Stellaris is a space 4x game that uses energy as a universal currency. The Endless Space games are also 4x games that use ancient nanomachines called Dust as currency.

And yes, concentrating energy increases mass. E=MC^2, which means more Energy must necessarily mean more Mass. So basically gravity will be your hard limit, theoretically stuffing enough energy into small enough a place will create a black hole, though I assume if you’re talking electricity then there’s probably some physical limit you would hit first.

Also important to remember most of the traditions about it are pagan. Christ wasn’t even born in December. They just decided to celebrate it then to coincide with the existing solstice traditions. Many places celebrated the solstice as a new beginning, the days were now getting longer, and people needed a pick-me-up in the dark season. It was often one of the biggest annual celebrations. So it was co-opted with one of the most obvious Christian signs matching the theme, Christ’s birth being the beginning of the end of a time of darkness. First by giving a new meaning to Saturnalia, then adding more bits from other regions they were trying to convert.

Not just Saturnalia, that was just the first. More was incorporated from various traditions as they sought to convert them. But yeah, that was sort of the foundation the rest was laid upon.

IIRC, the biggest uncertainty is about the singularity. I don’t know if it’s still true, but my understanding was that the consensus is that it isn’t really a true point of infinitely dense mass. That is how our current models say it must be, but many assumed our current models are incomplete and that more accurate ones will show that it must have some volume. And given the extreme nature of them, any updates to our models might have some significant repercussions in other aspects of them too.

Time is relarive to your frame of reference. You are always the source of your own frame of reference, so you can never feel the effect of time dilation on yourself. At worst, it would look like the universe outside the horizon started to accelerate to unimaginable speeds. But you would never feel trapped in an unending, at worst that is simply what it would look like to us.

So is New York City, lol.

My first thought was to scan it to see if they at least got Boston in the NYC section. Only to realize NYC is not in NYC but is actually in Nomansland.