Look how the floor of heaven
Is thick inlaid with patens of bright gold,
There’s not the smallest orb which thou behold’st
But in his motion like an angel sings,
Still quiring to the young-eyed chérubins.
Do you remember the post about matter and antimatter?
I’ll jog your memory if it’s a bit weak (as mine!): I wrote that after the Big Bang only a small surplus of particles survived from the annihilation between matter and antimatter; the result of this annihilation is the Cosmic Microwave Background Radiation.
Let’s go far into space and far back in time and discover what the CMBR is!
Originally, the universe was very hot and dense, and energy and matter were the same thing. However, as the universe expanded and cooled, protons and electrons formed neutral atoms and the radiation (photons) separated from the matter. The recombination epoch refers to the formation of neutral atoms: before, high temperatures had prevented electrons from combining with protons. Photon decoupling occurred when the radiation started to travel through space and time. The wavelength of photons increased over time (and became less energetic according to Plank’s relation) because of the expansion of space; in particular, it has stretched into the wavelength part of the electromagnetic spectrum and the temperature is about 2.73° above absolute zero.
Cosmic Microwave Background Radiation was discovered by Arno Penzias and Robert Wilson in 1964, when they noticed a strange background noise in their antenna radio. It was spread all over the universe and it had the same intensity everywhere, as the COBE (Cosmic Background Explorer) satellite measured in every direction observed. Recent studies have also found that there are little variations in temperature: the special power spectrum contains small “anisotropies” (irregularities) which depend on the density of the regions. If these fluctuations had not occurred, there wouldn’t have been galaxies or planets like our Earth, because no element would have been attracted by the gravitational force. This image represents variations in the temperature of the background radiation.
Now I’m going to tell you something that, at the beginning, really astonished me: one of the earliest learned facts of science is that outside our atmosphere the vacuum of the space should be silent; however, space hasn’t always been so empty, because at the time of the Big Bang, the Universe was much smaller and hotter and it was filled with gas, so it was a sort of atmosphere. This means that our Universe had a particular sound.
The first sound waves were created by gases: they fell into valleys, got compressed and glowed brighter; then they rarefied and they got dimmer. As the oscillation continued, the sound waves were created. This video will let you listen to “the sound of the Big Bang” produced by John Cramer of Washington University.
The CMB is one of the most fascinating topics of cosmology: I compare it to a photo; it’s something which reminds us what happened in the past, a cold thing that talks about a hot situation, a hot moment that now is over!
And you? What can you compare the cosmic background radiation to?
What do you think about the sound of our Universe?