<p>"Was it as loud as we think" is difficult to answer, since it's opinion-based. But since sound is nothing but longitudal oscillations in a gaseous medium, <strong>Big Bang was not at all silent</strong>.</p>

<p>If the Universe were completely homogeneous, it would stay like that. But primordial quantum fluctuations ensured that space was a tiny bit more dense in some places, and a tiny bit more dilute in other places.</p>

<p>Gravitation then ensured that the overdensities attracted matter and grew in size, until the pressure thus built up resisted further compression, and waves traveled outward from these overdensities. They then contracted and expanded again a few times, until 380,000 years after Big Bang when the photons <a href="https://en.wikipedia.org/wiki/Decoupling_%28cosmology%29" rel="nofollow noreferrer">decoupled</a> from the gas, relieving the gas of its pressure, and freezing the waves in (comoving) space.</p>

<p>This phenomenon is called <a href="https://en.wikipedia.org/wiki/Baryon_acoustic_oscillations" rel="nofollow noreferrer">baryonic acoustic oscillations</a> (BAOs). You may also be interested in <a href="https://physics.stackexchange.com/questions/162184/what-is-the-speed-of-sound-in-space/162210#162210">my answer to the question "What is the speed of sound in space?"</a></p>

<p>However, humans wouldn't be able to hear it, since the wavelength (at decoupling) were roughly half a million lightyears, and the corresponding frequency thus orders of magnitues below the human threshold of ~20 Hz. Due to the expansion of space, the frequency increases as we go back in time, and scaling by a factor of $\sim10^{26}$, it is possible to get a notion of what the early Universe sounded like. This has been done e.g. by <a href="http://faculty.washington.edu/jcramer/BBSound_2013.html" rel="nofollow noreferrer">John Cramer from U. of Washington</a> on the basis of <a href="http://WMAP" rel="nofollow noreferrer">WMAP</a>'s observations of the <a href="https://en.wikipedia.org/wiki/Cosmic_microwave_background" rel="nofollow noreferrer">cosmic microwave background</a> which hold information about the BAOs.</p>

<p>You can hear it <a href="http://faculty.washington.edu/jcramer/BigBang/Planck_2013/BBSnd100.wav" rel="nofollow noreferrer">here</a>. It doesn't really sound nice, though.</p>

CC BY-SA 3.0
2015-08-19T09:35:29.270Z
2015-08-19T10:29:14.503Z
2017-04-13T12:40:15.377Z
pela
<p>As we all know, There is no sound in space, because sound waves don't travel in a vacuum.
But even if Big Bang did sound, what was the main source of it's cause?</p>

CC BY-SA 3.0
2015-08-17T21:05:20.337Z
You need to clarify the question. Sound is caused by perturbations in an existing medium, as you say there was no sound - so what are you asking?
adrianmcmenamin
CC BY-SA 3.0
2015-08-17T21:44:19.707Z
What does quark soup sound like?   What does the inside of the sun sound like?   What did the universe sound like when it was dense with particles and millions of degrees?    I'm not smart enough to answer these questions but I would guess, in addition to being very hot and very energetic, the moments after the big bang were also very loud, but I'm not sure how one would go about measuring such a thing.   The sun is, I gather, very loud, if you stand close enough to it to hear the sound waves, but I don't recommend that.
userLTK
CC BY-SA 3.0
2015-08-18T03:44:37.113Z
Since I hear the sun is pretty hot, it would sound like the inside of the sun would be hotter??
NuWin
CC BY-SA 3.0
2015-08-18T04:32:47.990Z
Here's a kind of fun article on how loud the sun is.   http://www.spaceanswers.com/deep-space/how-loud-would-stars-be-if-space-was-full-of-air/
userLTK
CC BY-SA 3.0
2015-08-18T09:21:04.023Z
@adrianmcmenamin What i was trying to say was, if by any chance the Big Bang did sound, what would be the reason that it made a sound in that giant space? Which is lack of air that helps sound waves to travel into it...
Future-B
CC BY-SA 3.0
2015-08-19T13:11:15.837Z
Listening to the Big Bang: http://www.washington.edu/news/2013/04/04/listening-to-the-big-bang-in-high-fidelity-audio/
Wayfaring Stranger
CC BY-SA 3.0
2015-08-20T13:54:04.113Z
Big bang sound waves explain galaxy clustering: https://www.newscientist.com/article/dn6871-big-bang-sound-waves-explain-galaxy-clustering/ A little old. There are also pressure waves involved in galactic arm formation. Some call *these* sound waves.
Wayfaring Stranger
<big-bang-theory><space><wavelength>
Did Big Bang sound as loud as we think?
Future-B
# Did Big Bang sound as loud as we think?

