Post by Ed LakePost by Odd BodkinPost by Ed LakePost by Tom RobertsThere are DOZENS of different definitions [of the word "photon"]. Generally,
the BEST definitions are something like: "A photon is the smallest discrete
amount or quantum of electromagnetic radiation. It is the basic unit of all light."
You are confusing popularizations of physics with physics. In different
popularizations, different meanings of words are used. In physics, the
"an excitation of the quantum field of electromagnetism".
[This inherently includes the fact that photons do not
oscillate, and that individual photons do not "have"
a speed; but coherent beams of myriad photons do
oscillate (under the right conditions), and do have a
definite speed (which is c in vacuum, relative to any
locally inertial frame). I am speaking loosely here.]
Tom Roberts
I've found DOZENS of different versions of Einstein's Second Postulate
in college physics textbooks. I've never researched definitions of "photon."
I suspect there will be dozens of different definitions of that, too.
But, as I recall, it was difficult to find the word photon in some college
physics textbooks.
Well, that’s because freshmen physics textbooks don’t touch on that subject
much. What a photon is, exactly, is an subtle thing that cannot be defined
simply for laypeople, unless they read a lot of non-photon content FIRST.
You have to learn what “field” means. You have to learn what “particle”
means. You have to learn what “quantum” means. You have to learn what
“quantum spin” means. You can’t learn a topic in physics by looking up an
encyclopedia article or by searching for the word in a PDF file or a web
page.
But you can learn what different textbooks say about a subject. I just browsed
through five more textbooks (choosing the ones with the most editions), and
Oh good, yet’s look.
Post by Ed Lake----- start quotes --------
From “College Physics” 9th edition, by Hugh D. Young
Page 772
The picture
of light as an electromagnetic wave isn’t the whole story, however. Several
effects associated with the emission and absorption of light reveal that it also has
a particle aspect, in that the energy carried by light waves is packaged in discrete
bundles called photons or quanta. These apparently contradictory wave and particle
properties have been reconciled since 1930 with the development of quantum
electrodynamics, a comprehensive theory that includes both wave and particle
properties. The propagation of light is best described by a wave model, but
understanding emission and absorption by atoms and nuclei requires a particle
approach.
Yes, now notice several things. “Quanta” and “photons” are not defined or
described in any detail here other than “discrete bundles”, which tells you
nothing. Also notice that it says that “apparently contradictory…properties
have been RECONCILED since 1930.” It also does not say that the photons are
either particles or waves, but that the PROPAGATION of light is best
described by a wave model but that emission and absorption requires a
particle model. Not just one or the other.
This is repeated again on the later page….
Post by Ed LakePage 932
What is light? The work of Maxwell, Hertz, and others established
firmly that light is an electromagnetic wave. Interference, diffraction,
and polarization phenomena show convincingly the wave
nature of light and other electromagnetic radiation.
But there are also many phenomena, particularly those involving the emission
and absorption of electromagnetic radiation, that show a completely different
aspect of the nature of light, in which it seems to behave as a stream of particles. In
such phenomena, the energy of light is emitted and absorbed in packages with a
definite size, called photons or quanta. The energy of a single photon is proportional
to the frequency of the radiation, and we say that the energy is quantized.
From “College Physics” 9th Edition, by Raymond A. Serway & Chris Vuille
Page 762
In 1905, Einstein published a paper that formulated the theory of light quanta
(“particles”) and explained the photoelectric effect. He reached the conclusion
that light was composed of corpuscles, or discontinuous quanta of energy. These
corpuscles or quanta are now called photons to emphasize their particle-like nature.
According to Einstein’s theory, the energy of a photon is proportional to the frequency
of the electromagnetic wave associated with it,
So in the final analysis, is light a wave or a particle? The answer is neither and
both: light has a number of physical properties, some associated with waves and
others with particles.
Yes, notice “the answer is NEITHER and BOTH”. You on the other hand say
that you do not accept this answer, even though it is true. Just because
you do not understand how it is possible does not make it untrue or
inconceivable. It just means that this presentation doesn’t resolve it or
answer it for you.
Post by Ed LakePage 1154
In 1905, Einstein proposed that electromagnetic radiation (or simply light) is
quantized and exists in elementary amounts (quanta) that we now call photons.
This proposal should seem strange to you because we have just spent several
chapters discussing the classical idea that light is a sinusoidal wave, with a
wavelength x, a frequency f, and a speed c such that f=c/x.
Furthermore, in Chapter 33 we discussed the classical light wave as being an
interdependent combination of electric and magnetic fields, each oscillating at
frequency f. How can this wave of oscillating fields consist of an elementary
amount of something—the light quantum? What is a photon?
The concept of a light quantum, or a photon, turns out to be far more subtle
and mysterious than Einstein imagined.
Indeed, it is still very poorly understood.
