tries to draw a layman-friendly picture, as I mentioned. At a slightly higher level of mathiness are Barton Zwiebach’s String Theory for Pedestrians lecture videos. (Yes, that’s the same Zwiebach who taught the class and wrote the book.) The AdS/CFT correspondence stuff appears in the second and third lectures of the three-lecture series.

(Tip o’ the string theorist’s beret to Peter Steinberg.)

All the News that Fits, We Print

I have a theory about science journalism.

Well, perhaps “model” or “hypothesis” would be a better word. Also, the basic idea isn’t original with me, but I think I can pull together pertinent evidence from a wider variety of stories than most writing-watchers have done, thereby casting (I hope) a little more light.

I don’t know how many of my skeptical blagofriends are in the habit of reading Mind Hacks, so I figured I’d convey along this post by Vaughan about “electronic smog”.

The Independent on Sunday has the dubious honour of publishing one of the worst pieces of science journalism I have ever read on today’s front cover — claiming to ‘reveal’ that children are at risk from Wi-Fi computer networks because of their developing nervous systems.

The headlines include “Children at risk from electronic smog”, “Revealed: radiation threat from new wireless computer networks”, “Fears rise over health threat to children from wifi networks” and “Danger on the airwaves”.

This is despite the fact that not one single study has found a health risk for wifi networks.

Gotta love those extra letters in funny foreign words like honour.
Continue reading All the News that Fits, We Print

I Guess It’s a Deuteron

Seed has just offered the world a “Cribsheet” on string theory. It looks pretty slick, although their portrayal of a “hydrogen atom” seems to have an extra nucleon (as Wolfgang notes in the Cosmic Variance thread). I’m inclined to forgive the multiple electron orbits, since they only show one actual electron — and besides, ellipses aren’t that great a way of drawing orbitals anyway.

(Incidentally, if you want to see orbitals in video, check out episode 51 of The Mechanical Universe, available for free online via Annenberg Media.)

They do cite Barton Zwiebach’s First Course in String Theory (2004), which gives me a slight tinge of pride. I mean, somebody had to work the problems in the last five chapters to see if they were solvable by students and not just professors.

The portion of this post below the fold is a rough draft of several different rants, developed in embryonic form and smushed together. Read only if you’re exceptionally curious.
Continue reading I Guess It’s a Deuteron

String Kings: The Director’s Cut

Via Cosmic Variance, this may be the best thing to come out of theoretical physics cinema since String Wars: The Popper Menace. Steven Miller at Science Mobster (with a very familiar-looking theme) gives us String Kings: The Director’s Cut. Longtime aficionados of the genre will recall the theatrical release and DVD version, but like Ridley Scott’s Blade Runner, Scorsese’s String Kings grows beyond compare when seen as the director intended.

Meanwhile in New York City, Peter Woit (Turturro) is seen in his apartment practising with a gun in front of a mirror in a scene Scorsese has very obviously recycled from his previous urban alienation classic “Taxi Driver”. Like de Niro before him, Turturro gives a compelling and subtle performance here, depicting a man on the edge and giving us hints at the festering rage bubbling underneath as he toys with the loaded weapon and talks to himself repeatedly: “Listen you stringheads…you anthropicists…this is one man one who isn’t going to take it anymore….One man who stood up against the…the orbifolds, the fluxes…the stabilized moduli, the braneworlds, the landscape, the swampland…Someday new real data is gonna come and rain down…rain down…rain down and wash the Arxiv clean…Now I see it clearly…my whole life is pointed in this one direction…I see that now…there was never any choice for me”.

Look for the sequel in late 2008.