Editing List of unsolved problems in physics

This is a list of some of the major '''[[List of unsolved problems|unsolved problems]] in [[physics]]'''. Some of these problems are [[theory|theoretical]], meaning that existing theories seem incapable of explaining a certain observed [[phenomenon]] or experimental result. The others are [[experiment]]al, meaning that there is a difficulty in creating an experiment to test a proposed theory or investigate a phenomenon in greater detail.<!-- cleanup because looks like Original Research. Needs objective criteria for what is or is not an unsolved problem. For example list of problems reported in abc or listed by xyz. Similar to [[Hilbert]]'s list, or as listed by [[NASA]]. Suggest cite each one to one of the external links? What are the criteria for reputable source or authority? -->

==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 these problems are strongly interrelated. For example, [[extra dimensions]] or [[supersymmetry]] may solve the [[hierarchy problem]]. It is thought that a full theory of [[quantum gravity]] should be capable of answering most of these problems (other than the [[Island of stability]] problem).

===Quantum gravity, cosmology, and general relativity===
; [[Vacuum catastrophe]]: Why does the predicted mass of the [[Vacuum state|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]])?<ref>{{citation|url=http://query.nytimes.com/gst/fullpage.html?res=9D0DE7DB1639F931A15754C0A960958260|title=Don't Pull the String Yet on Superstring Theory|date=July 22, 1996|newspaper=New York Times|author=Alan Sokal}}</ref> 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 hole]]s, [[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 [[String theory#Gauge-gravity duality|Gauge-gravity duality]], or not, as implied by [[Hawking radiation|Hawking]]'s original calculation? If not, and black holes can evaporate away, what happens to the information stored in them (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 [[No hair theorem|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 "see" evidence of higher spatial dimensions?
; [[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? If inflation happened at one point, is it [[chaotic inflation|self-sustaining through inflation of quantum-mechanical fluctuations]], and thus ongoing in some impossibly distant place?
; [[Multiverses]]: Are there physical reasons to expect other universes that are fundamentally non-observable? For instance: Are there quantum mechanical "alternative histories" or [[many worlds interpretation|"many worlds"]]? 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?
; 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?<ref>{{Citation | last = Joshi | first = Pankaj S. | title = Do Naked Singularities Break the Rules of Physics? | magazine = [[Scientific American]] | date = January 2009 | url = http://www.sciam.com/article.cfm?id=naked-singularities }}</ref> Similarly, will the [[closed timelike curve]]s 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]]?
; [[Arrow of time]]: What do the phenomena that differ going forward and backwards in time tell us about the nature of [[time]]? How does time differ from space? Why are [[CP violation]]s 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 (physics)|causality]]? Is there a single possible past? Is the [[present#Philosophy and science|present]] moment physically distinct from the past and future or is it merely an emergent property of consciousness? Why do people appear to agree on what the present moment is? (See also Entropy (arrow of time) below)
; [[Principle of locality|Locality]]: Are there non-local phenomena in quantum physics? If they exist, are non-local phenomena limited to transfers of information, or can energy and matter 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 relate to [[quantum entanglement]]? How does this elucidate the proper interpretation of the fundamental nature of quantum physics?
; [[Ultimate fate of the universe|Future of the universe]]: Is the universe heading towards a [[Big Freeze]], a [[Big Rip]], a [[Big Crunch]] or a [[Big Bounce]]? Is our universe part of an infinitely recurring [[cyclic model]]?

