December 2010

Hits of the Year

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Have you folks seen Ed Yong’s massive multi-part year-end round up at Not Exactly Rocket Science? Let’s just say he’s currently on Part Nine, with little sign of slowing down.

Here at Cosmic Variance we’re not nearly as prolific as Ed (there are only seven of us, and one of him), but the idea of a year-end wrap-up is a good one. I.e., it seems to create content in the slow intra-holiday period, without actually coming up with anything new. So here are some of my own favorite posts from the last year, with a few guest posts thrown in for good measure.

If I were a braver person, I’d do a corresponding list of my worst blog posts of the year. And if my grandmother had wheels, she’d be a trolley.

Happy New Year, everyone.

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Observing the Multiverse (Guest Post)

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It’s a big universe out there — maybe bigger that we think. A lot of people these days are contemplating the possibility that the wider world isn’t just more of the same; it could be that there are regions very different from ours, even with different low-energy laws of physics, outside our observable universe. It’s an old idea, which we now label the “multiverse,” even though we’re talking about regions of space connected to ours. A lot of other people are aghast that this is considered science. Personally I think science talks about unobservable things all the time, and this question is going to be resolved by people doing hard work to make sense of multiverse scenarios rather than by pronouncements about what is or is not science.

Matt Johnson We’re very happy to have a guest post from one of the people who is doing exactly that hard work — Matt Johnson, who guest-blogged for us before. He and his collaborators just come out two papers that examine the cosmic microwave background, looking for evidence of “bubble collisions.”

First Observational Tests of Eternal Inflation
Stephen M. Feeney (UCL), Matthew C. Johnson (Perimeter Institute), Daniel J. Mortlock (Imperial College London), Hiranya V. Peiris (UCL)
arXiv:11012.1995

First Observational Tests of Eternal Inflation: Analysis Methods and WMAP 7-Year Results
Stephen M. Feeney (UCL), Matthew C. Johnson (Perimeter Institute), Daniel J. Mortlock (Imperial College London), Hiranya V. Peiris (UCL)
arXiv:1012.3667

The hope is that these other “universes” might not be completely separate from our own — maybe we collided in the past. They’ve done a very careful job going through the data, with intriguing but inconclusive results. (See also Backreaction.)

Looking for this kind of signature in the CMB is certainly reminiscent of the concentric circles predicted by Gurzadyan and Penrose. But despite the similarities, it’s different in crucial ways — different theory, different phenomenon leading to the signal, different analysis, different conclusions. The road to sorting out this multiverse stuff is long and treacherous, but our brave cosmological explorers will eventually guide us through.

Here’s Matt.

———————————————————————–

Observing other universes: is this science fiction?

Perhaps not. Stephen Feeney, Daniel Mortlock, Hiranya Peiris and I recently performed an observational search for the signatures of colliding bubble universes in the cosmic microwave background. Before getting to our results, let me explain some of the back-story.

The idea that there might be other universes is taken quite seriously in high energy physics and cosmology these days. This is mainly due to the fact that the laws of physics, and the various “fundamental” constants appearing in them, could have been otherwise. More technically worded, there is no unique vacuum in theories of high energy physics that involve spontaneous symmetry breaking, extra dimensions, or supersymmetry. Having a bunch of vacua around is interesting, but to what extent are they actually realized in nature? Surprisingly, when a spacetime region undergoing inflation is metastable, there are cases when all of the vacua in a theory can be realized in different places and at different times. This phenomenon is known as eternal inflation. In an inflating universe, if a region is in a metastable vacuum, bubbles containing different vacua will form. These bubbles then expand, and eat into the original vacuum. However, if the space between bubbles is expanding fast enough, they never merge completely. There is always more volume to convert into different vacua through bubble formation, and the original vacuum never disappears: inflation becomes eternal. In the theory of eternal inflation, our entire observable universe resides inside one of these bubbles. Other bubbles will contain other universes. In this precise sense, many theories of high energy physics seem to predict the existence of other universes.

…

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Science of TRON

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I don’t know about any of you, but I was extremely excited about the release of TRON: Legacy. Partly because the light cycles are cool, but also for a personal reason: this was the first movie I helped consult on as part of the early days of the Science and Entertainment Exchange. And I’ll be honest; that extremely tenuous personal connection was enough to make me feel personally invested in the success of the movie. I am shallow. Haters gonna hate, but my mind is made up. More objective reviews have ranged across the spectrum, but for many of us it was a thrilling feast of eye candy that makes for a great holiday film.

