# Understanding how the rate of time changes

The rate at which time passes is relative depending on speed and the gravity as predicted in general relativity. This theory has been tested by scientists by comparing two identical atomic clocks, one on Earth the other on a rocket speeding at escape velocity. The initially synchronised clocks measured different amounts of time when the rocket returned.

Given the current scientific definition of time rate,

"The second is the duration of 9 192 631 770 periods of the radiation corresponding to the transition between the two hyperfine levels of the ground state of the caesium 133 atom",

does this mean that 1) the above definition is only true on the surface of an object with Earths mass and 2) the fundamental properties of sub-atomic particles change on the speeding rocket so the rate at which electrons of the caesium 133 atom oscillate between the two energy levels is different?