A bubble is a region of gas or vapour enclosed within another phase, most commonly a pocket of air trapped in a liquid film or a dispersed gas phase inside a liquid or solid matrix. Bubbles form in everyday life, industry and nature: soap bubbles, boiling vapour bubbles, gas bubbles in fermentation, metal foams, and bubbles produced by cavitation or decompression processes.

Physical properties and governing principles

Surface tension forces tend to minimise surface area and therefore produce near‑spherical shapes for isolated bubbles. The pressure difference across a curved interface is described qualitatively by the Young–Laplace principle: smaller bubbles have higher internal pressure than larger ones. Thin liquid films that form soap bubbles show shimmering colours from thin-film interference. Collections of bubbles (foams) meet at characteristic angles and form edges known as Plateau borders; the geometry is closely related to minimal surface problems studied by 19th‑century scientists.

Formation, stability and dynamics

Bubbles originate from nucleation at defects, dissolved gas coming out of solution, boiling, or mechanical entrainment. Stability depends on drainage of the film, evaporation, and the presence of surfactants or particles that lower surface tension or arrest thinning. Rapid collapse of bubbles can generate strong local pressures and jets; this underlies cavitation damage and effects exploited in cleaning, sonochemistry and medical ultrasound. Very small bubbles and oscillating bubbles are described by dynamical models such as the Rayleigh–Plesset approach.

Types and applications

  • Soap bubbles: thin films used for demonstration, play and optical effects.
  • Vapour bubbles: form during boiling and phase change.
  • Foams: packed bubbles used for insulation, cushioning, fire suppression and lightweight engineering materials.
  • Microbubbles: engineered for contrast in ultrasound imaging and investigated for targeted drug delivery and water treatment.

Cultural, economic and metaphorical roles

Beyond physical science, "bubble" is a common metaphor for transient concentrated phenomena. In economics an "asset bubble" denotes rapid price inflation often followed by sharp correction. Socially, a "bubble" can describe isolated communities or information environments. Bubbles remain a rich subject for both scientific study and cultural imagination because they combine simple appearance with complex behaviour.