From the perspective of physics, I think we need to start with Einstein's special theory of relativity. In physics, we consider the speed of light to be the limit of speed, which is a central idea of special relativity.

Anyone who knows a little about the theory of relativity knows that the special theory of relativity is based on two basic assumptions: 2. The propagation velocity of light in a vacuum is constant for all inertial frames of reference. 0. The laws of physics are of the same form in all inertial frames of reference. Based on these two assumptions, Einstein came to many surprising conclusions through rigorous mathematical and physical reasoning. These include the famous mass-energy equation E=mc², which also revealed the consequence of Newtonian mechanics such as time expansion, length contraction, and the fact that the mass of a moving object is greater than the mass at rest.

These formulas show that the closer an object's velocity is to the speed of light, its mass tends to infinity, whereas there is no object with infinite mass in the real world. This also means that any object with a mass at rest cannot travel faster than the speed of light. In other words, both the energy and mass required to accelerate an object to the speed of light tend to infinity, and we cannot provide this infinite energy to achieve this acceleration.

In summary, the speed of light as the upper limit of speed is a direct corollary of the special theory of relativity. So, if you're wondering why this inference holds, you're actually asking why special relativity is correct. Since the entire theoretical system of special relativity is based on the above two basic assumptions, your question can be transformed into: Why are these two fundamental assumptions correct?

So why are these two basic assumptions true? We usually think of them as axioms of physics, fundamental laws that have been summarized through extensive experiments and studies. Like axioms in mathematics, they do not need to be proved, they can only be verified experimentally. But such an answer may not be enough to satisfy you. So, I'm trying to explain these two basic assumptions with my own understanding.

First, let's look at the second hypothesis: in all inertial frames of reference, the laws of physics have the same form. I admit that there is no additional understanding of this, because it is like an axiom that cannot be proved, and there is no deeper reason for it, and we can only assume that it is true (in fact, this hypothesis fits very well with traditional human scientific understanding). However, based on this assumption, I logically derive the first assumption: the speed of light is constant in all inertial frames of reference. You might think I'm talking nonsense, but in reality, we can think about it: how is the speed of light in a vacuum derived? It is calculated from Maxwell's equations (the specific calculation process will not be repeated), and its mathematical expression is:

It can be seen that the speed of light in a vacuum is actually determined by two fundamental physical constants. Based on the second assumption that the laws of physics are of the same form in all inertial frames of reference, then in all inertial frames of reference, the physical constants should remain constant, just like the gravitational constant G, Planck's constant h, Boltzmann's constant k. In this case, it is logical that the speed of light remains constant across all inertial frames of reference.

After this series of analyses, the speed of light as the upper limit of speed seems to be a natural conclusion. Our argument process is roughly as follows: First, it is assumed that the two basic assumptions of special relativity are correct. Next, we deduce that the special theory of relativity itself is correct. Then we know that all the conclusions of special relativity are correct. Because the upper limit of speed is the speed of light is a corollary of special relativity, this conclusion is also correct.

Do you find this argument convincing?

In fact, we can also understand it from another angle: according to the conclusion of special relativity, if the speed of an object exceeds the speed of light, then in a certain frame of reference, the causal relationship will be broken. For example: I shot once, and there was a bullet hole left in the target. The shot is the "cause", and the appearance of bullet holes is the "effect". If the speed of the bullet does not exceed the speed of light, the "cause" always precedes the "effect", no matter which inertial frame of reference you are observing. But if the speed of the bullet exceeds the speed of light, you'll see that in a certain frame of reference, the target has a bullet hole first, and I shoot. This violates cause and effect. That's why we say that going faster than the speed of light goes back in time, because the order of "cause" and "effect" is reversed. To prevent the disruption of cause and effect, the universe can only set the speed of light as the upper limit of speed.

Of course, if you don't want to listen to this explanation that doesn't touch on the nature of the universe, you may need to go to the philosophical level. Why is the speed of light so special? Why is the upper limit of the speed of the universe exactly this value? That may only be known to the Creator. Perhaps the entire universe is a supercomputer of the Creator, and the speed of light may simply be due to the power limitation of the computer, while quantum effects may simply be due to the resolution limitation of the computer. Maybe one day, the Creator will get tired of it and turn off this computer.

How do we know?