I've also now read
The Traveler by Joseph Eckert, like many other forumites - and loved it!
Such a readable SF story - it's fairly rare I really look forward to coming back to a book, but that was the case here. I thought the author did a pretty good job of predicting what a far future could look like, and interlocking that future with his son Lyle was also well done.
There was a moment of doubt when there's full-on weaponising and I thought the novel was going to turn down this path for the remainder, but luckily I wasn't disappointed. A few have mentioned the ending wasn't great but I thought it was OK; the idea it self was good, maybe just not executed the best way, but also it would be a tricky book to end perfectly anyway.
A very profound time travel novel, and a favourite (maybe the favourite) of the year for me.