Re: Photons

On Aug 10, 3:37 pm, John Kennaugh
<J...@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx> wrote:
PD wrote:
On Aug 10, 6:50 am, John Kennaugh
<J...@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx> wrote:
PD wrote:
On Aug 9, 3:52 am, John Kennaugh
<J...@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx> wrote:

That is sloppy thinking. In classical electrodynamics circa Maxwell a
'field' was a physical stress in the aether. Action-at-a-distance force
between charges was transferred via this stress and the stress could
propagate through the aether at c in the form of light. Despite the fact
that relativity owes its existence to Einstein's belief in some sort of
aether, the concept of the aether has become highly unfashionable
resulting in the almost universal acceptance of the 'no aether
doctrine'. The fallout of this is that while physicists still talk in
terms of 'fields' the word no longer has a meaning.

It is true that the term "field" means something different than it
originally did. That does not mean that it is now without meaning.

I would be obliged if you would explain what meaning it now has.

To explore that deeply would mean opening a book. But I'll give you a
head start -- a pointer, if you will.

The modern definition of a field means that every point in space (and
time) is associated with a *value*, such that the value obeys certain
constraints and has some physical relevance.
If it is a vector field, then there are three values
associated with each point in spacetime.

You are describing mathematically what a field is not its physical
nature. For example each point in an electrostatic field is defined by
an amplitude (or intensity) and a direction, and is governed by the
inverse square law. If a charge were placed at a specific point in that
field our knowledge of the field will allow us to predict the force
acting on that charge and the direction.

That is perfectly consistent with both of my physical descriptions of
what a field might be which the maths is describing. One is that it is a
physical stress in a physical aether as per Maxwell.

The other I suggested , a field consistent with there being no aether is
that we simply accept that all force ultimately acts at-a-distance. Our
problem is that our world appears to be solid and if something moves it
is because some 'connecting rod' has made it move. We therefore look for
the 'connecting rod' which makes one charge move another and we invented
the aether to make the physical link we envisaged as being necessary.

What physics now teaches us is that even things we consider as solid are
mainly empty space and it is a misconception to believe that a 'solid'
hammer hits a 'solid' nail and drives it into the wood. Physics tells us
that when the atoms of the hammer come close to the atoms of the nail
(what we see as hitting it) the action at a distance force of repulsion
between the two sets of atoms drives the nail in. i.e. all force acts
'at a distance' not merely the forces which early physics were aware
did.

My second suggestion therefore was that a 'field' simply maps the field
of influence of the action at a distance force.

The difference is important in that while a physical stress in the
aether is real and physical, a field which is simply mapping the action
at a distance force which WOULD occur IF a unit charge were placed at a
point is a metaphysical field. Where as a physical stress can propagate
and carry energy with it a metaphysical field is solely dependent upon
the existence of whatever it is, the potential influence of which is
being mapped. You may be able to suggest a 3rd alternative but I have
not come across one.

This is where Tom's description of a photon falls down. My non aether
field mapping action at a distance force isn't physical so cannot store
physical energy and cannot exist in the absence of something (in this
case moving charge) to provide the action at a distance force the field
is mapping. Put simply, unless you or Tom can come up with a third
physical description (not a mathematical description) of what a field is
my two options are that either a photon contains massless charge which
is responsible for the action at a distance field or there is an aether
and a photon is a dynamic stress pattern in that aether.

The sort of answer I expect is 'who cares? Physics is about predictions
and mathematics. Physical description is no longer an essential part of
physics". I don't agree with that view point. Even if it were valid
physics is inconsistent in that it says "there is no aether". i.e. It
makes pronouncements of a physical nature and therefore makes itself
answerable at the physical level. If physics says "there is no aether"
then it has to be prepared to say what physically a field is if it is
not a stress in the aether. If physics decides that it is simply a
branch of mathematics where having a mathematical model which gives
accurate predictions is all that counts it has no business saying there
is no aether as it has put such matters beyond its remit.





If it is a 4-vector field,
there are four values associated with each point in spacetime. More
than one field can apply at each point in spacetime. Laws of physics
tell you how something about how the values of a particular field can
vary from point to point. For example, the mathematical divergence
(which tells you something about how the values of the field can
change from point to point) of the vector magnetic field must always
be zero, even though there are many configurations of the magnetic
field that will satisfy this rule. The divergence of the electric
field, on the other hand, does not have to obey this rule, and it
obeys a different rule instead. It is also true that if a particle
with certain properties inhabits a point where there is a field, then
the behavior of that particle will depend on the value(s) of the field
at that point.

That's what a field is, for starters. At least that what it's
understood to be today, as opposed to 150 years ago.

Anything further read into it -- for example, that the value of the
field tells you something about a stress or distortion in some "stuff"
at that location -- is usually unwarranted.

It depends whether you consider physics to be simply a branch of
mathematics or whether it should try to understand physical processes.
--
John Kennaugh
"The nature of the physicists' default was their failure to insist sufficiently
strongly on the physical reality of the physical world." Dr Scott Murray- Hide quoted text -

- Show quoted text -- Hide quoted text -

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It is actually more than a mathematical prescription. However, I say
this with a caution. What you propose are two of the likely physical
descriptions that correspond to something familiar from macroscopic
experience. That is, you either allow that a number (the value of a
field at a location) must be a property of some material "stuff", or
that it is an artifact of one material body reaching out across a void
to influence another material body (the force-at-a-distance model). It
is apparently not permissible in your mind that *spacetime itself*
might have a field value without there being some "stuff" occupying
that space. It is also apparently not permissible in your mind that a
property of empty *spacetime* could directly influence a material
body. In your mind, apparently, only material bodies can influence
material bodies, and physical descriptions that adhere to these
constraints are the only ones to be entertained.

As it turns out, the field can be quantized, and so the field at a
particular location can be made logically and functionally equivalent
to the emission and absorption of things that behave in every way like
particles -- carrying definite energy, momentum, and other properties.
However -- and this is a crucial caveat -- it would be a mistake to
think of these quanta as behaving the same way as little billiard
balls or bullets or other macroscopic objects. They are *unlike*
anything we know at the macroscopic level. No amount of forcing will
make them appear to be like something familiar.

PD

.

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