Representations of Light:

1. The Light Ray Representation of Light: This is the most common way that we think about the motion of light.  It is useful for considering reflection, refraction, and the bending of light by prisms.

2. The Plane Wave Representation of Light: This representation of light shows that it moves as a wave.  It is useful for considering diffraction and the interference properties of light.

3. Maxwell’s Electro-Magnetic Representation of Light:
The theory behind this model (Maxwell's equations) uses electro-magnetic fields and predicts the correct speed of light based upon two constants of space, permittivity (associated with an electric field) and permeability (associated with a magnetic field).

It is from this model that we get the concept of light as electro-magnetic radiation.  This model is most useful for producing and measuring light using devices (antennas) that operate electro-magnetically. Electro-magnetic theory as developed via Maxwell is the theory that most people believe ”really” represents light.

I disagree with the view that light “is” electro-magnetic radiation. Just because we know how to couple to light via devices (antennas) that operate electro-magnetically, does not mean that the light itself is electro-magnetic.

4. The Particle Representation of Light: This way of thinking about light considers it an object like a golf ball.

It is useful when thinking about how photons knock electrons out of a metal
in the photo-electric effect. See
section 16 for more on the photo-electric effect.

1. 5.The λ-hopping Representation of Light (as developed in this DWT website): This model of the nature of light has both particle and wave aspects. It is the digital wave in digital wave theory.

The photon consists of what I call a Planck Instant and the λ-hop. The Planck Instant is postulated to be something that exists for as short a distance and time that nature can produce. It will be assumed that this is the Planck length and Planck time. It is a fiducial mark that marks the progress of the photon. This will give light the best chance of being the best fit for Einstein’s special relativity (will be discussed shortly). I also think this Planck Instant could be a neutrino.  Yes, this is more than a bit speculative, but I think it is a possibility, and I use the words Planck Instant and neutrino interchangeably.

How the speed of light changes with wavelength: The speed of a given wavelength of light is the average speed over the wavelength (see above diagram). The speed is zero where the Planck Instant appears and “c” for the remainder of the wavelength (where it disappears). Therefore, this theory has the speed of light varying with the wavelength of the light, and blue light will travel slightly slower then red light.

Also seen in the above diagram, the velocity of a particular wavelength of light λ is:
Velocity = c [λ-PL]/λ where PL is the Planck Length. Let’s choose a worst case and make λ equal to 10-15 meters. This corresponds to a highest frequency light, gamma rays, that have ever been detected. We know that the Planck Length is 1.616x10-35 meters.  We can calculate the velocity for this wavelength as: Velocity = c[10-15-10-35]/10-15 = c[1-10-20] This velocity deviation from c is so close to c that it is hard to imagine how we could possibly detect it experimentally. We can measure c to about one part in a million. To be able to see the speed change with wavelength we will need another 14 orders of magnitude resolution on the speed of light. See Section 30 for a visualization of how relativity works.

This subtle changing of the speed of light with wavelength creates a small deviation in general relativity (see Section 21) where acceleration in space-time makes light look like it is moving in a medium with an index of refraction. We already know that light changes its wavelength with speed changes. This is the doppler effect that gives a red shift to the expanding universe. What is pointed out here is that this wavelength change always comes packaged with a small change in the speed of light.

Yes, the speed of light changes with wavelength is a very, very .... very small effect.

Why does light need a small speed variation with wavelength?

Answer: Light can come in a wide range of wavelengths and yet maintains it speed as c (to a very good approximation). I maintain that the λ-hopping model presented above is the best one for keeping the speed of light as close to c (the maximum speed of space-time) as possible for all wavelengths of light.

The Fundamental Axiom of Light is that the particle that is the constituent of all light (postulated to be the Planck Instant (aka the neutrino) always appears with zero velocity with respect to the observer. All individual Planck Instances (neutrinos) have zero speed with respect to any observer (see diagram above) no matter how the observer moves relative to the rest of the universe. This zero velocity is an exact speed that exists for a very short time, but it takes away from the ultimate speed of light c. It is this fact that makes the speed of light c the same for all observers an approximation. Light itself does change its speed relative to an observer whenever there is a wavelength change (doppler shift), but for all practical purposes this speed change is so small that Einstein’s relativity is valid as a very very good approximation. And the big question is can we make an experiment to show that this is the case?