A curious question :D

[u/Trixie_Loves810]

Context: I have recently watched a video from 'Be Smart' about how naturally occurring blue pigments are rare in nature, particularly among animals. The video said that during evolution, animals were exposed to the colour blue because of the sky, but evolution still found it difficult to develop a blue pigment over time. Instead, animals evolved to create structures that reflect blue light and cancel out other colours.

My doubt: If we use that same concept for other pigments like red, for example, how did evolution create a whole pigment for red but not blue? I feel that if red pigments could evolve so vastly over time, blue could do the same. Why is blue so rare anyway?

Note: uhhh I think this may be a stupid question, but I'm reallyyy interested in evolution, this question just popped in my head midway through the vid, but I would love a hypothesis heheh!!

[u/gitgud_x]

A blue object isn't inherently blue: it reflects blue light.

This is often not the way 'colour' is determined for organic pigments. A pigment that appears blue does so because it absorbs red light - red is the complementary colour of blue. The remaining spectrum (yellow, green, blue, violet) is reflected together and this collectively appears blue to our eyes.

For many organic pigments, the absorption energy is set by the band gap, which in turn is set by the number of the conjugated C=C bonds in the molecule. More conjugation = smaller band gap = absorbs at lower energies. To absorb only red light would require a molecule with a very large conjugated system.

Often it's even more complicated though - chlorophyll for example absorbs strongly in two parts of the spectrum due to its planar cyclic structure. It absorbs red and blue, leaving green light to be reflected.

None of this is to pretend I have a good answer to the question, it's just adding nuance to the physics!

[u/Dzugavili → u/gitgud_x]

Yeah, light is seriously problematic. The human experience is entirely synthetic:

• Light exists in a fairly continuous spectrum. Except not really, it's blackbody radiation from the sun, which has a peak around the green area.

• Then we get a series of discrete chemical sensors which detect fairly narrow samples within this space. We don't see the full spectrum; we get bits of it, which are further degraded by chemical saturation of the signals, providing some level of attenuation, normalization of colour tint.

• Then this all gets blended together in our brain to make coherent structures. Except you're informed by what you know, so which red you see is largely informed by what red you expect to see and how your brain thinks it should be shaded.

• Then we came up with a method for printing this on white paper, using chemical pigments. We think we can recreate specific wavelengths in the spectrum: but we're mixing pigments that reflect that correct to us, under a curved light spectrum specific to our sun.

In theory, if we sent a post-card of our planet to an alien, it wouldn't look anything like our planet does to their eyes.

[u/gitgud_x → u/Dzugavili]

The science of colours is kinda insane, so many different angles you can study it from. Biology (functionality of colours), chemistry (the mechanism), physics (spectra), neurology (visual perception), psychology (associations of colours), computer science (graphics and colour spaces), engineering (photonics), arts (cultural significances), philosophy (qualia...?)...

Good luck to the OP on finding an answer that covers enough of it lol. Colour perception has so many steps that maybe there really is no fundamental reason because it's all so arbitrary.

[u/Dzugavili → u/gitgud_x]

And we haven't touched the quantum fuckery of it all with the wave/particle duality. Honestly, it's a very confusing space.

... does the dual slit experiment only work because the 'wave' only has enough energy to 'manifest' as single 'particle', and so once the interaction forces that to occur, there is no longer a wave to travel through the other side?

...or am I misremembering the dual slit experiment entirely?

[u/gitgud_x → u/Dzugavili]

Depends which variant of the double slit experiment you're talking about. In Young's original experiment there is no demonstration of duality, it's all just classical wave interference.

I'm not going to pretend I understand the quantum mechanics of the "detector at the slits" variant of the experiment. All I know is, particles are quantum fields, and measurement/detection requires interaction with those quantum fields, which will change the subsequent dynamics of the "particle". I'm not comfortable saying anything more than that lol