When thinking about the future of energy production, aside from renewable energy like solar power, fusion is something which immediately springs to mind. Clean, efficient, and the same thing which stars have been using for around 13 billion years. But imagine for a moment, if there was another energy source available which was dramatically more potent.
A paper published recently in Nature discusses the idea of quark fusion. For anyone who’s uncertain what that means, it’ll require a brief trip down the rabbit hole.. So matter, as you probably know, is made up of atoms. And atoms are made up of electrons and nucleons. Nucleons come in two types, protons and neutrons, and are a subtypes of a whole family of subatomic particles called baryons. Baryons, in turn, are made up of quarks. Quarks, as far as we can currently prove, are the most fundamental building block of matter there is★, and they come in six types. Every baryon contains three of them – so, as an example, in its most fundamental terms, a hydrogen atom is a structure made from two up quarks, one down quark, and an electron.
Still with me? Cool. So Marek Karliner and Jonathan Rosner, a pair of physicists working in Tel Aviv and Chicago respectively, published their work all about the idea of directly fusing quarks. Specifically bottom quarks.
Now, I’m not a particle physicist or a nuclear physicist, so I may be missing a few of the finer points in all of this, but the concept concerns bottom quarks – the second heaviest type. One of these quarks alone is already over 4 times as massive as an entire proton. Apparently, fusing two of them releases a hilarious amount of energy.
How much energy? Here’s a comparison.
238U ⟶ 92Kr + 141Ba + 3 1n ……………… ~0.9 MeV
3He + 3He ⟶ 4He + 2 1H ……………….. 12.86 MeV
Λb + Λb ⟶ Ξbb + 1n ………………………… 138 MeV
Splitting uranium into krypton and barium produces about 0.9 MeV of energy per reaction and spits out 3 neutrons (most fission reactions give out roughly this amount of energy). Fusion of helium-3 is the most energy efficient fusion reaction, producing one helium-4 atom, and 2 protons, and gives 12.86 MeV of energy.
The symbols in the third reaction may be less familiar. Λ and Ξ are types of baryon (quarks don’t really exist outside baryons or mesons), but the important part is those b symbols. Λb is a lamba baryon containing one bottom quark. Ξbb is a xi baryon containing two bottom quarks. Karliner and Rosner describe this as being a quark level analogue of a nuclear fusion reaction.
The amazing part is the energy released! The quark fusion reaction releases 138 MeV, which is 10.7 times as much as helium-3 fusion, and 153.3 times as much energy as a nuclear fission reaction!
The biggest difference is that the other reactions here are chain reactions. The additional products can go on to set off additional reactions, which is what makes them useful in energy production (and scary in weaponry). Just like Meitner, Karliner was concerned by the potential implications of such a huge energy release from a single reaction. However, quark fusion is exactly that – a single reaction. Bottom quarks only exist for a fleeting moment at most, so with no means of easily producing or storing them, and no means for a chain reaction, a quark fusion reaction like this is just a one off.
So sadly, there’s not much scope for any future source of energy here. At least not yet. Guess we’ll have to stick with solar and trying to make helium-3 fusion economically viable.
★ String theorists will argue this point, and as soon as someone has evidence that strings exist, I’ll gladly concede.