# How does the power spectrum relate to cosmic sound waves?

**URL:** <https://boards.straightdope.com/t/how-does-the-power-spectrum-relate-to-cosmic-sound-waves/619974>\
**Category:** Factual Questions\
**Created:** [April 26, 2012, 1:30am UTC](https://boards.straightdope.com/t/how-does-the-power-spectrum-relate-to-cosmic-sound-waves/619974 "2012-04-26T01:30:37Z")\
**Posts on this page:** 2\
**Page:** 1

<div class="post-metadata">

**Author:** ![larryhughs](https://avatars.discourse-cdn.com/v4/letter/l/8baadc/32.png) [@larryhughs](https://boards.straightdope.com/u/larryhughs)\
**Post date:** [April 26, 2012, 1:30am UTC](https://boards.straightdope.com/t/how-does-the-power-spectrum-relate-to-cosmic-sound-waves/619974/1 "2012-04-26T01:30:37Z")

</div>

I dont understand, is it just the thing used to measure/chart the soundwaves left in the cosmic microwave background?

pls help!

---

<div class="post-metadata">

**Author:** ![JWT\_Kottekoe](https://avatars.discourse-cdn.com/v4/letter/j/3ec8ea/32.png) [@JWT\_Kottekoe](https://boards.straightdope.com/u/JWT_Kottekoe)\
**Post date:** [April 26, 2012, 2:45am UTC](https://boards.straightdope.com/t/how-does-the-power-spectrum-relate-to-cosmic-sound-waves/619974/2 "2012-04-26T02:45:35Z")

</div>

Sound waves in the early universe leave an imprint of spatial variations in the intensity/temperature of the cosmic background radiation. We can measure these variations from a spaceprobe that maps the temperature of the background radiation as a function of the position in the sky. This map is then transformed by a mathematical algorithm to show a spectrum of variations as a function of separation in angle between two points in the sky. In mathematical jargon, one computes the Fourier transform of the autocorrelation function of the temperature. This give us the “Power Spectrum” of variations. This power spectrum can be computed theoretically from a model of the Big Bang. The results from the Wilkinson Microwave Anisotropy Probe agree remarkably well with theoretical predictions and provide an amazingly precise value for the age of the universe, as well as solid estimates for the amount of dark matter and dark energy in the universe.

[WMAP](http://en.wikipedia.org/wiki/Wilkinson_Microwave_Anisotropy_Probe)