Re: Physical interpretation in physics.

Martin Hogbin wrote:

"John Kennaugh" <JKNG@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx> wrote in message
news:KGawZwBr4RVHFwf7@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx

Quite late on Einstein wrote:

" Most [theories] are constructive. They attempt to build up a picture
of the more complex phenomena out of the materials of a relatively
simple formal scheme from which they start out. Thus the kinetic theory
of gases seeks to reduce mechanical, thermal, and diffusional processes
to movements of molecules i.e., to build them up out of the hypothesis
of molecular motion. When we say that we have succeeded in understanding
a group of natural processes we invariably mean that a constructive
theory has been found which covers the processes in question.... The
advantages of the constructive theory are completeness, adaptability,
and clearness."

I would take issue with Einstein about completeness.

By all means but I think you are too late.

He wrote the above as a preface to the declaration that relativity is a
principle theory - he defined what he meant and his definition is
indistinguishable from a mathematical model based upon empirical
starting points. He had tried to make relativity into a constructive
theory, a theory where physical interpretation is an essential part but
had given up. He was now forced to described relativity as 'putting
forward no specific hypothesis'.

Lorenz had come up with a constructive theory - a theory having a
physical interpretation complimenting the maths.


You have changed your wording here. You describe LET as
having a 'physical' interpretation without saying what you mean.

This whole thread is explaining what I mean. Do you have difficulty with the English language?

If you mean a constuctive interpretation, as defined by Einstein,
then you should say so.

Same thing.

Einstein objected to
the physical interpretation of Lorentz's theory (what he referred to as
the theoretical structure). While his theory shares the same maths as
that of Lorentz's he had failed to come up with an alternative physical
interpretation without the asymmetry he objected to in Lorentz's theory.

Again, you have used the word physical without defining what you mean.

OK if you are determined to be silly. The following is not necessarily comprehensive but off the top of my head:

Physical things - Those things which you can touch feel smell or hear with your senses. Those things which you can detect with scientific instruments (effectively extensions of your senses), those things whose existence you can deduce to exist from the effect they have on other physical things (to explain experiment).

Physical effect - a measurable change to a physical thing.

Physical process - the interaction between physical things resulting in a physical effect.

Physical properties - properties of physical things - things you can measure relating to physical things.

Physical interpretation - the constructional explanation of a theory in terms of physical things, physical properties, physical effects and physical processes.

Metaphysical - things like uncertainty, probability, prediction, knowledge, an equation (although the ink and paper may be physical), mathematics, wishful thinking, a field of influence, hope. None of which can have a measurable effect on physical things in the natural world.




Physicists up until, and including Einstein would not have had to ask
the question "What is meant by physical interpretation?"

How do you know that?

At that time all physical theory included a physical interpretation. If it was a mathematical relationship without any physical interpretation it was called a 'law'. e.g. Charle's law.

It was
considered as an essential part of science and had played a vital role
in physics. Students today are taught that we cannot hope to understand
nature. All we can do is construct models of it. Physical interpretation
is considered as a poor alternative to a mathematical model rather than
what had been the case in the past that both together constituted a
theory.

You mind is stuck in a one-track definition of 'understand'. When you
say 'understand' you mean describe in terms that are familiar to us.

I was expressing the modern viewpoint as stated by Tom Roberts. He uses the word 'know' rather than 'understand' but it means the same in this context.

"In the abstract, it should be QUITE CLEAR that the most that human
beings can aspire to is to make models of the world -- we can never
actually "know" what Nature herself is really doing. We can only make models and test them, which is known as science." Tom Roberts

Sometimes someone started with an idea, an alternative physical
interpretation, does the maths and find it fits - an example might be
Galilao. Idea! 'suppose the planets go around the sun?' - do the maths
and it checks out. Now one could say that Galilao's maths would work
just as well without assuming that physical interpretation. It could be
argued that if someone had stumbled upon them without an assumption of
the sun centred solar system then that would be just as satisfactory. In
modern physics 'maths' is described as 'physics theory' and all that is
expected of it is accurate prediction not physical explanation. However
having a 'physical interpretation' gives the maths authority.

