Margherita Hack on the size of our universe

For the original Italian version, go here.
Some Einsten's musings about this question.

Transcript

Science

Continuing our series with the eminent 90-year-old Italian astrophysicist Margherita Hack, Euronews asked whether she thought the universe was finite or infinite?

It could be infinite. We know that the universe is flat. It means it obeys Euclidean geometry.

If the universe were finite and closed like the surface of a sphere... obviously we couldn't be certain it's finite. But from the way in which light propagates and certain measures that could be taken on the structure observed in the early universe, you can deduce that our universe is flat.

But what does a flat universe mean? That it's infinite. It could be infinite as the Euclidean universe the one we study in geometry and high school.

But the concept of infinity is almost a philosophical concept. Not really. There's a practical example. Numbers. Numbers are infinite. So the concept of infinity is one very palpable when you think about numbers.

But numbers are something that have been created by man. Well, the universe is there and it's almost scary to think of it as something infinite. But if we think of something finite then what is there outside it? It seems to me even more difficult.

I prefer much more the hypothesis of an infinite universe. It's always been there. It's always existed and it has no borders. We think of the universe as everything that exists, but it's a mistake we've made before that the earth was unique and the sun was the centre of the universe, that our galaxy was the center, which was unique. It might be that what we call the universe is just one of countless other universes. And so this could be yet another solution. What's
outside our universe? Other universes.