# Why we measure the universe | Professor Wendy Freedman | TEDxChicago Source: https://www.youtube.com/watch?v=0LAaOOaDq0k Recap page: https://rapidrecap.app/video/0LAaOOaDq0k Generated: 2026-02-03T22:33:13.136+00:00 --- ## Quick Overview Professor Wendy Freedman explains that the Hubble Tension, a discrepancy in measuring the Hubble Constant (the universe's expansion rate), is being addressed by combining three major astronomical breakthroughs: Henrietta Leavitt's discovery of Cepheid variable stars as cosmic beacons, Edwin Hubble's discovery of universal expansion, and the development of CCDs to pierce cosmic dust, all culminating in the construction of massive next-generation telescopes like the Giant Magellan Telescope to achieve higher precision and potentially reveal new physics. **Key Points:** - The Hubble Tension arises from a persistent discrepancy between two primary methods of measuring the Hubble Constant (H0), the rate of the universe's expansion. - Henrietta Leavitt's discovery of Cepheid variable stars allows astronomers to measure distances to galaxies, serving as 'cosmic beacons'. - Edwin Hubble used Cepheid data to show that galaxies are moving away from us, proving the universe is expanding. - CCDs (Charge-Coupled Devices) allow for infrared observations, which pierce cosmic dust that obscures light from distant stars like Cepheids, improving measurement accuracy. - The Webb Telescope, launched in 2021, offers 10 times the image clarity of Hubble, allowing better measurement of Cepheid brightness variations. - The speaker's team is working on next-generation telescopes, like the 80-foot diameter Giant Magellan Telescope, to resolve the Hubble Tension, which currently sits between an H0 value of 67 (from early universe data) and 73 (from local universe data). - The ultimate goal of resolving this tension is to potentially uncover new physics beyond the Standard Model of Cosmology, which currently accounts for only 5% of the universe's composition (atoms). ![Screenshot at 14:10: The speaker illustrates the Hubble Tension using a timeline showing the discrepancy between the Hubble Constant value of 67 \(implying an age of 20 billion years\) and 73 \(implying an age of 10 billion years\), with the expected consensus value of 70 highlighted.](https://ss.rapidrecap.app/screens/0LAaOOaDq0k/00-14-10.jpg) **Context:** Professor Wendy Freedman discusses the long-standing cosmological problem known as the Hubble Tension—the disagreement between different methods of calculating the Hubble Constant, which dictates the expansion rate and age of the universe. She frames this challenge within the context of three historical breakthroughs that underpin modern distance measurements: Leavitt's work on Cepheid variables, Hubble's observation of cosmic expansion, and the advent of CCD technology that overcomes dust obscuration. ## Detailed Analysis Professor Wendy Freedman begins by recounting her childhood awe of the night sky, contrasting it with the scientific work she now does measuring the cosmos. She introduces the three major breakthroughs that have enabled precise cosmic distance measurements: Henrietta Leavitt's discovery of Cepheid variables as standard candles, Edwin Hubble's proof of the universe's expansion using these beacons, and the development of CCDs that allow instruments like the Hubble Space Telescope to see through cosmic dust. She notes that the Hubble Constant (H0), the rate of expansion, is crucial for determining the universe's size and age. The tension arises because measurements derived from the early universe (like the Cosmic Microwave Background, yielding H0 ≈ 67) conflict with measurements from the local universe using Cepheids (yielding H0 ≈ 73). This discrepancy, which translates to a 10-billion-year difference in the calculated age of the universe, is significant enough to suggest a crack in the Standard Model of Cosmology, which only accounts for 5% of the universe (atoms). Freedman highlights the power of the James Webb Space Telescope (JWST) and the future Giant Magellan Telescope (GMT) in providing greater clarity (JWST offers 10x the clarity of Hubble) to resolve this tension, perhaps pointing toward new physics, as the current model leaves 95% of the universe (Dark Matter and Dark Energy) mysterious. ### Historical Foundations - Leavitt's Cosmic Beacons - Hubble's Discovery of Expansion - CCDs Sweeping Away Cosmic Dust ### The Hubble Tension - Discrepancy between H0=67 (CMB, 20 billion years) and H0=73 (Cepheids, 10 billion years) - The conflict suggests flaws in the Standard Model of Cosmology. ### Next-Generation Tools - The James Webb Space Telescope offers 10x the image clarity of Hubble to better measure Cepheids - The Giant Magellan Telescope (GMT) is being built in the Andes to further improve precision. ### Cosmic Composition - The 'Cosmic Pie' shows atoms are only 5% of the universe; 95% is Dark Matter (25%) and Dark Energy (70%). ![Screenshot at 00:01: Opening graphic showing two hands nearly touching across a disintegrating red 'X', symbolizing connection or data transfer related to the talk's theme.](https://ss.rapidrecap.app/screens/0LAaOOaDq0k/00-00-01.jpg) ![Screenshot at 00:30: A stunning night sky image showing the Milky Way over a silhouette of trees, illustrating the distant objects whose light is being measured.](https://ss.rapidrecap.app/screens/0LAaOOaDq0k/00-00-30.jpg) ![Screenshot at 02:01: A slide defining the Hubble Constant as 'The rate at which the universe is expanding,' setting up the core scientific concept of the talk.](https://ss.rapidrecap.app/screens/0LAaOOaDq0k/00-02-01.jpg) ![Screenshot at 08:07: A slide listing the '3 breakthroughs to measure the cosmos': Leavitt's Cosmic Beacons, Hubble's Discovery of Expansion, and CCDs Sweeping Away Cosmic Dust.](https://ss.rapidrecap.app/screens/0LAaOOaDq0k/00-08-07.jpg) ![Screenshot at 14:10: A graphic displaying the Hubble Tension on a number line, showing measurements centering around 67 and 73, with the conflicting age estimates of 20 billion years versus 10 billion years.](https://ss.rapidrecap.app/screens/0LAaOOaDq0k/00-14-10.jpg)