#REDIRECT [[ Category:UnsolvedList of unsolved problems in astronomy | ]] ▼
{{Mergeto|Unsolved problems in physics|date=June 2009}}
There are a variety of problems in astronomy regarding the universe.
Some of them are:
=== [[Physical cosmology|Cosmology]] and [[astronomy]] ===
; [[Accelerating universe]] and the [[Cosmological constant]]: Why doesn't the [[zero-point energy]] of the [[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 [[anthropic principle|right time]]? Or is the nature of the [[dark energy]] driving this acceleration differently?
; [[Baryogenesis|Baryon asymmetry]]: Why is there far more [[matter]] than [[antimatter]] in the [[observable universe]]?
; [[Dark matter]]: What is dark matter?<ref name = "newscientist">[http://www.newscientist.com/article/mg18524911.600-13-things-that-do-not-make-sense.html 13 things that do not make sense] newscientistspace, 19 March 2005, Michael Brooks</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?
; [[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>Open Questions, Particle Physics, item 6</ref> or does nature make use of strong dynamics in breaking electroweak symmetry, as proposed by [[Technicolor (physics)|Technicolor]]?
; [[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>Open Questions item 4</ref>
; [[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 the same. 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 only 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?
; [[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, or is it the Poincaré space, or is it another 3-manifold?
; [[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?
=== [[Astronomy]] and [[astrophysics]] ===
; [[Accretion disc]] jets: Why do the accretion discs 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 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?
; [[Corona#Coronal heating problem|Corona heating problem]]: Why is the Sun's Corona (atmosphere layer) so much hotter than the Sun's surface?****
; [[Extraterrestrial life]]: Is there life outside of Earth? There have been many claimed pieces of evidence of its existence, but none of them are widely accepted.
; [[Gamma ray burst]]s (short duration): How do these short-duration high-intensity bursts originate?<ref>Open Questions, Cosmology and Astrophysics, item 11</ref>
; Observational anomalies:
: [[Hipparcos|Hipparcos anomaly]]: How far away are the [[Pleiades (star cluster)|Pleiades]], exactly?**
: [[Pioneer anomaly]]<ref name="newscientist" />: What causes the apparent residual sunward acceleration of the [[Pioneer program|Pioneer]] spacecraft?<ref>Open Questions, Particle Physics, item 13</ref><ref>newscientistspace item 8</ref> ****
: [[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 ''[[Ultra-high-energy cosmic ray|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]]?<ref>Open Questions, Cosmology and Astrophysics, item 12</ref><ref>newscientistspace item 3</ref>
==References==
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{{unsolved problems}}
▲[[Category:Unsolved problems in astronomy| ]]
[[Category:Lists of unsolved problems|Astronomy]]
[[Category:Astronomy lists]]
[[fi:Astronomian ratkaisemattomat ongelmat]]
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