• Question: If a car is travelling down a road at an infinite speed, what evidence can you use to prove that it is there?

    Asked by anon-181141 on 25 Jun 2018.
    • Photo: Lauren Burns

      Lauren Burns answered on 25 Jun 2018:

      Instead of infinite speed, I will talk about the speed of light (rather than the mathematical infinite as I cannot possibly calculate that), you couldn’t see the car because of the Doppler effect. It’s relative movement compared to any observer would “shift” any light outside the range of the human eye, and potentially any detectors we could build. More than that, the closer something gets to the speed of light the more energy it needs to be accelerated, the Large Hadron Collider can get a proton to a little above .9c (90% of the speed of light) and that’s the limit of our technology, theoretically for something to move at the speed of light it has to have zero mass, which cars most certainly do not have, so really not possible – there is probably some really clever physicists that can give you the mathematical proof of why this won’t work, they frequently quote Einstein saying that “light in a vacuum is the speed limit of the universe” but unfortunately I do not have that knowledge!

    • Photo: Liza Selley

      Liza Selley answered on 27 Jun 2018:

      One of the key principles of forensic science is that ‘every contact leaves a trace’. This basically means that if two objects touch each other they will leave a little bit of themselves on the other. Leaving fingerprints at a crime scene for example.

      A car traveling at infinite speed would put a huge amount of stress on its tyres. The heat and friction would be enormous and the tyre material would wear out quickly to be left behind on the road (think how regularly F1 cars need tyre changes in a race!). If you studied the surface of the road with a microscope you could spot these tiny bits of tyre. If you really wanted to prove it came from a specific car you could do some spectrometry tests to compare the chemical makeup of your sample and the car’s tyre.

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