With the rumors of a Higgs Boson detected at Fermilab now getting the sort of official denial that in politics would mean the rumors were about to be confirmed in spectacular fashion, it’s looking like we’ll have to wait a little while longer before the next “Holy Grail” of physics gets discovered.
Strictly speaking, the only thing I recall being officially dubbed a “Holy Grail” that’s been discovered was Bose-Einstein Condensation (BEC), first produced by eventual Nobelists Carl Wieman and Eric Cornell in 1995. Somebody, I think it was Keith Burnett of Oxford, was quoted in the media calling BEC the Holy Grail of atomic physics, which drew a bit of eye-rolling mockery at the time (but thankfully not the sort of overreaction that “God particle” for the Higgs gets). It’s a little overwrought, but not a completely terrible analogy: BEC in dilute atomic vapors was something that had been predicted 70-ish years previously, and actively sought for something like 20 years (depending on who you ask) before its discovery, so it had a decent quest aspect to it.
Of course, the problem with the analogy is that in Arthurian mythology, there was one and only one Holy Grail. In physics, there are lots of them, or at least lots of things that might fairly be called the Holy Grail of one subfield or another. The Higgs is probably the best known one currently being sought, and almost certainly the most expensive, but it’s far from the only one.
The Holy Grail of solid-state physics is a working theory of high-temperature superconductivity. The phenomenon was discovered in the mid-1980’s, to the delight of physics demo shows everywhere, who can now levitate magnets with just a little liquid nitrogen and a chunk of ceramic, but as yet we do not have a comprehensive theory of how these systems work comparable to the BCS theory that explains normal superconductivity. Lots of people are looking, and whoever comes up with one is more or less assured of a trip to Stockholm the next December, but for now, it remains out of reach.
Positive detection of gravitational waves has most of the characteristics of a Holy Grail. Despite an early claim by Weber that basically nobody believes, nobody has ever definitively detected a gravitational wave passing by. Their effects have been observed indirectly in the behavior of pulsars and the like, but a clear and unambiguous signal from one of the gravity-wave detectors now working or in development would be pretty spectacular.
Similarly, dark matter remains a Holy Grail, despite a few tantalizing hits that there might be something peeking out of the CDMS data, or one of the other experiments that have sorta-kinda-maybe seen something. Explaining the nature of dark energy would be an even bigger accomplishment, though that particular quest might be too recent in origin for it to count as a Grail.
Closer to the areas that I follow closely, the best current Grail candidate would be an electric dipole moment of the electron or another fundamental particle. In the cold-atom world, a degenerate Fermi gas might’ve been a good candidate to follow BEC as a cold-atom Grail, but it was achieved a little too quickly– Deb Jin and colleagues at JILA reached Fermi degeneracy five-ish years after BEC– and while it’s proven to be a rich source of physics (dozens of DAMOP talks on the subject), it never had the sense of suspense about it that BEC did. I’m not sure there is a cold-atom Grail at present, actually.
Those are the Holy Grails of the moment, at least the ones I can think of. What am I missing in physics? What are the Holy Grails of other areas of science?