The Pew Research Center collaborated with the American Association for the Advancement of Science (AAAS) to create a Science Knowledge Quiz aiming to evaluate the scientific literacy of the American public. Click through to take the quick twelve question test. After the break I’ll explain how the Pew Center and AAAS managed to demonstrate their own scientific ignorance by screwing up one of their science questions.
Remember Question 4?
GPS relies on which of these to work?
Think carefully. The question isn’t asking which is most important – it asks which is required for GPS to work. The intended answer is satellites. But GPS can be deployed using “pseudolites” instead of satellites. Pseudolites are transmitters that can be used to extend GPS indoors or to provide GPS availability under jamming or other circumstances where GPS satellite signals are unavailable. However for the sake of argument, let’s grant that GPS relies on satellites and this is a valid answer.
How do those satellites aim and orient themselves? One technique involves a star tracker. This stellar orientation fix helps the satellite keep its radio signals pointed down and its solar panel aimed at the sun (a star). So, GPS satelites rely on stars for both guidance and power.
Another satellite guidance technique uses a magnetometer to measure the magnetic fields from the Earth. In this sense, GPS relies on the Earth acting as a magnet. Also, older GPS satelites used radiation-hardened ferrite core magnetic memories, without which their on board computers would not function. Here again, GPS is doubly reliant on magnets – for guidance as well as for memory.
GPS uses a time-of-flight distance measurement that wouldn’t be accurate without very precise timing from atomic clocks. Older atomic clocks use microwave lasers (Masers), while the latest atomic clocks use laser cooled atomic fountains. Atomic clocks rely on lasers, and GPS relies on atomic clocks.
In other words, all four answers are correct. GPS relies on satelites, stars, magnets, AND lasers. Both the Pew Research Center and the AAAS should have known better.
Update: For the record, if I had to pick one, I’d answer “(d) Lasers.” While it is possible to operate GPS using pseudolites instead of satellites, without precise timing from laser-reliant atomic clocks, GPS simply won’t work. Constructing good multiple choice questions is hard work, and if you are going to do so, you need to understand the subject well enough to construct valid and unambiguous questions.