Quantum theory (or quantum mechanics) is the foundation of our modern world. Without it, we wouldn't have computers, the Internet, GPS, and so many other inventions that we've come to take for granted.
I'm fascinated by quantum theory.
Though it is generally associated with goings-on at the atomic and subatomic level, not at the level of everyday life, since everything is made up of particles and energy, obviously the existence of we humans and all that surrounds us is dependent on quantum processes.
This is where much of the mystery of quantum theory resides: how is it that the uncertain, shape-shifting, probabilistic realm of quantum mechanics becomes the certain, dependable, deterministic realm of the world we inhabit?
The April 19, 2025 issue of New Scientist features a cover story, "The Idea That Shook Reality," in honor of 100 years of quantum physics. Two of the articles about quantum physics particularly appealed to me.
Physicist Carlo Rovelli tackled the history of quantum mechanics and how a misunderstanding of one of the pioneers in this field affects how we look upon quantum physics today. Here's a PDF file of his article, along with an excerpt that talks about how Rovelli views quantum phenomena.
Download Carlo Rovelli on what we get wrong about the origins of quantum theory | New Scientist
What quantum phenomena tell us about reality is still debated (see “What does quantum theory really tell us about the nature of reality?”). There are various interpretations. I think that Schrödinger’s waves are only a mathematical representation of the information that a physical system has about another. This reading of quantum phenomena is called “relational”, because it emphasises that we can only describe how systems affect one another, not how they are in isolation. In other interpretations, such as “QBism“, quantum states only code our own knowledge of a system.
In light of these ideas, it is clear to me that Schrödinger’s waves obscured, rather than clarified, the theory developed by Göttingen’s wizards and Dirac. It misled the community into viewing quantum theory as a revelation about mysterious waves (or mysterious “quantum states”), instead of reading it in the straightforward Göttingen way: a theory of the probabilities of the manifestations of a system to any other system.
I think what quantum phenomena tell us is that the world is genuinely probabilistic and granular at the scale fixed by the Planck constant, and that reality is constituted by manifestations of physical systems to one another. This is captured in the words of Niels Bohr: “In quantum physics the interaction with the measuring apparatus is an inseparable part of the phenomenon. The unambiguous description of a quantum phenomenon is required in principle to include a description of all the relevant aspects of the experimental arrangement.”
Little about this idea needs to be changed, a century later: all that is required is to replace “the measuring apparatus” with “any other physical system” the object is interacting with. The world is the ensemble of ways that physical systems affect one another. This is what quantum physics seems to me to be about. That is quantum mechanics as Max Born, the scientist who named it, had conceived it.
I like Rovelli's perspective. It downplays the view of some physicists that the measurement or observation of some quantum phenomenon by a conscious being is what converts the probabilistic "could be this, could be that" quantum realm into the certain "it is this, not that" nature of everyday reality.
When mangled by New Age types who have a very shallow knowledge of quantum mechanics, that view becomes "we create our own reality" -- which isn't at all what quantum theory says. As Rovelli noted, it is likely that any physical system that a quantum object is interacting with results in the so-called collapse of the wave function.
That collapse manifests in a shift from a probability that a quantum phenomenon will take on some value, to a certainty that it has that value. This is why quantum computing is so difficult. In order to preserve the quantum nature of computing, which is highly powerful in some unusual ways, the workings of a quantum computer have to be isolated from the outside world or the quantum phenomena go away.
A curious thing about quantum mechanics is that while the mathematics are well known and highly effective, the meaning behind all that math is hotly debated. Some physicists take the "shut up and calculate" attitude in which the search for meaning is downplayed in favor of practical applications.
Daniel Cossins takes on the question of meaning in his New Scientist article. It's fairly long, so here's a PDF file. Since I like the notion of objective collapse, which seems to be Rovelli's position, I'll share some of what Cossins says about this subject.
Download What does quantum theory really tell us about the nature of reality? | New Scientist
But there is also objective collapse, a suite of models proposing that quantum mechanics is incomplete and that something else has to be tacked onto the Schrödinger equation to explain wave function collapse. “The [key] difference with the standard interpretation is that the collapse of the wave function is not something that occurs by magic at the end of the measurement process,” says Angelo Bassi, a theorist at the University of Trieste in Italy. “It’s just part of the dynamics.”
Collapse models have garnered more attention than most in recent years, partly because they offer a plausible explanation of how classical reality emerges without reference to human observers. We don’t see large objects like picture frames and paint brushes in a superposition, it says, because the collapse process works in such a way that the more interacting particles there are, the more readily collapse occurs.
What triggers this continuous collapsing isn’t entirely clear. Some models don’t say, others posit that it is just gravity. But Bassi says there may ultimately be no good answer – it may just be a property of nature. “That’s why I like collapse models, because they try to open the door to a new world which we don’t understand at the moment – something beyond quantum mechanics that we are not grasping.”
What really sets collapse models apart, however, is that they can be put to the test. Uniquely, they make explicit observational predictions that differ from what standard quantum mechanics predicts. The idea is that this constant process of spontaneous collapse should cause quantum objects such as particles to constantly jiggle around, which, in turn, means they emit excess energy that should be detectable, even if the signal is extremely faint.
The bottom line is that physicists don't agree about the meaning of quantum theory -- what it tells us about the nature of reality. This is the way of science: disagreement, debate, theorizing, experimentation, uncertainty, open doors, blind alleys, progress, setbacks.
Anyone who believes that they know what the meaning of quantum theory is doesn't really understand quantum theory. I speak from experience here. I read a lot of books about quantum mechanics when I was researching my first book, God's Whisper, Creation's Thunder, which is about the relation of modern physics and ancient mysticism.
I was quite accurate in discussing the basics of quantum theory. Where I went astray was trying to make the meaning of quantum theory fit with the teachings of the religious group I belonged to at the time, Radha Soami Satsang Beas. In other words, I embraced a view of quantum physics that matched my personal philosophical view of reality rather than taking a more objective and dispassionate perspective.
Live and learn. That's a good scientific motto. Also a good motto for everyone else, certainly including me.
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