## Friday, 19 November 2021

### Speed of light in glass

I want to prove that light is a wave that propagates through a medium.  To highlight this point I want to consider the speed of light as it moves through glass.  The best explanation from the establishment about the speed of propagation through glass is in these two videos:

However, what they are describing is movement of the atoms in the glass.  Which to my mind means propagation through the medium.

## A better explanation

The speed of light is governed by two constants.  They are the permittivity of free space and the permeability of free space.  In addition to these two constants there are also relative permeability and relative  permittivity.

## Glass

I looked at the internet for the values of relative permittivity and permeability of glass, and found relative permeability to be between 5 and 10, so I used the value of 5 for the calculation. The given relative permittivity value was 3/8.  The following picture shows the results:

## Plastic

I have just done the same calculation for plastic.  I used a relative permittivity of 2.25 for polyethylene and a relative permeability of 1.  The result was 2 x 10^8 which according to the internet is correct!

## Water

Unfortunately, I could not do the same for water as I could not find any reliable information.

## Diamond

The speed of light in the Diamond is 1.24 x 10 ^ 8 metres per second.  To obtain this speed I used the relative permittivity of 5.8 and a relative permeability of 1.0037.  The Internet gave the range of 5.5 to 10 for the relative permittivity.

### Update to gravity

At the moment, I am considering what happens to Particles and light as they propagate through the medium. What seems to be happening is that particles lose frequency and light gains frequency. So the two effects seems to be cancelling each other out. This agrees with the idea of time dilation. However I intend to study this in more detail before I publish the results.

## Schoolboy error

Light also loses frequency on board the spaceship.  With the gamma factor of 2, a 1 MHz radio frequency on board the spaceship, would translate to 2 MHz for the earthbound Observer.  So the frequency on board the spaceship is lower than it is for the Earthbound Observer.  I was assuming that the frequency on board the spaceship had increased to 2 MHz, but in reality it is the 2 MHz frequency, that has reduced to 1 MHz.

## The medium exists

I am now convinced that this medium exists.  Particles propagate through the medium.  Time dilation and length contraction are simply due to the change of frequency and wavelength.