Some of the major unsolved problems in physics
are theoretical, meaning that existing theories
seem incapable of explaining a certain observed
phenomenon or experimental result.
The others are experimental, meaning that
there is a difficulty in creating an experiment
to test a proposed theory or investigate a
phenomenon in greater detail.
There are still some deficiencies in the Standard
Model of physics, such as the origin of mass,
the strong CP problem, neutrino oscillations,
matter–antimatter asymmetry, and the nature
of dark matter and dark energy.
Another problem lies within the mathematical
framework of the Standard Model itself—the
Standard Model is inconsistent with that of
general relativity, to the point that one
or both theories break down under certain
conditions (for example within known spacetime
singularities like the Big Bang and the centers
of black holes beyond the event horizon).
== Unsolved problems by subfield ==
The following is a list of unsolved problems
grouped into broad areas of physics.
=== General physics/quantum physics ===
Arrow of time (e.g. entropy's arrow of time):
Why does time have a direction?
Why did the universe have such low entropy
in the past, and time correlates with the
universal (but not local) increase in entropy,
from the past and to the future, according
to the second law of thermodynamics?
Why are CP violations observed in certain
weak force decays, but not elsewhere?
Are CP violations somehow a product of the
second law of thermodynamics, or are they
a separate arrow of time?
Are there exceptions to the principle of causality?
Is there a single possible past?
Is the present moment physically distinct
from the past and future, or is it merely
an emergent property of consciousness?
What links the quantum arrow of time to the
thermodynamic arrow?
Interpretation of quantum mechanics: How does
the quantum description of reality, which
includes elements such as the superposition
of states and wavefunction collapse or quantum
decoherence, give rise to the reality we perceive?
Another way of stating this question regards
the measurement problem: What constitutes
a "measurement" which apparently causes the
wave function to collapse into a definite
state?
Unlike classical physical processes, some
quantum mechanical processes (such as quantum
teleportation arising from quantum entanglement)
cannot be simultaneously "local", "causal",
and "real", but it is not obvious which of
these properties must be sacrificed, or if
an attempt to describe quantum mechanical
processes in these senses is a category error
such that a proper understanding of quantum
mechanics would render the question meaningless.
Grand Unification Theory/Theory of everything:
Is there a theory which explains the values
of all fundamental physical constants?
Is there a theory which explains why the gauge
groups of the standard model are as they are,
and why observed spacetime has 3 spatial dimensions
and 1 temporal dimension?
Do "fundamental physical constants" vary over
time?
Are any of the fundamental particles in the
standard model of particle physics actually
composite particles too tightly bound to observe
as such at current experimental energies?
Are there fundamental particles that have
not yet been observed, and, if so, which ones
are they and what are their properties?
Are there unobserved fundamental forces?
Yang–Mills theory: Given an arbitrary compact
gauge group, does a non-trivial quantum Yang–Mills
theory with a finite mass gap exist?
(This problem is also listed as one of the
Millennium Prize Problems in mathematics.)
Physical information: Are there physical phenomena,
such as wave function collapse or black holes,
that irrevocably destroy information about
their prior states?
How is quantum information stored as a state
of a quantum system?
Dimensionless physical constant: At the present
time, the values of the dimensionless physical
constants cannot be calculated; they are determined
only by physical measurement.
What is the minimum number of dimensionless
physical constants from which all other dimensionless
physical constants can be derived?
Are dimensional physical constants necessary
at all?
Fine-tuned Universe: The values of the fundamental
physical constants are in a narrow range necessary
to support carbon-based life.
Is this because there exist other universes
with different constants, or are our universe’s
constants the result of chance, or some other
factor or process?
Quantum field theory: Is it possible to construct,
in the mathematically rigorous framework of
algebraic QFT, a theory in 4-dimensional spacetime
that includes interactions and does not resort
to perturbative methods?
=== Cosmology and general relativity ===
Problem of time: In quantum mechanics time
is a classical background parameter and the
flow of time is universal and absolute.
