I returned a week ago from a few days at Penn State University, where I was chairing and speaking in the session on cosmology at the Inaugural Conference of the Institute for Gravitation and the Cosmos. This was a delightful trip for a number of reasons, not least because I could drive there rather than dealing with the increasing difficulties posed by flying. Driving also meant that it was easy to take along a couple of my graduate students - Alessandra Silvestri and Michele Fontanini.

The conference took place Thursday through Saturday and my duties were all on Thursday afternoon, meaning that the rest of the meeting was free for me to focus on what others had to say and take advantage of chances for some individual physics discussions. There were some excellent talks, with particularly nice ones, in my opinion, from Joe Polchinski (The Black Hole Information Paradox), Slava Mukhanov (The Origin of the Big Bang: Inflation After WMAP) and Frans Pretorius (Black Hole Collisions).

Slava is a master of these kinds of talks and even on topics I’m supposed to know a lot about, I always find I learn something new from him, although we did disagree about the importance of fine tuning in whatever microphysical theory underlies inflation. In his talk Joe expressed his personal opinion that the information loss paradox is now solved within string theory, although the audience did not universally share this view, and he faced some polite questioning from Institute Director Abhay Ashtekar.

Another plenary talk was delivered by Roger Penrose, who discussed what he described as “a crazy idea” to address the cosmological entropy problem in the context of cyclic universes. I did not follow the proposal entirely, but the session ran out of time before I could get a clarification.

The conference was not without some down time either, with an enjoyable banquet, after which I joined Deidre Shoemaker, Pablo Laguna, and several others to watch their colleague, my friend, and former Quantum Diaries contributor Stephon Alexander sit in as saxophonist with a jazz band playing at a local bar. Here he is, second from the right in this rather poor iPhone photo

Right now I’m supposed to be in Puebla, Mexico, delivering a set of lectures at the Dual C-P Institute of High Energy Physics workshop on SUSY and String Phenomenology. However, my travel schedule had no room for error in it, and due to bad weather all possible flights were canceled on Friday evening, guaranteeing that I would miss two out of my three talks and making my trip pointless. So I’m home cooking Mexican food to make myself feel better.

While I wish I’d been able to make this trip, there’s a lot to be said for not traveling these days, and right now I find myself in the extremely unusual position of having over five weeks without travel stretching ahead of me, before I go to California for some guy’s wedding and then off for a long trip to Australia. To offset this apparent freedom, however, our semester begins in one week!

Absolutely fascinating story of missed scientific opportunity over at Steinn Sigurdsen’s blog.

Apparently the US Airforce discovered pulsars.

I’m normally not one to jump on the latest press release, but this image is awfully purty.

The blue blob is not a comet, but is actually hot gas thrown off by an aging, rather famous star named Mira. (I realize this is sounding very “Sunset Boulevard”, but stay with me.)

Different types of stars are often named after the first one discovered, and, as Mira was one of the first stars of its type discovered, there is a whole class of pulsating red stars known as “Mira variables” in its honor. These “asymptotic giant branch” stars form when a moderately massive star begins to run out of fuel. After losing its most stable source of energy generation (hydrogen fusion in the very center), the star procedes to go through a series of conniption fits as it attempts to find alternate sources of fuel. During these fits, the star becomes quite creative about the ways in which it fuses hydrogen and helium into more massive elements. Fusion normally happens in the very center of a star, but at the end of its life, the star has already used up all the hydrogen & helium in the center. Instead, the star is forced to fuse these elements in shells surrounding the core (forming an onion of inert carbon ash, surrounded by a layer of helium fusing to carbon, another layer of hydrogen fusing to helium, and then an outer layer of inert hydrogen). At this point, the going gets rough for the star. First, because all the star’s energy is being generated much further out, the outer layers get pushed outwards, and the star expands to hundreds of times its initial size. Due to this swelling, the outer layers become only weakly bound to the star, making them easy to strip off. Then, to make things worse, the star begins to pulsate due to its inability to find a stable state of shell burning. During these pulsations, the star usually pushes off a good fraction of these outer layers in a “stellar wind”, depositing much of the star’s mass into the gas that pervades the galaxy.

What’s most striking to me is not just that you can see this hot expanding gas in the ultraviolet image above, but that you can see the bow shock (on the right hand side) where the stellar wind goes plowing into the gas that was already drifting through the galaxy. Like a person running into the ocean too fast, the hot gas from the wind stops when it hits the dense cool galactic gas, and shock heats to a high temperature, making a characteristic arc of very hot, luminous gas. This interaction with the surrounding gas shaped the highly asymmetric structure. There either was more dense galactic gas on the right side of the image than on the left, or more likely, the star was moving rapidly to the right, increasing the chances of forming a shock front in that direction. The shock confined the stellar wind on one side, but left it free to expand on the other. Moreover, if the star was racing to the right, material that got blown off would be left behind, leaving the long trail drifting off to the left, like a contrail behind an airplane.

