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We study the junction conditions for R to show that a co-moving observer, like us, located anywhere inside R, measures the same background and has the same past light-cone as an observer in an infinite FLRW with the same density. We also estimate the mass M inside R and show that in the observed universe R&lt;rS\u22612 GM, which corresponds to a Black Hole Universe (BHU). We argue that this original Friedmann\u2013Lemaitre model can explain the observed cosmic acceleration without the need of Dark Energy, because rS acts like a cosmological constant \u039b=3\/rS2. The same solution can describe the interior of a stellar or galactic BHs. In co-moving coordinates the BHU is expanding while in physical or proper coordinates it is asymptotically static. Such frame duality corresponds to a simple Lorentz transformation. The BHU therefore provides a physical BH solution with an asymptotically deSitter metric interior that merges into a Schwarzschild metric exterior without discontinuities.<\/jats:p>","DOI":"10.3390\/sym14091849","type":"journal-article","created":{"date-parts":[[2022,9,8]],"date-time":"2022-09-08T09:51:09Z","timestamp":1662630669000},"page":"1849","update-policy":"https:\/\/doi.org\/10.3390\/mdpi_crossmark_policy","source":"Crossref","is-referenced-by-count":16,"title":["The Black Hole Universe, Part I"],"prefix":"10.3390","volume":"14","author":[{"ORCID":"https:\/\/orcid.org\/0000-0001-9632-0815","authenticated-orcid":false,"given":"Enrique","family":"Gaztanaga","sequence":"first","affiliation":[{"name":"Institute of Space Sciences (ICE, CSIC), 08193 Barcelona, Spain"},{"name":"Institut d Estudis Espacials de Catalunya (IEEC), 08034 Barcelona, Spain"}]}],"member":"1968","published-online":{"date-parts":[[2022,9,5]]},"reference":[{"key":"ref_1","doi-asserted-by":"crossref","first-page":"2.33","DOI":"10.1111\/j.1468-4004.2008.49229_1.x","article-title":"Opposing the multiverse","volume":"49","author":"Ellis","year":"2008","journal-title":"Astron. 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