this post was submitted on 24 Aug 2024
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cross-posted from: https://lemmy.ml/post/19504984

It's all relative

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[–] lugal@lemmy.dbzer0.com 30 points 3 months ago (1 children)

Color is a social construct

[–] JackGreenEarth@lemm.ee 34 points 3 months ago (2 children)

Well, the names for different parts of the color spectrum are, I suppose. Wavelength of EM radiation, and how your brain interprets it as color, is 'real'.

[–] tate@lemmy.sdf.org 3 points 3 months ago (1 children)

I think they were alluding to a different use of the word color.

[–] JackGreenEarth@lemm.ee 2 points 3 months ago (1 children)

What use? The only thing I can think of is 'colourful' language, which doesn't seem to really make sense in this context.

[–] tate@lemmy.sdf.org 2 points 2 months ago

"People of color."

This technically goes down a very interesting line of thought that Vsauce covered once.

[–] noodles@sh.itjust.works 20 points 3 months ago* (last edited 3 months ago) (5 children)

OK I need someone to explain this to me cause AFAIK light speed is constant no matter how fast moving the source is

[–] gnutrino@programming.dev 52 points 3 months ago (1 children)

Light speed is constant but the apparent frequency and wavelength (which roughly corresponds to what colour we see) change due to the Doppler effect

[–] Track_Shovel@slrpnk.net 11 points 3 months ago (1 children)
[–] tate@lemmy.sdf.org 8 points 3 months ago

Chill, Spock.

[–] captainlezbian@lemmy.world 8 points 2 months ago

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 you’re walking away from it. The Doppler effect is that but with light waves and velocities that make it relevant

[–] Skalix@lemmy.world 2 points 2 months ago

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

[–] bjoern_tantau@swg-empire.de 2 points 3 months ago (1 children)

Which is achieved by spacetime dilation which can in turn stretch or compress the light waves.

[–] BB84@mander.xyz 2 points 2 months ago

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)

[–] TheSlad@sh.itjust.works 18 points 3 months ago (4 children)

How fast would the rose have to be going to blueshift that much? Someone please do the math

[–] itslilith@lemmy.blahaj.zone 23 points 3 months ago (1 children)

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

[–] BB84@mander.xyz 4 points 3 months ago* (last edited 3 months ago) (1 children)

Kinetic energy or total energy? Assuming the rose weight 10 grams I get that 1.12PJ total energy, but only 0.23PJ is kinetic.

[–] itslilith@lemmy.blahaj.zone 8 points 3 months ago (1 children)

In hindsight I was a bit generous with the weight, I assumed 50g

[–] BB84@mander.xyz 7 points 3 months ago (1 children)
[–] Fuck_u_spez_@sh.itjust.works 2 points 2 months ago (1 children)

Only 10MT instead of 50 then?

[–] BB84@mander.xyz 2 points 2 months ago (1 children)

One ton of TNT is 1E9 calories which is 4 gigajoules. So 0.2 petajoules should be only 50 kilotons of TNT?

[–] Fuck_u_spez_@sh.itjust.works 2 points 2 months ago

A fart in the wind next to the Tsar Bomba. My disappointment is immeasurable and my day is ruined.

[–] vrek@programming.dev 4 points 3 months ago* (last edited 3 months ago) (1 children)

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.

[–] itslilith@lemmy.blahaj.zone 4 points 3 months ago* (last edited 3 months ago) (1 children)

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

[–] vrek@programming.dev 4 points 3 months ago

Actually I think that would then add a additional charge for registration fraud

[–] FleetingTit 3 points 3 months ago

60% of lightspeed, according to another commenter.

[–] tacosanonymous@lemm.ee 3 points 3 months ago* (last edited 3 months ago)

Impossibly fast and it would have to be coming right at us.

[–] Sam_Bass@lemmy.world 7 points 3 months ago (2 children)
[–] andrew_bidlaw@sh.itjust.works 3 points 3 months ago* (last edited 3 months ago)

Speed kills, coming down the mountain
Speed kills, coming down the street
Speed kills with presence of mind
Speed kills, if you know what I mean

[–] itslilith@lemmy.blahaj.zone 3 points 3 months ago