They use superfluid helium to cool the superconducting magnets. One of the many weird properties of this stuff is that it has zero viscosity. Which means that, if there’s any sort of hairline fracture anywhere in the 27 kilometer long tunnel, the stuff comes spewing out, and very, very bad things happen. Every component, every joint, every one of the tens of thousands of tiny connections has to be perfect. It is this sort of failure which brought the machine to its knees shortly after commissioning, over a year ago.

The magnets are kept very, very cold; the superfluid helium is at 1.9 Kelvin (-271 Celsius), or a couple of degrees above absolute zero. We’re not talking a little vial in a laboratory being kept at this temperature. We’re talking many thousands of tonnes of magnets, kept just above absolute zero (using 96 tonnes of liquid helium). As things cool down, they naturally contract. The decks on bridges do the same thing, hence those serrated grills at the ends of bridges to absorb the expansion and contraction due to weather (if you’ve ever motorcycled across a bridge, you know exactly what I’m talking about). There are equivalent serrated joints in the LHC beam pipe to ensure that it doesn’t contract and rip open upon cooling (which, needless to say, would be bad). But upon reheating a section of the LHC, it turned out some of these devices left little fibers in the beam tube. Not good. How to find them, without ripping open the entire collider (costing millions of dollars and setting the project back precious months)? They ended up blowing a ping pong ball (with electronics embedded) down the tube, and tracking where it would get stuck. A simple, elegant, cheap solution to fix a multi-billion dollar enterprise.

For a while during the construction they ended up with roughly a billion dollars worth of superconducting magnets being stored in a parking lot at CERN. For reference, this is comparable to the entire GDP of many small countries (Bhutan, Guyana, Burundi, etc.), sitting out in the rain and snow. Big science.

Hopefully sometime in the next few days they’ll be running at 3.5 TeV. Apparently it’s been slow going because the system to prevent catastrophic quenching of the magnets (which is what “broke” the machine previously) is on a hair-trigger, setting off all sorts of false alarms (and when it goes off it quenches the magnets [in a controlled manner]). You can keep track of the progress on the LHC webpage (clicking on the image of the ring gives real-time data on the temperature of the magnets). Although this would be the highest energy ever achieved, it still doesn’t significantly surpass the science reach of Fermilab’s Tevatron, since the latter has run for many years (albeit at a lower energy of 1 TeV+1TeV). Both energy and (integrated) luminosity matter in this game, and the Tevatron has gotten more than 8 inverse fb (femtobarns; one of the best units in all of science [think "there's no way to miss it, it's as big as a barn"]). The LHC is shooting for 1 inverse fb. All being well, in a few months they’ll bump the energy up to 5 Tev on 5 TeV. This should significantly open up the scientific discovery space, and could conceivably kick off the next revolution in particle physics. Exciting times!

Dust isn’t only an annoyance — it’s also pretty. Planck hasn’t released any data about the CMB yet, but they just released a map of the cold dust in our local vicinity, looking for all the world like an abstract expressionist painting. (I want to suggest a particular artist, but my mind is blanking.) Click to embiggen.

It’s a false-color image, of course; the dust is very cold (tens of degrees above absolute zero), and the image is constructed from microwaves, not from visible light. You can see the plane of the galaxy, and the filamentary structures arising from all the churning of the interstellar medium from supernovae, star formation, magnetic fields, and so on.

Okay, pretty time is over. Let’s see the CMB.

The White Mountain from charles on Vimeo.

For me, it really captures the best parts of how observing feels.

It misses the not-so-good parts, where the instrument breaks, or you’re shut down for wind in perfectly clear weather, or you’re trying desperately to stay awake on a diet of nothing but reheated bagel dogs.

I suppose I’m feeling rather maudlin about it, because its now been years and years since I’ve set foot at an observatory. During the past decade, almost all of my data has been ordered up from satellites or the observing queue, in contrast to my years at Carnegie, where I was observing for more than a month each year. My scientific life is much more “family friendly” as a result, but I still do miss the cold nights and big skies.

