On Tuesday, the Department of Energy announced that Lawrence Livermore National Laboratory scientists made a “holy grail” discovery when they maintained a fusion reaction between two hydrogen atoms, generating 20 percent more energy than what was contributed. It is the first time humans have generated a net gain from a fusion reaction, a topic that has seen decades of research and experiments. The breakthrough could signal a future of clean energy.

The California-based laboratory described the fusion ignition as “a major scientific breakthrough decades in the making that will pave the way for advancements in national security and clean energy.”

However, some experts are warning that commercialization of fusion energy won’t be seen “anytime soon”, despite the recent announcement.

Journalist and author Robert Bryce advised people to take the announcement with “a big grain of salt” on Twitter after news broke Monday that President Joe Biden’s administration was expected to announce a scientific breakthrough on Tuesday. Bryce explained that although the news was very positive for the science community, fusion energy has been a topic of discussion for decades.

“It’s kind of the holy grail of energy technologies, but it’s extraordinarily tricky,” Bryce said.

Bryce went on to explain that to create fusion energy, the reaction must be contained and requires the use of “lasers or plasmas” to control the experiment because of high radiation levels.

Bryce compared fusion energy’s development timeline to that of fission energy. Scientists ran the first fission nuclear reactor in 1942, but the commercialization of fission energy took an additional 15 years.

Bryce said billions of dollars are funding fusion energy research, and although the research is moving forward, it is slow progress.

Other experts expressed similar reactions to the announcement. Scientist and professor Michael E. Mann said economic viability from fusion energy requires a much greater rate of energy gain than what scientists recently discovered.

“I’d be more excited about an announcement that U.S. is ending fossil fuel subsidies,” Mann tweeted.

Other experts and legislators are celebrating the breakthrough even as they acknowledge it was an imminent discovery.

Climate and energy policy professor Leah Stokes tweeted that “the importance of this news cannot be overstated.”

U.S. Representative Don Beyer called the discovery a “watershed moment”. Many tweets from other experts touted the discovery as “fascinating”.

Newsweek reached out to Lawrence Livermore National Laboratory for comment.