# Simultaneity (working backwards) and absolute time [closed]

If two events happen at different times and at different places in two different reference frames (observers) couldn't the observers work backwards (considering the finite speed of light) to find out when and where the events took place ? Is this God's-eye perspective correct ?

## closed as unclear what you're asking by WillO, John Rennie, Jon Custer, Kyle Kanos, Aaron StevensJul 25 at 17:15

Please clarify your specific problem or add additional details to highlight exactly what you need. As it's currently written, it’s hard to tell exactly what you're asking. See the How to Ask page for help clarifying this question. If this question can be reworded to fit the rules in the help center, please edit the question.

• If an event takes place in front of me but behind you, can't we work backwards to figure out where it took place? – WillO Jul 18 at 11:03
• If a series of events happen in a single reference frame, couldn't the observer work backwards to find out when and where the events took place relative to them? It's not clear to me why you expect this to be any different than most observations. – JMac Jul 18 at 12:08

Assume that observer A is next to the earth. Let's say that event $$E_1$$ took place in earth at $$t_1=0$$ according to A, while event $$E_2$$ happens at $$t_2$$ in the sun. Of course, A should consider the distance between earth and sun to measure the time of event $$E_2$$ correctly. That's, if he has received a signal from sun at let's say $$t_{2i}=8~min$$ he should subtract it by $$8~min$$ as well. So he will asume that $$E_2$$ took place at $$t_2=0$$ in reality. (This is "couldn't the observers work backwards (considering the finite speed of light) to find out when and where the events took place?" sure they can. They should.). So according to A, $$E_1$$ and $$E_2$$ are "simultaneous" even though he has not received their signal simultaneously. As you can see, location of A doesn't matter, because he can always measure the distance between himself and the event and by substracting the time that light crosses this distance, he will find the "real" time of events.
Now let's assume another observer, B, who is moving at velocity $$v$$ w.r.t. A. Just like A, position of B doesn't matter, he can substract extra times easily. However, there is something weird about B. according to Lorentz transformation, you can see that B will disagree with A about simultaneously of events. B says that although $$E_1'$$ happened at $$t'_1=0$$, $$E'_2$$ took place at $$t_2'=-\gamma vD/c^2$$ where D indicate the distance between A and the sun. Why is that? Well that's another question. But as for your question, they can, and they should, but in the end of the day, they will disagree.