Gravitational waves – a statistical breakthrough?

Recently, headlines were made with the discovery of gravitational waves – ripples in space and time that were predicted a century ago by Albert Einstein in his general theory of relativity. Our colleague Jonathan Gair, who works jointly with the University of Edinburgh’s School of Mathematics and Biomathematics and Statistics Scotland, was part of the team that made this historic breakthrough. Today Mairi interviewed Jonathan about his involvement in the project.

gravitationalwaves

Although gravitational waves belong well and truly in physics, it was statistics that allowed their existence to be confirmed. Gravitational waves are detected using what’s called a laser interferometer. When a reading is detected, the big question is whether a genuine gravitational wave has been detected, or whether the reading is a false alarm caused by background noise. In order to find out, the team had to perform what’s called a statistical hypothesis test.

To do this, the team first needed to know what kind of readings are typical in background noise. Of course, most background noise will give relatively small readings, and it’s rare that background noise would cause a large reading. However, for the team to be certain that their reading was a genuine gravitational wave, they had to take into account even extremely rare high background noise readings. In fact, they needed to ensure that the chance that their reading was a false alarm was less than a one in a billion chance.

In order to check this, the team used 20,000 computers, each running for 100 days, to simulate the equivalent of 200,000 years worth of background noise data. They found that in all of this data, there was no reading anywhere near as high as the reading they detected, and so they were able to conclude that the chance of their reading being a false alarm was far less than one in a billion. This led to the confirmation that gravitational waves exist.

Watch our interview with Jonathan and find out more about the power of statistical testing in Week 6 of the course!

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