If you want a working lightsaber, you might consider making it from glueballs 鈥� bundles of particles made entirely of force. There鈥檚 just one problem. Although theorists are adamant glueballs must exist, those of a more practical bent are equally adamant we鈥檙e unlikely ever to prove it. 鈥淵ou can鈥檛 do an experiment and know they exist,鈥� says of the University of Oxford.
Glueballs are bundles of gluons, particles from the standard model of particle physics that transmit the strong nuclear force. In that respect, gluons are rather like photons 鈥� the particles of light that transmit the electromagnetic force. Gluons bind together the particles called quarks to form protons and neutrons in the atomic nucleus.
Gluons have an odd quirk. Whereas photons themselves do not carry electric charge, gluons do carry strong-force charge. This means that, unlike photons, gluons can stick to themselves. So while you鈥檒l never see a lump of light, a glueball is not just a possibility, but a theoretical necessity.
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Simulations of a world chock-full with gluons even say what sort of energy you would need to make a glueball: around 1500 megaelectronvolts (MeV), or about one-and-a-half times the energy contained in a proton. On the face of it, experiments bear that out. In 1995, Close and fellow theorist Claude Amsler of the University of Zurich in Switzerland showed that two particle 鈥渞esonances鈥� with energies of 1370 and 1500 MeV, which had just been discovered at CERN, . In more recent years, a third resonance at 1710 MeV has also attracted a lot of interest as a possible glueball.
Sadly, it鈥檚 almost undoubtedly not that simple. The strong force is notoriously hard to do calculations with, and for simplicity鈥檚 sake glueball simulations tend to assume a world with a whole load of gluons and not much else. 鈥淭hat is not what the real universe is like,鈥� says Close. 鈥淚f things can mix together, they will.鈥�
It means that in the real universe, by the time you measure a glueball state, quarks will have also begun to stick to it like burrs on a sock, making it nigh-on impossible to prove there was ever a pure glueball there. For that reason, says Close, the explanation for the three suggestive resonances is probably a substantial pot of glue contaminated by varying amounts of different quarks.
So while basic physics makes it more or less certain glueballs exist, basic physics makes it almost equally certain we can never isolate them. 鈥淚f nature was kind, something might stick out,鈥� says Close. 鈥淏ut I鈥檓 not optimistic.鈥� Our inability to isolate them doesn鈥檛 fundamentally change anything 鈥� but it is a frustrating example of how nature seems to give with one hand, and take away with the other. And it means you鈥檙e probably better off banking on a conventional lightsaber.
Read more: 11 scientific wonders we know exist 鈥� but we鈥檝e never seen