In general relativity time is one component
of four-dimensional spacetime, and the flow
of time changes depending on the curvature
of spacetime and the spacetime trajectory
of the observer.
How can these two concepts of time be reconciled?
Cosmic inflation: Is the theory of cosmic
inflation in the very early universe correct,
and, if so, what are the details of this epoch?
What is the hypothetical inflaton scalar field
that gave rise to this cosmic inflation?
If inflation happened at one point, is it
self-sustaining through inflation of quantum-mechanical
fluctuations, and thus ongoing in some extremely
distant place?
Horizon problem: Why is the distant universe
so homogeneous when the Big Bang theory seems
to predict larger measurable anisotropies
of the night sky than those observed?
Cosmological inflation is generally accepted
as the solution, but are other possible explanations
such as a variable speed of light more appropriate?
Origin and future of the universe: How did
the conditions for anything to exist arise?
Is the universe heading towards a Big Freeze,
a Big Rip, a Big Crunch, or a Big Bounce?
Or is it part of an infinitely recurring cyclic
model?
Size of universe: The diameter of the observable
universe is about 93 billion light-years,
but what is the size of the whole universe?
Does a multiverse exist?
Baryon asymmetry: Why is there far more matter
than antimatter in the observable universe?
Cosmological constant problem: Why does the
zero-point energy of the vacuum not cause
a large cosmological constant?
What cancels it out?
Dark matter: What is the identity of dark
matter?
Is it a particle?
Is it the lightest superpartner (LSP)?
Or, do the phenomena attributed to dark matter
point not to some form of matter but actually
to an extension of gravity?
Dark energy: What is the cause of the observed
accelerated expansion (de Sitter phase) of
the universe?
Why is the energy density of the dark energy
component of the same magnitude as the density
of matter at present when the two evolve quite
differently over time; could it be simply
that we are observing at exactly the right
time?
Is dark energy a pure cosmological constant
or are models of quintessence such as phantom
energy applicable?
Dark flow: Is a non-spherically symmetric
gravitational pull from outside the observable
universe responsible for some of the observed
motion of large objects such as galactic clusters
in the universe?
Axis of evil: Some large features of the microwave
sky at distances of over 13 billion light
years appear to be aligned with both the motion
and orientation of the solar system.
Is this due to systematic errors in processing,
contamination of results by local effects,
or an unexplained violation of the Copernican
principle?
Shape of the universe: What is the 3-manifold
of comoving space, i.e. of a comoving spatial
section of the universe, informally called
the "shape" of the universe?
Neither the curvature nor the topology is
presently known, though the curvature is known
to be "close" to zero on observable scales.
The cosmic inflation hypothesis suggests that
the shape of the universe may be unmeasurable,
but, since 2003, Jean-Pierre Luminet, et al.,
and other groups have suggested that the shape
of the universe may be the Poincaré dodecahedral
space.
Is the shape unmeasurable; the Poincaré space;
or another 3-manifold?
=== Quantum gravity ===
Vacuum catastrophe: Why does the predicted
mass of the quantum vacuum have little effect
on the expansion of the universe?
Quantum gravity: Can quantum mechanics and
general relativity be realized as a fully
consistent theory (perhaps as a quantum field
theory)?
Is spacetime fundamentally continuous or discrete?
Would a consistent theory involve a force
mediated by a hypothetical graviton, or be
a product of a discrete structure of spacetime
itself (as in loop quantum gravity)?
Are there deviations from the predictions
of general relativity at very small or very
large scales or in other extreme circumstances
that flow from a quantum gravity theory?
Black holes, black hole information paradox,
and black hole radiation: Do black holes produce
thermal radiation, as expected on theoretical
grounds?
Does this radiation contain information about
their inner structure, as suggested by gauge–gravity
duality, or not, as implied by Hawking's original
calculation?
