# Is there experimental evidence that gravity affects time itself instead of time measurement?

Atomic clocks tick differently with different gravity. That's a fact. This implies either one of the following statements: (1) Gravity affects time itself OR (2) Gravity affects time measurement only

Relativity supports hypothesis 1, but I wonder: is there any experimental evidence against hypothesis 2? Or the two are equivalent?

Example: a clock on the Earth measures 1 minute while a clock in the space measures 2 minutes. Why do we say that "time is slower on Earth" instead of just saying "clocks tick slower on Earth"? How can we be experimentally sure that time-dilation is real, and not just an illusion due to the side-effects of gravity on instrumentation?

• Most physicists simply consider time to be what clocks measure. If you believe clocks don’t measure time, how do you propose to measure it? – G. Smith Jun 10 at 22:42
• Do you think different types of clocks will measure different times because they are affected by gravity differently? – 511mev Jun 10 at 23:44
• Maybe. Let's imagine an "human clock". Will he perceive time differently than an atomic clock in his same reference frame? Will he perceive time in an "absolute way" and see the clock run slower/faster? I mean: the theory says he wouldn't but this cannot be experimentally proven. Aside from my "human clock" example, I'm just asking: is time-dilation experimentally confirmed by more than one type of time measurement? – agdev84 Jun 11 at 0:00
• Yes, by the decay times of unstable particles. The “internal clock” of every kind of unstable particle runs slow by the same $\gamma$ factor when the particle is moving fast. For example, this is why muons produced in the upper atmosphere have enough time to reach the surface. – G. Smith Jun 11 at 0:21
• Thanks, I was missing this piece of the puzzle – agdev84 Jun 11 at 0:52