"Factoring Humanity" by Robert J. Sawyer, 1999
For a "first contact" sci-fi story, there isn't a lot of "hard SF". This book is more like "hard SF-lite".
This one borrowed heavily from Sagan's "Contact" (which was hard SF, par exemplar, and also had great character development and deep philosophical implications on several levels, but I digress..) and dabbles a bit in 4 dimensional geometry, quantum computing and cosmic consciousness. The characters are sort of ill-defined (except for the AI who seemed deeper and more human than the homo sapiens), but the plot keeps things moving. If you want an enjoyable light read that has just a bit of science in the fiction, Sawyer is your guy for plot-driven page-turners
My Rating: ★★★☆☆ (3 out of 5 stars) - I liked it.