#bell's experiment

Background The triple polarizers experiment is a simple experiment that you can easily do at home. And yet it offers fundamental clues to the nature of light, reality and the Universe!

The experiment is often mentioned in connection with Bell’s Theorem and Bell’s Experiment (see adjoining essays) but that is a little bit confusing because it is not a proper Bell’s Experiment. It does not involve so-called ‘entangled’ pairs of sub-atomic particles. In some ways you could think of it as half a Bell’s Experiment. It does however shed some light (pun intended) on Einstein’s belief that the Copenhagen Interpretation of quantum mechanics is somewhat lacking. Conversely, some authors claim that the experiment shows that Einstein’s views about determinism and reality are deficient.

I think it simply shows that the conventional wave-particle model of light is intrinsically self contradictory and fundamentally deficient. Such a heavy debate from such a simple experiment!

The Triple Polarizers Experiment All you need for this experiment is a torch and three sheets of polarized film. If you already have a source of polarized light, such as is emitted from many types of computer screen, all you need is two polarized lenses from a pair of polaroid sunglasses.

If you pass a normal beam of light through a reasonably good polarizing filter about half of it gets through. If you then try to pass the emerging beam through another extra polarizer turned through 90 degrees then no light gets through. But if you insert a third polarizer between the other two then, aligned at 45 degrees to both of them, then about 25% of the incident light comes out of the third and final polarizer.

The essential point is that adding an extra filter results in more light coming at the end, not less.

You can vary the experiment. The angles aren’t critical as long as the orientation of the middle lens is between the planes of polarization of the other two. You can insert extra lenses as well and get even more light out at the end.

It is almost as if each inserted lens sort of ‘twists’ some’ of the light and thus helps it pass through the next filter. In fact, I think that is getting close to the truth. So why is it a big deal?

Evidence against Einstein? Einstein was inclined to believe that photons and sub-atomic particles acquire definite properties when they are created and that these inherent properties pre-determine what happens when those particles interact with subsequent detection equipment. If not precisely, then at least in a probabilistic way.

The Copenhagen interpretation of quantum mechanics is that particles have a variety of potential properties all sort of stacked together and when an observation is made one of the states for one of the properties triumphs and all the other possibilities for that particular disappear.

Some physicists/authors inclined to the Copenhagen Interpretation (CI) say that the three polarizers experiment is evidence against the Einstein viewpoint. The say that the experiment consists of photons passing through or not passing through a sequence of filters. Each photon is either absorbed in a filter or it passes through that filter and on to the next one. If Einstein’s Hidden Variables (HV) view is correct, then the likelihood that a particular photon will pass through first filter is already pre-coded in that photon. It will also have pre-coded instructions for what do if it meets the middle filter and pre-coded instructions for what do if it meets the last filter. The instructions for whether to pass through the last filter or not affected by the first two filters because the photon passed straight through those two filters. So they say that the HV view cannot explain why the presence or otherwise of the middle filter is making a difference to the outcomes at the third filter.

Other physicists argue that the middle filter must be ‘disrupting’ the experiment somehow. It was because of this argument that Bell developed his clever idea for testing things in a different way.  

Bell’s Clever Idea In 1964 the Irish physicist John Stuart Bell suggested that a potential way to resolve the argument would be to split the experiment into two halves and send some photons though filters on one side and the others through filters on the other side. Put as large a distance as possible between the A side and the B side. Then any ‘disruption’ would be quarantined to one side or the other. If the effects of disruption still occurred, then it would be evidence that what happens on one side is able to influence what happens on the other side, instantaneously or almost instantaneously.

But there is one more crucial step. The photons going left and right have to be exactly the same as each other, or at least exact mirror images. They have to be born simultaneously in exactly identical circumstances, preferable from the same event. In other words they have to be identical twins, also known as a mirrored pair, also known as an entangled pair.

This is the origin of the famous but controversial Bell Experiment. I have discussed it in another essay. Let us return to the three polarizers experiment.

Comments on Interpreting the Triple Polarizers Experiment I have so many objections and complaints about the conventional explanations for the triple polarizers experiment that it hard to know where to begin. Try reading multiple textbooks or online lectures in an effort to find a simple explanation of this simple experiment. You will soon discover a mixture of different explanations that contradict, complicate and confuse each other.

I am convinced that the experiment is a simple demonstration about the true nature of light and we need to recognize what it is telling us.

Let us start with the conventional view that light is both a wave and a particle. That it has a dual nature and its behaviour depends upon the type of experiment that is being performed. I do not regard this as a clever model but rather as an admission of failure. It is self-contradictory, inconsistent, incomplete and unsatisfactory. Simply to accept the model because it works pretty well is to deny the opportunities for further insights and a fuller understanding.

