We propose to develop a fast, thin silicon sensor with gain capable to concurrently measure with high precision the space (∼10μm) and time (∼10ps) coordinates of a particle. This will open up new application of silicon detector systems in many fields. Our analysis of detector properties indicates that it is possible to improve the timing characteristics of silicon-based tracking sensors, which already have sufficient position resolution, to achieve four-dimensional high-precision measurements. The basic sensor characteristics and the expected performance are listed, the wide field of applications are mentioned and the required R&D topics are discussed. •We are proposing thin pixel silicon sensors with 10's of picoseconds time resolution.•Fast charge collection is coupled with internal charge multiplication.•The truly 4-D sensors will revolutionize imaging and particle counting in many applications.