Blogs / Cosmic Variance

09:37 PST: Like many of my colleagues, I’ve been eagerly awaiting word that the LHC has successfully threaded the proton beam around the whole ring. In recent days they have gotten it half way around the 27 km circumference, and within hours, they should be able to circulate it and I assume “capture” it with the RF, which creates stable bunches in the synchrotron. Everything has gone very smoothly to this point, so I expect success shortly!

Once beam has circulated stably in both rings, some time next week the LHC team will attempt to collide protons at the injection energy of 450 GeV (a total center of mass energy of 900 GeV). While this is much less than the Tevatron is colliding presently, it could provide some sorely needed initial data for the detectors to do timing and calibration of the various subsystems. There will even hopefully be a few collision events recorded with clear “dijet” structure – collisions where quarks and/or gluons inside the protons hit head on and effectively bounce sideways into the detector, giving two back-to-back collimated sprays of particles. Pictures of such events will be great to see, at long last!

You can follow progress live on twitter: http://twitter.com/cern and I will update this post as I learn more.

10:32 PST: The LHC has gotten beam around clockwise, to Point 6! Woo hoo!

10:45 PST: Magnet quench – should be recovered soon…

11:25 PST: Beam has reached Point 7!

11:30 PST: Point 8! Next beam will be sent past Point 1 where ATLAS is…

11:39 PST Beam all the way around the ring! WOO HOO!! It’s baaaaaack! The LHC Page 1 display shows that the injection probe beam made it more than once around the machine:

11:54 PST: Next goals: do the same with the counterclockwise beam. Will they attempt RF capture tonight? Trying to find out…

13:11 PST: Turns out (no pun intended) they decided to go for RF capture of the clockwise beam rather than probe counterclockwise. They are up to 10 million turns with the RF on! Fantastic!

13:30 PST: Having captured the beam for several minutes, the LHC will now switch to counterclockwise.

14:53 PST: About to go for a full orbit of the counterclockwise beam…done!! Now to RF capture!

15:30 PST: Counterclockwise beam is RF captured! The LHC is operational…colliding beams within a week? Stay tuned.

This past weekend saw the first beam particles in the LHC since the magnet quench incident of September 2008. Protons and lead ions were threaded in two directions around part of the ring before being dumped, and everything worked without a hitch. The graphs show the ion beam spot entering Collision Point 2 before being dumped.

The LHC machine commissioning will pick up where it left off more than a year ago, and the plan is, if all goes well, to collide beams of protons in the experiments at a center of mass energy of 7 TeV (3.5 TeV per beam) before the end of the year. The luminosity will not be large at first, but should increase steadily with time until next fall, when the long shutdown to retrofit the remaining magnets with new quench detection and helium pressure relief systems begins. By that point the experiments hope to have accumulated upwards of 200 pb^-1 of integrated luminosity. This initial data sample is sorely needed to shake down the detectors and start tuning up the event reconstruction and analysis. And who knows, maybe we’ll see something totally unexpected. (Please, no black hole comments!)

The next main milestone will be beam circulating around the whole ring and captured by the RF system. That should happen by mid-November. Fingers crossed!

Some of you may have followed the threat to the historic Mt. Wilson observatory from the fires in Los Angeles earlier this month. Below is a fantastic time lapse video shot from one of the facilities on the mountain. You can see how close the fire came (though thankfully, the firefighters did a superb job in protecting observatory with targeted back burns to create firebreaks around the site).

As this video shows, astronomical observatories are frequently at risk from wildfires, since both tend to occupy dry remote mountaintops. Indeed, close to seven years ago, one of Australia’s major observatories on Mt. Stromlo was nearly obliterated by the fires that raced through the area:

Thankfully, Mt. Wilson survived this round.

PS. You can find a bit more about some of the ground breaking work that was done at Mt. Wilson along with some terrific old Life magazine photos here.

Here at Discover Media LLC, we are dedicated to bringing you news of the cutting-edge technology that will change your life. So we dispatched our Cosmic Variance automotive editor (me) to test-drive the car of the future: the all-electric Tesla Roadster. (No real secret actually; I have a friend who owns the car.) Thus, yesterday’s picture.

Fancy titles notwithstanding, I’m by no means a true car nut, so I can’t offer the insider perspective of a real expert. My take is that of an ordinary person who just had a chance to drive an exotic car through the hills north of San Francisco. After considering the experience carefully, my considered judgment could be expressed as follows: pretty frikkin’ awesome.

