The Universe might not be flat (and cosmologists are quietly freaking out)

Everything we know about the shape of the Universe could be completely wrong. This is one of the most fascinating unsolved problems in cosmology, and it almost never gets talked about outside of research papers. It's called the curvature tension, and it links in to the "crisis in cosmology". Astrophysicists have always thought the geometry of the Universe is flat, not its shape, its geometry: which is a very different thing. But back in 2019, a careful analysis of 6 years worth of data from the Planck telescope suggested the geometry of the Universe wasn't flat, and instead was closed. And since then, the debate has gone back and forth in the scientific literature, with some data pointing to a curved Universe and some to a flat one. This video will dive into the details of the curvature tension! Papers mentioned Di Valentino et al. (2019) - https://arxiv.org/pdf/1911.02087 Handley (2019) - https://arxiv.org/pdf/1908.09139 Wu & Xhang (2025) - https://arxiv.org/pdf/2411.06356 Calabrese et al. (2026) - https://arxiv.org/abs/2503.14454 Louis et al. (2025) - https://iopscience.iop.org/article/10.1088/1475-7516/2025/11/062/pdf Addison et al. (2016) - https://iopscience.iop.org/article/10.3847/0004-637X/818/2/132 Rosenberg et al. (2022) - https://academic.oup.com/mnras/article/517/3/4620/6717656 Tristram et al. (2024) - https://www.aanda.org/articles/aa/full_html/2024/02/aa48015-23/aa48015-23.html Bernardis (2000; - behind paywall) - https://www.nature.com/articles/35010035 Spergel et al. (2003) - https://arxiv.org/pdf/astro-ph/0302209 Hinshaw et al. (2013) - https://arxiv.org/pdf/1212.5226 Planck 2015 results - https://arxiv.org/pdf/1502.01589 Planck 2015 constraints on inflation - https://arxiv.org/pdf/1502.02114 Planck 2018 results - https://arxiv.org/pdf/1807.06209 00:00 - Introduction 01:05 - I - What is the difference between the shape and geometry of the Universe? 03:22 - II - Why we care about whether the Universe is flat or not 05:15 - III - How we measure if the Universe is flat 08:33 - IV - The curvature tension and what different data is telling us 15:01 - Bloopers Video filmed on a Sony ⍺7 IV Video edited by Martino Gasparrini: [email protected] Video produced by Marina Hui & Dr Becky Smethurst --- 📚 My book, "A Brief History of Black Holes", out NOW in hardback, paperback, e-book and audiobook (which I narrated myself!): http://lnk.to/DrBecky --- 👕 My merch, including JWST designs, are available here (with worldwide shipping!): https://dr-becky.teemill.com/ --- 🎧 Royal Astronomical Society Podcast that I co-host: podfollow.com/supermassive --- 🔔 Don't forget to subscribe and click the little bell icon to be notified when I post a new video! --- 👩🏽‍💻 I'm Dr. Becky Smethurst, an astrophysicist at the University of Oxford. I love making videos about science with an unnatural level of enthusiasm. I like to focus on how we know things, not just what we know. And especially, the things we still don't know. If you've ever wondered about something in space and couldn't find an answer online - you can ask me! My day job is to do research into how supermassive black holes can affect the galaxies that they live in. In particular, I look at whether the energy output from the disk of material orbiting around a growing supermassive black hole can stop a galaxy from forming stars. http://drbecky.uk.com