Take the 2-minute tour ×
Physics Stack Exchange is a question and answer site for active researchers, academics and students of physics. It's 100% free, no registration required.

According to recent measurements our observable universe is roughly 93 billion light years in diameter; also it appears (according to WMAP measurements) that spacetime is flat.

Supposing space is infinite.

It seems to me that it isn't outside logical possibility that there is another observable universe completely outside of our observational range and so far away it has no appreciable effect on the curvature of our universe.

Note, I'm not using the word universe here as everything in space.

share|improve this question
Perhaps you might be interested in Tegmark's Parallel Universes, arXiv:astro-ph/0302131, in particular Level I: Regions beyond our cosmic horizon ("the uncontroversial cosmological concordance model"). –  Glen The Udderboat May 13 '13 at 22:22
I'm not clear on what's being asked. How can an "observable universe" be "completely outside of our observational range?" Doesn't that mean it's observable and unobservable, which would be a contadiction? Why do you only care about this other region's effect on the curvature of our region? All interactions propagate at a maximum speed of c, including gravity, which is what propagates curvature effects (gravity is curvature). To the extent that I understand what's being asked, I think the answer is yes, cosmological event horizons exist, and 2 observers can be in disjoint observable regions. –  Ben Crowell May 13 '13 at 22:29
@BenCrowell (and Mozibur) I presume that te OP means (non-intersecting) Hubble volumes? –  Glen The Udderboat May 13 '13 at 22:31
@Crowell: It's difficult to express exactly what I'm saying given I'm not aware of current terminology here. It would perhaps be easier with a diagram. I think my title says it a lot better than the body of the question. –  Mozibur Ullah May 13 '13 at 22:38
@Gugg: I don't think that interpretation makes sense, since the OP uses the word "observable," and the Hubble volume is smaller than the observable volume: physics.stackexchange.com/q/12819/4552 –  Ben Crowell May 13 '13 at 22:38

1 Answer 1

up vote 3 down vote accepted

As noted above in comments, I'm not competely sure I understand the question. But anyway, I'll give it a shot.

The answer is model-dependent. The standard cosmological model at the moment is the Lambda-CDM model. This model has various parameters. Depending on these parameters, the spatial curvature can be positive, negative, or zero. Observation puts (model-dependent) bounds on the spatial curvature: What is the curvature of the universe? Given these bounds, we can put (model-dependent) bounds on the size of the universe: Size of the universe . We then find that the universe is much larger than our own observable region. Therefore the (model-dependent) answer to the question (as I construe it) is yes: there are other regions of the universe in which observers would have observable regions that don't intersect our observable region (and probably never will, given the acceleration of expansion).

share|improve this answer
this is what I was looking for. –  Mozibur Ullah May 13 '13 at 22:55

Your Answer


By posting your answer, you agree to the privacy policy and terms of service.

Not the answer you're looking for? Browse other questions tagged or ask your own question.