This is why reading the original Lamport paper is useful. This distributed nature of things isn’t due to bad clocks or software or anything. It is an irreducible part of the physics of our world, with relativity. Perfect clocks won’t help with space like separations and different velocities or gravitational force. You have to build communication into it. The causality relationship is inherently a partial order.
This isn’t really true: it’s not got anything to do with relatively specifically, it’s just because of the finite and varying time for messages to travel between points in a distributed system. So it’s about physics but not about relativistic physics. A Newtonian universe with finite speed of light would have the same phenomenon.
That said, the analogy with causality in relativity and light cones etc is useful, and it’s no coincidence that Lamport wrote a book on general relativity before he turned to distributed systems.
What makes relativity special is that everybody agrees on the speed of light. So Alice is passing Bob at say 0.1% of c, she detonates a big firecracker or other bright sudden event, the light from that event forms a big bubble that expands away from her in all directions at speed c.
If you imagine that light is like sound, that it propagates through a medium called the lumineiferous ether, then maybe Bob is at rest relative to the luminiferous ether. If so, he thinks that the bubble is centered on a fixed point in space, and Alice is just a smidge closer to one of the sides of the bubble than she is to the other. Alice, on this account, sees the center of the bubble drifting “backwards” relative to her motion and agrees that she is closer to one edge than the other. If they were right next to each other when the light burst went off, Alice agrees that Bob is the true center of the light bubble.
Special relativity says that there is no ether: Bob thinks that this expanding light bubble is indeed expanding from a fixed point and that Alice is closer to this side than that, and he's right... but Alice thinks that this bubble is expanding out uniformly with herself at the center, and she is also 100% right. According to her, Bob is closer to one side of the bubble than the other, and Alice is the true center.
This has a bunch of consequences. The first one is that it makes the Zeno paradox into a real life thing. To outrun a light beam, you first have to accelerate to half the speed of the light beam, at which point if you look to see how fast it's going away from you, it is receding at speed c still, so you accelerate again to half the speed of the light beam and it is still moving at speed c away from you, and you can never catch up to it. Bob watching this must agree that Alice never catches up to the leading edge, even though he sees her dumping tremendous amounts of energy into her motion. So nobody can accelerate faster than the speed of light, it takes infinite energy to get there. (The converse of this has now become engineering reality, all of our particle accelerators dump huge amounts of energy into small particles and operate under the simplifying assumption that they all max out at speed c.)
The Newtonian universe with finite speed of light is the first situation, the relativistic universe is the second.
No, a Newtonian universe with finite speed of light is consistent. People were able to do physics in that model for two centuries. Special relativity flows from the much stronger and more radical assumption that the speed of light is constant in all frames of reference, which is what the Michelson-Morley experiment showed to be true in our universe.
there is no sense of simultaneity that crosses coordinate systems. there are three relationships between events a and b. a is before b, b is before a, and neither. to get the total ordering, you have to arbitrary and non physically pick a or b.
in that Newtonian universe, good enough clocks and time stamps could be used to break the tie. good enough clocks will never be enough in our universe, there is no canonical way to say of two events separated in a space like way is first. in a newtonian universe you can.
