15 The 3 Polarizers Problems by Adam

Jake Graham (B

Jake Graham (Bn

Brief introduction

Science experiments that you can do at home are often very simple, or at least have simple explanations. The ‘signature’ do-at-home science experiment would be mixing bicarbonate of soda

and vinegar which results in lots of bubbles being formed. The concept of two things reacting to form a new product is simple, and the chemistry behind said reaction is not too hard either. How-

ever, there is an experiment which delves past the simple observations of the human eye, an experiment that baffled the top scientists for years. All it takes is 3 polarizing filters and a source of light.

The experiment.

Let me set up the experiment: a ray of light is shone through a single polarising filter. On the other side, the intensity of the light is reduced by 50%. This is expected, as roughly half of the light is filtered out by the polarising filter. A second polarising filter is placed behind the first filter, perpen-

dicular to it. On the other side of the second fil-

ter, the light intensity is reduced to 0%. This is also as expected. The reason for this as is follows. Here is a sketch of unpolarised light passing through 2 polarising filters:

The explanation (sort of!)

Light is a wave made of oscillating electronic and magnetic radiation. Of course, the direction of oscillation can change. As shown in the diagram, the first polarizing filter only allows light of a specific direction of oscillation to pass through. The second polarizing filter’s “angle of polarization” (i.e. whatever direction of oscillation is allowed to pass through) is perpendicular to the first one.

The first one has filtered out anything that is not in a specific direction so when it meets the second

filter none of the light from the first one is able to get through, as shown in the picture below.

This makes logical sense, as all of the light is “pointing” in one direction after the first filter, and the second filter only lets light through that is pointing in the complete opposite direction. The real mystery is revealed when we add in a third filter, in between the two original filters at a 45 degree angle. Most people would think that this filter doesn’t change anything, and that no light would get through in the end. However, upon performing the test, we find that this is not the case. Instead, we find out that instead of all of the light being filtered out, we find that roughly 75% of

the light is filtered out, as shown below.

With a classical understanding of physics, this would be impossible. The filter does not physically change the properties of light, and thus adding a third filter at a different angle should not change anything. There is no way that the third filter could “know” whether or not there is a filter at

Further explanation

The explanation for this experiment goes beyond the realms of classical mechanics and takes a dive

into quantum mechanics. The reason for this, is that photons or particles of light, are so small that they do not act how we expect particles to act. They act in strange ways never thought possible. This experiment showcases one of the weird ways these particles behave.

However, quantum physics is not simple. The majority of concepts in quantum physics do not have any sort of real-world analogues or analogies. It is so different from classical mechanics that an en-

tirely different mathematical alphabet was created to just attempt to describe the mysteries of the quantum world. So, instead of trying to explain it in the last few words of this article, I will simply leave it here. If you do wish to learn more about this, I recommend first learning about bra-ket notation before reading more about this subject.