QUANTUM WEIRDNESS

Introduction

Many accounts of quantum theory, particularly those in the popular non specialist publications, describe some rather weird events. Just a few of them are summarised below:

·        A particle can be in two different places at the same time.

·        A neutron and its spin can separate and move in different directions.

·        Photons can instantly influence each other, even when they are millions of light years apart.[1]

Although it may be interesting, general knowledge and common sense should be enough to tell us that the weirdness can't happen and shouldn't be taken seriously. But not everybody agrees with that. After all if the weirdness can't happen why do some seemingly successful interpretations of the theory suggest that it can?

There's an impasse between different points of view and this may be partly resolved by taking a fresh look at the theory and any models and concepts that are used to inform the theory.

This work will go back to basics and show that the theory may benefit by a little bit of a rethink. The work is very simple and obvious. It applies to quantum objects in general but the main focus is on light and matters related to quantum entanglement and interference. There is no maths but the conclusions reached are relevant to the assumptions upon which the maths and the theory are based.

Quantum Theory

Despite its successes quantum theory is often interpreted as coming up with weird predictions that defy common sense. One area of weirdness is that it can be interpreted as predicting the existence of quantum superposition states where all possible states happen at the same time despite the states being mutually exclusive. The statement that a particle can be in two different places at the same time is an example of a description of a weird quantum superposition state.[2]

When trying to make sense of the weirdness it should be remembered that all theories are informed by observations and within their domains of applicability they should conform to observations. if a theory is able to make predictions then ideally it would be possible, even if just in principle, to make observations that can validate those predictions.

Quantum theory does not meet the above ideal because of the assumption that attempts made to observe the weirdness puts an end to the weirdness and prevents it from being observed. Catch twenty two is at work. As an example if we try to observe a particle being in two different places at the same time what we actually observe is the particle being in one place only. Some of the predictions may be weird but the observations are not weird.

It can be argued that physics should consider only those things that can be observed and if we can't observe the predicted weirdness we should ignore it. There's a lot of substance to that argument. At the very least we should be more thorough when considering the limitations of quantum theory and other theories we use.

Models of Light

Most people like to think of light as being something that's real, for example something that can leave a light source and travel through the surroundings to wherever it goes. But what is light? Is it waves or could it be particles?  Or should we think of light in other ways such as in terms of electromagnetic fields or quantum fields?[2]

One answer is that it doesn't matter what light is. When we think of light in terms of waves or particles or anything else we are using a model and from a practical point of view we can choose models that are suitable for the task in hand. For example, when working on geometrical optics the model that light travels as rays can be useful. When calculating resolving power we would use the model that light travels as waves[3]. Models, like theories have their own domains of applicability.

Things are different when it comes to theoretical physics and when we try to get a deeper understanding of what's really going on. Theoreticians should not only be aware of the different models of light but should also have a much greater awareness of the limitations of those models and other models they use.

A simple and basic photon model, in summary, is that each photon emitted from a source travels at the speed of light until it encounters something to interact with, for example the eye, or a particle that scatters the photon, or an atom that absorbs the energy of the photon and then emits a copy of that photon.[3]It's a model that seems to make sense but it has the following major limitation:

Photons cannot have any interactions, or be detected directly at empty places. They can interact or be detected only when entering places that are suitably occupied such that interactions can occur.

Any attempt at setting up a photon interaction directly at an empty place requires that something suitable be put at that place, thereby making it non empty. Catch twenty two is at work again

The limitation applies to all models of light and raises the possibility that since light has no interactions or directly observable existence at empty places it may have no real existence at empty places. Whether light is real or not in empty places is open to question and from a physics perspective can usually be ignored. The limitations of the models, however, should not be ignored.

 It should be made clear that in the context of this work an empty place is defined as a place that is devoid of anything that interacts with light.

Properties of Light

Is it correct to assume that light has properties? To answer the question it can be helpful to consider summarised pairs of statements such as those below:

·       
      A property of light is that it can be reflected.

·        A property of a mirror is that it can reflect light.

·        A property of a polarising film is that it can polarise light.

·        A property of light is that it can be polarised.

·        A property of light is that it can excite an atom.

·        A property of an atom is that it can be excited by light.

Statement such as those above reveal the following principle which is obvious but quite often overlooked:

No observations should be interpreted as revealing properties of light or of a limited part of the system only, but as revealing properties of the whole system within which the observations are made.

The system can be defined as being everything that has an effect on the observations. To pin down everything that is relevant and non negligible is a challenging if not impossible task. But that's a problem faced by theorists in general who often, by necessity, use concepts such as self contained or closed systems where everything external to the system can be ignored as being negligible in its effects. It's impossible to take everything into account and it can happen that in certain cases things considered as negligible  turn out not to be so.

