We’re Weird

Preparing to move to Denmark, it strikes me just how strange what I’m doing would seem to most people. I’m moving across the ocean to a place where I don’t know the language. (Or at least, don’t know more than half a duolingo lesson.) I’m doing this just three years after another international move. And while I’m definitely nervous, this isn’t the big life changing shift it would be for many people. It’s just how academic careers are expected to work.

At borders, I’m often asked why I am where I am. Why be an American working in Canada? Why move to Denmark? And in general, the answer is just that it’s where I need to be to do what I want to do, because it’s where the other people who do what I want to do are. A few people seed this process by managing to find faculty jobs in their home countries, and others sort themselves out by their interests. In the end, we end up with places like Perimeter, an institute in the middle of Canada with barely any Canadians.

This is more pronounced for smaller fields than for larger ones. A chemist or biologist might just manage to have their whole career in the same state of the US, or the same country in Europe. For a theoretical physicist, this is much less likely. I also suspect it’s more true of more “universal” fields: that most professors of Portuguese literature are in Portugal or Brazil, for example.

For theoretical physics, the result is an essentially random mix of people around the world. This works, in part, because essentially everyone does science in English. Occasionally, a group of collaborators happens to speak the same non-English language, so you sometimes hear people talking science in Russian or Spanish or French. But even then there are times people will default to English anyway, because they’re used to it. We publish in English, we chat in English. And as a result, wherever we end up we can at least talk to our colleagues, even if the surrounding world is trickier.

Communities this international, with four different accents in every conversation, are rare, and I occasionally forget that. Before grad school, the closest I came to this was on the internet. On Dungeons and Dragons forums, much like in academia, everyone was drawn together by shared interests and expertise. We had Australians logging on in the middle of everyone else’s night to argue with the Germans, and Brazilians pointing out how the game’s errata was implemented differently in Portuguese.

It’s fun to be in that sort of community in the real world. There’s always something to learn from each other, even on completely mundane topics. Lunch often turns into a discussion of different countries’ cuisines. As someone who became an academic because I enjoy learning, it’s great to have the wheels constantly spinning like that. I should remember, though, that most of the world doesn’t live like this: we’re currently a pretty weird bunch.

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Join the Dark Side: Become a Seminar Organizer

Attending talks is the bane of many a physicist’s existence. Taking an hour out of your busy schedule to listen to someone you know you’ll only understand for fifteen minutes, hoping that they’ll at least give you a vague idea of why you should care but expecting that they won’t…who would willingly subject people to that?

Well, I would.

I’ve signed up to be the High Energy Theory Seminar organizer for the Niels Bohr Institute this year. Most physics institutes hold regular seminars, usually once or twice a week, where they invite speakers from the surrounding region and all over the world. Organizing these seminars is a job often handed to one of the local postdocs: in this case, me.

In the past I’ve put some thought into the purpose of seminars, but mostly from the perspective of someone attending and occasionally giving them. Now that I’m involved in organizing them, entirely new questions present themselves.

Are seminars for work, or for fun? On the one hand, seminars can be a way to keep up with your own field and pick up useful techniques from others. Looked at in that way, I should invite speakers whose interests line up with the researchers at NBI. On the other hand, seminars can be a good way to find out what’s going on outside of your own field, to satisfy your curiosity about the “next big thing”. Sometimes you see a paper and wish you could ask the author what they were thinking, seminars let you ask face to face.

Is it better to invite big names, or grad students? The big-name people might give better talks on more interesting topics, and they enhance the prestige of the seminar series. They also tend to be busy, and don’t need the talks as much as the grad students do.

People from nearby, or far away? It’s cheaper to invite people from nearby, but you want at least a few big names from farther away.

For most of these, the right approach is a balanced one. You want to invite people whose interests line up with your colleagues, but also a few more distant people for breadth. You want a mix of established big-name people and younger researchers, nearby people and far away ones.

The Niels Bohr Institute does a lot of seminars, typically two per week. Even with a co-organizer filling half of them, that’s a lot of ground to cover, a lot of room to balance all of these goals.

Seminar organizers get exposed to a wide range of researchers working on a wide range of topics. It’s supposed to be good for the career, the ultimate networking experience. For myself, I’m still quite specialized, so I’m hoping this will be a good opportunity to broaden my interests and learn about what others are doing. Along the way, perhaps I’ll get a better idea of what seminars are really for.

