Camera obscurer: How the Doppler Effect could get you out of a speeding ticket

Posted by ap507 at Mar 21, 2014 10:53 AM |
Physics and Astronomy students find it would be possible to become invisible to speed cameras – if you could travel at a sixth of the speed of light
Camera obscurer: How the Doppler Effect could get you out of a speeding ticket

Source: Wikimedia Commons

Our physics students are a cunning bunch. In a paper for this year’s Journal of Physics Special Topics, a group of four MPhys students from the Department of Physics and Astronomy worked out how you could avoid getting a speeding ticket - by driving so fast your car would become invisible to speed cameras.

It’s all down to the Doppler Effect – the physical phenomenon which allows light from an object to be “shifted” upwards or downwards along the spectrum as the object moves to or from an observer.

According to the well-trodden formula astronomers use for working out the “red shift” of stars, you could theoretically drive fast enough for your number plate to be shifted out of the visible spectrum, rendering it undetectable to even the most beady-eyed of yellow boxes.

But the paper’s authors - students Dan Worthy, Robert Garner, Jenny Gregory and Jessica Taylor-Ashley - are certainly not recommending you try out this dangerous and highly-illegal tactic for yourself.

Besides, it’s going to be a little while before we’ve developed anything that could reach the necessary speeds. According to their calculations, you would have to be going at 119 million miles per hour to shift the yellow light of the number plate from its usual frequency at 515 terahertz to its required value at less than 400 terahertz, the boundary of visible light.

That’s a sixth of the speed of light – almost 800 times faster than the quickest man-made vehicle of all time, the Helios Probe.

In other words, it’s still best to stick to the speed limit - for all concerned.

The Journal of Physics Special Topics is a peer-reviewed student journal run by our Department of Physics and Astronomy.