===High energy physics/Particle physics===
{{see also|Beyond the Standard Model}}
; [[Higgs mechanism]]: Does the Higgs particle exist? What are the implications if it does not?  Is there only one of them?
; [[Hierarchy problem]]: Why is [[gravity]] such a weak force? It becomes strong for particles only at the [[Planck scale]], around 10<sup>19</sup> [[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 [[renormalization|quantum corrections]] on the order of the Planck scale? Is the solution [[supersymmetry]], [[extra dimensions]], or just [[anthropic principle|anthropic]] [[fine-tuning]]?
; [[Magnetic monopole]]s: 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]].<ref>[[Paul Dirac|Dirac, Paul]], "[http://users.physik.fu-berlin.de/~kleinert/files/dirac1931.pdf Quantised Singularities in the Electromagnetic Field]". ''[[Proceedings of the Royal Society]]'' '''A 133''', 60 (1931).</ref>
; [[Proton decay]] and [[Grand unification theory|unification]]: How do we unify the three different [[Quantum mechanics|quantum mechanical]] [[fundamental interaction]]s of [[quantum field theory]]? As the lightest [[baryon]], are [[proton]]s absolutely stable? If not, 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 comprise [[dark matter]]?
; [[Generation (particle physics)|Generations of matter]]: Are there more than three generations of [[quark]]s and [[lepton]]s? Why are there generations at all? Is there a theory that can explain the masses of particular quarks and leptons in particular generations from first principles (a theory of [[Yukawa coupling]]s)?
; [[Symmetry in physics|Fundamental symmetries]] and [[Neutrinos]]: What is the nature of the [[neutrinos]], what are their masses, and how have they shaped the evolution of the [[universe]]? Why is there now more detectable matter than [[antimatter]] in the universe? What are the unseen forces that were present at the dawn of the universe but disappeared from view as the universe evolved?

===Nuclear physics===
; [[Quantum chromodynamics]]: What are the phases of strongly interacting matter, and what roles do they play in the [[cosmos]]? What is the internal landscape of the [[nucleons]]? What does QCD predict for the properties of strongly interacting matter? What governs the transition of [[quarks]] and [[gluons]] into [[pions]] and nucleons? What is the role of gluons and gluon self-interactions in nucleons and nuclei? What determines the key features of QCD, and what is their relation to the nature of [[gravity]] and [[spacetime]]?
; [[atomic nucleus|Nuclei]] and [[Nuclear astrophysics]]: What is the nature of the [[nuclear force]] that binds [[protons]] and [[neutrons]] into [[Stable isotope|stable nuclei]] and rare isotopes? What is the origin of simple patterns in complex nuclei? 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?
; [[Island of stability]]: What is the heaviest possible stable or metastable nucleus?

===Other problems===
; [[Quantum mechanics]] in the [[correspondence principle|correspondence limit]] (sometimes called [[Quantum chaos]]): Is there a preferred [[interpretation of quantum mechanics]]? How does the quantum description of reality, which includes elements such as the [[quantum superposition|superposition]] of states and [[wavefunction collapse]] or [[quantum decoherence]], give rise to the reality we perceive? Another way of stating this is the [[Measurement problem]] - what constitutes a "measurement" which causes the wave function to collapse into a definite state?
; [[Physical information]]: Are there physical phenomena, such as [[black hole]]s or [[wave function collapse]], which irrevocably destroy information about their prior states?
; [[Theory of everything]] ("[[Grand Unification Theory]]"): Is there a theory which explains the values of all [[fundamental physical constants]]?<ref name="Open Questions">{{cite web |url=http://math.ucr.edu/home/baez/physics/General/open_questions.html |title=Open Questions in Physics |last=Baez |first=John C. ||authorlink=John C. Baez |date=March 2006 |work=Usenet Physics FAQ |publisher=[[University of California, Riverside|University of California, Riverside: Department of Mathematics]] |accessdate=March 7, 2011}}</ref> Is there a theory which explains why the [[gauge group]]s of the [[standard model]] are as they are, why observed [[space-time]] has 3&nbsp;+&nbsp;1 dimensions, and why all laws of physics are as they are? Do "fundamental physical constants" vary over time? Are any of the 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 implied by a theory that explains other unsolved problems in physics?
;[[Gauge theory]]: Do non-Abelian gauge theories with a [[mass gap]] actually exist?

