Travel far enough in the universe and you could end up back where you began. Measurements from the Planck space observatory have shown that the universe might be shaped like a sphere rather than a flat sheet, which would change nearly everything we think we know about the cosmos. The Planck observatory, which operated from 2009 to 2013, mapped the cosmic microwave background, a sea of light left over from the big bang. One set of observations showed that there was more gravitational lensing – stretching of the light due to the shape of space-time, which can be distorted by...