If the stars we see are light from millions of light years away and they see our Sun’s light the same, is the whole universe “existing” in the same time?

Question

Hi all, I didn’t know how to formulate the question in a non stupid way so I’ll explain.

If the light we see from stars in the sky are actually “the past” as they’ve left their source light years ago, from another point in the universe another planet sees our Sun’s light the same way, correct?

If that’s the case, if there was an “universal year” or an “Universe’s current year”, would all the stars and planets be living in the same year?

Maybe I am 5, I feel 5 right now.

Thanks 🙂

In: 466

Answer 1

Hi /u/Almeidaboo!

>[T]the stars we see are light from millions of light years away

The distance of stars visible to us with the naked eye is one of the exceedingly rare instances where laypeople **overestimate** astronomical distances. The furthest star we can see unaided is V762 Cassiopeiae, which is 16,300 lightyears away from us. Thus, all the starlight we see is less than 17,000 years “old”.

>is the whole universe “existing” in the same time?

Sort of. Not really.

The theory of relativity does indeed tell us, that two events which occur simultaneously from the point of view of one observer O do not generally occur simultaneously for another observer O’ moving at a high speed relative to O.

Furthermore, two events A and B which occur in the order A, B from the POV of observer O may occur in the order B, A from the POV of O’.

**However**, the order of two events A, B can only be different to two observers, if they are not causally connected. That is, if event A can theoretically influence event B under the constraint of traveling at or below the speed of light, then the order of events is the same for all observers.