This is a list of some of the unsolved problems in physics. Some of these problems are theoretical, meaning that existing theories seem incapable of explaining some observed phenomenon or experimental result. 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. This is a list of lists of unsolved problems in various subjects: Unsolved problems in biology Unsolved problems in chemistry Unsolved problems in cognitive science Unsolved problems in computer science Unsolved problems in economics Unsolved problems in Egyptology Unsolved problems in governance Unsolved problems in mathematics Unsolved problems in medicine... Physics (Greek: (phúsis), nature and (phusiké), knowledge of nature) is the science concerned with the discovery and characterization of universal laws which govern matter, energy, space, and time. ... The word theory has a number of distinct meanings in different fields of knowledge, depending on their methodologies and the context of discussion. ... In the scientific method, an experiment (Latin: ex-+-periri, of (or from) trying), is a set of actions concerning phenomena. ...

Phenomena lacking clear scientific explanation

Cosmology

Accelerating universe and the Cosmological constant

Why doesn't the zero-point energy of vacuum cause a large cosmological constant? What cancels it out? Is a non-total cancellation of the cosmological constant responsible for the observed accelerated expansion (deSitter phase) of the Universe? If it is, why is the energy density of the cosmological constant 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? Or is the nature of the dark energy driving this acceleration different?

Baryon asymmetry

Why is there far more matter than antimatter in the universe?

Dark matter

What is dark matter?^[1] Is it related to supersymmetry? Do the phenomena attributed to dark matter point not to some form of matter but actually to an extension of gravity?

Entropy (arrow of time)

Why did the universe have such low entropy in the past, resulting in the distinction between past and future and the second law of thermodynamics? ?^[2]

Physical cosmology, as a branch of astrophysics, is the study of the large-scale structure of the universe and is concerned with fundamental questions about its formation and evolution. ... The Accelerating universe is the idea that our universe is undergoing accelerated expansion: distant objects are receding from our galaxy with speeds that increase over time. ... The cosmological constant (usually denoted by the Greek capital letter lambda: Λ) was proposed by Albert Einstein as a modification of his original theory of general relativity to achieve a stationary universe. ... In physics, the zero-point energy is the lowest possible energy that a quantum mechanical physical system may possess; it is the energy of the ground state of the system. ... Look up Vacuum in Wiktionary, the free dictionary. ... The cosmological constant (usually denoted by the Greek capital letter lambda: Λ) was proposed by Albert Einstein as a modification of his original theory of general relativity to achieve a stationary universe. ... In physics and cosmology, the anthropic principle is an umbrella term for various dissimilar attempts to explain the structure of the universe by way of coincidentally balanced features that are necessary and relevant to the existence of observers (usually assumed to be carbon-based life or even specifically human beings). ... In physical cosmology, dark energy is a hypothetical form of energy that permeates all of space and tends to increase the rate of expansion of the universe. ... Baryogenesis is the generic designation for the physical processes that generate matter (more specifically, a class of fundamental particle called baryon) from an otherwise matter-empty state (such as it is generally believed to be the state of the Universe at its onset, the so-called Big Bang). ... This article or section does not cite any references or sources. ... In particle physics, antimatter extends the concept of the antiparticle to matter, whereby antimatter is composed of antiparticles in the same way that normal matter is composed of particles. ... In astrophysics and cosmology, dark matter refers to hypothetical matter of unknown composition that does not emit or reflect enough electromagnetic radiation to be observed directly, but whose presence can be inferred from gravitational effects on visible matter. ... This article or section is in need of attention from an expert on the subject. ... Unsolved problems in physics: Arrow of time: Why did the universe have such low entropy in the past, resulting in the distinction between past and future and the second law of thermodynamics? Entropy is the only quantity in the physical sciences that picks a particular direction for time, sometimes called... Ice melting - classic example of entropy increasing[1] described in 1862 by Rudolf Clausius as an increase in the disgregation of the molecules of the body of ice. ... The past is the portion of the timeline that has already occurred; it is the opposite of the future. ... Look up Future in Wiktionary, the free dictionary. ... The second law of thermodynamics is an expression of the universal law of increasing entropy. ...