In an earlier essay I used a platypus as an analogy. When a platypus was first shown to western scientists they were not sure whether it was a duck (because it has a bill, webbed feet and lays eggs) or a rodent (because it has fur and burrows underground). But it is not a duck, and it is not a beaver, nor is it a duck or a beaver depending on how it is viewed, or a duck and a beaver until it is revealed to be one or the other by the act of viewing it. It is what it is. Likewise a photon.

Some writers describe the polarization of light by comparing it to a rope passing through a picket fence and being shaken up and down in the form a wave. I think this is a terrible analogy. For a start, a standing wave can pass through a picket fence in any orientation if it has a null point (node) at the point of intersection.

Other explainers talk about light consisting of electromagnetic vector field waves that can be thought of as having a component parallel to the plane of polarization and a component perpendicular to the plane of polarization. They then say that one component gets absorbed and the other passes through. I think this is also wrong and misleading. If one component gets absorbed then the emerging light would have lower energy (i.e. be red-shifted) and this is not what is observed in practice.

Other authors switch to the model of light as little photonic bullets. They talk about probabilities of being absorbed or passing through the filters. But then they have to explain what happens at the polarizers. Some skewer the bullets with a hypothetical little sideways stick and say that the photons pass through if the stick lines up with the polarizing molecules in the filter, but otherwise not. How then to explain the fact that 50% of the light get through a polarizing when the incident polarization is randomly oriented? Let alone the full experiment.

Some authors have a bet each way and start with the wriggly little worm electromagnetic wave model for light but then chop the wave into short pieces to try to represent its quantization.  

Attempts to describe circular polarization add further confusing complexity. The representation of light as a double electromagnetic wave seems useful, but does this mean that all light is a double electromagnetic wave? Wouldn’t this make it easy to split into two? And how does it reconcile with the photon idea. Are we to believe that light consists of a double photon? Or perhaps the photon is spinning as it travels. If so, how does this accord with quantized spin?

Furthermore, no author I have yet read recognizes the fact that the photons are travelling at the speed of light and hence must obey the lessons of Special Relativity taken to its logical limit. Why teach Special Relativity if you don’t believe it?

I have written another essay about what I suspect all the evidence is telling us about the true nature of light and have come up with suggestion for a new model that seems to work. In order to break away from older inappropriate analogies I invented a new word – I say that light consists of phots.  

However, for the purposes of this essay I want to focus on trying to understand the triple polarizers experiment. Why is it perplexing? Is Nature playing some sort of trick on us? If so – where is the subterfuge? Where are we misunderstanding what is going on? Are some of our assumptions wrong? Are we misinterpreting what we think we are seeing?

It’s a simple experiment. I think it should have a simple description that makes sense and is consistent with the rest of physics.

Suggested Explanation for the Three Polarizers Experiment A simple explanation is that we are deceived when we think that photons pass straight through a polarized film. They look like they do but it’s a trick. What might happen (and I think it does) is that the incident photons are absorbed into the filter and they are either absorbed or they cause a new and very similar ‘child’ photon to be produced which resumes travelling on the other side of the filter and in the same direction as the incident photon. The process is effectively instantaneous.

It is now quite easy to describe the three polarizers experiment. Let us start with light that is initially unpolarized. In other words it consists of photons that are polarized in random orientations. The first polarizer absorbs all the photons and recreates about half as many child photons. The child photons have an orientation more closely aligned to the first polarizer’s plane of polarization. The photons that arrived attuned to the first filter’s plane of polarization are the ones that tend to give rise to child phots with a similar persuasion. The others are the ones that tend to be absorbed.

The middle polarizer absorbs all the phots it receives and emits many (about half for 45 degree relative orientation) ‘grand child’ phots. The child phots have an average orientation more aligned to the plane of polarization of the middle polarizer. This gives the effect of twisting the beam of photons. Note that you cannot watch a particular photon or chain of photons in motion. You can only observe the consequences of a photon being destroyed. (The most common one being that a new photon is created which then enters your eye or a photomultiplier or camera or similar device).

Likewise at the third polarizer. The ‘grandchild’ photons emitted by the middle polarizer are oriented in a way that leads to about half as many ‘great grandchild’ photons being created and emitted by the final polarizer.

The hidden variables idea is not being contradicted at all. Simply for the reason than none of the initial photons every reach the second and third polarizers. Their offspring reach the additional filters but not them. And like all offspring (!) the new generation photons have their own ideas about how they should interact with any polarizers they should happen to meet.