If not, and black holes can evaporate away,
what happens to the information stored in
them (since quantum mechanics does not provide
for the destruction of information)?
Or does the radiation stop at some point leaving
black hole remnants?
Is there another way to probe their internal
structure somehow, if such a structure even
exists?
Extra dimensions: Does nature have more than
four spacetime dimensions?
If so, what is their size?
Are dimensions a fundamental property of the
universe or an emergent result of other physical
laws?
Can we experimentally observe evidence of
higher spatial dimensions?
The cosmic censorship hypothesis and the chronology
protection conjecture: Can singularities not
hidden behind an event horizon, known as "naked
singularities", arise from realistic initial
conditions, or is it possible to prove some
version of the "cosmic censorship hypothesis"
of Roger Penrose which proposes that this
is impossible?
Similarly, will the closed timelike curves
which arise in some solutions to the equations
of general relativity (and which imply the
possibility of backwards time travel) be ruled
out by a theory of quantum gravity which unites
general relativity with quantum mechanics,
as suggested by the "chronology protection
conjecture" of Stephen Hawking?
Locality: Are there non-local phenomena in
quantum physics?
If they exist, are non-local phenomena limited
to the entanglement revealed in the violations
of the Bell inequalities, or can information
and conserved quantities also move in a non-local
way?
Under what circumstances are non-local phenomena
observed?
What does the existence or absence of non-local
phenomena imply about the fundamental structure
of spacetime?
How does this elucidate the proper interpretation
of the fundamental nature of quantum physics?
=== High-energy physics/particle physics ===
Hierarchy problem: Why is gravity such a weak
force?
It becomes strong for particles only at the
Planck scale, around 1019 GeV, much above
the electroweak scale (100 GeV, the energy
scale dominating physics at low energies).
Why are these scales so different from each
other?
What prevents quantities at the electroweak
scale, such as the Higgs boson mass, from
getting quantum corrections on the order of
the Planck scale?
Is the solution supersymmetry, extra dimensions,
or just anthropic fine-tuning?
Planck particle: The Planck mass plays an
important role in parts of mathematical physics.
A series of researchers have suggested the
existence of a fundamental particle with mass
equal to or close to that of the Planck mass.
The Planck mass is however enormous compared
to any detected particle.
It is still an unsolved problem if there exist
or even have existed a particle with close
to the Planck mass.
This is indirectly related to the hierarchy
problem.
Magnetic monopoles: Did particles that carry
"magnetic charge" exist in some past, higher-energy
epoch?
If so, do any remain today?
(Paul Dirac showed the existence of some types
of magnetic monopoles would explain charge
quantization.)
Proton decay and spin crisis: Is the proton
fundamentally stable?
Or does it decay with a finite lifetime as
predicted by some extensions to the standard
model?
How do the quarks and gluons carry the spin
of protons?
Supersymmetry: Is spacetime supersymmetry
realized at TeV scale?
If so, what is the mechanism of supersymmetry
breaking?
Does supersymmetry stabilize the electroweak
scale, preventing high quantum corrections?
Does the lightest supersymmetric particle
(LSP or Lightest Supersymmetric Particle)
comprise dark matter?
Generations of matter: Why are there three
generations of quarks and leptons?
Is there a theory that can explain the masses
of particular quarks and leptons in particular
generations from first principles (a theory
of Yukawa couplings)?
Neutrino mass: What is the mass of neutrinos,
whether they follow Dirac or Majorana statistics?
Is the mass hierarchy normal or inverted?
Is the CP violating phase equal to 0?
Colour confinement: Why has there never been
measured a free quark or gluon, but only objects
that are built out of them, such as mesons
and baryons?
How does this phenomenon emerge from QCD?
Strong CP problem and axions: Why is the strong
nuclear interaction invariant to parity and
charge conjugation?
Is Peccei–Quinn theory the solution to this
problem?
Could axions be the main component of dark
matter?