If only you could tell us what you mean by 'physical interpretation'

Have done. Try learning English.


The maths
of Galilao can be believed in as they are not merely an ad hoc
expression which gives empirical accuracy. One could use the same
physical model to construct maths which would predict what a man on Mars
would see in the night sky and fully expect that when we get there that
it will be as predicted. Physical interpretation drives the maths.

Sometimes a physical law - the mathematical relationship - has been
known for a long time like Boyles law and eventually a physical
explanation is found involving moving molecules. Moving molecules is a
physical model. It does not mean we 'understand nature' but it does mean
we have a better understanding of nature than we had previously when we
thought of gas as homogeneous.

A classic example of the importance of physical interpretation occurred
in the case of the black body radiation curve. Wien produced an
expression which fitted very well but it was purely empirical. Lord
Rayleigh produced a law which was based upon accepted theory, accepted
physical interpretation, waves bouncing backwards and forwards in the
box, but was not a good fit at short wavelengths. Rayleigh's law had to
be taken seriously because it was based upon a physical interpretation
i.e. on an understanding of what was happening - the physical processes
involved. It was based upon accepted theory. The fact that it gave the
wrong answer was described as the 'ultraviolet catastrophe'. It meant
the physical interpretation, the understanding of the physical processes
involved was wrong. Planck took up the challenge. Although Wein's law
was empirical, it was some help to Planck in coming up with what we now
believe is the correct physical interpretation that light is quantized.
Deriving the maths from that physical interpretation gave the right
answer. The reason we have confidence in the maths is because it is
derived from a physical understanding of what is going on which gives it
authority. Wein's law, although a good mathematical model lacked that
authority. Even if Wein's mathematical expression had been identical to
Planck's it would have lacked any authority because the physics - the
physical process was not explained.

Your so-called 'physical processes' are simply mental models.

Mental models are metaphysical.

Light is physical it causes measurable effects.
Black body radiation (light) is physical it can be detected, it can be measured.

The physical nature of light as waves had been deduced from the numerous physical wavelike properties it exhibits. It appeared from this experiment that the physical nature of light deduced from previous experiments is inconsistent with this experiment. Planck explained the black body curve by deducing from it that light has a different physical nature to what was previously thought. While it is a model in the sense that it has had to be deduced rather than directly observed (which is impossible), a better physical model is progress in our understanding.


Maxwell's electrodynamics was based upon an understanding of what was
going on in the physical sense. The idea of aethers had been an
essential part of physics for a couple of hundred years first introduced
to explain magnetic and electrostatic action at a distance forces. The
aether is sneered at these days but it was argued that a magnet could
not pick up a pin if there was genuinely nothing in the space between
them. Think about it and you can see where they were coming from.

Yes, a religious belief that everything must be just like we find things in
everyday life.

A rather short sighted comment. Maybe you can explain how a magnet picks up a pin.

Later
the luminiferous aether was hypothesised for light waves to propagate
in. Maxwell's theory was accepted not because of its accurate
predictions - they were not testable for some time - but on the elegance
of the physical interpretation. What Maxwell did (with help from
Faraday) was unify 3 branches of physics and show that only one aether
is required to explain action at a distance and light propagation while
at the same time showing a link between light and charge and putting it
on a sound mathematical footing. Charge causes a stress in the aether -
that stress pattern is what is described as a 'field' and that stress
can propagate through the aether at c, as derived from two properties of
the aether its permittivity and permeability. Again the authority of
Maxwell derives from the fact that he was able to describe in physical
terms what is going on and it fitted together so elegantly.

More so without the aether.

Without the physical interpretation all you have are equations which are metaphysical. You really need to understand the difference. The TV signal reaching my aerial is not carried there by Maxwell's equations neither does it propagate from the aerial because of Maxwell's equations. Energy (that is physical as it has measurable physical effects) leaves the transmitter aerial (also physical) and arrives at my aerial (also physical) the energy causes current to flow (also physical - it can cause physical change).....