High energy physics

Electroweak symmetry breaking

What is the mechanism responsible for breaking the electroweak gauge symmetry, giving mass to the W and Z bosons? Is it the simple Higgs mechanism of the Standard Model?^[3] or does nature make use of strong dynamics in breaking electroweak symmetry, as proposed by Technicolor?

Neutrino mass

What is the mechanism responsible for generating neutrino masses? Is the neutrino its own antiparticle?

Proton Spin Crisis

As initially measured by the European Muon Collaboration, the quarks of the proton account for about 12% of its total spin. What accounts for the rest of it?

Quantum chromodynamics (QCD) in the non-perturbative regime

The equations of QCD remain unsolved at energy scales relevant for describing atomic nuclei, and only mainly numerical approaches seem to begin to give answers at this limit. How does QCD give rise to the physics of nuclei and nuclear constituents?

Strong CP problem and Axions

Why is the strong nuclear interaction invariant to parity and charge conjugation? Is the Peccei-Quinn theory (i.e. mechanism) the solution to this problem? What are the properties of the predicted axion?

Particle physics is a branch of physics that studies the elementary constituents of matter and radiation, and the interactions between them. ... The Higgs mechanism, originally discovered by the British physicist Peter Higgs (building on a previous suggestion by Philip Anderson in condensed matter physics), is the mechanism that gives masses to all elementary particles in particle physics. ... In physics, the W and Z bosons are the elementary particles that mediate the weak nuclear force. ... The Higgs mechanism or Anderson-Higgs mechanism, originally proposed by the British physicist Peter Higgs based on a suggestion by Philip Anderson, is the mechanism that gives mass to all elementary particles in particle physics. ... The Standard Model of Fundamental Particles and Interactions For the Standard Model in Cryptography, see Standard Model (cryptography). ... Technicolor models are theories beyond the Standard Model (sometimes, but not always, GUTs) which do not have a scalar Higgs field. ... The neutrino is an elementary particle. ... Neutrinos are elementary particles denoted by the symbol ν. Travelling close to the speed of light, lacking electric charge and able to pass through ordinary matter almost undisturbed, they are extremely difficult to detect. ... Neutrinos are elementary particles denoted by the symbol ν. Travelling close to the speed of light, lacking electric charge and able to pass through ordinary matter almost undisturbed, they are extremely difficult to detect. ... Corresponding to most kinds of particle, there is an associated antiparticle with the same mass and opposite charges. ... Nucleons (protons and neutrons) are spin=1/2 subatomic particles, composed of quarks. ... The European Muon Collaboration (EMC) is a group that conducts high energy particle physics experiments at CERN. In 1983, it discovered that nucleons inside an nucleus have a different distribution of momentum among their component quarks. ... These are the six flavors of quarks and their most likely decay modes. ... In physics, the proton (Greek proton = first) is a subatomic particle with an electric charge of one positive fundamental unit (1. ... Quantum chromodynamics (QCD) is the theory of the strong interaction, a fundamental force describing the interactions of the quarks and gluons found in nucleons (such as the proton and neutron). ... It has been suggested that lattice field theory be merged into this article or section. ... In particle physics, the strong CP problem is the puzzling question why Quantum Chromodynamics (QCD) does not seem to break the CP-symmetry. ... The axion is an exotic subatomic particle postulated by Peccei-Quinn theory to resolve the strong-CP problem in quantum chromodynamics (QCD). ... A Feynman diagram of a strong proton-neutron interaction mediated by a neutral pion. ... In physics, a parity transformation (also called parity inversion) is the simultaneous flip in the sign of all spatial coordinates: A 3×3 matrix representation of P would have determinant equal to –1, and hence cannot reduce to a rotation. ... C-symmetry means the symmetry of physical laws over a charge-inversion transformation. ... In particle physics, the Peccei-Quinn theory is the most famous proposed solution to the strong CP problem, involving new particles called axions. ... The axion is an exotic subatomic particle postulated by Peccei-Quinn theory to resolve the strong-CP problem in quantum chromodynamics (QCD). ...

