Two9A

So this came up with this user a few days ago, and apparently ð fell out of use later in Old English and its usage was merged into þ for hundreds of years.

I remain unconvinced.

Whenever I come across ASCII art in the comments, it’s a good day. Here’s one from the day job:

There’s a short story (more of a novella) by Stephen Baxter on this exact topic, for what it’s worth. Touching Centauri: https://www.e-reading.mobi/chapter.php/1035265/30/stephen-baxter-phase-space.html