STORY OF THE FIRST SOUND WAVES OF UNIVERSE - (BIG BANG-4)

1 million years have passed since the beginning of everything and now we are close to the things very interesting. Today we are going to talk about the first sound waves ever and how they helped in shaping and understanding the universe. 

The first sound waves have a fancy name - 

BARYON ACOUSTIC OSCILLATIONS

But don't freak out eh !

BARYON - The particles like neutrons , protons (1*)

ACOUSTIC- Dealing with sound 🔊

OSCILLATIONS- To and fro movement 🔔

Following the story till now , the universe is a hot 🌡️ place full of baryons , photons , electrons and dark matter . Electrons and protons formed a hot soup 🍵, plasma coupled with photons due to continuous scattering of photons by charged particles. 

The baryon photon plasma is opaque that means that there is no light in the universe till now 😲 .

The distribution of all the components was inhomogeneous ..a lil bit more here , a lil bit less there. 

How the inhomogeneity ?  They were considered to be the remenants of random quantum fluctuations of baby subatomic universe. 

The result of these fluctuations is two dominant agents coming into play - Gravity and Pressure

Each overdense region pulled matter towards it. 

Dark matter(2*) is not effected by light, and it was also far back the dominant as compared to the ordinary baryons so it flowed inwards towards density peak . Overdensity leads to Overpressure.

The photons coupled with baryons were also present there and they exerted enormous outward pressure and , the spherical sound waves were produced .

GREEN REGION- PHOTONS
RED REGIONS- BARYONS
BLUE REGION- DARK MATTER

The spherical shell travelled fast ⚡at half the speed of light . The shell expanded fast , so did the universe. The universe eventually became cooler, the photons were redshifted to lower energy. At  370,000 years the plasma hit a critical temp of 3000K  recombination( I don't know why  recombination cuz they combined for the first time )took place - protons , neutrons and electrons combined to form neutral atoms . Light wasn't able to able to interact very much now with the atoms formed from baryons. 

Gravity pulled the newly formed matter in and the photons were finally free to stream through the universe and there was 'light' for the very first time - now called Cosmic Microwave Background

 ( more about this in the next blog )

So finally , light and matter decoupled . Light was free to travel through cosmos but the distribution of baryon inhomogeneity was frozen at a distance 'r' from the centre of intial overdensity which is referred to as sound horizon. Its value is about 450,000 light-years. If this distance is rescaled to today, taking into account the expansion of universe, it's about 500 million light-years or 150 megaparsecs (1 pc = 3.26 light-years). The dark matter and the ordinary one flowed together to make the structures we see today.

And how can we see them now? 

Well we can see it imprinted in the form of galaxies. The shells of over and under densities all were  overlapping at the time of recombination. And the pattern looked like this - 

Detecting🕵️ it required the most detailed surveys of sky💻 and we entered the era of precision cosmology .

How we did that ? We made the map of universe , (with the help of galaxy redshift surveys). The resulting pattern shows the galaxies to be dominantly found in the central density peak regions and the regions where the sound horizons intersect i.e there were slight excess with separation of 150 megaparsecs from centre. All the galaxy surveys confirm this and we are getting more and more precise with every measurements .

SDSS-III DATA RELEASE

every pixel in this image represents entire galaxy

Baryon Acoustic Oscillations tell us a great deal about position🚩 of galaxies . They also hold the key to understanding the expansion of universe . It confirms that dark energy behaves the way as predicted by Einstein's cosmological constant. 

The first sound waves carry so much information and thrill with it !!

Neil deGrasse Tyson rightly said - "Not only we are in the universe , the universe is in us . I don't know of any deeper spiritual feeling than what that brings upon me "

Any questions , anything you wanna express or share ?

Drop it down in comments !

(1*) - To know more about baryons check my blogpost here  -WHAT THE HECK IS PARTICLE PHYSCIS

(2*) -To know more about dark matter check my blogpost here - DARK MATTER