You might like to ponder the fact while you look at you high definition, multi-channel, interactive colour TV with high quality sound that physics has no better idea now as to what it is which travels from the transmitter to the aerial on your roof than it did 100 years ago. You might wonder why technology has made such progress and physics hasn't.


So elegantly
that later Einstein continued to assume the absolute authority of
Maxwell when he produced SR and ignored the fact that it had been
compromised by his own work on photoelectric effect.

Planck had assumed that although the production of light was quantized
that somehow that was temporary and that it then 'turned into' Maxwell's
waves in aether. Einstein showed that light remained quantized by
producing a physical interpretation of the photo-electric effect which
works. Light arrives in discreet lumps of energy which depending on the
colour has, or hasn't enough energy to dislodge a photon. It is hard to
see how that bit of our understanding could have been achieved without a
physical interpretation on which to base the thinking.

We can only speculate on many of the thought processes that lead
physicists to their theories.

Don't be silly. You are simply in denial.


Lorentz started with a physical interpretation proposed by Fitzgerald
that if the arm of the MMX apparatus got shorter due to travelling
against the aether by just the right amount it explains the null result.


But what 'physically' causes this?

Premature interjection. The explanation followed.

Lorentz postulated that matter is made up of a matrix of positive and
negative charges held together by action at a distance forces
transferred via the aether. When the aether was moving he calculated
that the matter would get shortened in the direction of travel of the
aether by the required amount (note Bohr's model of the atom was much
later). Lorentz derived the Lorentz transforms based on an assumption of
the physical processes involved.


Which he simply made up to suit the observations.

And works mathematically. It is called 'deducing the physical processes involved from the physical effects produced' or simply coming up with a physical theory which fits the physical facts.

I have no objection to
that but I am surprised that you do not.

Why? I may believe he came up with the wrong answer but I have no objection whatever to his approach. You had this massive evidence in favour of light being waves. Maxwell had combined 3 branches of physics so now a single aether explained action at a distance and light propagation. He showed the electromagnetic nature of light. His impact was massive. Everything fitted except this one experiment - the MMX. It was perfectly logical to look for a fix.

Einstein is a different matter. By then the particulate nature of light was known. He himself had got a Nobel prize for explaining the photoelectric effect and he ignored it. He carried on as if Maxwell's wave in aether theory was in no way compromised by the fact that light isn't waves. He tried, and failed to come up with a better theory than Lorentz's. SR is simply Lorentz's aether theory without the theory and with the aether disguised.


Even today I understand that if you
replace Lorentz's matrix of charged particles with electrons in orbit
around nuclei then if you assume the action at a distance force is
transferred by the aether and the aether is in motion the orbits become
elliptical - causing length contraction.

Einstein's heroes were Maxwell and Lorentz - both of whom relied heavily
on physical interpretation. He described Lorentz as making the greatest
contribution to electrical theory since Maxwell. His objection to
Lorentz's theory was that in the physical interpretation - what Einstein
described as 'the theoretical structure' - was a unique FoR stationary
w.r.t the aether which is essential to the physical description but
which in practice is indistinguishable from an infinite number of other
FoR. Einstein could not believe that nature would be so perverse as to
hide something from us which was so essential to theory and assumed that
it must be possible to come to the same conclusion without an assumption
of this unique FoR.

And most physicists, including myself, agree with him.

I agree too - The problem is he didn't.

What should have happened is that Einstein should have come up with an
alternative physical explanation which did not require Lorentz's unique
FoR.

Hi did!

Not one which gained acceptance. His physical explanation was that the nature of the aether is such that every observer is naturally stationary w.r.t it - which is silly. It doesn't make it any less silly to rename the 'aether which every observer is stationary w.r.t' - 'the observers FoR' and treat that as if it were an aether stationary w.r.t the observer - having the same properties.

