The CMB or the Cosmic Microwave Background is one of the most amazing finds of cosmology. Despite the fact that it looks like an art accident involving pigeons, paints and a careless five-year-old, it hides an insane amount of information. To understand what it means let’s go back to my favorite epoch in the history of the universe when we were all just a bunch of harmless particles stewing in a nice, hot soup of radiation.
(Also what we could soon be, just saying you know.)
After the Big Bang and at the end of Inflation, the universe was a hot chaotic mess of particles and radiation. We had protons and electrons and photons and neutrinos bumping into each other and flying apart. In science-speak, the universe was opaque. This just means that photons couldn’t travel a large enough distance before they came in contact with a charged particle like an electron and changed their direction. As the universe expanded and consequently cooled, the protons and electrons could combine to form neutral hydrogen atoms. Since photons can’t electromagnetically interact with neutral atoms, as soon as this process –called recombination– took place, they became free streaming. The universe became transparent. It is these photons that we see in the CMB today. Light traveling from billions of years ago, (keep in mind, recombination took place ~370,000 years after the big bang which itself was 13.8 billion years ago), carrying a snapshot of what the universe looked like then.
You might have heard that when we look at stars what we actually see is what they looked like in the distant past. So if you look at Orion’s belt, for instance, you are looking anywhere from 800 to 1300 years in the past. As fantastical as that sounds, it doesn’t even compare to the billion-years-old picture that we see in the CMB. Not only this, with the kind of precise experiments that we have today, the information that can be gleaned from this one map is insane. We can tell, for instance, what the difference in temperature was between two points to an accuracy of 0.00001K. We can figure out how much matter there should be in our universe. We can pinpoint the seeds which would eventually form galaxies and galaxies clusters. We can even get an idea about the dark matter content of our universe. It is truly incredible.
Of course, science aside, it also has a very interesting origin story. Which I have recreated on napkins. (Some advice: don’t draw on cheap napkins with a gel pen. Also, why would you do that if you have perfectly good paper?) For your viewing pleasure:
Until next time.
Questions? Comments? Some retrospection on the good old days before consciousness? The comment box is open.