Why Is There a Maximum Speed Limit in the Universe?
By Jon Therkildsen, MSc MBA from University of Århus (2004)
This article will address and answer the following:
Why does light move at the cosmic speed limit?
Why is there a speed limit?
What is Space-time?
The typical answer to this question often fiddles around how light speeds require an infinite amount of energy and jada jada. While this is true, such answers seem to misunderstand the real issue. The cosmic speed limit is not because of a limited ability to utilize the latest diesel technology. It is not because of infinite accretion of relativistic mass (a term often grossly misused). No, the limit is a fundamental property of space. Before I will answer how that is, I will first explain why light is the one thing that moves faster than anything else.
Why does light move at the cosmic speed limit?
A light quantum is called a photon, a fundamental (elementary) particle. And we have discovered that photons, through the vacuum of space, always travel at the cosmic speed limit of 300 000 km/s. It doesn’t matter how quickly you may run towards a photon, or after a photon; the relative speed to you is always the same.
The highest-energy photon and the lowest-energy photon ever observed, travel at precisely the same speed. Always.
I say “energy”, because when its velocity remains constant, its energy changes depending on your position or your own relative velocity. Were you to move towards a photon, it will appear bluer (a higher level of energy). Move away, and it will appear redder (a lower level of energy). But no matter how you move, how you make the light move, or how you change the energy; the speed is always the same. That the speed of light is the same for all observers is known as Maxwell’s equations.
But why does it move at the highest possible speed?
Light moves at exactly the cosmic speed limit because it has zero mass.
This is just like how you can ride your bike faster the lesser you carry. And if your load were zero, you too would reach your maximum cycling speed. You cannot drop more luggage, and therefore you cannot increase your speed - assuming, you already gave it your all. Light has no “luggage,” it already moves as fast as is possible. Anything with zero mass will move as fast as possible.
Why is there a speed limit?
The real wonder is rather; why not faster than this cosmic speed limit, why any limit at all?
It is hard just to accept that there is an upper limit by principle. I mean, why not?? To understand this, we have to realize that space is a geometric form bound by dimensions, and so by definition, also bound by limitations.
The reason why a circle, for example, has only 360 degrees, no more and no less, is geometry. There is no such thing as a 361-degree circle. Some rules cannot be broken, no matter the level of creativity or power. We can, of course, mathematically add more degrees, and we can redefine what a degree means, but it does not change the fact.
We cannot make a circle more circular. And so it is for the cosmic speed limit; we cannot make it speedier.
Geometry is the real answer to this question.
Our universe is composed of a 3-dimensional space and a 1-dimensional time, through which all interactions happen. This relationship (in a geometric coordinate system we call the universe) between a moving particle and space-time - in which one is producing an effect on the other - necessitates a finite end result.
Simply said; there must be limits for our reality to work.
When we speed up, time relatively slows down, and space relatively contracts. 101 in Special and General Relativity. At the speed of light, time completely stops, and space completely flattens in the direction of motion.
You cannot stop time more than completely, and you cannot flatten space more than flat.
Sounds banal, and it is… but this is the answer. We have the same issue as with the circle example above. We cannot add more degrees to a circle’s circumference either. It is both impossible and nonsensical. Thus, it is a limit.
The illustrated coordinate system is a representation on how time flattens space. Y becomes X the faster you move.
A different way to say this: When the cosmic speed limit is reached, time essentially ceases to exist and mass/energy becomes infinite. Therefore, it is not “speed” or amount of mass that is limited per se, but the effect speed has on our space-time geometry, when it reaches 300 000 km/s.
Geometry is why nothing can go past the cosmic speed limit.
And the rules of geometry cannot be broken, without breaking reality itself.
Photos via Google