Relativistic worldline differences produce real, measurable physical consequences. These consequences are commonly described in the language of time dilation, and time dilation as a between-frames registration relation is real. But the consequences themselves are not produced by an intrinsic slowing of any clock. A massive object's proper time accrues locally along its worldline at its own proper rate, always. Dilation is the between-frames relation by which one frame's accumulated proper time is registered through another frame's measurement apparatus. The relation is genuine; the registration is genuine; the consequences are genuine. What is absent is any modification of either frame's intrinsic proper time. This paper states a narrow no-go: there is no such thing as a frame's own dilated time. A frame's intrinsically dilated time would have to be definable without reference to any other frame, but the only time-quantity definable using only quantities belonging to that frame is the proper time integrated along its own worldline. Any modification of this quantity requires reference to a second frame, a coordinate choice external to the first, or a registration by another apparatus — each of which violates intrinsicness. The familiar physical consequences described in the language of dilation — muon survival, asymmetric twin aging, GPS clock corrections — are determined by integrated proper times along worldlines and by the correct between-frames registration relation. They are not consequences of any frame's clock being slowed in itself. Dilation lives at the registration interface, not inside the object. Standard Special Relativity is preserved throughout. The only claim is that the dilation relation is not licensed as an intrinsic property of either party to it.
John Christian William McKinley (Sat,) studied this question.
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