Astronomy

Accretion disc jets

Why do the accretion discs surrounding certain astronomical objects, such as the nuclei of active galaxies, emit relativistic jets along their polar axes?

Corona heating problem

Why is the Sun's Corona (atmosphere layer) so much hotter than the Sun's surface?

Gamma ray bursts (short duration)

What is the nature of these extraordinarily energetic astronomical objects that last less than two seconds?^[4]

Hipparcos Anomaly

How far away are the Pleiades, exactly?

Pioneer anomaly

What causes the apparent residual sunward acceleration of the Pioneer spacecraft?^[5][6] ****

Ultra-high-energy cosmic ray

Why is it that some cosmic rays appear to possess energies that are impossibly high (the so called Oh-My-God particle), 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?^[7][8]

A giant Hubble mosaic of the Crab Nebula, a supernova remnant Astronomy is the science of celestial objects (such as stars, planets, comets, and galaxies) and phenomena that originate outside the Earths atmosphere (such as auroras and cosmic background radiation). ... Artists conception of a binary star system with one black hole and one main sequence star An accretion disc (or accretion disk) is a structure formed by diffuse material in orbital motion around a central body. ... An active galaxy is a galaxy where a significant fraction of the energy output is not emitted by the normal components of a galaxy: stars, dust and interstellar gas. ... Relativistic Jet. ... A corona is a type of plasma atmosphere of the Sun or other celestial body, extending millions of kilometres into space, most easily seen during a total solar eclipse, but also observable in a coronagraph. ... The image above shows the optical afterglow of gamma ray burst GRB-990123 taken on January 23, 1999. ... Hipparcos (for High Precision Parallax Collecting Satellite) was an astrometry mission of the European Space Agency (ESA) dedicated to the measurement of stellar parallax and the proper motions of stars. ... A shorter exposure shows less nebulosity. ... The Pioneer anomaly or Pioneer effect refers to the observed deviation from expectations of the trajectories of various unmanned spacecraft visiting the outer solar system, notably Pioneer 10 and 11. ... The US Pioneer program of unmanned space missions was designed for planetary exploration. ... Unsolved problems in physics: Why is it that some cosmic rays appear to possess energies that are theoretically too high? In high-energy physics, an ultra-high-energy cosmic ray (UHECR) is a cosmic ray (subatomic particle) which appears to have extreme kinetic energy, far beyond both its rest mass... Adjectives: Terrestrial, Terran, Telluric, Tellurian, Earthly Atmosphere Surface pressure: 101. ... The Greisen-Zatsepin-Kuzmin limit (GZK limit) is a theoretical upper limit on the energy of cosmic rays from distant sources. ...

Condensed matter physics

Amorphous solids

What is the nature of the transition between a fluid or regular solid and a glassy phase? What are the physical processes giving rise to the general properties of glasses?

High-temperature superconductors

What is the responsible mechanism that causes certain materials to exhibit superconductivity at temperatures much higher than around 50 kelvins?^[9]

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)?^[10]

Condensed matter physics is the field of physics that deals with the macroscopic physical properties of matter. ... An amorphous solid is a solid in which there is no long-range order of the positions of the atoms. ... In physics, a phase transition, (or phase change) is the transformation of a thermodynamic system from one phase to another. ... In the physical sciences, a phase is a set of states of a macroscopic physical system that have relatively uniform chemical composition and physical properties (i. ... Unsolved problems in physics: Why do certain materials exhibit superconductivity at temperatures much higher than 50 kelvins? The term high-temperature superconductor was initially employed to designate the new family of cuprate-perovskite ceramic materials discovered by J.G. Bednorz and K.A. Müller in 1986. ... A magnet levitating above a high-temperature superconductor, cooled with liquid nitrogen. ... The kelvin (symbol: K) is a unit increment of temperature and is one of the seven SI base units. ... Long exposure image of multi-bubble sonoluminescence created by a high intensity ultrasonic horn immersed in a beaker of liquid. ... In fluid dynamics, turbulence or turbulent flow is a flow regime characterized by chaotic, stochastic property changes. ...

