(Inside Science) -- Quantum physics, cosmology, existentialist philosophy and morality may seem like disparate subjects. But Sean Carroll, a theoretical physicist at Caltech, ties them all together into a cohesive and comprehensive worldview he calls "poetic naturalism." He lays out his views while trying to find meaning in a vast and chaotic universe in his newly published book, "The Big Picture" (Dutton, Penguin Random House Inc.).
Having written two previous popular physics books as well as being active on Twitter and his blog, Carroll takes an interest in communicating complex scientific discoveries. In his new book, he describes some of the fundamental ideas in modern physics with a philosophical lens, while exploring life's biggest mysteries: the origin of the universe and the meaning of life itself. At the same time, with references to Wile E. Coyote, Captain Kirk and "Bill and Ted's Excellent Adventure," he avoids an overly serious tone.
In recent years, prominent scientists like Neil deGrasse Tyson, Bill Nye and Stephen Hawking have downplayed the importance of philosophy or even denigrated it. Carroll is not among this crowd.
"There are a lot of scientists and science promoters who have said not entirely complimentary things about philosophy, but that misses the point about what it's for," Carroll said in an interview. "The purpose of philosophy is not to be the handmaiden of science."
Though his Ph.D. is in physics, Carroll has a strong interest in philosophy as well, and minored in it in college. He sees philosophy as a method for interpreting science and for a deeper understanding of physical phenomena. He uses philosophical concepts such as causality, determinism and mind-body dualism to explore everything from the tiniest subatomic particles to the accelerating expansion of the universe -- as well as the role humans play somewhere in between.
For Carroll, naturalism means that there's one world, the natural world, it obeys the laws of nature, and you can discover it using science. To this he adds that "there are many ways of talking about the world," stories that people can tell to make sense and meaning of the world and their place in it. He even address issues of free will, consciousness, ethics, and life after death.
Carroll describes physicists' "Core Theory," the quantum field theory of quarks, electrons, neutrinos, electromagnetism, gravity and nuclear forces. This includes a discussion of virtual particles thought to flick in and out of existence, as well as of the conception of "fields," like electric or gravitational fields, which occupy all space without being tangible things. He acknowledges that scientists could uncover new particles, forces or interactions, but he believes they will only matter at very high energies or extremely small scales.
"We're not going to discover any new particles that are inside you that are relevant to understanding how you behave," Carroll said.
He also discusses differences between space and time, and how the arrow of time in the universe always points in one direction (toward the future). Carroll argues that entropy, or disorderliness, increases with time, with an analogy of mixing cream into a cup of coffee. It's impossible to remove the cream after it is poured and stirred into the coffee. But although entropy always increases, after a few stirs with a spoon the coffee-cream mixture eventually reaches a uniform color, becoming simple again.
Scott Aaronson, a theoretical computer scientist at MIT, collaborated with him on a simulation of cream and coffee mixing together. "Complexity is highest when you see the tendrils of milk in the middle," Aaronson said. "Sean figured out that this is like the universe as a whole, where only in the middle do you have stars and galaxies."
The situation becomes murkier when Carroll discusses quantum mechanics, the interpretation of which has continually generated debates among physicists and philosophers since Max Planck and Albert Einstein discovered light "quanta" in the early 20th century. Physicists interpret quantum systems with probabilities: for example, for a hydrogen atom, the electron doesn't have a particular position or momentum, but if someone measures them, it has probabilities of being observed in particular states.
Carroll supports the controversial "many-worlds interpretation" in which every quantum possibility is literally a separate world (or universe). We happen to live in one of them, and we have no way of seeing or even confirming the existence of the many unobservable parallel universes. This interpretation seems to conflict with his claim of endorsing a "sparse ontology," which would mean accepting only a few fundamental concepts for describing the natural world.
"What I took Carroll to be promoting was a kind of 'verificationism': what is true is what can be measured," said Elise Crull, philosopher of science at the City College of New York. "But what counts as 'measurable,' and how we distinguish theoretical from observational statements, are complex issues." This is why, she argues, philosophers considered the view problematic and abandoned it long ago.
Carroll was influenced by Carl Sagan, an agnostic, and the philosopher Daniel Dennett, an atheist, among others. In the end, he refers to the famous existentialist Albert Camus and argues that people have the freedom to find or create meaning in a universe without God. This is where the "poetry" of his "poetic naturalism" comes in.
"The construction of meaning is a fundamentally individual, subjective, creative enterprise, and an intimidating responsibility," he writes. "We need to make our peace with a universe that doesn't care what we do, and take pride in the fact that we care anyway."
The goal of his book, as of his philosophy, is a practical one. "I'm trying to set up a way of talking about the origin of the universe and the meaning of life," Carroll said, "but the book is much more an invitation to start the conversation rather than 'here's the final answer.'"