Bits and bobs from the world of physics

This is a simple work which goes back to basics to examine a few different areas of physics, it leans towards the experimental side of the subject and maths is kept to a minimum. Some parts of the work may be of interest to physicists, amateur as well professional, who like to think about, question and discuss some of the foundations upon which physics is based.

Some topics are developed as the work progresses and certain questions are built up to. These include the following:

Is the evidence strong enough to show that all electrons are identical?
How meaningful is it to assume that light has properties?
Are fields really more fundamental than particles?

PART 1. SIMPLIFYING ASSUMPTIONS

When analysing events and developing theories it’s impossible to take everything into account and so it’s necessary to make simplifying assumptions. Events are often analysed as thought experiments by imagining them as taking place in isolated systems which are defined here as self contained systems within which any influences from the surroundings can be ignored.

Knowing what the influences are and what ones to ignore can be a problem.

PART 2 a. A VERY FAMOUS THOUGHT EXPERIMENT

Arguably, thought experiments are useful if they can be adapted and investigated in terms of real world experiments where it would be possible to make the relevant observations. A very famous thought experiment which doesn’t meet these criteria is the over hyped Schrodinger’s cat experiment:

Schrodinger imagined an isolated system containing a cat and a radioactive atom which is linked to a killing device in such a way that if the atom decays the killing device gets switched on and kills the cat. That’s a nasty situation.
But there’s a fairly common belief that the atom can reach a quantum superposition state which has been described as it being decayed and not decayed at the same time. It has been suggested that the result of this would be that the killing device would be triggered into a superposition state of being switched on and off at the same time and the cat would be triggered into a superposition state of being dead and alive at the same time. That’s a weird situation.
There’s also a common belief that quantum superposition states can happen and be maintained but only if there are negligible interactions with the surroundings. Because of this the supposed superposition states cannot be adequately observed because any attempts to make the observations will break the isolation of the system and knock the states out of superposition before the observations can be made. That’s a catch twenty two situation.

Of course the weirdness can’t happen and common sense alone should be enough to tell us that. In fact Schrodinger knew it and was trying to prove it with his thought experiment. But what exactly are superposition states? And have there been any real experiments that have provided observational evidence that shows unambiguously and conclusively that there can be real world weird superposition states? Despite any claims that have been made it may be best to keep an open mind and give the question some consideration. We will come back to it.

Carrying out some thought experiments can be described as the act of applying the laws of physics to imaginary systems that don’t obey the laws of physics.

PART 3. PARTICLE TRAJECTORIES

A recurring theme in this work will relate to the concept of moving objects and the paths they follow. Although it’s widely accepted that objects, including particles, can move in classically defined paths it’s widely accepted that quantum mechanics does not incorporate the concept of particles moving in classical paths, or any types of path. This is illustrated by the following often quoted comment made by Landau and Lifschitz in a 1977 publication:

In quantum mechanics there is no such concept as the path of a particle.

The comment, on its own, does not deny the existence of paths but it does indicate a limitation of quantum mechanics. In some respects the limitation is fairly well expressed by the correspondence principle and can be revealed by carrying out some simple thought experiments and real experiments informed by readily available observations.

Before that we need to look at some introductory stuff.

PART 4. CLASSICAL AND QUANTUM OBJECTS

Atoms, atomic nuclei, and many other very smallish things are often described as being quantum objects one reason being that it’s assumed they have properties which are best described by using quantum physics. An electron is an example of a quantum object.

Bigger things and that includes most of the things that can be seen without magnifying instruments, are often described as being classical objects because they have properties that can be described with classical physics. A largish lump of metal is an example of a classical object.

The terms quantum objects and classical objects are widely used but it should be realised that every object has properties that are best described with quantum physics as well as properties that can be successfully described with classical physics. A couple of examples are given below.

