Friday, January 27, 2017

              JOURNEY TO THE CENTER OF THE EARTH  2.0                                 

Monday,  I get my first look at  the  Holy Grail of solid state physics.

Scientists  have  been  hunting  metallic  hydrogen  since the material was  first  theoretically predicted in 1935. If you wonder how hard it can be to realize so simple an elemental transformation, consider that while 15 years sufficed  to get from the discovery of fission to fuse hydrogen isotopes  into artifical stars, getting them to solidify as metal took fully another lifetime. Yet though  alien to Earth, metallic hydrogen's existence has never rbeen  in  doubt: the  mass of Jupiter and Saturn militates for its  existance  as the  most  common  form of  condensed matter in the solar system. Gas  giant  planets,  have central  pressures  so  high that all the matter  deep within them must necessarily be squashed into the metallic state, but  their overall densities are far too low to be accounted for by denser elements, like aluminum or iron, leaving metallic hydrogen, solid or molten, (in the sense that water is molten ice), to account for the bulk of the solar sysytem's planetary mass.

The phenomenal static pressure needed to condense the gas into a solid was achieved by the antithesis of Big Science. Instead of a border-spanning cyclotron like CERN's giant hadron collider , this experiment took place between the pointy ends of two  utterly flawless diamonds of less than engagement ring size. held together in a high tech vise you can hold in the palm of your hand.

The hunt has long been led by Harvard's  Cabot Professor of Natural Science,  Isaac Silvera,  winner of the  physics  Nobel for getting to molecular hydrogen.

He did't stop there. In a glorious throwback to the days when Newton ground his own telescope mirrors and lenses, Silvera went the full Spinoza to achieve his goal. Having shattered, and dented  dozens of  commercially-made diamond anvils  trying to get past the three million atmospere limit that frustrated his experimental competitors, he philosophically decided to go to Amsterdam and train as a diamond cutter himself, the better to understand why diamond anvils break, and find ways to move forward to the glittering ten micron speck I saw today.  

Though  mirror-like, the world's first sample of metallic hydrogen  appears  warmer  in tone  than polished  silver  or  aluminum,  though this  hint of color  may be an artifact - the absorbtion  spectrum of the diamond through which it  is viewed  is subject to a pressure-driven red shift , and  the 4.95 million atmosphere  pressure in question rivals that at the center of the Earth.

Created in December out of  liquid  hydrogen held close to absolute zero, it has since been warmed to the relatively torrid temperature of liquid nitrogen, 77 K, where it has hung around for the last month-  it seems to be an honest to gosh solid. Skeptics have raised complaints , and will doubtless do so until they make some for themselves, but so far there is no optical  evidence of some transient trick of high pressure quantum chemistry, like protons creating a sort of shiny fools hydrogen by attacking the  sapphire nanofilm that isolates the hydrogen from the diamond anvil.  

I know Silvera  through shared  fascination with high pressure  minerals - he operates at pressures of up to five million atmospheres- a hundred times higher than I need to implode basalt into a mixture of garnets and jade, has led to us compare notes over the decades. 

From the 70's to the 90's  I worked   just across the street  from Ike, on making  diamonds out of just one kind of atom, and finding archaeological jade sources, in  the Peabody Musem and the Hoffman Center for Experimental Geophysics.  Having followed his progress towards the conditons prevailing at the literal center of the Earth, I'm prepared to believe my eyes-- if the silvery glint seen in this clip is what it seems - the first glimpse of the simplest metal, Ike & Co.'s experimental journey may end with an encore  in Stockholm.

So what has this got to do with  climate change?  Possibly a lot , since if  metallic hydrogen proves metastable, as diamonds are, at room temperature,  high temperature superconductivity could move out of the lab,  and  into the arena of energy conservation.

It could also slash the cost of going into space in single stage vehicles-  Imagine the space shuttle going into orbit without a booster-  as Ike pointed out in 2010:
Metastable  metallic hydrogen would be a very light-weight,  low volume,  powerful rocket  propellant.  
One of the characteristics of a propellant is its specific impulse,  Isp.  Liquid (molecular)  hydrogen-oxygen  used in modern rockets has an Isp of ~460s; metallic hydrogen has a theoretical  Isp of 1700s !   
Detailed analysis shows that such a fuel  would allow single-stage rockets  to enter into orbit  or  carry economical payloads  to the moon.