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Sean Carroll: Universe a ‘tiny sliver’ of all there is

The "many worlds" theory in quantum mechanics suggests that with every decision you make, a new universe springs into existence containing what amounts to a new version of you. Bestselling author and theoretical physicist Sean Carroll discusses the concept and his new book, "Something Deeply Hidden," with NewsHour Weekend's Tom Casciato.

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  • Hari Sreenivasan:

    The term "quantum mechanics" describes the strange doings of the tiniest particles in the universe, where, for example, two objects can occupy the exact same space at the same time, or affect each other even though they're millions of miles apart.

    But if that sounds outlandish, hold on to your hat.

    Within the realm of quantum mechanics, there is a highly abstract and controversial theory known as "many worlds." It describes the idea that with every decision you make, an entirely new universe springs into existence … containing a new version of yourself!

    As bizarre as it sounds, some theoretical physicists believe that "many worlds" is an exact description of reality. Sean Carroll has staked his reputation on it. He's a bestselling author and a professor of physics at the California Institute of Technology.

    NewsHour Weekend's Tom Casciato recently visited him at Caltech to discuss his latest book and its implications not just for physics, but for all of us.

  • Tom Casciato:

    To speak with Caltech theoretical physicist Sean Carroll about Quantum Mechanics is to confront a basic contradiction.

  • Tom Casciato:

    Sean, you've written that one of the premises of science is that it renders the world intelligible. You've also written that Quantum Mechanics tells us that what we see isn't what's really happening. That already starts to sound a little unintelligible.

  • Sean Carroll:

    Well it is. I think that Quantum Mechanics historically is the great betrayal of the goal of science, which is to understand how the world works, right?

  • Tom Casciato:

    And that's the problem, says Carroll. While scientists use Quantum Mechanics all the time, it's made possible the transistor, the personal computer, the laser and much more, they don't really understand it. He lays it all out in his new book, "Something Deeply Hidden."

  • Sean Carroll:

    The problem is what's called the measurement problem, right? You know, we always talk about an electron for example, an elementary particle. We say, well, it has a position, you know, there it is.

  • Tom Casciato:

    When I was a kid in science class, they showed the little nucleus and then the electrons were going around it.

  • Sean Carroll:

    Yup.

  • Tom Casciato:

    That's not what's happening?

  •  Sean Carroll:

    Lied, you were lied to, right.

  • Sean Carroll:

    In Quantum Mechanics, there's no such thing as the position of the electron. What there is is where you would see it were you to look, and we really have trouble wrapping our brains around that concept.

  • Sean Carroll:

    So here you are, and you have not yet observed the particle.

  • Tom Casciato:

    In fact, that concept led to a split in the physics community. On one side, saying the theory that the observer is critical to the position of a particle was the famed Danish physicist, Nobel-Prize winner Niels Bohr. It's known as the "Copenhagen Interpretation." Carroll writes that no less a scientist than Albert Einstein was unsatisfied with the Copenhagen Interpretation. Bohr's and Einstein's disagreement was dramatized in the National Geographic series, "Genius."

  • Niels Bohr:

    It functions. And it allows us to make use of the quantum world.

  • Albert Einstein:

    The goal of scientific pursuit should not be merely to make use of the world around us. It should be to understand it fundamentally.

  • Tom Casciato:

    In the end, Niels Bohr prevailed.

  • Sean Carroll:

    And he decisively won the public relations battle. Einstein sort of sat in his office in Princeton, would occasionally write a paper, wrote a lot of letters to his friends, but in the physics community Bohr was just given the victory prize, like OK we're going to do what you say. It got so bad that you know people were pushed out of the field if they tried to question the quantum dogma.

  • Tom Casciato:

    So the dogma that had hardened under Niels Bohr was that the observer was the important thing, that there was an element to Quantum Mechanics that involved observation.

  • Sean Carroll:

    Absolutely, so the dogma says that the act of observation is crucial, but then you say, well OK, what counts as an observer. Does it have to be a human being? Could it be a cat? What about a rock? What if I just like glanced at the system rather than looking at it directly, and the Copenhagen Interpretation says no, no, no, don't answer those questions.

  • Tom Casciato:

    Really, don't answer those questions?

  • Sean Carroll:

    We have nothing to say about that. It's obvious what an observer is. Let's get on with our lives.

  • Tom Casciato:

    Sean Carroll is among a group of theoretical physicists who reject the orthodoxy and refuse to just "get on with their lives. They call themselves "Everettians," after a lesser known 20th century American physicist who Carroll thinks should be a lot better known. His name was Hugh Everett.

