Stephen Hawking’s final research paper was A Smooth Exit from Eternal Inflation? Submitted shortly before his death in March 2018, it was primarily concerned with the very early universe, specifically the 10⁻³³ to 10⁻³² second inflationary epoch that he believed immediately followed the Big Bang.

The key aspects of his research include:

• The “Exit” from Inflation: The paper focused on finding a “smooth exit” from the theory of eternal inflation, which is believed to occur around $$ seconds.
• Limiting the Multiverse: Hawking and co-author Thomas Hertog aimed to move away from the idea of an infinite, chaotic fractal multiverse. Instead, they proposed that the inflationary period resulted in a much simpler and finite structure.
• Testable Physics: A primary goal was to make the theory of the early universe testable. They suggested that the physical conditions at the end of inflation left an imprint on the background radiation, which could be measured by future space telescopes.
• Holographic Framework: The theory utilized string theory to describe this moment ($$ s) as a “timeless state” on a 2D surface, rather than relying solely on Einstein’s general relativity, which breaks down at that point. 

This work served as an update to Hawking’s original 1983 “no-boundary” proposal, attempting to make the theory of the early universe mathematically consistent and scientifically observable.