What if the big bang was hotter than expected ?
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How did the universe come into being ? Since the idea of a Big Bang was first proposed by George Lemaitre, there multitude of theories on this subject have been proposed. Many of these explain the overall homogeneity and isotropy of the observable universe by postulating a brief period of accelerated cosmic expansion during the first split-seconds of its existence, known as cosmic inflation. Many theoretical ideas have been proposed to explain this acceleration. However, almost all of these require the existence of new elementary particles that cannot be detected in any near future experiments, making a direct test of the underlying theory in the laboratory impossible.
It is usually assumed that the rapid dilution of particles rendered space cold and empty during this phase, raising the question how it was subsequently populated with the hot plasma that we see in the Cosmic Microwave Background (CMB). A new model proposed by scientists from Caltech, UCLouvain and the Max Planck Institute for Physics aims to rewrite cosmic history: In this scenario, the accelerated expansion is driven by a so-called axion field. The axion interacts with gluons, the particles that mediate the well-known strong nuclear force which holds protons and neutrons together. This interaction leads to a kind of friction and populates the cosmos with a hot plasma of elementary particles during inflation.
While the idea of a “warm inflation” has been proposed before, the new model is the first one that can explain the observed CMB by one of the established forces of nature, i.e., without requiring a sizeable number of hypothetical new elementary particles. Moreover, the only new particle needed – the axion – could be found in experimental searches on Earth. Axions have been proposed for other reasons, e.g. in the context of Dark Matter, and there are many experiments looking for them. This opens up a unique opportunity to probe the connection between the Big Bang and fundamental physics in the laboratory.
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