Blogs / Cosmic Variance

Sorry for the radio silence — Thanksgiving really took it out of me. (The food was excellent — may have eaten too much.) Just got back from a workshop at Stanford, where we had a mini Cosmic Variance gathering, since I saw both Daniel and Risa. Had JoAnne not been delayed on her flight back to California, we might have been able to get four co-bloggers in the same room for probably the first time ever.

Since today is Casual Friday, I’d like to put science aside and do a review of Jonathan Franzen’s new book, Freedom: A Novel. I am hampered in that goal by the fact that I haven’t read the book, and don’t plan to any time soon. (I think Franzen is a great writer, but I’m very behind in my reading list.)

So instead I’ll outsource this one to Washington Post book reviewer Ron Charles, who delivers his critique in video format. It gives me some ideas. (Hat tip to Ariel Kalil.)

Here’s how it starts. Click over to Abstruse Goose to see the exciting conclusion.

Message to science journalists: if this actually happened, it would be pretty awesome.

This year we give thanks for an idea that is absolutely crucial to how our understanding of nature progresses: effective field theory. (We’ve previously given thanks for the Standard Model Lagrangian, Hubble’s Law, the Spin-Statistics Theorem, and conservation of momentum.)

“Effective field theory” is a technical term within quantum field theory, but it is associated with a more informal notion of extremely wide applicability. Namely: if we imagine dividing the world into “what happens at very short, microscopic distances” and “what happens at longer, macroscopic distances,” then it is possible to consistently describe the macroscopic world without referring to (or even understanding) the microscopic world. This is not always true, of course — our macroscopic descriptions have very specific domains of applicability, past which the microscopic details begin to matter — but it’s true very often, for a wide variety of situations with direct physical relevance.

The most basic examples are thermodynamics and fluid mechanics. You can talk about gasses and liquids very well without having any idea that they are made of atoms and molecules. Once you get deep into the details, we start talking about effects for which the atomic granularity really matters; but there is a very definite and useful regime in which it is simply irrelevant that air and water are “really” made of discrete units rather than being continuous fluids. Fluid mechanics is the “effective field theory of molecules” in the macroscopic domain.

How awesome is that? If it weren’t for the idea of effective field theory, it’s hard to imagine how we would ever make progress in physics. You wouldn’t be able to talk about atmospheric science without knowing all the details of microscopic physics (known in the trade as the ultraviolet completion), all the way down to the Planck scale! Fortunately, the universe is much more kind to us.

In particle physics, this idea is absolutely central. Protons, neutrons, and pions constitute an effective field theory that describes how quarks and gluons behave over sufficiently large distances. Another great example comes from Enrico Fermi’s theory of the weak interactions. Back in the 1930’s, Fermi proposed a theory that made use of the new “neutrino” particle. It involved processes that looked like this interaction of a proton plus electron converting into a neutron plus neutrino.

Nowadays we know better. What’s really going on is that the proton is made of two up quarks and a down quark, while the neutron is made of two downs and an up. The electron exchanges a W boson with one of the quarks, converting into an electron neutrino in the process.

But the miracle is: it doesn’t matter. Knowing that the weak interactions are “really” carried by W bosons is completely irrelevant, as long as we are concerned only with large distances. In quantum mechanics, large distances correspond to low energies. (Remember that the energy of a wave decreases as its wavelength increases; quantum mechanics is all about waves.) So for low-energy processes, the effective field theory provided by Fermi is all you need to know about the weak interactions.

The universe is kind, but that kindness comes at a price. Sometimes you want to care about the microscopic realm — for example, if you’re a physicist trying to figure out what is going on down there. When we look at spacetime on length scales of 10^-33 centimeters, do we see vibrating strings, or noncommuting matrices, or spin networks, or what? Hard to tell, because it makes no difference at all to the large-distance/low-energy physics we can actually observe.

That’s okay. A world described by a succession of effective field theories of ever-higher resolution helps us make sense of the world, while leaving physicists plenty of puzzles to think about. Very deserving of our thanksgiving.

It’s guest week at XKCD, as Randall Munroe deals with a family illness. (Fortunately for the guest artists, it’s relatively easy to mimic his style.) Today’s contribution came from Bill Amend of Foxtrot fame, who gives us what might be the best Heisenberg’s Uncertainty Principle joke I’ve seen.

There are more.

There was some excitement last week about a Maxwell’s-Demon-type experiment conducted by Shoichi Toyabe and collaborators in Japan. (Costly Nature Physics article here; free arxiv version here.) It’s a great result, worth making a fuss about. But some commentators spun it as “converting information into energy.” That’s not quite right — it’s more like “using information to extract energy from a heat bath.”

