[Marxism] What Does Quantum Physics Actually Tell Us About the World?

Louis Proyect lnp3 at panix.com
Sun May 13 11:41:04 MDT 2018


NY Times, May 8, 2018
What Does Quantum Physics Actually Tell Us About the World?
By James Gleick

WHAT IS REAL?
The Unfinished Quest for the Meaning of Quantum Physics
By Adam Becker
370 pp. Basic Books. $32.

Are atoms real? Of course they are. Everybody believes in atoms, even 
people who don’t believe in evolution or climate change. If we didn’t 
have atoms, how could we have atomic bombs? But you can’t see an atom 
directly. And even though atoms were first conceived and named by 
ancient Greeks, it was not until the last century that they achieved the 
status of actual physical entities — real as apples, real as the moon.

The first proof of atoms came from 26-year-old Albert Einstein in 1905, 
the same year he proposed his theory of special relativity. Before that, 
the atom served as an increasingly useful hypothetical construct. At the 
same time, Einstein defined a new entity: a particle of light, the 
“light quantum,” now called the photon. Until then, everyone considered 
light to be a kind of wave. It didn’t bother Einstein that no one could 
observe this new thing. “It is the theory which decides what we can 
observe,” he said.

Which brings us to quantum theory. The physics of atoms and their 
ever-smaller constituents and cousins is, as Adam Becker reminds us more 
than once in his new book, “What Is Real?,” “the most successful theory 
in all of science.” Its predictions are stunningly accurate, and its 
power to grasp the unseen ultramicroscopic world has brought us modern 
marvels. But there is a problem: Quantum theory is, in a profound way, 
weird. It defies our common-sense intuition about what things are and 
what they can do.

“Figuring out what quantum physics is saying about the world has been 
hard,” Becker says, and this understatement motivates his book, a 
thorough, illuminating exploration of the most consequential controversy 
raging in modern science.

The debate over the nature of reality has been growing in intensity for 
more than a half-century; it generates conferences and symposiums and 
enough argumentation to fill entire journals. Before he died, Richard 
Feynman, who understood quantum theory as well as anyone, said, “I still 
get nervous with it...I cannot define the real problem, therefore I 
suspect there’s no real problem, but I’m not sure there’s no real 
problem.” The problem is not with using the theory — making 
calculations, applying it to engineering tasks — but in understanding 
what it means. What does it tell us about the world?

 From one point of view, quantum physics is just a set of formalisms, a 
useful tool kit. Want to make better lasers or transistors or television 
sets? The Schrödinger equation is your friend. The trouble starts only 
when you step back and ask whether the entities implied by the equation 
can really exist. Then you encounter problems that can be described in 
several familiar ways:

Wave-particle duality. Everything there is — all matter and energy, all 
known forces — behaves sometimes like waves, smooth and continuous, and 
sometimes like particles, rat-a-tat-tat. Electricity flows through 
wires, like a fluid, or flies through a vacuum as a volley of individual 
electrons. Can it be both things at once?

The uncertainty principle. Werner Heisenberg famously discovered that 
when you measure the position (let’s say) of an electron as precisely as 
you can, you find yourself more and more in the dark about its momentum. 
And vice versa. You can pin down one or the other but not both.

The measurement problem. Most of quantum mechanics deals with 
probabilities rather than certainties. A particle has a probability of 
appearing in a certain place. An unstable atom has a probability of 
decaying at a certain instant. But when a physicist goes into the 
laboratory and performs an experiment, there is a definite outcome. The 
act of measurement — observation, by someone or something — becomes an 
inextricable part of the theory.

The strange implication is that the reality of the quantum world remains 
amorphous or indefinite until scientists start measuring. Schrödinger’s 
cat, as you may have heard, is in a terrifying limbo, neither alive nor 
dead, until someone opens the box to look. Indeed, Heisenberg said that 
quantum particles “are not as real; they form a world of potentialities 
or possibilities rather than one of things or facts.”