Theoretical problems

The following problems are either fundamental theoretical problems, or theoretical ideas which lack experimental evidence and are in search of one, or both, as most of them are.

Some of the following problems are strongly interrelated. For example, extra dimensions or supersymmetry may solve the Hierarchy problem. It is thought the most of these problems (not including the Island of stability problem) should be answered by a full theory of quantum gravity. Kaluza-Klein theory (or KK theory, for short) is a model which sought to unify classical gravity and electromagnetism. ... This article or section is in need of attention from an expert on the subject. ... In theoretical physics, a hierarchy problem occurs when the fundamental parameters (couplings or masses) of some Lagrangian are vastly different (usually larger) than the parameters measured by experiment. ... 3-dimensional rendering of the theoretical Island of Stability. ... This article or section does not adequately cite its references or sources. ...

Quantum gravity and cosmology

Quantum gravity

How can gravity and general relativity be realized as a fully consistent quantum field theory? Is string theory (M-theory) the correct approach? More pressing, how much experimental information can be extracted about physics near Planck scale?

Black holes, Black hole information, Black hole radiation and structure

Do black holes really exist? Do they radiate, 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 it? (Quantum mechanics does not allow information to be destroyed) 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?

Cosmic inflation

Is the theory of cosmic inflation correct, and if so, what are the details of this epoch? What is the hypothetical inflaton field giving rise to inflation? Is there a natural explanation for its peculiar proposed potential? If inflation happened at one point, is it self-sustaining through inflation of quantum-mechanical fluctuations, and thus ongoing in some impossibly distant place?

Multiple universes

Are there physical reasons to believe in other universes that are fundamentally non-observable? For instance: Are there quantum mechanical "alternate histories"? Are there "other" universes with physical laws resulting from alternate ways of breaking the apparent symmetries of physical forces at high energies, possibly incredibly far away due to cosmic inflation? Is the use of the anthropic principle to resolve global cosmological dilemmas justified? ***

This article or section does not adequately cite its references or sources. ... Physical cosmology, as a branch of astrophysics, is the study of the large-scale structure of the universe and is concerned with fundamental questions about its formation and evolution. ... This article or section does not adequately cite its references or sources. ... Gravity is a force of attraction that acts between bodies that have mass. ... General relativity (GR) [also called the general theory of relativity (GTR) and general relativity theory (GRT)] is the geometrical theory of gravitation published by Albert Einstein in 1915/16. ... Quantum field theory (QFT) is the quantum theory of fields. ... Interaction in the subatomic world: world lines of pointlike particles in the Standard Model or a world sheet swept up by closed strings in string theory String theory is a model of fundamental physics whose building blocks are one-dimensional extended objects called strings, rather than the zero-dimensional point... M-theory is a solution proposed for the unknown theory of everything which would combine all five superstring theories and 11-dimensional supergravity together. ... In physics, Planck units are physical units of measurement defined exclusively in terms of the five universal physical constants shown in the table below in such a manner that all of these physical constants take on the numerical value of one when expressed in terms of these units. ... Simulated view of a black hole in front of the Milky Way A black hole is an object with a gravitational field so powerful that a region of space becomes cut off from the rest of the universe – no matter or radiation (including light) that has entered the region can... Simulated view of a black hole in front of the Milky Way A black hole is an object with a gravitational field so powerful that a region of space becomes cut off from the rest of the universe – no matter or radiation (including light) that has entered the region can... In physics, Hawking radiation (also known as Bekenstein-Hawking radiation) is a thermal radiation thought to be emitted by black holes due to quantum effects. ... Simulated view of a black hole in front of the Milky Way A black hole is an object with a gravitational field so powerful that a region of space becomes cut off from the rest of the universe – no matter or radiation (including light) that has entered the region can... Simulated view of a black hole in front of the Milky Way A black hole is an object with a gravitational field so powerful that a region of space becomes cut off from the rest of the universe – no matter or radiation (including light) that has entered the region can... Interaction in the subatomic world: world lines of pointlike particles in the Standard Model or a world sheet swept up by closed strings in string theory String theory is a model of fundamental physics whose building blocks are one-dimensional extended objects called strings, rather than the zero-dimensional point... In physics, Hawking radiation (also known as Bekenstein-Hawking radiation) is a thermal radiation thought to be emitted by black holes due to quantum effects. ... Fig. ... In astrophysics, the no-hair theorem states that black holes are completely characterized only by three externally observable parameters: mass, electrical charge, and angular momentum. ... Kaluza-Klein theory (or KK theory, for short) is a model which sought to unify classical gravity and electromagnetism. ... In physics, spacetime is a mathematical model that combines space and time into a single construct called the space-time continuum. ... In physical cosmology, cosmic inflation is the idea that the nascent universe passed through a phase of exponential expansion that was driven by a negative-pressure vacuum energy density. ... The inflaton is the generic name of the unidentified scalar field (and its associated particle), that may be responsible for an episode of inflation in the very early universe. ... It has been suggested that this article or section be merged with Scalar potential. ... The idea that the universe that we can observe is only part of the whole physical reality led to the definition of multiverse, the set of multiple possible universes. ... In physics and cosmology, the anthropic principle is an umbrella term for various dissimilar attempts to explain the structure of the universe by way of coincidentally balanced features that are necessary and relevant to the existence of observers (usually assumed to be carbon-based life or even specifically human beings). ...

