The Golden Transcendence by John C. Wright
This is the third book of the trilogy begun with The Golden Age and Phoenix Exultant.
After the comparatively low-tech events of Phoenix Exultant, we are back to the ultra-hi-tech of the far future in The Golden Transcendence. We also seem to be more on our central course than we were in the second book. We are also back to issues of what is real and what is illusion.
This far future tech could probably create quite a bit of illusion even by external manipulations. However, in the future described in these books, people use artificial brains that can directly interact with various devices that are capable of changing the mental constructs or even replace one mind with a previously archived version of a person's mind. It is "normal" for a person to have software to adjust their emotions, restrict their sensory experience, check their minds for inconsistencies and help make corrections if desired, create partial duplicates of one's mind to allow one to "be in two places at once", delete unwanted memories, and store backup copies of one's mind.
And, of course, there are other possibilities unscrupulous entities could carry out on others.
The third book begins with Phaethon coming back into control of his starship, the Phoenix Exultant. It has more or less been established that a threat exists to humanity in our solar system from entities from the lost human colony at Cygnus. Humanity's military man, Atkins, is prepared to fight the enemy, but we're told his methods of taking on the threat involve unacceptable risks - and there is an alternative solution Phaethon is capable of carrying out.
The Phoenix Exultant is now owned by a Neptunian of uncertain intentions. But Phaethon with his space armor is the only one truly able to pilot the starship. He must first go to meet the Neptunian and learn what he can. There are some surprises in the encounter.
We learn more about the enemies from the Cygnus colony. The Phoenix Exultant dives deep into the Sun in search of the enemy AI. There are technical puzzles to be worked on and huge battles to be fought.
The term “Golden Transcendence” refers to an event that takes place once every 1000 years in their society. All the humans / post-humans who wish to join their minds into a single mental organization to decide the course of society during the coming 1000 years. While the Transcendence is pre-occupied with those matters, humanity may be more vulnerable to the enemy AI.
Phaethon also faces issues with his "wife". (That is, the modified "duplicate" of his wife that Phaethon has not accepted as his true wife.)
I felt The Golden Transcendence was a stronger part of the trilogy than Phoenix Exultant. However, it wasn’t mesmerizing the way the first book was. It ends in a manner that would easily permit further books either about Phaethon or about the new direction of human society. A lot of potential matter could be based on the scenario at the end of the book. To the best of my understanding, Wright has not written any other related books.
Some of the events in the book fall into that category of very advanced tech that may be "indistinguishable from magic". There were times I had a hard time remaining convinced it was "indistinguishable" rather than simply "magic". I was aware that these were not in areas I had enough knowledge to make clear objections to it - so, perhaps Wright knew more about those things than I do. It seems safe to say that even if Wright knows more about the Sun’s interior than I do, some of the technology is entirely speculative. The story takes place thousands of years in the future, so it’s understandable that there is technology we haven’t even started researching. But I find some possibilities more believable than others.