Chapter 21
SED and Polarisation

Light is a wave with transverse electric and magnetic fields recreating each other from their opposites in a sinusoidal manner. A sinusoid is merely circular motion viewed from the side and not the front, because light is always a circular wave and not just the sin waves as shown in most physics textbooks. Normally it forms a kind of spiral or helix as it both spins and moves forward at light speed, with the spin axis parallel to the direction of travel. The equation for this motion is based on eix , just like matter particles are. However somehow it can spin on different axes that are at right angles or perpendicular to the forward motion. Light is incredibly mysterious and wonderous.

When we say light is polarised we simply mean that spin direction is shared by many photons at once. They all have their electric fields aligned the same way. Experiments show that light can be polarised in three different ways: vertical. horizontal and circular. Each type corresponds to the direction of movement the electric field vibrates in, as the photon or particle of light moves through space. There are three possibilities for this, analogous to the X, Y and Z axes of normal 3-D space.

Figure 41 - Visualisation of sinusoidal motion derived from circular motion

The whole concept behind these three different states is that of orientation of the spin direction of the light itself, compared to its travel direction. Vertical and horizontal polarisation are just circular motion viewed from the side and above. This is because light photons will always spin in a plane and carry an angular momentum of h. All photons do this.

Normally light is disorganised and decoherent, because the individual photon’s spins do not line up parallel but are randomly oriented. However moving through certain materials like specially prepared glass can make it so by aligning the photons together. Vertically polarised light cannot pass through a horizontally aligned polariser and vice versa. This is the principle of these sunglasses. Earlier in the 1930’s attempts were made to have all car windscreens polarised one way and the glass in headlights oppositely polarised, making the dangerous glare for the oncoming driver vastly reduced. Non polarised light from all other sources would still be visible. For various reasons this idea did not gain enough support and was eventually abandoned.

Another more modern use for polarising is with 3-D movies at cinemas. The viewer wears special left and right glasses oppositely polarised, and the screen has two slightly different images projected onto it. This causes our eyes and brain to be tricked into perceiving depth. There are other more natural ways to polarise light including certain low angle reflections which make it become slightly polarised in the right conditions. Possibly the future will reveal more.

The Origin of Everything
(Online Edition)