You can actually see these shocks all over the place in astronomy. The most famous is probably the Bullet Cluster, which Sean discussed here.

See that red cone on the right? Another bow shock, formed as the hot gas from one galaxy cluster rammed into the gas from another galaxy cluster, as the two were pulled together by their gravitational attraction.

Another great example can be seen in the Orion nebula, a young region of star formation that appears as one of the “stars” in Orion’s sword:

The difference is that here, instead of the star ramming into some more slowly moving gas, some fast moving gas is probably ramming into the gas around the star. (To bring this full circle, the fast moving gas is probably due to stellar winds and radiation from dying stars off to the right of the image.)

These sorts of shocks happen on earth was well, most notably around the noses of planes moving at supersonic speeds. However, the shocks produced on earth almost never get hot enough to light up, leaving astronomy to provide the most dramatic visualizations of the phenomena.

We’ve been hearing a lot over the last few days about the damage to the tiles on the shuttle Endeavour. Roland Piquepaille at ZDNet blogs has now posted some exclusive pictures of the affected region, provided by Neptec Design Group.

I don’t know how serious this is, but now at least I understand what they mean by a gouge in the tiles. Here’s keeping our fingers crossed for the safety of the astronauts on board.

Just got back from a great trip to Beijing, very enjoyable if a bit tiring, where much musing was done on the Primordial Existential Question, about which more anon. But I also mused a bit about what this blog needs, and I came to the conclusion that must have been obvious to everyone else long ago: more videos of me.

So, here you are. Thanks to some heroic efforts on the part of folks who would just as soon lurk behind the scenes, we now have video captured from the C-SPAN broadcast of our science panel at YearlyKos. Here is my talk, conveniently divided into two pieces to appease the YouTube gods. They are a little fuzzy, but you get the idea. I used the mysterious beauty of dark matter and dark energy as an excuse to make some didactic points about science and rationality and politics. (If I weren’t an atheist, I would have made a good preacher.) You can also find videos of Chris’s talk and Ed’s talk at their respective sites; Tara, who felt sorry for me for being given the impossible task of making the universe sound interesting, has the Q&A up as well.

But! Behind the fold, the true payoff!

Continue reading ‘Hey, I Uploaded a Video’

My temporary officemate runs down to the vending machine and buys a bag of gummi bears. He dumps them on the desk, sorts them by color, and then procedes to eat them in order of increasing bin size (i.e. the pile of 1 orange one, then the pile of 3 yellow ones, then the pile of 4 green ones, etc).

If I buy a bag of M&M’s, I sort them by color, then figure out a division that lets me arrange them in a triangle, with one color per horizontal row, but allowing colors to be repeated (i.e. it’s ok for 9 red M&M’s to show up as a row of 7, and then further up, a row of 2). I then eat off each diagonal, producing a progressively smaller triangle, but one that maintains the horizontal color structure till the tasty end.

My kids, who I suspect inherited a geek-streak a mile wide, also sort multicolored candy into patterns and make up an algorithm for eating it.

The non-scientists who I have asked about this habit look at me like I’m nuts. (So do people who grew up in large families, because someone was bound to snarf the candy before they could take the time to develop this particular neurosis.)

So, is algorithmic consumption of multicolor candy a geek phenotype?

T-Rex of Dinosaur Comics realizes that his personal kink involves reversing the arrow of time. And further contemplation just makes things worse.

The construction of jokes involving Boltzmann’s Brains and onanism is a temptation better left resisted.

Below the fold: hott entropy action! Not safe for work, perverts!

Continue reading ‘Exponentially Unlikely Fetishes’

Greetings from the International Congress on Logic, Methodology and Philosophy of Science in Beijing. I once read, in Ray Monk’s biography of Bertrand Russell, about a year that Russell spent lecturing on philosophy in Beijing. He was extremely taken with the city and the country, predicting that it would flower into a leading role in the world. This momentarily puzzled me, as my vision of China didn’t seem in sync with Russell’s democratic ideals. But then common sense clicked in, and I realized that we were talking about a period just after World War One, during the Sun Yat-sen era. The new Republic of China was struggling to emerge out from Imperial rule, and the Communist takeover was decades in the future. One could have easily imagined that this sprawling country, united by a common language and a rich heritage of culture and innovation, would rapidly take its place among the free and prosperous nations of the world. The fact that it didn’t is one of the great tragedies of twentieth-century history.