But … Science? Well, yes, a little. Dan Vergano has some of the scoop. There was a huge amount of science and technology that went into making the film, of course, but also some underlying the story. The director, Joe Kosinski, and producers, Sean Bailey and Jeff Silver, were very enthusiastic about science from the start, and always wanted to learn more. At the same time, it’s essentially a fantasy movie, not a documentary or even hard SF, and nobody was tempted to over-explain what was going on. Our consult occurred after the initial script was already in place, so it wasn’t as if we exerted a noticeable influence on the direction of the plot. What we did was help fill in the backstory. If there is a sequel, some of the ideas we talked about could end up playing a more substantial role.

Early in the movie, the Alan Bradley character waxes enthusiastic about the advances of technology, and includes a bit of technobabble about “genetic algorithms” and “quantum teleportation.” But in fact, that bit of babble is very relevant. One of the most interesting aspects of the new grid world is the existence of “Isos” — programs that arose spontaneously, rather than being constructed by a programmer. And of course one of the main conceptual hurdles in the plot is how you teleport a physical human being into the grid. We talked a lot in the consult about conservation of mass. And in the final result, the laser that miraculously disassembles Sam Flynn and transports him into the grid is equipped with canisters of raw materials (oxygen, carbon, etc.) that can be used to re-assemble people back into reality. You won’t even notice them when you watch the movie, but they’re there, and I count that as a small victory.

Realistic science that you’d be happy to show your class? No. But a decent example of how a bit of science can help add depth to a story. Scientists can play a much more substantial if they consult right at the beginning, when a script is first coming together — and hopefully we’ll start seeing the fruits of some of those consultations before too long. But every little bit helps. A movie like TRON doesn’t force you to think against your will — you can perfectly well just sit back, turn off your brain, and enjoy the ride. But if you’re predisposed to thinking, there’s plenty of food for thought.

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A Mixed Day for Basic Human Decency

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Nothing focuses the mind of an elected representative like the prospect of their vacations being cut short, and Congress has been busy in the days leading up to the Christmas holiday. The big news today:

  • “Don’t Ask, Don’t Tell” is being repealed. DADT was the ugly political compromise that allowed gay and lesbian soldiers to serve in the military, as long as they stayed in the closet. It was opposed by the military, most Americans, and even most members of Congress. Repeal was only difficult because of the bizarre filibuster rule that allows 40% of the U.S. Senate to gang together to block legislation they oppose on the basis of fundamental principles, such as the principle that homosexuals should be discriminated against. Oh, and the energetic opposition of Crazy John McCain, who was a longtime opponent of DADT until he decided it was politically expedient to switch sides. (“There will be high-fives all over the liberal bastions of America,” he said, taking the nonpartisan high road.) The legislative strategy for repeal is a hard-won victory for Obama, who could have overturned the policy by executive order, but argued that passing a law would yield a much more solid and lasting result.
  • The DREAM Act has failed. Again, not because it couldn’t get a majority, but because it couldn’t muster the votes to overcome a filibuster. (A handful of Democrats joined with the Republicans on this one.) In this case, the principled objection was to a bill that allowed non-citizens who were brought to this country illegally as children (when they were younger than 16) to attain citizenship if they graduated from high school and either completely two years of college or joined the military. Obviously we wouldn’t want people like that in our country.

Sorry to be snarky, truly. I much prefer having polite discussions about honest disagreements. But these aren’t examples of that; opposition to these measures arises from combinations of craven political posturing and straightforward bigotry. Nothing principled about it; just politicians preying on people’s fears. And I honestly believe that we have a more healthy political dialogue by admitting that outright, rather than pretending that opposition to bills like this is in any way honorable.

DADT repeal is a big deal. Congratulations to all the servicemen and -women who no longer have to live a lie (at least not because of official government policy; informal discrimination is harder to eradicate). High fives all over!

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TEDxCaltech

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Everyone knows about the TED talks — the great, and mercifully short, presentations whose videos are among the most-shared on the web. Even clicking on a completely random talk, you’re likely to be rewarded with something interesting. Part of that is the extraordinary level of quality control — not only in choosing speakers, but in working with speakers ahead of time to fine-tune their presentations. And holding them to a time limit.

Besides the big TED conferences, there are also independently-organized events known as TEDx. Caltech is going to host such an event for the first time, TEDxCaltech, on January 14. The theme is “Feynman’s Vision: The Next 50 Years.” In practice that means three groups of talks: Conceptualization and Visualization in Science, Frontiers of Physics, and Nanoscience and Future Biology. Check out the list of speakers. If it weren’t for the fact that I am on it myself, I’d emphasize what a great program this is — any event that includes both Scott Aaronson and Lyle Mays shows quite a bit of promise. Throw in Leonard Susskind and Craig Venter, and it might be worth a special trip.

All are welcome to come! The flip side of the fact that so much work goes into making the talks successful is that a corresponding level of commitment is asked of the audience — so you don’t simply buy a ticket, you apply, and it does cost money. But who can put a price on inspiration?

