At the Relativistic Heavy Ion Collider (RHIC) on Long Island, the four large detector groups agreed, for the first time, on a consensus interpretation of several year’s worth of high-energy ion collisions: the fireball made in these collisions -- a sort of stand-in for the primordial universe only a few microseconds after the big bang -- was not a gas of weakly interacting quarks and gluons as earlier expected, but something more like a liquid of strongly interacting quarks and gluons (PNU 728).

Other top physics stories for 2005 include, in general chronological order of their appearance throughout the year, the following:

the arrival of the Cassini spacecraft at Saturn and the successful landing of the Huygens probe on the moon Titan (PNU 716);
the development of lasing in silicon (Nature 17 February);

the biggest burst of light ever recorded from outside the solar system, from a soft gamma repeater (PNU 721);
further evidence for superfluid behavior in a solid (PNU 724);

detection of infrared radiation directly from an exoplanet (PNU 724);

zeptogram mass sensitivity in a cantilever sensor (PNU 725);

splashless impact of droplets at low pressures (PNU 725);

the demonstration of pyrofusion, fusion reactions created with a pyroelectric crystal (PNU 729);

the best-yet prediction of hadron masses using lattice QCD (PNU 731);

the best measurement yet of the weak nuclear force (PNU 736);

superfluidity directly observed in a sample of ultracold fermi atoms (PNU 734);

extension of the "comb" technique for measuring frequency (a topic pertaining to the 2005 Nobel prize in physics) into the ultraviolet (PNU 735);
geoneutrinos observed (PNU 739);

hybrid atom-molecule dark states (PNU 744);

using statistical mechanics to predict the effectiveness of flu vaccines (PNU 724);
hydrophobic water (PNU 747);

2005 Nobel Prize (PNU 748);

molecules that walk (PNU 751);

phonon Hall effect (PNU 750);

short gamma ray bursts identified as coming from in-spiraling neutron stars (Nature 6 October);
hyperentangled states (PNU 754);

further progress in research concerning left-handed or negative-refraction materials, including perfect lensing (Science 22 April), almost perfect lensing in the mid-infrared (PNU 750),

and extension of negative-index behavior into the near-infrared region (PNU 756).
http://www.aip.org/pnu/2005/split/757-1.html