High energy 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 of order of the Planck scale? Is the solution supersymmetry, extra dimensions or just anthropic fine-tuning?

Island of stability

What is the largest theoretically possible stable atom?

Magnetic monopoles

Do particles that carry "magnetic charge" exist?

Proton decay and Unification

How do we unify the three different quantum mechanical fundamental interactions of quantum field theory? As the lightest baryon, are protons absolutely stable? If current theoretical ideas are correct, quarks and leptons are ultimately unified and thus nothing in principle forbids proton decay. If so, then what is the proton's half-life?

Supersymmetry

Is spacetime supersymmetry realized in nature? If so, what is the mechanism of supersymmetry breaking? Does supersymmetry stabilize the electroweak scale, preventing high quantum corrections? Does the lightest supersymmetric particle make up the dark matter?

Particle physics is a branch of physics that studies the elementary constituents of matter and radiation, and the interactions between them. ... In theoretical physics, a hierarchy problem occurs when the fundamental parameters (couplings or masses) of some Lagrangian are vastly different (usually larger) than the parameters measured by experiment. ... Gravity is a force of attraction that acts between bodies that have mass. ... In physics, Planck units are physical units of measurement originally proposed by Max Planck. ... A GEV (or Ground Effect Vehicle) is vehicle that takes advantage of the aerodynamic principle of ground effect (or Wing-in-ground). ... In particle physics, the electroweak scale is the energy scale around 250 GeV, a typical energy of processes described by the electroweak theory. ... A GEV (or Ground Effect Vehicle) is vehicle that takes advantage of the aerodynamic principle of ground effect (or Wing-in-ground). ... In particle physics, the electroweak scale is the energy scale around 250 GeV, a typical energy of processes described by the electroweak theory. ... The Higgs boson is a hypothetical massive scalar elementary particle predicted to exist by the Standard Model of particle physics. ... Figure 1. ... In physics, Planck units are physical units of measurement originally proposed by Max Planck. ... This article or section is in need of attention from an expert on the subject. ... Kaluza-Klein theory (or KK theory, for short) is a model which sought to unify classical gravity and electromagnetism. ... In physics and cosmology, the anthropic principle is an umbrella term for various dissimilar attempts to explain the structure of the universe by way of coincidentally balanced features that are necessary and relevant to the existence of observers (usually assumed to be carbon-based life or even specifically human beings). ... Fine Tuning is the name of XM Satellite Radios eclectic music channel. ... 3-dimensional rendering of the theoretical Island of Stability. ... In physics, a magnetic monopole is a hypothetical particle that may be loosely described as a magnet with only one pole (see electromagnetic theory for more on magnetic poles). ... In particle physics, proton decay is a hypothetical form of radioactive decay in which the proton decays into lighter subatomic particles, usually a neutral pion and a positron. ... It has been suggested that this article or section be merged into Unified field theory. ... Fig. ... A fundamental interaction is a mechanism by which particles interact with each other, and which cannot be explained by another more fundamental interaction. ... Quantum field theory (QFT) is the quantum theory of fields. ... In physics, the proton (Greek proton = first) is a subatomic particle with an electric charge of one positive fundamental unit (1. ... Half-Life For a quantity subject to exponential decay, the half-life is the time required for the quantity to fall to half of its initial value. ... This article or section is in need of attention from an expert on the subject. ... In particle physics, the electroweak scale is the energy scale around 250 GeV, a typical energy of processes described by the electroweak theory. ... Figure 1. ... In astrophysics and cosmology, dark matter refers to hypothetical matter of unknown composition that does not emit or reflect enough electromagnetic radiation to be observed directly, but whose presence can be inferred from gravitational effects on visible matter. ...

