Polarised Light And Our Left Handed Flesh

Polarization of electromagnetic fields An ordinary incandescent bulb (just like the Sun`s radiation) emits (many wave packets of) photons pointing in random directions so its radiation is not said to be Polarised in any one direction.

The propagating ripple that is an (individual) electromagnetic wave comprises intertwining electric and magnetic fields. By definition its direction of polarization is defined to be the direction in which the electric field is oscillating up and down.

We can have both plane waves or circularly polarised waves.In the latter while looking at the source, the vector of (just) the electric field part of the light coming toward you appears to be rotating counterclockwise and the light is said to be right-circularly polarized. Using such a wave descri ption, the electric field vector (and it`s complimentary magnetic field vector) of circularly polarized radiation describes a helix.

As with all field equations those of Maxwell`s varying electromagnetic fields are invariant to the reversal of time: change t to - t and they still work . (This is in contrast to what we know from his Thermodynamics where the arrow of time points only in the direction of increasing entropy, to a universe sinking to a final equilibrium state of zero useful working energy). That is, the helix is palindromic in time in the sense that the horizontally oriented helix is identical whether traversed into or out of the page in the diagram above. A reversal merely inverts the direction of the propagation of the light and does not modify the sign of the helicity. By convention though we define left handed helicity by the motion of the Helicity vector scribing the tip of the hands of a standard clock as it moves with the light ray with its face directed forwards. The question is whether this choice of Helicity reflects a real certain handedness present in the light.

Unlike the inversion of time there is a real effect of inverting the sign of spatial directions on the descri ption of the light ray. Such an inversion operation is called a Parity transformation. It turns out that the study of such orientation dependence has had deep influence in the building of fundamental particle theories.The inversion of space transforms right-circularly polarized radiation into left-circularly polarized radiation. As such the Helicity of radiation flips sign with a parity transformation and thus we can assert that circularly polarized radiation possesses a handedness called chirality.

Optical Rotation and CMBR Given the linear nature of Maxwell`s field equations, linearly polarized radiation can be described as composed of both right-circularly polarized and left-circularly polarized radiation. When such radiation traverses a medium that is chiral in the sense that it is made of chiral molecules, one of the circularly polarized components is propagated less rapidly than the other and the plane of the polarized light beam is rotated. This phenomenon is called optical rotation. If the beam is traversing a medium that is chromophoric, one of the two circularly polarized components is absorbed more than the other resulting in the phenomenon of circular dichroism.

The question you might ask then is why is their an apparent handedness choice present in the chiral compounds of the universe. In particular, why is it that almost exclusively there are only left handed amino acids within life on earth. Is this due to some handedness in the radiation that was emitted at the Big Bang? More precisely does the light emitted from the surface of last scattering that has a polarized signature in the Cosmic Microwave Background Radiation reflect some very early choice that has been made?