When the Universe Opened Its Eyes

Key Points:

• François, a Swiss astronomer, reflects on the cosmic microwave background (CMB), the oldest light in the universe, discovered accidentally in 1964 by Arno Penzias and Robert Wilson, which earned them the Nobel Prize in 1978.
• The CMB originated about 380,000 years after the Big Bang, when the universe cooled enough for electrons and protons to form neutral hydrogen atoms, allowing light to travel freely and creating a "surface of last scattering" visible today as a faint microwave glow.
• This ancient light carries tiny temperature fluctuations that represent the primordial density variations which seeded the formation of galaxies and large-scale structures; satellites like COBE, WMAP, and Planck have mapped these ripples with high precision.
• The CMB measurements have helped determine key cosmological parameters, including the universe’s age (13.8 billion years) and composition, but also highlight unresolved puzzles like the "Hubble tension," a discrepancy in the measured expansion rate of the universe.
• François emphasizes the profound significance of the CMB as a cosmic message from the universe’s infancy, urging readers to find hope and unity in this shared heritage, despite earthly divisions and challenges.