(Asked by: username_0 on 2015-08-17)

As we all know, There is no sound in space, because sound waves don't travel in a vacuum.
But even if Big Bang did sound, what was the main source of it's cause?

**Tags:** big-bang-theory, space, wavelength

> **Comments:**
> **username_1**: You need to clarify the question. Sound is caused by perturbations in an existing medium, as you say there was no sound - so what are you asking?  
> **username_2**: What does quark soup sound like?   What does the inside of the sun sound like?   What did the universe sound like when it was dense with particles and millions of degrees?    I'm not smart enough to answer these questions but I would guess, in addition to being very hot and very energetic, the moments after the big bang were also very loud, but I'm not sure how one would go about measuring such a thing.   The sun is, I gather, very loud, if you stand close enough to it to hear the sound waves, but I don't recommend that.  
> **username_3**: Since I hear the sun is pretty hot, it would sound like the inside of the sun would be hotter??  
> **username_2**: Here's a kind of fun article on how loud the sun is.   http://www.spaceanswers.com/deep-space/how-loud-would-stars-be-if-space-was-full-of-air/  
> **username_0**: @username_1 What i was trying to say was, if by any chance the Big Bang did sound, what would be the reason that it made a sound in that giant space? Which is lack of air that helps sound waves to travel into it...  
> **username_4**: Listening to the Big Bang: http://www.washington.edu/news/2013/04/04/listening-to-the-big-bang-in-high-fidelity-audio/  
> **username_4**: Big bang sound waves explain galaxy clustering: https://www.newscientist.com/article/dn6871-big-bang-sound-waves-explain-galaxy-clustering/ A little old. There are also pressure waves involved in galactic arm formation. Some call *these* sound waves.  

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## 1 answers

### Answer by username_5 on 2015-08-19. Score: 4 | Accepted answer

"Was it as loud as we think" is difficult to answer, since it's opinion-based. But since sound is nothing but longitudal oscillations in a gaseous medium, **Big Bang was not at all silent**.

If the Universe were completely homogeneous, it would stay like that. But primordial quantum fluctuations ensured that space was a tiny bit more dense in some places, and a tiny bit more dilute in other places.

Gravitation then ensured that the overdensities attracted matter and grew in size, until the pressure thus built up resisted further compression, and waves traveled outward from these overdensities. They then contracted and expanded again a few times, until 380,000 years after Big Bang when the photons [decoupled](https://en.wikipedia.org/wiki/Decoupling_%28cosmology%29) from the gas, relieving the gas of its pressure, and freezing the waves in (comoving) space.

This phenomenon is called [baryonic acoustic oscillations](https://en.wikipedia.org/wiki/Baryon_acoustic_oscillations) (BAOs). You may also be interested in [my answer to the question "What is the speed of sound in space?"](https://physics.stackexchange.com/questions/162184/what-is-the-speed-of-sound-in-space/162210#162210)

However, humans wouldn't be able to hear it, since the wavelength (at decoupling) were roughly half a million lightyears, and the corresponding frequency thus orders of magnitues below the human threshold of ~20 Hz. Due to the expansion of space, the frequency increases as we go back in time, and scaling by a factor of $\sim10^{26}$, it is possible to get a notion of what the early Universe sounded like. This has been done e.g. by [John Cramer from U. of Washington](http://faculty.washington.edu/jcramer/BBSound_2013.html) on the basis of [WMAP](http://WMAP)'s observations of the [cosmic microwave background](https://en.wikipedia.org/wiki/Cosmic_microwave_background) which hold information about the BAOs.

You can hear it [here](http://faculty.washington.edu/jcramer/BigBang/Planck_2013/BBSnd100.wav). It doesn't really sound nice, though.


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