Colors in the spectrum and entropy

[petrushka.googol]

From one perspective light in it's component colors represents am increase in entropy.

 

However a color could be thought of as an aggregation of similar pixels to create the notion of color, which represents a decrease of entropy.

 

Which of these views is correct ?

 

Please opine.

[Strange]

Which of these views is correct ?

 

I'm going to go for "neither".

 

What has entropy got to do with colour?

[swansont]

I'm also not seeing a connection. Entropy is a property of a system. "The notion of color" really doesn't apply.

[John Cuthber]

From one perspective light in it's component colors represents am increase in entropy.

 

 

What perspective is that?

Does " a profound lack of understanding of thermodynamics" count as a perspective?

[Sensei]

Photons are emitted by hot objects in the all directions (inverse-square law).

The higher temperature of object, the more energy have photons emitted by object.

Everyday objects are emitting photons at infrared/microwave range, because they're pretty cold.

But can be seen by f.e. IR camera (that way IR thermometer reads temperature of body from distance without touching it, just by analyzing black body emission).

Black body emission is shifted depending on temperature, in one direction or other.

 

If body has same temperature as environment, it receives pretty much as much energy as it emits, and there is balance.

 

BTW, it's pretty cool to see world using IR camera at 100 FPS, and observing objects that are transparent for visible spectrum photons, but reflective for IR photons.

 

[petrushka.googol]

 

I'm going to go for "neither".

 

What has entropy got to do with colour?

 

May be my choice of words is incorrect. Should I use the words "order" and "disorder" ? My question could be rephrased as "Of monochrome white light and monochrome RGB which represents an intrinsically more ordered state ?

[Mordred]

The problem is finding a correlation between color and entropy.... color vs frequency).

How is this connected to thermodynamic entropy?

Edited June 24, 2015 by Mordred

[imatfaal]

 

May be my choice of words is incorrect. Should I use the words "order" and "disorder" ? My question could be rephrased as "Of monochrome white light and monochrome RGB which represents an intrinsically more ordered state ?

 

 

What is monochrome white light? And RGB is by it nature a mix of three and thus not monochrome.

 

Is it possible you are asking whether there is a difference say between an RGB source giving a nice orange (255,130,0) and monochromatic orange light of around 617nm

[studiot]

Actually I don't see this as a dumb question and Boltzman's distribution can be applied to this.

 

However there is only one available energy level unless the light interacts with something and then the system changes anyway.

 

Any colour is a mixture of frequencies of light, whether they are combined or split up by prism.

 

However left to their own devices there is no tendency for say red light to self convert to blue light and unless this can happen there is only onefrequency and therefore energy level available to the red photons.

 

So there is no entropy change when we split light containing red photons and blue photons by prism.

The red remains red and the blue remains blue.

[petrushka.googol]

 

 

What is monochrome white light? And RGB is by it nature a mix of three and thus not monochrome.

 

Is it possible you are asking whether there is a difference say between an RGB source giving a nice orange (255,130,0) and monochromatic orange light of around 617nm

 

Yes

[swansont]

Actually I don't see this as a dumb question and Boltzman's distribution can be applied to this.

 

However there is only one available energy level unless the light interacts with something and then the system changes anyway.

 

Any colour is a mixture of frequencies of light, whether they are combined or split up by prism.

 

However left to their own devices there is no tendency for say red light to self convert to blue light and unless this can happen there is only onefrequency and therefore energy level available to the red photons.

 

So there is no entropy change when we split light containing red photons and blue photons by prism.

The red remains red and the blue remains blue.

 

 

While I agree, I think its a little more subtle. Entropy depends on the number of states. While this may be energy, It doesn't have to be — two separate possible paths are two different states. The question is whether the two paths and two colors being correlated matters; I think it does. Monochromatic light going through a beamsplitter will increase entropy.

 

As far as RGB vs white light (assuming a continuous spectrum), The RGB light would have a lower entropy, since there are fewer states in the system.

[studiot]

Forgive my ignorance but how will monochromatic light be split into other colours?

[swansont]

Forgive my ignorance but how will monochromatic light be split into other colours?

 

I didn't say it would be split into colors. A beamsplitter creates two paths for the light.

[studiot]

Unless there is energetic interaction in the different paths there is no entropy difference in one path or one hundred paths.

[swansont]

Unless there is energetic interaction in the different paths there is no entropy difference in one path or one hundred paths.

 

If you shine a couple of lasers on some atoms you can cool them down. What you are doing is increasing the low entropy of the light, and lowering that of the atoms. That comes because the light is scattered in random directions. It's the same transition, so the energy is the same.

 

also

http://www.nature.com/nphoton/journal/v7/n2/fig_tab/nphoton.2012.342_F1.html

"Our main technical result is a proof that no matter what product state is prepared on X and Y, the beamsplitter always increases entropy"

 

One could also consider diffuse vs specular reflection, in terms of being a reversible process.

[studiot]

Thank you for that information, I will need to look at it.

 

Can the scattering be considered elastic or inelastic?

[John Cuthber]

Imagine some monochromatic light bouncing round inside a box made of perfect mirrors- nothing much happens.

Now put some gas in the box. from time to time the photons are scattered inelastically and lose or gain energy.

Eventually the photons will end up with a spread of energies.

Since that's a spontaneous process and spontaneous processes are accompanied by a rise in entropy, I'd say that monochromatic light is (in a rather obscure sense) a lower entropy state than a broad spectrum.

[studiot]

Thank you, John, so you have described an energetic process, which is all I said in the first place.

[John Cuthber]

Essentially any process involving photons is going to be energetic.

Given long enough I suspect you would end up with black-body radiation at the temperature of the scattering gas. (the temperature after the gas has been warmed up a bit).

[studiot]

 

Essentially any process involving photons is going to be energetic.

 

Light can travel indefinitely hrough a vacuum, without energetic encounters.

 

This is just a silly argument.

 

All I said was that light has an energy level so you can apply entropy considerations to it.

In circumstances where there is only one level available there will be zero entropy change.

 

Most light propagation is not like this since it spreads out, reducing the energy density, distributing it over the available volume, thus increasing the entropy.

[swansont]

All I said was that light has an energy level so you can apply entropy considerations to it.

In circumstances where there is only one level available there will be zero entropy change.

 

Most light propagation is not like this since it spreads out, reducing the energy density, distributing it over the available volume, thus increasing the entropy.

Splitting light into multiple paths reduces the energy density.

[petrushka.googol]

Imagine some monochromatic light bouncing round inside a box made of perfect mirrors- nothing much happens.

Now put some gas in the box. from time to time the photons are scattered inelastically and lose or gain energy.

Eventually the photons will end up with a spread of energies.

Since that's a spontaneous process and spontaneous processes are accompanied by a rise in entropy, I'd say that monochromatic light is (in a rather obscure sense) a lower entropy state than a broad spectrum.

 

The implication is that light cannnot remain indefinately in a "split" state as it is relatively unstable. It falls back into it's more stable (white) mode as soon as the opportunity arises.

[John Cuthber]

Not really " as soon as...". light is about a million times more likely to be scattered elastically then inelastically. And the process only happens at all when it hits something..