B Why does light diffract into only seven colours?

[louis_slicka]

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?

 

[berkeman]

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.

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:

https://en.wikipedia.org/wiki/Light

 

[hutchphd]

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.

 

[berkeman]

I swear there are seven colors when I look at the rainbow.

I see 4096...

https://en.wikipedia.org/wiki/Chromaticity

 

[hutchphd]

So you have binary vision.
Dangit I see seven colors in the CIE chart too...

 

[phinds]

... 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.

 

[vanhees71]

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.

 

[hutchphd]

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

 

[PeroK]

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!

 

[berkeman]

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...

 

[hutchphd]

I'm not sure we haven't been trolled here.

and I got interested in something tangential and wandered off into the woods...

 

[PeterDonis]

I see 4096

Obviously you haven't gotten the video card upgrade to 16.7 million colors...

 

[phinds]

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.

 

[hilbert2]

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

 

[berkeman]

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://www.giantfreakinrobot.com/wp-content/uploads/2021/03/predator-netflix-scaled.jpg

 

[hilbert2]

Here's one news article about that, but it's about research conducted by the Chinese:

https://www.slashgear.com/night-vision-eyedrops-nanoparticles-research-infrared-vision-28567893/

 

[Demystifier]

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!

 

[Vanadium 50]

There are also seven sizes of olives: medium, large, extra large, jumbo, giant, colossal and super colossal.

Coincidence?

Anyway, I am late for my next universe.

 

[jim mcnamara]

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

 

[vela]

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/.

 

[anorlunda]

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

 

[James Demers]

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.

 

[Merlin3189]

And I think George Miller might suggest that we generally perceive seven gradations of anything.

 

[darth boozer]

"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.

 

[DaveC426913]

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 )

 

[Herman Trivilino]

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.

 

[rsk]

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.

 

[artis]

I only see "50 shades of grey"... oh wait, it's because I'm watching an old Hitchcock movie.

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"...

 

[sophiecentaur]

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.

 

[Vanadium 50]

Please, everybody knows there are 96 colors. (Used to be only 64)

 

[hutchphd]

and only the rich kids got to see in 64 colors..

That way you could see in the dark and locate people by "seeing" how their body temperature is higher than ambient.

Here's one news article about that, but it's about research conducted by the Chinese:

https://www.slashgear.com/night-vision-eyedrops-nanoparticles-research-infrared-vision-28567893/

I think the distinction between "night vision" (which is Near Infrared (NIR) often actively illuminated usually silicon detected devices) and thermal imaging FIR devices needs to be emphasized here. Only the thermal imaging devices will see the glowing enemy combatant in the dark field but these are very different from usual silicon optics or eyeballs.
I once had to explain this to a client who had already spent a fair sum of money trying to develop a silicon CCD-based imaging thermometer. Lack of understanding can be expensive, and I felt like the Grinch as I invoiced him for my services.

 

[LCSphysicist]

?

 

[LCSphysicist]

What was that i had just read

 

[LCSphysicist]

Please, everybody knows there are 96 colors. (Used to be only 64)

View attachment 289324

Mine was just twelve

 

[phinds]

Mine was just twelve

Lucky guy. Mine was one. It was coal. It was a lump of coal. We had to color everything black. If there hadn't been lines in the coloring book then when we got done it would have been just all black. And sometimes you couldn't see the lines and it WAS all black. You young whippersnappers with your fancy "colors". Bah humbug.

 

[Vanadium 50]

Coal? You had coal? When I was a kid your so-called coal was still dinosaurs.

 

[DaveC426913]

Loogxury.

 

[louis_slicka]

Hi all thanks for the detailed and varied replies to my very flawed question! I realized as soon as I posted that there are an almost infinite variations on the basic seven colours. It's like asking how long is a piece of string

 

[hutchphd]

We have managed to play with that piece of string for quite a while! Good fun for all..

 

[hilbert2]

I think the distinction between "night vision" (which is Near Infrared (NIR) often actively illuminated usually silicon detected devices) and thermal imaging FIR devices needs to be emphasized here. Only the thermal imaging devices will see the glowing enemy combatant in the dark field but these are very different from usual silicon optics or eyeballs.
I once had to explain this to a client who had already spent a fair sum of money trying to develop a silicon CCD-based imaging thermometer. Lack of understanding can be expensive, and I felt like the Grinch as I invoiced him for my services.