More Travel

I’m visiting the Niels Bohr Institute this week, on my way back from Amplitudes.

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You might recognize the place from old conference photos.

Amplitudes itself was nice. There weren’t any surprising new developments, but a lot of little “aha” moments when one of the speakers explained something I’d heard vague rumors about. I figured I’d mention a few of the things that stood out. Be warned, this is going to be long and comparatively jargon-heavy.

The conference organizers were rather daring in scheduling Nima Arkani-Hamed for the first talk, as Nima has a tendency to arrive at the last minute and talk for twice as long as you ask him to. Miraculously, though, things worked out, if only barely: Nima arrived at the wrong campus and ran most of the way back, showing up within five minutes of the start of the conference. He also stuck to his allotted time, possibly out of courtesy to his student, Yuntao Bai, who was speaking next.

Between the two of them, Nima and Yuntao covered an interesting development, tying the Amplituhedron together with the string theory-esque picture of scattering amplitudes pioneered by Freddy Cachazo, Song He, and Ellis Ye Yuan (or CHY). There’s a simpler (and older) Amplituhedron-like object called the associahedron that can be thought of as what the Amplituhedron looks like on the surface of a string, and CHY’s setup can be thought of as a sophisticated map that takes this object and turns it into the Amplituhedron. It was nice to hear from both Nima and his student on this topic, because Nima’s talks are often high on motivation but low on detail, so it was great that Yuntao was up next to fill in the blanks.

Anastasia Volovich talked about Landau singularities, a topic I’ve mentioned before. What I hadn’t appreciated was how much they can do with them at this point. Originally, Juan Maldacena had suggested that these singularities, mathematical points that determine the behavior of amplitudes first investigated by Landau in the 60’s, might explain some of the simplicity we’ve observed in N=4 super Yang-Mills. They ended up not being enough by themselves, but what Volovich and collaborators are discovering is that with a bit of help from the Amplithedron they explain quite a lot. In particular, if they start with the Amplituhedron and do a procedure similar to Landau’s, they can find the simpler set of singularities allowed by N=4 super Yang-Mills, at least for the examples they’ve calculated. It’s still a bit unclear how this links to their previous investigations of these things in terms of cluster algebras, but it sounds like they’re making progress.

Dmitry Chicherin gave me one of those minor “aha” moments. One big useful fact about scattering amplitudes in N=4 super Yang-Mills is that they’re “dual” to different mathematical objects called Wilson loops, a fact which allows us to compare to the “POPE” approach of Basso, Sever, and Vieira. Chicherin asks the question: “What if you’re not calculating a scattering amplitude or a Wilson loop, but something halfway in between?” Interestingly, this has an answer, with the “halfway between” objects having a similar duality among themselves.

Yorgos Papathansiou talked about work I’ve been involved with. I’ll probably cover it in detail in another post, so now I’ll just mention that we’re up to six loops!

Andy Strominger talked about soft theorems. It’s always interesting seeing people who don’t traditionally work on amplitudes giving talks at Amplitudes. There’s a range of responses, from integrability people (who are basically welcomed like family) to work on fairly unrelated areas that have some “amplitudes” connection (met with yawns except from the few people interested in the connection). The response to Strominger was neither welcome nor boredom, but lively debate. He’s clearly doing something interesting, but many specialists worried he was ignorant of important no-go results in the field that could hamstring some of his bolder conjectures.

The second day focused on methods for more practical calculations, and had the overall effect of making me really want to clean up my code. Tiziano Peraro’s finite field methods in particular look like they could be quite useful. There were two competing bases of integrals on display, Von Manteuffel’s finite integrals and Rutger Boels’s uniform transcendental integrals later in the conference. Both seem to have their own virtues, and I ended up asking Rob Schabinger if it was possible to combine the two, with the result that he’s apparently now looking into it.

The more practical talks that day had a clear focus on calculations with two loops, which are becoming increasingly viable for LHC-relevant calculations. From talking to people who work on this, I get the impression that the goal of these calculations isn’t so much to find new physics as to confirm and investigate new physics found via other methods. Things are complicated enough at two loops that for the moment it isn’t feasible to describe what all the possible new particles might do at that order, and instead the goal is to understand the standard model well enough that if new physics is noticed (likely based on one-loop calculations) then the details can be pinned down by two-loop data. But this picture could conceivably change as methods improve.

