Why does light diffract into only seven colours?

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Summary:: If relativity causes wavelengths to change I.e the redshift effect (or blue shift effect for objects moving towards us) does the presence of 7 different colours denote seven different changes?

If the doppler effect shows that direction of trajectory changes wavelength and colour of light does that mean the seven colours of the rainbow are a breakdown of seven different universal direction changes or that an object with a preposterous gravitational mass has entered and left our universe seven time's? Causing the seven different splits in colours of light?
 
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louis_slicka said:
Summary:: If relativity causes wavelengths to change I.e the redshift effect (or blue shift effect for objects moving towards us) does the presence of 7 different colours denote seven different changes?

If the doppler effect shows that direction of trajectory changes wavelength and colour of light does that mean the seven colours of the rainbow are a breakdown of seven different universal direction changes or that an object with a preposterous gravitational mass has entered and left our universe seven time's? Causing the seven different splits in colours of light?
Welcome to PF. :smile:

The naming of some of the colors is for human convenience; there is actually a continuum of frequencies in the visible spectrum, as with the rest of the EM spectrum:

1631577418393.png

https://en.wikipedia.org/wiki/Light
 
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But why seven??It is a good Talmudic number and we seem to like it as humans. I really have no idea why we have seven. Do the Inuit describe seven basic colors? When was the spectrum first so divided ?
After all we have only three distinct eye pigments and yet I swear there are seven colors when I look at the rainbow.
Roy G Biv, your rainbow is a mystery to me.
 
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louis_slicka said:
... does that mean the seven colours of the rainbow are a breakdown of seven different universal direction changes ... ?
No, it means you don't understand the rainbow spectrum. See Berkeman's post directly above.
 
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One should be aware of the fact that "color" is a physiological rather than a physical phenomenon. It's much more complicated to describe than just the frequencies/wave lenghs in a spectrum of the electromagnetic wave field.

The rainbow is a continuous spectrum, i.e., you have a continuum of frequencies/wave lengths in the solar spectrum (which is pretty much thermal radiation). I also don't see a discrete set of "seven colors" but a continuum in a rainbow.
 
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vanhees71 said:
I also don't see a discrete set of "seven colors" but a continuum in a rainbow.
It may well be a sign of age and familiarity but my brain certainly wants to break up that continuum into seven sections. Is there any psycho-linguistic research...I think I will give it look-see.Edit: This is pretty interesting about cultures and rainbow colors:

https://theconversation.com/red-yel...w-the-worlds-languages-name-the-rainbow-68641
 
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PeroK said:
I'm not sure we haven't been trolled here. "... an object with a preposterous gravitational mass has entered and left our universe seven times?" Really!
Hah, that's funny. I never finished reading the OP before replying. We'll give him one more day to reply to this thread and go from there...
 
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berkeman said:
I see 4096
Obviously you haven't gotten the video card upgrade to 16.7 million colors... :wink:
 
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hutchphd said:
my brain certainly wants to break up that continuum into seven sections
Sure, and if you look carefully you'll see that all 7 of them have shades of color, not just one color.
 
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The human central nervous system (of which the retina is one part) can normally only produce sensations of three primary colors. That limits the amount of nameable colors we can describe. Some people, all of who are women, can sense four primary colors because they have four types of retinal cone cells with different pigments. The ability for this is coded in the X-chromosome, that's why male people can't have that ability. Some species of birds can even sense five primary colors. As far as I know, the US military is preliminarily researching a possibility to make people see infrared radiation with some kind of eye drops that temporarily add new pigment molecules to your retina. That way you could see in the dark and locate people by "seeing" how their body temperature is higher than ambient.

https://en.wikipedia.org/wiki/Tetrachromacy
 
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louis_slicka said:
does the presence of 7 different colours denote seven different changes?
No, it represents 7 different sizes of T-shirts: XS, S, M, L, XL, XXL, XXXL. Now if you ask me why in Universe there are no T-shirts of other sizes, it's due to quantization, obviously. Duh! :rolleyes:
 

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FWIW - one language I'm familiar with has different names for colors - green turquoise when translated to Navajo is either blue stone or sometimes 'sky' stone because it the same color as the clear sky. In Navajo.
This is not a unique feature of just one language.

Our brains use the language we speak and it's color designations. Plus we get fooled:
Adelson - move your cursor off the line drawn box completely and back onto the checkerboard a couple of times...
https://www.illusionsindex.org/ir/checkershadow
 
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From archeology, not physics, comes the argument that ancient humans did not see the color blue. Should the OP modify his argument to make it 6 colors, not 7?

https://thedoctorweighsin.com/history-purple-blue/
https://www.sciencealert.com/humans-didn-t-see-the-colour-blue-until-modern-times-evidence-science
 
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Fun fact: not all colors are found in the rainbow. There's no magenta, and no cyan. Which proves that "color" isn't just a function of wavelength - it's the end result of our visual and neural systems' processes. (Any yellow you think you see on your computer screen isn't really there ... at least, it's not due to yellow light, which the screen cannot produce.)
Makes you wonder what other colors might be "seen" by different species with different wetware.
 
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"Some people, all of who are women, can sense four primary colors..."

So why does my wife only see red when I suggest going for a beer?

When looking at a spectrum, at what point does "red" become "orange" etc.? What we call colours are a man-made concept and because of the way we perceive colour, with three frequency-dependent structures and an amplitude-dependent structure, we see six basic colours plus black and white as well as every shade in between.
 
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vela said:
I read Newton shoehorned in extra colors so they'd match up with the seven notes in the musical scale. See, for example, https://sciencetrends.com/7-colors-rainbow-order/.
This is my recollection too. Newton decided there should be seven. (I think he inserted indigo )
 
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hutchphd said:
But why seven??It is a good Talmudic number and we seem to like it as humans. I really have no idea why we have seven. Do the Inuit describe seven basic colors? When was the spectrum first so divided ?
After all we have only three distinct eye pigments and yet I swear there are seven colors when I look at the rainbow.
Roy G Biv, your rainbow is a mystery to me.
People see 3 or at most 4 colors in a rainbow. The whole 7 color thing originates with Newton and his mysticism.
 
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hutchphd said:
But why seven??It is a good Talmudic number and we seem to like it as humans. I really have no idea why we have seven. Do the Inuit describe seven basic colors? When was the spectrum first so divided ?
After all we have only three distinct eye pigments and yet I swear there are seven colors when I look at the rainbow.
Roy G Biv, your rainbow is a mystery to me.
I read that Newton could actually only see 6 colours and invented a 7th to fit his number fetish/superstitions.

I always tell this to my students when they protest that they can't tell the difference between indigo and blue/violet.
 
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I only see "50 shades of grey"... oh wait, it's because I'm watching an old Hitchcock movie.
louis_slicka said:
object with a preposterous gravitational mass has entered and left our universe seven time's?
I find your label of gravity "repulsive"..., I would call it rather "size + gravitational mass" , I mean we don't want to offend any gravitational mass out there, after all gravity is all about "attraction"...
 
rsk said:
I read that Newton could actually only see 6 colours and invented a 7th to fit his number fetish/superstitions.

I always tell this to my students when they protest that they can't tell the difference between indigo and blue/violet.
Newton never went as far as constructing the CIE Chromaticity chart which identifies a range of non-spectral colours. There a colours round behind white and nowhere near the spectral locus. So it has to be seven plus.