(h/t Andrew Sullivan)

Excerpt:

Fortunately, we (and Boltzmann) only need a judicious medium-strength version of the anthropic principle. Namely, imagine that the real universe is much bigger (in space, or in time, or both) than the part we directly observe. And imagine further that different parts of this bigger universe exist in very different conditions. Perhaps the density of matter is different, or even something as dramatic as different local laws of physics. We can label each distinct region a “universe,” and the whole collection is the “multiverse.” The different universes within the multiverse may or may not be physically connected; for our present purposes it doesn’t matter. Finally, imagine that some of these different regions are hospitable to the existence of life, and some are not. (That part is inevitably a bit fuzzy, given how little we know about “life” in a wider context.) Then—and this part is pretty much unimpeachable—we will always find ourselves existing in one of the parts of the universe where life is allowed to exist, and not in the other parts. That sounds completely empty, but it’s not. It represents a selection effect that distorts our view of the universe as a whole—we don’t see the entire thing, we only see one of the parts, and that part might not be representative. Boltzmann appeals to exactly this logic.

After the amusing diversions of the last chapter, here we resume again the main thread of argument. In Chapter Eight we talked a bit about the “reversibility objection” of Lohschmidt to Boltzmann’s attempts to derive the Second Law from kinetic theory in the 1870’s; now we pick up the historical thread in the 1890’s, when a similar controversy broke out over Zermelo’s “recurrence objection.” The underlying ideas are similar, but people have become a bit more sophisticated over the ensuing 20 years, and the arguments have become a bit more pointed. More importantly, they are still haunting us today.

One of the fun things about this chapter is the extent to which it is driven by direct quotations from great thinkers — Boltzmann, of course, but also Poincare, Nietzsche, Lucretius, Eddington, Feynman. That’s because the arguments they were making seem perfectly relevant to our present concerns, which isn’t always the case. Boltzmann tried very hard to defend his derivation of the Second Law, but by now it had sunk in that some additional ingredient was going to be needed — here we’re calling it the Past Hypothesis, but certainly you need something. He was driven to float the idea that the universe we see around us (which, to him, would have been our galaxy) was not representative of the wider whole, but was simply a local fluctuation away from equilibrium. It’s very educational to learn that ideas like “the multiverse” and “the anthropic principle” aren’t recent inventions of a new generation of postmodern physicists, but in fact have been part of respectable scientific discourse for over a century.

It’s in this chapter that we get to bring up the haunting idea of Boltzmann Brains — observers that fluctuate randomly out of thermal equilibrium, rather than arising naturally in the course of a gradual increase of entropy over billions of years. I tried my best to explain how such monstrosities would be the correct prediction of a model of an eternal universe with thermal fluctuations, but certainly are not observers like ourselves, which lets us conclude that that’s not the kind of world we live in. Hopefully the arguments made sense. One question people often ask is “how do we know we’re not Boltzmann Brains?” The realistic answer is that we can never prove that we’re not; but there is no reliable chain of argument that could ever convince us that we are, so the only sensible way to act is as if we are not. That’s the kind of radical foundational uncertainty that has been with us since Descartes, but most of us manage to get through the day without being overwhelmed by existential anxiety.

Several years ago, before pi-day was famous, a student called the phone number associated with the digits in pi that appear after the decimal point, i.e., 1-415-926-5358. Apparently this is rather common now, and in fact, appears to be promoted as a mnemonic for the first 10 decimal places for those folks we need to have those numbers handy at all times. But this story happened in earlier times, back before the Bay Area split into several area codes. And, as the clever reader has already guessed, that student reached the SLAC main gate. How cool to phone pi and reach the main gate of a major national scientific research laboratory!

Alas, time and phone numbers march on, and nowadays phoning pi yields a “your call cannot be completed as dialed” message. (And I’m told that I cannot publish this post without noting that 3-14-15 will be a more accurate pi day.)

