(I’m coming to this rather late, and will entirely understand if Said doesn’t want to resurrect an old discussion; if not, I hope no reader will take the lack of response to indicate that my points were just so compelling that Said had no answer to them.)
There is no such thing as “purple photons” [...]
I am unconvinced by your argument here (which may just indicate that I haven’t grasped what it is). The following position seems pretty reasonable to me: There are violet photons but not magenta photons. There are orange photons, but because of metamerism you can see something orange without any orange photons being involved. Violet photons are not violet in the same way as a piece of paper covered in violet dye is violet, but it’s reasonable to use the same word for both.
Would you care to make more explicit your reasons for saying that there is no such thing as a violet photon? (You actually said purple, as Charlie had done in the comment you were replying to, but I’m fairly sure your position is not “there are photons of some colours but not of others”. My apologies if I’ve misunderstood.)
What would the atom look like in ordinary illumination [...]
Like many things, it would look different in different conditions of illumination. Unlike most things we look at, its spectrum is composed of a few sharp peaks, so the relationship between its illumination and the colour we see (given sufficient “amplification” since of course a single atom can neither emit nor scatter very much light) is a bit unusual. (One can make macroscopic materials with similar properties and I don’t see any particular reason to deny that they have colour.)
There is no fact of the matter as to whether Neptune “is blue”. [...]
This seems like a matter of definitions, and I don’t like your definitions. Whatever difficulties there are about assigning a colour to Neptune are simple a consequence of the fact that it’s a long way away from us. (I think it’s clear that there’s a fact of the matter as to whether Mars is red: it is. If Neptune’s orbit were where Mars’s is, there’d be no difficulty saying that Neptune is blue.) Are you sure you want to say that whether a thing has a definite colour can change merely on account of the distance between it and us? If we sent astronauts to Neptune instead of just probes, would there then be a fact of the matter as to whether Neptune has a colour? If there were an accident and the astronauts died, would Neptune’s colour-having-ness change? If I take an orange, lock it in a vault (illuminated, let’s say, by an incandescent bulb in the vault), and throw away the key, does there stop being a fact of the matter as to whether the orange is orange?
Incidentally: yes, the reporter is wrong about something. A quarter of a nanometre is not 2.5 x 10^-7 metres.
(I’m coming to this rather late, and will entirely understand if Said doesn’t want to resurrect an old discussion; if not, I hope no reader will take the lack of response to indicate that my points were just so compelling that Said had no answer to them.)
I am unconvinced by your argument here (which may just indicate that I haven’t grasped what it is). The following position seems pretty reasonable to me: There are violet photons but not magenta photons. There are orange photons, but because of metamerism you can see something orange without any orange photons being involved. Violet photons are not violet in the same way as a piece of paper covered in violet dye is violet, but it’s reasonable to use the same word for both.
Would you care to make more explicit your reasons for saying that there is no such thing as a violet photon? (You actually said purple, as Charlie had done in the comment you were replying to, but I’m fairly sure your position is not “there are photons of some colours but not of others”. My apologies if I’ve misunderstood.)
Like many things, it would look different in different conditions of illumination. Unlike most things we look at, its spectrum is composed of a few sharp peaks, so the relationship between its illumination and the colour we see (given sufficient “amplification” since of course a single atom can neither emit nor scatter very much light) is a bit unusual. (One can make macroscopic materials with similar properties and I don’t see any particular reason to deny that they have colour.)
This seems like a matter of definitions, and I don’t like your definitions. Whatever difficulties there are about assigning a colour to Neptune are simple a consequence of the fact that it’s a long way away from us. (I think it’s clear that there’s a fact of the matter as to whether Mars is red: it is. If Neptune’s orbit were where Mars’s is, there’d be no difficulty saying that Neptune is blue.) Are you sure you want to say that whether a thing has a definite colour can change merely on account of the distance between it and us? If we sent astronauts to Neptune instead of just probes, would there then be a fact of the matter as to whether Neptune has a colour? If there were an accident and the astronauts died, would Neptune’s colour-having-ness change? If I take an orange, lock it in a vault (illuminated, let’s say, by an incandescent bulb in the vault), and throw away the key, does there stop being a fact of the matter as to whether the orange is orange?
Incidentally: yes, the reporter is wrong about something. A quarter of a nanometre is not 2.5 x 10^-7 metres.