What better way to illustrate the concept of redshift than with that bane of speedy motorists, the radar gun?
That's how a crew for the National Geographic Channel wound up filming a radar-gun-wielding detective at Fermilab earlier this month. It will be part of a film about the evolution of the early universe--the period shortly after the big bang--in the "Naked Science" series.
To better understand the evolution of the universe, cosmologists are eager to measure the speed of celestial objects moving away from Earth. They determine the redshift--or change in color--in the light emitted by a star. This corresponds to a shift in wavelength (and frequency) of the light. The shift in wavelength also happens with sound waves; a siren's pitch, for instance, becomes lower as it moves away, a phenomenon known as the Doppler effect.
When it comes to celestial objects, the redshift also indicates their distance from Earth: The faster a star moves away from Earth, the more its color shifts toward the red end of the spectrum and the farther away it is from Earth.
A radar gun measures the speed of passing cars by using electromagnetic waves, which travel at the speed of light. It sends out microwaves that bounce off a car and back to the device. If the car is moving at the same speed as the radar gun, the returning waves have the same wavelength and frequency as the waves that leave the gun. If the car is moving away from the radar gun, the returning waves have a wavelength and frequency different from the outgoing ones. The size of the shift indicates the speed of the car.
The film crew recruited Detective Shawn Mazza (right) of the City of Batavia Police Department to operate and pose with a radar gun. Cameraman Andrei Khabad (second from left) spent more than an hour capturing Mazza in action, for what will probably be a minute-long explanation in the documentary. Khabad filmed the detective from every angle, from close-ups of Mazza holding the radar gun to shots of him chasing a speeding car. At least, that's what it will look like in the final cut; in reality, the police car rarely moved more than 10 feet in any of the scenes they filmed.
According to producer Melisa Akdogan, the documentary will air some time next year.