Let’s get some basics out of the way: the Tesla, with a body based on the Lotus Elise, is a tiny car — a two-seater with a trunk that can at best be described as decorative. And it’s low to the ground; climbing inside is a bit of a process for the uninitiated. Inside, the electronics are all state-of-the-art (as one might expect), but the Roadster is not a cushy luxury car. It’s not uncomfortable, but you’re not being coddled by piles of plush leather. Removing the convertible soft top is a matter of unsnapping and stowing by hand; takes just a few seconds, but we’re not talking about a top-of-the-line Mercedes where there are separate buttons to stow the top, clean your sunglasses, and freshen your martini. The Tesla experience is about the driving; fripperies are for future incarnations.

So you sit down, turn the key to start the engine, and: nothing. That’s to be expected, and should be familiar to anyone who has driven a Prius or other hybrid. The electric motor doesn’t need to be turning when the car isn’t moving, so turning the vehicle on just means some lights come on. Spooky at first, but you get used to it.

Actually pulling out into the road and driving is a different story. There are basically three things that distinguish the Tesla driving experience from that of your typical Ford Taurus or what have you. First, as you may have heard, the Tesla doesn’t believe in a little thing called a “transmission.” Technically, there is a transmission, but really it’s just a reduction mechanism that translates a certain number of motor revolutions to a certain fixed number of tire revolutions — there are no gears, so there is no shifting, manual or otherwise. The original plans called for a two-speed transmission, but it proved unreliable, so they said screw it, let’s just have one gear. As a result, the rate at which the motor is turning is directly proportional to the rate at which your car is moving. That includes reverse; when you’re backing up, the motor is spinning in the opposite sense from when you’re moving forward. In a conventional car with an automatic transmission, there can be a bit of a delay between when you push down on the accelerator and when you actually accelerate, as the car tries to decide what gear it should be in. No such hesitation in the Tesla.

The second thing, which you may not have heard, is that there is no power steering. I don’t know whether that was a matter of cutting down on weight, or whether it was just thought that power steering wouldn’t be keeping it real. But despite its diminutive profile, the Tesla is not a light car, coming in at about 2,700 pounds — a third of that in the form of batteries. (The Elise, in comparison, is only about 2,000 pounds; but a Mazda Miata comes in at 2,500 pounds and a BMW Z4 at 3,200 pounds, so the Tesla isn’t unreasonable.) To those of us who have gotten used to having the car practically steer for us, the Tesla is a bit of an adjustment. But the adjustment happens quickly, and it’s very much in keeping with the sporty nature of the car — you’re here for performance, not coddling.

The single gear and the lack of power steering combine to create an effect I hadn’t really anticipated before the drive: a visceral connection between the driver and the ground. It’s hard to imagine a driving experience that is on the one hand that fast, and on the other hand features so little mediation between what you do at the controls and how the car responds. The engine turns, and the car zips along, at precisely the speed you tell it to, no more, no less; and the wheels turn at an angle precisely proportional to the attitude of the steering wheel in your hands. You are in control.

And — to come to the third crucial distinguishing feature — you’re in control of a lot. (more…)

“Astronaut”

Doesn’t that word conjure up the majesty of space exploration? The triumph of human drive and ingenuity?

Or perhaps, it makes you think of an automated laser-guided milking machine?

Seriously. Wrap your mind around that. “Automated laser-guided milking machine”.

Cow walks in when it decides it’s ready to be milked. Sensors read a tag around the cow’s neck to determine if the cow is indeed ready to be milked. If so, the machine launches a veritable Pink Floyd Lasarium around the udder, locating the teats, which are then cleaned and hooked up to the milking units. Sensors then disconnect when the milk flow drops, and the cow goes on its way.

Lasers and cows. Two fine things that I never thought I’d see together.

(and below, an informative video, if you really, really care)

For a long time, the government has been responsible for space travel in the United States. That’s about to change.

Government is the appropriate agent for certain forms of collective action: roads, public schools, national defense. It’s also good for big-picture things without immediate financial payoff, like support for the arts or basic scientific research. It makes perfect sense for the government to shoulder the burden for developing the technologies to get us into space, and it will continue to make sense for them to play an active role in astronomical research in space. But for commercial purposes, like launching satellites, it ultimately makes a lot more sense for space travel to be a private-sector enterprise. We’re on the brink of seeing it happen.

SpaceX is a private company founded by Elon Musk, who previously co-founded PayPal and the electric car company Tesla Motors. For a while now, SpaceX has been developing reusable launch vehicles and space capsules. They’ve been awarded a contract from NASA to take over re-supplying the International Space Station after the Shuttle fleet is mothballed next year. And they’ve had one launch that reached orbit, but also a few failures; until yesterday, they hadn’t succeeded in putting a satellite into orbit.

But now they’ve done it. I was watching on live webcam last night as the Falcon 1 rocket launched a Malaysian satellite into orbit.

