This Science White Paper, prepared in response to the ESA Voyage 2050 call for long-term mission planning, aims to describe the various science possibilities that can be realized with an L-class space observatory that is dedicated to the study of the interactions of cosmic microwave background (CMB) photons with the cosmic web. Our aim is specifically to use the CMB as a backlight – and survey the gas, total mass, and stellar content of the entire observable Universe by means of analyzing the spatial and spectral distortions imprinted on it. These distortions result from two major processes that impact on CMB photons: scattering by free electrons and atoms (Sunyaev-Zeldovich effect in diverse forms, Rayleigh scattering, resonant scattering) and deflection by gravitational potential (lensing effect). Even though the list of topics collected in this White Paper is not exhaustive, it helps to illustrate the exceptional diversity of major scientific questions that can be addressed by a space mission that will reach an angular resolution of 1.5 arcmin (goal 1 arcmin), have an average sensitivity better than 1 μK-arcmin, and span the microwave frequency range from roughly 50 GHz to 1 THz. The current paper also highlights the synergy of our Backlight mission concept with several upcoming and proposed ground-based CMB experiments.

为响应ESA Voyage 2050的长期任务计划而编写的本科学白皮书，旨在描述专用于研究宇宙间相互作用的L级太空天文台可以实现的各种科学可能性具有宇宙网的微波背景（CMB）光子。我们的目标是专门使用CMB作为背光，并通过分析刻在其上的空间和光谱畸变来测量整个可观测宇宙的气体，总质量和恒星含量。这些畸变是由影响CMB光子的两个主要过程引起的：自由电子和原子的散射（各种形式的Sunyaev-Zeldovich效应，瑞利散射，共振散射）和重力引起的偏转（透镜效应）。μ K-弧分，并且跨越从约50 GHz到1太赫兹的微波频率范围。本论文还强调了我们的Backlight任务概念与即将进行的和拟议的地面CMB实验的协同作用。