Say you have a box of gas with a certain temperature at maximum entropy — thermodynamic equilibrium. That is, the gas is smoothly spread throughout the box. (We can safely ignore gravity.) There’s certainly energy in there, but it’s not very useful. Indeed, one way of thinking about entropy is as a measure of how useless a certain amount of energy is. If we have a low-entropy configuration, we can extract useful work from the energy inside, such as pushing a piston. If we have a high-entropy configuration, the energy is useless; there’s nothing we can do to consistently extract it.

Here’s an example from my book. Consider two pistons with the same number of gas particles inside, with the same total energy. But the top container is in a low-entropy state with all the gas on one side of the piston; the bottom container is in a high-entropy state with the gas equally spread out.

You see the difference — from the top configuration we can extract useful work by simply allowing the piston to expand. In the process, the total energy of the gas goes down (it cools off). But in the bottom piston, nothing’s going to happen. There’s just as much energy inside there, but we can’t get it out because it’s in a high-entropy state.

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Here is a fantastic TED talk by JJ Abrams, the guy behind many of the most interesting genre movies and TV shows in recent years (Alias, Lost, Star Trek, Cloverfield, Fringe). It’s about the fundamental role played by mystery and the unknown in storytelling.

I’m posting it here because, as wonderful as the talk is, I disagree with it at a deep level. Yes, indeed, the concept of “mystery” is absolutely crucial to what makes a story compelling. But I think Abrams takes the idea too far, valorizing mystery for its own sake, rather than as motivation for the characters and the audience to try to solve the mystery. The reason why mysteries are interesting is because we want to figure them out! If they are simply irreducibly mysterious — if there is no sensible explanation that ultimately makes sense of all the clues — then it’s simply frustrating, not magical.

This isn’t just jousting with words — it has consequences for how stories are told. That’s why I chose Star Trek as my one movie to complain about in our Comic-Con panel last summer (as much as I enjoyed the movie overall). The dangerous planet-killing substance in that case was “red matter.” Shiny, red, and ominous-looking, red matter is not anything known to modern science. Which is fine; modern science doesn’t know about warp drive or Vulcans, either, but they work well in this particular fictional context. The problem is that red matter wasn’t associated with any sensible properties even within this fictional world. We never knew where it came from, why it did what it did, how it would react to different circumstances, etc. (Why did it have to be deposited in the exact middle of a planet, rather than just splashed on the surface?) It was simply “mysterious.” But this particular bit of mystery didn’t make it more compelling — it prevented the audience from engaging with the menace that the red matter presented. If we knew something about it, we wouldn’t just be going “okay, that’s the bad stuff, gotcha”; we’d be following along as Kirk and Spock tried to defuse the danger, understanding what might and might not do the trick. Not all mystery is good storytelling — sometimes a bit of understanding helps grab the attention.

Just to draw the distinctions even more carefully, let me come out in favor of ambiguity as opposed to mystery. The end of Inception is quite famously amenable to more than one interpretation. (To go back further, ask whether Deckard was a replicant.) This drives people crazy, trying to figure out which one is “right,” an impulse I think is misguided. It’s okay to accept that we don’t know all the answers! But in theses cases we understand quite well the space of all possible answers. There is no black box whose operation is simply mysterious. We don’t need to know all the final answers once and for all; but it’s better storytelling if we understand what the answers could be, and that they make sense to us.

Hopefully it’s not too hard to read between the lines here, and see the consequences for science as well as for movies. There are those who argue that science destroys the magic of the world by figuring things out. That’s exactly backwards — the scientific quest to solve the world’s puzzles is one of the things that makes the story of our lives so interesting.

If I ever give up blogging for good, it will be because of comments like this:

I just don’t get it. What a lame blog topic that should have been left on the cutting room floor. There is no science here. Evidently cited just to provide an opportunity to express a personal belief. Why not blog on the news of the day..the successfully trapping the first “anti-atom” and its potential implications? This is real news, real science and in keeping with your expertise. You could teach me something. Instead you give me this?

Obviously the sensible reaction is to laugh and move on, but few of us achieve that level of Zen detachment in dealing with the world. Many of the comments at CV are great, and I’ve certainly learned a lot from the interactions here, but quite a high percentage are of this form. When you put a lot of work into the blog and care about how it turns out, this kind of stuff wears you down. Why are people like this? I understand that not every post will interest every person; is it really more satisfying to take time to lash out in the comment section (when you have never left a constructive comment yet), rather than just skipping to something else on the vast and endlessly amusing internet?