In this book, we shall discuss only some of the basic aspects of the photon
concept, somewhat along the lines of Einstein’s proposal
So notice several things. It says that the photon is NOW KNOWN to be much
different than the particle that Einstein imagined in 1905. This is not a
surprise, as there’s been more than a century’s work on understanding
photons since then. There are also a few unanswered questions about
photons, but it is simply not true that they are veiled completely in
mystery. (Jearl’s comment that they are very poorly understood is actually
incorrect.) Also notice that Jearl says directly that he’s NOT going to
describe all the things that have been learned in the century since
Einstein and is only going to leave things IN THIS BOOK at the level that
was understood a century ago. For better and more modern descriptions,
you’d need a more advanced book than this one.
Post by Ed LakeFrom “Physics for Scientists and Engineers – With Modern Physics” - 6th
edition, by Paul M Fishbane; Stephen Gasiorowicz; Stephen T Thornton
Page 1079
The propagation of light is governed by its wave properties, whereas the exchange
of energy between light and matter is governed by its particle properties.
This wave–particle duality is a general property of nature. For example, the propagation
of electrons (and other so-called particles) is also governed by wave properties,
whereas the exchange of energy between the electrons and other particles is
governed by particle properties.
Yes, again, just like the others say, SOME properties of light are better
described by a wave model and SOME properties of light are better described
as a particle model. Not just one or the other. The fact that you insist
that it needs to be one or the other is irrelevant. I get that YOU
PERSONALLY are unhappy with there not being one, single, comprehensive
description of something, but that doesn’t mean that physicists should be.
As I’ve mentioned to you, basic physics courses teach freshmen that several
different models describe the same phenomenon, and that’s a GOOD thing.
Post by Ed LakeFrom “Physics for Scientists and Engineers – With Modern Physics” - 6th
edition, by Paul A. Tipler & Gene Mosca. (This textbook has a whole
section on “Wave-Particle duality.”)
We have seen that light, which we ordinarily think of as a wave, exhibits
particle properties when it interacts with matter, as in the
photoelectric effect or in Compton scattering. Electrons, which we
usually think of as particles, exhibit the wave properties of
interference and diffraction when they pass near the edges of obstacles.
All carriers of momentum and energy (for example, electrons, atoms, or
photons) exhibit both wave and particle characteristics. It might be
tempting to say that an electron, for example, is both a wave and a
particle, but what does this mean? In classical physics, the concepts of
waves and particles are mutually exclusive. A classical particle behaves
like a piece of shot; it can be localized and scattered, it exchanges
energy suddenly at a point in space, and it obeys the laws of
conservation of energy and momentum in collisions. It does not exhibit
interference or diffraction. A classical wave, on the other hand, behaves
like a sound or light wave; it exhibits diffraction and interference, and
its energy is spread out continuously in space and time. A classical wave
and a classical particle are mutually exclusive. Nothing can be both a
classical particle and a classical wave at the same time.
After Thomas Young observed the two-slit interference pattern by using
light in 1801, light was thought to be a classical wave. On the other
hand, the electrons discovered by J. J. Thomson were thought to be
classical particles. We now know that these classical concepts of waves
and particles do not adequately describe the complete behavior of any phenomenon.
Everything propagates like a wave and exchanges energy like a particle.
Yes! Notice this: “EVERYTHING propagates like a wave and exchanges energy
like a particle.” It’s not just light. It’s everything.
Though it’s not called that here, that’s what a quantum field is like. A
field quantum propagates like a wave and exchanges energy and momentum like
a particle. It’s not a mystery. It’s a new kind of thing.
Please notice that all of these books are very consistent in what they say.
They don’t offer contradictory statements.
Post by Ed Lake---------- end quotes --------
Best quotes: "The concept of a light quantum, or a photon, turns out to
be far more subtle and mysterious than Einstein imagined. Indeed, it is
still very poorly understood.
and
"We now know that these classical concepts of waves and particles do not
adequately describe the complete behavior of any phenomenon."
Right. The CLASSICAL concepts of waves and particles do not adequately
describe. A quantum field DOES adequately describe.
Now, you may be frustrated why these books don’t then describe quantum
fields. There’s a very simple reason. They are FIRST-YEAR textbooks, aimed
for the ONE physics course a student will take in the first year of
college. Keep in mind that a student who aims to go into physics will take
another five or six years of physics courses, and from this point on,
they’ll take six to eight courses a year.
What you looked up in the index and read took maybe 10 minutes of your
time. Students take 10,000 hours to learn what photons are really like, and
how quantum fields behave. We’ve had this conversation before. You’ve said
that this is silly and that nothing should take 10,000 hours to learn. But
this is not a number just pulled out of my hat. That’s a standard metric
for the hours needed to become competent in a subject.
I know you’d like a simple explanation that could be digested in an hour or
so that will answer all your questions about light and what photons are.
Sorry, it can’t be done. If it could be done, then it wouldn’t take 10,000
hours to learn. There are no shortcuts, even for an “analyst”.
Post by Ed LakeOscillating photons appear to adequately describe how photons
Why do authors of physics textbooks refuse to view things that way?
It appears they are waiting for someone to make a declaration that
almost everyone else immediately accepts as the correct solution
to the "problem" of particle-wave duality.
No one wants to write a textbook that is immediately attacked and
thrown in the trash by people who are content and INSIST on leaving
the issue as "poorly understood."
Ed
--
Odd Bodkin -- maker of fine toys, tools, tables