Wednesday was math-focused. We had a talk by Francis Brown on his conjecture of a cosmic Galois group. This is a topic I knew a bit about already, since it’s involved in something I’ve been working on. Brown’s talk cleared up some things, but also shed light on the vagueness of the proposal. As with Yorgos’s talk, I’ll probably cover more about this in a future post, so I’ll skip the details for now.

There was also a talk by Samuel Abreu on a much more physical picture of the “symbols” we calculate with. This is something I’ve seen presented before by Ruth Britto, and it’s a setup I haven’t looked into as much as I ought to. It does seem at the moment that they’re limited to one loop, which is a definite downside. Other talks discussed elliptic integrals, the bogeyman that we still can’t deal with by our favored means but that people are at least understanding better.

The last talk on Wednesday before the hike was by David Broadhurst, who’s quite a character in his own right. Broadhurst sat in the front row and asked a question after nearly every talk, usually bringing up papers at least fifty years old, if not one hundred and fifty. At the conference dinner he was exactly the right person to read the Address to the Haggis, resurrecting a thick Scottish accent from his youth. Broadhurst’s techniques for handling high-loop elliptic integrals are quite impressively powerful, leaving me wondering if the approach can be generalized.

Thursday focused on gravity. Radu Roiban gave a better idea of where he and his collaborators are on the road to seven-loop supergravity and what the next bottlenecks are along the way. Oliver Schlotterer’s talk was another one of those “aha” moments, helping me understand a key difference between two senses in which gravity is Yang-Mills squared ( the Kawai-Lewellen-Tye relations and BCJ). In particular, the latter is much more dependent on specifics of how you write the scattering amplitude, so to the extent that you can prove something more like the former at higher loops (the original was only for trees, unlike BCJ) it’s quite valuable. Schlotterer has managed to do this at one loop, using the “Q-cut” method I’ve (briefly) mentioned before. The next day’s talk by Emil Bjerrum-Bohr focused more heavily on these Q-cuts, including a more detailed example at two loops than I’d seen that group present before.

There was also a talk by Walter Goldberger about using amplitudes methods for classical gravity, a subject I’ve looked into before. It was nice to see a more thorough presentation of those ideas, including a more honest appraisal of which amplitudes techniques are really helpful there.

There were other interesting topics, but I’m already way over my usual post length, so I’ll sign off for now. Videos from all but a few of the talks are now online, so if you’re interested you should watch them on the conference page.

Amplitudes 2017

I’ve been at Amplitudes this week, in Edinburgh. There have been a lot of great talks, most of which should already have slides online. (They’ve been surprisingly quick about getting slides up this year, with many uploaded before the corresponding talks!) Recordings of the talks should also be up soon.

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We also hiked up local hill Arthur’s Seat on Wednesday, which was a nice change of pace.

I’ll have more time to write about the talks later, a few of them were quite interesting. For now, take a look at some of the slides if you’re curious.

Bootstrapping in the Real World

I’ll be at Amplitudes, my subfield’s big yearly conference, next week, so I don’t have a lot to talk about. That said, I wanted to give a shout-out to my collaborator and future colleague Andrew McLeod, who is a co-author (along with Øyvind Almelid, Claude Duhr, Einan Gardi, and Chris White) on a rather cool paper that went up on arXiv this week.

Andrew and I work on “bootstrapping” calculations in quantum field theory. In particular, we start with a guess for what the result will be based on a specific set of mathematical functions (in my case, “hexagon functions” involving interactions of six particles). We then narrow things down, using other calculations that by themselves only predict part of the result, until we know the right answer. The metaphor here is that we’re “pulling ourselves up by our own bootstraps”, skipping a long calculation by essentially just guessing the answer.

This method has worked pretty well…in a toy model anyway. The calculations I’ve done with it use N=4 super Yang-Mills, a simpler cousin of the theories that describe the real world. There, fewer functions can show up, so our guess is much less unwieldy than it would be otherwise.

What’s impressive about Andrew and co.’s new paper is that they apply this method, not to N=4 super Yang-Mills, but to QCD, the theory that describes quarks and gluons in the real world. This is exactly the sort of thing I’ve been hoping to see more of, these methods built into something that can help with real, useful calculations.

