There is a universal now. Just because you are in a different location it doesn't change what now is. We have clocks all over the earth synced close to each other depsite being located in different places. While physically it may be impossible to perfectly sync clocks in theory we could have theoretically synced clocks.
I don't think this is true. General relativity says that time slows down under greater gravitational forces. This has been experimentally proven. Therefore clocks at different elevations run at different speeds.
Yes. In addition, Special relativity says clocks moving faster through space tick slower than clocks that move more slowly.
So let's say you're a GPS satellite. GR says your clock ticks too fast because you're farther from the center of the earth's gravity well than the wristwatches of people on the surface.
But SR says your clock ticks slower than a wristwatch on the surface because you're whizzing through space at ~15,000 km/hour.
Which is right? Both. And they do not exactly cancel each other out (in general). So both GR and SR have to be taken into account to make GPS satellites produce accurate locations and times.
You can refer to it differently, but time progresses at different rates at the different places. So in your example, physical processes (i.e rusting, aging) at place B happen 2X as fast as those at place A.
>but time progresses at different rates at the different places.
What's the problem? We can still have a now defined as I mentioned above. t1=t2=0 at the start. Now when t1=x for place A will refer to when t2=2*t1 at place B.
"the distances and even temporal ordering of pairs of events change when measured in different inertial frames of reference (this is the relativity of simultaneity); and the linear additivity of velocities no longer holds true."
>the distances and even temporal ordering of pairs of events change when measured in different inertial frames of reference (this is the relativity of simultaneity)
I'm not saying to use different frames of reference. I am saying to use a single universal frame of reference.