This is disturbing to philosophers as well as physicists. It led 
Einstein to say in 1952, “The theory reminds me a little of the system 
of delusions of an exceedingly intelligent paranoiac.”

So quantum physics — quite unlike any other realm of science — has 
acquired its own metaphysics, a shadow discipline tagging along like the 
tail of a comet. You can think of it as an “ideological superstructure” 
(Heisenberg’s phrase). This field is called quantum foundations, which 
is inadvertently ironic, because the point is that precisely where you 
would expect foundations you instead find quicksand.

Competing approaches to quantum foundations are called 
“interpretations,” and nowadays there are many. The first and still 
possibly foremost of these is the so-called Copenhagen interpretation. 
“Copenhagen” is shorthand for Niels Bohr, whose famous institute there 
served as unofficial world headquarters for quantum theory beginning in 
the 1920s. In a way, the Copenhagen is an anti-interpretation. “It is 
wrong to think that the task of physics is to find out how nature is,” 
Bohr said. “Physics concerns what we can say about nature.”

Nothing is definite in Bohr’s quantum world until someone observes it. 
Physics can help us order experience but should not be expected to 
provide a complete picture of reality. The popular four-word summary of 
the Copenhagen interpretation is: “Shut up and calculate!”

For much of the 20th century, when quantum physicists were making giant 
leaps in solid-state and high-energy physics, few of them bothered much 
about foundations. But the philosophical difficulties were always there, 
troubling those who cared to worry about them.

Becker sides with the worriers. He leads us through an impressive 
account of the rise of competing interpretations, grounding them in the 
human stories, which are naturally messy and full of contingencies. He 
makes a convincing case that it’s wrong to imagine the Copenhagen 
interpretation as a single official or even coherent statement. It is, 
he suggests, a “strange assemblage of claims.”

An American physicist, David Bohm, devised a radical alternative at 
midcentury, visualizing “pilot waves” that guide every particle, an 
attempt to eliminate the wave-particle duality. For a long time, he was 
mainly lambasted or ignored, but variants of the Bohmian interpretation 
have supporters today. Other interpretations rely on “hidden variables” 
to account for quantities presumed to exist behind the curtain. Perhaps 
the most popular lately — certainly the most talked about — is the 
“many-worlds interpretation”: Every quantum event is a fork in the road, 
and one way to escape the difficulties is to imagine, mathematically 
speaking, that each fork creates a new universe.

So in this view, Schrödinger’s cat is alive and well in one universe 
while in another she goes to her doom. And we, too, should imagine 
countless versions of ourselves. Everything that can happen does happen, 
in one universe or another. “The universe is constantly splitting into a 
stupendous number of branches,” said the theorist Bryce DeWitt, “every 
quantum transition taking place on every star, in every galaxy, in every 
remote corner of the universe is splitting our local world on earth into 
myriads of copies of itself.”

This is ridiculous, of course. “A heavy load of metaphysical baggage,” 
John Wheeler called it. How could we ever prove or disprove such a 
theory? But if you think the many-worlds idea is easily dismissed, 
plenty of physicists will beg to differ. They will tell you that it 
could explain, for example, why quantum computers (which admittedly 
don’t yet quite exist) could be so powerful: They would delegate the 
work to their alter egos in other universes.

Is any of this real? At the risk of spoiling its suspense, I will tell 
you that this book does not propose a definite answer to its title 
question. You weren’t counting on one, were you? The story is far from 
finished.

When scientists search for meaning in quantum physics, they may be 
straying into a no-man’s-land between philosophy and religion. But they 
can’t help themselves. They’re only human. “If you were to watch me by 
day, you would see me sitting at my desk solving Schrödinger’s 
equation...exactly like my colleagues,” says Sir Anthony Leggett, a 
Nobel Prize winner and pioneer in superfluidity. “But occasionally at 
night, when the full moon is bright, I do what in the physics community 
is the intellectual equivalent of turning into a werewolf: I question 
whether quantum mechanics is the complete and ultimate truth about the 
physical universe.”




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