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Farewell, Pioneer Anomaly?

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Here’s an excellent article in Popular Science about the Pioneer anomaly. (Via Dan Vergano on Twitter.) The Pioneer spacecraft, launched in the early 1970’s, have been moseying through the outer regions of the Solar System for quite some time now. But a careful analysis of tracking data indicated that the acceleration of the two spacecraft didn’t quite match what we’d expect from gravity; there appears to be an anomalous acceleration, nearly constant over time and pointing toward the Sun. Many new-physics explanations have been proposed, but it’s always been a difficult scenario to master; it’s very hard to imagine a new force that would account for the Pioneer data but not also show up in observations of the outer planets. (The Voyager spacecraft aren’t as useful for this purpose, as they are guided by tiny thrusters that overwhelm the signal, while the Pioneers float freely and are pointed using gyroscopes.)

File-Pioneer_11_Saturn_RingsThe most likely explanation has always been that we didn’t completely understand the spacecraft, or the tracking system. Indeed, it’s been recognized for a while that a small imbalance in how the spacecraft radiated heat could account for the acceleration — but that imbalance didn’t seem to be supported by what we knew about the vessels. That may be changing, however. The Popular Science article is a little cagey, but it mentions a new and unprecedentedly thorough analysis by Viktor Toth and Slava Turshyev that should be coming out soon. Here is as much as they would let on:

Five years have passed. Using the telemetry data, the two scientists created an extremely elaborate “finite element” 3-D computer model of each Pioneer spacecraft, in which the thermal properties of 100,000 positions on their surfaces are independently tracked for the duration of the 30-year mission. Everything there is to know about heat conduction across the spacecraft’s surfaces, as well as the way that heat flow and temperature declined over time as the power of the generators lessened, they know. The results of the telemetry analysis? “The heat recoil force accounts for part of the acceleration,” said Turyshev. They wouldn’t tell me how significant a part. (Turyshev: “We’d like to publish that in the scientific literature.”) But according to Toth, “You can take it to the bank that whatever remains of the anomaly after accounting for that thermal acceleration, it will at most be much less than the canonical value of 8.74 x 10-10 m/s2, and then, mind you, all those wonderful numerical coincidences people talk about are destroyed.”

Doesn’t look good for people who prefer to imagine that wild new physics is responsible. Not that they will go away — the power of wishful thinking is strong. You can already hear them staking out territory, even before the new report comes out:

Other physicists are more combative. “Heat? That’s simply not the right explanation. They are wrong,” commented Johan Masreliez, an independent researcher in Washington who supports the expanding spacetime model of cosmology, for which it is crucial that the value of the Pioneer anomaly equals c times H. “But then I’m biased,” he added.

Even if the new analysis gives a very sensible and believable account of the Pioneer anomaly in terms of very ordinary physics, expect the true believers to hang on for years to come. The rest of us will move on — at least until the next exciting anomaly pops up.

Also: big props to Natalie Wolchover, who wrote the PopSci piece. Very measured tone, carefully researched and well-written.

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Translational Invariance and Newton’s God

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Tim Maudlin is writing a two-volume introduction to the philosophy of physics, and I was fortunate enough to get a peek at a draft of Volume One, about space and time. There is one anecdote in there about Leibniz’s objections to Newtonian physics that is worth passing along. This came up in the course of the Leibniz-Clarke correspondence.

Leibniz was quite fond of proclaiming overarching a priori principles. Perhaps the most famous/infamous is the Principle of Sufficient Reason, which states that everything that happens does so for some good reason. But there was also the Principle of Identity of Indiscernibles, which states that if two things have all the same properties, they are really the same thing. Sounds reasonable enough (although one might worry what qualifies as a “property”), but it can get you in trouble if you take it too far.

Remember that Newton believed in absolute space — a rigid three-dimensional set of points that forms the arena in which physics takes place. Leibniz, on the other hand, claimed that space should be thought of purely in terms of relations between different points, without any metaphysical baggage of “absoluteness.” (From a modern perspective, Leibniz was closer to correct, given Galilean relativity; but once we allow for spacetime curvature in general relativity, the relational view becomes less useful.)

So far, so good. The weird part, to modern ears, comes in when we consider Newtonian cosmology. In order to explain matter in the universe, Newton departed from the strict consequences of his Laws of Motion. Instead, he imagined that empty space existed for an infinite period of time, before eventually God decided to create matter in it.

That’s the part Leibniz couldn’t go along with. He didn’t believe God would work that way, for reasons that amount to what we would now call the translational invariance of space. If God is going to create all this matter in empty space, Leibniz reasons, He has to put it somewhere. But where? Every point is equally good! Therefore there can’t be any “sufficient reason” to create it in one place rather than in some other place. Therefore there must be a deep metaphysical flaw at the heart of Newton’s theory. Interestingly, he didn’t go for “matter has been around forever,” but instead came down on the side of “there is no such thing as absolute space.”