==Empirical phenomena lacking clear scientific explanation==
===Cosmology and astronomy===

; [[Big Bang|Existence of the Universe]]: What is the origin of [[matter]], [[energy]] and [[spacetime]] that form the [[universe]] / [[multiverse]]?
; [[Baryon asymmetry]]: Why is there far more [[matter]] than [[antimatter]] in the [[observable universe]]?
; [[Cosmological_constant_problem#Cosmological_constant_problem|Cosmological constant problem]]: Why doesn't the [[zero-point energy]] of the [[vacuum]] cause a large [[cosmological constant]]? What cancels it out?
; [[Dark energy]]: What is the cause of the observed [[accelerated expansion]] (deSitter 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 [[anthropic principle|right time]]? Is dark energy a pure cosmological constant, or are models of [[Quintessence (physics)|quintessence]] such as [[phantom energy]] applicable?
; [[Dark matter]]: What is dark matter?<ref name="newscientist">{{cite news |title=13 Things That Do Not Make Sense |first=Michael |last=Brooks |url=http://www.newscientist.com/article/mg18524911.600-13-things-that-do-not-make-sense.html |newspaper=[[New Scientist]] |id=Issue 2491|date=March 19, 2005 |accessdate=March 7, 2011}}</ref> 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]]?<ref name="Open Questions"/>
; [[Horizon problem]]: Why is the distant universe so homogeneous, when the [[Big Bang theory]] seems to predict measurable anisotropies of the night sky larger than those observed? Possible approaches to a solution are [[inflation (cosmology)|inflation]] and the [[variable speed of light]] hypothesis.
; [[Copernican_principle#Ecliptic_alignment_of_cosmic_microwave_background_anisotropy|Ecliptic alignment of CMB anisotropy]]: 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 coordinates|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 [[Homology_sphere#The_Poincar.C3.A9_homology_sphere_in_cosmology|Poincaré dodecahedral space]]. Is the shape unmeasurable, the Poincaré space, or another 3-manifold?

===High energy physics/Particle 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]],<ref name="Open Questions"/> or does nature make use of strong dynamics in breaking electroweak symmetry, as proposed by [[Technicolor (physics)|Technicolor]]?
; [[Neutrino mass]]: What is the mechanism responsible for generating [[neutrino]] masses? Is the neutrino its own [[Antineutrino|antiparticle]]? Or could it be an antiparticle that simply cannot join and annihilate with a normal particle because of its irregular state?
; [[Inertial mass]]/[[gravitational mass]] ratio of elementary particles: According to the [[equivalence principle]] of [[general relativity]], the ratio of inertial mass to gravitational mass of all elementary particles is [[one|unity]]. However, there is no experimental confirmation for many particles. In particular, we do not know what the weight of a macroscopic lump of [[antimatter]] of known mass would be.
; [[Nucleon spin structure|Proton spin crisis]]: As initially measured by the [[European Muon Collaboration]], the three main ("valence") [[quark]]s of the [[proton]] account for about 12% of its total spin. Can the gluons that bind the quarks together, as well as the "sea" of quark pairs that are continually being created and annihilating, properly account 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, among others, mainly [[lattice QCD|numerical approaches]] seem to begin to give answers at this limit. How does QCD give rise to the physics of nuclei and nuclear constituents?
; [[Color confinement|Confinement]]: Why has there never been measured a free quark or gluon, but only objects that are built out of them, like [[Meson]]s and [[Baryon]]s? How does this phenomenon emerge from [[Quantum chromodynamics|QCD]]?{{Citation needed|date=October 2010}}
; [[Strong CP problem]] and [[axion]]s: Why is the [[strong nuclear interaction]] invariant to [[parity (physics)|parity]] and [[charge conjugation]]? Is [[Peccei-Quinn theory]] the solution to this problem?
; [[List of particles#Hypothetical particles|Hypothetical particles]]: Which of the hypothetical particles predicted by supersymmetric theories and other fairly well-known theories actually occur in nature?

