page_title: List of unsolved problems in physics
section_title: Condensed matter physics
hierarchical_section_title: List of unsolved problems in physics / Unsolved problems by subfield / Condensed matter physics
caption_attribution_description: Polski: Ułamkowy Kwantowy Efekt Halla (FQHE). Widoczny "schodek" ułamkowy 8/5. Pomiary wykonane w Instytucie Fizyki PAN we Warszawie al. Lotników w dniu 27.01.2000
context_page_description: 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 questions beyond the Standard Model of physics, such as the strong CP problem, neutrino mass, 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.
context_section_description: 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?
  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  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.
  Superfluid transition in helium-4: Explain the discrepancy between the experimental and theoretical determinations of the heat capacity critical exponent α.
caption: Magnetoresistance in a 
    
      
        
          u
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          8
          
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   fractional quantum Hall state.
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