Sure Lightarrow. I'm not disputing a proper mass, or the definition of how this 'mass energy' comes to be. What makes you want to define it this way is the same thing that bothers me I think. The impossibility of measuring this energy locally in a uniform motion. It won't exist in any local measurements I know of, and placing it in the vacuum becomes just too weird for me. If it is existing as a relation to the vacuum it has to be different from a Higgs field. Then again, a momentum is also a locally untouchable experimentally, until a collision or annihilation. When Einstein thought up the stress energy tensor it seems to me that he described it from a continuum, a whole SpaceTime of a defined magnitude in which you had certain parameters, as motion and mass (energy), that would tweak this continuum, locally defined. Then again, if you can't measure it, what is it and where does it reside? I can construct three observers in different uniform motion at different velocities, and they all will define two different time dilations per observer. They also will define a different energy which now either is defined to exist inside this continuum 'simultaneously', which I think it has to be defined as, if I want it to be a SpaceTime continuum, or it all becomes a illusion to me

A Higgs field is either a local definition or I should meet a same problem defining what this acceleration is. And that is locality to me. The one place where you can define things, and agree on measurements.

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In a continuum simultaneity must exist, as I think. The moment I start to define a continuum locally, disputing that we can agree on a SpaceTime position experimentally I either has to define 'time' as a illusion, to keep my continuum, or let the continuum disappear. And it seems very strange disputing the fact that we all die. At the moment we're 7? (and assorted others) billion experiments proving that fact. A rather heavy indication of there existing a 'time' I would say. So then you get rid of the continuum, but that leaves you a universe, or SpaceTime, that only exist locally described, constants, principles, rules and properties joining it.