t happened before the beginning? That’s a question that Stephen Hawking aims to answer in his newest film, “Before the Big Bang 5: The No Boundary Proposal,” which is available now for free on YouTube.

The 50-minute video explains Hawking’s model of origins of the universe, a topic that he has dedicated as the focus of his research for many years now. The film specifically covers Hawking’s “No Boundary Proposal,” which he developed with James Hartle. This proposal explains a quantum theory of what may have occurred long before the Big Bang.

“In my doctoral thesis I showed that, according to Einstein’s theory of relativity, the universe must have had a beginning,” Hawking explained on his verified Facebook page yesterday. “But the theory of relativity did not say how the universe had begun.”

All evidence suggests that the universe is around 13.8 billion years old, but everything must have had a beginning. The Big Bang theory is widely accepted as how the universe came to be. This theory explains that a very hot, very dense singularity eventually gave birth to the entire universe, which has been expanding ever since. But what caused the Big Bang?

The No Boundary Proposal involves tracing the origins of the universe in reverse. The universe is constantly expanding, but by following this process in reverse, you would see the universe get smaller and smaller until it was at a subatomic level, How Stuff Works reported. At this point, space would become separated from time and, as a result, time would no longer exist (at least as how we think of it now). Therefore, the No Boundary Proposal suggests it's impossible to measure events before the Big Bang. Time literally did not exist at this point. If that's true, it would mean the universe has no boundary.

he theory, of course, remains just an idea and is not widely accepted by all physicists and scientists. Hawking is no stranger to controversial ideas on the origin of the universe. In 2013 he caused a stir by proposing that the Big Bang did not need God to begin. According to Hawking, though many individuals—scientists included—like to counter divine intervention into our universe’s creation, when you do the hard research, an all-knowing power simply does not explain our existence.

Whether you agree with Hawking or not, his theories are fascinating. Catch up with his latest for free on YouTube, and further expand your own understanding of quantum physics and the beginning of time itself.