We tested Albert Einstein’s theory of gravity on the scale of the universe
Everything in the universe has gravity – and feels it too. Yet this most common of all fundamental forces is also the one that presents the biggest challenges to physicists.
Albert Einstein's theory of general relativity has been remarkably successful in describing the gravity of stars and planets, but it doesn't seem to apply perfectly on all scales.
General relativity has passed many years of observational tests, from Eddington's measurement of the deflection of starlight by the Sun in 1919 to the recent detection of gravitational waves.
However, gaps in our understanding start to appear when we try to apply it to extremely small distances, where the laws of quantum mechanics operate, or when we try to describe the entire universe.
Our new study, published in Nature Astronomy, has now tested Einstein's theory on the largest of scales.
We believe our approach may one day help resolve some of the biggest mysteries in cosmology, and the results hint that the theory of general relativity may need to be tweaked on this scale.
Faulty model?
Quantum theory predicts that empty space, the vacuum, is packed with energy. We do not notice its presence because our devices can only measure changes in energy rather than its total amount.
However, according to Einstein, the vacuum energy has a repulsive gravity – it pushes the empty space apart.
Interestingly, in 1998, it was discovered that the expansion of the universe is in fact accelerating (a finding awarded with the 2011 Nobel prize in physics).
However, the amount of vacuum energy, or dark energy as it has been called, necessary to explain the acceleration is many orders of magnitude smaller than what quantum theory predicts.
Hence the big question, dubbed “the old
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