Stephen Hawking mentions in his book 'A Brief History of Time' that quarks are much smaller than the wavelength of visible light so they do not have any color in the normal sense. What exactly does the size of the object with respect to the wavelength of visible light have to do with it's color?

What is color int the normal sense? What other colors exist?

  • $\begingroup$ Well also take into consideration that if an object is smaller than the wavelength of light, it only partially reflects/scatters it. So you will only see a very faint/blurred image of that object. $\endgroup$ – rahulgarg12342 Jun 28 '14 at 9:25
  • $\begingroup$ Hi Arul, could you specify whether you asking "how does an object's size relate to color in the normal sense?" or "how does an object's size relate to color in the quark sense?" or "what's the difference between normal color and quark color?" $\endgroup$ – user10851 Jun 28 '14 at 9:31
  • $\begingroup$ Read a better book. $\endgroup$ – akrasia Sep 10 '14 at 9:37
  • $\begingroup$ Any recommendations @akrasia ? $\endgroup$ – Arul Sep 12 '14 at 12:08
  • $\begingroup$ Hi @ChrisWhite! I think I am confused about what the difference is between normal color and quark color. $\endgroup$ – Arul Sep 12 '14 at 12:10

Almost nothing. Hawking was probably just building up to the fact that quarks are "colored" under the strong interaction force (a whimsical name, nothing more), but not actually colored in terms of visible electromagnetic radiation. Collections of atoms/molecules that really are about the same size as visible light wavelengths tend to scatter all frequencies more or less uniformly, which is why milk and clouds (with fat globules and water droplets about the size of or larger than visible light wavelengths) are white (see Mie Scattering).

The size of an object CAN influence its color indirectly; think of the energy level spacing of a particle in a box. There will be some dependence on the size of the box. This is usually not very closely related to the wavelength of light emitted/absorbed (which depends on energy level differences).


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