# How the universe began—and how it is likely to end | Prof Carlos Frenk | TEDxDurham Source: https://www.youtube.com/watch?v=yFfgV_7EKfE Recap page: https://rapidrecap.app/video/yFfgV_7EKfE Generated: 2025-12-22T17:38:19.663+00:00 --- ## Quick Overview The standard model of cosmology ($\Lambda$CDM), which posits a universe dominated by dark energy causing accelerated expansion, is facing significant challenges from new data provided by the Dark Energy Spectroscopic Instrument (DESI), suggesting that dark energy is not constant but is declining over time, potentially leading to a future Big Crunch scenario rather than perpetual expansion or a Big Rip. **Key Points:** - Astronomers observe that all galaxies are moving away from us at a speed proportional to their distance, confirming the universe is expanding (0:12). - Georges Lemaître first formulated the relationship $v = H_0 d$ in 1927, known as the Hubble-Lemaître law, describing this expansion (0:42). - The current understanding of the universe's composition is that only 5% is normal matter, 25% is dark matter, and 70% is dark energy, which opposes gravity and accelerates expansion (4:25). - The DESI experiment has measured distances to over 40 million galaxies to track the expansion history of the universe through cosmic time (12:22). - DESI data indicates that dark energy is not constant ($\Lambda$ is not a cosmological constant) but is declining over time, meaning the standard $\Lambda$CDM model is incompatible with the latest observations (12:50, 12:58). - If dark energy diminishes, the universe might eventually collapse into a singularity (a Big Crunch) in about 30 billion years, suggesting a potential cyclical universe (15:08). - The presentation concludes that a new paradigm is needed to describe the universe, as the current models based on constant dark energy appear to be broken (13:11, 13:59). ![Screenshot at 12:50: The slide presents the headline from the New York Times noting that DESI data suggests astronomers may have fundamentally misunderstood dark energy, contradicting the standard $\\Lambda$CDM model.](https://ss.rapidrecap.app/screens/yFfgV_7EKfE/00-12-50.jpg) **Context:** The presentation by Professor Carlos Frenk at TEDxDurham discusses the current state of cosmological models, particularly the $\Lambda$CDM model, which incorporates a cosmological constant (Lambda) representing dark energy that drives the universe's accelerated expansion. Frenk traces the history from Lemaître's discovery of cosmic expansion to modern challenges posed by new data from the Dark Energy Spectroscopic Instrument (DESI), which suggests dark energy might not be constant, leading to potential alternative end-of-universe scenarios like the Big Crunch. ## Detailed Analysis Professor Carlos Frenk begins by reiterating the observational fact that the universe is expanding, citing the Hubble-Lemaître law established by Georges Lemaître in 1927, where recession velocity ($v$) is proportional to distance ($d$) via the Hubble constant ($H_0$). He then explains the bizarre content of the universe according to the standard $\Lambda$CDM model: 5% normal matter (ordinary atoms), 25% dark matter (which does not emit light), and 70% dark energy, a mysterious repulsive force causing accelerated expansion. Frenk details how the $\Lambda$CDM model, incorporating Einstein's cosmological constant (Lambda), has been the foundation of modern cosmology. He introduces the Dark Energy Spectroscopic Instrument (DESI), which has already measured distances to over 40 million galaxies to precisely track the expansion history. The critical finding presented is that the initial DESI data appears incompatible with the standard $\Lambda$CDM model, indicating that dark energy is not constant but is declining over time. This suggests a fundamental flaw in our current understanding. If dark energy declines, the expansion could eventually reverse, leading to a Big Crunch in about 30 billion years—a scenario that could imply a cyclical universe. Frenk shows simulations (EAGLE simulations) illustrating galaxy formation under these different scenarios (Big Crunch, Indefinite Expansion, Big Rip) to emphasize the implications of the new data, concluding that a new paradigm is needed to fully describe the universe. ### Cosmic Expansion Confirmed - Galaxies recede from us at speeds proportional to distance, described by Lemaître's 1927 $v = H_0 d$ law - The universe is expanding (0:12). ### The $\Lambda$CDM Model Composition - Universe is 5% normal matter, 25% dark matter, and 70% dark energy, which causes acceleration (4:25). ### The Role of DESI - The Dark Energy Spectroscopic Instrument has measured distances to over 40 million galaxies to test the $\Lambda$CDM model with subpercent accuracy (11:22). ### New Data Challenges Standard Model - DESI data suggests dark energy is not constant but is declining in time, making it incompatible with the standard $\Lambda$CDM model (12:50, 12:58). ### Future Fates of the Universe - If dark energy declines (left scenario), the universe might collapse in a Big Crunch after reaching maximum expansion (15:08), possibly leading to a cyclical universe. ![Screenshot at 00:02: TEDxDurham event branding featuring a stylized image of Durham Cathedral against a cosmic backdrop.](https://ss.rapidrecap.app/screens/yFfgV_7EKfE/00-00-02.jpg) ![Screenshot at 00:35: Slide illustrating the timeline of the Big Bang, showing particle formation, cooling radiation, and the formation of galaxies over 13.7 billion years.](https://ss.rapidrecap.app/screens/yFfgV_7EKfE/00-00-35.jpg) ![Screenshot at 02:31: Slide detailing the discovery of the Cosmic Microwave Background radiation \('echo of the Big Bang'\) by Penzias and Wilson.](https://ss.rapidrecap.app/screens/yFfgV_7EKfE/00-02-31.jpg) ![Screenshot at 04:14: Pie chart illustrating the bizarre composition of the universe: 70% Dark Energy, 25% Dark Matter, and only 5% Normal Matter.](https://ss.rapidrecap.app/screens/yFfgV_7EKfE/00-04-14.jpg) ![Screenshot at 12:14: Slide promoting the Dark Energy Spectroscopic Instrument \(DESI\) which features 5000 robotic arms to measure 5000 galaxies simultaneously.](https://ss.rapidrecap.app/screens/yFfgV_7EKfE/00-12-14.jpg)