Ask Ethan: Is the Universe the same age everywhere?

"For stars within our own galaxy, those distances are measured in light-years, up to tens-of-thousands of light-years for the most distant Milky Way stars. For other galaxies, those distances range from hundreds-of-thousands of light-years to billions of light-years. And for the leftover glow from the Big Bang itself, that distance corresponds to 46.1 billion light-years: the farthest we can see, at present."

"The reason we can't see farther isn't because the Universe just ends after a certain point in space, but rather because our Universe - even though it's expanding - has a finite age: an age set by the onset of the hot Big Bang. That's why, from our perspective, the Universe appears to be 13.8 billion years old, and why the farther away we look, the farther back in time we're seeing."

"However, if we were located anywhere else, the Milky Way would look younger, and we'd see that location as 13.8 billion years old. At least, that's what our intuition tells us. But is that correct? That's what Steven Dzik wants to know, inquiring: "One thing I was curious about is, we always say the Universe is 13.8 billion years old. That implies every place in the Universe is on the same clock. We know it is not. What is the frame of reference in which the Universe is that age?""

"Of course, we only have one perspective to view the Universe from: our own. It's in our own frame of reference that we see the Universe as 13.8 billion years old. Here's what determines what an observer would see. To start, let's talk about what we, ourselves, actually see, and why we see the Universe"

Light collected from any direction arrives after traveling across space from emitting sources to the observer. Because of this finite travel time, distant objects are seen as they were long ago. Distances within the Milky Way are measured in light-years, while other galaxies span hundreds of thousands to billions of light-years, and the Big Bang’s leftover glow corresponds to about 46.1 billion light-years. The limit on how far we can see comes from the Universe’s finite age, set by the hot Big Bang, not from an abrupt spatial edge. The Universe appears about 13.8 billion years old from our perspective, and different locations would imply different apparent ages.

Read at Big Think