These days China is increasingly prosperous, but not quite free. Upon landing at Beijing International Airport, one fills out the usual customs declaration form, full of admonishments against bringing in firearms or questionable agricultural products. But there is an extra item on the list of dangerous imports: writings, recordings, or other collections of information that could be judged as a threat to the political, moral, or social good of the nation. The didn’t actually ask to search my laptop, but the warning was there.

It’s well known that the People’s Republic of China (PRC) censors blogs, so I’ve been poking around using the internet connection here in my hotel room, trying to judge the extent to which this is true. (The flipside, of course, is the perilous situation of bloggers located in China; apparently they’ve been required to register in order to blog, but I don’t have the latest on that. I should mention that there are all sorts of blogs about China, not that I have any expertise about them.) Access to most websites is fine, but certain addresses are certainly being blocked. Of course it’s impossible for me to distinguish between the actions of the local ISP, the city of Beijing, or the Chinese government itself, but you draw conclusions using the data you have, not the data you wish you had.

Any blog on Blogspot is definitely off-limits (so I can’t visit Preposterous Universe for old time’s sake). You can type in the address or click a link, and the browser will think for a minute, and then return a “Problem loading page: The connection has timed out” error. My impression is that that’s been true for a long time, although apparently it’s been on and off for a while now. Typepad blogs are also off-limits, so no Cocktail Party Physics for me, although that might be a recent development. Livejournal seems to be unavailable, and likewise Xanga, but blogs hosted on Wordpress.com seem to be available. You can search on Google Blog Search or Bloglines, but Technorati is blocked. I haven’t found any individually-hosted blogs that were off-limits, although certain news sites like philly.com are mysteriously banned. The Eagles are in the middle of training camp, how am I supposed to keep up? Also, the New York Times is readily accessible, so make of that what you will. I also couldn’t reach the BBC, although I can actually watch the BBC news channel on my hotel room TV.

Google, of course, is available, in the wake of their somewhat-infamous deal struck with the Chinese government. But Wikipedia is a little confusing — blocked at times, available at others. Apparently this is an ongoing skirmish. I typed in “China” to Google, and the first link was the the Wikipedia page, so I clicked there, and saw it no problem. Then I typed “China internet” into the Wikipedia search box, and was given a list of pages, including Internet Censorship in the People’s Republic of China. But when I clicked there, it briefly began to load, before switching to a “The connection was reset” error. A little spooky, to be honest. Right now I seem to be able to see most Wikipedia pages, although apparently not those specifically about the PRC (although the main China page is still okay). You might think, no problem, I can just look at the Google cache pages for whatever Wikipedia article I’m interested in. But no, you can’t; nothing in Google’s cache seems to be available. So much for infamous deals.

None of which has prevented me from reading any of my favorite blogs. I just do what I always do, and read the feeds via Bloglines. They’re all perfectly visible, even for the blocked sites. Google reader works just as well. A lack of internet savvy on the part of the censors, or an intentional oversight? The one thing that one can’t do is leave comments (or start up your own blog, obviously), and maybe that’s the point.

(I also notice that when I visit google.com, I am not automatically redirected to the local version google.cn, which seems to happen in European countries. Is this because the hotel’s service provider is rigged for foreigners, and ordinary citizens have different rules? Not sure.)

It could be much worse, of course. I mean, here I am, typing away on my own blog, with little fear that the secret police are going to burst into my hotel room in the middle of the night to haul me away. But the biggest single reason I don’t have that fear is that I know that word would get around, and that it wouldn’t look good — free information protects free people. Amnesty International has a campaign, irrepressible.info, to protest against internet censorship around the world. The more noise people make about this issue, the more pressure governments will feel to keep the web free.

Update: In the United States, we prefer to have our censoring-for-political-content performed by corporations, rather than directly by the government. Different cultures, different systems.

I’ve just spent a few days living like an undergraduate; and I loved it!

For most of us, the path to a scientific paper is an extremely nonlinear one, as Sean described in his recent trilogy (I, II, III). In a collaboration this is compounded by the fact that (for theorists at least) there are several people working simultaneously. These people are calculating independently at times, mixing notations, making their own approximations, using their favorite techniques, and writing things their own ways. Regular meetings, either in person, or on video or teleconference calls then hopefully iron out the differences.

