Stephen Hawking pushed off of this mortal coil last week, but the world-famous physicist was pondering some of humanity’s most puzzling questions right up until the end. Hawking spent decades of his life theorizing about the existence of parallel universes, crunching numbers and thinking in abstract ways in an attempt to make it all work.

His most recent work was an update to his paper titled A Smooth Exit from Eternal Inflation in which he attempts explain how the existence of parallel universes would mesh with our current understanding of physics. The idea that an infinite number of universes were born alongside our own isn’t particularly new, but actually proving that hypothesis to be fact is a monumental challenge that Hawking puzzled over in the paper updated just ten days before his death.

In his paper, Hawking ventured some very educated guesses as to the conditions under which the existence of a parallel universe could be detected. The biggest hurdle to testing his theory is one of technology, as the scientist suggests that deep space probes would need to search for and detect the faint whispers of background radiation left over from the creation of these parallel realities.

Past research has suggested that evidence of parallel universes might be hiding just out of reach. Last year, an investigation of a “cold spot” in space led to the incredible theory that the spot may be the resulting bruise of a time when another universe collided with our own. Actually proving this is the case is well out of humanity’s scientific grasp, but Hawking’s work could one day lead to indisputable proof that we are living in one of an infinite number of universes much like ours.

As The Times notes, the discovery of a parallel universe (if it ever does happen) will undoubtedly be worthy of top scientific honors, meaning a Nobel Prize. Unfortunately for the late Hawking, the prize has never been awarded posthumously, and therefore he would be ineligible for the honor despite his wealth of work in the field.