DAVID LEE鈥檚 job is to make seconds. By international consensus, a second is defined as 9 192 631 770 cycles of a caesium atom vibrating at its natural frequency. Every 60 days, Lee measures this frequency, and his colleagues use it to recalibrate the atomic clocks by which all others in the US set their time. The process takes about ten days, and this year one of those days is Christmas. So while the rest of us are tucking into turkey and Christmas pudding, Lee will be hard at work. And he is only one of many scientists who must shepherd laboratory work or research that simply won鈥檛 take a holiday.
Lee works at the US National Institute of Standards and Technology in Boulder, Colorado. To measure 1 second, he passes a beam of caesium atoms through a cavity, and shines a beam of microwaves onto them. He adjusts the frequency of this radiation until a maximum amount is absorbed by the caesium atoms, at which point the frequency of the microwaves is the same as the natural resonance of caesium.
Because he must be accurate, Lee has to take a large number of measurements over 10 days, and average them. The atomic clocks at NIST can wander just like any other clocks, so Lee鈥檚 colleagues use his frequency to adjust their atomic clocks to make sure that they are all ticking in perfect time.
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The clocks Lee鈥檚 colleagues are calibrating are accurate to within half a nanosecond per day. At the end of two months, they might be out by all of 30 nanoseconds. So why not skip it just this Christmas? Why not live dangerously and let the atomic clocks get out of whack by 60 nanoseconds one way or the other before resetting them?
Lee says that his colleagues wouldn鈥檛 be happy. They have to transmit the time and frequency signals from radio station WWV at Fort Collins, Colorado. These are picked up by navigation systems which prevent ships sailing off course and planes missing the runway, and by the latest VCRs which can reset themselves. Besides, the US has to regularly transmit its definition of a second by satellite to Europe for averaging with seconds from other countries, to set the Coordinated Universal Time-the global time standard.
Lee is not the only one who will work over Christmas. Carol Polanskey鈥檚 team at the Jet Propulsion Laboratory in Pasadena, California, may have to spend the holidays downloading data from the Galileo space probe which might otherwise be erased. Galileo will fly by Europa, one of the moons of Jupiter, before Christmas. During the closest approach on 19 December, the probe鈥檚 magnetometer will record any magnetic field it detects from Europa. 鈥淭his will be a really big discovery if it comes through,鈥� says Polanskey.
Because of competition with Galileo鈥檚 other instruments for transmission time, the first chance Polanskey will have to download data from the magnetometer will be 22 December. If it doesn鈥檛 all come through, which is highly possible, the next chance will be 25 December. Thanks to the Internet, the data can be downloaded from home, Polanskey says. But if she cannot download all the data on Christmas Day, instructions will have to be sent to Galileo to prevent it from overwriting the data. That will mean a trip to the office for one of the team-Polanskey herself hopes to be with her family in Pennsylvania.
Michele Arduengo, who recently finished her doctoral research at Emory University in Atlanta, also hopes to spend Christmas at home this year. 鈥淭he graduate students are the ones you need to talk to,鈥� she says. 鈥淲e鈥檙e the ones who show up for the holidays.鈥� In the past, Arduengo has had to check her research several times over Christmas.
The research subjects that couldn鈥檛 wait were sexually maturing nematodes, microscopic worms Arduengo was using to study a gene that helps control sperm differentiation. She tried to time the breeding so she didn鈥檛 have to work on holidays. 鈥淏ut a lot of times the worms didn鈥檛 celebrate Christmas,鈥� she says. The nematodes take about three days to develop from egg to adult, and Arduengo had to catch them after their sex became apparent, but before they reached maturity. Because hatching and maturing rates naturally vary, Arduengo had to go in over Christmas armed with her platinum worm scoop to prise apart any amorous nematodes trying to mate at random and ruin her experiment.
Whether artificial life celebrates Christmas or not, Andy Pargellis, a computer scientist at Bell Laboratories in Murray Hill, New Jersey, plans to take his research home with him over the holidays. Pargellis uses a computer to produce sequences of computer code, analogous to the nucleic acids thought to have existed millions of years ago on Earth before the start of life as we know it. He installs a program which mimics evolution by altering bits of code at random, in the same way that mutations occur in nature. He then lets the program to run until some codes begin to replicate. The resulting codes are like artificial life forms, and by analysing them Pargellis thinks he can gain insights into how evolution works and how life began on Earth.
Pargellis doesn鈥檛 have to work over Christmas, but is so attached to his evolving 鈥渙rganisms鈥� that he brings them home to breed while he tucks into his festive fare. It doesn鈥檛 matter if the program runs in his lab or on his home computer. 鈥淭he great thing is I can have a lot of fun with the family, and still get something done,鈥� he says.
While Pargellis is having fun at home, Nancy Love will probably be baby-sitting her bioreactors on Christmas Day. Love鈥檚 research, at Virginia Polytechnic Institute and State University in Blacksburg, is looking at new treatments for industrial waste water. Her bioreactors use bacteria to break down some of the organic chemicals found in industrial effluent. To prevent the bacteria dying from lack of nutrients, Love must run her machines 24 hours a day for months at a time.
Usually her students look after the reactors. 鈥淏ut I often get pulled in to take care of things around Christmas,鈥� she says. 鈥淎nyone who runs continuous flow bioreactors understands. They are like babies-they are very dependent and must be tended to.鈥�
Bioreactors are not alone in requiring constant attention. Although seismologists from the University of California at Santa Barbara will be able to check their instruments via their home computers, they will spend Christmas Day on alert for signs of an earthquake. The team from the university鈥檚 Institute for Crustal Studies looks after a dozen automatic monitoring stations near Palm Springs, and if all is calm and quiet there, they can start unwrapping their presents.
But if a big earthquake hits at Christmas, the researchers will have to leave the socks and aftershave and rush into the field. 鈥淲e really don鈥檛 want to miss a large earthquake. We might only get one chance,鈥� says Ralph Archuleta, associate director of the Institute. 鈥淚f it鈥檚 magnitude six or bigger, all of us know we have the responsibility to get instruments into the field. We know that the big aftershocks occur almost immediately after the big shock, and it can be over quickly.鈥�
By contrast, subjects for research can be almost guaranteed on Christmas Day at the Savannah River Ecology Laboratory near Aiken, South Carolina, run by the US Department of Energy. Whit Gibbons is in charge of a project that monitors the health of wetlands in the area, a study that includes monitoring the animals that migrate in and out during the year. Gibbons uses pitfall traps to capture animals such as salamanders, frogs and mice that pass through the area. Every morning a researcher has to count the animals and release them.
Some Christmases, Gibbons himself checks the traps. He takes along his kids and makes it a family outing. 鈥淪omebody has to get out into the field Christmas and every other day,鈥� he says. The team doesn鈥檛 decide until quite near the time who鈥檒l be emptying the traps on Christmas Day, but according to Gibbons a volunteer normally emerges. 鈥淚t鈥檚 usually whoever has the most in-laws visiting.鈥