But if “time” is the thing that clocks measure, and they change how long they say a “second” is under a gravitational field, why not say that the clocks are still measuring time, but it is the time itself that has been altered? If you say time has not changed, then you must have some invariant reference to measure it against to show that it has not been altered by the gravity. What is that reference?This question is of no relevance to the conversation. The changes in gravity affect atomic clocks to a degree predicted by relativity. There is no reason to say that the abstract, intangible noun, time, is affected. You might as well try to convince us that gravity affects love.