Carlo Rovelli

The conversation opens with the guest, physicist Carlo Rovelli, describing his work broadly: science, philosophy, "some politics", and enjoying life. He then narrows it down: "Officially, my job description is a physicist. I do quantum gravity, theoretical physics." Joe Rogan brings up the book he was pitched, given in the transcript as "On the equality of all things". Rogan says he has "always sort of intuitively suspected" that its central idea is true, and that hearing a physicist say it makes him feel he may be "on the right track". Rovelli answers that he is not surprised the idea feels natural, and that sets up the main thread of this part of the interview.

Rovelli's starting point is everyday experience. We deal with people through the way they interact with us, and "We always see things from our own perspective." He says science, and physics in particular, seemed to promise something different: an objective, fixed reality that could be seen from outside, made of little things that each have their own properties. He argues that physics itself undermined this picture in the last century, through quantum mechanics.

He is careful to say he is not denying reality. Pointing at Rogan and at a pen, he says both are "real, of course". His point is that each observer sees the pen from a different side. The real question is whether all those perspectives fit together into one objective pen:

And the question is, do all this perspective match perfectly into a unique objective reality of the pen? And I think quantum mechanics telling us, no.

His alternative is that "Reality is this ensemble of perspectives." The pen's position, colour and length are, on this view, not properties the pen has by itself. They describe how the pen appears to one person or another. Rovelli widens this beyond human observers: it also covers how the pen "clashes another pen, how it affects another pen." He calls this a network of interactions and says he finds it a more beautiful picture than one where we stand outside the world looking in: "We're inside reality. We are part of reality."

He applies the same reasoning to people and objects. Asked, in effect, who Joe Rogan really is, he lists his own view, Rogan's view of himself, and the views of listeners, and concludes that Rogan is "this collection of perspectives" with "no final one". A cup of water works the same way. Chemistry, different branches of physics, quantum gravity and psychology each describe it, and even calling it "a cup of water" reflects the fact that we drink from it. "I don't think there's a final one," he says. The cup is the collection of perspectives on it.

Rovelli does not throw out the senses. "To some extent, our senses are reliable, of course," he says, and gives the example of putting down a cup that is hot. The problem comes when we take the senses "too literally, too seriously", and he says there are many cases where we later find out we were wrong. He says what he loves about science is when "it corrects us in some big way."

His example is the sunset. It looks as if the sun is going down, but science tells us the sun stays put while the Earth, "a big rock that is spinning", carries us out of its light. Watching a sunset with this in mind, he says, one can think: "oh my senses cheat me in telling me that the sun is moving but it's not moving I am moving". He offers this as a case where science showed that things are not exactly as we see them.

Rogan takes the sunset in another direction and asks what the evolutionary benefit of its beauty might be. He compares it with food: an orange tastes good because it is nutritious. He asks what the equivalent explanation is for the feeling people get from sunrises, sunsets and mountains, and suggests there is "some weirdness" to it that cannot simply be reduced to measurement.

Rovelli welcomes the question but does not claim a full answer. He says sunrise and sunset matter to us because evolution, over a very long time, shaped humans to sleep at night and be active by day, and he notes that cats do the opposite. Beyond that, he says plainly that he does not know exactly where the emotion comes from. What he does take from it is a broader point: our relationship with the world "it's not about knowledge about what to do. It's always emotional, right?" Food, mountains, wild animals and other people all reach us first through emotion.

He presents rational thought as coming afterwards, as a way to correct ourselves and "do it a little bit better", and he is careful not to dismiss it: "I'm not denying the utility for the rational part, but this is an addendum to what we are." Rogan repeats the phrase back to him when the conversation resumes after a sponsor break.

Rogan suggests that quantum physics must have thrown the study of the world "into a giant tizzy", because at the smallest observable level "you have magic." Rovelli agrees with the basic idea, though not with the word. He says physics was supposed to be the route to objectivity: whatever our emotions and perspectives, underneath there would be simple physics with atoms and forces, "and that's it." Instead, he says, 20th-century physicists found that the world at that level is "even more perceptible, more complicated than in our everyday life."

He describes the history as a time of real confusion. Physicists were measuring atoms, radiation and electrons and could not make sense of the results. A Copenhagen-based figure, whose name the transcript garbles as "Neil Spore" and "Inillsborough" (from the context, evidently Niels Bohr), was the first to say that the problem was philosophical, not only a matter of finding the right equation: "We have to change the way we think about the world." Rovelli puts this alongside earlier shifts, such as realising that the Earth moves and the discovery of electric fields, as one of the jumps that changed how people think about reality.

When Rogan asks how long it took physicists to accept that observing quantum systems affects them, Rovelli answers with atomic spectra, not with the particle-and-wave experiments Rogan mentions. Measurements "piled up" through the first 20 years of the 20th century. Atoms emit light in specific colours, and physicists tried and failed to explain how electrons move to produce that light. The Copenhagen school then argued that to understand the atom, one has to understand how one looks at it: "If we look at it in one way, we see one thing. If we look at another way, we see another thing." Rovelli admits this "was very confused." His answer on acceptance is short: "It worked so well that people accepted even if it was confused."

