Yes, 13.8Gy is the approximate age of the universe and yes the researchers used that number. But it's not like they made this up and conveniently landed there: they computed a range of options and worked back from that specific number to prove it'd work for as long as we could possibly care.

Turns out the biggest decay factor is nanograting and the biggest contributing physical quantity is temperature. They plotted what decay would look like on an Arrhenius plot. They both computed estimates and measured to confirm: the measurements are quite accurate. The specific claim is that they computed that at a specific temperature (462K) the medium will last 13.8Gy -- but their point is that it would last as long as the age of the universe at that temperature, not that the pulled a number out of their backsides.

The actual paper is here: https://www.researchgate.net/publication/297892219_Eternal_5...

I don't think that's as long as we could possibly care, but it's a good concrete number. The Stelliferous Era is predicted to last some 10¹³ years; looking at their Arrhenius plot, we probably need to keep the temperature below about 400 K to last that long. (However, I suspect that over such long time scales, other decay mechanisms such as cosmic-ray damage will be more important.)

Most likely, for long-term archival, we need to make copies of the data from time to time. But this technique will likely allow those intervals to be longer than the current age of the universe, and it offers higher density than you can get with techniques like Norsam's planar discs, which is a useful improvement over existing media.

Ok, we get it. No need to copy-paste the same comment multiple times.