Do I look flat in this? (Image ESA)

WE LIVE in a special time. For the past two decades, most of my colleagues and I have been working under the assumption that we can know everything about the universe. We know the amount of matter and energy it contains. We know its shape is flat. We can trace its history from the earliest moments after the big bang and we can even predict its fate. Or at least we thought we could.

Why were we so confident? Exquisite measurements of the radiation left over from the big bang led us to believe that we could work out the curvature of the universe to within a few per cent. In doing so, we have determined how much energy the universe contains and that most of it is in an exotic form called dark energy, which is driving the expansion of space.

However, recent discoveries have left me wondering if these claims were premature. As we learn more about dark energy and its effect on the expansion of space and time, we find that dark energy and the shape, or geometry, of the universe are worryingly intertwined.

By changing our assumptions about dark energy we can radically modify our constraints on the shape of the universe. Equally, without a much more precise measurement of the geometry, it is impossible to determine the nature and evolution of dark energy. Our picture of the universe has, to some extent, been blown wide open again.

This state of affairs has serious implications for how we proceed in our exploration of the universe. A host …