Tag Archives: press

Why You Should Be Skeptical about Faster-than-Light Neutrinos

While I do love science, I don’t always love IFL Science. They can be good at drumming up enthusiasm, but they can also be ridiculously gullible. Case in point: last week, IFL Science ran a piece on a recent paper purporting to give evidence for faster-than-light particles.

Faster than light! Sounds cool, right? Here’s why you should be skeptical:

If a science article looks dubious, you should check out the source. In this case, IFL Science links to an article on the preprint server arXiv.

arXiv is a freely accessible website where physicists and mathematicians post their articles. The site has multiple categories, corresponding to different fields. It’s got categories for essentially any type of physics you’d care to include, with the option to cross-list if you think people from multiple areas might find your work interesting.

So which category is this paper in? Particle physics? Astrophysics?

General Physics, actually.

General Physics is arXiv’s catch-all category. Some of it really is general, and can’t be put into any more specific place. But most of it, including this, falls into another category: things arXiv’s moderators think are fishy.

arXiv isn’t a journal. If you follow some basic criteria, it won’t reject your articles. Instead, dubious articles are put into General Physics, to signify that they don’t seem to belong with the other scholarship in the established categories. General Physics is a grab-bag of weird ideas and crackpot theories, a mix of fringe physicists and overenthusiastic amateurs. There probably are legitimate papers in there too…but for every paper in there, you can guarantee that some experienced researcher found it suspicious enough to send into exile.

Even if you don’t trust the moderators of arXiv, there are other reasons to be wary of faster-than-light particles.

According to Einstein’s theory of relativity, massless particles travel at the speed of light, while massive particles always travel slower. To travel faster than the speed of light, you need to have a very unusual situation: a particle whose mass is an imaginary number.

Particles like that are called tachyons, and they’re a staple of science fiction. While there was a time when they were a serious subject of physics speculation, nowadays the general view is that tachyons are a sign we’re making bad assumptions.

Assuming that someone is a republic serial villain is a good example.

Why is that? It has to do with the nature of mass.

In quantum field theory, what we observe as particles arise as ripples in quantum fields, extending across space and time. The harder it is to make the field ripple, the higher the particle’s mass.

A tachyon has imaginary mass. This means that it isn’t hard to make the field ripple at all. In fact, exactly the opposite happens: it’s easier to ripple than to stay still! Any ripple, no matter how small, will keep growing until it’s not just a ripple, but a new default state for the field. Only when it becomes hard to change again will the changes stop. If it’s hard to change, though, then the particle has a normal, non-imaginary mass, and is no longer a tachyon!

Thus, the modern understanding is that if a theory has tachyons in it, it’s because we’re assuming that one of the quantum fields has the wrong default state. Switching to the correct default gets rid of the tachyons.

There are deeper problems with the idea proposed in this paper. Normally, the only types of fields that can have tachyons are scalars, fields that can be defined by a single number at each point, sort of like a temperature. The particles this article is describing aren’t scalars, though, they’re fermions, the type of particle that includes everyday matter like electrons. Those sorts of particles can’t be tachyons at all without breaking some fairly important laws of physics. (For a technical explanation of why this is, Lubos Motl’s reply to the post here is pretty good.)

Of course, this paper’s author knows all this. He’s well aware that he’s suggesting bending some fairly fundamental laws, and he seems to think there’s room for it. But that, really, is the issue here: there’s room for it. The paper isn’t, as IFL Science seems to believe, six pieces of evidence for faster-than-light particles. It’s six measurements that, if you twist them around and squint and pick exactly the right model, have room for faster-than-light particles. And that’s…probably not worth an article.

Misleading Headlines and Tacky Physics, Oh My!

It’s been making the rounds on the blogosphere (despite having come out three months ago). It’s probably showed up on your Facebook feed. It’s the news that (apparently) one of the biggest discoveries of recent years may have been premature. It’s….

The Huffington Post writing a misleading headline to drum up clicks!

