waves all around

Stumbled across a short but informative video by Minute Physics on gravitational waves. Check it and other great bits on their YouTube channel. Seeing the video reminded me of a feeling I had shortly after learning of the results of the first LIGO detection.

I saw that the ripples in spacetime caused by the gravitational waves detected by the Laser Interferometer Gravitational-wave Observatories in the US was like us seeing the small waves on the surface of a pond, ripples caused perhaps by a stone tossed into the water, or a fish surfacing to catch a bug.

Scientists determined that the detected gravitational waves were produced during the merger of two black holes approximately 1.3 billion light years away. Something predicted but never observed previously.

Albert Einstein's theory of general relativity says that a pair of black holes orbiting around each other lose energy through the emission of gravitational waves. Over billions of years they slowly approach each other. In the final seconds, they move together very quickly. When they collide, they convert a portion of the combined mass to energy. This energy is emitted as a burst of gravitational waves. Spacetime stretching and flexing. A large rock thrown into a vast ocean.

Elasticity and a source of energy are required for periodic motion. When the elastic object is an extended body, like a pond, then the periodic motion takes the form of traveling waves. It is easy to see these sinusoidal waves. Consider a disturbance in air. A change in air pressure at a single point produces a spherical traveling pressure wave. Or sound. Like a sonic boom. The invisible sound wave in air is a longitudinal wave. 3D.

Of course, the fascinating thing is that space is three-dimensional. The surface of the lake or ocean is two-dimensional and correspondingly easy for us to visualise and grasp. But consider, for a moment, that ripples are being generated all around us in every direction. Every direction. Behind you, above, left, right, from straight ahead.

The other mind-blowing thing to me is to consider that gravitational waves should be produced constantly. Things throughout the Universe are vibrating and shaking and collapsing together. Pulsars, black holes, other cataclysmic events. And, so far, we are only detecting the big events, like black holes merging. But imagine what it will be like when our detection methods improve and our resolution and sensitive increases.

We will, no doubt, see spacetime rippling like a pond in never-ending rain.

Credits:

• gravitational waveforms readings by the LIGO detectors from Caltech
• rain drops on Mew Lake in Algonquin by Blake Nancarrow