Insights from spectroscopic experiments led to the development of quantum mechanics as the common theoretical framework for describing the physical and chemical properties of atoms, molecules and materials. Later, a full quantum description of charged particles, electromagnetic radiation and special relativity was developed, leading to quantum electrodynamics (QED). This is, to our current understanding, the most complete theory describing photon–matter interactions in correlated many–body systems. In the low-energy regime, simplified models of QED have been developed to describe and analyse spectra over a wide spatiotemporal range as well as physical systems. In this Review, we highlight the interrelations and limitations of such theoretical models, thereby showing that they arise from low-energy simplifications of the full QED formalism, in which antiparticles and the internal structure of the nuclei are neglected. Taking molecular systems as an example, we discuss how the breakdown of some simplifications of low-energy QED challenges our conventional understanding of light–matter interactions. In addition to high-precision atomic measurements and simulations of particle physics problems in solid-state systems, new theoretical features that account for collective QED effects in complex interacting many-particle systems could become a material-based route to further advance our current understanding of light–matter interactions.

光谱实验的见识导致了量子力学的发展，量子力学是描述原子，分子和材料的物理和化学特性的通用理论框架。后来，对带电粒子，电磁辐射和相对论的完整量子描述得到了发展，从而产生了量子电动力学（QED）。根据我们目前的理解，这是描述相关多体系统中光子-物质相互作用的最完整的理论。在低能状态下，已开发出简化的QED模型，以描述和分析宽时空范围以及物理系统中的光谱。在这篇评论中，我们着重介绍了此类理论模型的相互关系和局限性，从而表明它们源自完整QED形式主义的低能耗简化，其中反粒子和原子核的内部结构被忽略了。以分子系统为例，我们讨论了一些低能QED的简化如何挑战我们对光-质相互作用的传统理解。除了高精度原子测量和固态系统中粒子物理问题的模拟外，解释复杂相互作用的多粒子系统中的集体QED效应的新理论特征可能会成为基于材料的途径，以进一步推动我们对当前的理解光与物质的相互作用。