There are situations where electrons move in paths that can be described by classical physics, for example in cathode ray tubes, but quantum physics does not incorporate the concept of classical paths.
Many thermal properties of classical objects are well described with classical physics but quantum physics is needed to best describe how radiated energy is distributed amongst the frequencies emitted.

Despite their shortcomings the terms quantum objects and classical objects will sometimes be used in this work where a start can be made in examining some of the links between the quantum and classical realms.

Quantum objects are often described as being microscopic and classical objects described as being macroscopic. Often these are good descriptions but when we want to be fussy how, if at all, can they be quantified?

PART 5. CLASSICAL AND QUANTUM PATHS

Physics studies events, events happen within systems and systems within which events occur have more than one part. Here we carry out some simple thought experiments by considering events in simple isolated bound systems of two charged objects only, one being positive and the other one negative.

Let the events start at an instant when the objects are widely separated with negligible kinetic energies. Because of the attraction between the objects we might expect the events to continue with the objects approaching and then colliding. By using knowledge gained from observations of real systems we can attempt to describe how the event proceeds in different types of isolated system. We can define three systems of relevance:

a. Pure Classical Systems

These can be defined as imaginary systems where both objects are classical. We shall consider a system where both objects are lumps of metal.

By carrying out a thought experiment informed by observations from electrostatics and other areas of physics we may conclude that if the pure classical system could exist as a real system the metals would approach each other in classical paths, they would move directly towards each other with increasing accelerations. Some effects of the collision for example the emission of infra red photons may best be described with quantum physics.

Mixed Systems

These can be defined as imaginary systems for which one object is classical and the other one is quantum. We shall consider a system containing a lump of metal and an electron.

Observations of events in certain real systems for example X-ray tubes, mass spectrometers cathode ray tubes and particle accelerators, show that quantum objects as well as classical objects can move in classical paths. Bearing that in mind we may conclude that if the mixed system could exist as a real system the electron would approach in a classical path. And so would the metal if its motion was considered and not ignored as being negligible. Any effects caused by the collision, for example the emission of a photon characteristic of the metal atoms or Bremmstrahlung photons may best be explained by quantum physics.

c. Pure Quantum Systems

These can be defined as systems where both objects are quantum objects. We shall consider a system of an electron and a proton in other words the basic hydrogen atom. This is a simple real system and one which can be fairly well isolated.

Atomic events are usually best described with quantum physics and this does not seem to recognise the concept of classical paths. However, we can describe a sort of approach event by referring to concepts such as de excitation transitions, expectation values and most probable radii.

Imagine an excited hydrogen atom which returns to the ground state via one or more de excitation transitions. For each transition a photon is emitted and the most probable separation between the proton and electron gets smaller. This is a probabilistic reduction of separation and can be defined here as a quantum approach event.

The term most possible separation is used because the concept of reduced mass will not be used in this work.

PART 6. COMMON FEATURES OF APPROACH EVENTS

A common feature in the classical and mixed systems is that there can be classical approaches with properties deviating from classical behaviour as separations enter the miniscule values within which quantum behaviour seems to occur. This begs the following question:

Can the proton and electron of the hydrogen atom also approach classically?

The answer is yes and this can be predicted from the correspondence principle which in turn can be predicted from observations. Observations show that classical paths in real systems are big enough to be described as being macroscopic in size and this provides evidence to suggest that the proton and electron of the hydrogen atom might start approaching classically if the initial separation between them is big enough. For this to happen the atom in its initial state must be very highly excited in other words have a very high principle quantum number. It could, for example, be a Rydberg hydrogen atom of the type found in the very low pressure environments of interstellar space.

On the other hand it might be argued that there is no known separation dependent limitation of the quantum theoretical analysis of the hydrogen atom, for example there is no known upper limit to the value of n, the principle quantum number. If this is so it can be argued that regardless of the initial excited state of the atom the whole approach can be described as a probabilistic quantum approach. However, since the average separation between the proton and electron is directly proportional n squared and the energy of each excited state is inversely proportional to n squared we can say that quantum effects become less apparent for increasing separations. One way to quantify this, which is compatible with the correspondence principle, is to refer to certain numbers such as the value of n. We can write, for example, that as n approaches infinity events become more smoothly continuous and classical in nature and that as n approaches one events become more probabilistic and quantum in nature. In summary we can say that, depending on the initial separation, approach events can morph from classical like behaviour to quantum like behaviour as the separation reduces.