The article linked above is titled “Scientists Raise Doubts About Higgs Boson Discovery, Say It Could Be Another Particle”. And while that is indeed technically all true, it’s more than a little misleading.

When the various teams at the Large Hadron Collider announced their discovery of the Higgs, they didn’t say it was exactly the Higgs predicted by the Standard Model. In fact, it probably shouldn’t be: most of the options for extending the Standard Model, like supersymmetry, predict a Higgs boson with slightly different properties. Until the Higgs is measured more precisely, these slightly different versions won’t be ruled out.

Of course, “not ruled out” is not exactly newsworthy, which is the main problem with this article. The Huffington Post quotes a paper that argues, not that there is new evidence for an alternative to the Higgs, but simply that one particular alternative that the authors like hasn’t been ruled out yet.

Also, it’s probably the tackiest alternative out there.

The theory in question is called Technicolor, and if you’re imagining a certain coat then you may have an idea of how tacky we’re talking.

Any Higgs will do…

To describe technicolor, let’s take a brief aside and talk about the colors of quarks.

Rather than having one type of charge going from plus to minus like Electromagnetism, the Strong Nuclear Force has three types of charge, called red, green, and blue. Quarks are charged under the strong force, and can be red, green, or blue, while the antimatter partners of quarks have the equivalent of negative charges, anti-red, anti-green, and anti-blue. The strong force binds quarks together into protons and neutrons. The strong force is also charged under itself, which means that not only does it bind quarks together, it also binds itself together, so that it only acts at very very short range.

In combination, these two facts have one rather surprising consequence. A proton contains three quarks, but a proton’s mass is over a hundred times the total mass of three quarks. The same is true of neutrons.

The reason why is that most of the mass isn’t coming from the quarks, it’s coming from the strength of the strong force. Mass, contrary to what you might think, isn’t fundamental “stuff”. It’s just a handy way of talking about energy that isn’t due to something we can easily see. Particles have energy because they move, but they also have energy due to internal interactions, as well as interactions with other fields like the Higgs field. While a lone quark’s mass is due to its interaction with the Higgs field, the quarks inside a proton are also interacting with each other, gaining enormous amounts of energy from the strong force trapped within. That energy, largely invisible from an outside view, contributes most of what we see as the mass of the proton.

Technicolor asks the following: what if it’s not just protons and neutrons? What if the mass of everything, quarks and electrons and the W and Z bosons, was due not truly to the Higgs, but to another force, like the strong force but even stronger? The Higgs we think we saw at the LHC would not be fundamental, but merely a composite, made up of  two “techni-quarks” with “technicolor” charges. [Edited to remove confusion with Preon Theory]

It’s…an idea. But it’s never been a very popular one.

Part of the problem is that the simpler versions of technicolor have been ruled out, so theorists are having to invoke increasingly baroque models to try to make it work. But that, to some extent, is also true of supersymmetry.

A bigger problem is that technicolor is just kind of…tacky.

Technicolor doesn’t say anything deep about the way the universe works. It doesn’t propose new [types of] symmetries, and it doesn’t say anything about what happens at the very highest energies. It’s not really tied in to any of the other lines of speculation in physics, it doesn’t lead to a lot of discussion between researchers. It doesn’t require an end, a fundamental lowest level with truly fundamental particles. You could potentially keep adding new levels of technicolor, new things made up of other things made up of other things, ad infinitum.

And the fleas that bite ’em, presumably.

[Note: to clarify, technicolor theories don’t actually keep going like this, their extra particles don’t require another layer of technicolor to gain their masses. That would be an actual problem with the concept itself, not a reason it’s tacky. It’s tacky because, in a world where most physicists feel like we’ve really gotten down to the fundamental particles, adding new composite objects seems baroque and unnecessary, like adding epicycles. Fleas upon fleas as it were.]

In a word, it’s not sexy.

Does that mean it’s wrong? No, of course not. As the paper linked by Huffington Post points out, technicolor hasn’t been ruled out yet.

