Physics problems solved in recent decades
Manjunath R
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Manjunath R
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- 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.
- Existence of time crystals (2012–2016): In 2016, the idea of time-crystals was proposed by two groups independently Khemani et al. and Else et al. Both of these groups showed that in small systems which are disordered and periodic in time, one can observe the phenomenon of time crystals. Norman Yao et al. extended the calculations for a model (which has the same qualitative features) in the laboratory environment. 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 lab-setting, showing that for short times the systems exhibited the dynamics similar to the predicted one.
- 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.
- 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.
- 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.
- Existence of ball lightning (1638–2014): In January 2014, scientists from Northwest Normal University in Lanzhou, China, published the results of recordings made in July 2012 of the optical spectrum of what was thought to be natural ball lightning made during the study of ordinary cloud–ground lightning on China's Qinghai Plateau. At a distance of 900 m (3,000 ft), a total of 1.3 seconds of digital video of the ball lightning and its spectrum was made, from the formation of the ball lightning after the ordinary lightning struck the ground, up to the optical decay of the phenomenon. The recorded ball lightning is believed to be vaporized soil elements that then rapidly oxidize in the atmosphere. The nature of the true theory is still not clear.
- Higgs boson and electroweak symmetry breaking (1963–2012): 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.
- 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 July 12, 2012 OPERA updated their paper by including the new sources of errors in their calculations. 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 spacecraft as they left the Solar System. It is believed that this is a result of previously unaccounted-for thermal recoil force.
- 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. In 2005 (annus mirabilis of numerical relativity) when three groups devised the breakthrough techniques.
- Long-duration gamma-ray bursts (1993–2003): Long-duration bursts are associated with the deaths of massive stars in a specific kind of supernova-like event commonly referred to as a collapsar. However, there are also long-duration GRBs that show evidence against an associated supernova, such as the Swift event GRB 060614.
- Solar neutrino problem (1968–2001): Solved by a new understanding of neutrino physics, requiring a modification of the Standard Model of particle physics—specifically, neutrino oscillation.
- Create Bose–Einstein condensate (1924–1995): Composite bosons in the form of dilute atomic vapours were cooled to quantum degeneracy using the techniques of laser cooling and evaporative cooling.
- 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.
- Nature of quasars (1950s–1980s): The nature of quasars was not understood for decades. They are now accepted as a type of active galaxy where the enormous energy output results from matter falling into a massive black hole in the centre of the galaxy.