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Is a wheel oval just because we see it sideways? If you rode around 24 hours you would have a smooth road! Mass/energy and space/time in special relativity are not absolute, so by finding lots of observers, we might find who is at rest or in motion, I believe this is necessary to uphold energy conservation.

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Changes in redshift mean changes in thermodynamics. A flame or other chemical processes like the shift of electrons in the atoms on the slower starship will burn faster. On the high speed ship the stove on the starship would never burn sometimes, while on the low speed ship the observer might say it would.