Why Didn’t The Universe Collapse After The Big Bang? We Have Gravity To Thank


According to physics, the Universe shouldn't be here. Theories dictate that because the Universe was so unstable after the Big Bang, it should have quickly collapsed. However, it didn't. And now we know why: gravity.

In 2012, CERN discovered the mysterious Higgs particle, which is an elementary particle in the standard model of particle physics. After studying the Higgs, physicists determined that the Big Bang, which resulted in the Universe expanding at an unprecedented rate, should have made it so unstable that it collapsed.

Of course, fortunately, for us, it didn't. But how do we explain why?

Some physicists think that the answer requires an entirely new area of physics that hasn't yet been discovered. However, physicists at the Imperial College London, as well as at the University of Copenhagen and the University of Helsinki, think the answer is much simpler. Gravity held the Universe together when it was unstable.

In modern physics, gravity is part of Einstein's general theory of relativity and is the result of the curvature of spacetime. These physicists believe that it was this effect that held the Universe together when it was expanding so rapidly, shortly after the Big Bang.

The physicists studied how the Higgs particle and gravity interact with each other, based on different scenarios. They determined that even a small interaction between gravity and the Higgs was enough to keep the Universe stable, preventing collapse.

"This parameter cannot be measured in particle accelerator experiments, but it has a big effect on the Higgs instability during inflation," says Professor Arttu Rajantie, from the Department of Physics at Imperial College London. "Even a relatively small value is enough to explain the survival of the universe without any new physics!"

Sometimes, even in science, the best answer is the easiest one. But this theory still needs further investigation. The physicists hope to use cosmological observations to study the interaction between the Higgs particle and gravity and how that affected the growth of the Universe after the Big Bang. They'll study data from both current and new missions by the European Space Agency (ESA) and learn more about cosmic microwave background radiation, as well as gravitational waves.

Of course, we're still trying to detect gravitational waves, but once scientists turn on the Laser Interferometer Gravitational-Wave Observatory (LIGO) detectors again next year, there's a chance we'll find direct evidence of those waves, as well as learn more about black holes.

"Our aim is to measure the interaction between gravity and the Higgs field using cosmological data," says 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."

[Photo Credit: NASA, ESA, T. Megeath (University of Toledo) and M. Robberto (STScI)]

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