Nobel Lecture: From the Big Bang to the Nobel Prize and beyond*

NASA’s Cosmic Background Explorer satellite mission, the COBE, laid the foundations for modern cosmology by measuring the spectrum and anisotropy of the cosmic microwave background radiation and discovering the cosmic infrared background radiation. I describe the history of the COBE project, its scientific context, the people who built it, and the scientific results. The COBE observed the universe on the largest scales possible by mapping the cosmic microwave and infrared background radiation fields and determining their spectra. It produced conclusive evidence that the hot Big Bang theory of the early universe is correct, showed that the early universe was very uniform but not perfectly so, and that the total luminosity of post–Big Bang objects is twice as great as previously believed. The COBE concept was developed by a Mission Definition Study Team appointed by NASA in 1976, based on three competing proposals submitted in 1974. The COBE was built in-house by Goddard Space Flight Center, with a helium cryostat provided by Ball Aerospace, and was launched on a Delta rocket built by McDonnell Douglas. It is in a circular orbit 900 km above the Earth, in a plane inclined 99° to the equator and roughly perpendicular to the line to the Sun. It carried three instruments, a far infrared absolute spectrophotometer FIRAS , a differential microwave radiometer with three channels DMR , and a diffuse infrared background experiment DIRBE . The helium cryostat cooled the FIRAS and DIRBE for 10 months until the helium was exhausted, but operations continued for a total of 4 years. Subsequent observations have confirmed the COBE results and led to measurements of the main cosmological parameters with a precision of a few percent.