Reply To: A Christmas Photonic Teaser

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Steve Holmes

Hello again Alan,

I put the quotation marks in because the word absorbed is usually employed in the sense of water being absorbed into a sponge, and that is not really what happens in the case of retinal stimulation or photosynthesis as it implies that the absorbed object stays within the absorber, albeit perhaps in some altered physical form. The danger here is in thinking of photons as objects, like little snooker balls. They in fact have no corporeal form, being merely packets of pure energy. When the amount of energy a photon carries matches the energy required to excite a molecule it encounters to a higher energy state the photon ceases to exist and the energy it carried is transferred to the molecule (all molecules vibrate and flex to some exent and the higher energy states correspond to modes of greater vibration or flexion). In its turn, the molecule can then pass on that energy to another molecule (dropping back to its original state as it does so) and so on. The end result of such a chain of transfers is often the production of a new molecule, the additional energy perhaps being used to overcome a repulsive force between constituent parts of the new molecule which would prevent that molecule being formed were it not for the intervention of the photon down the line.

Therefore, because a photon ceases to exist when it is “absorbed”, we do not embody every star etc. that we observe because the very act of seeing it destroys the photons coming from it. Again, the danger is to imagine photons as little balls which somehow lodge within us – not so! We do, of course, embody “star stuff” a different way, in that we are constructed from elements only produced in supernovae, but that is another subject entirely!


P.S. No, not involved in setting the Christmas Quiz but I am always open to being asked!

  • This reply was modified 1 month, 2 weeks ago by Steve Holmes.