{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,3,24]],"date-time":"2026-03-24T20:28:31Z","timestamp":1774384111680,"version":"3.50.1"},"reference-count":22,"publisher":"MDPI AG","issue":"4","license":[{"start":{"date-parts":[[2023,4,4]],"date-time":"2023-04-04T00:00:00Z","timestamp":1680566400000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"funder":[{"name":"Penn State MRSEC, Center for Nanoscale Science","award":["NSF DMR-1420620"],"award-info":[{"award-number":["NSF DMR-1420620"]}]},{"name":"Penn State MRSEC, Center for Nanoscale Science","award":["HR00111720032"],"award-info":[{"award-number":["HR00111720032"]}]},{"DOI":"10.13039\/100000185","name":"DARPA\/DSO Extreme Optics and Imaging (EXTREME) Program","doi-asserted-by":"publisher","award":["NSF DMR-1420620"],"award-info":[{"award-number":["NSF DMR-1420620"]}],"id":[{"id":"10.13039\/100000185","id-type":"DOI","asserted-by":"publisher"}]},{"DOI":"10.13039\/100000185","name":"DARPA\/DSO Extreme Optics and Imaging (EXTREME) Program","doi-asserted-by":"publisher","award":["HR00111720032"],"award-info":[{"award-number":["HR00111720032"]}],"id":[{"id":"10.13039\/100000185","id-type":"DOI","asserted-by":"publisher"}]}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["Symmetry"],"abstract":"<jats:p>Time-varying materials bring an extra degree of design freedom compared to their conventional time-invariant counterparts. However, few discussions have focused on the underlying physical difference between spatial and temporal boundaries. In this letter, we thoroughly investigate those differences from the perspective of conservation laws. By doing so, the building blocks of optics and electromagnetics such as the reflection law, Snell\u2019s law, and Fresnel\u2019s equations can be analogously derived in a temporal context, but with completely different interpretations. Furthermore, we study the unique features of temporal boundaries, such as their nonconformance to energy conservation and causality.<\/jats:p>","DOI":"10.3390\/sym15040858","type":"journal-article","created":{"date-parts":[[2023,4,4]],"date-time":"2023-04-04T02:30:15Z","timestamp":1680575415000},"page":"858","update-policy":"https:\/\/doi.org\/10.3390\/mdpi_crossmark_policy","source":"Crossref","is-referenced-by-count":6,"title":["Fundamental Asymmetries between Spatial and Temporal Boundaries in Electromagnetics"],"prefix":"10.3390","volume":"15","author":[{"ORCID":"https:\/\/orcid.org\/0000-0003-0326-7707","authenticated-orcid":false,"given":"Wending","family":"Mai","sequence":"first","affiliation":[{"name":"Electrical Engineering Department, The Pennsylvania State University, University Park, PA 16802, USA"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Jingwei","family":"Xu","sequence":"additional","affiliation":[{"name":"Electrical Engineering Department, The Pennsylvania State University, University Park, PA 16802, USA"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"ORCID":"https:\/\/orcid.org\/0000-0001-5629-6478","authenticated-orcid":false,"given":"Douglas H.","family":"Werner","sequence":"additional","affiliation":[{"name":"Electrical Engineering Department, The Pennsylvania State University, University Park, PA 16802, USA"}],"role":[{"role":"author","vocabulary":"crossref"}]}],"member":"1968","published-online":{"date-parts":[[2023,4,4]]},"reference":[{"key":"ref_1","unstructured":"Pozar, D. 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