Why We Measure the Universe: Professor Wendy Freedman on Cosmic Expansion

The Quest to Measure the Cosmos

• 🌌 Professor Wendy Freedman's scientific career was inspired by a childhood experience of gazing at stars and questioning their distance and the universe's size.
• 🔭 Her work focuses on the Hubble constant, a critical quantity that determines the universe's size, age, and fundamental physical laws.
• 💡 The Hubble constant is not just a number; it's a key to understanding humanity's place in the cosmos and its origin and future fate.

Historical Milestones in Cosmic Measurement

• 🌟 Henrietta Leavitt's 1908 discovery of Cepheid variables provided "cosmic beacons" to measure stellar distances based on their brightness-period relationship.
• 🚀 In the 1920s, Edwin Hubble used Cepheids to discover that our Milky Way is one of billions of galaxies and that the universe is expanding.
• 🔬 Early measurements of the Hubble constant led to a fierce debate (50 vs. 100), resulting in a 10-billion-year uncertainty in the universe's age.

The Hubble Constant and Its Challenges

• 🌫️ A major challenge was cosmic dust, which scatters and absorbs starlight, making accurate brightness measurements difficult.
• 💻 The 1980s brought breakthroughs with digital detectors (CCDs) and infrared instruments, allowing astronomers to peer through dust.
• ✅ The Hubble Space Telescope Key Project, led by Freedman, measured the Hubble constant at 72, settling the debate and establishing the universe's age at 13.7 billion years.

Unraveling the Hubble Tension

• ⚠️ A new scientific mystery, the Hubble tension, emerged as measurements from the Big Bang's afterglow (67) conflicted with Cepheid-based values (73).
• 🧩 This tension suggests either undetected errors in measurements or a missing piece of physics beyond the standard cosmological model, which includes dark matter and dark energy.
• 🔭 The James Webb Space Telescope (JWST), launched in 2021, offers unprecedented clarity and infrared capabilities, making it ideal for precise cosmic distance measurements.

New Tools and Future Discoveries

• 📈 Freedman's team is using the JWST to improve the accuracy of the Hubble constant by observing Cepheids, red giants, carbon-rich stars, and supernovae.
• 🌌 Their current JWST observations yield a value of 70, which aligns well with the standard model but still leaves room for the possibility of new physics.
• 🌱 Science is presented as an ongoing, collective human endeavor that opens new chapters and inspires future generations to explore the vast, dark frontier of the universe.