cross-posted from: https://lemmy.ml/post/19504984
It's all relative
Color is a social construct
OK I need someone to explain this to me cause AFAIK light speed is constant no matter how fast moving the source is
Light speed is constant but the apparent frequency and wavelength (which roughly corresponds to what colour we see) change due to the Doppler effect
Fascinating
Chill, Spock.
So light is a wave. Shorter wavelengths are bluer longer wavelengths are redder. When you walk towards a wave you hit the peaks and troughs faster than had you been still. They come slower if youβre walking away from it. The Doppler effect is that but with light waves and velocities that make it relevant
Which is achieved by spacetime dilation which can in turn stretch or compress the light waves.
While it is true that space time dilation can cause red/blueshift, that is a distinct from the doppler effect which is the primary effect here.
(dilation plays only a small role: without time dilation our answer going from 700nm to 350nm would be 0.5c instead of the 0.6c calculated below)
Adding to the other comments; I once saw a interesting video of a visual demonstration of that effect and other weird things that happen close to the speed of light. It was this one if i remember correctly: https://www.youtube.com/watch?v=ge_j31Yx_yk
How fast would the rose have to be going to blueshift that much? Someone please do the math
For a shift from about 700nm to 350nm: coming right at you at 0.6c
It would also have a kinetic energy of about 1.1234 Petajoules, on the order of magnitude of the Tsar Bomba
Kinetic energy or total energy? Assuming the rose weight 10 grams I get that 1.12PJ total energy, but only 0.23PJ is kinetic.
In hindsight I was a bit generous with the weight, I assumed 50g
chonk rose π³
Only 10MT instead of 50 then?
One ton of TNT is 1E9 calories which is 4 gigajoules. So 0.2 petajoules should be only 50 kilotons of TNT?
A fart in the wind next to the Tsar Bomba. My disappointment is immeasurable and my day is ruined.
I don't know about blue but here is all the math to turn a red light green.... Don't think of doing it though while you could probably get out of a ticket for running a red light I don't even know what the fine is for driving many thousand times the speed limit is.
Edit: just realized I forgot to post the actual link.... https://sciencenotes.org/fast-go-make-red-light-look-green-relativistic-doppler-effect/#:~:text=If%20we%20take%20the%20speed%20of%20light%20to,to%20convert%20to%20km%2Fhr%2C%20you%20get%20197%2C640%2C000%20km%2Fhr.
To bad the traffic light is in the speed radar's reference frame, when your licence plate is on the photo I doubt the judge will care that your yellow car is clearly blue in the photo
Actually I think that would then add a additional charge for registration fraud
60% of lightspeed, according to another commenter.
Impossibly fast and it would have to be coming right at us.
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