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Can't we imagine a bag of clocks at the Big Bang origin that were synchronized and allowed to travel in all directions along with various sections of the ejecta, including one on Earth? One could imagine events that happen at the same clock reading as ours in all the different parts of the visible and non-visible universe.

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The effects of relativity cause that thought experiment to fall apart quickly. I build two clocks, and send one to alpha centauri and back in a spaceship. When the travelling clock gets back to Earth it will be showing a different time (because of time dilation during acceleration). What does "the same clock reading" mean then?

Yes of course they won't show the same time if you bring them back. But the point is to argue that it is possible for there to be a "right now," as defined by what the traveling clock shows, outside of our light cone.

It's totally possible that such clocks could then touch each other in one place, while both showing widely different readings. Which one is right then?

PS: by the way, Poincare proved that there's no way to synchronize clocks perfectly, only up to a some margin.

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