Will the big bang be seen as 13.7 billion years ago by all observers in the universe regardless of their velocities ? I mean I read that in SR one has to abandon notions of simultaniety. And an event which has already occured for one observer may be in future for another observer. I guess for cosmological purposes GR is used so things must be drastically different from SR. So my basic doubt is that since we have abandoned notions of simultaneity , how can big bang be 13.7 billion years ago for all observers. Note - newbie here and don't have physics background,so please bear if this question is outright silly. Please point out where I am goofing up. also if this has been already discussed please point out the thread. cheers.