Does that mean I think people shouldn’t study it? Again, no. If you really find technicolor meaningful and interesting, go for it! Maybe you’ll be the kick it needs to prove itself!

But good grief, until you manage that, please don’t spread your tacky, un-sexy theory all over Facebook. A theory like technicolor should get press when it’s got a good reason, and “we haven’t been ruled out yet” is never, ever, a good reason.

 

[Edit: Esben on Facebook is more well-informed about technicolor than I am, and pointed out some issues with this post. Some of them are due to me conflating technicolor with another old and tacky theory, while some were places where my description was misleading. Corrections in bold.]

(Interstellar) Dust In The Wind…

The news has hit the blogosphere: the team behind the Planck satellite has released new dust measurements, and they seem to be a nail in the coffin of BICEP2’s observation of primordial gravitational waves.

Some background for those who haven’t been following the story:

BICEP2, a telescope in Antarctica, is set up to observe the Cosmic Microwave Background, light left over from the very early universe. Back in March, they announced that they had seen characteristic ripples in that light, ripples that they believed were caused by gravitational waves in the early universe. By comparing the size of these gravitational waves to their (quantum-small) size when they were created, they could make statements about the exponential expansion of the early universe (called inflation). This amounted to better (and more specific) evidence about inflation than anyone else had ever found, so naturally people were very excited about it.

However, doubt was rather quickly cast on these exciting results. Like all experimental science, BICEP2 needed to estimate the chance that their observations could be caused by something more mundane. In particular, interstellar dust can cause similar “ripples” to those they observed. They argued that dust would have contributed a much smaller effect, so their “ripples” must be the real deal…but to make this argument, they needed an estimate of how much dust they should have seen. They had several estimates, but one in particular was based on data “scraped” off of a slide from a talk by the Planck collaboration.

Unfortunately, it seems that the BICEP2 team misinterpreted this “scraped” data. Now, Planck have released the actual data, and it seems like dust could account for BICEP2’s entire signal.

I say “could” because more information is needed before we know for sure. The BICEP2 and Planck teams are working together now, trying to tease out whether BICEP2’s observations are entirely dust, or whether there might still be something left.

I know I’m not the only person who wishes that this sort of collaboration could have happened before BICEP2 announced their discovery to the world. If Planck had freely shared their early data with BICEP2, they would have had accurate dust estimates to begin with, and they wouldn’t have announced all of this prematurely.

Of course, expecting groups to freely share data when Nobel prizes and billion-dollar experiments are on the line is pretty absurdly naive. I just wish we lived in a world where none of this was at issue, where careers didn’t ride on “who got there first”.

I’ve got no idea how to bring about such a world, of course. Any suggestions?

No, Hawking didn’t say that a particle collider could destroy the universe

So apparently Hawking says that the Higgs could destroy the universe.

HawkingHiggs

I’ve covered this already, right? No need to say anything more?

Ok, fine, I’ll write a real blog post.

The Higgs is a scalar field: a number, sort of like temperature, that can vary across space and time. In the case of the Higgs this number determines the mass of almost every fundamental particle (the jury is still somewhat out on neutrinos). The Higgs doesn’t vary much at all, in fact it takes an enormous (Large Hadron Collider-sized) amount of energy to get it to wobble even a little bit. That is because the Higgs is in a very very stable state.

Hawking was pointing out that, given our current model of the Higgs, there’s actually another possible state for the Higgs to be in, one that’s even more stable (because it takes less energy, essentially). In that state, the number the Higgs corresponds to is much larger, so everything would be much more massive, with potentially catastrophic results. (Matt Strassler goes into some detail about the assumptions behind this.)

For those who have been following my blog for a while, you may find these “stable states” familiar. They’re vacua, different possible ways to set up “empty” space. In that post, I may have given the impression that there’s no way to change from one stable state, one “vacuum”, to another. In the case of the Higgs, the state it’s in is so stable that vast amounts of energy (again, a Large Hadron Collider-worth) only serve to create a small, unstable fluctuation, the Higgs boson, which vanishes in a fraction of a second.

