What defines the speed of light?

It could be said, it just is. I find this a very unsatisfactory answer. Let’s try and find the real answer using just the concept of time.

Photons travel instantaneously, they exist in only the now. Another way of looking at this is they travel at infinite speed.

How can a photons infinite speed be measured to approximately 300,000 Km per second. Surely, infinity is infinity?

Let’s take a brief look at time. What are its attributes? There is an arrow of time and it can ‘flow’ (be dilated or contracted) at different rates. At the two extremes time can ‘flow’ infinitely fast (ultimate contraction) or it can ‘flow’ ultimately slow (ultimate dilation) and stop. ‘Infinitely’ slow (stopped) is a finite quantity.

Where time stops can be viewed as an absolute. It is very similar concept to the temperature of absolute zero. You cannot go colder, that is where the scale ends. Time cannot ‘flow’ slower than stopped.

To a photon, the clock has stopped. It cannot go faster than that. To do so would require the reversal of time.

The faster anything moves, the slower time passes (dilates). This puts an upper limit on speed as ultimately the clock would stop. The same upper limit is reached when viewed from the perspective of energy and mass.

Whilst a photon exists in its own timeless world, its nevertheless in a universe dominated by gravity where gravity everywhere dilates time. Everywhere, in the universe ‘feels’ the effects of gravity. Therefore everywhere in the universe is feeling the effect of dilated time. It can be extrapolated backwards, that without gravity time would be infinitely contracted. It is mass that gives an arrow to time so without mass time would be infinitely contracted in both directions at once. (Everything happens at once with no causality. There is no time, as we know it.) Mass causes gravity causes time. However, that is an oversimplification. In a black hole, a place of infinite gravity time is infinitely dilated, it stands still. From the point of view of the photon, there is no such thing as time as it travels instantaneously. Put the two together and the interaction of gravity and energy equals time. To put it another way, gravity ‘slows’ photons to create time. We can never be aware of this ‘slowing’ as time dilates in just the right manner to compensate, to ensure the speed of light in a vacuum remains a constant.

Whilst a photon exists in its own timeless world, it still experiences causality, as it exists in a universe that contains time.