QBism is the most mind-blowing scientific view of reality I’ve ever encountered

What is reality? This is a really important question. Maybe the most important question of all. It’s also a really difficult question to answer. Humans have been attempting this throughout recorded history. And probably long before, extending to the first time one of our prehistoric ancestors looked upon the world and thought something like, What’s this all about?

Most of us, me certainly included, either consciously or unconsciously view reality as being comprised of two main branches: objective and subjective. This was a focus of the first book I wrote, God’s Whisper, Creation’s Thunder, where I attempted to relate principles of ancient mysticism with findings of the new physics.

I shared the schema that I used in the book in a 2012 post called “Does an objective non-symbolic world exist?” The quotes are from a revised version of my book.

First, there’s a subjective and objective reality.

“Is there a reality independent of ourselves? If so, it is objective. Is there a reality that only exists within our own personal consciousness? If so, it is subjective. This produces a distinction between the objective domain of science and the subjective domain of art. A scientific truth exists whether or not any particular individual does, while a work of art springs from a personal rather than universal consciousness.”

Second, there’s a symbolic and non-symbolic reality.

“In human consciousness there are private and public domains. The public part is what can be shared with other people through symbols. The private part is what remains essentially incommunicable, known only to the person experiencing it.… Not everything that is experienced is expressible. Further, there never is an exact correspondence between a symbol and reality. Something always is missing from the description. For example, even though the symbolic language of mathematics is extraordinarily effective in describing the laws of nature, a mathematical description of how nature operates is far removed from the reality of nature itself.”

I argued that this produces four states of being, which I pithily described with the italicized words: (1) subjective and non-symbolic, feeling; (2) subjective and symbolic, thinking; (3) objective and symbolic, observing; (4) objective and non-symbolic, contemplating. The last state of being is by far the most controversial. I still consider it to be a possibility, but I no longer believe in it as strongly as I did when I wrote the book.

I mention this not because my schema is a brilliant bit of philosophizing (it isn’t). I just wanted to show that I’ve been fascinated by the nature of reality for my entire adult life. Initially I believed that the world, and our universe as a whole, is as real as reality can be. Then, in my religious phase, eastern religion variety, I believed that the world is illusory compared to supernatural realms of reality that are far closer to Truth with a capital “T.”

However, in each instance, I assumed that really real reality is something out there, independent of us, waiting to be known by consciousness. This, I believed, is true whether or not ultimate reality is to be found in this physical universe or in some supernatural domain of existence.

Which brings me to a conception of reality described in In Search of Now: The Science of the Present Moment by Jo Marchant, a book that I’ve been blogging about and am enjoying a lot. In a chapter called “Bursts of Creation,” Marchant explores an approach to quantum theory called QBism. She takes quite a few pages to describe it.

These few paragraphs give you the lay of the QBist land. Hopefully you’ll get the gist of what QBism is all about from these passages. Keep in mind that QBism sprang from the minds of sophisticated quantum physicists seeking to understand the meaning of quantum mechanics, not just the mathematics. So these aren’t the ramblings of some New Age type.

Fuchs and his colleagues used mathematical principles inspired by de Finetti to come up with their own interpretation of quantum mechanics. At first, they called the approach ‘Quantum Bayesianism’. But de Finetti’s insistence that probabilities are purely personal is too extreme for most Bayesian mathematicians, so now they just call it QBism (pronounced ‘cubism’). Fuchs hopes that like the art movement, it might help us to see the world in a radically new way.

That’s because unlike any of the other interpretations of quantum mechanics, QBists aren’t just coming up with a new physical structure for the universe: they’re changing the story of what quantum physics is, what it’s about. They argue that we should let go of the idea that wave functions and quantum states relate to anything outside of our own experience.

Rather than being physical states of matter, they are personal: an expression of the experimenter’s own beliefs. A measurement isn’t a dry physical interplay but an agent’s action. The outcome is an experience, what happens to the agent as a result of the action they took.

