Imagine a car race where the recording didn’t start at the beginning. On video, the car appears to slow down as it nears the finish line, when in reality it’s accelerating. A similar oddity popped up in the study of the Universe.

In the 1920s, Edwin Hubble and Georges Lemaître found that galaxies are moving apart. Later, Saul Perlmutter used distant supernovae to prove that this expansion is accelerating. Today, two large surveys give conflicting results. The first, studying distant galaxies and quasars via spectral analysis of their light, records strong redshift and barely notices the nearby neighborhood. The second covers that as well. When the first survey’s data was combined with observations of the ancient light of the Big Bang, gravitational lensing by massive objects, and properties of ghostly neutrinos, it turned out: the Universe might be decelerating today. But once nearby galaxy results were added, acceleration returned.

It’s like a truncated video recording — without the start, it’s easy to misjudge the pace. Telescopes need to collect more data on nearby galaxies. Then we’ll discover whether the Universe keeps accelerating, or if deceleration will lead billions of years from now to a reversed collapse.