Primordial Light
Just before the start of Hanukkah this year, I heard a drash from Rabbi Kleinbaum at CBST on the topic of light. She explained that the creation narrative in Genesis 1 has light created on the first day, but the sun and the moon and the stars weren't created until the fourth day, and the rabbis of the Talmud have an explanation for this discrepancy. They say that the light of the first day (called "Or HaGanuz") was a different sort, by which people could see "from one end of the world to the other".
Of course, we now know a lot more about how this planet came to exist. We know that sometime in the unimaginably-distant past, there is a point where space and time lose all conventional meaning. Matter as we know it did not yet exist; all the energy of the universe was bound up in a singularity, like a breath being held. And then the universe breathed out.
In the first tiny fractions of a second, the fundamental forces of the universe became established and elementary particles began to form. By ten seconds, the universe was an opaque soup of atomic nuclei, electrons, and photons, but the temperature was too high to allow electrons to bind to nuclei and form atoms. These photons kept bouncing off the free electrons, getting basically nowhere, and it remained like this for three hundred and seventy thousand years, until the universe cooled enough to allow hydrogen atoms to form.
Once the first hydrogen atoms formed, the universe stopped being opaque. Light could actually travel distances worth talking about. All those photons that formed in that first second of time were suddenly free, and light shone in the universe for the very first time.
That primordial light would have had a color temperature of about 3000K, an orangeish-white color, shining from its last interaction with the opaque universe. The universe today is a very different place. Space has expanded immensely from that primordial cosmos, and with this expansion, the primordial light has been "red-shifted"; its wavelength has increased, and now this primordial light is microwave radiation: the "cosmic microwave background". (If you owned an analog tv, and you tuned it to channel 3, some of the static you would see on screen was coming from this cosmic microwave background.)
The cosmic microwave background is everywhere in the universe, so faint that it took incredibly sensitive antennas to isolate it. It was the first light there ever was, and it is still here with us, and it shines from one end of the universe to the other.