There is some evidence to show that classical to quantum changes start to become observable for separations of the order of 0.1 mm.

PART 7. ELECTROMAGNETIC INDUCTION

To generate electricity by induction we need three main things:

A source of magnetism, for example a bar magnet.
A suitable conductor, for example a closed loop of wire.
An energy input.

We need to put energy into the system so that the electrons in the loop experience a changing magnetic field. This can be done by moving the magnet only or moving the coil only or moving both, but in such a way that the separation between them changes.

There is an assumption that if the loop and magnet formed an isolated system the induced electricity would depend, amongst other things, on the relative motion, for example the changing currents induced when the magnet moves towards the stationary loop would be the same as when the loop moves towards the stationary magnet in a symmetrical way.

A problem is that the assumption can be difficult to prove experimentally because the motional symmetry that can exist in an imaginary isolated system does not exist in real systems where there are other interacting parts such as connecting wires, measuring instruments, and metals within which eddy currents can be induced.

It may be possible to design experiments where the effects of the surroundings are reduced to an extent that they become immeasurable using current technology but if theory suggests that there are effects it can, in some circumstances, be counterproductive to ignore them.

Certain observations on electromagnetic induction are well known but some consequences of these seem to have been overlooked despite the fact that they give extra clues about the nature of the propagation of electromagnetic waves.

PART 8. EHRENFEST THEOREM

In part six it was suggested that there is no separation dependant limitation of quantum theory albeit that classical behaviour become more appreciable for increasing separations. But can we turn that idea round and claim that there is no separation dependant limitation of classical theory albeit that quantum behaviour becomes more appreciable for reducing separations? In other words can it be claimed that classical theory still works within the very small separations within which quantum effects seem to dominate? The answer is yes, but possibly only in some limited ways. One of the ways is that quantities such as momentum and energy are conserved in quantum theory as well as in classical theory. Another possible way can be expressed by the Ehrenfest theorem which is that in certain circumstances the relevant expectation values for events within very small separations approximate to values that would be obtained from classical theory.

But does the Ehrenfest theorem apply to any parts of the approach events described in this work?

PART 9. BASIC CONCEPTS

Mass length and time are just three of the basic concepts used in physics and it seems to be fairly widely accepted that these concepts are well understood and clearly defined. But are they? What, for example, is the definition of mass?

At one level we might define mass in terms of amount of matter. Or perhaps we could define it in terms of inertia. Such definitions can seem to be rather vague despite the fact that by accepting them it might seem easy to get an intuitive feeling of what mass is.

In order to be more rigorous we might try to define mass in terms of other concepts such as force and acceleration. Perhaps we should try to define it in terms of the energy something has when it has zero momentum, or refer to it in terms of quantum mechanical operators. Doing any of these may usually require definitions of other concepts and it can become a chicken and egg situation with definitions going round in circles.

To add to the difficulties there are different labels attached to the concept of mass, such as bare mass, Komar mass, inertial mass, gravitational mass and invariant mass. Plus there is relativistic mass, a concept which is taken to be obsolete by what seems to be a majority of the physics theorist community.

One thing we can do with a high degree of clarity is to define a unit of mass. The Kilogramme is a widely used unit and for many years had been defined with reference to a certain lump of metal which is stored in Paris. Nowadays it’s defined with reference to Planck’s constant.

It seems that we have the expertise to very accurately measure some masses. For example the electron mass can currently be measured to nine decimal places. But the question remains:

Is there a really good definition of mass, not a definition related to any units of mass or how mass is measured but a definition of what mass actually is?

