“Researchers Silvera and Dias of Harvard University used diamond anvils, applying more pressure than is found at the centre of the Earth”“Converting metallic hydrogen back into molecular hydrogen would release all the energy built up inside of it, which could be used for a rocket propulsion system”James Barden gives us the details of a recent controversial, yet potentially game changing, experiment.[br]ICE, water and steam are solid, liquid and gas respectively. Everyone knows these three basic forms of matter. We know that when you heat water it boils, and when you cool it, it turns to ice, and that’s pretty much it. We also, however, have elements such as carbon. Add pressure to its solid form and it changes to diamond, which chemically is the same as graphite, but is different structurally. Even when the pressure is removed, it no longer melts or turns into a gaseous state.While diamond is well known, metal hydrogen is not. That’s because up to recently it didn’t exist physically. So why now and why should you care?The concept of metal hydrogen has existed for quite some time, 82 years in fact. However, since its debut in a paper by physicists Wigner and Huntington no one was able to create the correct conditions for it. That is, no one had been able to cool hydrogen to a solid state and apply enough pressure to form the Bravais lattice (a type of crystal structure), until researchers Silvera and Dias of Harvard University used diamond anvils to do so, applying more pressure than is found at the centre of the Earth.What could this mean for the wider world? Metallic hydrogen is predicted to be stable once the pressure is removed, just like a diamond. It is also a theoretical super conductor at room temperature. That is why it could revolutionise many different aspects of our daily lives. With metallic hydrogen, MRI scanners would no longer need helium and power grids could be made that lose none of their power as heat.These are obvious benefits but what else can this wonder material do? Converting metallic hydrogen back into molecular hydrogen would release all the energy built up inside of it, which could be used for a rocket propulsion system. This could make reaching the most extreme planets and even the plutoids in our solar system easier than ever before.However, there is one important caveat. The research published by Silvera and Dias was released before they removed the pressure, and before replicating the result. This has led to their paper facing criticism as they can’t be sure it is metallic hydrogen and they can’t be sure that it can be done again. One of the most fundamental tenets of the scientific method is to be able to replicate the results. Eugene Gregoryanz of the University of Edinburgh criticised the experiment for containing “no raw data” and only “three iPhone photos”As such we shall have to wait and see the development of the experiment, and for Silvera and Dias to send the sample to Illinois to determine whether the structure is metallic hydrogen. If it is it will be an important advancement for high-pressure physics, and our lives in general.