Alex W. asked: Eroica wrote: Tim Thompson implied that a photon while traveling does have a wavelength to be stretched. And he wrote:Thank you all for the thought provoking comments that led me to clarify my ideas. Let me first respond to Tim Thompson's last quoted statement.

Assume for a moment that two observers in different reference frames could measure the energy of the same photon. Which of the two energies would the photon have? Wouldn't it be more correct to state that the energy of a photon is independent of the observer, but that the energy measured by an observer depends on the reference frame of the observer?

Perhaps my interpretation (model) of a photon will answer some of your questions. We are all familiar with the notion of a point on the x-y plane describing a circular motion around the origin at a constant angular velocity. The y-displacement of the point's coordinates plotted as a function of time yields a wavelike sinusoidal curve. We can assign a period and wavelength to the curve. However, we would not call the circularly moving point itself a wave.

A photon is analagous to that circularly moving point. A photon's electric and magnetic vectors are at a right angle to the photon's direction of motion. Assume a photon traveling in the x-direction with its electric vector lying on the x-z plane and its magnetic vector lying on the x-y plane. A plot of the electric vector intensity as a function of distance (or time) traveled gives us a wavelike sinusoidal curve. The same is true for the magnetic vector. We can assign a period and wavelength to those curves. However, we should not call a photon itself a wave.

Quantum theory defines the photon as a particle with zero rest mass and spin 1. I would imagine that the spin has two components of 1/2 associated with each of the two vectors. I take the sinusoidal nature of the time functions of the vector amplitudes as evidence of those spins.

Now we investigate whether a photon is in any way extended in space. Your microwave oven gives the answer. The openings in the viewing shield are small enough to prevent passage of microwave photons but large enough to allow passage of visible photons. Diffraction experiments with pinholes or slits give similar evidence. Therefore, a photon has extension at right angles to its direction of travel. Indeed, Maxwell's equations imply that a photon's electric and magnetic vectors have displacements only in the plane transverse to the direction of travel.

If you were the photon you would see everything else rushing by. You would also see your electric vector stretching out above you and below you and coming back. Similarly you would see your magnetic vector stretching out sidewise from you and coming back. However, they would not make the least attempt to move in front of you or behind you. If you didn't look at the other things it would be as if you were standing still and merely extending and retracting your four arms.

If a photon passes the edge of an opaque material and one of its fields touches that edge, the photon will be pushed off course. After all, those fields are force fields. That is a simple explanation for the physical basis of diffraction. Add to it the periodic nature of the fields and you can understand why a quantum (particle) of electromagnetic energy can display wavelike behavior. If my memory serves me, a collimated beam of hot metal ions has also been diffracted.

Since the electric and magnetic vectors of a photon are in phase with each other, they must have zero extension when they have zero amplitude and a maximum extension when they have maximum amplitude. The extension of the electric field occurs on both sides of the line of travel and similarly for the magnetic field. The fields expand at the velocity of light. The extension of a field on one side of the line of travel after 1/4 of a photon's period is 1/4 of its period times the velocity of light. That is the farthest it could travel in that time. For the two sides, then, the total extension of a field is 1/2 the period times the velocity of light. That is the maximum transverse extension attained by a photon.

One half period after attaining the above maximum extension a photon has a second similar maximum transverse extension, differing from the first only by polarity. Now 1/2 the period times the velocity of light is called 1/2 the wavelength of light. Thus, a photon is never extended a full wavelength. It is only extended a half wavelength for two brief instants of its period.

The extension of a photon's fields takes place as the photon moves in its direction of travel. Thus, as its fields extend from zero to 1/2 a wavelength, a photon travels forward a distance equal to 1/4 of its wavelength during the first 1/4 of its period. After traveling a distance equal to 1/2 wavelength its fields have zero extension. When a photon travels a distance equal to 3/4 of its wavelength its fields are again extended to 1/2 a wavelength, but with opposite polarity. When a photon has traveled a distance of one wavelength, it again has no extension of its fields.

The motion of a photon in the x-direction takes place at the velocity of light in a vacuum, c. The extension of its fields in the y-direction or z-direction also takes place at the velocity of light in a vacuum. Thus, the maximum transverse extensions of the photon's fields and the distance the photon travels during its period are both functions of only the duration of the period of the photon and the velocity of light. The period of light and the velocity of light determine the wavelength of light.

An increase in the wavelength of light requires either an increase in the velocity of light to extend a photon's fields faster, and hence farther in a 1/4 period, an increase in its period to allow more time for the extension of its fields, or both. The cosmological red shift hypothesis makes no claim that expanding space alters the velocity of light. The only remaining property of a photon that could be altered to increase its wavelength is its period. If the proponents of that hypothesis cannot produce a reason that expanding space should increase the periods of photons traveling through it, the cosmological red shift hypothesis would seem to be implausible.

Here is a bonus idea to think about. Where is the photon's energy when both its electric and magnetic vectors simultaneously have zero amplitude? (Maxwell's equations say they are in phase with each other.) Is that energy then stored as "the energy of a vacuum" or might it imply that electromagnetic radiation is a propagating disturbance of a gravitational field?

A gravitational field can both store and supply energy. Gravitational fields are everywhere in space. There is a gravitational line of force between every object that is a source of radiation and every object that will react with that radiation. Is the gravitational field the required 'ether' at the heart of 18th and 19th century developments in optical knowledge? I think it is the gravitational field that does the waving. (P.S. I published these last ideas in 2001) Thanks again for your interest and your comments.