Instead of proving a picture of the physical world beyond us, Fuchs describes quantum mechanics as a ‘user’s manual’ or ‘guide to experience’. It’s a personal tool rather than an impartial description: a handsaw, not a map. The equations enable a physicist to assign probabilities to the possible consequences of each action she might take, in a self-consistent way.

Let’s say she calculates the quantum state of an electron. In QBism, this doesn’t relate to any actual ‘electron’ already out in the world, it is simply her prediction of what she will experience if she makes a particular measurement. In other words, the equations and relationships of quantum mechanics aren’t revealing a physical terrain of particles, fuzzy or otherwise.

They’re telling us about our personal, internal worlds. They’re expressing the structure of what each of us can experience, believe and know. QBists go much further than the relatively tame idea that our perspective influences how things in the world will look to us. For Fuchs, belief is everything. There’s no solid ground sitting out there beyond all observers, he insists, no universal kernel of realness on which everyone must agree.

Quantum physicists assign probabilities for outcomes between zero and one, where zero means that something definitely won’t happen, and one means it definitely will. Einstein — along with two colleagues, Boris Podolsky and Nathan Rosen — famously suggested that if you calculate the probability of a particular outcome as ‘one’ or definite, then that phenomenon can be said to have an objective, independent existence. It will be true for everyone, and still true even if there is no one to observe it.

QBists, on the other hand, say that even a probability of one doesn’t guarantee pre-existing reality. Another experimenter with different knowledge or experience might still assign a different probability. A probability of one just means you, personally, are certain, not that the phenomenon is ‘real’.

In one swoop, swathes of what we’re used to thinking of as physical reality — electrons, photons, atoms, the entire microscale that makes up our universe — dissolve away. If we think back to Rovelli’s relational cosmos, these entities were recast as ‘interactions’ that can’t be captured by a single point of view. But within the network of those interactions, there’s still an unarguable truth to what exists, to how things must appear from any particular perspective.

In QBism, though, this landscape is wiped out. Erased. There are no phenomena ‘out there’ at all. Just personal beliefs, inside physicists’ heads. Perhaps you think that sounds ridiculous, but stick with me. There are some practical advantages to this way of seeing the world. And QBists aren’t getting rid of reality — far from it. It just doesn’t look how we thought.

So what is that fresh view of reality QBism brings us? Though this post already is long, I don’t want to leave you without a hint of the answer. I find what follows highly persuasive. Also, inspiring. Philosophically, it seems to be a lot like the love child of Buddhism and Quantum Mechanics.

The physicists are still working out what all this means. But one thing is clear. Although in QBism the predictions of quantum mechanics are personal, the underlying structure is the same for everyone. It tells us how to organise our bets, how we weigh up the consequences of different actions and what to check for to ensure that each moment is consistent with the next.

We’re not dreaming the world, and we can’t conjure just anything with our minds. We’re all part of the same game, playing by the same statistical rules.

Far from getting rid of reality, then, QBists suggest — unlike pretty much all other schools of physics — that reality must consist of more than just physical interactions ticking along. We have to include ourselves because the things we talk about, from photons to planets, have no meaning or existence on their own. In each moment, in everything we observe, we’re bringing something to the table through our choices and experiences.

Fuchs told me that one of his aims for QBism is to flesh out this principle to cover not just conscious human measurements but reality more generally, to develop the idea that ‘whatever it is that we understand as an experience for ourselves, is actually part of the stuff of the world’.

I think that’s an exciting vision for Now because it would mean that we’re not just ‘microphysics configurations’, we’re players. Nothing is set in stone: we have a say in what the universe is and where it goes. When we probe our environment — even something as simple as detecting a photon — we’re not uncovering what’s already there but helping to create something new.

And, in whatever tiny way, that changes the trajectory of reality, of what can come next. ‘If you don’t take the action, you have a different universe than if you do take an action,’ Fuchs told me. ‘And if you do take an action, it depends on which kind of action you take.’