Maybe he was worried about Boltzmann Brains?

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Email Addresses

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On the one hand, it’s extremely convenient for young academically-oriented people to grab an email account with Gmail or some other generic provider. The nature of the profession is that you will jump around from institution to institution — grad school, postdocs, faculty positions — and it’s extraordinarily annoying to have to keep switching email addresses with every move. Changing jobs is hassle enough as it is.

On the other hand — it’s letter-of-recommendation season, and there are still some backwards institutions out there who refuse to accept letters submitted from non-academic email addresses. Grrr. Get with the program, people!

Okay, not every blog post will be deep.

Update: prodded by Anil in comments, I verified that indeed Gmail is smart enough to let you use Gmail to send from any other email address you have. Just go to “Settings,” then “Accounts and Import,” then “Send Mail As.” Obviously you can’t use just any address, only ones you can verify. Hooray for Gmail!

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No Labels, No Point

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Michael Bloomberg and a posse of self-styled centrists have proclaimed a new movement that will save America from the tyranny of partisan gridlock: No Labels.

Maybe I’ve been radicalized by reading blogs for too long, but this is one of the dumbest ideas of all time. It doesn’t even have novelty to recommend it; an organization like this pops up every few years. (Remember Unity08?)

Sure, putting aside our differences and working together for the common good sounds like a lofty goal. Fine. But how is it actually supposed to work? Efforts like this are based on a fundamental unfixable mistake: the idea that what matters about politics is process, not issues. The idea that it doesn’t really matter what we do, only that we do it in a civil and constructive matter. The idea, in other words, that substance doesn’t really matter.

Here is an early post from the No Labels blog:

Lately, I find myself fielding variations of this question: “so what position will No Labels take on (insert issue)? The honest answer is I don’t know and to answer with exactness is premature. It’s not that there aren’t a lot of issues of importance out there. From the start, we’ve known that we want better approaches in the areas of the deficit, economic growth and education just to name a few examples.

Right. “Better approaches.” Why didn’t anyone think about this earlier. My predictions: they will come out firmly in favor of a lower deficit, more economic growth, and improved education. My heart beats faster just thinking about it.

Politics has a bad reputation. People don’t like it. You see family members saying silly things and then getting overly emotional about their commitments. There is an appealing fantasy that we could just learn to work together and get along, and then all of our problems would be solves.

But at the end of the day, the marginal rate of the top tax bracket has to be a certain number. There is or is not a public option for health insurance. We do or do not invade Iraq. People disagree about these issues. And politics is the way we make decisions in the face of those disagreements. Pretending otherwise is not principled, it’s wankery.

Politics might be distasteful, but it’s necessary, and taking it seriously is a virtue. Pretending to float above it all is not.

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Leaking Wikis

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Obviously everyone in the world has heard about Wikileaks and its associated controversies. It seems like the site itself has to keep moving to avoid various attacks, but at the moment it can be found here.

My strong first impulse is to be in favor of shining light in secret places. This can be taken to extremes, of course; there is such a thing as appropriate privacy, for governments and corporations as well as for individuals. But the natural tendency on the part of governments (or bureaucracies more generally) is to go too far to the other extreme, making secrecy routine where it should be exceptional — and using it to cover up embarrassment rather than protecting people’s lives. Something like Wikileaks is a great corrective to this tendency.

I don’t really see, however, how something like the wholesale release of diplomatic cables helps this cause. Some of the cables might have been covered up for pernicious reasons, but for the most part diplomats should have an expectation of privacy in these kinds of communications, as much as an ordinary citizen would when making a phone call. This doesn’t seem like a brave strike against government corruption as much as a bit of leering Peeping-Tommery. I’d personally be happier if Wikileaks were a bit more selective in what it shared with the world.

Personally, the most depressing aspect of the whole affair — even more than the cartoonish responses from craven politicians — has been the attitude of the established media. Sure, they will publish the stories, although usually accompanied by some sort of meek apologia. But on TV and in the op-ed pages, there is enormously more discussion about Julian Assange and Wikileaks itself than about what we have actually learned from the documents. A lot of people in the media these days consider themselves to be more like partners with government, rather than respectful adversaries. I’d love to see more thoughtful pieces about what we’ve learned from all these documents about how the world actually works.

Regardless of the ambiguities, I certainly hope Wikileaks keeps going. As Thomas Jefferson put it, “The press, confined to truth, needs no other legal restraint.” Or as Ruben Bolling more recently tweeted: “If a journalist is walking down the street, and happens to find a box of secret government documents, what should he do?” Telling the truth is always a good first strategy.

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