Big Bang Acoustics

I have been looking into the sound-waves created by the big bang and also how those waves, that still exist today, can be used to interpret the size and structure of the universe, since the big bang.

It seems amazing, to think of sound-waves existing in space, after all, we often think of space as cold dark and silent, apart from the odd star and planet populating its regions.  However, that is only half the story.   At the time of the big bang, for about the first 40,000 years; the universe was a hot dense 'fog' of materials, including photons, sub-atomic particles in a photon-baryon gas and also dark mattter.  This 'fog' transmitted sound waves through it, and these waves, still exist today, although the 'fog' of materials, is now more of a fine mist! caused by the expanding universe, reducing its density.

From these waves, and using what we already know about how waves behave, as they travel through different materials and densities, at different frequencies and wavelengths; we can compare the waves created by the universe, as it developed over the last 15 billion years, with these 'benchmarks' of known physics / wave properties.  This provides us with a sound spectrum, that can be crunched in a computer programme, giving us a very accurate indication of what the universe is made from.

What has been discovered, is that the sound-waves of the universe indicate that its composition consists of 4% atomic matter and 23% dark matter.  No other combination of matter, holds true, for these waves.

These type of investigations, show that cosmologists are really just technical-historians.  They are always dealing in events that happened in the past.  For example, the light from the nearest star, our sun, takes 8 minutes to reach us, so we are always viewing what has happened in the past, and not what is happening in the present.  This is caused by the fact that the speed of light is fixed, and that nothing in the universe can travel as fast as that speed.

Therefore, information from anything that is very far away from us, such as a galaxy or a primordial sound wave, take years or even centuries, to reach us.  Until then, we can know nothing about the secrets, that are waiting to be discovered.

However, it is this precise property of light, and the universe, that allows us to see the first moments of the big bang, as some of  that information is only just reaching us from the outer parts of the expanding universe.  That means that some of the light reaching us now, is billions of years old and has been travelling through the universe for a very long time.