===Astronomy and astrophysics===
; [[Accretion disc jet]]s: Why do the [[accretion disc]]s surrounding certain astronomical objects, such as the nuclei of [[active galaxy|active galaxies]], emit [[relativistic jet]]s along their polar axes? Why are there [[quasi-periodic oscillation]]s 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?
; [[Corona#Coronal heating problem|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?
; [[Gamma ray burst]]s: How do these short-duration high-intensity bursts originate?<ref name="Open Questions"/>
; [[Supermassive black hole]]s: What is the origin of the [[M-sigma relation]] between supermassive black hole mass and galaxy velocity dispersion?<ref>{{Citation
 | last = Ferrarese | first = Laura | last2 = Merritt | first2 = David | author2-link = David Merritt | title = A Fundamental Relation between Supermassive Black Holes and their Host Galaxies | journal = The Astrophysical Journal | volume = 539 | issue =
 | pages = L9-L12 | date = | origyear = | year = 2000
 | month = | url = http://adsabs.harvard.edu/abs/2000ApJ...539L...9F
 | doi = | id = }}</ref>
; Observational anomalies:
: [[Hipparcos|Hipparcos anomaly]]: What is the actual [[Pleiades (star cluster)#Distance|distance to the Pleiades]]?{{Citation needed|date=October 2010}}
: [[Pioneer anomaly]]<ref name="newscientist"/>: What causes the small additional sunward acceleration of the [[Pioneer program|Pioneer]] spacecraft?<ref name="Open Questions"/><ref name="newscientist"/>
: [[Flyby anomaly]]: Why is the observed energy of satellites [[Gravity assist|flying by earth]] 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 center of galaxies, or is it something else?
; [[Supernova]]e: What is the exact mechanism by which an implosion of a dying star becomes an explosion?
; [[Ultra-high-energy cosmic ray]]<ref name="newscientist"/>: Why is it that some cosmic rays appear to possess energies that are impossibly high (the so called ''OMG 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]]?<ref name="Open Questions"/><ref name="newscientist"/>
; [[Pulsar Time Dilation]]: Why do the emissions from pulsars at great cosmological distances fail to exhibit the predicted time dilation properties?
; 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? <ref>{{cite web
|url = http://www.nasa.gov/mission_pages/cassini/media/cassini-062804.html
|title = Scientists Find That Saturn's Rotation Period is a Puzzle
|date = June 28, 2004
|publisher = NASA
|accessdate = 2007-03-22}}</ref>

===Condensed matter physics===
; [[Amorphous solid]]s: What is the nature of the [[glass transition]] between a fluid or regular solid and a glassy [[phase (matter)|phase]]? What are the physical processes giving rise to the general properties of [[glass]]es?<ref>{{citation |url=http://www.nytimes.com/2008/07/29/science/29glass.html |title=The Nature of Glass Remains Anything but Clear |journal=[[The New York Times]] |date=July 29, 2008 |author=Kenneth Chang}}</ref><ref>"''The deepest and most interesting unsolved problem in solid state theory is probably the theory of the nature of glass and the glass transition.''" {{citation|author=[[Philip Warren Anderson|P.W. Anderson]]| journal=Science|volume=267|year=1995|page=1615|title=Through the Glass Lightly}}</ref>
; [[Cold fusion]]: What is the explanation for the controversial reports of excess heat, radiation and transmutations?<ref name = "newscientist">[http://www.newscientistspace.com/article.ns?id=mg18524911.600 13 things that do not make sense] newscientistspace, 19 March 2005, Michael Brooks</ref><ref>{{citation|title=The World's 20 Greatest Unsolved Problems|author=John R. Vacca|publisher=Prentice Hall|year=2004|ISBN= 9780131426436|url=http://books.google.com/books?id=ouMmAAAACAAJ}}</ref><ref name=Feder2004>{{citation | last1 = Feder | first1 = T. | last2 = John | first2 = O. | year = 2004 | journal = Physics Today | pages = 27 | url = http://www.physicstoday.com/pt/vol-58/iss-1/PDF/vol58no1p31a.pdf | doi = 10.1063/1.1881896}}</ref>
; Cryogenic electron emission: Why does the electron emission in the absence of light increase as the temperature of a [[photomultiplier]] is decreased?<ref>http://www.physorg.com/news187421719.html</ref><ref>{{doi|10.1209/0295-5075/89/58001}}</ref>
; [[High-temperature superconductor]]s: What is the mechanism that causes certain materials to exhibit [[superconductivity]] at temperatures much higher than around 50 [[kelvin]]?<ref name="Open Questions"/>
; [[Sonoluminescence]]: What causes the emission of short bursts of light from imploding bubbles in a liquid when excited by sound?<ref>{{citation |journal=Proceedings: Mathematical, physical, and engineering sciences |volume=453 |publisher=[[Royal Society]] |year=1997 |quote=An unsolved problem in modern physics concerns the phenomenon of sonoluminescence}}</ref>
; [[Turbulence]]: Is it possible to make a theoretical model to describe the statistics of a turbulent flow (in particular, its internal structures)?<ref name="Open Questions"/> Also, under what conditions do [[Navier–Stokes existence and smoothness|smooth solutions to the Navier-Stokes equations]] exist? This is probably the last unsolved problem in Classical or [[Newtonian Physics]].

