# If a person passes near me at Mach 2 speed would I see him?

1. Dec 13, 2015

### genu6

If a person is moving at Mach2 (1522 mph/h , 2469.6 km/h) and he passes close by me in a radius of 2-3 meters, would I be able to see him? Please for the sake of the question, ignore sound effects, sound barrier details etc. I'm only interested in the speed and the visual part. IF yes, what exactly am I going to see? A short term blur with very little details or more like everything?

Also, if I see him at that speed, what speed do you think he's gonna need to be moving at in order for me not to see him at all? (e.g. bullet)

2. Dec 13, 2015

### rootone

The answer to this will be mostly determined by the rate at which the visual cortex of the brain is able process signals incoming from the optic nerves, and the speed + amount (bandwidth?), of signals that the optic nerves themselves are capable of.
I would think this could vary between different individuals, (well maybe not the signal transmission rate).
The size of the passing object makes a difference too.
It is as you say impossible to see a bullet in flight, but an aircraft traveling at the same speed would be visible.

My guess is that you would see an object the size of a person approaching, but wouldn't really register much detail at the stage of it passing by.
Our visual systems have not evolved in an environment whereby there would be an advantage in noticing supersonic objects.
However they DID evolve in an environment whereby minute movements of objects are readily seen, and that certainly would have an advantage.

Last edited: Dec 13, 2015
3. Dec 13, 2015

### genu6

Thank you, that's very informative! :)

Imagine however you are standing at the beginning of a 50 meter long street, the person travels 50 meters, steals your wallet and goes back 50 meters to exit the street, this is all happening at Mach 2, what do you think you would you see in this scenario?

4. Dec 13, 2015

### genu6

Mach 2 is 686 meters per second, I think 50 meters would take 7.28 centiseconds. You would observe a total of 15-16 centiseconds. Jeez, I just realized how fast that is. Guess I answered my own question.