Both men insist this is serious science. Rogan says "This isn't woo-woo," and Rovelli adds, "It's not just smoking joint and getting high." These results came from physicists, "the one who was supposed to be the most rational objective guys."

Rovelli separates two things: how well quantum mechanics works, and how well we understand it. The mathematical theory that came out of this period "works very well" and is "used today everywhere". He points to the studio microphone and to circuits designed using the quantum properties of matter. "So quantum mechanics is solid."

What the theory does not give, he says, is an account of what happens in between. It says that if you do one thing you will see one result, and if you do another you will see another. It does not tell a story of what happened to the electron or the quantum system itself. That gap is what confused physicists:

So quantum mechanics is a strange theory. We know how to use it. It's like a black box. But we don't know what is inside the box.

He extends this to current technology: "Even in a quantum computer, we don't know really what happened inside." When Rogan calls that strange, Rovelli replies that it "works fantastically" anyway.

Rovelli is open that this is still unsettled: "we're still debating about us, right?" He says physicists and philosophers are still arguing about what quantum mechanics has taught us, and the debate is "sometimes furious." He describes the main positions this way:

- Extra variables: some physicists hold that there are additional variables, in principle impossible to see, that determine what happens. - Parallel worlds and a universal wave function: others speak of "this immense wave function of the universe, other universe and stuff like that". Rovelli reads this as an attempt to hold on to something absolutely objective by "trying to multiply reality to make it objective." - Relational view (Rovelli's own, shared with others): drop the idea that anything exists "just by itself". What exists is what affects me, what affects you, or what affects another piece of matter.

He states his own position firmly: "The dream of an absolute objectivity is a mistake." He sums up the alternative this way:

So we have to think of reality as processes of things affecting one another. Relations.

This view differs from how Rogan frames the issue. Rogan talks about watching things and having "a measurable effect" on them. Rovelli's relational account does not make human observers special: the relevant interactions include how things affect "another piece of matter" and how one pen affects another. He presents this as one side of an ongoing debate, not as an agreed result. He also argues that, on this view, basic physics turns out to be more like everyday life, which is full of perspectives, than the abstract objectivity people once expected.

To show how well quantum mechanics works, Rovelli uses the periodic table, which he remembers from the wall of his primary school classroom in Italy. He says there are "about 100" elements, and everything we see is made of them, as chemists worked out across the 18th, 19th and 20th centuries. The theory had to explain why there are these particular elements and why the table has its peculiar structure. His account is that with quantum mechanics "you just write an equation and bingo": it has a set of solutions, "one per each element." He adds that people could predict properties of elements before measuring them and then check. He gives this compact version without the underlying details.

He places this within a broader pattern of prediction coming before observation. Electromagnetic waves, which carry the podcast's broadcast, "were not discovered by seeing them" but were predicted, and he names Maxwell and Hertz. A small circuit on one side of a room produces a wave detected on the other side, and later the same works between Europe and the US. Black holes were predicted by Einstein from the equations of gravity and found later. "That's the strength of science," he says.

He brings the argument back to quantum technology. Engineers building quantum circuits no longer rely on trial and error, because calculations predict what will happen. That success is exactly why the interpretive question remains open:

The question open is that you can have something that works very, very well, and you don't know why.

This segment states Rovelli's relational view more than it argues for it in technical detail. He sets it against hidden-variable and many-worlds approaches but does not go through the evidence or arguments that would decide between them, and he describes the field as still in heated debate. His answer on how quickly physicists accepted the new picture is brief and anecdotal. On the evolutionary role of beauty, he openly says he does not know. The section ends with sponsor material, which is left out of this account.

Asked what the double-slit experiment shows and why it confused physicists, Carlo Rovelli first calls it one of "a number of extremely confusing experiments" and then sets up the basic arrangement. A wall has two slits, and a single particle is sent from one side to the other. If you check which slit it uses, it always goes through one or the other and never through both.

Then comes what he calls the "magic." With only one slit open, a particle can reach a given point on the far screen. With only the other slit open, it can reach that same point too. With both slits open, it never arrives there. Rovelli says this makes less sense the longer you think about it. The only explanation seems to be that the particle somehow goes through both slits and the two parts "forbid each other" from reaching that spot. Yet whenever the slits are watched, it only ever goes through one. He says people have been confused by this "for a century."

His proposed way out is to reject the question. Asking where the particle is when nothing is interacting with it is, in his words, "a wrong question." A particle cannot be understood as something that always has a position. It has a position only when it interacts with something else. He calls this both the mystery and the magic of quantum mechanics, and a challenge to the idea of an objective particle that exists independently of its interactions.

The particle is only the effect it has on the screen, on the detectors.

Joe Rogan asks for a theory of why observation or measurement changes the pattern. Rovelli separates his view from the idea of a scientist taking a reading. The "measurement" is "Just interaction with anything." The physics differs completely depending on whether something is there to interact with. He offers a picture of a particle that "snaps here and then it snaps there," each snap happening when it hits something. Physics can predict probabilistically where the snaps will occur, but asking what happened between them "makes no sense."

The particle is just these interactions.