And that would be the full story, were it not for a curious phenomenon called quantum tunneling.

If you’ve heard someone else describe quantum tunneling, you’ve probably heard that quantum particles placed on one side of a wall have a very small chance of being found later on the other side of the wall, as if they had tunneled there.

Using their incredibly tiny shovels.

However, quantum tunneling applies to much more than just walls. In general, a particle in an otherwise stable state (whether stable because there are walls keeping it in place, or for other reasons) can tunnel into another state, provided that the new state is “more stable” (has lower energy).

The chance of doing this is small, and it gets smaller the more “stable” the particle’s initial state is. Still, if you apply that logic to the Higgs, you realize there’s a very very very small chance that one day the Higgs could just “tunnel” away from its current stable state, destroying the universe as we know it in the process.

If that happened, everything we know would vanish at the speed of light, and we wouldn’t see it coming.

While that may sound scary, it’s also absurdly unlikely, to the extent that it probably won’t happen until the universe is many times older than it is now. It’s not the sort of thing anybody should worry about, at least on a personal level.

Is Hawking fear-mongering, then, by pointing this out? Hardly. He’s just explaining science. Pointing out the possibility that the Higgs could spontaneously change and end the universe is a great way to emphasize the sheer scale of physics, and it’s pretty common for science communicators to mention it. I seem to recall a section about it in Particle Fever, and Sean Carroll even argues that it’s a good thing, due to killing off spooky Boltzmann Brains.

What do particle colliders have to do with all this? Well, apart from quantum tunneling, just inputting enough energy in the right way can cause a transition from one stable state to another. Here “enough energy” means about a million times that produced by the Large Hadron Collider. As Hawking jokes, you’d need a particle collider the size of the Earth to get this effect. I don’t know whether he actually ran the numbers, but if anything I’d guess that a Large Earth Collider would actually be insufficient.

Either way, Hawking is just doing standard science popularization, which isn’t exactly newsworthy. Once again, “interpret something Hawking said in the most ridiculous way possible” seems to be the du jour replacement for good science writing.

“China” plans super collider

When I saw the headline, I was excited.

“China plans super collider” says Nature News.

There’s been a lot of worry about what may happen if the Large Hadron Collider finishes its run without discovering anything truly new. If that happens, finding new particles might require a much bigger machine…and since even that machine has no guarantee of finding anything at all, world governments may be understandably reluctant to fund it.

As such, several prominent people in the physics community have put their hopes on China. The country’s somewhat autocratic nature means that getting funding for a collider is a matter of convincing a few powerful people, not a whole fractious gaggle of legislators. It’s a cynical choice, but if it keeps the field alive so be it.

If China was planning a super collider, then, that would be great news!

Too bad it’s not.

Buried eight paragraphs in to Nature’s article we find the following:

The Chinese government is yet to agree on any funding, but growing economic confidence in the country has led its scientists to believe that the political climate is ripe, says Nick Walker, an accelerator physicist at DESY, Germany’s high-energy physics laboratory in Hamburg. Although some technical issues remain, such as keeping down the power demands of an energy-hungry ring, none are major, he adds.

The Chinese government is yet to agree on any funding. China, if by China you mean the Chinese government, is not planning a super collider.

So who is?

Someone must have drawn these diagrams, after all.

Reading the article, the most obvious answer is Beijing’s Institute of High Energy Physics (IHEP). While this is true, the article leaves out any mention of a more recently founded site, the Center for Future High Energy Physics (CFHEP).

This is a bit odd, given that CFHEP’s whole purpose is to compose a plan for the next generation of colliders, and persuade China’s government to implement it. They were founded, with heavy involvement from non-Chinese physicists including their director Nima Arkani-Hamed, with that express purpose in mind. And since several of the quotes in the article come from Yifang Wang, director of IHEP and member of the advisory board of CFHEP, it’s highly unlikely that this isn’t CFHEP’s plan.