Other problems

Emergent phenomena

Is a complete understanding of particle physics sufficient to fully understand all physical phenomena, or are there emergent phenomena in physics whose existence cannot be definitively predicted from a complete understanding of the fundamental particles and forces that govern the universe? ***

Quantum mechanics in the correspondence limit

Is there a preferred interpretation of quantum mechanics? How does the quantum description of reality, which includes elements such as the superposition of states and wavefunction collapse, give rise to the reality we perceive? ***

Physical information

Are there physical phenomena, such as black holes or wave function collapse, which irrevocably destroy information about their prior states? **

Theory of everything

Is there a theory which explains the values of all fundamental physical constants? ^[11] Do "fundamental physical constants" vary over time? Is there a theory which explains why the gauge groups of the standard model are as they are, why observed space-time has 3+1 dimensions, and why all laws of physics are as they are? Is string theory and the anthropic principle correct directions? Are there any testable consequences of that?***

Emergence is the process of deriving some new and coherent structures, patterns and properties in a complex system. ... Fig. ... In physics, the correspondence principle is a principle, first invoked by Niels Bohr in 1923, which states that the behavior of quantum mechanical systems reduce to classical physics in the limit of large quantum numbers. ... It has been suggested that Quantum mechanics, philosophy and controversy be merged into this article or section. ... The term superposition can have several meanings: Quantum superposition Law of superposition in geology and archaeology Superposition principle for vector fields Superposition Calculus is used for equational first-order reasoning This is a disambiguation page — a navigational aid which lists other pages that might otherwise share the same title. ... In certain interpretations of quantum mechanics, wavefunction collapse is one of two processes by which quantum systems apparently evolve according to the laws of quantum mechanics. ... Physical information refers generally to the information that is contained in a physical system. ... Simulated view of a black hole in front of the Milky Way A black hole is an object with a gravitational field so powerful that a region of space becomes cut off from the rest of the universe – no matter or radiation (including light) that has entered the region can... In quantum mechanics, quantum decoherence is the process by which quantum systems in complex environments exhibit classical behavior. ... This article or section is in need of attention from an expert on the subject. ... In physics, fundamental physical constants are physical constants that are independent of systems of units and are in general dimensionless numbers. ... Gauge theories are a class of physical theories based on the idea that symmetry transformations can be performed locally as well as globally. ... The Standard Model of Fundamental Particles and Interactions For the Standard Model in Cryptography, see Standard Model (cryptography). ... In special relativity and general relativity, time and three-dimensional space are treated together as a single four-dimensional pseudo-Riemannian manifold called spacetime. ... Interaction in the subatomic world: world lines of pointlike particles in the Standard Model or a world sheet swept up by closed strings in string theory String theory is a model of fundamental physics whose building blocks are one-dimensional extended objects called strings, rather than the zero-dimensional point... In physics and cosmology, the anthropic principle is an umbrella term for various dissimilar attempts to explain the structure of the universe by way of coincidentally balanced features that are necessary and relevant to the existence of observers (usually assumed to be carbon-based life or even specifically human beings). ...

Problems solved recently

Long duration gamma ray bursts (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.

