For decades, scientists have been trying to generate energy by nuclear fusion.
In France on Tuesday, scientists reached a key milestone in that journey starting the main construction for ITER, the world's largest nuclear fusion reactor.
Seven countries are working together on the project, including South Korea, France and the U.S.
and it has taken them 10 years to get this far.
"Today's a historical moment. Fusion energy is a gift of Gods."
The idea is to create the energy in the same way that drives the sun.
Fusion power combines or "fuses" two or more hydrogen atoms at very high temperatures,….to generate a lot of energy.
It's opposite of conventional nuclear power, which splits atoms to release energy.
South Korea's president has previously called nuclear fusion an "artificial sun" which gives hope to the world by providing a clean and safe energy source.
"An artificial sun is an energy source of dreams. It is clean energy that utilizes seawater and can be produced in almost infinite amounts while posing no danger from radiation and emitting no greenhouse gases."
South Korea is expected to play a key role in the project, given its past experience of creating a fusion reactor, as well as making major contributions in the project's early stages.
"The celebration for the start of machine assembly was possible because South Korea sent key parts. Korea's contribution basically accounts for 70 to 80 percent."
Despite the theoretical benefits, there are questions over whether nuclear fusion will actually work in the real world.
And ITER looks to find the answer to that by 2025.
Lee Kyung-eun, Arirang News.