While collaboration has some of the drawbacks above, it has many positives, not least of which is the creativity and array of technical skills that several people can bring to an initially ill-formed idea. But perhaps the main reason I love collaborating, and choose to do it so often, is that I truly enjoy the process. Discussing fascinating physics with talented colleagues is a delightful part of my job, and I wouldn’t give it up for the world. So whether someone comes to me with an idea they want to discuss, or I have a good idea of my own, I frequently take advantage of having other scientists with common interests around, and more often than not collaborate.

However, one thing that one needs to do in any collaboration is to check all the equations independently. Much of this checking is ongoing as the project progresses, but sometimes you take something complicated that a collaborator has done on faith in order to push ahead and see where an idea is going, coming back later to double check the details. This has been the process in many of my collaborations, and it is a perfectly enjoyable and rigorous way to work. One checks everything, of course, but not in order, and not in one continuous sitting.

In the last week, however, I got to do something unusual, for me at least. One lengthy collaborative paper I’m working on is nearing completion and I realized that there were a number of these technical results that I needed to go over in detail. But in this case, I also felt that the paper was getting sufficiently long, and we’d changed notations sufficiently many times, that the structure of the equations appearing in the draft (but not the ideas, or the heart of the calculation, of course) had become a little murky to me. So I decided to sit down with our draft and go through every single calculation, from the beginning, to make sure not only that I checked the things I hadn’t checked before, but also that I was completely happy with the notation, the structure, and the arguments. Usually this isn’t required at this stage, but here I really felt I’d benefit from it.

And it turned out to be remarkably nostalgic fun, as well as practically useful for our paper! You see, I hadn’t quite thought of it this way, but working through a draft like this is rather like an extreme, lengthy version of the kinds of initial parts of exam questions one gets as a student. You know the kind - the ones that start

“Show that such and such a result is true. Now, using this result and such and such a definition, do such a transformation and thereby prove that this unlikely looking expression is true. Interpret this in the light of this interesting observation.”

This kind of problem tests a certain skill set, but not necessarily the same one that one uses to make progress on problems to which one doesn’t know the answer. It can be a bit like working out to build muscles that will be useful for a particular sport. The muscles will definitely help, but unless you have the actual skill to play the game itself, they will only get you so far.

Too many of these kinds of exercises can be dreary indeed. Nevertheless, for me there was always a bit of a thrill to sitting down in front of a clean and empty pad of paper and working my way through a maze of reasoning to get to the required answer. I’d typically hit a dead end several times before figuring out a correct strategy, and those dead ends invariably taught me something deep about problem solving in general, and the specific physics or mathematics at hand.

In this case, my task turned into the equivalent of a three day exam, with the end result being thirty or more pages of calculations (and I write quite small and neatly - yes, I am extremely anal), and a couple of Maple worksheets to help me check various approximations. I had little boxes around important results and everything. It was just like being a student again, although wasn’t accompanied by vats of coffee and a late night run to the college bar for a quick pint at last orders.

Luckily nothing major was wrong, although I found a number of typos and one missing term. However, my picture of what we’ve done is now much clearer and more coherent. It is unlikely that I’ll do anything so formally organized with many future papers, but this was such fun! It almost made me want to take a class in something technical I don’t know much about, before reality crashed in and I realized that I basically have negative time to devote to anything like that.

I probably should have been more clear at the beginning of this post - I was living the working life of an undergraduate. Hope you weren’t looking for stories of drinking games, walks of shame and quick bong hits before class, although I do hear those are the subject of Daniel’s next post.

The “sensible anthropic principle” says that certain apparently unusual features of our environment might be explained by selection effects governing the viability of life within a plethora of diverse possibilities, rather than being derived uniquely from simple dynamical principles. Here are some examples of that principle at work.

• Most of the planetary mass in the Solar System is in the form of gas giants. And yet, we live on a rocky planet.
• Most of the total mass in the Solar System is in the Sun. And yet, we live on a planet.
• Most of the volume in the Solar System is in interplanetary space. And yet, we live in an atmosphere.
• Most of the volume in the universe is in intergalactic space. And yet, we live in a galaxy.
• Most of the ordinary matter in the universe (by mass) consists of hydrogen and helium. And yet, we are made mostly of heavier elements.
• Most of the particles of ordinary matter in the universe are photons. And yet, we are made of baryons and electrons.
• Most of the matter in the universe (by mass) is dark matter. And yet, we are made of ordinary matter.
• Most of the energy in the universe is dark energy. And yet, we are made of matter.
• The post-Big-Bang lifespan of the universe is very plausibly infinite. And yet, we find ourselves living within the first few tens of billions of years (a finite interval) after the Bang.

That last one deserves more attention, I think.