From what I understand, the light from CMB that we can observe is the result of the last scattering from the big bang which happened 380,000 years prior to the pattern we can see.

Referencing: enter image description here

While it seems that the CMB is the limit of our observable universe, I'm understanding that there this isn't the limit to the whole universe. Meaning there is still space from when the CMB pattern was formed and the distance that the universe has expanded out from the origin of the big bang. Is there any way of knowing if this region of space is still active in some scale to the creation energy that the big bang produced but being so far away that it isn't ever going to be observable to us given expansion and inflation?

  • $\begingroup$ Are you asking if we can look far enough back to directly observe the Big Bang itself? $\endgroup$ May 20, 2021 at 16:24
  • $\begingroup$ Essentially I suppose. I'm picturing the BB as a cosmological ground 0 from which all of spacetime extends from. And the CMB is the last light from the recombination that is still able to reach us, and anything "before" that is too far away to be observable. Question being, is there anything between the theoretical place the BB occurred in relation to current space that exists beyond the observable CMB and would it be possible that galactic events on a smaller scale to the BB are still occurring. I apologize if my understanding is wrong, no physics background, just a curious observer $\endgroup$ May 20, 2021 at 16:42

1 Answer 1


The analogy of looking at the surface of a cloud isn't bad, but there's a crucial difference: the edge of the cloud is at a particular place, while the edge of the plasma that produced the CMB is at a particular time.

Light travels at a finite speed, so visible objects that are more distant in space (in any direction) are also more distant in time (in the past direction). Therefore it can be hard to tell the difference between a boundary in space and in time. On top of that, every familiar example of a boundary is spatial. So you'll often hear it said (even by me) that the edge of the observable universe is 46 billion light years away, but it's really better to say that it's 13.7 billion years ago.

The origin of the universe is "behind" the CMB surface, but that means it's at an earlier time, not a more distant position – and in particular, it's not at the spatial center of the universe (there isn't any).

That said, it's possible that part of the initial state of the universe, whatever it may be, is outside our past light cone. That would mean that it hasn't unambiguously happened yet (nor unambiguously not happened yet).

  • $\begingroup$ That totally makes sense, that the light from the CMB that we can observe is from 13.7b ly AGO rather than AWAY. I suppose my question was really based on the idea of whether there could still be some part of the universe that is akin to the event we call the big bang, producing conditions similar to that at the beginning of everything. $\endgroup$ Jun 3, 2021 at 15:46

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