  • Sean Carroll:

    Hugh Everett was a graduate student at Princeton. And Hugh Everett came along saying, well what if we studied the whole universe as a quantum mechanical system? Then we wouldn't have a system and an observer. We only have the system, so Everett said we need to understand quantum mechanics in and of itself. And he realized that that implied the existence of many worlds.

  • Sean Carroll:

    And you know Everett got treated very badly. He got ridiculed. He was told he didn't understand Quantum Mechanics, and we figured this out 20 years ago, the whole bit. So he didn't even apply for a faculty job as a physicist. He left and worked in the defense industry.

  • Sean Carroll:

    But we've learned a lot more about how Quantum Mechanics works since the 1950s. So in fact in my mind everything we've learned has made his case stronger. And we look at and say, yes ,I see the worlds, there they are. I see them in my math. I don't see them in my telescopes or microscopes.

  • Tom Casciato:

    So what does the math tell you about the universe?

  • Sean Carroll:

    It tells us that the universe is an abstract mathematical structure that evolves in a very certain way and with a very remarkable consequence that when you look at a quantum system, when you observe it, different copies of your universe are created. The universe you see around you is a tiny, tiny sliver of everything that there is.

  • Tom Casciato:

    Here's where it starts to sound really crazy. In the many-worlds interpretation, every time you make an observation, a new universe splits off from the one you were just in. Does that mean there are now two yous?

  • Sean Carroll:

    There's a difficult question in many-worlds as to how we should deal with personal identity, right?

  • Tom Casciato:

    Is it like that 90's movie Sliding Doors, where Gwyneth Paltrow catches the train, but she also misses the train? Sort of.

  • Sean Carroll:

    The people in other worlds aren't me. They might have come from the same youngster as I did.

  • Tom Casciato:

    They might have.

  • Sean Carroll:

    But they're a different person.

  • Tom Casciato:

    Slow down. What do you mean they might have come from the same youngster that you were?

  • Sean Carroll:

    So in other words in many worlds there was a youngster. There was a person who I have descended from over the last some number of years, and the world has branched many, many times since then, and so there are other people in these other worlds who were me back then but now they're different people because the world has branched since then, and so we have to expand what we mean by personal identity because your world line is a tree, right. It's like you're an amoeba that branches and splits.

  • Tom Casciato:

    Is there a person who used to be me who is the point guard for the Portland Trail Blazers?

  • Sean Carroll:

    There is. Yes.

  • Tom Casciato:

    At my height?

  • Sean Carroll:

    And you won the NBA Championship, yes.

  • Tom Casciato:

    With my lack of physical ability.

  • Sean Carroll:

    You know so this is hinting at a crucially important problem for many worlds, which is how do you weigh the relative likelihood of different things happening? Not every world is created equal in some sense. So the worlds that you think of as crazy or unlikely really are. You are, again, less likely to find yourself in those worlds than in the normal ones.

  • Tom Casciato:

    Are there people who think you're out of your mind?

  • Sean Carroll:

    Yeah, there's plenty of people who think that I'm out of my mind, and that's part of what is troubling. Not that they think that I'm wrong, but that we haven't settled this yet. I mean these were all questions that should have been hashed out in the 1920s and 30s. But as a field, physics decided not to face up to this puzzle, and I think that it's been holding us back as physicists. I think that our understanding of cosmology and gravity isn't nearly as good as it could have been had we worked harder at understanding Quantum Mechanics.

  • Tom Casciato:

    Many worlds suggests a new you is created in a new universe thousands of times per second. So the you in this universe won't be surprised to learn the theory is controversial. The online math-and-science journal "Quanta Magazine" has called it the most polarizing of interpretations, saying "some physicists consider it almost self-evidently absurd."

  • Tom Casciato:

    Do you say this at some risk to yourself? You are a best-selling author, and you teach at Caltech, you're in a pretty firm position as these things go.

  • Sean Carroll:

    I'm not in a super firm position, cause I don't have tenure at Caltech, so, but I don't care either. Like I think it's more important to me at this point in my life to try my best to get it right. And it's not like I'm going to be blackballed or ostracized by the community, there's plenty of other people who are Everettians. It's not so much that I'm a fan of many worlds, it's that I care about the foundations of Quantum Mechanics.

  • Tom Casciato:

    I'm just wondering if decades from now we're going to find you on the corner with a bottle, babbling about many worlds.

  • Sean Carroll:

    There is a world in which that happens, yes. But you know what, I could change my mind next week if someone showed me a better theory that didn't have some of these problems and still have all the benefits. I think it's unlikely. I would love to be the person to come up with that theory myself. But I think that we should have the courage to follow our best theories and accept what they predict.

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