There is no such thing as a universal frame of reference is the somewhat depressing outcome of Einstein's theories.
Even though time runs faster on sattelites, and the signal delay differs based on position. Because the vectors of sattelites and the moon is constant, as well as the moons gravity, you could calculate what those offsets should be and synchronise clocks anyway.
To put it another way, you normalise the clock drift and the delay, whats left over is the same clock drift you'll need to account for when you have a quartz clock in your computer and a time server that runs an atomic clock.
The point being, clock drift can become a huge issue unless you define a specification that allows any equipment to sync up with any other clock in Time And Relative Dimensions In Space.
Relativity doesn't make time-keeping impossible. It just requires more clarity. UTC was implemented after Einstein passed away.
As far as we can tell any observer would come to similar conclusions about that reference frame would be. It’s just not a particularly useful reference.
If you want to stick to special relativity, the Andromeda paradox will show the problem with simultaneity with distance, and Einstein's train thought experiment about trains will show the problem of simultaneity with high speed.
The order of events, timing of events, and even causal structure of events are not fixed.
Even the Conventional Celestial Reference System is only quasi-inertial, only inertial like over small periods of time.
The incredible smoothness of the earth approximating a co-rotating frame with a high error tolerance is the only reason we can treat time as absolute on the surface of the Earth.
But to derive the new definition of the Kilogram requires lots of corrections as do modern atomic clocks.
Don't confuse the ability to choose a reference frame with the Newtonian concept of universal reference frames.
When making measurements SR is a framework that allows you to pick any reference frame that is convenient, but the speed of causality(light) prevents the existence of a universal reference frame.
Isn’t that like, speed of light or wavefront of event propagation in the universe isn’t consistent but unavoidably potato shaped - but if so, wouldn’t it be at least difficult to have multiple potatoes intersecting, or potato being shaped like Klein bottle? Self intersecting potato shaped space-time would be cool, though.
Really this is beyond typical human intuition and requires math, but here is a quick minutephysics video that quickly demonstrates fairly well it without me typing out a bunch of math that no one wants anyway.
You can calculate observed order of events for any reference frame from any reference frame. Thus they are fixed once everyone agrees to using a given reference frame.
It’s not much more complicated than seismic detectors recording the seismic waves from an earthquake at different times based on their location. Sure detector X see earthquakes in order A, B, C and detector Y sees them in order C, B, A they would both agree that detector Z should see them in order A, C, B based on it’s location, the timing of the events, and wave propitiation speeds.
It only seems unintuitive because you aren’t used to accounting for such issues.
For constant velocity motion in flat spacetime:
Δτ^2Δs^2 = c^2Δt^2-Δx^2-Δy^2-Δz^2
The spacetime interval is invariant, but notice it is also a scaler that combines space and time, and note that time is multiplied by c^2.
Also note Δt is the time as observed but an inertial observer that is present at both events.
You have three types of intervals here represented by one scaler.
Timelike: Δτ^2 > 0 Spacelike: Δτ^2 < 0 Lightlike: Δτ^2 = 0
In the case of Δτ^2 = 0, that is equivalent to an inertial observer that is present at both events at the same time. Which will seem to be simultaneous.
Δτ and Δt are practically the same in situations we commonly experience and an assumption of constant velocity motion in flat spacetime is usually accurate enough.
And will an assumption of constant velocity motion in flat spacetime, you can CHOOSE a Δτ that is 0.
There is no universal reference frame where Δτ =0.
More importantly your observations are of the past for distant observers, and don't have a universal concept of 'now' outside of the local case.
Mission Control on earth, a moon base, and mars would all experiencing time at a different rate and those rates would vary based on the orbits of each body. However assuming we needed extreme precision, such as telescope interferometry, people can pick one of them arbitrarily or perhaps due to politics some arbitrary 4th option. Whatever their choice everyone’s timelines based on that choice end up being absolutely identical.
The math simply works without any ambiguity. So because there’s an obvious choice based on the actual universe we live in, ie maximum amount of time since the Big Bang, then in theory trillions of civilizations across many different galaxies might all use the exact same reference even if no particle experienced it.
Edit: Well not exactly the same there’s uncertainty for such calculations but effectively the same.
I wasn't suggesting we should have a true universal time, I was suggesting that we rename the mislabelled universal coordinated time that we already have to something else... :) )
All for zero benefit because the Earth is variable number of minutes from Mars so there will always be variation. Mars day is different from Earth have to calculate Earth time anyway.
Which is exactly what OP was suggesting, everyone else went off on a tangent.
That means everything happening is happening forever, all at once.
I guess if you live a shitty existence, then its infinitely shittier, but if not, its infinitely meh.
Guess it depends on how you look at it.