Tõnu Laas - What are Gravitational Waves?
Recently the World was rocked by the official announcement of gravitational waves. How to explain one of the biggest scientific discoveries of our day in simple terms? Tõnu Laas, Professor of applied physics at the Tallinn University School of Natural and Health Sciences gives it a try.
Recently the World was rocked by the official announcement of gravitational waves. How to explain one of the biggest scientific discoveries of our day in simple terms? Tõnu Laas, Professor of applied physics at the Tallinn University School of Natural and Health Sciences gives it a try.
"We must start by noting that the time-space around us is curved. Time and space are bent by mass and energy, although we need a very large mass to see the effect. For example, the mass of the Earth is so small that the most precise measuring devices would only see minor effects caused by the curvature.
Nevertheless, if we measured distances on the Earth with its practically flat time-space, and someone measured the same distance near an astronomical object with enormous mass (e.g. a black hole), the results would be different. The time acts different in these places, as well. This is expressed by the curvature of time-space.
For us, gravitational waves would be the bends in a flat time-space. Let us try to explain that: if a gravitational wave that is a billion times stronger than the one recently recorded, a sphere with a diameter of one metre would grow by the diameter of an atom in one direction, and shrink by the diameter of an atom in the other direction. Then the growing part will shrink, and vice versa, in a periodic manner.
As the effect of the bending space is so small, it takes an enormous astrophysical event to create gravitational waves. The waves that the LIGO team noted last year came from the fusion between two black holes that had the mass of about 30 Suns.
The most intensive part of gravitational waves was emitted during the final period of the rotation of these black holes – during the very last seconds, when both of the black holes moved at half the speed of light. During the final 0,05 seconds, energy equivalent to three Suns was emitted as gravitational waves.
As we are more than a billion light years away from the source, the sphere described earlier would only grow or shrink by the diameter of a millionth of an atom. Registering such a wave is currently the most accurate we are capable of.
The previous explanation considered bends in space. Time also bends locally. If we were much closer to the source, the gravitational waves passing through us would age our cells faster in one direction than the other, and then vice versa. How to cope with that? Here I run out of imagination."