So what’s going on here? On one level, it could be a problem on the journalists’ side. News editors love to rewrite headlines to be more misleading and click-bait-y, and claiming that China is definitely going to build a collider draws much more attention than pointing out the plans of a specialized think tank. I hope that it’s just something like that, and not the sort of casual racism that likes to think of China as a single united will. Similarly, I hope that the journalists involved just didn’t dig deep enough to hear about CFHEP, or left it out to simplify things, because there is a somewhat darker alternative.

CFHEP’s goal is to convince the Chinese government to build a collider, and what better way to do that than to present them with a fait accompli? If the public thinks that this is “China’s” plan, that wheels are already in motion, wouldn’t it benefit the Chinese government to play along? Throw in a few sweet words about the merits of international collaboration (a big part of the strategy of CFHEP is to bring international scientists to China to show the sort of community a collider could attract) and you’ve got a winning argument, or at least enough plausibility to get US and European funding agencies in a competitive mood.

This…is probably more cynical than what’s actually going on. For one, I don’t even know whether this sort of tactic would work.

Do these guys look like devious manipulators?

Indeed, it might just be a journalistic omission, part of a wider tendency of science journalists to focus on big projects and ignore the interesting part, the nitty-gritty things that people do to push them forward. It’s a shame, because people are what drive the news forward, and as long as science is viewed as something apart from real human beings people are going to continue to mistrust and misunderstand it.

Either way, one thing is clear. The public deserves to hear a lot more about CFHEP.

Insert Muscle Joke Here

I’m graduating this week, so I probably shouldn’t spend too much time writing this post. I ought to mention, though, that there has been some doubt about the recent discovery by the BICEP2 telescope of evidence for gravitational waves in the cosmic microwave background caused by the early inflation of the universe. Résonaances got to the story first and Of Particular Significance has some good coverage that should be understandable to a wide audience.

In brief, the worry is that the signal detected by BICEP2 might not be caused by inflation, but instead by interstellar dust. While the BICEP2 team used several models of dust to show that it should be negligible, the controversy centers around one of these models in particular, one taken from another, similar experiment called PLANCK.

The problem is, BICEP2 didn’t get PLANCK’s information on dust directly. Instead, it appears they took the data from a slide in a talk by the PLANCK team. This process, known as “data scraping”, involves taking published copies of the slides and reading information off of the charts presented. If BICEP2 misinterpreted the slide, they might have miscalculated the contribution by interstellar dust.

If you’re like me, the whole idea of data scraping seems completely ludicrous. The idea of professional scientists sneaking information off of a presentation, rather than simply asking the other team for data like reasonable human beings, feels almost cartoonishly wrong-headed.

It’s a bit more understandable, though, when you think about the culture behind these big experiments. The PLANCK and BICEP2 teams are colleagues, but they are also competitors. There is an enormous amount of glory in finding evidence for something like cosmic inflation first, and an equally enormous amount of shame in screwing up and announcing something that turns out to be wrong. As such, these experiments are quite protective of their data. Not only might someone with early access to the data preempt them on an important discovery, they might rush to publish a conclusion that is wrong. That’s why most of these big experiments spend a large amount of time checking and re-checking the data, communicating amongst themselves and settling on an interpretation before they feel comfortable releasing it to the wider community. It’s why BICEP2 couldn’t just ask PLANCK for their data.

From BICEP2’s perspective, they can expect that plots presented at a talk by PLANCK should be accurate, digital plots. Unlike Fox News, scientists have an obligation to present their data in a way that isn’t misleading. And while relying on such a dubious source seems like a bad idea, by all accounts that’s not what the BICEP2 team did. PLANCK’s data was just one dust model used by the team, kept in part because it agreed well with other, non-“data-scraped” models.

