An interconnected system of routes or links enabling movement.A network is any interconnected system of routes, links, or nodes that enables the movement of things — whether those things are electrons, data packets, signals, or even species in an ecosystem. The concept is central to physics because it describes how local interactions between individual components give rise to global behavior. From the quantum internet, where entanglement is used to transmit information, to the electrical conductivity of disordered materials, where electrons hop between localized sites, networks provide the structural backbone for understanding complex systems.
Network theory as a formal discipline emerged in the 20th century, with roots in graph theory (Euler's 1736 Königsberg bridges problem) and later developments in random graph theory by Erdős and Rényi in the 1950s. The modern physics of networks, including small-world and scale-free properties, was pioneered by Watts, Strogatz, and Barabási in the late 1990s.
At its core, a network is defined by nodes (the entities) and edges (the connections between them). The behavior of the whole system emerges from the rules governing these connections — for example, whether they are strong or weak, directed or undirected, static or dynamic. In physics, this abstraction allows researchers to model everything from neural connectivity (why neurons can't connect to all others) to ecological interactions (how landscape gaps create diversity) and even the flow of electricity in power grids.
Networks are used to design resilient power grids, optimize transportation systems, understand the spread of diseases, and build the infrastructure for quantum communication networks.
The human brain contains roughly 86 billion neurons, but each neuron connects to only about 1,000 others on average — a sparse network that balances efficiency with metabolic cost.