Perhaps some ideas and a good working definition can be found in philosophy. Without a good definition things can get a little bit tricky. An example of this is related to the debates about the pros and cons of relativistic mass. Not everyone rejects the concept of relativistic mass and there are some people still in favour of it. But how can there be a constructive and meaningful debate about something without an agreed definition of what that something actually is?

Come to think of it might be a good idea to keep re visiting definitions of other concepts we use.

10. QUANTUM SPIN PART AND THE LANGUAGE OF PHYSICS

Arguably, spin is very high on the list of counter intuitive concepts in quantum physics. Atomic particles have the property of spin, a property which is quantised and assumed to be a sort of intrinsic angular momentum which is coupled with an intrinsic magnetic moment. Because of the angular momentum we might expect that objects that have spin have some sort of rotational motion. But they don’t seem to have some sort of rotational motion, or any type of motion related to the classical concept of spin. Yikes!

Detailed accounts of the theory of spin can be found in the works of certain physicists such as Paul Dirac. It’s all very clever stuff which describes the nature of spin with relatively few words but with a bunch of heavy duty maths. Ask an expert what the maths really means and you might be told that maths is the language of physics and that the maths of spin and certain other tricky topics is difficult to explain in everyday language. Some might walk away scratching their heads trying to get a better understanding of what spin is all about whilst advising you to read a book. That’s fair enough, there’s nothing wrong in thinking about spin and other difficult stuff and trying to suss it out.

Goodness gracious it’s enough to make your head spin

PART 11. SHOULD THE BOHR SOMMERFIELD MODEL OF THE HYDROGEN ATOM BE DEMOTED TO THE DUSTBIN OF SCIENTIFIC CURIOSITIES?

Some theorists may think that the Bohr Sommerfield model is obsolete and is of historical interest only however, there are some good reasons why we shouldn’t ignore the model and a few are given below.

The model can be used. There are situations where the approximate answers obtained are good enough for the task in hand and where the use of modern theories may require a level of mathematics that can be overly demanding.
Arguably, the model is interesting and not too difficult to understand. As such it can be considered as a good topic to include in introductory courses on quantum physics.
The model predicts the existence of classical orbits and some evidence of these has recently been gained from the study of highly excited Rydberg hydrogen atoms.
The model can be described as being semi quantum due to its high classical physics content. It’s a model that is quite successful and because of its classical and quantum mix it’s a model that may be worth studying in more detail.
A big advantage of the model is its relative simplicity. It has its limitations but using it to analyse certain events can reveal details which can otherwise be hidden behind the mathematics of more up to date models.

You can’t see the wood for the trees. Or should it be you can’t see the events for the maths?

PART 12. ENERGY TRANSITIONS

Earlier in this work we considered approach events of two oppositely charged objects in different system structures. We now look at the events in a bit more detail to see how the events may proceed a bit further and become separation events

The Pure Classical Systems of Two Lumps of Metal

We can describe that the classical objects will collide and although it may be possible to describe major aspects of the collision part of the event in terms of quantum mechanics there are certain aspects of the event that can be described successfully with classical mechanics. One example is related to the deformation that results from the collision.

Plastic deformation results in energy loss due to the objects getting permanently distorted but there can be some recovery with more elastic type deformation this resulting in a partial reversal of the event, with the objects bouncing and separating a bit. Both quantum and classical physics predict that the smaller the distortion the greater the bounce and this is very easy to demonstrate for example by testing different types of ball in Newton’s Cradle type arrangements.

A relevant point is that the heat generated as a result of the collision will affect the radiant energy exchanges between the metals and the surroundings and this can contribute to the nature of the collision.

Collision type interactions in all types of systems will result in some energy being radiated to the surroundings.

The Mixed System of a Lump of Metal and an Electron

When the electron and metal smash into each other there are energy changes some of which can result result in photons being radiated to the surrounding, for example there may be a photon which is characteristic of the metal atoms or there may be Bremmstrahlung photons.

