{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2025,10,11]],"date-time":"2025-10-11T01:23:09Z","timestamp":1760145789664,"version":"build-2065373602"},"reference-count":39,"publisher":"MDPI AG","issue":"9","license":[{"start":{"date-parts":[[2024,9,3]],"date-time":"2024-09-03T00:00:00Z","timestamp":1725321600000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"funder":[{"name":"Spain MCIN\/AEI\/10.13039\/501100011033","award":["PGC2018-102021-B-100","PID2021-128989NB-I00","CEX2020-001058-M","LACEGAL 734374","EWC 776247"],"award-info":[{"award-number":["PGC2018-102021-B-100","PID2021-128989NB-I00","CEX2020-001058-M","LACEGAL 734374","EWC 776247"]}]},{"name":"Unidad de Excelencia Mar\u00eda de Maeztu","award":["PGC2018-102021-B-100","PID2021-128989NB-I00","CEX2020-001058-M","LACEGAL 734374","EWC 776247"],"award-info":[{"award-number":["PGC2018-102021-B-100","PID2021-128989NB-I00","CEX2020-001058-M","LACEGAL 734374","EWC 776247"]}]},{"name":"European Union","award":["PGC2018-102021-B-100","PID2021-128989NB-I00","CEX2020-001058-M","LACEGAL 734374","EWC 776247"],"award-info":[{"award-number":["PGC2018-102021-B-100","PID2021-128989NB-I00","CEX2020-001058-M","LACEGAL 734374","EWC 776247"]}]},{"name":"Generalitat de Catalunya","award":["PGC2018-102021-B-100","PID2021-128989NB-I00","CEX2020-001058-M","LACEGAL 734374","EWC 776247"],"award-info":[{"award-number":["PGC2018-102021-B-100","PID2021-128989NB-I00","CEX2020-001058-M","LACEGAL 734374","EWC 776247"]}]}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["Symmetry"],"abstract":"<jats:p>In relativity, the Newtonian concepts of velocity and acceleration are observer-dependent quantities that vary with the chosen frame of reference. It is well established that in the comoving frame, cosmic expansion is currently accelerating; however, in the rest frame, this expansion is actually decelerating. In this paper, we explore the implications of this distinction. The traditional measure of cosmic acceleration, denoted by q, is derived from the comoving frame and describes the acceleration of the scale factor a for a 3D space-like homogeneous sphere. We introduce a new parameter qE representing the acceleration experienced between observers within the light cone. By comparing qE to the traditional q using observational data from Type Ia supernovae (SN) and the radial clustering of galaxies and quasars (BAO)\u2014including the latest results from DESI2024\u2014our analysis demonstrates that qE aligns more closely with these data. The core argument of the paper is that \u039b\u2014regardless of its origin\u2014creates an event horizon that divides the manifold into two causally disconnected regions analogous to conditions inside a black hole\u2019s interior, thereby allowing for a rest-frame perspective qE in which cosmic expansion appears to be decelerating and the horizon acts like a friction term. Such a horizon suggests that the universe cannot maintain homogeneity outside. The observed cosmological constant \u039b can then be interpreted not as a driver of new dark energy or a modification of gravity but as a boundary term exerting an attractive force, akin to a rubber band, resisting further expansion and preventing event horizon crossings. This interpretation calls for a reconsideration of current cosmological models and the assumptions underlying them.<\/jats:p>","DOI":"10.3390\/sym16091141","type":"journal-article","created":{"date-parts":[[2024,9,3]],"date-time":"2024-09-03T08:38:47Z","timestamp":1725352727000},"page":"1141","update-policy":"https:\/\/doi.org\/10.3390\/mdpi_crossmark_policy","source":"Crossref","is-referenced-by-count":2,"title":["On the Interpretation of Cosmic Acceleration"],"prefix":"10.3390","volume":"16","author":[{"ORCID":"https:\/\/orcid.org\/0000-0001-9632-0815","authenticated-orcid":false,"given":"Enrique","family":"Gaztanaga","sequence":"first","affiliation":[{"name":"Institute of Cosmology & Gravitation, University of Portsmouth, Dennis Sciama Building, Burnaby Road, Portsmouth PO1 3FX, UK"},{"name":"Institute of Space Sciences (ICE, CSIC), 08193 Barcelona, Spain"},{"name":"Institut d Estudis Espacials de Catalunya (IEEC), 08860 Barcelona, Spain"}]}],"member":"1968","published-online":{"date-parts":[[2024,9,3]]},"reference":[{"key":"ref_1","first-page":"395","article-title":"Die Grundlage der Physick","volume":"3","author":"Hilbert","year":"1915","journal-title":"Konigl. 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