Currently, what they can do is still fairly limited. For the particular problem they’re looking at, the functions required ended up being relatively simple, involving interactions between at most four particles. So far, they’ve just reproduced a calculation done by other means. Going further (more “loops”) would involve interactions between more particles, as well as mixing different types of functions (different “transcendental weight”), either of which make the problem much more complicated.

That said, the simplicity of their current calculation is also a reason to be optimistic.  Their starting “guess” had just thirteen parameters, while the one Andrew and I are working on right now (in N=4 super Yang-Mills) has over a thousand. Even if things get a lot more complicated for them at the next loop, we’ve shown that “a lot more complicated” can still be quite doable.

So overall, I’m excited. It looks like there are contexts in which one really can “bootstrap” up calculations in a realistic theory, and that’s a method that could end up really useful.

The Way You Think Everything Is Connected Isn’t the Way Everything Is Connected

I hear it from older people, mostly.

“Oh, I know about quantum physics, it’s about how everything is connected!”

“String theory: that’s the one that says everything is connected, right?”

“Carl Sagan said we are all stardust. So really, everything is connected.”

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It makes Connect Four a lot easier anyway

I always cringe a little when I hear this. There’s a misunderstanding here, but it’s not a nice clean one I can clear up in a few sentences. It’s a bunch of interconnected misunderstandings, mixing some real science with a lot of confusion.

To get it out of the way first, no, string theory is not about how “everything is connected”. String theory describes the world in terms of strings, yes, but don’t picture those strings as links connecting distant places: string theory’s proposed strings are very, very short, much smaller than the scales we can investigate with today’s experiments. The reason they’re thought to be strings isn’t because they connect distant things, it’s because it lets them wiggle (counteracting some troublesome wiggles in quantum gravity) and wind (curling up in six extra dimensions in a multitude of ways, giving us what looks like a lot of different particles).

(Also, for technical readers: yes, strings also connect branes, but that’s not the sort of connection these people are talking about.)

What about quantum mechanics?

Here’s where it gets trickier. In quantum mechanics, there’s a phenomenon called entanglement. Entanglement really does connect things in different places…for a very specific definition of “connect”. And there’s a real (but complicated) sense in which these connections end up connecting everything, which you can read about here. There’s even speculation that these sorts of “connections” in some sense give rise to space and time.

You really have to be careful here, though. These are connections of a very specific sort. Specifically, they’re the sort that you can’t do anything through.

Connect two cans with a length of string, and you can send messages between them. Connect two particles with entanglement, though, and you can’t send messages between them…at least not any faster than between two non-entangled particles. Even in a quantum world, physics still respects locality: the principle that you can only affect the world where you are, and that any changes you make can’t travel faster than the speed of light. Ansibles, science-fiction devices that communicate faster than light, can’t actually exist according to our current knowledge.

What kind of connection is entanglement, then? That’s a bit tricky to describe in a short post. One way to think about entanglement is as a connection of logic.

Imagine someone takes a coin and cuts it along the rim into a heads half and a tails half. They put the two halves in two envelopes, and randomly give you one. You don’t know whether you have heads or tails…but you know that if you open your envelope and it shows heads, the other envelope must have tails.

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Unless they’re a spy. Then it could contain something else.

Entanglement starts out with connections like that. Instead of a coin, take a particle that isn’t spinning and “split” it into two particles spinning in different directions, “spin up” and “spin down”. Like the coin, the two particles are “logically connected”: you know if one of them is “spin up” the other is “spin down”.

What makes a quantum coin different from a classical coin is that there’s no way to figure out the result in advance. If you watch carefully, you can see which coin gets put in to which envelope, but no matter how carefully you look you can’t predict which particle will be spin up and which will be spin down. There’s no “hidden information” in the quantum case, nowhere nearby you can look to figure it out.

That makes the connection seem a lot weirder than a regular logical connection. It also has slightly different implications, weirdness in how it interacts with the rest of quantum mechanics, things you can exploit in various ways. But none of those ways, none of those connections, allow you to change the world faster than the speed of light. In a way, they’re connecting things in the same sense that “we are all stardust” is connecting things: tied together by logic and cause.

So as long as this is all you mean by “everything is connected” then sure, everything is connected. But often, people seem to mean something else.

