Doppler

Here's the original image. It was originally posted in 2017 and has been shared so many times it was difficult to find a good copy. I had to use wayback to get this copy.

That car is speeding
- They'd only get a light sentence anyway.
  
  Depending on the frequency of the offence
- I bet that guy feels like he gets where he's going in no time at all!

Okay, just back of the envelope math. Assuming the car is truly 550nm, so the blue car is 400nm, and the red car is 700nm... How fast is the car going?
Napkin math says 0.27c.
Δλ=λ(V/c)
Now someone else can figure out the kinetic energy of the car and why the whole continent just exploded...
- OK now how fast did old man's head move
  
  Okay, napkin math... his nose is about 20cm long, and assuming it rotated about a perfect circle. The car moved say 10m. At the speed the car is moving, it covers that distance in ~120ns. So he has to move the end of his nose around a quarter circle of radius 20cm in 120ns. Let's say 30cm total movement, for easy math. 0.25cm/ns or 0.00025m/ns. The speed of light is 0.300m/ns, so we're talking about ~0.001c at the tip of his nose. Which is incidentally very close to the speed of sound in air.
  So, probably not quite a sonic boom off the end of his nose. Assuming my math is correct. Very strong neck muscles. Also, he's been vapourized.
- Did you take into account that the car is not driving directly towards the viewer?
  
  I ain't doing hyperbolic equations on my napkin ;)
- someone else can figure out the kinetic energy of the car and why the whole continent just exploded...
  It's not on fire or melting the asphalt beneath it, so it must be really aerodynamic, and have really low rolling resistance tyres...
- So about 180 million MPH. I hope he doesn't get a ticket!
- now calculate the Lorentz contraction
  
  Instructions unclear, car stuck in dick.
- Why explode, the car didn't accelerate or interact with the continent
  
  Even ignoring the tires interacting with the road, you have air molecules. I don't think that would be enough to destroy a continent, but it would be very destructive.
  Here is a cool What If? from xkcd about throwing a baseball at 0.9c.
  
  For the same reason this baseball causes an expanding plasma-ball disintegrating everything. Fusion with air molecules that can't get out of the way fast enough https://what-if.xkcd.com/1/

One shift
Two shift
Red shift
Blue shift
- Blue Shift?
  
  Damn, remember when Valve made half life games? It was a better time back then.

Pretty sure the sonic boom of this car passing will kill this poor man
- Well, when that finally happens the car will be fine, far away from Earth.

thats one FAST car
- And one fast head turn
- Only as it's moving away.

If that guy is keeping track of that car, his neck is def broken
- Everything around the car would be broken too, including the car

what a beatiful green car

For some reason I can never remember which causes red or blue shift, but with this I might actually remember it
- Blue has a smaller wavelength, so when something is approaching fast it "squishes" the light, making a smaller wavelength.
- Maybe it's slightly convoluted but here's how I tackle it in my head: I just think of infrared and ultraviolet, ultraviolet being greater frequencies than violet and infrared being the opposite for red. Blue is on the way from infrared to ultraviolet, so blue has a greater frequency than red.

You can either know the position of the car or the momentum, but not both.

But why is the car stretched? And why doesn't it appear rotated?
- It's how Doppler works.
  I don't understand it enough to actually explain but Wiki does a pretty good job.
  
  The poster you are replying to is pointing out the inaccuracies that this comic didn't consider relativistic effects.
  
  (Relativistic doppler effect)
  But does it affect the object that is emitting the wave?
- How would you rotate it?
  
  If you look at an object that is moving near the speed of light, it appears rotated, see https://en.wikipedia.org/wiki/Terrell_rotation.

eeeeeeeeeeeeeeeeeeeyowwwwwwwwwwww

This is also playing on red-shift/blue-shift.
- what do you mean "also"?
- They are the same effect just using different kinds of wave.

I know just enough about the light spectrum and the red shift to understand why this is funny (thanks Prof. Brian Cox!), but it underlines how shallow my knowledge is. So much cosmology, so little time...

YEA! SCIENCE JOKES!

I love it!

Doppler's Politics