Margaret Wertheim is a science journalist and author of "The Bead Gates of Cyberspace: A History of Dante's Space to the Internet" and "Physics on the Edge".
"I think I can not say anyone understands quantum mechanics," Richard Feynman wrote in 1965, when he received the Nobel Prize for his work on quantum theory, and nearly 100 years after the discovery of the first quantum laws, physicists are still debating
Does quantum mechanics mean that there is no true reality at the subatomic level, does this mean that the universe is constantly splitting itself into billions of copies of itself? Explain to us that reality is inherently random Or that consciousness brings the world into being, or are there any deeper laws that produce quantum laws? Two great new books, one by Adam Becker and one by Philip Ball, both of them physicists, lure us deeply into the most persistent questions
At The core of quantum mechanics is the "wave particle" D ualism, a short form for the amazing fact that in studying nature on subatomic and atomic scales, the objects of our study sometimes act like waves and sometimes like particles, but not all at once. Niels Bohr, the Danish theorist, whose philosophical ideas about the quantum world still dominate physics, called this phenomenon "complementarity" – although what he meant by that term has since been disputed.
In our direct experience, we observe things that are acting waves or particles – think of waves whizzing across a pond against a baseball flying through the air. Particles are inherently localized, waves are naturally dispersed.
But light works in both modalities. In the famous double-slit experiment, light passing through two slits produces an interference pattern of light and dark bands, which can only be described using wave equations. Still, Albert Einstein showed in 1905 that light travels as particles called photons, each of which can knock an electron out of an atom like a miniature billiard ball.
And here's the eerie part: If we do the double-slit experiment and rotate Because the light is so low that only one photon ever passes the slits, we still get the interference pattern – which means that the particle itself bothers. Somehow the presence of waves manifests, although, as far as we can tell, nothing waves. Feynman said this experiment "has the heart of quantum mechanics"
This wave behavior goes across all phenomena on the quantum scale, so we can do the double-slit experiment with electrons or atoms, even molecules and still take the wave-controlled interference pattern. Atoms and molecules are quantum systems and, in addition to their particle sets, also wave descriptions. As in the concept of complementarity, there are two completely different but ultimately equivalent mathematical formulations of quantum phenomena – Erwin Schrödinger's wave equation and Werner Heisenberg's matrix mechanics, the latter highlighting particulate behavior.
How can we understand the wave motion? – what quantum particles show? And how does this quantum confusion result in the world of the human scale described by the classical laws of physics?
In answering these questions, Becker cites a historical approach that leads us through answers with Bohr, the de facto leader of a group of early quantum theorists, including Heisenberg (discoverer of the Uncertainty Principle), Max Born, and Pascual Jordan who together formulated the influential "Copenhagen Interpretation" – although strictly speaking, there is no unified view.
Despite their philosophical differences, Becker, Bohr, Heisenberg, and the rest of the Copenhagen group noted that "in the face of wave-particle duality, it was meaningless to talk about what really happened in the quantum world." Isolated Material particles are abstractions, their properties on quantum theory are definable and observable only through their interaction with other systems. "Heisenberg was equally blunt:" Elementary particles are not so real [as phenomena in daily life]: they shape a world of possibilities or possibilities and not of things or facts.
The idea that quantum waves can be understood as a set of possibilities was demonstrated by Born, who showed that the Schrödinger equation for a particle describes a set of probabilities for the values of their various properties, such as their position and their impulse Unlike baseball, which can always be said to be here or there, a quantum particle appears to be in many places at the same time until we measure it, in which case it manifests itself in a particular location. The number of places we can find follows a statistical pattern defined by the wave equation, but until we take a measurement, we have no idea where it will be Wave function "collapses."
Jordan interprets the collapse of the wave function as an observer "producing the results of the measurement In the 1930s, Eugene Wigner (a future Nobelist) took this a step further, pointing out that consciousness brings reality to life. To say the least, this has been controversial, though it has inspired countless books of popular science, science fiction, and New Age philosophy.
Using profound research, accompanied by charming anecdotes about the scientists, Becker outlines attempts to understand the wave-particle dualism, focusing on the work of three mid-century radicals: David Bohm, John Bell, and Hugh Everett. The latter is responsible for the much-debated "Many-World Interpretation," which states that every time a quantum reaction occurs, the universe splits into many, nearly identical copies, each of which provides one of the statistically available options.
Becker's intention is not to bring us to one of the newer interpretations; Rather, he hopes to convince us that the Copenhagen interpretation has over-influenced physics for historical reasons, including Bohr's oversimplicity.
Bohr was known to have found that there was no solution to the cognitive dissonance of wave-particle duality: "It's wrong to think that the job of physics is to find out what nature is," he explained , For the Copenhageners, we have to be satisfied with equations as calculation formulas and refrain from understanding the nature of reality.
Becker has none of this: "There is something real, somewhere in the world that somehow resembles the quantum." He insists. "We just do not know what that means, and it is the job of physics to find out."
Ball also wants to know that, and his gloriously clear text brings us to the edge of contemporary theorising on the foundations of quantum mechanics. "Beyond Weird" is easily the best book I've read on the subject. Currently available in the UK, it will be released in October in the United States.
One of Ball's achievements is to show how a bridge between the quantum and classical domains can be built by means of a decoherence process developed by a new generation of theoreticians including Dieter Zeh. As a particle crosses with the wider world, it gradually becomes quantum mechanically entangled with its environment. The wave feeling does not disappear; it continues to spread. So Ball says, "the classical world is what the quantum world becomes." For proponents of decoherence, the entire universe is quantum mechanical – only to the extent that we live is quantum effects too blurred.
Instead of asking why the quantum world is not like the macroscopic world, Ball turns the question upside down, claiming that we should not assume that human effects and logic reach microscopically.
Which brings us to another aspect of complementarity: the dualism between our mathematical representations of quantum phenomena and our lived experience. We know that quantum mathematics work – microchips, lasers and stunning new materials are proof of that – but the more sophisticated our equations are, the less they seem to literally and viscerally make sense. As our symbolic power increases, our perceptual insights on the real in the smallest realm become less and less valid, and we are pushed beyond the boundaries of natural language into a domain of abstract, seemingly bizarre formalisms. As Ball puts it: "It is not so much understanding or even intuition that quantum mechanics defies, but our sense of logic itself."
But why should atoms adapt to human norms? "We have absolutely no reason to expect it to be reality," writes Ball. By "reality" he means a well-defined world in which things have given properties. Instead of a universe of "Isness", Ball believes that quantum mechanics describes a world of "ifness" in which there is a logic of probability.
"Is there an Isness beyond the Ifness?" He finally asks. Possibly. If so, it will not be like the isness people are used to. Feynmans Echo: "I hope you can understand nature as it is – absurd."
What is it really?
The Unfinished Quest for the Significance of Quantum Physics
By Adam Becker
Basic. 370 pp $ 32
Why all you thought you knew about quantum physics is different
By Philip Ball
384 pages. $ 26