Ever since we discovered that distant galaxies are racing away from us, there has been a heated debate over just how fast the Universe is expanding.
At the beginning of the 21st century, we thought we knew the answer. But now, two very different viewpoints have emerged. And they are dividing the scientific community.
The Sky at Night meets leading astronomers and cosmologists on both sides of the debate. Which team has the right answer? Or could both teams be right? If so, we may need to rethink everything we think we know about the Universe.