And most importantly, don’t forget to join us MARCH 13, at 1pm for the PLUTO IS A PLANET PROTEST MARCH AND RALLY. The march starts at the Greenwood Space Travel Supply store (8414 Greenwood Ave N) and will end at Neptune Coffee (8415 Greenwood Ave N).

But really, Greenwood Space Travel Supply is all kinds of awesome, even if they’re weirdly co-dependent with small rocks in the outer solar system. They’re the Seattle branch of the 826 network, which is a non-profit writing center for kids.

They also have cool t-shirts.

Monday morning I talked on the phone with Emily Lazar, a researcher for the show. I was really impressed right from the start: it was clear that she wanted to make it easy for me to get across some substantive message, within the relatively confining parameters of what is basically a comedy show. From start to finish everyone I dealt with was a consummate pro.

We got picked up at our hotel in a car that brought us to the Colbert studio, and hustled inside under relatively high security — people whispering into lapel microphones that we had arrived and were headed to the green room. Very exciting. The green room was actually green, which is apparently unusual. I got pep talks from a couple of the staff people, who encouraged me to keep things as simple as possible. They made an interesting point about scientists: they make the perfect foils for Stephen’s character, since they actually rely on facts rather than opinions.

Stephen himself dropped by to say hi, and to explain the philosophy of his character — I suppose there still are people out there who could be guests on the show who haven’t ever actually watched it. Namely, he’s a complete idiot, and it’s my job to educate him. But it’s not my job to be funny — that’s his bailiwick. The guests are encouraged to be friendly and sincere, but not pretend to be comedians.

We got to sit in the audience as the early segments were taped, which were hilarious. I feel bad that my own interview is going to be the low point of the show, laughs-wise. But I went out on cue, and fortunately I wasn’t at all jittery — too much going on to have time to get nervous, I suppose.

I had some planned responses for what I thought were the most obvious questions. Of which, he asked zero. Right off the bat Colbert managed to catch me off guard by asking a much more subtle question than I had anticipated — isn’t the early universe actually very disorderly? That would be true if you ignored gravity, but a big part of my message is that you can’t ignore gravity! The problem was, I had promised myself that I wouldn’t use the word “entropy,” resisting the temptation to lapse into jargon. But he had immediately pinpointed an example where the association of “low entropy” with “orderly” wasn’t a perfect fit. So I had to go back on my pledge and bring up entropy, although I didn’t exactly give a careful definition.

As everyone warned me, the whole interview went by in an absolute flash, although it really lasts about five minutes. There was a fun moment when we agreed that “Wrong Turn Into Yesterday” would make a great title for a progressive-rock album. Overall, I think I could have done a better job at explaining the underlying science, but at least I hope I successfully conveyed the spirit of the endeavor. We’ll have to see how it comes across on TV.

I shouldn’t end without including some good words about the bag of swag. Not only does every guest get a goodie bag that includes a bottle of excellent tequila, it also includes a $100 gift certificate for Donors Choose. How awesome is that?

And as we left the studio, there were some young audience members lurking around hoping for a glimpse of the great man himself. They had to settle for me, but they sheepishly asked if I would pose for a picture with them. Not yet having perfected my diva act, I happily complied. I hope they take away some great memories of the night.

Yesterday’s book club post referred to a somewhat-whimsical vision of Maxwell’s Demon as a paradigm for life. The Demon takes in free energy and uses it to maintain a separation between hot and cold sides of a box of gas — a sustained departure from thermal equilibrium. But what if we reversed the story? Instead of thinking that the Demon takes advantage free energy to help advance its nefarious anti-thermodynamic agenda, what if we imagine that the free energy is simply using the Demon — that is, the out-of-equilibrium configurations labeled “life” — for its own pro-thermodynamic purposes?

Energy is conserved, if we put aside some subtleties associated with general relativity. But there’s useful energy, and useless energy. When you burn gasoline in your car engine, the amount of energy doesn’t really change; some of it gets converted into the motion of your car, while some gets dissipated into useless forms such as noise, heat, and exhaust, increasing entropy along the way. That’s why it’s helpful to invent the concept of “free energy” to keep track of how much energy is actually available for doing useful work, like accelerating a car. Roughly speaking, the free energy is the total energy minus entropy times temperature, so free energy is used up as entropy increases.

