The second [...] is defined by taking the fixed numerical value of the caesium frequency, ΔνCs, the unperturbed ground-state hyperfine transition frequency of the caesium 133 atom, to be 9192631770 when expressed in the unit Hz, which is equal to s−1.

Do not matter for relativity though, always same change.

[–] Resonosity@lemmy.world 2 points 7 months ago (2 children)

So are you saying that a caesium-133 atom observed on both the Earth and the Moon to oscillate 9,192,631,770 times will not represent the same absolute span of time?

So, one observer will see those oscillations happen faster than the other?

Does this have to do with the specific gravity fields of both observers, in that those fields affect how the atom oscillates?

Or is there something else I'm missing?

If special relativity is the answer, all good. I'm an electrical engineer trained in classic physics, so I'll rest knowing that I'd probably need to study that to understand the time differences.

[–] NielsBohron@lemmy.world 5 points 7 months ago* (last edited 7 months ago)

So, one observer will see those oscillations happen faster than the other?

Not quite. In each observer's frame of reference, time appears to pass the same; it's only when you try to reconcile the between two objects that are not at rest with respect to each other does relativity show up.

Basically, when you bring someone back to Earth, the observers will find that their watches don't match up even though both observers experience time passing the same way as normal (because the oberserver is by definition at rest with respect to their own frame of reference).

TL; DR: Relativity is a pain in the ass and makes no sense in everyday terms.

edit: disclaimer - I am not a physicist and have not taken physics classes in a decade plus, but I do teach science at a college. I'm going mostly on half-remembered lectures and some random one-off discussions I've had with my buddy in the physics department over the past few years.

[–] ricecake@sh.itjust.works 4 points 7 months ago (1 children)

It's that relativity thing where each person will see the oscillations happening correctly, but when they look at what the other person did, the answer will seem wrong.

The difference is small enough that it really only matters if you're NASA and building moon GPS. MPS?

[–] WldFyre@lemm.ee 1 points 7 months ago

I vote for LPS, Lunar Positioning System, vs our Global one.