Relativity, yes we are doing this, it is what it is, it’s not as bad as it seems.

We are bounded in a nutshell of Infinite space: Blog Post #12, Free Form #2: Relativity, yes we are doing this, it is what it is, it’s not as bad as it seems.

On one of the most recent entries, we went over the nature of relativity and the role it plays when analyzing microlensing and other astrophysical phenomena that have to do with light and gravity. But what exactly is relativity, the mythical and wonderful description of the universe compiled, proved, and understood first by Albert Einstein in the first decade of the twentieth century?

As we had presented in an earlier blog post:

“Relativity describes the nature of the Four-dimensional world we inhabit, these dimensions being length, width, height, and time, 3 space dimensions and a time dimensions. Working off this knowledge, Einstein developed a description of all space as truly being a sort of fabric, a space-time fabric, whose perception is changed based on individual reference frames (from where you observe the event(s) ). Adding in the nature of the speed of light in a vacuum, the one absolute constant in the universe, and the nature of gravity and how it warps space time, bending the fabric, we can understand how light is affected by gravity.”

Thus, we have briefly explained the effect of gravity and light when these two interact with one another, but we have not delved into the inner nature of relativity, and the most important realization that serves to understand the what is actually occurring not only when gravity is in play, but in all physical reality.

The understanding that cements all relativity, and re-defined physics, was establishing that there is one universal constant in the universe, one fact that never changes, from which all of relativity is derived: the speed of light is the maximum speed of the universe, an unchangeable value that will always be the same while in a vacuum (light can change speed and direction when it changes the medium it goes through). Why is light constant?, you might ask: because it needs to be, and the evidence that proves it is more than conclusive. But another explanation for why it is constant is that light (and by this we mean the entire electromagnetic spectrum) is one of the 4 fundamental forces of nature, and thus mold much of reality around themselves.

Regardless, the fact is that light is assumed to be constant in any case, and because of this, many sets of equations were created, none of which have been dis-proven after many tests and experiments, essentially confirming that relativity with a constant speed of light is the most plausible system.

Now then, as to the actual effect light has on objects and reference frames, this is when things get a bit more confusing. So light we have just seen that it has to be constant in any circumstance, so all other variables, like space and time, are the ones that must change and make accommodations in order to maintain a constant speed of light. The classic example Einstein gives in his papers on Special and General Relativity is the case of two persons, one on a train heading in a direction towards a point where a lightning bolt just hit the ground, and another person stands some distance away and can observe both the train and the lightning bolt.  In this scenario, the person on the train is moving at a speed v, who will hit the rays of light with this speed and thus (one would expect to) perceive the speed of photons as the intrinsic speed of light minus the speed of the person. This would differ from the person outside the train, seeing the lightning bolt come and thus (expect) to perceive light at its normal speed.

However, the speed of light must be CONSTANT at all times, so the person on the train must have something change in order for him to experience the speed of light at the correct value. What happens is, as Einstein describes in Special Relativity, that the person moving with speed v experiences time (and length and differently, it slows down in his (moving) reference frame and so the speed of light he perceives is maintained at the constant rate.

For the person outside the train, he would see the light coming from the lightning bolt at its normal speed, without any special considerations to be taken into account. But as he sees the light going towards the train in the distance, he would clearly see the light in direction of the train has the same speed as the light that reached his reference frame, maintaining the constant speed of light and set consolidated with the perception of the person on the train, instead of two people experiencing two different speeds of light.  

This sums up the overall principles of relativity, but additionally gravity comes into play in a deeper sense and with it the entanglement of quantum mechanics and how it can (or cannot) be consolidated with general relativity, which we will leave for another time.

Nevertheless, this sums up a lot of the intuitive nature of relativity, and hopefully compels you to believe the speed of light never changes, but of you are not, go and prove it (just bear in mind people have been trying to do just that for about a century).