I don’t really understand it, could someone explain in basic terms?
Are we saying if a star is 120 million lightyears away, light from the star would take 120 million years to reach us? Meaning from the pov of time on earth, the light left the star when the earth was still in its Cretaceous period?
In: 292
Answer: It is tricky.
When we look out into space, it takes time for light to reach us. 8 minutes for our dear Sol to reach Tellus (Earth).
So as we pan out we learn that our galaxy is pretty big. About 150 thousand lightyears across. Oh.
Means that most stars emitted their light before we could catch them. The stars are not there anymore. But gravity is also travelling at the speed of consequence, so in that sense they are there. We feel them as they was there now.
And it hits a border. We have learned that the oldest light hit us about 13.7 billion light years ago.
This is called the big bang. It was very smol and it didn’t bang.
One way to understand this is to realise that our universe is expanding. And it is expanding everywhere. There is no center.
So our border is 13.7 billion years away. Now if you could hop n’ skip to that border, it would be 46 billion light years away as spacetime has been expanding during all that time.
And if you could magically teleport there and look back at our home; it would look the same. A 13.7 billion year barrier border that is background radiation. Because our Sol didn’t happen yet. Or it did, but it will take 13.7 billion years to even notice the beginning and end of the star that Sol was made from. It took a while.
This is our observable universe and it must be a lot smaller than the actual universe. Or so we like to think.
So what is outside of our observable universe? The cop out answer is more stuff. In the same way we see galaxys all over the place, you should see the same wherever you are. It could be infinite as far as we know. But we don’t know.
Yet..
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