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Gravitational Waves

The announced detection of a gravitational wave signal arriving from the inspiral of two black holes resulting in their inglobation into a final more massive black hole has now travelled around the world.

We all have an enormous practical experience in the detection of waves. Actually, almost all of the information that we receive about the surrounding world arrives to us in the form of waves: Sight – our eyes are extremely sensitive detectors of electromagnetic waves; Sound – our ears can detect a large range of sound waves; Touch – our body detects certain frequencies of electromagnetic radiation coming from the sun (it warms our skin).

Each of these waves is detected as a function of the way that it travels through an elastic medium. The medium of electromagnetic waves and also of gravitational waves is the vacuum. To observe the universe more completely science has developed detectors to extend the range of seeing and hearing well beyond the range accessible by our body, and this has enabled us to observe a huge variety of events in the universe.  These detectors have extended our range of vision in electromagnetic waves well beyond the visual ight of our everyday experience – and this has led our investigation of the properties of matter and spacetime deep into the microscopic and cosmological realms. As a consequence of this extended vision the theory of quantum mechanics was developed and refined.

Gravitational waves are a simple prediction of Einstein’s general theory of relativity, a theory that celebrated its 100th anniversary in November of 2015, and which continues to be confirmed as a spectacularly successful theory of gravity with no close contenders. The construction of gravitational wave detectors began in the early 1970’s but up until last year they were never sensitive enough to detect the gravitational waves that we expected should arrive from cataclysmic events in remote regions of the universe. The construction of gravitational wave detectors is extremely demanding due to the incredible weakness of the gravitational field and it is only with the dedication of experimental physicists continually refining the detectors that we have finally arrived at the actual observation of at least one, and probably various other, gravitational waves.

The magnitude of this discovery is completely out of reach or our everyday experience. The difference in strength between the gravitational force and the electromagnetic force is on the order of forty zeroes. Forty zeroes. This number is really beyond imagination. If we take a huge number, for instance the distance to the big bang is on the order of twenty zeroes in seconds, then it is still excruciatingly small compared to a number with forty zeroes.

What will the future bring now that we have opened a new window of perception on our universe? The most evident lessons are related to black hole physics. The observation of this gravitational wave is the most direct evidence of the existence of black hole like objects almost all the way to their horizon – the famous point of no return and the source of all the subtleties of black hole physics.

Black holes, like gravitational waves, we’re first discovered as solutions to Einstein’s equations almost 100 years ago. It is beautiful to ponder that these two predictions are finally coming into view at the level of observation and are amongst the more profound confirmations of Einstein’s theory and at the same time the most likely to lead to the further evolution and extension of this theory into the quantum world.

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Categories: Physics
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