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 🙂
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> 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?
Yes.
> 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?
They might be, but there’s no way for us (or them) to know.
The five-year old explanation:
Bobby lives on one side of town. Alice lives on the other side of town. Neither family has phones or Internet or chimneys for smoke signals (it’s a very poor town).
The only way Bobby and Alice can talk to each other is to ride a bicycle across town — about a 30 minute bike ride — and deliver the message in person.
Alice’s little brother is shooting baskets. He’s up to ten consecutive baskets! This is big news (it’s also a very boring town), so Alice hops on her bike and rides 30 minutes across town to tell Bobby the news.
She arrives at Bobby’s house. “Bobby, Bobby,” she yells, “my dumbass little brother Toby hit ten free throws in a row!”
Pete — being appropriately amazed — says “THAT’S AMAZING! How many freethrows is he up to *right now*?!?”
So. Can any of these hypothetical people (Bobby, Pete, or Alice) know the answer to this question? Of course not.
We can make guesses about what Li’l Dumbass Toby is doing right now: maybe he’s up to 300 free throws, maybe he missed at #12, maybe he quit and went inside for a sandwich … or maybe the *entire house was swallowed by a sinkhole* killing Toby and Alice’s parents and Alice is now an orphan.
There are many things that could be happening with Toby *at the same time* Bobby and Alice are having this conversation, but there is *no way for Bobby and Alice to know for sure* because **information** from that side of the town can only travel to the other side of the town at the speed of bicycle.
Now let’s replace this with astronomy.
Star 1 is on one side of the galaxy. Star 2 is on the other side of the galaxy.
The only way information from Star 2 to get to Star 1 is for electromagnetic radiation (e.g. light or radio waves or whatever) to travel at the speed of light across the galaxy — about 100,000 years from Star 2 to Star 1.
Star 2 is unstable and the wavelength and intensity of the light it is giving off indicates it might explode as a supernova. This is big news! That light that indicates “possible supernova” starts traveling across space, across the entire galaxy at the speed of light, as one does if you’re light.
100,000 years later that light hits a telescope on a tiny blue marble of a planet. And the astronomer looking at that light (whose name is Bobby) says “Dude, dude, look at this light — this star looks like it might explode!”
The other astronmer, Pete — being appropriately amazed — says “THAT’S AMAZING! Has it exploded or is it still there *right now*?!?”
As above, we can only make guesses about whether Star 2 exploded alread or hasn’t yet.
There are many things that could be happening with Star 2 *at the same time* Astronomer Bobby and Astronomer Pete are having this conversation, but there is *no way for them to know for sure* because **information** from that side of the galaxy can only travel to the other side of the galaxy at the speed of light.
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