Helion’s nuclear fusion promises have garnered the attention of Silicon Valley—and raised concerns amongst scientists wary of its aggressive timeline.

A US start-up whose backers include tech billionaires Sam Altman and Peter Thiel has raised $425mn to keep it on track to achieve its target of producing electricity from nuclear fusion in 2028. Helion has the most ambitious timeline among start-ups racing to develop nuclear fusion,

Seattle-area company Helion Energy gets $425 million from investors including Sam Altman and Softbank to pursue clean energy's "Holy Grail."