Ripples at the Edge of the Universe
The Cosmic Background Explorer satellite was launched twenty five years after the discovery of the microwave background radiation in 1964. In spectacular fashion in 1992, the COBE team announces that they had discovered `ripples at the edge of the universe’, that is, the first sign of primordial fluctuations at 100,000 years after the Big Bang. These are the imprint of the seeds of galaxy formation.
These appear as temperature variations on the full sky picture that COBE obtained. They are at the level of only one part in one hundred thousand. Viewed in reverse the Universe is highly uniform in every direction lending strong support for the cosmological principle.
The thumbprint image below shows the temperature of the universe in all directions projected onto a plane (similar to a map of the earth):
- The raw temperature map (top) has a large diagonal asymmetry due to our motion with respect to the cosmic microwave background – a Doppler shift.
- The temperature fluctuations after subtraction of the velocity contribution, showing primordial fluctuations and a large radio signal from nearby sources in our own galaxy (the horizontal strip).
- The primordial fluctuations after subtraction of the galaxy signal.