A teaching showcase unveils the links between special relativity and the birth of quantum physics

Quantum effects scale up with the frequency of electromagnetic waves. Therefore, modern synchrotron sources of high-frequency x-rays-that can be visited by students either personally or online-offer an opportunity for a captivating introduction to basic quantum notions. We discuss here how they also unveil fascinating and often neglected links between quantum physics and special relativity, and in particular their role in the original thinking of Albert Einstein.