That's the term scientists use for the theorized super-dense essence of what went bang at the Big Bang. According to general relativity, the initial state of the universe, at the beginning of the Big Bang, was a singularity: a point in spacetime in which gravitational forces cause matter to have an infinite density and zero volume.
It strikes me that the first Christmas was a bit of a reverse Big Bang.
Out of all the galaxies spread out across the incomprehensively-massive universe, God seems to have focused his attention on one called the Milky Way.
From among the tens of billions of solar systems in the Milky Way, he picked one swirling around a fairly unremarkable yellow sun, as described by Douglas Adams in The Hitchhiker's Guide to the Galaxy, "far out in the uncharted backwaters of the unfashionable end of the Western Spiral arm of the [Milky Way]."
The Lord of the Universe then paid particular attention to the third planet out from that small star.
On that planet, with seven great continents to choose from, Yahweh picked out the mostly-desert land-bridge between Africa and Asia, and made it the homeland of an insignificant fellowship of twelve tribes, full of slaves and sheepherders.
Choosing one of those tribes, and one particular family line within that tribe, the God of all creation looked across the entire scope of human history - past, present, and future - and went to a young teenage girl in an insignificant village in a time of political oppression.
At that singular time, at that singular place, as part of the hopes and dreams of that singular people, the supreme being of the universe, who spoke the world and everything beyond it into existence, caused himself to become...a single...human...cell.
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Truth is...the Lord has come; joy to the world!