Blogs / Cosmic Variance

Okay, it’s time to come clean - I am a ham. That is, I am an FCC-licensed amateur radio operator, call sign KI6GDQ. I got into it a few years ago because my wife’s parents and sister and brother in law are hams, and we all go camping in northern California every summer. Obviously a little hand held ham transceiver is not a bad way to communicate when there’s no cell phone coverage, though the range is limited to a few miles in the mountains up there.

And, living here in California, which a friend of mine notes is a beautiful land with a decidedly savage side, it’s not bad to have a means of communication that doesn’t depend on the grid, be it the electric grid or the Internet/phone grid. My in-laws live in Pacifica, south of San Francisco, which is hemmed in on all sides: the ocean to the west, mountains to the north and south, and the San Andreas fault to the east. A big earthquake could easily isolate them from the rest of the peninsula. So my father in law (N6FG) helps run a 2-meter repeater on a nearby mountaintop; he and and my mother-in-law (K6IIP) participate in local emergency response groups.

A friend of mine joked that amateur radio is the original social networking tool. (Well, unless you count the postal service.) Early in the last century, when radio was young, the advent of high-power vacuum tubes made it possible for amateurs to build transmitters that allowed them to talk to other hams all over the country, and around the world, ionospheric conditions permitting. At night, when the lower layers generated by solar radiation dissipate, a vast electromagnetic mirror called the F layer forms several hundred miles up. Signals from the surface can bounce off this mirror essentially all the way around the planet. Hard-core DXers still go to great lengths with antennas and legal-limit (1500 watt) transmitters to make contacts with Morse code. (And then there are the truly crazy ones who go on expeditions to remote islands off Antarctica solely for the purpose of making nearly 100,000 ham radio contacts all over the world.)

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Back in 1996, after the initially very mysterious explosion and crash of Flight 800 from JFK to Rome, there were numerous eyewitness accounts of a “streak in the sky” just before the crash. This led to the “missile theory” of the crash, which was eventually attributed to the explosion of the center fuel tank by the NTSB. But, also at the time, it was suggested that a meteor of sufficient size could have struck the plane, bringing it down.

Could a meteor have brought down Air France 447? Today we are starting to see reports that there actually may have been a meteor:

However, both pilots of an Air Comet flight from Lima to Lisbon sent a written report on the bright flash they said they saw to Air France, Airbus and the Spanish civil aviation authority, the airline told CNN.

“Suddenly, we saw in the distance a strong and intense flash of white light, which followed a descending and vertical trajectory and which broke up in six seconds,” the captain wrote.

Obviously for any given flight the chances are very, very small that a meteor will bring down an airliner, but as Hailey and Helfand pointed out in a letter to the NYT in 1996, the correct question to ask is this: “What is the probability that, for all flights in history, one or more could have been downed by a meteor?” They concluded that there was a 1-in-10 chance that this could happen…let’s use their logic, brought up to date somewhat, for 2009, for Flight 447.

Helfand, an astronomer, is presumably the one who estimated that “approximately 3,000 meteors a day with the requisite mass strike Earth”. This is a difficult number to get. How much mass? How fast does it need to be moving? But let’s assume that this number is correct; it translates to 125 meteors per hour.

Next we need to know the total number of flight hours at altitude for all commercial planes. In 2000 there were about 18 million flights per year. Clearly in the past 20 years (which we’ll take as our reference, since it spans 1989-2009, with both flights 800 and 447) it was not always so…but let’s take a guess that the 18 million figure is roughly correct for that 20 year period. That would yield 360 million commercial airline flights from 1989-2000. Hailey and Helfand assumed that each flight was two hours in duration. Again, a tough number to find on line, so we’ll take it at face value, giving us 720 million flight hours in our reference period.

They also claim that if there were 3500 planes in the air at any time, this would correspond to covering two-billionths of Earth’s surface. Now the earth’s surface area is 5×10¹⁴ m². Using my trusty HP-15c, I get that this would imply an average target area for a commercial airliner of 291 m², which is reasonable. Each plane, that is, covers 5.7×10^-13 of Earth’s surface. If a meteor hits the earth it has that probability of hitting a given plane on average.

