The color of water.

[peter]

I have a white enamelled bath at home. I fill it with pure [?] water out of the tap [ie no salts or stuff added] and when it is deep enough I notice that the white of the bath, when seen through the foot or so of water, has taken on a slightly blue tinge. Why is this? Is it just an optical illusion - a trick of the light; why blue and not say red? Is it related to the old chestnut 'why is the sky blue?' [and does anyone yet really and truly know the answer to that question {significant because it was asked to my 9yo grand daughter in her homework last week}].

[I'm Murrin]

1) Water absorbs blue wavelengths slightly less than the other end of the spectrum.
2) Blue wavelengths are scattered more easily by the particles of the air.

[peter]

What happens to the wavelengths that are absorbed Murrin? I'm guessing they go in some way to heating up the water a bit - but the actual photons; where do they go?

re The sky one; is that 'done and dusted' now [ie 100% established as the answer with no 'if's or but's'].

[I'm Murrin]

They're... absorbed. As energy.

And yes, very well established. It also makes the sun look yellower than it really is: The blue light is more likely to scatter laterally, so the direct light from the sun has less blue in it than it would if viewed in space.

[Zarathustra]

Why is the sky blue? Because God made it that way! (One in a long list of unsatisfactory answers I was given as a child.)

Does anyone else notice a color difference in their own eyes? Ever since I was little I noticed that one eye sees things kind of red and the other sees things kind of blue. Taken together, they seem to average out, but it's distracting in those rare times when I can only see something with one eye (like around a corner, or with one eye blocked).

[I'm Murrin]

I sometimes get the impression that one of my eyes sees slightly brighter colours than the other. Most noticable first thing on a morning, I think.

[Orlion]

What happens to the wavelengths that are absorbed Murrin? I'm guessing they go in some way to heating up the water a bit - but the actual photons; where do they go?

They become energy, probably mostly translational. The water molecules will move about. There might also be some vibrational and rotational movement going on, but not so much....with visible light, anyway.

[Morning]

What happens to the wavelengths that are absorbed Murrin? I'm guessing they go in some way to heating up the water a bit - but the actual photons; where do they go?

They become energy, probably mostly translational. The water molecules will move about. There might also be some vibrational and rotational movement going on, but not so much....with visible light, anyway.

en.wikipedia.org/wiki/Talk%3AElectromagnetic_absorption_by_water

[sgt.null]

water has no taste.

does that help peter?

[peter]

In that we are at least 'brothers' in the continual struggle of existance Sarge!

Gosh - this is ridiculous; I've read x number of books on physics, watched all the Stephen Hawking and Brian Cox programs on telly and I still seem to know shit! I'm just going to run this out to see where it goes. Light can be both wave and particulate in nature. It goes into my bath, the red end stuff gets absorbed more leaving the blue end stuff to bounce back to my eye, bingo - the [previously white] bath looks a bit blue. The red end stuff that has been absorbed is converted from [good] light energy to [bad] heat energy, thereby maintaining the temp of the bath that fraction longer than if it were in a dark room. If we think of the case in terms of light as particles [as opposed to waves], there is a bit more of a problem because we have to consider the ok, small, but never the less existant mass of the photons, and what happens to it. Here [if I get this correct] we say that rather than the photons actually entering the nuclei of the water molecules, thereby increasing their mass [albeit fractionally] and creating new isotopes or whatever, the mass of the photon becomes energy, or more specifically energy of motion [kinetic energy] that is added to the mater molecules nuclei's existing kinetic energy, thereby increasing it's heat energy in the same way as if we considered the light just as a wave energy rather than a particle. [nb The heat energy will ultimately become dissipated ala the 2nd Law - hence bad energy as any conversion to heat of energy is always a minute step towards 'the end'.]

That, I think, sums it up.

[I wonder if all the light in the Universe weighs as much as a baseball .]

[Vraith]

If we think of the case in terms of light as particles [as opposed to waves], there is a bit more of a problem because we have to consider the ok, small, but never the less existant mass of the photons, and what happens to it. Here [if I get this correct] we say that rather than the photons actually entering the nuclei of the water molecules, thereby increasing their mass [albeit fractionally] and creating new isotopes or whatever, the mass of the photon becomes energy, or more specifically energy of motion [kinetic energy]

I think there are a couple problems here. First, you run into difficulties of various kinds and scales with pretty much all of physics if you give photons a non-zero rest mass. Problems that may make the existence of things like us people impossible.
Second, the photon very rarely gets anywhere near the nuclei in your tub. It interacts mostly with the electrons.
[[I think lots of things can happen in the rare nucleus cases...like the photon splitting into an electron/positron pair...but I don't think a new isotope by creating a new neutron is possible. I THINK that would require enormous numbers of photons in gamma-ray ranges...and I think even in that case the actual event would be splitting nuclear particles into quarks or somesuch.]]

