The nature of the Universe On the largest scales, we work to understand the properties of the Universe. After its origin in a Big Bang, the Universe has expanded and cooled. We can measure the temperature of leftover radiation to extraordinary levels of accuracy, for example using data from ESA’s Planck satellite, to understand the origin of the fundamental physics of matter, and how the initial structure of the Universe may have been imprinted from the quantum mechanics of subatomic particles. Because gravity is always attractive, the mutual attraction of matter in the Universe should lead to its expansion rate slowing, but measurements in the last two decades have shown that it is increasing. The amount of energy required to increase the expansion rate is enormous; it is most of the energy in the Universe. As we have no understanding of its nature, we call it Dark Energy. Also, after many years of ingenious investigations, we have found that most of the matter in the Universe appears to be unlike normal atoms and molecules, so we call this Dark Matter, and it causes increasing clumpiness in the Universe as it ages. Although this material isn’t as concentrated as in the regions around black holes, it bends the light travelling to us from distant galaxies; a process called weak gravitational lensing. These slight distortions provide powerful constraints on the clumpiness of the Dark Matter, and, as we look further away and back in time, on how the clumpiness has evolved. Because this clumpiness is affected by how much Dark Energy there is, we can study both Dark Energy and Dark Matter using weak gravitational lensing. We are building the camera for ESA’s Euclid satellite to make exquisite images of billions of distant galaxies, and developing the advanced mathematical and statistical techniques to extract the cosmological information from them.
Why is the expansion of the Universe accelerating? How can we use large surveys to measure the properties of the Universe?
Artist’s impression of Euclid / ESA/C. Carreau
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