The Speed of Dark?

[Johnathan Clayborn]
Here's a fun philosophical/physics quandary for you, a conversation I had with several of my coworkers a few years ago: what is the speed of dark? This question isn't intended as a joke, but as a serious thought for discussion. Logically, this question only has two possible answers: either the speed of dark is 0, or the speed of dark is the same as the speed of light. Scientifically this could be expressed as ds=0 or ds=ls.

To answer to this question it is going to require a little bit of discussion about the nature of dark. What exactly is dark anyway?

When this question first came up in the original discussion one of my coworkers immediately fired back with the comment that there was "no such thing as dark". I found this to be a perplexing statement. No such thing as Dark? Really? When I questioned him he said that Dark was really just the absence of light, and therefore not a real construct. But, if Dark is just the absence of light, and therefore not real, then what possible way would they have to measure that light against in order to assign it a lumens rating, or candlepower? It could be argued that "Dark" is simply 0 on the lumens scale, but being that it is an integral part of that scale and the basis of all luminosity measurements, then it certainly seems like it would be a real and valid construct.

Okay, so if we operate on the assumption that dark is a valid theoretical construct, how does that help us to understand how fast this thing moves? The answer to that question lies in understanding the nature of that thing. How does it work? What is it comprised of? In the case of light, this is easily understand. Light is an energy wave that is comprised of photons. These photon have energy, but no mass. So light is not a solid thing. What about darkness?

Darkness, on the other hand, does not intrinsically contain photons, although it does abosorb them. It then converts these photons into heat energy (which is why black cars are hotter than white cars). These heat-releated properties are explained by many of the principles of thermodynamics.

To recap, light is an energy wave that contains protons and moves with momentum. Darkness is a construct that absorbs photon energy and re-emits it as heat. But does it move? What happens when light spills into a void where darkness once was? Does the darkness vacate that space at the same speed at which the light enters? Or does the darkness linger and allow the light to permeate through it?

Although not immediately obvious, the answer, is that the speed of darkness is actually 0. Darkness doesn't flee before the light. Darkness absorbs the light until a specific threshold is reached and no more photons can be absorbed, and then it essentially becomes light.

How can we know that this is true? The answer has been in front of us the whole time: light and dark can occupy the same space at the same time. We know this because dimmer switches are possible. It is possible to adjust how much light floods a space by increasing the intensity of the light emissions. Once the light stops being emitted, the influx of photons ceases and the darkness bleeds off the photons it has absorbed and returns to being darkness once more.

References:
http://en.wikipedia.org/wiki/Lumen_(unit)

http://en.wikipedia.org/wiki/Thermodynamics