Scientists in Switzerland have started up a machine designed to accelerate sub-atomic particles to nearly the speed of light and then smash them into each other in a bid to find out how the universe began.
The project began operations on Wednesday, but its critics fear that it could go wrong and create a black hole that would destroy the Earth.
The Large Hadron Collider, housed in a tunnel 100 metres below ground straddling the French-Swiss border, has cost more than $5.4bn and has been almost two decades in the making.
The collider began work at 9.30am local time (0730 GMT) with the first protons injected into the 27km, ring-shaped tunnel at the headquarters of the European Organisation for Nuclear Research (Cern).
Scientists monitoring the collider on computer screens burst into applause when Lyn Evans, the project leader, announced: "We've got a beam on the LHC."
More than two thousand scientists from around the world have worked on the project which hopes to observe a particle known as a Higgs Boson, or the "God particle", that scientists hope will explain how particles pick up mass.
The phrase "big bang" was coined in 1949 by Fred Hoyle, a British scientist.
Hoyle was trying to disparage the then emerging theory, which countered his own "steady state" view - that the universe had always existed and was evolving but was not expanding.
The big-bang theory suggests the universe began as a speck at extremely high temperature and density and rapidly expanded and in doing so cooled.
The Higgs was named after Peter Higgs, a British physicist who devised the theory of its existence in 1964.
Archana Sharma, a physicist with Cern, told Al Jazeera that the experiment could be equated to the discovery of X-rays or electricity.
"We are precisely at that kind of moment in science -something new is going to come about," she said.
"In addition, there are theories - to be technical - that explain the universe on the astronomical scale and their are theories that explain it on a subatomic scale... There is a connection between these two where the origin of mass is explained by a mechanism called the Higgs mechanism. Our primary scientific goal is to find the Higgs."
The collider will send protons in opposite directions along a 27km circuit - the protons will travel the 27km 11,000 times per second - and at four points the protons will intersect and smash together.
Scientists will monitor the collisions and collect data on the particles created by these collisions, which they say will come close to re-enacting the "big bang" - the theory that a colossal explosion created the universe.
The project could also help prove the theory of supersymmetry, a theory in particle physics that suggests every particle has a corresponding partner particle.
The end of the world?
Prior to the launch, the internet was abuzz with rumours that the particle accelerator could create black holes or an as-yet hypothetical particle called a strangelet that would grow and destroy the earth.
A black hole has a gravitational field so powerful that it pulls particles, including light, into itself.
But staff on the project have reject the claims.
"Nothing's going to happen here that's not already happening in nature," Mario Nessi, the projects technical director, said.
Cern says it has commissioned a panel to verify its calculations that such risks are virtually impossible.