![]() These hot spots and cold spots, which differ in temperature by only millionths of a degree, can be interpreted as very slight difference in the crowding together of matter in the young universe.īy examining the imprint of these wiggles, astronomers can build a template for how the modern universe was formed, with the hot spots becoming the seeds of super-clusters of galaxies and the cold spots giving rise to relative voids. So, we can talk about 'acoustic baryon waves' or more informally 'baryonic wiggles'. The sound waves left their imprint in the distribution of this early matter. Instead we had a plasma of protons, neutrons and related particles, collectively called baryons. ![]() Back then, matter had not yet formed into atoms. The explanation for these fluctuations is that they come from a sound wave that echoed around the early universe. These temperature differences seem to have a certain regularity, with peaks and troughs recurring in a detectable rhythm. Image adapted from: ESA and the Planck Collaboration The 'hot' and 'cold' spots in the cosmic microwave background correspond to today's galaxies and voids. Hot spots have slightly more matter than average cold spots a bit less. These hot spots and cold spots, which differ in temperature by only millionths of a degree, can be interpreted as very slight differences in the crowding together of matter in the young universe. Pictures constructed from satellite data show very subtle variations in the strength of the microwave signal. The CMB is almost, but not exactly, the same whichever direction we look. Now, nearly 14 billion years later, the universe has expanded and cooled so much that the CMB has mostly been reduced to a gentle wash of microwaves, not unlike those that are generated in your microwave oven. When the CMB was set loose, only 400,000 years after the Big Bang, the universe was very hot and dense and the CMB had the same amount of energy as that produced by a light bulb. The cosmic microwave background (CMB) is a whisper of radiation that reaches detectors on Earth from all over the sky.
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