Two physicists say that they have crushed hydrogen under such immense pressures that the gas became a shiny metal — a feat that physicists have been trying to accomplish for more than 80 years.

But other researchers have serious doubts about the claim, the latest in a field with a long history of failed attempts.

Ranga Dias and Isaac Silvera, both physicists at Harvard University in Cambridge, Massachusetts, first posted a report of their results on the arXiv preprint server last October1, which attracted immediate criticism. A peer-reviewed version of the report was published on 26 January in Science2, but sceptics say that it includes little new information.

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