Solar neutrino problem (2002)

Solved by a new understanding of neutrino physics, requiring a modification of the Standard Model of particle physics — specifically, neutrino oscillation.

Quasars (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 center of the galaxy.

In astronomy, gamma-ray bursts (GRBs) are flashes of gamma rays that last from seconds to hours, the longer ones being followed by several days of X-ray afterglow. ... 2003 (MMIII) was a common year starting on Wednesday of the Gregorian calendar. ... Multiwavelength X-ray image of the remnant of Keplers Supernova, SN 1604. ... A collapsar is a fast-rotating Wolf-Rayet star with a massive (greater than 30 solar masses) core, which collapses to form a large, rotating black hole, drawing in the surrounding envelope of stellar matter at relativistic speeds with a Lorentz factor of around 150, making collapsars the fastest celestial... The solar neutrino problem was a major discrepancy between measurements of the neutrinos flowing through the Earth and theoretical models of the solar interior, lasting from the mid-1960s to about 2002. ... For album titles with the same name, see 2002 (album). ... Neutrinos are elementary particles denoted by the symbol ν. Travelling close to the speed of light, lacking electric charge and able to pass through ordinary matter almost undisturbed, they are extremely difficult to detect. ... The Standard Model of Fundamental Particles and Interactions For the Standard Model in Cryptography, see Standard Model (cryptography). ... Thousands of particles explode from the collision point of two relativistic (100 GeV per ion) gold ions in the STAR detector of the Relativistic Heavy Ion Collider. ... Neutrino oscillation is a quantum mechanical phenomenon predicted by Bruno Pontecorvo whereby a neutrino created with a specific lepton flavor (electron, muon or tau) can later be measured to have a different flavor. ... The introduction to this article provides insufficient context for those unfamiliar with the subject matter. ... An active galaxy is a galaxy where a significant fraction of the energy output is not emitted by the normal components of a galaxy: stars, dust and interstellar gas. ... Simulated view of a black hole in front of the Milky Way A black hole is an object with a gravitational field so powerful that a region of space becomes cut off from the rest of the universe – no matter or radiation (including light) that has entered the region can...

Notes

** Problems marked with two stars are considered by a significant number of physicists to be resolved, though there is still significant debate about them.

*** Problems marked with three stars are considered by some physicists to be outside the purview of physics, more properly philosophical in nature.

**** The existence of problems marked with four stars is disputed.

See also

• String theory
• High energy physics
• Astrophysics

Interaction in the subatomic world: world lines of pointlike particles in the Standard Model or a world sheet swept up by closed strings in string theory String theory is a model of fundamental physics whose building blocks are one-dimensional extended objects called strings, rather than the zero-dimensional point... Particle physics is a branch of physics that studies the elementary constituents of matter and radiation, and the interactions between them. ... Spiral Galaxy ESO 269-57 Astrophysics is the branch of astronomy that deals with the physics of the universe, including the physical properties (luminosity, density, temperature, and chemical composition) of celestial objects such as stars, galaxies, and the interstellar medium, as well as their interactions. ...

References

1. ^ 13 things that do not make sense newscientistspace, 19 March 2005, Michael Brooks, item 5
2. ^ Open Questions item 4
3. ^ Open Questions, Particle Physics, item 6
4. ^ Open Questions, Cosmology and Astrophysics, item 11
5. ^ Open Questions, Particle Physics, item 13
6. ^ newscientistspace item 8
7. ^ Open Questions, Cosmology and Astrophysics, item 12
8. ^ newscientistspace item 3
9. ^ Open Questions, Condensed Matter and Nonlinear Dynamics, item 2
10. ^ Open Questions, Condensed Matter and Nonlinear Dynamics
11. ^ Open Questions, Particle Physics, item 12

External links

• Physics News Update A weekly physics news bulletin hosted by the American Institute of Physics.
• Open Questions in Physics
• New Scientist: 13 things that do not make sense.
• Science Magazine: the most compelling puzzles and questions facing scientists today.
• List of links to unsolved problems in physics, prizes and research.
• Ideas Based On What We’d Like To Achieve
• 2004 SLAC Summer Institute: Nature's Greatest Puzzles