The question is - is there any flaw in this explanation, or it is the right explanation in general language?
Let me break the explanation into two parts -
- Why there is a certain speed of electromagnetic waves (which happens to be $c$)?
Speed of any wave is property of the medium through which it travels. So, it is property of empty space that electromagnetic waves travel at a certain speed (no more, no less). It is a property, not a limit. If it was a limit, then light (or EM) could travel at < c through empty space. But it travels exactly at c, in empty space. So, it is a property. If you have problem with this explanation, then you should also have problem with - sound having a certain speed through air, and need to go to more basic level. If you accept a certain speed of sound, I will expect you to accept this property in case of EM waves as well. The value of this property happens to be c. (Per modern physics, the EM waves are fields that have a property that they propagate exactly at c through empty space. It is still a property, not a limit).
A lot of people are objecting to space being a medium. My questions on this is - what are ripples in space. If space can - 1. curve, 2. it can distort, 3. it can expand, 4. it can tell mass how to move, 5. it can fall into a black hole and carry light with it, why it can not be a medium?
- Why any material body (or, a collection of massive fields) can not move faster than $c$?
This is a direct consequence of (1) and so, turns out to be a limit. (It is limit because bodies can move at any speed as long as it does not exceed c)
Let us consider how do we increase speed of a mass - we apply a force on it. For example, we can make a standing car move by pushing it with our hands. The electrons in our hands, and the ones in the car (where we touch it) repel each other and that repulsive force causes increase in the speed of the car. Suppose you were running at your maximum speed and a car passes by you at 300 miles/hour. Can you increase speed of the car by pushing with your hands when it passes by you? Answer is no (a normal human being can not move the hands faster than 300 miles/hr). To increase the speed of a moving body, the force has to act on it faster than the speed of the moving body.
Any force we apply to accelerate a body, the force is ultimately exerted on the body as one of the fundamental forces. All the fundamental forces themselves travel at c. Just as example, electromagnetic force propagate at the same speed as EM waves i.e. c. For simplicity let us agree that all fundamental forces propagate at c as a property per (1) Therefore they can not increase speed of any material body that is already moving at a speed of c to > c.
Note that the forces have to travel faster than c through space in order to cause a speed greater than c. But we know they move at c. So even the fundamental forces become ineffective for a body that is already moving at c.
Even if the force emanates very next to the moving body, to act on the body, it has to travel through space and because the body is already travelling through space at c, the force can not reach the body through space. Even if it did (because it emanated inside the body itself), it still has to act through space and can not increase the speed of the body to more than its own speed.
The forces become ineffective in the direction of movement of the body at c. They are still effective in other directions and , so body can be slowed down etc.
Therefore, speed of propagation of fundamental forces is a property (not a limit). This property has highest value in empty space which happens to be c. And, nothing can propagate faster than the forces themselves - what will cause anything to do so? Speed of forces (a property just like speed of sound) turns out to be a speed limit for material bodies. Which should not be any mystery.
May I also comment that in particle accelerators, they use the electric/magnetic fields to accelerate the particles and obviously can not accelerate them faster than c. Even accelerating them to very close to c will be very challenging.