Continuing the discussion from Is Cosmic Expansion the Best Fit Model?:
Somehow I think there are in fact cosmic standards for these things. Aren’t there @physicists?
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I am not sure what @nwrickert meant by “standards” of time or distance. Whether these really exist or not depends on what is meant by these “standards”:
- In terms of practical measurements, there are standards that are nonlocal, e.g. standard rulers (such as the baryon acoustic oscillation) that can serve as “standards” for distance.
- Philosophically, every frame is equivalent in general relativity, i.e. there is no “standard” distance or time in this sense. So if this is what one is referring to, one can say that there is no “standard” distance or time.
- However, certain spacetimes have natural frames that are “more preferred” than others. For example, in the expanding cosmology, there is a frame that is expanding along the Universe. This might also be what one meant by “standard” time and distance.
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Can we rule out the possibility that the cosmos is a homeostatic system with a local appearance of aging and expansion?
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I have not come across a model that fits all the evidence the way the expanding cosmos does. This does not mean that such a model does not exist, but I suspect it to have to be very concocted or ad-hoc.
Edit:
As an example, the model that @Dan_Eastwood jested about on the other thread:
WHAT IF it’s not expansion … trying to wrap my head around this one … if the universe is not expanding, then the frequency of light is slowing down over time …
Has been proposed before, and failed the Tolman Surface Brightness test.
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