Of course by declaring SR to be a 'principle theory' a mathematical model which makes no attempt at physical interpretation it does not attempt to address questions related to what is physically responsible for what it is describing and therefore has nothing whatsoever to say on the subject of whether there is or there isn't an aether. The accepted 'no aether' doctrine which has been accepted in physics is totally separate from relativity but most relativists in this NG seem to be confused about that.


If one assumes the authority of Maxwell then the MMX showed that an
observers speed relative to the aether is zero. The question that first
Lorentz and then Einstein were trying to answer was therefore :

"Why does an observer always appear to be stationary w.r.t the aether?"

Discarding Lorentz's explanation the only explanation left to Einstein
was that the nature of the aether is such that this arises naturally
from it. If you study his 1920 lecture he is attempting to argue just
that. His 'aether without the immobility of Lorentz's'. He rejects
Lorentz's aether FoR but time and again returns to the need for some
sort of aether. As that idea was not accepted Einstein's alternative
theory was in effect rejected. He had failed to come up with an
alternative theoretical structure to that of Lorentz to give the maths
authority.

History does not show that Einstein's theory was rejected and that of
Lorentz retained.

What actually happened is bizarre. Einstein didn't consider his second
postulate as in any way controversial. It was his first which he thought
to be a radical departure which is why he justifies it at length. His
second needed no justification, it simply described how the MMX was
generally interpreted. SR in effect gives the observer's FoR the
properties of an aether stationary w.r.t the observer as per the MMX if
interpreted assuming the authority of Maxwell's theory. Somehow
Einstein's followers got it into their heads that Einstein had come up
with a theory which didn't need the aether.

Which it does not.

The second postulate simply describes what an observer stationary w.r.t the aether would observe. From the PoV of physical interpretation he has incorporated those properties of the aether he needed to do the maths into the second postulate. If you say otherwise then you have to produce an alternative physical interpretation leading to the second postulate.


The aether concept was
ridiculed despite the fact that it had not been replaced. Remember it
was required to justify the assumption of source independence, to
explain action at a distance, to explain the physical nature of fields
and for light waves to be physical waves in.

No it is not.

Explain. I'm not playing the yes it is, no it isn't, yes it is....., game. I explain all my statements. Please do the same.


Alternatives were not put
forward instead the rule book was re-written such that the emphasis was
placed on the maths and eventually the notion of physical interpretation
as an essential part of physics was consigned to history. I do not
believe that that was in the best interests of physics. It has resulted
in intellectual anarchy.

At any particular time a physical interpretation may be wrong and at
some stage have to be replaced with something better. A physical
interpretation is a model of nature and has its limitations. A physical
model based upon the planets going around the sun is a better reflection
of nature than one which has the earth at the centre - it does nothing
to explain what gravity is. The particulate model of light gives better
overall understanding of the nature of light but we don't know the
structure of a photon nor how on-mass they can so convincingly act like
waves. Limited understanding is better than none and better
understanding of physical processes is progress.

Are you ever going to tell us what you mean by a 'physical explanation'?

Have done but it should have been obvious.

Physical interpretation should go along with maths as they mutually
discipline each other. Its no use having a physical understanding if the
maths derived from it give the wrong answer (ref Rayleigh) and it is no
use having the right maths on their own (Ref Wein) as a physical
understanding which allows those maths to be derived from it gives an
insight into nature which the equation itself lacks.

Basically physics abandoned physical interpretation as an essential aim
in physical theory because it wanted to accept a mathematics model which
had no conceivable physical interpretation other than the one they
rejected vehemently. They changed the rules as to what a theory is, as
to what physics is, so that maths could be accepted as a theory. Today
Wein's law could be classed as a theory in that it provides accurate
predictions - all that is required of a modern theory as a modern theory
is not required to have an explanation of the physical processes
involved. At the time it was not considered to have any weight as it did
not explain the physical processes. At the time it prompted Planck to
investigate alternative physical interpretations. To me Planck made one
of the momentous discoveries in physics.

--
John Kennaugh
The problem with maths is that an awesomely impressive equation may be
describing an incredibly silly idea.
.

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