The problem with most alternative suggestions to relativistic time dilation is that they would also result in time-incoherence and bad spectral blurring.

Ordinary Doppler shifting would result in similar light cones to relativity, but not time dilation as calculated in relativistic models. When distant supernova light curves are studied, the number of days the event occurs over is assumed to have expanded by the 'z factor', correlating with redshift of the spectral lines. Simple 'tired light' models generally assume energy has been depleted from the spectrum; and any time element lost during radiation transfer and such is assumed to be trivial (yes? No?). ExpErd man has a point, but it would help to elaborate a little.

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jwj

It's ok not to know. We should try harder to find out.