If now a photon of sufficient energy is incident on the metal a separation event can be triggered for example a photoelectron may be emitted.

The Pure Quantum System of the Proton and Electron

For pure quantum systems an energy transition, to the ground state is analogous to the collisions as described for the other two system types. These systems seem to be unique in different ways one being that for certain systems it can be relatively common place for them to participate in events which alternate between being fairly symmetrical approaches and separations. For example a ground state atom can transition to an excited state as a result of absorbing a photon from the surroundings and then make a single transition back to the ground state by emitting a photon back to the surroundings.

It’s interesting to note that photon triggered separation events, which can happen in mixed and pure quantum systems, require the presence of external energy sources for example photon emitters. Does that mean that approach events, which transition to lower energy states by emitting photons require the presence of external energy absorbers for example photon absorbers? It’s a question worth thinking about and we will come back to it. To clarify the question, photon absorbers are defined here as things where specific photon interactions occur.

Atoms are good examples of being both emitters and absorbers, emitters when they transition to lower energy states and absorbers when they absorb photons and transition to higher energy states.

PART 13. WHAT IS A HYDROGEN ATOM?

Can a system of a very widely separated electron and proton, both of which can be considered as having a negligible kinetic energy, be described as being a hydrogen atom?

It may be assumed that one way by which a system such as that described above can be approached is when the hydrogen atom in its ground state receives an input of energy equal to the ionisation energy. All or parts of the event that follows may best be described by modern quantum physics but for now we shall forget the relevant quantum mechanical concepts and present a simple mainly classical description of the event. The description may not seem to be too plausible but it will be looked at again in certain sections of the work that follows.

THE EVENT

It may be assumed that the ionisation energy input results in an initial increase of the kinetic energy of the electron and the proton and as a result they start to move further apart. Due to momentum conservation the bulk of the kinetic energy is gained by the electron.

As the separation proceeds kinetic energy is converted to potential energy and so the particles slow down and approach states of rest. In very low pressure environments, for example in interstellar space, some final separations reached can be large enough to be described as being macroscopic in size, as is the case with some very high n value Rydberg atoms.

A tendency of the more widely separated particles is to return to the ground state via one or more energy level transitions. At each transition energy is radiated back to the surroundings and ignoring other energy losses, the total energy radiated is equal to the original input of ionisation energy. The tendency to return to the ground state reduces if the particles become unbound and free of each other. The unbound system is not really an atom.

Probably, one major objection to the description as it stands above is that it implies that quantum objects can be considered as particles that can move in classical paths and this concept is often considered as being meaningless in the realm of quantum mechanics.

But it’s still worth investigating further so that’s a good reason to keep coming back to it.

PART 14. THE MUCH DISCUSSED CONCEPT OF WAVE- PARTICLE DUALITY

Many physicists, particularly some theorists, consider wave particle duality to be an outmoded concept and don’t bother with it. But there are other physicists, particularly some experimentalists and physicists who participate in physics popularisations, who seem to pursue the subject. It seems that the concept of duality as understood by some theorists is different to that as understood by some experimentalists and popularisers.

Duality is regularly mentioned in reports of quantum interference experiments, those involving De Broglie matter waves as well as those involving photons. And many of the experiments have gained a bit of a reputation for being weird when compared to classical interference experiments. But should quantum interference experiments be considered as being less weird if the observations made can be predicted by using the knowledge gained from classical interference experiments?

What we know from classical interference.

Provided all the necessary conditions are met division of wave front type interference can be produced with any number of slits or sources. Diffraction, which can be described as an interference effect, is always evident for example as an intensity modulating envelope of the interference fringes observed in the double slit experiment.

Consider the classic double slit experiment being set up in a perfectly symmetrical way so that light has access to the image plane via both slits equally. By doing this we would observe a pattern of highly visible interference fringes. If now access to the detector via one of the slits is increasingly disturbed, for example by reducing the width of the slit to zero, the regions of constructive interference become less intense and the regions of destructive interference become more intense and the double slit pattern morphs into the single slit diffraction pattern of the undisturbed slit. In other words the visibility of the double slit pattern reduces as the visibility of the undisturbed single slit pattern increases.