So, in our reference 20-year period we have 720 million hours of flight time, times 125 meteors per hour, times 5.7×10^-13 = 0.051, which we can take as the average number of airliners struck by meteors in the period 1989-2009. That’s a one-in-twenty chance of some plane going down for this reason in that 20 year period. Extrapolating to all flights ever would require a better estimate of total flight hours, but it’s not twenty times the number in the past 20 years, for sure - that is, it’s not yet close to one.

Obviously there are a lot of uncertainties in this estimate; perhaps a factor of two from the number of meteors of sufficient mass per day, the average flight duration and number of flights?

Anyway the meteor idea is not crazy, though not likely. The weather seems more likely to be at the root of the tragedy…but we may never know. One thing, though, is clear: if we keep flying big planes at high altitude, eventually one will get hit by a meteor.

The space shuttle Atlantis made a safe landing yesterday morning, capping the end to a truly historic mission. Over the past two weeks the shuttle crew rendezvoused with the Hubble Space Telescope, performed five space walks, fixed two failing instruments (the Advanced Camera for Surveys and the Space Telescope Imaging Spectrograph), installed two new instruments (the Cosmic Origins Spectrograph and the Wide Field Camera 3), did a host of other repairs and refurbishment, and then released a completely transformed telescope.

We have a tendency to forget just how remarkable this is. It is a highly non-trivial endeavor to send seven people into space (and get them back down safely). It is nothing short of miraculous to have them spend over 30 hours space “walking”, performing a major overhaul of an aging instrument (12 meters by 4 meters, weighing over 13 tons [it’s “weightless” in space, of course; though it might have some inertia if you tried to move it]). You’ve got bulky gloves on, you can’t hear anything, you’re floating around with no balance, and you really, really don’t want anything to go wrong. Even something as trivial as a sticky bolt can derail months of preparation and millions of dollars of investment. There is a very slim margin for error.

The Atlantis mission is one of the finest examples of what excites people about manned space flight. It was an incredible success, from start to finish. And we can hope for a decade of mind-blowing science to prove it. It helps that Hubble is perhaps the most remarkable scientific instrument ever built. (Okay, the LHC is pretty cool too, but it doesn’t produce pretty pictures. And it isn’t working yet.) Without a doubt, the fact that Hubble was “serviceable” has played a large role in its success. With its initially flawed optics, Hubble would have been a catastrophic failure. It took a servicing mission to fix it, and provide us with an unparalleled scientific instrument. And now it is as if we have launched a brand new, state-of-the-art Hubble. These appear to be strong arguments in favor of manned maintenance of space telescopes.

But this mission is historic for another reason. It is likely to be the last time in our lives that human beings go to space to “fix” an orbiting scientific instrument. [Granted, prediction is very difficult, especially about the future.] It is incredibly expensive to send human beings up to fiddle on stuff in space. Furthermore, Hubble was placed in low-Earth orbit (600 kilometers up) to facilitate these sorts of repairs, which is a sub-optimal location for a telescope. The successor to Hubble, the James Webb Space Telescope (JWST), will be placed 1.5 million kilometers away at Lagrange point 2 (WMAP is already there, and Planck and Herschel are on their way). It will be a very long time before humans venture out that far from Earth. JWST is not being designed to be repaired or upgraded; it’s a one-shot deal. The additional costs of sending humans into space far outweigh the benefits. If you want to know whether there’s water on Mars, you send a rover. You do not spend many orders of magnitude more to send a human to dig with a shovel. Although the space shuttle is undeniably cool, and this latest Atlantis mission was astounding, manned space flight is not the economical way to do science.

With the successful landing of Atlantis we celebrate a transformed Hubble telescope. And we mark the end of the current era of human beings tinkering with telescopes in space.

CERN announced today that the final replacement LHC magnet was lowered into the tunnel, and is making its way to Sector 3-4 (between collision points 3 and 4). Last September’s incident led to 53 magnets - about half a kilometer of the 27-km ring - having to be removed, repaired or cleaned, and replaced. Check out the video of the final dipole going in on April 16.

