Baryon Acoustic Oscillations

Read this article on the BBC
www.bbc.co.uk...

Pretty neat, Id not heard of the technique although had always thought of it in terms of star formation. that you expect an approximately spherical shockwave to be produced during a massive supernovae of other shock front producing event.

www.sdss3.org...

Basic idea seems to be that the earliest stars to form would have been supermassive starts that would likely not really have formed stable sphere like shapes but would have undergone fusion and collapse as part of the formation process (live times for massive stars are very short)

The acoustic shock waves emanating from these events would seed star formation and even formation of clusters as the universe expands and cools. So it is not a long stretch of logic to suggest that if you could identify these spherical structures in deep space surveys, they would give you a good handle to the size of the universe. Which is basically what the BOSS group did.

ErosA433
The acoustic shock waves emanating from these events would seed star formation and even formation of clusters as the universe expands and cools. So it is not a long stretch of logic to suggest that if you could identify these spherical structures in deep space surveys, they would give you a good handle to the size of the universe. Which is basically what the BOSS group did.

Hmm, I'm no expert on this, but how can it give a "handle" to the size of the universe?
From your linked article..

"While we can't say with certainty, it's likely the universe extends forever in space and will go on forever in time. Our results are consistent with an infinite universe,"

Just wondering

Im no expert in this area either, though do have some astronomy background. I think it is all about multiple checks and measurements.

Pretty nice explanation here

en.wikipedia.org...

The oscillation stems from the formation of areas of increased density during the early universe. These would have been regions of early star formation and early galaxy formation. You expect these early density regions take on an almost acoustic propagation of shockfronts due to the high density of matter in the early universe.

As the universe cools and expands these density ripples form the seeds of early galaxy formation, which continues to propagate as the universe expands. It is then the idea that if you know the redshift of the objects you can measure their distances also and then do a 3D search into deeper and deeper fields. The acoustic rings are thought to be a standard length of 490M light years in todays universe. It is the idea that if the universe started out as a hot soup, as it cooled you would expect that all regions of space are somehow connected, at least at the time the CMB was formed. So you would expect distribitions of galaxies and clusters to be related but also isotropic. Seeding for these galaxies would have been from the same time the CMB froze out. So it allows you to identify objects that are acoustically linked (at the time the CMB froze out)

If you look at a field of galaxies and clusters, you can use other methods at your disposal to figure out the radial distance to an object, the location on the plane gives you spacial distance and if you can attribute locations to be caused by an acoustic shockfront, then you can say that depending on the distance of the objects, they should have a standard distance between them, because the universe has been expanding for x amount of time.

Im not sure if that makes sense, I do understand it but lack the expertise to fully explain it. id have to think about it a bit more.

to me it seems like ink propagating on the surface of water. If you know drop ink on water it should expand in a circle, if you did the same experiment at differnt distances from you, the observer, you expect to see different sized rings, but you know that they are all the same. So it allows you to say... hey that ink circle over there is 5 meters away. When you take this to cosmological scales it allows you to monitor the expansion of the universe and figure out if it is linear, accelerating, or decelerating.

reply to post by VoidHawk


What he means is the size of the visible universe. There are physical reasons (to do with relativity and cosmic inflation) why we can only see part of the whole universe. So it's the size of the visible universe he now knows to within 1% accuracy.

What's been discovered is that the distribution of matter according to the pattern of these 'acoustic oscillations' (or ripples) is pretty uniform throughout the visible universe. That is consistent with a universe that extends to infinity in all directions.

It doesn't prove that the universe is infinite, but it increases our suspicion that it is so.

reply to post by Astyanax


Thanks for clearing that up
Not proven, but possibly infinite....that means.....anything and everything could be out there!!

We humans need to find a way to live forever because I want to see it ALL!