Modern Relativity Principle and Maxwell's Equations

Einstein held that if the modern principle of relativity were correct, then the laws of electromagnetism would be the same for all inertial observers, and thus Maxwell's equations would have the same shape for all of these observers. If this is the case, then Maxwell's equations in the vacuum predict that light propagates at a specified constant speed, and this means that Maxwell's equations themselves would predict if we accept the modern principle of relativity that the speed of light should be the same for all inertial observers.

This is a very great revelation, as the result that everyone thought was negative is that the speed of light is the same for all observers as a natural consequence of the modern principle of relativity. But hey we have to wait, is it really that simple? Is it conceivable for something to move at the same speed for all observers? This contradicts the concept of absolute time in Newton and Galileo. According to the concept of absolute time, we can deduce the familiar law of summation of velocities, which is called summation of Galilean velocities, which I shall simplify as follows:

If you are a boat deck, let's say that this boat is moving from south to north at 40 km / h, and then you roll a ball on the roof of the boat at 5 km / h for you, then the speed of this ball will be relative to your friend on a boat who is still on the water surface Equal to 45 km / h as it will be combined with the speed of the boat. So according to this concept, how is it possible if a person carrying a source of light and moving, does not combine the speed of light with the velocity of the source? Here Einstein revisited the postulate of absolute time intuitively accepted by Newton and Galileo and dived into its depths and discovered something absolutely amazing!