Classical Physics

Classical physics encompasses the principles that govern macroscopic bodies, fields and continua in regimes where quantum and relativistic effects may be neglected. At its foundation lie Newton’s laws, which prescribe how forces determine the time evolution of positions and momenta, and yield conserved quantities such as energy, momentum and angular momentum. Electromagnetism unifies electric and magnetic phenomena in Maxwell’s equations and predicts the propagation of electromagnetic waves through the wave equation and the Poynting vector for energy flux. Thermodynamics and statistical physics connect microscopic degrees of freedom to macroscopic observables via ensembles, the partition function and laws of thermodynamics, explaining equilibrium, fluctuations and phase transitions. Continuum mechanics treats fluids and solids through constitutive relations, conservation of mass and momentum, and the Navier–Stokes equations for flow. Wave phenomena in acoustics, elastodynamics and optics are described by linear wave equations, giving rise to diffraction, interference, dispersion and transduction between fields and structures. These unified frameworks underpin technologies from mechanical resonators to optical imaging and heat engines, while offering universal limits on performance through conservation laws and fundamental bounds.

Research from Nature Portfolio

Recent work has reformulated classical linear scattering bodies as collections of matrix‐valued oscillators whose intrinsic resonances enforce causality and passivity, yielding universal algebraic constraints on near‐field radiative heat transfer and clarifying maximum thermal conductance between closely spaced objects. Convex‐restriction techniques have recast broad classes of design problems in linear wave physics—including photonic and antenna design—as globally solvable convex programmes, enforcing local power‐conservation constraints to derive tight bounds on figures of merit such as radiative Purcell enhancement. In micro‐actuation, advances in spin‐current volume effects have enabled high‐power density mechanical vibrations through spin‐transfer torque in magnetostrictive films, achieving actuation levels an order of magnitude above conventional microactuators and pointing towards miniaturised acoustic diagnostic and microfluidic devices.

Topic trend for the past 5 years

The graph below shows the article count in Nature Index journals for classical physics.

Technical terms

Memory kernel: A time‐dependent function characterising how past states influence the present response in a generalised Langevin equation.

Analytical continuation: Extension of a multivalued complex function beyond its original domain to reveal branch points and cuts, key to diffraction analysis.

Hamiltonian structure: A formulation of continuum or fluid dynamics in terms of Poisson brackets and energy functionals, integrating reversible and dissipative effects.

Convex restriction: A method that transforms nonconvex design objectives subject to local power‐conservation into globally solvable convex optimisation hierarchies.

Poynting vector: The cross‐product of electric and magnetic fields giving the instantaneous electromagnetic energy flux density.

Notable articles in classical physics

1. Operator Hydrodynamics, OTOCs, and Entanglement Growth in Systems without Conservation Laws. Physical Review X (2018).
2. Fundamental limitations for quantum and nanoscale thermodynamics. Nature Communications (2013).
3. Effective Theory for the Measurement-Induced Phase Transition of Dirac Fermions. Physical Review X (2021).
4. The free-energy cost of accurate biochemical oscillations. Nature Physics (2015).
5. Information-to-work conversion by Maxwell’s demon in a superconducting circuit quantum electrodynamical system. Nature Communications (2018).
6. The power of a critical heat engine. Nature Communications (2016).
7. Stochastic Time Evolution, Information Geometry, and the Cramér-Rao Bound. Physical Review X (2020).
8. Squeezed Thermal Reservoirs as a Resource for a Nanomechanical Engine beyond the Carnot Limit. Physical Review X (2017).
9. Quantum engine efficiency bound beyond the second law of thermodynamics. Nature Communications (2018).
10. All electromagnetic scattering bodies are matrix-valued oscillators. Nature Communications (2023).

Position of Classical Physics in Nature Index by Count

Top 5 leading collaborators in Classical Physics

Collaborating institutions