Anomalous magnetic dipole moment: Why is the
experimentally measured value of the muon's
anomalous magnetic dipole moment ("muon g−2")
significantly different from the theoretically
predicted value of that physical constant?
Proton radius puzzle: What is the electric
charge radius of the proton?
How does it differ from gluonic charge?
Pentaquarks and other exotic hadrons: What
combinations of quarks are possible?
Why were pentaquarks so difficult to discover?
Are they a tightly-bound system of five elementary
particles, or a more weakly-bound pairing
of a baryon and a meson?
Mu problem: problem of supersymmetric theories,
concerned with understanding the parameters
of the theory.
Koide formula: An aspect of the problem of
particle generations.
The sum of the masses of the three charged
leptons, divided by the square of the sum
of the roots of these masses is
Q
=
2
3
{\textstyle Q={\frac {2}{3}}}
, to within one standard deviation of observations.
It is unknown how such a simple value comes
about, and why it is the exact arithmetic
average of the possible extreme values of
1/3 (equal masses) and 1 (one mass dominates).
=== Astronomy and astrophysics ===
Astrophysical jet: Why do only certain accretion
discs surrounding certain astronomical objects
emit relativistic jets along their polar axes?
Why are there quasi-periodic oscillations
in many accretion discs?
Why does the period of these oscillations
scale as the inverse of the mass of the central
object?
Why are there sometimes overtones, and why
do these appear at different frequency ratios
in different objects?
Diffuse interstellar bands: What is responsible
for the numerous interstellar absorption lines
detected in astronomical spectra?
Are they molecular in origin, and if so which
molecules are responsible for them?
How do they form?
Supermassive black holes: What is the origin
of the M-sigma relation between supermassive
black hole mass and galaxy velocity dispersion?
How did the most distant quasars grow their
supermassive black holes up to 1010 solar
masses so early in the history of the universe?
Kuiper cliff: Why does the number of objects
in the Solar System's Kuiper belt fall off
rapidly and unexpectedly beyond a radius of
50 astronomical units?
Flyby anomaly: Why is the observed energy
of satellites flying by Earth sometimes different
by a minute amount from the value predicted
by theory?
Galaxy rotation problem: Is dark matter responsible
for differences in observed and theoretical
speed of stars revolving around the centre
of galaxies, or is it something else?
Supernovae: What is the exact mechanism by
which an implosion of a dying star becomes
an explosion?
p-nuclei: What astrophysical process is responsible
for the nucleogenesis of these rare isotopes?
Ultra-high-energy cosmic ray: Why is it that
some cosmic rays appear to possess energies
that are impossibly high, given that there
are no sufficiently energetic cosmic ray sources
near the Earth?
Why is it that (apparently) some cosmic rays
emitted by distant sources have energies above
the Greisen–Zatsepin–Kuzmin limit?
Rotation rate of Saturn: Why does the magnetosphere
of Saturn exhibit a (slowly changing) periodicity
close to that at which the planet's clouds
rotate?
What is the true rotation rate of Saturn's
deep interior?
Origin of magnetar magnetic field: What is
the origin of magnetar magnetic field?
Large-scale anisotropy: Is the universe at
very large scales anisotropic, making the
cosmological principle an invalid assumption?
The number count and intensity dipole anisotropy
in radio, NRAO VLA Sky Survey (NVSS) catalogue
is inconsistent with the local motion as derived
from cosmic microwave background and indicate
an intrinsic dipole anisotropy.
The same NVSS radio data also shows an intrinsic
dipole in polarization density and degree
of polarization in the same direction as in
number count and intensity.
There are several other observation revealing
large-scale anisotropy.
The optical polarization from quasars shows
polarization alignment over a very large scale
of Gpc.
The cosmic-microwave-background data shows
several features of anisotropy, which are
not consistent with the Big Bang model.
Space roar: Why is space roar six times louder
than expected?
What is the source of space roar?
