What was the temperature of the universe during the Dark Ages?

Well, the temperature of what exactly, and when exactly during the cosmic dark age? We typically talk about temperature as a function of redshift z instead of time: it's a lot more convenient to calculate with. The redshift today is defined to be 0, while redshift increases as you go further back in time. read more

We typically talk about temperature as a function of redshift [math]z[/math] instead of time: it's a lot more convenient to calculate with. read more

During the Dark Ages, the temperature of the universe cooled from some 4000 K down to about 60 K, and only two sources of photons existed: the photons released during recombination/decoupling (as neutral hydrogen atoms formed), which we can still detect today as the cosmic microwave background (CMB), and photons occasionally released by neutral hydrogen atoms, known as the 21 cm spin line of neutral hydrogen. read more

The temperature continued to fall, and the infrared radiation that suffused the universe lengthened, shifting to radio waves. “Once you cool even further, the universe became a very dark place,” Loeb says. The dark ages had officially begun. Meanwhile, the simulations show, things began to stir. read more