Now, quite naturally (as it seems to me, at least =) I came to the question stated in the question title. Here is what I mean: time is measured in different units, which all stem from a second (which is a SI base unit). According to wikipedia, as one (probably) would expect (italic is mine):
... the historical definition of the unit (second) was based on this division of the Earth's rotation cycle ...
It is quite logical, since initially most of the things we measured time for were directly related to the Earth and it's rotation (i.e. ships leaving at the exact time etc.).
Following the quote above:
... the formal definition in the International System of Units (SI) is a much steadier timekeeper: 1 second is defined to be exactly "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" (at a temperature of 0 K). Because the Earth's rotation varies and is also slowing ever so slightly, a leap second is periodically added to clock time to keep clocks in sync with Earth's rotation.
With that said, moving to my questions now:
- What does it actually mean to say that on planet A time is twice as fast as on planet B? Does it mean that while 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 (at a temperature of 0 K)" will occur on planet B — on planet A 18,385,263,540 such radiations will occur?
- Are the radiations in Caesium-133 are consistently relative to the properties of all other elements? Basically what I am asking here is: if we were to change the said radiation of caesium-133 in the whole universe, then the physical world, as we know it, would completely change (if not cease to exist), is this correct?
- Any stable (under given conditions) property of any element could have been selected as a basis for second, and Caesium-133 was picked up, pretty much, arbitrary, am I right in stating this?