Because the Second Law of Thermodynamics tells us that entropy increases, the history of the universe is the story of dissipation of free energy. Energy wants to be converted from useful forms to useless forms. But it might not happen automatically; sometimes a configuration with excess free energy can last a long time before something comes along to nudge it into a higher-entropy form. Gasoline and oxygen are a combustible mixture, but you still need a spark to set the fire.

This is where life comes in, at least according to one view. Apparently (I’m certainly not an expert in this stuff) there are two competing theories that attempt to explain the first steps taken toward life on Earth. One is a “replicator-first” picture, in which the key jump from chemistry to life was taken by a molecule such as RNA that was able to reproduce itself, passing information on to subsequent generations. The competitor is a “metabolism-first” picture, where the important step was a set of interactions that helped release free energy in the atmosphere of the young Earth. You can read some background about these two options in this profile of Mike Russell (pdf), one of the leading advocates of the metabolism-first view.

I was reading a bit about this stuff because I wanted to move beyond the fairly simplistic sketch I presented in my book about the relationship between entropy and life. So I did a little research and found some papers by Eric Smith at the Santa Fe Institute. Smith has taken quite an academic path; his Ph.D. was in string theory, working with Joe Polchinski, and now he applies ideas from complexity to questions as diverse as economics and the origin of life.

On Saturday I was on a long plane ride from LA to Bozeman, Montana, via Denver. So I had pulled out one of Smith’s papers and started to read it. A couple sat down next to me, and the husband said “Oh yes, Eric Smith. I know his work well.” This well-read person turned out to be none other than Mike Russell, featured in the profile above. Here I was trying to learn about entropy and the origin of life, and one of the world’s experts sits down right next to me. (Not completely a coincidence; Russell is at JPL, and we were both headed to give plenary talks at the annual IEEE Aerospace Conference.)

So I explained a little to Mike (now we are buddies) what I was trying to understand, and he immediately said “Ah, that’s easy. The purpose of life is to hydrogenate carbon dioxide.” (See figure above, taken from one of Eric Smith’s talks.)

That might be something of a colorful exaggeration, but there’s something fascinating and provocative behind the idea. An extremely simplified version of the story is that the Earth was quite a bit hotter in its early days than it is today, and the atmosphere was full of carbon dioxide. At high temperatures that’s a stable situation; but once the Earth cools, it would be energetically favorable for that CO₂ to react with hydrogen to make methane (and other hydrocarbons) and water. That is to say, there is a lot of free energy in that CO₂, just waiting to be released.

The problem is that there is a chemical barrier to actually releasing the energy. In physicist-speak: the Earth’s atmosphere was caught in a false vacuum. There’s no reaction that takes you directly from CO₂ and hydrogen to methane (CH₄) and water; you have to go through a series of reactions to get there. And the first steps along the way constitute a potential barrier: they consume energy rather than releasing it. Here’s a plot from one of Russell’s talks of the free energy per carbon atom of various steps along the way; it looks for all the world like a particle physicist’s plot of the potential energy of a field caught in a metastable vacuum. (Different curves represent different environments.)

Here is the bold hypothesis: life is Nature’s way of opening up a chemical channel to release all of that free energy bottled up in carbon dioxide in the atmosphere of the young Earth. My own understanding gets a little fuzzy at this point, but the basic idea seems intelligible. While there is no simple reaction that takes CO₂ directly to hydrocarbons, there are complicated series of reactions that do so. Some sort of membrane (e.g. a cell wall) helps to segregate out the relevant chemicals; various inorganic compounds act as enzymes to speed the reactions along. The reason for the complexity of life, which is low entropy considered all by itself, is that it helps the bigger picture increase in entropy.

