Time crystals are a new phase of matter that exhibit periodic motion in their ground state, unlike ordinary crystals that maintain a fixed symmetry in space. They are considered four-dimensional due to their oscillating properties over time, allowing particles to oscillate between states in a predictable manner. Resources like Wikipedia and articles from Physics World provide foundational information, although some users find these explanations challenging to grasp. The concept suggests that time crystals could potentially enhance precision in atomic clocks. Overall, time crystals represent a fascinating intersection of physics and time, sparking ongoing interest and research.