Black holes in the early universe Artist's impression of an early supermassive black hole. (Courtesy: NASA/JPL-Caltech)"> Black holes in the early universe Artist's impression of an early supermassive black hole. (Courtesy: NASA/JPL-Caltech)

Imagine walking along the cable of a suspension bridge. You see the cable as a narrow path stretching forward and backward. But an ant crawling along the same cable experiences an extra direction: it can move around the cable’s curved surface, a direction effectively hidden from you. Our universe might work in a similar way. Although we see three dimensions of space, physicists have long considered the possibility of additional dimensions that could exist but are too small for us to notice.…