The universe is a big place, but do we really know how big? Scientists think they do, and use an array of methods to figure it out. Here are our CliffNotes.

If we know how big the observable Universe is, why can't we figure out how big the unobservable part is?

The universe exists because matter and antimatter are not good friends. Is there a scientific reason why the universe exists?

The cosmos has been expanding since the Big Bang, but how fast? The answer could reveal whether everything we thought we knew about physics is wrong.

A big Hubble constant also means a young universe: if the cosmos is expanding quickly, it has gotten to its present size quickly, and the Big Bang is relatively recent. A Hubble constant of 100 ...

How big is the universe? Could it be infinitely large? If the universe has an edge, what is beyond the edge? And if the universe had a beginning, what was going on before that? Our experience of ...

But knowing how big the observable universe is doesn't tell us everything we know about how many atoms are in it. We also need to know how much matter, or stuff, is in it.

But knowing how big the observable universe is doesn't tell us everything we know about how many atoms are in it. We also need to know how much matter, or stuff, is in it.