Lots of people went wild last month at the news that scientists had suddenly discovered some sort of physics holy grail: Metallic hydrogen, hydrogen that turned into a metal. Gizmodo didn't buy the hype. Well, according to ScienceAlert, that metal hydrogen sample has now disappeared.
Image: R. Dias and I.F. Silvera/Gizmodo
Many scientists don't believe metallic hydrogen was created to begin with. And yet, somehow, many of the same media outlets that reported this story credulously last month are now reporting that this possibly nonexistent jewel has mysteriously vanished.
Here's a quick recap of what the Harvard scientists behind the hydrogen hullabaloo said they saw, in results published recently in the journal Science:
The observation was made by a team of Harvard researchers, while they were squeezing hydrogen between diamonds at temperatures just above absolute zero, 5.5 Kelvin or -267C. As the scientists cranked up the pressure, they observed transparent hydrogen turn black. Finally, at a pressure five million times our own air pressure, the hydrogen turned reflective. The researchers presented this as proof that the hydrogen atoms had arranged into a regular, 3D structure like a metal, a behaviour first predicted by physicists Hillard Huntington and Eugene Wignerin in 1935.
The more scientists achieve the same result, the more robust that result is. On the flip side, there's reason to be sceptical when a single group claims to make a discovery based on a single observation.
As first reported last week, the team's lead researcher, Isaac F. Silvera, told ScienceAlert that while testing the sample earlier this month, the diamonds holding it cracked. He told them the sample disappeared, because it was either very small, or had turned back to gas.
But other scientists don't believe that Silvera's team had put forth sufficient evidence that they'd created metallic hydrogen at all.
"Maybe they had something in the first place," Alexander Goncharov, staff scientist at the Carnegie Institute for Science in Washington DC, told Gizmodo, "but it wasn't metallic hydrogen."
Goncharov and others have written several responses to Silvera's paper. In one, Goncharov says the results don't match the conclusion — the researchers saw a shiny material in the cell, but didn't track whether there was actually hydrogen present the whole time. "How do they know they actually had hydrogen at the time [during the experiment]," he asked me. "Hydrogen can escape at any pressure. Based on their photographs, I cannot say that" there was any hydrogen in the diamond vice.
Even Mikhail Eremets at the Max-Planck-Institut fur Chemie in Germany, who previously claimed to have created metallic hydrogen, took issue with Silvera's paper. Eremets thought that the Harvard researchers' pressure measurements were unreliable. Plus, even non-metallic hydrogen would reflect well at high pressures, he wrote.
I will not outright say that Silvera's lab didn't create metallic hydrogen, because we simply don't know. I will say that plenty of scientists were not convinced by his paper — and a disappearing sample in the face of so much dissent would certainly be a convenient excuse to try your experiment again under less scrutiny.
We reached out to Silvera for comment but had not heard back at time of writing.