New systems are being installed to better detect incipient magnet quenches, and the helium pressure relief systems are being upgraded. My understanding is that this will be done on the greater part of the LHC magnets this year, but not all of them.

The plan is to complete the installation of the replacement magnets, and then cool down all sectors. At present, half the machine is being held at liquid nitrogen temperatures, and the other half is at room temperature. It will take a couple months, once they start, to cool the whole machine down to superconducting temperature, about 2 degrees K.

So, by late summer the LHC commissioning can begin where it left off last September. Assuming all goes well, physics collisions are foreseen at 10 TeV by late fall. The machine will not run at the design energy of 14 TeV at least until the entire machine is retrofit with the new quench detection and pressure relief systems. And, the beam intensity (and hence collision luminosity) will not be anywhere near the ultimate goal during the first physics run.

The usual running pattern at CERN is to start in the spring, and collide beams through the late fall, and do machine maintenance, etc. during the winter when electric power is more expensive in Europe (they heat with nukes, basically; we burn fossil fuel in the US in winter).

But a decision was reached earlier this year to run the LHC through next winter, with only a brief two-week shutdown for Christmas and New Year.

What we can reasonably expect is that if all goes well, we can accumulate something like 100 inverse picobarns of collisions by spring 2010, and perhaps 200 pb^-1 by the end of the run in fall, 2010. Now, pb^-1 this is a strange unit - it has dimensions of inverse area. Formally we call it integrated luminosity. Basically it tells you how many collisions you’ve had, in essence. To get the number of some type of interesting events, you need to know the cross section - which has units of area - for producing that type of event. Then you simply multiply the cross section times the integrated luminosity.

Once the machine shuts down in late 2010, and if we do have a sample of about 200 pb^-1, there will ensue a long shut down in 2010-2011 to complete the magnet retrofit. The LHC will then not run until late 2011.

This means that the lower-energy, relatively small sample of physics data is all we will have to analyze until 2012, three years from now! The experiments have already been simulating collisions at the lower energy and retuning analyses.

Though everyone is waiting breathlessly for the LHC to discover the Higgs boson, with lower energy and a smaller sample, I would not bet on the LHC finding it any time before 2012. In fact, a full analysis of the Higgs sensitivity at 10 TeV is yet to be done in ATLAS and CMS. This is a huge task, and will take months, but there is no question that it is more difficult at the lower energy, and it’s already very hard for the LHC to see, say, a 120 GeV Higgs boson. As I wrote in my post in March, this is also very hard for the Tevatron in the same time period. Those of us looking for a standard model Higgs boson have to exercise a bit of patience while working very hard toward the ultimate goal!

Neverheless, there is a ton of new physics that *could* emerge from even the first LHC physics sample from the 2009/10 run. If nature has new high-mass particles giving observable pair-production resonances at energies not accessible at the Tevatron, they could stand out in sharp relief above the standard model. Similarly if there are extra dimensions of space time, we may see excess pair production of standard model particles. If supersymmetry exists, and the experiments manage to understand well the apparent missing momentum transverse to the beam direction (a big challenge) then a first observation of the presence of supersymmetric particles might be possible.

At this point, all you can do is admire the wisdom of the great Zen master Yogi Berra, who said “If this was easy it wouldn’t be so hard!” But then, maybe we’ll get lucky.

Via Brad DeLong, an article by Kevin Carey in the Chronicle of Higher Education starts with the obvious — the internet is killing newspapers as we knew them — and asks whether the same will happen to universities.

Much of what’s happening was predicted in the mid-1990s, when the World Wide Web burst onto the public consciousness. But people were also saying a lot of retrospectively ludicrous Internet-related things — e.g., that the business cycle had been abolished, and that vast profits could be made selling pet food online. Newspapers emerged from the dot-com bubble relatively unscathed and probably felt pretty good about their future. Now it turns out that the Internet bomb was real — it just had a 15-year fuse.

