A couple weekends ago, I burned a dead apple tree.
I cut it down first, of course, then spent basically all afternoon snapping branches with my bare hands, throwing piles of sticks onto the blaze. I had a cold beer or three and the sun felt warm on my face for what seemed like the first time in years—the mental aftereffects of a long Maine winter. It was, to put it mildly, a wonderful time.
While I was burning the tree, my wife was also there. She was doing some early spring gardening, sometimes mischievously throwing leaves on the fire, as she is wont to do. Wearing an oversized hat, our one-year-old daughter sat on the ground, shoving fistfuls of grass into her mouth. Our oldest, a three-year-old, scolded our dog for sitting on the cushions she’d put on the deck. We were all in our own little worlds, living in the moment, doing the things that we generally felt like doing.
Now, I’d like to juxtapose that viscerally satisfying physical experience with reading Helgoland—a satisfying mental experience. In which Carlo Rovelli, a theoretical physicist and quite accessible writer, states that our world basically doesn’t exist. At first, the two activities—burning a tree and reading heady science about quantum theory—don’t seem to square. But in my experience, they do. And not only do they square, they enhance each other. I’ll try to explain.
Because the satisfaction of burning a tree is fairly clear cut, let’s talk about Helgoland. Helgoland, the place, is the name of the North Sea island where a 23-year-old Werner Heisenberg devised the basis of quantum theory. Quantum theory, in practical terms, gave us LEDs, semiconductors, MRIs, GPS, electron microscopes, and the atomic bomb, to name a few innovations.
My understanding of the crux of the book is this: looking at the world through the lens of today’s quantum theory, nothing actually exists. Everything is an event, an interaction of multiple things with, most importantly, an observer. Without an observer and an interaction, existence literally ceases to be.
I’m not going to be able to explain this as we
ll as Rovelli, but that won’t stop me from trying.
Let’s start with an experiment by Anton Zeilinger, in his Innsbruck laboratory in Austria. The idea is this: a laser beam is split with mirrors (we’ll call this split 1), put back together with mirrors, then split again (split 2). Left alone, all of the photons of the laser end up going on what we’ll call the “down” part of the path after split 2. But if, after split 1, you place your hand in front of either path, photons after split 2 end up on both paths: the up and the down.
This isn’t the crazy part. The crazy part is that you don’t even need to obstruct the path with your hand. If you simply look at where the photons are going after split 1, it changes where they end up after split 2. Here are Rovelli’s words:
It seems that you only need to observe what is happening for it to change! Note the absurdity. If I don’t look for where the photon passes, it can end up above [after split 2]. The astonishing thing is that a photon can end up above even if I haven’t seen it. That is to say, the photon changes trajectory due to the fact that I was waiting for it at the gate, on the side where it hasn’t passed. Even if I haven’t actually seen it!
I don’t understand this. Luckily, in Rovelli’s own words, neither does anyone else. Theoretically, he explains what is happening as a result of “quantum superposition.” Where the wave function of the laser “collapses,” or converges to one point the moment we observe it. The science tells us that the wave is actually on both paths, but if you search for it, it collapses to a single path.
My monkey brain quakes.
A related, unresolved, and still hotly contested question of quantum theory can be summed up in a thought experiment devised by Erwin Schrodinger. There’s a box in which there is a cat and a bottle of sleeping serum. There’s a 50% chance that the sleeping serum has spilled and the cat is asleep, or that the sleeping serum has not spilled, and the cat is awake. Without opening the lid of the box, you don’t know which is right. And the cat is not either awake or asleep, the cat is in a quantum superposition of “cat-awake” and “cat-asleep.” The cat is the same as the wave going on both paths. Only after we observe it, by opening the box, will its position collapse to a single path: either “cat-awake” or “cat-asleep”.
The “hotly contested” parts: is the cat actually in a quantum superposition? Or is it simply either awake or asleep? And, how would the cat feel about this?
Who cares, right? What’s the point? (
At least that was what I thought when I first heard that one.) In Helgoland, Rovelli chooses not to try to solve that question, focusing rather on the importance of the person looking at the cat. To become real, the world requires an observer. In Rovelli’s words “the world is a dense web of interactions.”
To be more heady, as if we needed that, here we go with another Rovelli quote,
“The discovery of quantum theory, I believe, is the discovery that the properties of any entity are nothing other than the way in which that entity influences others. It exists only through its interactions.”
In essence, Rovelli is saying that nothing is a “thing.” Everything, when we try really hard to observe it at the smallest and most precise possible level, is an interaction. Everything is relational.
An example: we’re riding in a car; I ask how fast we’re going. You say “88 miles per hour.” I say sweet. But what if the question actually was, “how fast are we going, when factoring in the spin of the earth.” If we were on the equator, driving due east, we’d be going about 1,088 mph. But what if the question was, how fast are we going when factoring in the spin of the milky way galaxy? How fast are we going factoring in the movement of the known universe? And in what direction are we even driving? Each of these questions requires a set of parameters to make it make sense. They are all relative.
And in Helgoland, Rovelli is saying is that relativity actually applies to everything. An object is only how it interacts with other things. Say a soccer ball is kicked, it interacts first with the kicker’s foot, is then buffeted by wind, bounces off a tree, breaks the kitchen window, and finally comes to rest, pressing itself against the wooden boards of the deck due to the gravitational effects of earth. Which of these states is the true soccer ball? Is there a true soccer ball? Or is it just a certain arrangement of atoms, interacting with other atoms, at a particular point in time and space?
Yes? So, in thinking about me, burning my tree. Was it simply the burning that was satisfying? Was it the fact that my family was all there? Was it the nice weather? Was anyone else even enjoying themselves? All of these questions relate to one another. The entire situation was held thinly together by relations. And by being there, by observing each other, we were tangibly affecting that very reality. Like the lasers and the looking, simply being present, simply observing, changed everything.
Rovelli ends the book with an astonishing bit of modern medical research.
The question that a group of doctors was trying to solve: how do our brain and eyes interact? You’d expect it to be a one-way street, right? Your eyes see something, they send an electrical message to your brain, your brain interprets that information, and off you go, seeing stuff.
Turns out, that’s backwards. What actually happens is that, for the majority of the time, our brain is first sending the message of what we see to our eyes. We are viewing a projection of our brain. Only when our eyes detect a discrepancy between what our brain expects and what we actually see (that’s not a patch of rustling grass, that’s a tiger!) do our eyes send messages back. It means that most of our world is literally a figment of our imagination—a projection of what we expect to see, rather than any fundamental, objective, truth.
To reel this back in, all of these details point to a set of truths that appear endlessly in life, and in fiction. Meaning, quantum physics is re-proving the point that we truly can never know another person’s reality.
A red balloon might make one person smile because of the way the sun illumines its polychloroprene. The same balloon might make someone else smile because it reminds them, with bittersweet clarity, of a day they spent in childhood at Six Flags with their late mother. Different relations. Different realities.
But here’s the crux for me: both people are smiling.
On that day with the fire, we were all perhaps literally in our own realities. But we didn’t have to be experiencing the exact same reality to enjoy the same things. And the fact that we were all there changed the reality for each of us. The relationship between us made the moment more special. Our mutual observation of each other, our interactions as observers, all intertwined into a wonderful afternoon. And that feeling of being together, in the same time and space, experiencing as close to the same reality as was possible, needs no science to explain that it is a good feeling indeed.
IN SUMMARY: Quantum physics excites me in ways I literally cannot understand.
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