Breaking the sound barrier isn't arbitrary. Indeed even measuring it using the Mach number shows that. Mach 1 isn't fixed, it is variable based on a number of attributes.
At Mach numbers above 1 the compressibility of the air is entirely different. The medium in which the airplane operates behaves differently, in other words. The sound barrier was a barrier because the planes they were using stopped behaving predictably at Mach > 1. They had to learn to design planes differently if they wanted to fly at those speeds.
Mach 1 is an external constraint mandated by the laws of physics. There is a good reason that sound can't travel faster.
That is why it is a barrier to be broken. It is a paradigm shift imposed entirely by the properties of our physical world.
At Mach numbers above 1 the compressibility of the air is entirely different. The medium in which the airplane operates behaves differently, in other words. The sound barrier was a barrier because the planes they were using stopped behaving predictably at Mach > 1. They had to learn to design planes differently if they wanted to fly at those speeds.
Mach 1 is an external constraint mandated by the laws of physics. There is a good reason that sound can't travel faster.
That is why it is a barrier to be broken. It is a paradigm shift imposed entirely by the properties of our physical world.