The Standard Model of cosmology describes this history of the universe, from the first seconds after the Big Bang to the current day. The beauty of it: The model explains, with only six parameters, everything known today about the birth and evolution of the universe. Nonetheless, the model may now have reached its limits.
“New observational evidence points to the fact that the matter is distributed today in a different way than the theory predicts,” explains Dr. Florian Pacaud from the Argelander-Institut für Astronomie of the University of Bonn.
It all started with the measurements of the Planck satellite, which was launched by the European Space Agency (ESA) to measure the cosmic background radiation. This radiation is, to some extent, an afterglow of the Big Bang. It conveys crucial information on the matter distribution in the early universe; showing the distribution as it was only 380,000 years after the Big Bang.
According to the Planck measurements, this initial distribution was such that, over cosmic time, more galaxy clusters should have formed than we observe today. “We have measured with an X-ray satellite the number of galaxy clusters at different distances from ourselves,” explains Dr. Pacaud. The idea behind the measurements: The light from remote galaxy clusters has traveled for billions of years before reaching us, so we observe them today as they were when the universe was still young. Nearby clusters, on the other hand, are observed as they appeared much more recently.
“Our measurements confirm that the clusters formed too slowly,” said Dr. Pacaud. “We have estimated to which extent this result conflicts with the basic predictions of the Standard Model.” While there is a large discrepancy between the measurements and predictions, the statistical uncertainty in the present study is not yet tight enough to challenge the theory. However, the researchers expect to obtain substantially more constraining results from the same project within the next three years. This will finally reveal whether the Standard Model needs to be revised.
The study also supplies a glimpse into the nature of dark energy. This mysterious constituent of the universe acts as a kind of interstellar baking powder, causing the acceleration of cosmic expansion. The “amount” of dark energy—the cosmological constant—should have stayed the same since the Big Bang—or so assumes the Standard Model of cosmology. Many observations seem to point in this direction. “Our measurement also supports this thesis,” explains Dr. Pacaud. “But here again, we shall obtain more precise results in the near future.”
University of Bonn
Image credit: artist’s interpretation of the Big Bang, with representations of the early universe and its expansion. NASA’s Goddard Space Flight Center/CI Lab
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