It can be said that the classical two slit experiment has an inherent “which path marker” because the pattern produced gives some evidence about the path taken by the light. For example a high visibility of the pattern due to one of the slits gives an indication that light had greater undisturbed access to the detector via that slit.

Quantum Interference

Quantum double slit experiments use very low intensity sources, often one photon at a time, sources. As can be predicted from classical experiments, a pattern of interference fringes is detected but one which builds up relatively slowly and bit by bit across the image plane. As an explanation of these results it has been suggested that each photon interferes with itself.

It’s widely assumed that high visibility interference fringes cannot be observed if the apparatus has a certain type of “which path marker” which can determine with certainty the slit which each photon passes through. What is often promoted as being weird is that, depending on the experimental set up, the marker doesn’t need to be used and the fact that it may be part of the apparatus is enough to prevent the formation of fringes. One reads weird comments such as:

How does a photon know that we can know what slit it passes through?

It’s all a bit daft really because the results of which path marker experiments are predictable using classical physics. We shall look at two very well known experiments both of which use entangled photons with correlated orthogonal polarisations.

But that will be later on

PART 15. POTENTIAL ENERGY- A DIFFICULT CONCEPT?

Consider again a system containing two separated charged objects. The system has potential energy and as with all systems that have potential energy we cannot work out whether there is an absolute value of potential energy at any particular separation and if so what the magnitude of that potential energy might be. We can, however, calculate by how much the potential energy changes when the separation changes.

To help with calculations we often make two somewhat arbitrary choices, one regarding separation and the second regarding a value of the potential energy at the chosen separation. The most widely accepted and probably the most logical and useful choices are infinity for separation and zero for potential energy.

Using the above choices we would say that when oppositely charged objects are separated by infinity the potential energy of the system is zero and as the separation reduces the potential energy becomes more negative. That may sound strange to anybody coming across it for the first time particularly when it’s realised that for attracting objects the potential energy has a maximum value at an infinite separation. Dealing with differences in potential energy can take a bit of getting used to.

But could it be that potential energy actually does have absolute values and moreover can it be described as having locations? In any ensuing debate a good start could be made by referring to chemical energy sources such as a litre of petrol or a chocolate bar. We can describe, for example, that the energy of the chocolate bar is located within the chocolate itself. We can pin the energy down further by referring to the movement and kinetic energy of the particles in the chocolate and the potential energy due to the fields in the chocolate.

But can we pin it down further still and say, with some confidence, that whereas each particle may be described as having kinetic energy due to its motion it can also be described as having potential energy due to its location? In other words could it be that the potential energy in a system is somehow shared between the interacting parts? In a two part system one part might have some of the potential energy and the second part might have the rest of the potential energy. If this were so there is an implication that part of the field energy of a system of interacting particles is contained within the mass content of the particles. A broader implication is that all of the field energy is contained within the mass content of the particles and the fields do not extend into the surroundings. Suppose for a moment that this were the case. If so we might, cheekily perhaps, be able to summarise the situation by making the following claim:

THERE ARE NO FIELDS ONLY PARTICLES

It’s not a new idea and it’s more involved than it might seem to be at present. We shall return to it.

(Jumps on his space hopper and tries to escape from the pursuing quantum field theorists)

PART 16. THERE ARE NO PARTICLE ONLY FIELDS

Many physicists who have knowledge of quantum field theory will tell us that fields are the fundamental building blocks of everything and there are different fields associated with different particles and so there is an electron field, an up quark field a Higgs field and so on.

One hand wavy way to describe particles is to call them discrete excitations of their underlying fields, for example an electron may be described as a discrete excitation of the electron field.

If it seems a bit odd it might seem even odder when told that each field is assumed to exist throughout the whole of space.

