The phenomenal success of Isaac Newton’s theory of gravity in explaining the motions of bodies on the earth and in our solar system meant that the theory went unchallenged for about 300 years. Only slowly did astronomers realise that certain deviations from the predicted motion of the planet Mercury could not be understood with Newton’s theory.
It took the genius of Albert Einstein to replace the traditional idea of the gravitational interaction between two bodies by predicting the effects of curved space-time. Suddenly, the orbit of Mercury could be explained, and Einstein’s simultaneous prediction of the deflection of star-light at the Sun was confirmed spectacularly during the solar eclipse in 1919. Ever since, scientists have thought of new experiments to test Einstein’s general theory of relativity, as he called his theory of gravity, to ever better precision. So far, general relativity has passed all these tests with flying colours and not a single deviation from the theoretical prediction has been found in the experiments.
Quantum mechanics, developed at the same time as Einstein’s general relativity, is known to describe nature successfully at the sub-atomic level. It has been proposed that the ultimate theory of the Universe will involve the unification of general relativity with quantum mechanics. Although such a marriage is some way off, we can expect that this theory of quantum gravity produces somewhat different predictions than general relativity. But how can we measure such deviations? How can we test when – if at all – general relativity fails? We have to assume that so far we have not probed gravitational fields that are strong enough to show deviations from general relativity’s prediction. Tests in the solar system are made under weak-field conditions. Strong-field tests of gravity that will be carried out using pulsars and the SKA will provide some of the most stringent tests ever made.
If, using the SKA, we find deviations Einstein’s predictions, we will ultimately understand much more about the Universe.
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