It’s incredibly exciting, but just the beginning. The idea behind the Shuttle was to make trips to orbit cheap, reliable, and routine; it failed spectacularly on all counts, and NASA’s capabilities and plans for space flight have become somewhat disjointed (while its science missions continue to have amazing success). Hopefully we’re moving past the point where we have to rely on the government to get us to space.

I spent last week at Columbia University attending the Edoardo Amaldi Conference, the largest annual international meeting on gravitational waves. Short synopsis: GWs have not been found.

I was reminded that I still owe CV readers a discussion of gravitational waves, following-up from an ancient post on their convoluted theoretical history. While the theoretical community was arguing about the existence of gravitational waves, the observational community was essentially non-existent. The wave strengths expected at Earth are extraordinarily weak, with the most promising sources being the inspiral and merger of stellar-mass compact binary systems (e.g., neutron stars and/or black holes). It took great courage and vision to propose instruments to detect the waves at all. One of the pioneers of gravitational wave detection was Joe Weber, who first invented and built so-called Weber bar detectors. As the gravitational waves pass through a large cylindrical bar of material, they excite resonant modes of the bar, which might then be detectable. In 1969 Weber published an article in Physical Review Letters announcing the detection of gravitational waves by noting coincidences between two bar detectors separated by a thousand kilometers. These observations generated tremendous excitement, especially given that they suggested wave strengths greatly in excess of what was expected. Unfortunately, as other experimenters built ever more sophisticated follow-up detectors, they were unable to reproduce his findings. Over three decades later, and with many orders-of-magnitude improvement in detector sensitivity, gravitational waves have yet to be directly detected. An unfortunate side-note is that Weber continued to claim that he was seeing gravitational waves, even in the face of compelling counter evidence, right up until his death in 2000. Weber was an experimental master (having independently invented the maser and the laser), and is widely credited as the father of gravitational wave astronomy, but in his last decades he was an outcast of the very community he helped found.

A profound development in gravitational waves detection came in 1974 with the discovery by Hulse and Taylor of a binary pulsar. This system consists of a 59 millisecond pulsar in orbit with another star, with a period of 7.75 hours. The pulsar provides an exceedingly precise clock, allowing us to measure the spin-down of the binary system due to the emission of gravitational waves (using the same quadrupole formula mentioned in the previous post). Theory and observation agree spectacularly well, and Hulse and Taylor were awarded the Nobel prize for this indirect detection of gravitational waves. The community is now breathlessly awaiting the first direct detection of gravitational waves. So why am I nattering on about all this? Because of this:

This is a sensitivity plot of LIGO, the Laser Interferometer Gravitational Wave Observatory. LIGO is composed of two power-recycled Michelson interferometers with 4-km long Fabry-Perot arms, located in Hanford, Washington and Livingston, Louisiana. Each curve shows the noise floor, with LIGO sensitive to sources falling above the curve. The curves represent official science runs, and the steady progression shows the improvement since 2002 (1st science run). LIGO has been in development for decades, and has in the last few years (the red curve) reached its original design sensitivity (the solid black curve). LIGO has finished a year-long science run (S5), which constitutes by far the deepest look we’ve ever had at the gravitational wave Universe. It hasn’t seen anything yet; only upper limits. (At least, that is the public stance. Given the convoluted history detailed above, there will be a long period of double and triple checking before any sort of public announcement is made. Although it’s hard to imagine rumors of a first detection won’t leak out, and my rumor well is dry.) At the moment LIGO is being “Enhanced” (a factor of 2 improvement), with the installation of more powerful lasers. It should be back up and running within the year, will run for a year, and then will undergo a major upgrade. By 2014 LIGO will come back online at “Advanced” sensitivity (another factor of 5, which translates into a factor of 1000 in volume compared to today), at which point the first direct detection of gravitational waves is widely anticipated.

There is lots to say about LIGO, but I’d like to focus on one point: the scale on the y-axis of the plot above (which represents strain, the fractional change in the length of the LIGO arms). LIGO is sensitive, over a wide range of frequency, to a strain of better than 1 part in 10²². In other words, it measures changes in the relative length of its 4km arms to better than a thousandth of the size of a proton. This plot should absolutely blow your mind. If not, perhaps I’m being too abstract? This is the equivalent of monitoring changes in the distance between New York and San Francisco to better than one ten billionth the width of a human hair. LIGO is a technical tour-de-force. It is one of the most amazing instruments humankind has ever built.

N.B.: In the comments, Brian137 points out that LIGO will be back on starting tomorrow (7/7/09) for a month-long run! (From the LIGO blog.) And nicolas points out that I was remiss in neglecting to mention Virgo, which is a French/Italian GW detector currently operating in Italy. It is easily as impressive as LIGO, since it achieves similar sensitivity with 3km arms (instead of 4km for LIGO).

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.)

(more…)

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.