On the Origin of Time: Stephen Hawking’s Final Theory

Saturday - May 13 2023, 01:11 UTC - 1 year ago

Hawking and I worked together for twenty years to crack the riddle of cosmic design, tackling theoretical questions about the laws of physics, the multiverse, and quantum mechanics. We managed to explain the vastness and complexity of the cosmos and the life-engendering properties of matter and energy in the universe by adopting a theory from an observer’s perspective.

The late physicist Stephen Hawking first asked me to work with him to develop "a new quantum theory of the Big Bang" in 1998. What started out as a doctoral project evolved over some 20 years into an intense collaboration that ended only with his passing on March 14, 2018.

The enigma at the center of our research throughout this period was how the Big Bang could have created conditions so perfectly hospitable to life. Our answer is being published in a new book, On the Origin of Time: Stephen Hawking’s Final Theory.

Questions about the ultimate origin of the cosmos, or universe, take physics out of its comfort zone. Yet this was exactly where Hawking liked to venture. The prospect—or hope —to crack the riddle of cosmic design drove much of Hawking’s research in cosmology. "To boldly go where Star Trek fears to tread" was his motto—and also his screen saver.

Our shared scientific quest meant that we inevitably grew close. Being around him, one could not fail to be influenced by his determination and optimism that we could tackle mystifying questions. He made me feel as if we were writing our own creation story, which, in a sense, we did.

In the old days, it was thought that the apparent design of the cosmos meant there had to be a designer—a God. Today, scientists instead point to the laws of physics. These laws have a number of striking life-engendering properties. Take the amount of matter and energy in the universe, the delicate ratios of the forces, or the number of spatial dimensions.

Physicists have discovered that if you tweak these properties ever so slightly, it renders the universe lifeless. It almost feels as if the universe is a fix—even a big one.

But where do the laws of physics come from? From Albert Einstein to Hawking in his earlier work, most 20th-century physicists regarded the mathematical relationships that underlie the physical laws as eternal truths. In this view, the apparent design of the cosmos is a matter of mathematical necessity. The universe is the way it is because nature had no choice.Around the turn of the 21st century, a different explanation emerged. Perhaps we live in a multiverse, an enormous space that spawns a patchwork of universes, each with its own kind of Big Bang and physics. It would make sense, statistically, for a few of these universes to be life-friendly.

However, soon such multiverse musings got caught in a spiral of paradoxes and no verifiable predictions.

--- Turning Cosmology Inside Out --- .

Can we do better? Yes, Hawking and I found out, but only by relinquishing the idea, inherent in multiverse cosmology, that our physical theories can take a God’s-eye view, as if standing outside the entire cosmos.

It is an obvious and seemingly tautological point: cosmological theory must account for the fact that we exist within the universe. "We are not angels who view the universe from the outside," Hawking told me. "Our theories are never decoupled from us." .

We set out to rethink cosmology from an observer’s perspective. This required adopting the strange rules of quantum mechanics, which govern the microworld of particles and atoms.

According to quantum mechanics, particles can be in several possible locations at the same time, a property called superposition. It is only when a particle is observed that it (randomly) determines a single location.

Initially, Hawking and I suspected that quantum theory, which suggests the cosmos is built of infinite nested superpositions, would also require an infinite regress of observers to make sense.

We were wrong. Quantum theory allows for two effects, decoherence and entanglement, which Hawking and I used to explain the vastness and complexity of the cosmos.

Decoherence transforms Superpositions into classical physics, permitting particles to split apart, taking on different identities like those of the Big Bang’s matter and energy fields.

Entanglement links together particles separated by vast distances, allowing us to explain why the patterns in the cosmic microwave background—leftover heat from the Big Bang—are so uniform, implying that events that took place in separate regions of the early universe were entangled.