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“Understanding Science”: All from Nothing: The Structuring of our Universe



The “Understanding Science” lecture series continued on 22 May with a provocatively titled and engaging presentation on “All from Nothing” by Prof. Simon White, director of the Max Planck Institute for Astrophysics in Munich (Germany).  

Simon White took the audience on a journey deeper and deeper into space, which is equivalent to “closer and closer to the creation of the Universe”. His journey started with the structure of the Milky Way and nearby galaxies, which we can study in great detail, although these galaxies are fairly old (up to 10 billion years). Continuing to galaxies farther away, he presented observations which show galaxies to be distributed non-homogeneously: they are grouped in galaxy clusters, cosmic filaments and large volumes which are almost empty (“voids”). But how did this large-scale structure build up? It can only originate from structure being present already earlier! How, then, do we observe this underlying structure which was presumably present when no stars or galaxies had formed yet? Imaging the state of the Universe closest to its creation (the “Big Bang”) is currently only possible by observing the “cosmic microwave background” (CMB). This radiation was released about 400,000 years after the Big Bang, when the first atoms formed (from protons, neutrons and electrons) – the Universe had expanded and its content cooled down sufficiently to allow the formation of stable neutral atoms.

When neutral atoms had not yet formed, the photons (“particles of light”) were constantly scattered off the existing charged particles and forming atoms immediately dissolved when photons were absorbed. Therefore photons couldn’t escape the hot fireball of matter present after the Big Bang. Pictures of the “first light” (the CMB, observed by satellites such as COBE or WMAP) show large- as well as small-scale structures. These small-scale structures represent sound waves: density waves present in the matter distribution at the time of neutral atom formation. Taking these density wave patterns as input for simulations of the Universe’s evolution yields structures very closely resembling the observed distributions of galaxies today. Hence the current distribution of galaxies (at an age of the Universe of 13.7 billion years) is determined by sound waves from the time the Universe had an age of 400,000 years. 

By Peter Anders