Universities were also subject to a lot of fevered speculation back then. In 1997 the legendary management consultant Peter Drucker said, “Thirty years from now, the big university campuses will be relics…. Such totally uncontrollable expenditures, without any visible improvement in either the content or the quality of education, means that the system is rapidly becoming untenable.” Twelve years later, universities are bursting with customers, bigger, and (until recently) richer than ever before.

But universities have their own weak point, their own vulnerable cash cow: lower-division undergraduate education. The math is pretty simple: Multiply an institution’s average net tuition (plus any state subsidies) by the number of students (say, 200) in a freshman lecture course. Subtract whatever the beleaguered adjunct lecturer teaching the course is being paid. I don’t care what kind of confiscatory indirect-cost multiplier you care to add to that equation, the institution is making a lot of money — which is then used to pay for faculty scholarship, graduate education, administrative salaries, the football coach, and other expensive things that cost more than they bring in.

I’m not sure I buy it. Let’s think about what good purposes a college or university might serve. Off the top of my head, I can think of several:

1. Classroom-based education. Certainly important.
2. Extracurricular learning. This includes everything from “participating in actual academic research” to “serving on the school newspaper.”
3. Meeting different kinds of people. Not only do students get exposed to professors, and an academic way of thinking about problems, but they also meet other students, hopefully from a wide variety of backgrounds.
4. Establishing independence. For many people, going to college is the first time one lives away from home, and begins to establish an identity separate from one’s family.
5. Belonging to a community. From the university itself to numerous smaller subcultures within, college provides an opportunity to belong. As great as the Teaching Company is, it doesn’t have a basketball team in the Final Four.

Feel free to add your own. We can argue whether online learning can be effective in replacing the first of these — after all, hearing a recorded lecture is not the same as hearing it live. But it would appear very difficult to replace the others. The four years one spends at college are often the most formative (and perhaps the most enjoyable) years of one’s life. It’s not clear, of course, how much people are willing to pay for those other purposes, as important as they may be.

On the other hand, there is a long-established bargain at big research universities that could conceivably come unraveled at the hands of the internet. Namely: it is research and scholarship that attracts the faculty and establishes the academic reputation of a school, but it is teaching that brings in students and tuition dollars. This is not an arrangement based entirely on avarice; the top research schools bring in a lot more money from grants and gifts than they do from student tuitions. But it reflects a deep philosophical split, that might signal an underlying instability: from within academia, the purpose of the university is seen as the production of new scholarship; from outside academia, the purpose of universities is seen as the teaching of students.

In the case of newspapers, the internet made it harder to tightly bundle straightforward news with advertising and sections of the paper any one reader might not be interested in. In the case of universities, will the internet make it harder to bundle teaching and research? Quick, name the largest private university in the U.S. The answer is the University of Phoenix, founded in 1976, where 95% of faculty are part-time and the large majority of teaching happens completely online.

It could happen that more education-providing corporations (one hesitates to call them “universities”) could develop better ways to provide online classroom educations to a large number of students who are interested in the first purpose listed above but are unwilling to pay for the second. If that model catches on, it will cause dramatic upheaval in the economy of traditional universities. And, much as I love the internet, that would be too bad.

A good friend of mine, Andy Huibers, has just coded his first iPhone application. It’s called “Bump”, and is a way to transfer contact information effortlessly. You literally bump your iPhone with someone else’s iPhone (or iPod touch), and your contact information is swapped. The phones don’t talk to each other directly. An accelerometer in each phone responds to the bump and contacts a central server, which matches everything up. Pretty clever. Here’s a video:

Apparently it’s catching on. The Chicago Tribune even wrote an article about it. And, in what must be the height of fame for an iPhone application, David Pogue of the NYTimes has twittered it!

If you’ve got an iPhone or iPod Touch, check it out. It’s free.

Remember when that defunct Russian satellite crashed into the Iridium satellite a week or so ago? Lots of debris, some of which came down as weather?

Well, not all the debris came down. Most was left in orbit, and apparently has already had some effect on other satellites, as people had feared.

