I have heard that according to Hubble Telescope the universe is expanding like a balloon . A balloon expands in 3 dimensions . The Hubble Telescope sends reports to NASA and NASA said that universe is flat. Is NASA itself confused?

1 Answer
Sep 5, 2015


I am not a cosmologist, but I think the answer is roughly as follows...


I think there's a slight confusion of analogies and terms here.

When we think of the 'Big Bang' we tend to imagine the universe expanding out into three dimensional space from a point, but that's not accurate.

If I understand correctly, the universe is expanding like the three dimensional hypersurface of a four dimensional balloon. That does not however imply that the universe is a three dimensional manifold embedded in some four dimensional space, but it serves as a picture. The key word is 'surface'. The balloon analogy is a lower dimensional analogue.

The universe is approximately flat in that it is broadly uniform. In other words it looks similar in all directions. I guess that's what NASA meant.