Sound is a vibration in air. If we could see these sound waves, they would look like ripples moving through air molecules. All the sounds create these ripples, and all these sound ripples overlap. As a result, all the small noises in a stadium create a seemingly random variation of clustered air molecules.
But these variations are not entirely random. Since each sound wave spreads outward at the speed of sound (about 330 m/s), the size of these ripples are all very similar. If speed of sound were faster, the ripples would be more spread out, and if the speed of sound were slower they would be closer together. Thus, the scale of sound ripples in a stadium is determined by the speed of sound. If we could see the ripples in the stadium, we could use the scale of these ripples to deduce the speed of sound in the stadium.
In astrophysics a method similar to this is used, and it is extremely important to our understanding of dark energy. It is known as baryon acoustic oscillation (BAO). http://en.wikipedia.org/wiki/Baryon_acoustic_oscillations
From our position in the universe, we see a vast sea of galaxies in every direction, with the glow of the cosmic microwave background coming from the distant edge of the visible universe. This is not because the universe is an enclosed bubble, but because the more distant the source of light, the younger the universe was when the light began its journey. Still, this view is similar to the stadium, with the galaxies like air molecules and the stadium seats marking the oldest and most distant region of the visible universe.
[Ed's note: This sounds interesting, but it is unclear what the significance of this might be; are there any cosmologists or astronomers on SN who'd care to weigh in on this and explain it for the rest of us?]
(Score: 2) by aristarchus on Saturday September 20 2014, @08:42PM
Is this a rehash of the "listening to the stars" dark matter article we has a couple weeks ago? If so, it is phrased more plausibly. And if we could have an cosmologist, or an astronomer, but preferably an astrophysicist, explain, that would be nice. So, like a stadium, but not physical stadium, more like a time expanded stadium that is not a bubble where sound bounces of the "edges" so that by seeing the sound in the form of light we can know where the heck all that dark matter is! See! I am no astrophysicist!
And BAO, that is Dim Sum, right? Dark Matter, Dim sum, . . . . Get it?
(Score: 2) by mhajicek on Saturday September 20 2014, @11:24PM
Maybe we'd get it better if it were explained by a cosmetologist.
The spacelike surfaces of time foliations can have a cusp at the surface of discontinuity. - P. Hajicek
(Score: 0) by Anonymous Coward on Sunday September 21 2014, @03:20AM
This isn't too hard to get. There were fluctuations analogous to sound waves in the early universe when matter was still packed tightly together. As with the MBR these fluctuations have expanded with the universe, and we can see them by observing the clumping of galaxies. Its similar to the videos of sand forming patterns when on top of a speaker. By measuring the clumping we can extrapolate backwards and get an idea of what the baryons were doing. Theoretically of course... Dark energy is still a big ???
(Score: 2, Interesting) by GoodBuddy on Sunday September 21 2014, @05:50AM
Ed's note: This sounds interesting, but it is unclear what the significance of this might be
FTFA: "With the baryon acoustic oscillations, we now have another way to accurately determine the amount of dark energy."