Practice Tests
IELTS Reading (AC) Task 1 #179

A. Gravitational waves are invisible ripples in the fabric of spacetime, created by some of the most violent and energetic processes in the universe. Albert Einstein first predicted their existence in his general theory of relativity in 1916, proposing that massive accelerating objects—such as two black holes orbiting each other—would disrupt spacetime in a way that would send waves of gravitational energy propagating outwards at the speed of light.

B. For a century after Einstein''s prediction, gravitational waves remained purely theoretical because they are incredibly difficult to detect. The ripples that reach Earth from distant cosmic events are minuscule, distorting spacetime by a tiny fraction of the width of an atomic nucleus. Detecting such a small disturbance required the development of extraordinarily sensitive instruments.

C. The breakthrough came in 2015, when the Laser Interferometer Gravitational-Wave Observatory (LIGO) made the first-ever direct detection of gravitational waves. The signal came from the cataclysmic merger of two black holes more than a billion light-years away. LIGO consists of two identical detectors, located thousands of kilometres apart, each with two long perpendicular arms. A laser beam is split and sent down each arm. When a gravitational wave passes, it subtly stretches one arm and compresses the other, causing a tiny change in the laser light pattern that can be detected.

D. The ability to detect gravitational waves has opened up a completely new window to the universe. It is a new form of astronomy, allowing us to "hear" cosmic events that do not produce light, such as the collision of black holes. It provides a new way to test the fundamental laws of physics in extreme conditions and to study phenomena like neutron stars and supernovae. The detection of gravitational waves was a monumental scientific achievement, confirming a century-old prediction and heralding a new era of cosmic exploration.