Age–metallicity relation in the Galactic
disk: Is there a universal age–metallicity
relation (AMR) in the Galactic disk (both
"thin" and "thick" parts of the disk)?
Although in the local (primarily thin) disk
of the Milky Way there is no evidence of a
strong AMR, a sample of 229 nearby "thick"
disk stars has been used to investigate the
existence of an age–metallicity relation
in the Galactic thick disk, and indicate that
there is an age–metallicity relation present
in the thick disk.
Stellar ages from asteroseismology confirm
the lack of any strong age-metallicity relation
in the Galactic disc.
The lithium problem: Why is there a discrepancy
between the amount of lithium-7 predicted
to be produced in Big Bang nucleosynthesis
and the amount observed in very old stars?
Ultraluminous pulsar: The ultraluminous X-ray
source M82 X-2 was thought to be a black hole,
but in October 2014 data from NASA's space-based
X-ray telescope NuStar indicated that M82
X-2 is a pulsar many times brighter than the
Eddington limit.
Fast radio bursts: Transient radio pulses
lasting only a few milliseconds, from emission
regions thought to be no larger than a few
hundred kilometres, and estimated to occur
several hundred times a day.
While several theories have been proposed,
there is no generally accepted explanation
for them.
The only known repeating FRB emanates from
a galaxy roughly 3 billion light years from
Earth.
=== Nuclear physics ===
Quantum chromodynamics: What are the phases
of strongly interacting matter, and what roles
do they play in the evolution of cosmos?
What is the detailed partonic structure of
the nucleons?
What does QCD predict for the properties of
strongly interacting matter?
What determines the key features of QCD, and
what is their relation to the nature of gravity
and spacetime?
Do glueballs exist?
Do gluons acquire mass dynamically despite
having a zero rest mass, within hadrons?
Does QCD truly lack CP-violations?
Do gluons saturate when their occupation number
is large?
Do gluons form a dense system called Colour
Glass Condensate?
What are the signatures and evidences for
the Balitsky-Fadin-Kuarev-Lipatov, Balitsky-Kovchegov,
Catani-Ciafaloni-Fiorani-Marchesini evolution
equations?
Nuclei and nuclear astrophysics: Why is there
a lack of convergence in estimates of the
mean lifetime of a free neutron based on two
separate- and increasingly precise- experimental
methods?
What is the nature of the nuclear force that
binds protons and neutrons into stable nuclei
and rare isotopes?
What is the nature of exotic excitations in
nuclei at the frontiers of stability and their
role in stellar processes?
What is the nature of neutron stars and dense
nuclear matter?
What is the origin of the elements in the
cosmos?
What are the nuclear reactions that drive
stars and stellar explosions?
=== Atomic, molecular and optical physics
===
Abraham-Minkowski controversy: What is the
momentum of light in optical media?
Whether Abraham's or Minkowski's momentum
is right?Bose–Einstein condensation: How
do we rigorously prove the existence of Bose–Einstein
condensates for general interacting systems?
=== Classical mechanics ===
Singular trajectories in the Newtonian N-body
problem: Does the set of initial conditions
for which particles that undergo near-collisions
gain infinite speed in finite time have measure
zero?
This is known to be the case when N ≤ 4,
but the question remains open for larger N.
=== 
Condensed matter physics ===
High-temperature superconductors: What is
the mechanism that causes certain materials
to exhibit superconductivity at temperatures
much higher than around 25 kelvins?
Is it possible to make a material that is
a superconductor at room temperature?
Amorphous solids: What is the nature of the
glass transition between a fluid or regular
solid and a glassy phase?
What are the physical processes giving rise
to the general properties of glasses and the
glass transition?
Cryogenic electron emission: Why does the
electron emission in the absence of light
increase as the temperature of a photomultiplier
is decreased?
Sonoluminescence: What causes the emission
of short bursts of light from imploding bubbles
in a liquid when excited by sound?
