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Comment by herbstein | Hacker News Reader

If we imagine a third observer in a space craft traveling close to he speed of light, it's possible to construct the scenario in such a way that the pilot of the space craft would observe the two events happening at the same moment. Time is relative

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Ah yes that’s indeed true.

But from the Earth’s reference frame wasn’t the Pluto activity I mentioned earlier simultaneous with what happened 5 hours ago on Earth?

So couldn’t you say from Earth’s reference frame this black hole’s activity happened simultaneously with events 20 million years ago?

As an approximation it can be fine to speak that way in practical matters, but it's dangerous to go drawing any deep conclusions while doing so. Approximations shouldn't be allowed to go outside their operational parameters.

But it’s not an approximation right? In our reference frame it is the truth.

The approximation is the belief that things can happen simultaneously. It is approximating along the fact that we only need to concern ourselves with a single reference frame.

I think the difference in the scenario you proposed is that we can conceive of a practical situation in which someone on Pluto sends a message and waits for a reply. We can then say that they are going to have to wait at least 10 hours to receive a reply. This has meaning.

But when the distances become too great the urge is to resist believing that things have an existence beyond the interactions of particles. There is no practical reality to that object beyond our ability to observe it when the light reaches us.

I get what you're saying but you're also being incredibly dismissive to the common understanding which is still correct, otherwise most astrophysics wouldn't work, because it wouldn't be possible to predict where another planet will be at a later time. It's possible to have two alarm clocks go off at the same instant on two planets, though obviously each will observe the other going off later, after a delay.

It's obviously fair to say they happened at the same time in this scenario.

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