What is color? It seems like a simple question at first, but when you think about it, the reality of what we’re seeing is a pretty complex situation. Our human eyes sift through a small piece of the vast electromagnetic spectrum and translate it into every color of the rainbow. But there are other animals that see these same wavelengths in different ways, or even see colors beyond what we can perceive! And not all color is dependent on wavelengths of light: the brains of certain people, called synesthetes, work in ways that let them see colors tied to music, words, or other stimuli. Watch as host Alan Alda takes you on a surreal, scientific tour of the spectrum with the help of vision researcher Jay Neitz, along with neuroscientists David Eagleman, Kaitlyn Hova, and Bevil Conway.

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AN Whitehead wrote that "It takes an extraordinary intelligence to contemplate the obvious."

In a similar vein, Schrodinger said, "Thus, the task is, not so much to see what no one has yet seen; but to think what nobody has yet thought, about that which everybody sees."

Most of us see color, few of us think about it very much. Helmholtz was an exception: "Similar light produces, under like conditions, a like sensation of color."

We can both broaden and tighten this last observation with a little help from Heisenberg and say that the same state vector, acted upon by the same (matrix) operator, produces the same

spectrumof colors, sounds, and other secondary properties. Moreover, colors and sounds and so forth behave like vectors. Weyl, the father of gauge theory, gives us the go-ahead regarding color:"Thus the colors with their various qualities and intensities fulfill the axioms of vector geometry if addition is interpreted as mixing; consequently, projective geometry applies to the color qualities."

See the admirable text on

Sensory Qualitiesby Clark (Oxford) for the general situation.I emphasized the word

spectrumjust now because, as the mathematician Steen reminds us, early on in the history of 20th-century physics, "The mathematical machinery of quantum mechanics became that of spectral analysis...," which is just this business of matrices and vectors.Well, in a way, we have only restated the obvious: The same thing, under the same conditions, looks, sounds, tastes and feels the same.

Yet we can say this without leaving the familiar setting of Heisenberg's formulation of quantum mechanics (QM). Isn't that interesting?

Now, from a physical standpoint, it is naturally immaterial whether the relevant operator field is inside or outside our heads, and this would seem to moot the notion that color is somehow "subjective."

I mentioned gauge theory just now, which governs the symmetries of the universe, which then determine the QM

action.Weinberg put it like this:"Furthermore, and now this is the point, this is the punch line, the symmetries determine the action. This action, this form of the dynamics, is the only one consistent with these symmetries [...]"

Those who wish to explore the other matters discussed here are encouraged to consider the symmetries of color. As noted, color behaves like a vector, and vectors are useful in physics in large measure because they embody natural symmetries.

Scientist

Colour of a substance is d part of light falling on it which cant be absorbed but is reflected by d vry substance

oM

C

Nice

color is what we cannot see,because we see reflected light not absorbed one

Really dazzling.

NS

I apologize for the material repeated below in my reply to another poster -- not sure what happened there...

Note that we also observe the color of a star, flame, or other luminous body, which does not involve reflected light.

[Sorry for the duplication in what follows -- not sure what happened there...]

We also see the colors of glowing objects. The spectra emitted by atoms and molecules when heated were of fundamental importance to the beginnings of quantum theory.

_______

[It] was found possible to account for the atomic stability, as well as for the empirical laws govern- ing the spectra of the elements, by assuming that any reaction of the atom resulting in a change of its energy involved a complete transition between two so-called stationary quantum states and that, in particular, the spectra were emitted by a step-like process in which each transition is accompanied by the emission of a monochromatic light quantum of an energy just equal to that of an Einstein photon.

~Bohr

In Gottingen in 1925-26 Werner Heisenberg and Erwin Schrodinger created the theory of quantum mechanics. In Heisenberg's theory the physical fact that certain atomic observations cannot be made simultaneously was interpreted mathematically to mean that the operations which represented these operations were not commutative. Since the algebra of matrices is non-commutative, Heisenberg together with Max Born and Pascual Jordan represented each physical quantity by an appropriate (finite or infinite) matrix, called a transformation; the set of possible values of the physical quantity was the spectrum of the transformation. (So the spectrum of the energy of the atom was precisely the spectrum of the atom.)