A good point. You'd have to detect wave lengths over 1 micrometer to have temperature differences near room temperature be visible, and the chemical properties of surfaces would also affect the appearance at the same time.

 

[sysprog]

One of the 64 colors in the big Crayola crayon box was a pinkish color called 'Flesh'. I asked my Dad (who as an attorney and law professor did a lot of civil rights work) wasn't that a bit racist? $-$ my 'negro' friends didn't have close to that skin color $-$ Dad told me (I was maybe age 7) to not worry about it $-$ that was for grown people like him and Mom to deal with $-$ I should just keep on being my friends' friend.
:;

 

[Vanadium 50]

It is now "peach".

And no human being ever had skin that color.

 

[DaveC426913]

It is now "peach".

And no human being ever had skin that color.

Well true, but Macaroni and Cheese was never that colour either...
Nor Outer Space, that colour...

http://www.jennyscrayoncollection.com/2017/10/complete-list-of-current-crayola-crayon.html

 

[sophiecentaur]

Well true, but Macaroni and Cheese was never that colou

The colour named Indigo is often placed well inside the CIE graph, rather than on the spectral locus. It's a pretty dodgy part of our colour perception range around there.

 

[Anachronist]

Fun fact: not all colors are found in the rainbow. There's no magenta, and no cyan.

No, actually there is cyan in all rainbows, as well as white light split by a prism. But there is no magenta.

 

[sophiecentaur]

No, actually there is cyan in all rainbows

The problem with that statement is that Cyan is a mix of blue and green primaries (It can also be considered as -Red but that system is based on primaries. Primaries are not spectral wavelengths and can only add together to produce resulting colours on a straight line on the CIE chart. That means it cannot actually lay on the (very much curved) Spectral locus. A rainbow is not actually a very pure spectrum; it's very de-saturated because there's a lot of white in there. Basically, a rainbow is not a very good example of the spectrum of sunlight. The colours can often look impressive and vivid but nothing like as good as what you get in a dark room with a prism.

 

[DaveC426913]

The problem with that statement is that Cyan is a mix of blue and green primaries.

Maybe on a monitor, but there's a frequency of light between blue and green that correlates with cyan (at least, allowing for saturation, as you say).

The problem with magenta is that there is no single frequency, since magenta is a perceived mix of red and blue. If you took the frequency between red and blue, you'd get a green.

 

[sophiecentaur]

Maybe on a monitor, but there's a frequency of light between blue and green that correlates with cyan (at least, allowing for saturation, as you say).

The problem with magenta is that there is no single frequency, since magenta is a perceived mix of red and blue. If you took the frequency between red and blue, you'd get a green.

Yeah I can’t really disagree. I was being mischievous but no colour you can make with primaries is actually spectral. Lowering the saturation involves adding a third primary.

nothing is real with colours.

 

[MysticWizard]

https://en.wikipedia.org/wiki/Color_wheel

 

[Baluncore]

After all we have only three distinct eye pigments and yet I swear there are seven colors when I look at the rainbow.

There are a couple of ways to demonstrate why it might be seven.

We detect three different colours. Red, Green & Violet, that we sometimes call Blue.
That gives us a three bit binary number with 2³ = 8 possible combinatorial states.
But black is zero, so only 2³ - 1 = 7 colours remain.
If we are colour blind to one colour we see 2² - 1 = 3 colours.
If we had an extra detection pigment we would see 2⁴ - 1 = 15 colours.

But the rainbow is different because photons are ordered by wavelength, so in the rainbow detected Red cannot be adjacent to and mixed with Violet. Our Red and Green detectors are significantly overlapped which makes it all the more complicated. Anyhow, in the rainbow we see;
Red = Red.
Orange = Red, with a touch of green. (R+G with R>G).
Yellow = Green, with a touch of red. (R+G with R<G).
Green = Green.
Blue = Green, with a touch of violet.
Indigo = Violet, with a touch of green.
Violet = Violet.
So that gives us seven named and identifiable colours in a rainbow.

I am not surprised that most people agree on the presence and the spelling of 7 colours, even if some misspell the word colour.