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Comment by Swizec | Hacker News Reader

> Universe is our local observable space-time

So if we observe something beyond what is currently observable, would that not become observable and thus part of the universe?

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You're in a room. You give it label "room". Then you find a door, you go outside of the room, you don't call everything outside "room", you give new things new names.

For now we're stuck in our universe, we know it's expanding (in something, potentially). So we preemptively give the name "cosmos" to EVERYTHING. It's entirely possible that cosmos is equal to universe. But it's also possible there are other universes out there, or something entirely different.

In your scenario, the door is a clear divider between "room" and "not room." What's the equivalent divider in the universe scenario?

The term observable when used in the context of the observable universe doesn't necessarily mean something we can actually measure or look at, but rather that which could theoretically have interacted with anything we could interact with based on the speed of light, the age of the universe, and cosmic expansion. Think of it as a bubble of time and everything outside of it hasn't happened yet.

Yes, but it might also be the case that we don't observe something outside of it, but rather infer the existence of something outside of it through some other phenomenon (which is much more probable - observing something outside of the visible universe as we know it would violate relativity). In that sense, it would be there, but would never be visible.

That's a really interesting question. If something is indirectly observable (you can observe/measure its effect), does that make it observable or not?

Transitivit would say yes. If A implies B and B implies C then A implies C. That is, if you can observe A and that implies B, then you can observe B. Which makes it observable, no?

All observations are inferences from indirect phenomena.

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