Re: Did the Big Bang make a noise (or sound)?

You are correct in that sound waves need matter to propagate. Sound waves are pressure waves, which are variations in pressure in a medium. Those variations in pressure can make things vibrate, and produce in our ear the sensation that our brain interprets as sound.

Now all the universe is filled with matter, but the density of matter in space is (currently) too small to allow a sound wave to be heard. The faintest sound that the human ear can perceive will produce a variation in pressure close to 0.3 thousandth dynes per square centimeter (0.0003 dyn/cm^2). This means that I need at least this much pressure to produce an audible sound.

Pressure in a medium is the result of matter and temperature. When matter is heated, the atoms start moving around at high speed and the cumulative effect of all the atoms hitting a surface is what we call pressure. Pressure is the product of the density of matter times the temperature. The density is just the number of particles in a cubic centimeter. In the space around the Earth there are just a few atoms per centimeter, and the pressure is around one trillionth of what we need to produce audible sounds.

Just after the Big Bang, the density and temperature are exceedingly high, and the pressure was high enough to allow sound, but there was very little matter. Most of the universe was light. At 0.2 seconds, matter started to appear. The density and temperature decreased very quickly, and according to the Big Bang time line (and associated calculator) the density of 0.0003 dyn/cm^2 occurred about 4 billion years after the big bang.

Of course there was no one to hear them as far as we know.

Vladimir Escalante Ramírez