General physics/quantum physics • Perform a
loophole-free Bell test experiment (1970–2015): In October 2015, scientists from the
Kavli Institute of Nanoscience reported that the failure of the local hidden-variable hypothesis is supported at the 96% confidence level based on a "loophole-free Bell test" study. These results were confirmed by two studies with statistical significance over 5 standard deviations which were published in December 2015.
Cosmology and general relativity • Existence of
gravitational waves (1916–2016): On 11 February 2016, the
Advanced LIGO team announced that they had
directly detected gravitational waves from a
pair of black holes
merging, which was also the first detection of a stellar binary black hole. • Numerical solution for
binary black hole (1960s–2005): The numerical solution of the two body problem in general relativity was achieved after four decades of research. Three groups devised the breakthrough techniques in 2005 (
annus mirabilis of
numerical relativity). •
Cosmic age problem (1920s–1990s): The estimated age of the universe was around 3 to 8 billion years younger than estimates of the ages of the oldest stars in the Milky Way. Better estimates for the distances to the stars, and the recognition of the accelerating expansion of the universe, reconciled the age estimates.
High-energy physics/particle physics • Existence of
pentaquarks (1964–2015): In July 2015, the
LHCb collaboration at
CERN identified pentaquarks in the channel, which represents the decay of the bottom
lambda baryon into a
J/ψ meson , a
kaon and a
proton (p). The results showed that sometimes, instead of decaying directly into mesons and baryons, the decayed via intermediate pentaquark states. The two states, named and , had individual
statistical significances of 9 σ and 12 σ, respectively, and a combined significance of 15 σ—enough to claim a formal discovery. The two pentaquark states were both observed decaying strongly to , hence must have a valence quark content of two
up quarks, a
down quark, a
charm quark, and an anti-charm quark (), making them
charmonium-pentaquarks. • Existence of
quark-gluon plasma, a new phase of matter was discovered and confirmed in experiments at
CERN-
SPS (2000),
BNL-
RHIC (2005) and CERN-
LHC (2010).–2012): The mechanism responsible for breaking the electroweak gauge symmetry, giving mass to the
W and Z bosons, was solved with the discovery of the
Higgs boson of the
Standard Model, with the expected couplings to the weak bosons. No evidence of a strong dynamics solution, as proposed by
technicolor, has been observed. •
Origin of mass of most elementary particles: Solved with the discovery of the
Higgs boson, which implies the existence of the
Higgs field giving mass to these particles. •
Proton radius puzzle: A 2010 measurement of the
charge radius for the
proton found a significantly smaller value than past measurements. Measurements since 2019 supported the smaller value of . A 2022 reanalysis of old data with a revised theoretical model also supported the smaller value.
Astronomy and astrophysics • Origin of short
gamma-ray burst (1993–2017): From binary
neutron stars merger, produce a
kilonova explosion and short gamma-ray burst
GRB 170817A was detected in both
electromagnetic waves and
gravitational wave GW170817. •
Missing baryon problem (1998–2017): proclaimed solved in October 2017, with the missing baryons located in hot intergalactic gas. • Long-duration
gamma-ray bursts (1993–2001): Solved by a new understanding of
neutrino physics, requiring a modification of the
Standard Model of
particle physics—specifically,
neutrino oscillation. • Saturn's core spin was determined from its gravitational field.
Rapidly solved problems • Existence of
time crystals (2012–2016): The idea of a quantized time crystal was first theorized in 2012 by
Frank Wilczek. In 2016, Khemani et al. and Else et al. independently of each other suggested that periodically driven quantum spin systems could show similar behaviour. Also in 2016, Norman Yao at Berkeley and colleagues proposed a different way to create discrete time crystals in spin systems. This was then used by two teams, a group led by
Christopher Monroe at the
University of Maryland and a group led by
Mikhail Lukin at
Harvard University, who were both able to show evidence for time crystals in the laboratory setting, showing that for short times the systems exhibited the dynamics similar to the predicted one. •
Photon underproduction crisis (2014–2015): This problem was resolved by Khaire and Srianand. They show that a factor 2 to 5 times large metagalactic photoionization rate can be easily obtained using updated quasar and galaxy observations. Recent observations of quasars indicate that the quasar contribution to ultraviolet photons is a factor of 2 larger than previous estimates. The revised galaxy contribution is a factor of 3 larger. These together solve the crisis. •
Hipparcos anomaly (1997–2012): The High Precision Parallax Collecting Satellite (Hipparcos) measured the parallax of the
Pleiades and determined a
distance of 385 light years. This was significantly different from other measurements made by means of actual to apparent brightness measurement or
absolute magnitude. The anomaly was due to the use of a weighted mean when there is a correlation between distances and distance errors for stars in clusters. It is resolved by using an unweighted mean. There is no systematic bias in the Hipparcos data when it comes to star clusters. •
Faster-than-light neutrino anomaly (2011–2012): In 2011, the
OPERA experiment mistakenly observed
neutrinos appearing to travel
faster than light. On 12 July 2012 OPERA updated their paper after discovering an error in their previous flight time measurement. They found agreement of neutrino speed with the speed of light. •
Pioneer anomaly (1980–2012): There was a deviation in the predicted accelerations of the
Pioneer 10 and 11 spacecraft as they left the Solar System. == See also ==