Schrodinger, in contrast, advanced a less unorthodox theory based on his partial differential wave equation. Following some initial surprise that Schrodinger's "wave mechanics" and Heisenberg's "matrix mechanics"—two theories with substantially different hypotheses—should yield the same results, Schrodinger unified the two approaches by showing, in effect, that the eigenvalues (or more generally, the spectrum) of the differential operator in Schrodinger's wave equation determine the corresponding Heisenberg matrix. Similar results were obtained simultaneously by the British physicist Paul A. M. Dirac. Thus interest in spectral theory once again became quite intense.

~Steen

We also see the colors of glowing objects. The spectra emitted by atoms and molecules when heated were of fundamental importance to the beginnings of quantum theory.

_______

[It] was found possible to account for the atomic stability, as well as for the empirical laws govern- ing the spectra of the elements, by assuming that any reaction of the atom resulting in a change of its energy involved a complete transition between two so-called stationary quantum states and that, in particular, the spectra were emitted by a step-like process in which each transition is accompanied by the emission of a monochromatic light quantum of an energy just equal to that of an Einstein photon.

~Bohr

In Gottingen in 1925-26 Werner Heisenberg and Erwin Schrodinger created the theory of quantum mechanics. In Heisenberg's theory the physical fact that certain atomic observations cannot be made simultaneously was interpreted mathematically to mean that the operations which represented these operations were not commutative. Since the algebra of matrices is non-commutative, Heisenberg together with Max Born and Pascual Jordan represented each physical quantity by an appropriate (finite or infinite) matrix, called a transformation; the set of possible values of the physical quantity was the spectrum of the transformation. (So the spectrum of the energy of the atom was precisely the spectrum of the atom.)

Schrodinger, in contrast, advanced a less unorthodox theory based on his partial differential wave equation. Following some initial surprise that Schrodinger's "wave mechanics" and Heisenberg's "matrix mechanics"—two theories with substantially different hypotheses—should yield the same results, Schrodinger unified the two approaches by showing, in effect, that the eigenvalues (or more generally, the spectrum) of the differential operator in Schrodinger's wave equation determine the corresponding Heisenberg matrix. Similar results were obtained simultaneously by the British physicist Paul A. M. Dirac. Thus interest in spectral theory once again became quite intense.

~Steen

We also see the colors of glowing objects. The spectra emitted by atoms and molecules when heated were of fundamental importance to the beginnings of quantum theory.

_______

[It] was found possible to account for the atomic stability, as well as for the empirical laws govern- ing the spectra of the elements, by assuming that any reaction of the atom resulting in a change of its energy involved a complete transition between two so-called stationary quantum states and that, in particular, the spectra were emitted by a step-like process in which each transition is accompanied by the emission of a monochromatic light quantum of an energy just equal to that of an Einstein photon.

~Bohr

In Göttingen in 1925-26 Werner Heisenberg and Erwin Schrödinger created the theory of quantum mechanics. In Heisenberg's theory the physical fact that certain atomic observations cannot be made simultaneously was interpreted mathematically to mean that the operations which represented these operations were not commutative. Since the algebra of matrices is non-commutative, Heisenberg together with Max Born and Pascual Jordan represented each physical quantity by an appropriate (finite or infinite) matrix, called a transformation; the set of possible values of the physical quantity was the spectrum of the transformation. (So the spectrum of the energy of the atom was precisely the spectrum of the atom.)

Schrödinger, in contrast, advanced a less unorthodox theory based on his partial differential wave equation. Following some initial surprise that Schrödinger's "wave mechanics" and Heisenberg's "matrix mechanics"—two theories with substantially different hypotheses—should yield the same results, Schrödinger unified the two approaches by showing, in effect, that the eigenvalues (or more generally, the spectrum) of the differential operator in Schrödinger's wave equation determine the corresponding Heisenberg matrix. Similar results were obtained simultaneously by the British physicist Paul A. M. Dirac. Thus interest in spectral theory once again became quite intense.

~Steen