The electron gets excited, some energy become kinetic...and the rest is re-emitted later, [the electron doesn't like being excited] as a photon at a slightly different energy.


I'm fairly sure that that is all true.

[peter]

Is the zero rest mass problem related to the fact that a photon [presumably] only has one velocity, ie c?

Presumably the 'different energy' of a photon re-emitted from an en electron manifests itself as a different frequency or amplitude of the corresponding 'wave' form?

[Vraith]

Is the zero rest mass problem related to the fact that a photon [presumably] only has one velocity, ie c?

Presumably the 'different energy' of a photon re-emitted from an en electron manifests itself as a different frequency or amplitude of the corresponding 'wave' form?

On the first, I'm not sure if it is THAT it has one velocity [not true, btw, they go slower than c except in vacuum.] but what that velocity is: if it has any mass at all, it has huge [infinite? approaching infinite?] mass at c.
But I think there are others as well [although the others may just be connected to the one].

On the second, I think it gets weird here. Cuz of discrete/quantized photons.
A single absorbed photon exciting one level, an IDENTICAL one must be emitted after. [if excited MORE than one level, different frequency photons can be released stage by stage...the total energy will "add up" to same quantity as the single input]
We've moved above my paygrade.

[Hashi Lebwohl]

Experiements to determine upper limits for the rest mass of a photon. We know that photons cannot have any appreciable mass, even when compared to an electron, or they wouldn't be able to move on down the road at c but if their mass is exactly zero then if they stopped moving they would cease to exist, which doesn't even take into account that their momentum would be c*0 = 0 regardless of whether or not we take relativistic mass into consideration (the faster something is moving the greater its relativistic mass, at c this value should be infinity).

A photon may be absorbed without a subsequent emission; however, at some point a photon will be emitted and the overall energy sent out will equal the amount of energy originally absorbed. It is also possible for one high-energy photon to be absorbed and multiple lower-energy photons be released over time, an effect you can see in "glow in the dark" materials.

It is possible for photons to be emitted or absorbed directly into the nucleus but those are usually very high-energy photons.

[peter]

One of the problems I think I was encountering here was a misunderstanding, or better perhaps, a confusion between the concepts of 'weight' and 'mass'. I failed to see how anything that could have 'matter' [which pressumably a photon has, albeit in a very small quantity] could not have mass. The following line from the wikipedia page on mass might go some way to helping to clear this up, even if it's the wrong way arround [ish].

For everyday objects and energies, well described by Newtonian physics, mass describes the amount of matter in an object. However at very high speeds or for sub-atomic particles, special relativity shows that energy is an additional scource of mass.

This presumably works the other way around in the zero mass photon - ie it's absence of mass being reflected in it's high energy/velocity. {Mmm....that's not sounding right }

[Fist and Faith]

Does anyone else notice a color difference in their own eyes? Ever since I was little I noticed that one eye sees things kind of red and the other sees things kind of blue. Taken together, they seem to average out, but it's distracting in those rare times when I can only see something with one eye (like around a corner, or with one eye blocked).

Good! Lord! Yes!!
I've long since given up trying to tell people about this. Red and green for me, though. Been like this as long as I can remember.

[Vraith]

Does anyone else notice a color difference in their own eyes? Ever since I was little I noticed that one eye sees things kind of red and the other sees things kind of blue. Taken together, they seem to average out, but it's distracting in those rare times when I can only see something with one eye (like around a corner, or with one eye blocked).

Good! Lord! Yes!!
I've long since given up trying to tell people about this. Red and green for me, though. Been like this as long as I can remember.

Not color, no. But I discovered at basic training on the range at night that one eye is much better than the other in the dark. [the bad one even seems to interfere with the better one...I often close it when moving in darkness]

But I just happened to notice that, came here for a tangent article I ran across. This is the blurb about it:
www.techtimes.com/articles/19362/201411 ... riment.htm

The real paper isn't available without paying of course. But the last line of the article is:

Photon coupling and interaction was detailed in the journal Nature Photonics

Anybody but me find it very funny that there is a journal called "Nature Photonics?" and a little awed by the implications of the fact that such a topic apparently requires its own journal?

[peter]

Who knows what atrocities are being perpetrated in the murky depths of 'Nature Photonics' [what with all that 'photon coupling' and 'interaction' and all]?

[sgt.null]

as I get older I have trouble telling deep dark blue from black. not sure if that has anything to do with any of this. sorry.