In ordinary statistical mechanics, we say that high-entropy configurations are more likely than low-entropy ones because there are simply more of them. But that logic doesn’t quite go through if you can’t get to the high-entropy configurations in any straightforward way. Nevertheless, a sufficiently complicated system can bounce around in configuration space, trying various different possibilities, until it hits on something that looks quite complex and unlikely, but is in fact very useful in helping the system as a whole evolve to a higher-entropy state. That’s life (as it were). It’s not so different from other cases like hurricanes or turbulence where apparent complexity arises in the natural course of events; it’s all about using up that free energy.

Obviously there is a lot missing to this story, and much of it is an absence of complete understanding on my part, although some of it is that we simply don’t know everything about life as yet. For one thing, even if you are a metabolism-first sympathizer, at some point you have to explain the origin of replication and information processing, which plays a crucial role how we think about life. For another, it’s a long road from explaining the origin of life to getting to the present day. It’s true that we know of very primitive organisms whose goal in life seems to be the conversion of CO₂ into methane and acetate — methanogens and acetogens, respectively. But animals tend to produce CO₂ rather than consume it, so it’s obviously not the whole story.

No surprise, really; whatever the story of life might be, there’s no question it’s a complicated one. But it all comes down to the elementary building blocks of Nature doing their best to fulfill the Second Law.

Excerpt:

Schrödinger’s idea captures something important about what distinguishes life from non-life. In the back of his mind, he was certainly thinking of Clausius’s version of the Second Law: objects in thermal contact evolve toward a common temperature (thermal equilibrium). If we put an ice cube in a glass of warm water, the ice cube melts fairly quickly. Even if the two objects are made of very different substances—say, if we put a plastic “ice cube” in a glass of water—they will still come to the same temperature. More generally, nonliving physical objects tend to wind down and come to rest. A rock may roll down a hill during an avalanche, but before too long it will reach the bottom, dissipate energy through the creation of noise and heat, and come to a complete halt before very long.

Schrödinger’s point is simply that, for living organisms, this process of coming to rest can take much longer, or even be put off indefinitely. Imagine that, instead of an ice cube, we put a goldfish into our glass of water. Unlike the ice cube (whether water or plastic), the goldfish will not simply equilibrate with the water—at least, not within a few minutes or even hours. It will stay alive, doing something, swimming, exchanging material with its environment. If it’s put into a lake or a fish tank where food is available, it will keep going for much longer.

This chapter starts with something very important: the relationship between entropy and memory. Namely, the reason why we can “remember” the past and not the future is that the past features a low-entropy boundary condition, while the future does not. I don’t go into great detail about this, and we certainly don’t talk very specifically about how real memories are formed in the brain, or even in a computer. But when we get to the next chapter, about recurrences and Boltzmann brains, it will be crucial to understand how the assumption of a low-entropy boundary condition enables us to reconstruct the past. It’s hard for people to wrap their brains around the fact that, without such an assumption, our “memories” or records of the past will generally be unreliable — knowledge of the current macrostate wouldn’t allow us to reconstruct the past any better than it allows us to predict the future. (Which is only logical, since it’s only this hypothesis that breaks time-reversal symmetry.)

The rest of the chapter, meanwhile, is more about having fun and mentioning some ideas that are not directly related to our story, but certainly play a part in understanding the arrow of time. Information theory, life, complexity. I’m not an expert in any of these fields, but it was a lot of fun reading about them to pick out some things that fit into the broader narrative. The Maxwell’s Demon story, in particular, is one that every physicist should know (up through it’s relatively modern resolution), but relatively few do. And I think Jason Torchinsky did a great job with the illustrations of the Demon.

A lot of big ideas here, of course, and much of this stuff is still very much in the working-out stage, not the settled-understanding stage. We’re still arguing about basic things like the definition of “complexity” and “life.” It’s relatively easy to state the Second Law and explain how the arrow of time is related to the growth of entropy, but there’s a tremendous amount of work still to be done before we completely understand the way in which the universe actually evolves from low entropy to high.