Dear Dr B: What does the universe expand into?

“When the universe expands, into what is it expanding? In what medium is it expanding? Is the universe like a bubble in a higher dimension something?

[Anonymous], Indiana, USA”



[image: luftballon-profi.at]


This is a very good question and one, I should add, I get frequently. It is, I believe, to no small part caused by the common illustrations of a curved universe: it’s a rubber-sheet with