observable-universe

Astronomers' galaxy counts have swung from 100 billion to 2 trillion and back to hundreds of billions. Here's why the number keeps changing, and what it actually means.

The observable universe is 93 billion light-years across, but the real universe is far bigger — possibly infinite. Here's how we know.

Dark flow is the claimed observation that galaxy clusters across the observable universe are moving in the same direction, toward a region beyond what we can see. If real, it could indicate a gravitational pull from structures outside the observable universe. The claim is controversial and not accepted by most cosmologists.

The observable universe is 93 billion light-years across. The full universe is bigger — possibly infinitely so. Here's what we can measure, what we can't, and why.