MIAMI, United States (AFP) – A fourth gravitational wave has been detected — this time with help from Italy-based equipment — after two black holes collided, sending ripples through the fabric of space and time, researchers said Wednesday. Gravitational waves were predicted by Albert Einstein a century ago as part of his theory of general relativity, but the first hard evidence of their existence came only in 2015, when two US detectors found the first such signal. The […]