And worse for astronomers, Nature (subscription only) is now reporting that with the increased debris, the risk to the Space Shuttle and its crew may now have been pushed up to a level that precludes the upcoming servicing mission (SM4, currently scheduled for May). NASA is currently evaluating the situation, and we should all know more in a few weeks. But, if the servicing mission is cancelled, it’s going to be a huge blow for astronomers. (It wouldn’t be as tragic as losing another crew, however, so I completely support what NASA is doing in this case.) I’m speculating that if the servicing mission is cancelled, there might be an opportunity to try a robotic servicing mission, which would be good practice for learning how to eventually service satellites out at L2. But it seems unlikely that a robotic mission could bring the full complement of COS, WFC3, ACS, and STIC on-line, whereas the SM4 crew would have a good chance of getting them all in, along with other upgrades to the satellite’s systems.

(h/t to someone at dinner, who’d gotten a tip from Steinn’s blog.)

After the devastating quench incident on September 19 of last year, resulting in the rupture of the cryogenic vessels within the LHC magnets , CERN has worked furiously to repair the damage, prevent any future similar failure, and get the LHC back to its commissioning program. Following a meeting of technical experts and the leadership in Chamonix, France last wee, the CERN Directorate has issued a press release with the new plan for LHC restart:

The CERN Management today confirmed the restart schedule for the Large Hadron Collider resulting from the recommendations from the Chamonix workshop. The new schedule foresees first beams in the LHC at the end of September this year, with collisions following in late October. A short technical stop has also been foreseen over the Christmas period. The LHC will then run through to autumn next year, ensuring that the experiments have adequate data to carry out their first new physics analyses and have results to announce in 2010. The new schedule also permits the possible collisions of lead ions in 2010.

This new schedule represents a delay of 6 weeks with respect to the previous schedule which foresaw LHC “cold at the beginning of July”. The cause of this delay is due to several factors such as implementation of a new enhanced protection system for the busbar and magnet splices, installation of new pressure relief valves to reduce the collateral damage in case of a repeat incident, application of more stringent safety constraints, and scheduling constraints associated with helium transfer and storage.

In Chamonix there was consensus among all the technical specialists that the new schedule is tight but realistic.

The enhanced protection system measures the electrical resistance in the cable joints (splices) and is much more sensitive than the system existing on 19 September.

The new pressure relief system has been designed in two phases. The first phase involves installation of relief valves on existing vacuum ports in the whole ring. Calculations have shown that in an incident similar to that of 19 September, the collateral damage (to the interconnects and super-insulation) would be minor with this first phase.

The second phase involves adding additional relief valves on all the dipole magnets and would guarantee minor collateral damage (to the interconnects and super-insulation) in all worst cases over the life of the LHC. One of the questions discussed in Chamonix was whether to warm up the whole LHC machine in 2009 so as to complete the installation of these new pressure relief valves or to perform these modifications on sectors that were warmed up for other reasons. The Management has decided for 2009 to install relief valves on the four sectors that were already foreseen to be warmed up. The dipoles in the remaining four sectors will be equipped in 2010.

That the delay would be a year, in total, was not unanticipated given the magnitude of the incident, and the good news here is that the root cause is now believed to be understood. The retrofit to the quench detection and pressure relief systems should prevent this from happening or causing such great damage in the future.

Hopefully this was the worst of the birth pangs of the LHC! With such a complex and enormous machine, however, it would be overly optimistic to hope that it will be the last.

The experiment I work on, CMS, is open now and in March we are going to remove the innermost detectors, the forward pixels, do minor repairs, and reinstall them by mid-April. We are taking advantage of the fact that so far, anyway, the detectors have not become radioactive from high intensity beam, after which any work on them will be far more difficult.

And, we are preparing to do the physics once we do get data. The extra year, though painful, gave us extra time to refine our approaches, and physics will emerge faster as a result, I believe.