=== Biophysics ===
; [[Synaptic plasticity]]: It is necessary for [[neural networks|computational]] and [[BCM theory|physical]] models of the brain, but what causes it, and what role does it play in higher-order processing outside the [[hippocampus]] and [[visual cortex]]?
; [[Axon guidance]]: How do [[axon]]s branching out from [[neuron]]s find their targets? This process is crucial to [[nervous system]] development, allowing the building up of the brain.
; [[Stochastic process|Stochasticity]] and robustness to [[Signal-to-noise ratio|noise]] in [[gene expression]]: How do genes govern our body, withstanding different external pressures and internal stochasticity? [[Gene regulatory network|Certain models]] exist for genetic processes, but we are far from understanding the whole picture, in particular in [[Morphogenesis|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? What roles are played by stochasticity?

==Problems solved in recent decades==
;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]].
;[[Age Crisis]] (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 our galaxy. Better estimates for the distances to the stars and the addition of [[dark energy]] into the cosmological model reconciled the age estimates.
;[[Quasar]]s (1980s): The nature of quasars was not understood for decades.<ref name="quasar-jbo">{{cite web | url=http://www.jb.man.ac.uk/public/story/mk1quasars.html | title=The MKI and the discovery of Quasars | publisher=[[Jodrell Bank Observatory]] | accessdate=2006-11-23}}</ref> 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.<ref name="quasar-hubble">[http://hubblesite.org/newscenter/archive/releases/1996/35/image/a/ Hubble Surveys the "Homes" of Quasars] Hubblesite News Archive, 1996-35</ref>

==References==
{{Reflist|colwidth=30em}}

==External links==
* [http://www.sciencemag.org/sciext/125th/ What don't we know?] Science journal special project for its 125th anniversary: top 25 questions and 100 more.
* [http://www.aip.org/pnu/ Physics News Update] A weekly physics news bulletin hosted by the [[American Institute of Physics]].
* [http://www.openproblems.net/ List of links to unsolved problems in physics, prizes and research.]
* [http://www.nasa.gov/centers/glenn/technology/warp/ideachev.html Ideas Based On What We’d Like to Achieve]
* [http://www-conf.slac.stanford.edu/ssi/2004/Default.htm 2004 SLAC Summer Institute: Nature's Greatest Puzzles]
* [http://technology.newscientist.com/article/dn14179-glasss-dual-personality-explained-at-last.html Dual Personality of Glass Explained at Last]

{{unsolved problems}}

{{DEFAULTSORT:List Of Unsolved Problems In Physics}}
[[Category:Unsolved problems in physics| ]]
[[Category:Lists of unsolved problems|Physics]]
[[Category:Physics lists]]

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