About a decade ago, astrophysicists discovered an overlooked signal in some old telescope data: a flash of cosmic energy lasting only a few milliseconds. The signal seemed to have experienced a long and bumpy ride to Earth. Its radio waves had become distorted and were spread across a range of frequencies. This suggested that the radiation had traveled for billions of years, slowing down here and there as it sped through lush galaxies and luminous clouds of gas and dust. ...