In the middle of a lazy afternoon phone conversation with my grandfather, he says "Did you know they just made metallic hydrogen?" I know this is a very rare thing for me to say, but I was speechless. Of course I knew that hydrogen could become a solid at cold enough temperatures, but that is scary close to absolute zero. It never occurred to me that it could, even in a solid state, resemble anything like a metal.
Just typing 'metallic hydrogen' into Google brings up articles like this: Hydrogen turned into metal in stunning act of alchemy that could revolutionise technology and spaceflight. Bold claim, as the media is wont to do. And of course, just a few hours later, articles started popping up refuting the claim.
But digging a bit further, the search for metallic hydrogen goes much further back than a few days ago. It goes back to Wigner and Huntington.
First ever photograph of a hydrogen atom. Photo courtesy of io9.gizmodo.com
1935
In the early 20th century, Eugene Wigner and Hillard Bell Huntington published a paper titled: On the Possibility of a Metallic Modification of Hydrogen.
Basically, they predicted that with enough pressure hydrogen would start having metal like properties. Even though hydrogen is labeled as a "diatomic nonmetal" it could, theoretically, have metallic like properties like high electrical conductivity.
How high of pressures are we talking? Think about the average pressure the atmosphere is pushing against either side of your skin. That's roughly 14.6 pounds per square inch which is called an atmosphere of pressure (atm). Dive down 10 meters and that's roughly 2atm.
Wigner and Huntington theorized that to make metallic hydrogen, it would need to be at a pressure of 250...THOUSAND atm! To put that in perspective, the deepest part of the ocean only goes 11,034 feet. Our ocean would only produce around 4% of the pressure they theorized was needed to make hydrogen metallic. How on earth would anyone make it?
Interior of Jupiter. Metallic hydrgen might be the large gray part due to high gravity. Photo courtesy of R. J. Hall at NASA
1996
At the end of the 20th century, scientists at the Lawrence Livermore National Library stumbled on metallic hydrogen. Even though they were putting hydrogen under intense pressure (1.4 MILLION atm), they were not using solid hydrogen, which they thought was necessary to make it metallic.
What they found was that the more pressure that they put on the hydrogen, the electrical resistance kept dropping. This was especially exciting because our current metals loose 15% of energy through travel (such as through wires and chargers) where as metallic hydrogen, theoretically, would produce close to zero loss of energy transferred.
The biggest problem with the experiment wasn't that they accidentally made it, but that it was only created for a microsecond. Long enough to identify, but not do any lengthy experiments with.
While other experimentation have happened around metallic hydrogen, none have stood out since they have not been repeatable. Which brings us to...
Picture of the supposed metallic hydrogen in the 2016 experiment. Photo courtesy of The Independent.
2016
Ragna P. Dias and Isaac F. Silvera published an article with the thrilling title: Observation of the Wigner-Huntington transition to metallic hydrogen. I'll let them explain in their own words:
“With increasing pressure we observe changes in the sample, going from transparent, to black, to a reflective metal, the latter studied at a pressure of [4.89 Million atm]...The properties are those of a metal. Solid metallic hydrogen has been produced in the laboratory.”
Dias and Silvera reported finding the elusive metallic hydrogen at pressures around 2000 times greater than Wigner and Huntington first theorized. What they did was put bits of hydrogen between diamond presses, and photographed what they found (shown above).
Other scientists are against this claim however saying things like:
- The metallic properties could be the aluminium oxide used to coat the diamonds
- The measurements made were not detailed enough to accurately say how much pressure there was
- Dias and Silvera did not give proper time for the peer-reviewed process before publishing their findings
While this debate has been going on since October, the paper just came out to the public which has turned the media's gaze on this debate.
At this time we don't know whether metallic hydrogen was formed. Even if it was, could it be stable at room temperature? What could we use it for?
For now we just have to wait on the sidelines while the process wages on. This goes to show that science is not about finding the abosolute truth, but revealing more how the universe works one experiement at a time.