This topic is hard so it’s time to take a little break from it and come back to basics. We will look at the first field that many people are introduced to. We will look at the magnetic field.

And it will be very interesting. But perhaps not.

PART 17. WHO SAID ALL ELECTRONS ARE IDENTICAL?

There are people who claim that all electrons are identical and they have what might seem to be some convincing evidence to back up that belief. And a lot of the evidence, such as the measured value of the electron mass, is freely available for everyone to see. Just search the IOP or NIST websites and look the data up. Doing so will reveal that the current uncertainties of the measurements are so extremely small that any variations in properties allowed by the uncertainties are also extremely small, negligibly small perhaps. However, it should be realised that the data is very limited and applies only to those environments within which the measurements are actually made, for example within Penning traps.

It could be that properties such as electron mass are environment dependant in that the mass of each electron depends on the structure of the environment and the instantaneous location of the electron within that environment. If there are any variations in electron properties they could start to become appreciable within extremely small particle separations or other regions of extremely high fields. In other words the measured properties can be different at places where there are very few reliable measurements available as of yet. So, all electrons may be identical but only when they are in identical places. It may be worthwhile thinking about this in more detail.

A little bird once told me that at any one time there are approximately 10⁸⁰ electrons in the universe. I wonder how many of them have been inside Penning traps.

PART 18. BUT WHAT IS AN ELECTRON?

Let’s move on.

And of course, we mustn’t forget the standard model along with its funny name combinations, like charmed tops and strange bottoms.

PART 19. ALL PHOTONS START FROM SOMEWHERE AND GO TO SOMEWHERE?

There are different models describing the nature of radiant energy and one feature they all seem to agree on is that every photon starts from a source where an energy transition results in its creation and emission. In other words it’s reasonable to say that all photons start from somewhere. But is it also reasonable to say all photons go to somewhere, for example does each one eventually reach an absorber where an energy transition results in its destruction?

Depending on the frequency of a photon there are various interactions it may participate in which can result in its destruction for example a high enough energy photon can disappear as a result of transferring some of its energy to an electron that it interacts with and the rest of its energy to a new photon of lower frequency.

Some people might argue that there are photons that don’t necessarily go to somewhere, for example the sun seems to radiate in all directions regardless of what surrounds it. And some of the radiated photons may continue moving for ever through empty space.

That might be described as the universe containing energy which can’t be detected.

PART 20. THE MAGNETIC FIELD

Many of us are introduced to the concept of fields at a very young age when we use detectors such as iron filings to plot magnetic field lines. The results of such experiments and more sophisticated experiments can lead to the assumption that the magnet sets up a field and the field exists everywhere in the surroundings. Extending this it may be assumed that all other fields exist everywhere. The assumptions need clarifying:

Consider a place in the surroundings of a magnet which is empty in that there is nothing at that place that interacts that with the magnet. Because there is no interaction at the empty place it might seem reasonable to assume that the magnetic field does not exist at that place and does not exist at all other places that are empty. But is the assumption a good one, is it true that magnetic fields and all other fields for that matter, do not exist at empty places?

Promoters of quantum field theory might claim that there are no empty places and that the whole of space is occupied by fields. There’s nothing deeply questionable about the claim if fields are mathematical constructs only, but some people might further claim that fields are real and have substance and there truly are no places that are empty, temporarily or otherwise. So where is the experimental proof to give credence to the claims? Or indeed to give credence to any counter claims. To kick off any debate that might ensue a few comments are given:

1. Fields have effects only at locations where there are interacting parts.

2. Any form of detector would be an interacting part.

3. In any system the resultant field is due to the presence of all interacting parts.

4. If an interacting part changes its location the field changes at all locations where there are interacting parts.

In summary the effects of fields are felt the interacting parts only whether these parts be microscopic, such as electrons or macroscopic such as lumps of metal. These parts of the fields are real and have substance.

All occupied locations are interacting parts of fields. True or false?

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