Many older scientists and engineers grew up tinkering. Car engines were pulled, belts on washing machines were replaced, loose wires on toasters were soldered. Such experiences build a basic competence with the physical world, and develop an innate understanding that the devices around us are not powered by magic. For better or worse, however, gadgets have become both more electronic and more disposable, leaving few useful opportunities for fixing things. Moreover, many of us grew up in non-tinkering households, and even if we’d been raised during the glory days of Large Mechanical Devices Made of Steel, we wouldn’t have wound up tinkering ourselves. And finally, much of that tinkering was pretty clearly marked as a Guy Thing.

But, there is a possible cure. I give to you Snap Circuits.

This has to be one of the funnest, most accessible geeky kid’s toys ever. It completely takes away the overhead of electronics assembly, allowing even very little kids to assemble circuits well before you’d trust them with a soldering iron. All the pieces are color-coded in bright primary colors with the standard circuit notation imprinted on top. The projects are largely fun — things like driving a little motor that turns a fan blade, which, if you mount it upside down, eventually generates enough lift that it shoots off and sails up the ceiling. There’s no chance of exploding capacitors or burnt fingers (which I’m sure for some of you makes it completely un-fun, but we’re talking 5 year olds here). Instead, what kids get is fast understanding of how circuits work, at a level that they can understand and really enjoy.

On top of just being extremely cool, for some reason Snap Circuits seems to have way more cross-gender appeal than the old Heathkits. It somehow cracked the code of not seeming like a gender-coded toy. There are no pictures of kids on the package (male, white, or otherwise), and it’s brightly colored without being frilly. There is also no assumption of past apprenticeship, where one was supposed to have learned soldering and breadboard wiring from some older family member. As such, I know as many girls as boys who are enamored with Snap Circuits (and although I probably don’t hang with the most representative sample of kids ever, the Snap Circuits flickr pool seems to bear my impression out).

So, if you have a kid in your life and don’t mind being stigmatized as the adult who gives nerd presents, consider Snap Circuits.

CERN has issued a press release detailing the extent of the damage from the September 19 incident, the plans for retrofitting the magnets to ensure it does not happen again, and a new schedule. The skinny: the machine should be back up and running in July of next year, resuming the commissioning that was underway when the incident occurred. There are now some impressive photos of the damaged components, showing what tens of megajoules of energy can accomplish in a few seconds.

Six tons of helium was released in the incident, and is presumably gone into outer space now, since at atmospheric temperatures the helium atoms readily attain escape velocity. (Helium is not a renewable resource, per se, though it is continually being produced within the earth from radioactive decay.)

But what caused the incident to begin with? Here is a quote from a talk by Robert Aymar, the outgoing CERN Director General:

On 19 September 2008 morning, the current was being ramped up to 9.3 kA in the main dipole circuit at the nominal rate of 10 A/s, when at a value of 8.7 kA, a resistive zone developed in the electrical bus in the region between dipole C24 and quadrupole Q24. No resistive voltage appeared on the dipoles of the circuit, so that the quench of any magnet can be excluded as initial event. In less than 1s, when the resistive voltage had grown to 1 V and the power converter, unable to maintain the current ramp, tripped off, the energy discharge switch opened, inserting dump resistors in the circuit to produce a fast power abort. In this sequence of events, the quench detection, power converter and energy discharge systems behaved as expected.

Since the interconnect bus subsequently vaporized, it has been difficult to tell exactly what triggered the event. The retrofits to the magnets will improve the quench detection and helium pressure relief systems, but I’ve not heard what, if anything, CERN will do to prevent other interconnects from “developing resistive zones.” Hence the question: will it happen again? It is clear that the new systems will help prevent serious damage to the machine, but there are thousands of these interconnects, so…

Anyway, quite a number of magnets have been removed from the tunnel and are being refurbished and will be reinstalled in the coming months. The experiment I work on, CMS, is in the “open” state now with the end caps pulled back, allowing access to the inner detectors. Our team on the forward pixel detectors plans to remove and reinstall our detectors, making minor electrical and cooling repairs and modifications, starting in February. The photo of the detectors being installed last summer shows the beam pipe, the installation fixtures, and the detector half-cylinder going in, like a ship in a bottle.

Once more, from the top, this time with feeling!