Did gravity save the universe after the Big Bang?

European physicists have put forward an explanation as to why the universe did not collapse immediately after the Big Bang. Their theory follows studies of the Higgs particle - discovered at CERN in 2012 and responsible for giving mass to all particles - which suggest that the production of Higgs particles during the accelerating expansion of the very early universe (inflation) should have led to instability and collapse.

“The Standard Model of particle physics, which scientists use to explain elementary particles and their interactions, has so far not provided an answer to why the universe did not collapse following the Big Bang,” said Professor Arttu Rajantie from Imperial College London.

The team investigated the interaction between the Higgs particles and gravity - “the last unknown parameter in the Standard Model”, according to Professor Rajantie - taking into account how it would vary with energy. Writing in the journal Physical Review Letters, they explained that even a small interaction would have been enough to stabilise the universe against decay, thus enabling the universe to survive expansion in that early period.

“This parameter cannot be measured in particle accelerator experiments, but it has a big effect on the Higgs instability during inflation,” said Professor Rajantie. “Even a relatively small value is enough to explain the survival of the universe without any new physics!”

The team plans to continue its research using cosmological observations to look at this interaction in more detail and explain what effect it would have had on the development of the early universe. In particular, the researchers will use data from current and future European Space Agency missions measuring cosmic microwave background radiation and gravitational waves.

“Our aim is to measure the interaction between gravity and the Higgs field using cosmological data,” said Professor Rajantie. “If we are able to do that, we will have supplied the last unknown number in the Standard Model of particle physics and be closer to answering fundamental questions about how we are all here.”

The team comprised scientists from Imperial College London, the University of Copenhagen and the University of Helsinki. The research was funded by the Science and Technology Facilities Council, the Villum Foundation and the Academy of Finland.

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