Sometimes, they mean something explicitly mystical. They’re people who believe in dowsing rods and astrology, in sympathetic magic, rituals you can do in one place to affect another. There is no support for any of this in physics. Nothing in quantum mechanics, in string theory, or in big bang cosmology has any support for altering the world with the power of your mind alone, or the stars influencing your day to day life. That’s just not the sort of connection we’re talking about.

Sometimes, “everything is connected” means something a bit more loose, the idea that someone’s desires guide their fate, that you could “know” something happened to your kids the instant it happens from miles away. This has the same problem, though, in that it’s imagining connections that let you act faster than light, where people play a special role. And once again, these just aren’t that sort of connection.

Sometimes, finally, it’s entirely poetic. “Everything is connected” might just mean a sense of awe at the deep physics in mundane matter, or a feeling that everyone in the world should get along. That’s fine: if you find inspiration in physics then I’m glad it brings you happiness. But poetry is personal, so don’t expect others to find the same inspiration. Your “everyone is connected” might not be someone else’s.

Where Grants Go on the Ground

I’ve seen several recent debates about grant funding, arguments about whether this or that scientist’s work is “useless” and shouldn’t get funded. Wading into the specifics is a bit more political than I want to get on this blog right now, and if you’re looking for a general defense of basic science there are plenty to choose from. I’d like to focus on a different part, one where I think the sort of people who want to de-fund “useless” research are wildly overoptimistic.

People who call out “useless” research act as if government science funding works in a simple, straightforward way: scientists say what they want to work on, the government chooses which projects it thinks are worth funding, and the scientists the government chooses get paid.

This may be a (rough) picture of how grants are assigned. For big experiments and grants with very specific purposes, it’s reasonably accurate. But for the bulk of grants distributed among individual scientists, it ignores what happens to the money on the ground, after the scientists get it.

The simple fact of the matter is that what a grant is “for” doesn’t have all that much influence on what it gets spent on. In most cases, scientists work on what they want to, and find ways to pay for it.

Sometimes, this means getting grants for applied work, doing some of that, but also fitting in more abstract theoretical projects during downtime. Sometimes this means sharing grant money, if someone has a promising grad student they can’t fund at the moment and needs the extra help. (When I first got research funding as a grad student, I had to talk to the particle physics group’s secretary, and I’m still not 100% sure why.) Sometimes this means being funded to look into something specific and finding a promising spinoff that takes you in an entirely different direction. Sometimes you can get quite far by telling a good story, like a mathematician I know who gets defense funding to study big abstract mathematical systems because some related systems happen to have practical uses.

Is this unethical? Some of it, maybe. But from what I’ve seen of grant applications, it’s understandable.

The problem is that if scientists are too loose with what they spend grant money on, grant agency asks tend to be far too specific. I’ve heard of grants that ask you to give a timeline, over the next five years, of each discovery you’re planning to make. That sort of thing just isn’t possible in science: we can lay out a rough direction to go, but we don’t know what we’ll find.

The end result is a bit like complaints about job interviews, where everyone is expected to say they love the company even though no-one actually does. It creates an environment where everyone has to twist the truth just to keep up with everyone else.

The other thing to keep in mind is that there really isn’t any practical way to enforce any of this. Sure, you can require receipts for equipment and the like, but once you’re paying for scientists’ time you don’t have a good way to monitor how they spend it. The best you can do is have experts around to evaluate the scientists’ output…but if those experts understand enough to do that, they’re going to be part of the scientific community, like grant committees usually already are. They’ll have the same expectations as the scientists, and give similar leeway.

So if you want to kill off some “useless” area of research, you can’t do it by picking and choosing who gets grants for what. There are advocates of more drastic actions of course, trying to kill whole agencies or fields, and that’s beyond the scope of this post. But if you want science funding to keep working the way it does, and just have strong opinions about what scientists should do with it, then calling out “useless” research doesn’t do very much: if the scientists in question think it’s useful, they’ll find a way to keep working on it. You’ve slowed them down, but you’ll still end up paying for research you don’t like.

Final note: The rule against political discussion in the comments is still in effect. For this post, that means no specific accusations of one field or another as being useless, or one politician/political party/ideology or another of being the problem here. Abstract discussions and discussions of how the grant system works should be fine.