  The public and scientists constantly have different perspectives. While on a
time crystal, they stand in line and ask: What is a time crystal? Show me a
material that is spontaneously crystalline in time? This study synthesizes a
photonic material of Floquet time crystals and experimentally observes its
indicative period-2T beating. We explicitly reconstruct a discrete
time-crystalline ground state and reveal using an appropriately-designed
photonic Floquet simulator the rigid period-doubling as a signature of the
spontaneous breakage of the discrete time-translational symmetry. Unlike the
result of the exquisite many-body interaction, the photonic time crystal is
derived from a single-particle topological phase that can be extensively
accessed by many pertinent nonequilibrium and periodically-driven platforms.
Our observation will drive theoretical and technological interests toward
condensed matter physics and topological photonics, and demystify time crystals
for the non-scientific public.

Quantum Physics;Mesoscale and Nanoscale Physics;Other Condensed Matter;Optics