turbo-1 said:
The origin of inertia is a mystery,
I'm quoting the part of the message that I agree with.
In our physics theories inertia is described, but we have no way of moving the description to a deeper level.
As an aside:
Very often Ernst Mach is mentioned when the origin of inertia is discussed, and usually a point of view is attributed to Mach that was not Mach's point of view.
In one of his books Mach had discussed the following example (which had earlier been discussed by Newton in the Principia). A bucket is filled with water, and then you start a rapid spinning motion of the bucket (around a vertical axis). Initially the water is not co-rotating with the bucket, friction gradually spins up the water. Only when the water is spinning does the water's surface take the distinctive hollow shape.
The bucket example illustrates that it's not motion relative to the walls of the bucket that counts, but motion relative to some other, larger structure.
In his own discussion Mach mentions the suggestion: "What if the bucket would have walls that are miles and miles thick?" (Meaning the question: if the walls would be thick enough, would there be so much mass that the motion relative to those walls would be what counts.) Mach's answer to that boils down to: there's no need to think about that. Mach's philosophy of physics was that physics theories should be as economical and as sparingly as posible. Mach advocated a level of caution that was much higher than usual in science. For example, in his time Mach argued that the evidence for the existence of atoms was not strong enough. In Mach's time there was a lot of evidence for the existence of atoms (but only a fraction of what is known today), and it was all very
indirect evidence. Mach argued that science should only consider things as proven when the evidence was very strong and direct.
When Mach in writing mentioned the question: "What if the bucket would have walls that are miles and miles thick?", his attitude was to argue that such a question falls outside the scope of science. The job of physics, Mach argued, was to find the most economical way to formulate laws of physics. The laws of motion take their simplest form when they are formulated as motion relative to the fixed stars, so that is how laws of motion should be formulated. Speculations that "the fixed stars", or "distant matter" are the origin of inertia fall outside the scope of science, argued Mach.
Many years later Einstein had a thought about the origin of inertia, and he attributed that thought to Ernst Mach. Einstein formulated it in the form of a principle, and he coined the name "Mach's principle" for it. Instead of claiming the thought for himself Einstein credited Mach, but in this case Einstein didn't do Mach any favor.
Cleonis
