The world's unsolved problems
993 open questions across 14 fields, gathered from Wikipedia. Pick one and start thinking.
110 results in Physics · clear · surprise me
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The sixth problem of 1900 Hilbert's problems about the axiomatization of physics, the problem is either ill-defined or partially solved.
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The Navier–Stokes existence and smoothness and the Yang–Mills existence and mass gap problems of the Millennium Prize Problems, both remain…
The Navier–Stokes existence and smoothness and the Yang–Mills existence and mass gap problems of the Millennium Prize Problems, both remain unsolved.
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Navier–Stokes smoothness is also the 15th Smale's problem from 1998.
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United States DARPA issued 23 mathematical challenges in 2008. Physics problems included
advancing techniques in modelling fluid dynamics and soft matter, developing mathematics for quantum computing, applying quantum field theory and action principles to biology, and finding a relation between the geometric Langlands program and quantum physics.
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Theory of everything
Is there a singular, all-encompassing, coherent theoretical framework of physics that fully explains and links together all physical aspects of the universe?
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Dimensionless physical constants
At the present time, the values of various dimensionless physical constants cannot be calculated; they can be determined only by physical measurement. What is the minimum number of dimensionless physical constants from which all other dimensionless...
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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...
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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...
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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...
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Holographic principle
Is it true that quantum gravity admits a lower-dimensional description that does not contain gravity? A well-understood example of holography is the AdS/CFT correspondence in string theory. Similarly, can quantum gravity in a de Sitter space be understood...
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Quantum spacetime or the emergence of spacetime
Is the nature of spacetime at the Planck scale very different from the continuous classical dynamical spacetime that exists in general relativity? In loop quantum gravity, the spacetime is postulated to be discrete from the beginning. In string theory,...
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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...
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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.)
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Quantum field theory (this is a generalization of the previous problem)
Is it possible to construct, in a mathematically rigorous way, a quantum field theory in 4-dimensional spacetime that includes interactions and does not resort to perturbative methods?
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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 scalar field that gave rise to this cosmic inflation? If inflation happened at one point, is it self-sustaining...
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Cosmic coincidence problem
the energy densities of dark energy and dark matter are of the same order of magnitude in the Universe. Dark matter energy density decreased during the evolution of the universe, so it must have been very large in the past. Is there any relation between...
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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...
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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?
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Size of universe
The diameter of the observable universe is about 93 billion light-years (or equivalently a radius of about 14 Gpc), but what is the size of the whole universe? Is the universe infinite?
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Matter–antimatter asymmetry
Theoretical models suggest that the early universe should have produced equal amounts of matter and antimatter. However, observations indicate no significant primordial antimatter. Understanding the mechanisms that led to this asymmetry is a major unsolved...
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Cosmological principle
Is the universe homogeneous and isotropic at large enough scales, as claimed by the cosmological principle and assumed by all models that use the Friedmann–Lemaître–Robertson–Walker metric, including the current version of the ΛCDM model, or is the...
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Cosmological constant problem
Why does the zero-point energy of the vacuum not cause a large cosmological constant? What cancels it out?
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Dark matter
What is the identity of dark matter? Is it a particle? If so, is it a WIMP, axion, the lightest superpartner (LSP), or some other particle? Or, are the phenomena attributed to dark matter the result of an alternate theory of gravity separate from general...
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Dark energy
What is the cause of the observed accelerating expansion of the universe (the de Sitter phase)? Are the observations rightly interpreted as the accelerating expansion of the universe, or are they evidence that the cosmological principle is false? Why is...
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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?
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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...
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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?
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Hubble tension
The value of H0, which encodes the current expansion rate of the universe, has two values: one from near-universe measurements and one from cosmic microwave background measurements combined with the Lambda-CDM model. These two values disagree to a high...
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Hierarchy problem
The ratio between the strong force and gravity is on the order of . Why is gravity so much weaker than the strong force?
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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.)
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Data last refreshed 2026-10-20 03:01 UTC.