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Question
Suppose you are told that the linear size of everything in the universe has been doubled overnight. Can you test this statement by measuring sizes with a metre stick? Can you test it by using the fact that the speed of light is a universal constant and has not changed? What will happen if all the clocks in the universe also start running at half the speed?
Solution
The validity of this statement cannot be tested by measuring sizes with a metre stick because the size of the metre stick has also doubled overnight.
Yes, the fact that the speed of light is a constant and has not changed can serve as proof.
If the linear size of everything in the universe is doubled and all the clocks in the universe start running at half the speed, then we cannot test the validity of this statement by any method.
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