As an example of the above principle, consider observations on reflection using a semi silvered mirror which has been prepared such that on average a certain percentage of the light is reflected. From this example it should be clear that what is observed during reflection is not due solely to the properties of light or due solely to the properties of the mirror. Instead it's due to the properties of the whole system, which consists of the light along with the mirror and everything else that has an effect.

This brings into question the word property and what it means when applied to light. Does light have any properties at all that are exclusive to itself, in other words properties that do not depend on the rest of the system and on the method of observation? The constant speed of light is one example that comes to mind but it should be appreciated that even with examples like this the observations made reveal properties of the whole system.

Analysing Events

The list below summarises how the points described in this work can be taken into consideration when analysing certain events.

1. Any known shortcomings and limitations of the models and theories used should be more thoroughly taken into account and more care should be taken when making simplifying assumptions.                                                                                                                          

2. It should not be assumed that observations reveal properties that apply to limited parts of the system only but reveal properties that apply to the whole system.

3. There should be more reliance on general knowledge and common sense and more scepticism about any aspects of events where quantum weirdness is alleged to occur, particularly when it's not possible to observe the weirdness.

It may seem that the points above and everything else written in this work is so well known and obvious that it's already taken into account. However, that is not always the case.

Experiments with Light

In certain experiments, for example those where optical components are tested, a common assumption is that light enables observations to be made on certain properties of the system. In other experiments, for example those involving entanglement or interference, the assumption is the other way round which is that  the system enables observations to be made on the properties of light. Both assumptions are  limited and can cause problems.

One problem is associated with local hidden variable theories which are based on the assumption that light has definite properties exclusive to itself and which are independent of the system and the method of observation. The problem is that the assumption does not take into account the fact that the observations are due to the whole system.[4]

In spite of the above problem the theories have been tested by experiments and unsurprisingly, the results obtained are not those predicted by the local hidden variable theories, they are the results predicted by quantum theory.[5] The results provide evidence that light does not have properties exclusive to itself. This should be taken into account by anybody trying to derive a theory which removes the apparent weirdness associated with quantum entanglement.

The concept of wave particle duality has been beset by a similar problem.[1] It's known that it's possible to demonstrate the so called wave and particle effects separately by using the same light source but not by using the same experimental system. It's odd, therefore, that the different observations made are often interpreted as displaying different properties of light, which does not necessarily need to be changed and not displaying different properties of the whole system which does necessarily need to be changed. The interpretation is analogous to getting different values when measuring the mass of a fundamental particle by different methods and then attributing the differences to changes in the mass of the particle and not changes in the methods used to make the measurements.

Back to basics

A very simple system involving light would consist of what can be defined as a light source and what can be defined as a light detector, so arranged that the detector appears to react to the presence of light from the source. One thing that can be deduced with reasonable confidence is that there is a correlation between happenings at the detector and happenings at the source.

To further assume that light originates from the source, is real and moves through the interconnecting space from the source and to the detector is to devise a simple basic model involving light propagation. It's a model that has proved its worth and for the majority of endeavours involving light should continue to do so. In fact to not use the model, or the variations of it, would be a very hard habit to break. It should be better realised, however, that there may be occasions when it can be productive to be a little bit fussier than usual and take the limitations of the model and the variations of it, more thoroughly into account. Such occasions could include those times when attempts are made to explain away quantum weirdness.

In summary there are different models as to the nature of light and just three of them are briefly summarised below.

·       
     1. Light is real in empty places and has properties exclusive to itself which are independent of the system.

·        
      2.  Light may be real in empty places but its properties are not real until they are observed.

·       
      3.   Light may be real in empty places but what is observed is not due to the properties of light or a limited part of the system only, but due to the combined properties of the whole system.

The first model above is more classical than quantum. It has a wide area of applicability and is probably the most widely used model. The second model is more quantum in nature and closely related to the Copenhagen interpretation of quantum theory.

The third model is the one being promoted in this work and is the one with the smallest amount of assumptions that cannot be justified by experiments. It may be useful to consider this model when other models may break down for example when trying to explain quantum weirdness.

REFERENCES

1. The Quantum World/New Scientist: The Collection (pages include 27, 28, 11, 14, 15)

2. P.C.W. DAVIES: The Forces of Nature: Cambridge University Press: ISBN 0 521 22523 X (pages 23-26 114-130)

3. Nelkon and Parker: Advanced Level Physics: Fourth Edition: ISBN 0 435 68610 0 (Chapter 27)

4. J.S. BELL "On the Einstein-Podolsky-Rosen Paradox, Physics, 1: 195-200

5. Quantum Physics says goodbye to reality, physics world. com April 2007