For doppler shift to make a red traffic light look green. I would imagine its much faster than a car could ever go but I was just curious about the facts of a joke I heard.
“but officer I was going so fast it looked green to me”
very very very fast , things moving away (such as galaxies)
give off red shift , but then things moving towards give blueshift , it would have to be about 80% of what the speed the galaxies are moving apart which in your average car you can’t do , i recall somebody trying this in court once and it was thrown out because the prosecuting lawyer had done his homework and the defense did not
A red LED stoplight emits light with a wavelength ( [sym]l[/sym] ) of 700 nanometers. A green LED emits light at 525 nm.
For nonrelativistic speeds [sym]l[/sym][sub]observed[/sub] = [sym]l[/sym][sub]emitted[/sub] (1+v/c)
so 525 = 700(1 +v/300,000)
or v = 75,000 kilometers per second, towards the stoplight
That’s roughly 162 million miles an hour, which is pretty fast for a car.
My Rambler could do that, but only in second gear.
Beep beep!
Bumper sticker I’ve seen:
Next to a picture of a traffic light with all green lights -
“At Warp Factor 9, they ALL look green to me”
[sub]Good one, Kamandi[/sub]