Gravitational waves (II)

LIGO has announced the detection of gravitational waves.

This is a remarkable achievement made possible after steady technological progress on detector technology. The detection of gravitational waves is relevant for different reasons. First, it confirms one of the main predictions made by General Relativity, that space itself can be shaped and dragged by massive objetcs such as black holes and that ripples in the space-time can be produced by such moving objects and move at the speed of light. This idea, that gravity “moves” at the speed of light and is not instantaneous like in Newtonian physics,  is what got Einstein in the first place to develop an alternative theory to the classical (Newtonian) gravitational theory. If gravity travels at the speed of light, its natural to think of it as a wave, similar to photons.  Although the curvature of space was long confirmed by observations of gravitational lensing, and the influence of massive bodies over time has been also confirmed (and applied to current technology like the GPS) the gravitational wave prediction remained elusive form the experimental point of view. Indirect confirmations was provided nearly half a century ago by the slowing down of the periods of a pair of orbiting neutron stars.

Web_NASA_binary star merger__gravitational_waves
Two stellar objects sipinning around each other and “radiating” gravitational waves. The two-black hole picture would be similar except we could not see the black hoes.


The discovery of gravitational waves is important also because ot opens a new window for research, not only of cataclismic events like the collision of two massive black holes but also for studying the origin of the Universe. A different type of gravitational waves (the primordial type), created right after the formation of our Universe are expected to be detected in the near future. A year ago, a claim was made about their detection but it turned out to be a false alarm. The technology to detects this primordial gravitational waves is however advancing at great speed and is just a question of time (1-5 years) till we can see the primordial gravitational waves. Once detected, they will give us valuable information about new phenomena, such as inflation, responsible for the structure of the Universe that we see today.