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However, the melting process of a spacetime crystal and its underlying physical mechanisms have not yet been experimentally reported. Here, we present a direct observation of a classical continuous spacetime crystal melting in a table-top experiment with macroscopic active granular disks in 2 + 1 spacetime dimensions. The spacetime crystal is characterized by the spontaneous formation of a coherent, rigid-body rotation of a 2D triangular lattice that persists for almost a day and remains remarkably robust to noise. By tuning the disk packing fraction, we observe a complex three-stage melting process involving a spatially hexatic phase and multiple coexistence regions. Importantly, we show that spatial and temporal crystalline orders melt separately through distinct mechanisms: Spatial order is destroyed by the proliferation of topological defects, while temporal order is lost through the decay of directional persistence caused by the progressive weakening of many-body interactions. Our results demonstrate that the spontaneous breaking of spatial and temporal translational symmetries can be decoupled, leading to the emergence of exotic out-of-equilibrium classical phases of matter.<\/jats:p>","DOI":"10.1073\/pnas.2613063123","type":"journal-article","created":{"date-parts":[[2026,6,30]],"date-time":"2026-06-30T17:43:55Z","timestamp":1782841435000},"update-policy":"https:\/\/doi.org\/10.1073\/pnas.cm10313","source":"Crossref","is-referenced-by-count":0,"title":["Three-stage melting of a macroscopic continuous spacetime crystal"],"prefix":"10.1073","volume":"123","author":[{"ORCID":"https:\/\/orcid.org\/0009-0001-6007-4509","authenticated-orcid":false,"given":"Guoqing","family":"Liu","sequence":"first","affiliation":[{"id":[{"id":"https:\/\/ror.org\/0220qvk04","id-type":"ROR","asserted-by":"publisher"}],"name":"School of Physics and Astronomy, Shanghai Jiao Tong University","place":["Shanghai, China"]},{"id":[{"id":"https:\/\/ror.org\/0220qvk04","id-type":"ROR","asserted-by":"publisher"}],"name":"Institute of Natural Sciences, Shanghai Jiao Tong University","place":["Shanghai, China"]}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0009-0000-8055-211X","authenticated-orcid":false,"given":"Jimin","family":"Bai","sequence":"additional","affiliation":[{"id":[{"id":"https:\/\/ror.org\/0220qvk04","id-type":"ROR","asserted-by":"publisher"}],"name":"School of Physics and Astronomy, Shanghai Jiao Tong University","place":["Shanghai, China"]},{"id":[{"id":"https:\/\/ror.org\/0220qvk04","id-type":"ROR","asserted-by":"publisher"}],"name":"Wilczek Quantum Center, Shanghai Jiao Tong University","place":["Shanghai, China"]}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0001-9392-7507","authenticated-orcid":false,"given":"Matteo","family":"Baggioli","sequence":"additional","affiliation":[{"id":[{"id":"https:\/\/ror.org\/0220qvk04","id-type":"ROR","asserted-by":"publisher"}],"name":"School of Physics and Astronomy, Shanghai Jiao Tong University","place":["Shanghai, China"]},{"id":[{"id":"https:\/\/ror.org\/0220qvk04","id-type":"ROR","asserted-by":"publisher"}],"name":"Wilczek Quantum Center, Shanghai Jiao Tong University","place":["Shanghai, China"]}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-1326-8941","authenticated-orcid":false,"given":"Jie","family":"Zhang","sequence":"additional","affiliation":[{"id":[{"id":"https:\/\/ror.org\/0220qvk04","id-type":"ROR","asserted-by":"publisher"}],"name":"School of Physics and Astronomy, Shanghai Jiao Tong University","place":["Shanghai, China"]},{"id":[{"id":"https:\/\/ror.org\/0220qvk04","id-type":"ROR","asserted-by":"publisher"}],"name":"Institute of Natural Sciences, Shanghai Jiao Tong University","place":["Shanghai, China"]}],"role":[{"vocabulary":"crossref","role":"author"}]}],"member":"341","published-online":{"date-parts":[[2026,6,30]]},"reference":[{"key":"e_1_3_4_1_2","volume-title":"Introduction to Solid State Physics","author":"Kittel C.","year":"2018","unstructured":"C. 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Liu M. Baggioli J. Zhang J. Bai Data for \u201cThree-stage melting of a macroscopic continuous spacetime crystal.\u201d Zenodo. https:\/\/doi.org\/10.5281\/zenodo.19563267. 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