Turbulence: Is it possible to make a theoretical
model to describe the statistics of a turbulent
flow (in particular, its internal structures)?
Also, under what conditions do smooth solutions
to the Navier–Stokes equations exist?
The latter problem is also listed as one of
the Millennium Prize Problems in mathematics.
Alfvénic turbulence: In the solar wind and
the turbulence in solar flares, coronal mass
ejections, and magnetospheric substorms are
major unsolved problems in space plasma physics.
Topological order: Is topological order stable
at non-zero temperature?
Equivalently, is it possible to have three-dimensional
self-correcting quantum memory?
Fractional Hall effect: What mechanism explains
the existence of the
u
=
5
/
2
{\displaystyle u=5/2}
state in the fractional quantum Hall effect?
Does it describe quasiparticles with non-Abelian
fractional statistics?
Liquid crystals: Can the nematic to smectic
(A) phase transition in liquid crystal states
be characterized as a universal phase transition?
Semiconductor nanocrystals: What is the cause
of the nonparabolicity of the energy-size
dependence for the lowest optical absorption
transition of quantum dots?
Metal whiskering: In electrical devices, some
metallic surfaces may spontaneously grow fine
metallic whiskers, which can lead to equipment
failures.
While compressive mechanical stress is known
to encourage whisker formation, the growth
mechanism has yet to be determined.
=== Plasma physics ===
Plasma physics and fusion power: Fusion energy
may potentially provide power from abundant
resource (e.g. hydrogen) without the type
of radioactive waste that fission energy currently
produces.
However, can ionized gases (plasma) be confined
long enough and at a high enough temperature
to create fusion power?
What is the physical origin of H-mode?
Solar cycle: How does the Sun generate its
periodically reversing large-scale magnetic
field?
How do other solar-like stars generate their
magnetic fields, and what are the similarities
and differences between stellar activity cycles
and that of the Sun?
What caused the Maunder Minimum and other
grand minima, and how does the solar cycle
recover from a minima state?
Coronal heating problem: Why is the Sun's
corona (atmosphere layer) so much hotter than
the Sun's surface?
Why is the magnetic reconnection effect many
orders of magnitude faster than predicted
by standard models?
The injection problem: Fermi acceleration
is thought to be the primary mechanism that
accelerates astrophysical particles to high
energy.
However, it is unclear what mechanism causes
those particles to initially have energies
high enough for Fermi acceleration to work
on them.
Solar wind interaction with comets: In 2007
the Ulysses spacecraft passed through the
tail of comet C/2006 P1 (McNaught) and found
surprising results concerning the interaction
of the solar wind with the tail.
=== Biophysics ===
Stochasticity and robustness to noise in gene
expression: How do genes govern our body,
withstanding different external pressures
and internal stochasticity?
Certain models exist for genetic processes,
but we are far from understanding the whole
picture, in particular in development where
gene expression must be tightly regulated.
Quantitative study of the immune system: What
are the quantitative properties of immune
responses?
What are the basic building blocks of immune
system networks?
Unified brain processing theory : How to unify
physics and neuroscience?
Homochirality: What is the origin of the preponderance
of specific enantiomers in biochemical systems?
== Problems solved in recent decades ==
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.
Existence of pentaquarks (1964–2015): In
July 2015, the LHCb collaboration at CERN
identified pentaquarks in the Λ0b→J/ψK−p
channel, which represents the decay of the
bottom lambda baryon (Λ0b) into a J/ψ meson
(J/ψ), a kaon (K−) and a proton (p).
The results showed that sometimes, instead
of decaying directly into mesons and baryons,
the Λ0b decayed via intermediate pentaquark
states.
The two states, named P+c(4380) and P+c(4450),
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 J/ψp, hence must have
a valence quark content of two up quarks,
a down quark, a charm quark, and an anti-charm
quark (uudcc), making them charmonium-pentaquarks.
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.
== See also ==
Hilbert's sixth problem
Lists of unsolved problems
Physical paradox
