On the topic: where does inertia come from?

Here is a suggestion which may explain inertia as having a local cause.

Imagine we try to accelerate a truck (or any mass) by pushing it from the back, and continue, so that it's in constant acceleration.

The back of the truck must move slightly before the front does, and hence the truck will be in a state of compression whilst it is accelerating.

The amount of compression is determined by the acceleration and the speed of sound in the mass. The force required to produce this compression depends on the Youngs modulus.

To try and cut a long story short, it is not possible to decide which comes first, the chicken or the egg. i.e. does the speed of sound and the Youngs modulus create the feel of inertia - due to force required to produce the compression. Or is inertia pre-existing in the mass, and determine the speed of sound in it.

We could say that the constituent particles are known to have mass. So because the truck is made up of very many protons and electrons, which each have mass, then the mass of the truck is due to all these. However if we repeat the argument above on a smaller scale...

Does the inertia of protons come from the fact that they must be compressed or stretched when they are accelerated, and is the force necessary to produce this acceleration the force required to compress or stretch them.

The point is, that in principle, we need not assume that the presence of distant stars causes inertia in a body, but that the body can 'know' it is being accelerated, because of the compression which occurs in the body when it is.

Gravity dosn't act from one side, but accelerates a body 'throughout' , due to the curvature of spacetime (according to GR), so compressions don't occur when gravity accelerates a mass. However, this is OK, because bodies don't 'show' inertia in the gravitational field, all bodies accelerate equally.

What does anyone think of this as an alternative to Mach's principle?

John Hunter.