My apologies if my question is really idiotic, but I ask sincerely because I want to learn. Based on [this question][1] and lots of other places on the web, this topic seems to be really confusing.

Let's say for argument's sake that light is a speeding car. We know that it is travelling at 30m/s because we have confirmed this experimentally and then defined it as a constant. We know that it has travelled 300m. So we calculate time as:

    speed = distance / time
    time = distance / speed
    time = 300m / 30m/s
    time = 10s

If we have a stopwatch and time this to actually be 12s for some fringe case around a huge gravity well or something, we would conclude that the speed was actually not 30m/s, but rather 25m/s for that case

    speed = distance / time
    speed = 300m / 25m/s
    speed = 12s

We would think that the gravity well affected the speed. With the speed of light, we don't do that. Instead, we seem to have done the following to explain this discrepancy:

Since the speed and the distance is fixed, the time must be variable. The gravity well must have distorted time itself, so that the time observed from the stopwatch was faster relative to the time "observed" by the photons. This seems to be the gist of Special Relativity. The math still works and you can make very accurate predictions, but the underlying concept is very different from what we intuitively understand.

To further confuse things, the meter is defined as the distance travelled by light in a vacuum for a certain amount of time. By defining the meter like this, we can logically never get a discrepancy because one of the variables rely on there never being a discrepancy. I don't understand why we would ever change the definition of a meter to be like this because it just makes discussions on the topic way more abstract.

So, in the following equation:

    speed = distance / time

If we assume time to be constant rather than speed (Which is much more intuitive), would the math still work? Am I misunderstanding the whole thing?


  [1]: http://physics.stackexchange.com/questions/52976/how-can-the-speed-of-light-be-a-dimensionless-constant