In his book "A Brief History Of Time", Stephen Hawking explained the absolute speed of light very simply. It's not so much a matter of speed, but acceleration.
Here's the basis for his explanation: To reach a velocity, something must accelerate to that speed. To accelerate something takes energy. The more mass something has, the more energy it takes to accelerate it. That is newtonian physics. But newtonian physics neglects the affects of time and space... relativity. Relativity reveals that as an object gains speed, mass increases, so that at some point mass will approach infinity.
Ok, here's the simple part: As mass increases, it takes more energy to accelerate. When mass nears infinity, it takes an infinate amount of energy to accelerate it any further. Thus we have a natural limit to how fast something can travel, which has been measured as the speed of light.
It's called the speed of light because light is one of the few things we can normally observe that travels that fast. But light can and does commonly travel slower when it travels through some material, such as glass. How much it slows depends upon the affective density (transparency), length of time it travels through the material, and the fequency of the light. Thus the thicker the glass, the more light slows down. This is what makes lenses and prisms work... and sunsets.
My own observations: All this seems strange to us because space, time and mass are not what they appear to be. Mass isn't really some solid hunk of stuff that we see and feel, these are simple affects. For example, as you dissect an atom, you find an increasing number of smaller and smaller particals separated by relatively huge distances. Eventually the particals get so small they no longer have any mass to speak of. So when you completely dissect an atom, though it may be lead, you end up with nothing but the energy required to hold the atom together. Thus mass is not a solid material as it appears to be, but energy which gives it the properties we observe. So look not at the particals of an atom, the important part is the gaps between them... which is time and space... nothing but a relationship... relatively speaking.
grizzly
