Gravity Waves

Episode #6 of the course “Strangest Things in Space”

First predicted by Albert Einstein in 1916, gravity or gravitational waves are a part of his theory of general relativity. They are disturbances or ripples in the curvature of the space-time continuum created by the movement of matter. According to the First Law of Thermodynamics, which states that neither matter nor energy can be created or destroyed, matter from the beginning of time should still be rippling through the cosmos, albeit at less strength.

The effect of gravity waves is so infinitesimal that Einstein himself doubted that they could ever be detected. But, in 2016, gravity waves were first detected by the twin Laser Interferometer Gravitational-wave Observatory (LIGO) detectors, located in Livingston, Louisiana, and Hanford, Washington, USA. The observed gravitational waves were produced during the final moment of the merger of two black holes, 1.3 billion years ago.

LIGO interferometer uses lasers light split into two beams that travel back and forth down the 2.5-mile (4-km) long arms. The beams are used to monitor the distance between mirrors precisely positioned at the ends of the arms. When a gravitational wave passes, the distance between the mirrors changes by a tiny amount. A change in the lengths of the arms smaller than one-ten-thousandth the diameter of a proton (10^-19 m) can be detected.

What makes gravitational waves so interesting is that they are believed to be unaltered as they travel through the vast expanses of space. Therefore, we could theoretically rely on them to carry messages from the far corners of the universe, greatly expanding our knowledge in the process.

Additionally, although the thermal radiation left over from the Big Bang (Cosmic microwave background, or CMB) is the first light in the universe, it took over 300,000 years for it to appear after the Big Bang; the universe was simply too hot and too viscous to allow light to move anywhere before then. Gravity waves, on the other hand, started the moment the Big Bang happened, thus giving us a glimpse further into the past than the CMB can. In essence, gravity waves peel back the curtain on the first second of the universe.

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