It’s a shame that these experiments are so large and prestigious that they need to guard their data in such a potentially destructive way. My sub-field is generally much nicer about this sort of thing: the stakes are lower, and the groups are smaller and have less media attention, so we’re able to share data when we need to. In fact, my most recent paper got a significant boost from some data shared by folks at the Perimeter Institute.

Only time will tell whether the BICEP2 result wins out, or whether it was a fluke caused by caustic data-sharing practices. A number of other experiments are coming online within the next year, and one of them may confirm or deny what BICEP2 has showed.

Editors, Please Stop Misquoting Hawking

If you’ve been following science news recently, you’ve probably heard the apparently alarming news that Steven Hawking has turned his back on black holes, or that black holes can actually be escaped, or…how about I just show you some headlines:

FoxHawking

NatureHawking

YahooHawking

Now, Hawking didn’t actually say that black holes don’t exist, but while there are a few good pieces on the topic, in many cases the real message has gotten lost in the noise.

From Hawking’s paper:

ActualPaperHawking

What Hawking is proposing is that the “event horizon” around a black hole, rather than being an absolute permanent boundary from which nothing can escape, is a more temporary “apparent” horizon, the properties of which he goes on to describe in detail.

Why is he proposing this? It all has to do with the debate over black hole firewalls.

Starting with a paper by Polchinski and colleagues a year and a half ago, the black hole firewall paradox centers on contradictory predictions from general relativity and quantum mechanics. General relativity predicts that an astronaut falling past a black hole’s event horizon will notice nothing particularly odd about the surrounding space, but that once past the event horizon none of the “information” that specifies the astronaut’s properties can escape to the outside world. Quantum mechanics on the other hand predicts that information cannot be truly lost. The combination appears to suggest something radical, a “firewall” of high energy radiation around the event horizon carrying information from everything that fell into the black hole in the past, so powerful that it would burn our hypothetical astronaut to a crisp.

Since then, a wide variety of people have made one proposal or another, either attempting to avoid the seemingly preposterous firewall or to justify and further explain it. The reason the debate is so popular is because it touches on some of the fundamental principles of quantum mechanics.

Now, as I have pointed out before, I’m not a good person to ask about the fundamental principles of quantum mechanics. (Incidentally, I’d love it if some of the more quantum information or general relativity-focused bloggers would take a more substantial crack at this! Carroll, Preskill, anyone?) What I can talk about, though, is hype.

All of the headlines I listed take Hawking’s quote out of context, but not all of the articles do. The problem isn’t so much the journalists, as the editors.

One of an editor’s responsibilities is to take articles and give them titles that draw in readers. The editor wants a title that will get people excited, make them curious, and most importantly, get them to click. While a journalist won’t have any particular incentive to improve ad revenue, the same cannot be said for an editor. Thus, editors will often rephrase the title of an article in a way that makes the whole story seem more shocking.

Now that, in itself, isn’t a problem. I’ve used titles like that myself. The problem comes when the title isn’t just shocking, but misleading.

When I call astrophysics “impossible”, nobody is going to think I mean it literally. The title is petulant and ridiculous enough that no-one would take it at face value, but still odd enough to make people curious. By contrast, when you say that Hawking has “changed his mind” about black holes or said that “black holes do not exist”, there are people who will take that at face value as supporting their existing beliefs, as the Borowitz Report humorously points out. These people will go off thinking that Hawking really has given up on black holes. If the title confirms their beliefs enough, people might not even bother to read the article. Thus, by using an actively misleading title, you may actually be decreasing clicks!

It’s not that hard to write a title that’s both enough of a hook to draw people in and won’t mislead. Editors of the world, you’re well-trained writers, certainly much better than me. I’m sure you can manage it.

There really is some interesting news here, if people had bothered to look into it. The firewall debate has been going on for a year and a half, and while Hawking isn’t the universal genius the media occasionally depicts he’s still the world’s foremost expert on the quantum properties of black holes. Why did he take so long to weigh in? Is what he’s proposing even particularly new? I seem to remember people discussing eliminating the horizon in one way or another (even “naked” singularities) much earlier in the firewall debate…what makes Hawking’s proposal novel and different?

