The fantasy of metallic hydrogen, not known to the layman, is somewhat like performing alchemy for scientists. Metallic hydrogen was initially an impossible theory that received considerate acclaim and interest in the latter half of the 20th century. Metallic hydrogen is considered 'the Holy Grail of high-pressure physics'. Hydrogen is a diatomic molecule, meaning that it is a gas at room temperature and pressure but liquefies and solidifies only at extremely low temperatures (20 degrees Celsius and 14 degrees Celsius above absolute zero, respectively). It exhibits properties similar to those of the diatomic non-metals like the halogens.
However, physicists Eugene Wigner and Hillard Bell Huntington predicted that only under an immense pressure of around 25 GPa hydrogen would display metallic properties, that is, instead of H2 molecules, a bulk phase would form with a solid lattice of protons and the electrons delocalized throughout as in a metal lattice. Despite the estimated pressure required, was way low than what really was needed, scientists realized how very complex the structure of the hydrogen atom was. Since then the property of hydrogen being a metal drove scientists to experiment on it and some even commented that they sighted it for milliseconds and then gone.
The reason why metallic hydrogen is such a wanted miracle is because it has the potential to completely revolutionize our industries. Superconductors are very rare materials, active only in extremely low temperatures near the absolute zero (-273.15 degree Celsius). The idea of a superconductor is that it provides zero resistance to an electric current and would make everyday electricity generation and transmission vastly more efficient, as well as giving a massive boost to current uses of superconductivity such as the enormous magnets used in medical imaging machines. In 1968, Neil Ashcroft suggested that metallic hydrogen might be a superconductor, up to room temperature (290 K or 17 °C), far higher than any other known candidate material. This hypothesis is based on an expected strong coupling between conduction electrons and lattice vibrations.
There are no other known room-temperature superconductors in existence, meaning the applications are immense — particularly for the electric grid, which suffers for energy lost through heat dissipation. It could also facilitate magnetic levitation for futuristic high-speed trains; substantially improve performance of electric cars; allow development of faster supercomputers; and revolutionize the way energy is produced and stored. Metallic hydrogen could potentially enable rockets to get into orbit in a single stage, even allowing humans to explore the outer planets. Metallic hydrogen is predicted to be “metastable” — meaning if you make it at a very high pressure then release it, it’ll stay at that pressure. A diamond, for example, is a metastable form of graphite. If you take graphite, pressurize it, then heat it, it becomes a diamond; if you take the pressure off, it’s still a diamond. But if you heat it again, it will revert back to graphite. It will revolutionize the space travel because of the insane thrust it can produce!
A hydrogen fuel cell has a potential to form huge amounts energy, the only problem being that it is highly volatile. Now, imagine having metallic hydrogen, which is easy to store and can be made into shapes and sizes in which it is not very volatile. And now imagine using this hydrogen metal every day, everywhere for mechanical tasks to nuclear systems. The reactions for this metal can be controlled by using a definite surface area of it and achieving efficiency.
The sample of hydrogen metal, supposedly created by the Harvard researchers, as seen being held between two diamond anvils
And in December 2016, two physicists Thomas D. Cabot, Professor of the Natural Sciences, Isaac Silvera and postdoctoral fellow Ranga Dias, in Harvard claim that they have managed to form metallic hydrogen by applying pressures like 495 GPa (greater than the pressure of the Earth's core) on it by squeezing it between two diamond anvils. Whether the discovery is valid or not, verily the possibility of attaining a room-temperature superconductor with infinite potential is certainly worth waiting for.