Robert Heinlein, L. Sprague de Camp, and Isaac Asimov, Philadelphia Navy Yard, 1944.
When Isaac Asimov crafted his time travel novel, The End of Eternity, he depicted his time traveling characters as making the decision to give up on time travel. Why? "...we are not alone in the Galaxy. There are other stars with other planets, you know. There are even other intelligences. None, in this Galaxy at least, are as ancient as mankind, but in the 125,000 Centuries man remained on Earth, younger minds caught up and passed us, developed the interstellar drive, and colonized the Galaxy". While humans played around with time travel and used Eternity as a tool for attempts to perfect human existence on Earth, other intelligent species took over the galaxy. Eventually, with humans restricted to one small planet, they just died out.
If we adopt Asimov's suggestion that robots invented and used Eternity in an attempt to follow the Zeroth Law of Robotics and protect humanity, then we can take an additional step and wonder about the origins of those robots and the Laws of Robotics. In making a sequel to The End of Eternity (The Start of Eternity) there is an opportunity to fill in many murky details about robots that Asimov left unexplained. And what more can we say about those other "other intelligences" in our galaxy? Why is it that the planets where such species are evolving never got mentioned in Asimov's larger fictional universe where he describes how the entire galaxy is eventually colonized by humans? Why were other worlds with their own complex biospheres never described by Asimov? The Start of Eternity is full of "other intelligences" and provides an account for why it is the case that in all of Asimov's stories about the Foundation Reality those other life-bearing planets are not mentioned. In The Start of Eternity the Huaoshy are depicted as the dominant non-human species and details are provided about involvement of those aliens in the development of the human species. Other intelligent species from our galaxy, particularly the Imfulri, are also included and serve to explain the wheres and whats of extraterrestrials that Asimov only left to our imaginations.
What details can be provided concerning the origin of positronics and the Laws of Robotics? My assumption is that positronic robots were a human invention. Positronics was developed "under the noses" of the Huaoshy. I assume that positronic robots are much more difficult to produce than electronic robots, and it was a fluke that humans bothered to develop positronics, but once positronic robots were created, the possibility of telepathic robots was discovered and that provided a technological advance that the Huaoshy could not anticipate or control. The story of the origin of the Laws of Robotics must involve a small group of humans at Moon Base who built the first robot with a positronic brain. Should the details of how positronics developed be provided in The Start of Eternity or only be hinted at? I favor the idea of explicitly showing how positronic robots came into existence and how they created Eternity, but I'm not sure how (where) to add that account to the story. A major reason for giving the sequel to "The End of Eternity" the title "The Start of Eternity" was that the sequel should provide information about how robots invented time travel as a way to fulfill the requirements of the Zeroth Law of Robotics.
I've already inserted into The Start of Eternity a rather long "flash back" or "story within a story" (chapters 10-13) about how the Huaoshy first contacted another space-faring species. I feel like I need to find a way to insert another "story within a story" that will show the origin of positronics.
In addition to revealing events related to the creation of positronics, The Start of Eternity includes Issac Asimov as a character and Asimov is shown traveling through time. In his time travel novel, Asimov explored the issue of time travel paradoxes. For example, Asimov raised questions such as: could a person go back in time and see himself without disrupting the course of his own life and preventing that trip back in time from ever taking place? To further explore this, The Start of Eternity shows Asimov from the year 1947 going back in time and meeting himself in the 1930s. This allows Asimov to play a role in changing the flow of time and creating our Reality.