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Astronomers measured sound waves frozen in the distribution of galaxies using quasars and carbon clouds.
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The early universe was a hot soup of particles and light. In this soup, sound waves, fluctuations in density, spread outward from clumps of matter like ripples on a pond. When the universe cooled, these waves froze, leaving an imprint in the distribution of galaxies: they are slightly more abundant at a certain distance from each other. This distance is a 'standard ruler' for measuring the cosmos.
Astronomers from the DESI survey used a new tool: they looked not only at galaxies but also at quasars — bright cores of distant galaxies. Light from quasars passes through gas clouds, and carbon atoms absorb some of the light. These 'dark lines' in the spectrum reveal where the clouds are. By comparing the positions of quasars and carbon clouds, the scientists found the same acoustic imprint.
Carbon clouds are visible at vast distances — back to when the universe was just three billion years old. It's like finding an old photograph that shows the same ripples from a stone thrown into a pond.
The measurement yielded the distance to that era with 3% precision. That's like measuring the length of a room with an error of a couple of centimeters, but for the entire universe. Such precision helps us understand how the expansion of the universe has changed over time and what dark energy is accelerating it.