Here I will conclude this little three part series. You can find the other two parts here:

Part I: http://stargazerslou...3-part-i-space/

Part II: http://stargazerslou...-part-ii-space/

Up to this point, every wave known to science travelled relative to some medium, so where was the substance for light? Experiments were failing to find the Aether and Maxwell’s own equations did not conjure up such a substance, so what was going on?

It was simple, argued a young Einstein, light, unlike any other wave does not need a medium. Light's speed is relative to anything and everything. It doesn’t matter if you are travelling towards or away from light, for it will always be measured at a constant speed of 671 million mph.

The upshot

So what exactly is being said if we conclude that the speed of light is a constant?

As we have seen:

• velocity is a measure of space (distance travelled) divided by a measure of time (duration of journey) and,
  
• space and time were generally considered absolute.
  

With these two premises in place, it was concluded that any measurement between two spatially separated objects, any measurement in space, would always be absolute. It didn’t matter if you, I or some cosmic entity did the measuring, because, in principle, we should all agree on the measurements taken.

And exactly the same argument followed for time. It didn’t matter who measured how much time it took for something to happen, because, once again, in principle, all would agree on the measurements taken.

But according to Einstein, the old generations assumed too much with that second premise. People moving relative to each other will not find identical values for time and space and this follows from the premise: the speed of light is a constant.

Accordingly, if you chase light at 670 million mph, I will measure the light racing away from you at 1 million mph and you will measure the light running away from you at 671 million mph. The speed of light in either case has remained constant, yet space and time are rendered completely relative just as Kant had informed us more than a hundred years earlier. Namely, that each of us carries our own measuring rods of space and time.

Special Relativity

Before Einstein, it was generally believed that time and space were two very distinct entities, but, for argument’s sake, Einstein found them to be two sides of the same coin.

Imagine you’re driving your car in a straight line and all your car motion is going into that straight line. Imagine now that you take a curve up ahead and you do nothing to compensate for the curve, then some of your original straight line velocity will go into that curve, leaving you a little less for the straight line.

By analogy, if time and space are different sides to the same coin, then we can imagine a parked car which isn’t moving through space and so this means all of its motion is going through time. But if that car suddenly speeds away, some of its time motion will now be directed into space motion, meaning that there’s a little less motion for time, so it will literally slow down for the car.

In other words, just as some of the car’s straight line velocity was directed into the curve in the first example, in the second example, some of the car’s space motion is diverted into time motion.

And it is this very curious feature that Special Relativity is arguing; namely, that the combined velocity of any object through space and time is always equal to that of the speed of light. Thus, motion is a combination of motion through space and time and these two motions are absolutely complementary.

It follows that the faster you move through space, the slower time will pass and to give some idea of this ratio, for every three hours we pass at rest, two hours will pass at about 500 million mph and at the speed of light, when all your motion is directed into space motion, time should, in principle, stop.

The light from the stars and the planets you gaze upon at night have never aged when their pretty coloured photons hit your enquiring eye.

And this is one reason why it is considered that nothing can go faster than the speed of light. It is simply because there is no more time motion to draw upon, its all used up. Travelling at such a speed leaves no more time for time.

And that, for now, is the end of our little wander into space. I hope you enjoyed the read.

You can find the other two parts here:

Part I: http://stargazerslou...3-part-i-space/

Part II: http://stargazerslou...-part-ii-space/