[/grumpy]

That’s the name of a new paper by Akihisa Shioi, Takahiko Ban, and Youichi Morimune. Abstract:

The design of autonomously moving objects that resemble living matter is an excellent research topic that may develop into various applications of functional motion. Autonomous motion can demonstrate numerous significant characteristics such as transduction of chemical potential into work without heat, chemosensitive motion, chemotactic and phototactic motions, and pulse-like motion with periodicities responding to the chemical environment. Sustainable motion can be realized with an open system that exchanges heat and matter across its interface. Hence the autonomously moving object has a colloidal scale with a large specific area. This article reviews several examples of systems with such characteristics that have been studied, focusing on chemical systems containing amphiphilic molecules.

The journal is called Entropy, which I love. The paper discusses a variety of different systems that can travel, wiggle around, and respond to stimuli in ways that resemble living organisms. Not exactly building life in a test tube, but the boundary grows increasingly blurry.

Earlier today I learned of the passing of Allan Sandage. Allan was a tremendously broad astronomer, who had a lasting impact on fields of astronomy stretching from stellar evolution to the largest cosmological issues. He is perhaps best known for his work on the distance scale, and measurements of the Hubble Constant, but he had equally significant contributions to our understanding of stars.

The prominence of his work on the Hubble Constant is in part due to the rather contentious history of this subject over much of the 90’s and early 2000’s. Allan was at heart a stellar astronomer, but one who found himself tied to Hubble’s legacy by virtue of being Hubble’s telescope assistant in the years leading up to Hubble’s unexpected death in 1953. As one of the earliest pioneers (with Martin Schwarzschild) of the technique of using main sequence turnoffs to assign ages to globular clusters, Allan was deeply (and understandably) bothered by experiments that returned large values of the Hubble Constant — these values implied ages for the universe that were younger than the oldest globular clusters, which was clearly an implausible contradiction. Instead, Allan and his collaborators published a long series of papers attempting to deal will every uncertainty and bias in the distance scale, and found a consistently smaller value of the Hubble Constant than the other competing team (the “Hubble Key Project”, led by Wendy Freedman with many collaborators). In time, Allan’s group’s on-going evaluations of the distance calibration gradually pushed their value of the Hubble Constant up somewhat, while the Key Project’s values were being nudged down a bit (although they never did actually meet, particularly as error bars shrank in more recent years). Simultaneously, the discovery of dark energy changed the age estimates for the universe, allowing old globular clusters to co-exist harmoniously with a moderate value of the Hubble Constant.

During this time, Allan developed a reputation for being, well, difficult. His scientific disagreements on this issue unfortunately veered occasionally into the personal. That said, I had the pleasure of being a postdoc at the Carnegie Observatories during this time, and had an office a few doors down the hall from him. Allan was invariably gracious and kind to the postdocs. He was scientifically engaged, and always willing to share his knowledge, which was both deep and wide. I enjoyed having him for a colleague for 4 years, during a very scientifically vibrant stage of my astronomical training, and I am very sorry to hear of his passing.

The results from this weekend’s question are in: “What is the one concept in science that you really think should be explained better to a wide audience?” I tried to collate the answers from Twitter and Facebook as well as here, at least up to the point where my patience evaporated. Answers below the fold, grouped into three categories: big concepts, specific ideas, and meta issues.

Scott Aaronson wrote, “The skill of sharpening a question to the point where it could actually have an answer.” Which is a skill I should probably try to develop myself, as the question I asked was amenable to different interpretations. Many people answered “evolution,” but as Ed Yong pointed out on Twitter, evolution is actually explained quite well in many places. So when we ask what needs to be explained better, there are at least two issues at work: what we actually do a bad job at explaining, and what doesn’t succeed at penetrating out into the public consciousness. In contrast with evolution, for example, I would say that quantum mechanics is explained in many places, but very rarely is it explained well.

The winner by a wide margin was the meta issue of “the scientific method.” Which raises another question: do we agree on what the scientific method is? I suspect not. But I am completely on board with the idea that “how science works” is not explained very well, and possibly a higher priority than any particular scientific concept.

Others that did well: evolution, statistics, certainty/uncertainty, entropy, quantum mechanics, time, and gravity. I cannot refrain from pointing out that these last four were all addressed at some length in From Eternity to Here. Which makes me think that what people are really saying is, “more folks should read Sean’s book.” Only 40 more shopping days ’till Xmas…

Also of note is that there wasn’t actually a great deal of consensus; the list of concepts that came up is quite long. Clearly we need to do a better job of explaining.

Here are the answers:

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