The diagram above shows waves changing direction at the surface between two mediums. The change in direction is caused by a change in the speed of the wave. Changing the speed of particles (matter) requires energy. However, changing the speed of a wave does not require any energy. Its speed is determined by the medium carrying the wave. Notice that the frequency and energy of the wave are the same in both mediums. In contrast, the wave length and wave speed are different in both mediums.
Refraction Is Caused by a Change in Wave Speed
All known evidence supports the theory that the change in wave direction is caused by a change in its speed as it transitions between two mediums. This theory seems correct and is not being questioned. However, what causes waves to change speed?
Changing the Speed of a Wave
The principle of changing a wave speed is well understood. To change the speed of a sound wave the tension of the air is changed (warmer or colder). If we want the sound wave to travel even faster it can be transferred from air to a steel rod. A wave on a string can be made faster by increasing the tension on the string. An ocean wave travels slower as it traverses into shallow water near a shore. In each of these cases, changing the 'tension' of the medium changes the speed of the wave. None of these issues is being challenged. However, the story is different for light waves.
Changing the Speed of a Light Wave
If light is like all other waves, changing the tension of the medium would change the speed of the wave. However, that is not the accepted theory. Instead, the reason given for light changing speed in different mediums is that it is absorbed and re-emitted by electrons. In other words, light does not slow down, it takes detours. The frequency and duration of the detours determines how much additional distance light takes in traversing the medium. There is no doubt that light is absorbed and re-emitted. However, light absorption and re-emission would not cause refraction.
Packet Absorption Does Not Bend Light
In order to bend a wave, one side of the wave front must slow down before the other side. Absorption of light packets does not slow down one side before the other. Instead, entire packets of light (photons) are absorbed. Absorption of entire light packets does not cause refraction.
Absorption Does Not Retain Direction
Spectrum absorption lines are caused by a gas absorbing certain frequencies of light and then re-emitting them. Every photon absorbed is re-emitted, but the direction of re-emission is random. This is what creates the dark absorption bands in the spectrum. The light absorbed is reemitted, but not necessarily in the same direction as the original light. This is also true of solids. The following picture shows minerals that have absorbed various light frequencies and are re-emitting them (with changed frequencies). The absorbed light is re-emitted in every direction.
Absorption Affects Different Frequencies Differently
Every substance absorbs different frequencies of light. Most substances only absorb a few frequencies. In order for absorption to refract light, each lens substance would need to absorb all frequencies. That does not happen. Absorption can not cause refraction.
Summary: Absorption Does Not Cause Refraction
All waves, other than light, are refracted when tension in the medium slows down one side of the wave before the other. Absorption of light is a very different process. Absorption does not slow down one side of the light wave, instead it absorbs an entire light packet. Absorption does not even retain the direction of the light wave. Once a light packet is absorbed it can be emitted in any direction. Absorption does not affect all frequencies the same. Some are absorbed and others are not absorbed. Absorption would never cause refraction.
A Better Answer to Light Refraction
A simple answer to why light is refracted is that light refraction is just like all other waves. Waves bend as the tension of the medium slows down one side of the wave before the other side. If space, the medium through which light travels, is tensioned differently by different atomic structures surrounding the space, then light waves would bend just like every other wave. If space is a substance that can have different tensions, this issue is resolved very simply.
These pages will be expanded considerably in the coming months. These pages are in development. February 2014