The world's largest particle smasher restarted on Sunday after a two-year upgrade that will allow physicists to explore uncharted corners of what makes up the universe, including dark matter and antimatter.

"After two years of intense maintenance and several months of preparation for restart, the Large Hadron Collider, the most powerful particle accelerator in the world, is back in operation," the European Organization for Nuclear Research said.

Experiments at the collider have been seeking to unlock clues as to how the universe came into existence by studying fundamental particles, the building blocks of all matter, and the forces that control them.