This is the sort of thing you can use to draw in interest, editors of the world. Don’t just write titles that cause ignorant people to roll their eyes and move on, instead, get people curious about what’s really going on in science! More ad revenue for you, more science awareness for us, sounds like a win-win!

Hype versus Miscommunication, or the Language of Importance

A fellow amplitudes-person was complaining to me recently about the hype surrounding the debate regarding whether black holes have “firewalls”. New York Times coverage seems somewhat excessive for what is, in the end, a fairly technical debate, and its enthusiasm was (rightly?) mocked in several places.

There’s an attitude I often run into among other physicists. The idea is that when hype like this happens, it’s because senior physicists are, at worst, cynically manipulating the press to further their positions or, at best, so naïve that they really see what they’re working on as so important that it deserves hype-y coverage. Occasionally, the blame will instead be put on the journalists, with largely the same ascribed motivations: cynical need for more page views, or naïve acceptance of whatever story they’re handed.

In my opinion, what’s going on there is a bit deeper, and not so easily traceable to any particular person.

In the articles on the (2, 0) theory I put up in the last few weeks, I made some disparaging comments about the tone of this Scientific American blog post. After exchanging a few tweets with the author, I think I have a better idea of what went down.

The problem here is that when you ask a scientist about something they’re excited about, they’re going to tell you why they’re excited about it. That’s what happened here when Nima Arkani-Hamed was interviewed for the above article: he was asked about the (2, 0) theory, and he seems to have tried to convey his enthusiasm with a metaphor that explained how the situation felt to him.

The reason this went wrong and led to a title as off-base and hype-sounding as “the Ultimate Ultimate Theory of Physics” was that we (scientists and science journalists) are taught to express enthusiasm in the language of importance.

There has been an enormous resurgence in science communication in recent years, but it has come with a very us-vs.-them mentality. The prevailing attitude is that the public will only pay attention to a scientific development if they are told that it is important. As such, both scientists and journalists try to make whatever they’re trying to communicate sound central, either to daily life or to our understanding of the universe. When both sides of the conversation are operating under this attitude, it creates an echo chamber where a concept’s importance is blown up many times greater than it really deserves, without either side doing anything other than communicating science in the only way they know.

We all have to step back and realize that most of the time, science isn’t interesting because of its absolute “importance”. Rather, a puzzle is often interesting simply because it is a puzzle. That’s what’s going on with the (2, 0) theory, or with firewalls: they’re hard to figure out, and that’s why we care.

Being honest about this is not going to lose us public backing, or funding. It’s not just scientists who value interesting things because they are challenging. People choose the path of their lives not based on some absolute relevance to the universe at large, but because things make sense in context. You don’t fall in love because the target of your affections is the most perfect person in the universe, you fall in love because they’re someone who can constantly surprise you.

Scientists are in love with what they do. We need to make sure that that, and not some abstract sense of importance, is what we’re communicating. If we do that, if we calm down and make a bit more effort to be understood, maybe we can win back some of the trust that we’ve lost by appearing to promote Ultimate Ultimate Theories of Everything.

The (2, 0) Theory: Where does it come from?

Part One of a Series on the (2, 0) Theory

By semi-popular demand, I’m doing a guide on the (2, 0) theory. Over the course of this guide I’ll try to explain where the (2, 0) theory comes from, what its name means, and, more elusively, what it’s actually about.

The (2, 0) theory doesn’t get much press coverage, and when it does, it’s a bit silly. The article I just linked compares it to Star Wars’ Emperor Palpatine, in analogy with what George Musser and perhaps others call the Darth Vader theory, or N=4 super Yang-Mills.

The metaphor, as far as I can parse it, is the following: while N=4 super Yang-Mills is solid, powerful, and important (like Darth Vader), the (2, 0) theory is mysterious and yet somehow even more central (like the Emperor).

The thing is, while the (2, 0) theory is indeed sexy and mysterious, it isn’t especially central. Laymen haven’t heard of it for good reason: it’s really only specialists in the field who have a reason to be interested in it. So really, it’s more like the Mara Jade theory.

If you don’t know who this is, that’s my point

The (2, 0) theory is very much a theory, in the same sense as N=4 super Yang-Mills. It isn’t a “theory of everything”, and it isn’t supposed to describe the real world. With that in mind, let’s talk about the sort of world it does describe.

There are two ways to “define” the (2, 0) theory. One of them is to take a particular type of string theory (type IIB) with ten dimensions (nine space dimensions and one dimension for time), and twist four of those dimensions into a particular shape (called a K3 surface). There are six dimensions left (five space, one time), and in those six dimensions the world obeys the (2, 0) theory.

That definition may not seem particularly illuminating, and it really isn’t. You can get almost any theory in physics by taking some type of string theory and twisting up some of the dimensions in a particular way, so unless you’re familiar with that particular type of string theory or the particular shape of the dimensions, you don’t learn anything from that definition.

The second definition, though, is more appealing. The (2, 0) theory can be defined as the world-volume theory of a five-dimensional object called an M5-brane.

A world-volume theory is a theory that describes what it is like to live inside of the volume of some object, so that the object is your whole world. To understand what that means, think about Flatland.

Think upward, not northward

In Edwin A. Abbott’s Flatland, the characters are two-dimensional shapes living in a two-dimensional world. Because their whole world is two-dimensional, they cannot imagine a third dimension. Despite that, there is a third dimension, as demonstrated by a sphere who floats through the world one day and upsets the main character’s life. The theory of physics in Flatland, then, is the world-volume theory of a two-dimensional plane in three-dimensional space.

Imagine that the two-dimensional plane of Flatland was flexible, that is, more like a two-dimensional membrane. Such a membrane could move back and forth in the third dimension, rippling up and down.

Now remember that, in Flatland, nobody can imagine a third dimension. So if you are within Flatland, and the world around you is bouncing up and down, can you notice?

The answer is a counter-intuitive yes. It’s easy if there is gravity in the third dimension: when the world curves up, it would get harder to climb up, while if the world curves down, it would be easier. Even if there isn’t gravity, though, you can still notice the changes in energy. It takes energy to set the world vibrating, and that energy has to come from somewhere. That energy can come from movement within your dimension. What a Flatlander would observe, then, would be processes that seem to violate conservation of energy, by losing more energy than they put in: instead, that energy would go to making the world wiggle.

What a Flatland scientist would observe, then, would be a world in which there is some number that can change from place to place, and that can oscillate, carrying energy as it does so. Those of you who remember my older posts might recognize what’s going on here: this is precisely the way in which you discover the existence of a scalar field!

An M5-brane is a five-dimensional membrane that lives in M theory, a theory with eleven dimensions (ten space and one time). The world-volume theory of an M5-brane, then, is the theory of what it is like to have your whole world inside the five dimensions of the M5-brane, just like a person in Flatland has their whole world within the two dimensions of Flatland. And just like the two-dimensional Flatland would have one scalar field corresponding to its ability to vibrate in the third dimension, the five space dimensions of the (2, 0) theory have five scalar fields, corresponding to the five other directions (ten minus five) in which the M5-brane can move.

So the (2, 0) theory is the theory of what it’s like to live on a five-dimensional membrane in a ten-dimensional space, and because of that, the theory contains five scalar fields. But if it was just five scalar fields, it would hardly be mysterious. What else does the theory contain? And what does “(2, 0)” mean anyway? Tune in next week to find out!

Edit: I am informed by George Musser (@gmusser on twitter) that the Darth Vader thing was apparently all Nima Arkani-Hamed’s idea. So don’t blame him for the somewhat misleading metaphor!