The Long, Tempestuous Relationship Between Physics and Philosophy
published during a waxing gibbous moon.

About a year ago, several high-profile physicists got together to publicly discuss what’s known as the Simulation Hypothesis—a philosophical idea that our entire universe might be little more than a virtual construction sitting on some advanced being’s hard drive.

Though it’s essentially the computer geek’s version of ‘What if everything we know is just a dream?,’ Moderator Neil deGrasse Tyson was clearly a fan of the hypothesis, giving it 50-50 odds of being right. Now, the cosmos is a strange place, and Tyson is a champion of its sublime and mysterious nature. But it was a little peculiar that the famous astrophysicist would engage in such wagering at all. Back in 2010, he suggested that the discoveries of physics in the 20th century—quantum mechanics and general relativity—were so far outside what a rational person could have imagined about the true nature of reality that they rendered armchair philosophizing completely obsolete.

Tyson is not the only scientist to snub his nose at philosophy. More vociferous attacks have come from the likes of cosmologist Stephen Hawking, who stated in his 2012 book that “philosophy is dead.” Physicist Lawrence Krauss also engaged in some high-profile philosophy-bashing that same year. It’s somewhat sad that otherwise intellectual people feel the need to put down an entire field of human inquiry, especially considering that such antipathy hasn’t always been so widespread. Albert Einstein believed philosophy an important part of his educational training, writing to a friend in 1944 that the “independence created by philosophical insight is—in my opinion—the mark of distinction between a mere artisan or specialist and a real seeker after truth.”

For much of the past 100 years, physics and philosophy have had the kind of relationship usually only seen in soap operas. The two fields, quite close at the beginning of the 20th century, spent a decade or more growing apart after World War II, only to find one another again, and then reverse course. In recent years—comments from eminent science advocates such as those above notwithstanding—many prominent physicists have once again begun to embrace philosophical thinking as an integral part of their work. Ideas such as the multiverse and the philosophical foundations of quantum mechanics are among the hottest topics in physics. History suggests that when physics needs it most, philosophy is always there to lend a hand.

For most of human history, there wasn’t really a distinction between physics and philosophy. Aristotle engaged in both philosophical pondering and physical model building without anyone thinking twice. Even after the Scientific Revolution, people like Isaac Newton and Robert Hooke were actively debating philosophical ideas such the nature of light (‘is it a particle or a wave?’) that had important physical implications. Such traditions continued into the 1920s and ‘30s, where textbooks and classroom problem sets routinely asked students to consider what the quantum revolution meant for humanity’s ability to obtain trustworthy knowledge about the world and the role language plays in shaping our understanding.

“Part of the expected training of a physicist, especially when encountering something new like quantum mechanics, was to approach it philosophically,” says physicist and historian of science David Kaiser of the Massachusetts Institute of Technology in Cambridge.

Among the most famous philosophical debates of the time was whether the statistical descriptions of quantum physics represented the true nature of reality or merely our limited human understanding of it. People like Einstein and Erwin Schrödinger stood on the latter side, arguing that talking about reality as essentially probabilistic led to contradictory and paradoxical results. Schrödinger’s famous cat-in-a-box thought experiment is not really an illustration of subatomic strangeness but an attempt to show that quantum mechanics is absurd if taken to its logical conclusion.

Long, Tempestuous Relationship

Real-size cat figure in the garden of Huttenstrasse 9, Zurich, where Erwin Schrödinger lived 1921 – 1926. Depending on the light conditions, the cat appears either alive or not. Credit: Koogid

One of quantum physic’s major architects, Neils Bohr, led the opposing camp, eventually creating what’s known as the Copenhagen Interpretation. This states that quantum particles literally do not have defined properties when they’re not being observed. The act of measurement collapses their wavefunction and forces them to take on specific values for characteristics such velocity or spin. “Asking about their position before that is like asking the marital status of the number five,” says philosopher of physics, David Albert, of Columbia University in New York City. “It just doesn’t make any sense.”

Though the Copenhagen Interpretation has been embraced by most working physicists ever since it’s never been a perfectly satisfactory way of dealing with the weirdness of quantum mechanics. “There’s this puzzle about the act of measurement and why it’s special,” says Albert. “Bohr wrote it down as a postulate, but on the face of it, it doesn’t make any sense. What exactly do you mean by measurement? It’s a vague English word that has no right to appear in a fundamental theory.”

Everything changed after World War II. One of the war’s many casualties was the role of philosophy in physics curricula. “Soon after, that material vanishes,” says Kaiser. “It’s not that the philosophical problems were solved—physicists still disagreed—but the philosophical material got sharply deemphasized.”

Long, Tempestuous Relationship

A 21 kiloton underwater nuclear weapons effects test, known as Operation CROSSROADS (Event Baker), conducted at Bikini Atoll (1946). Credit: U.S. Army Photographic Signal Corps

As Kaiser has shown, this happened largely due to the new demands placed on physics and the incredible growth it sustained in the post-war period. Following the GI bill, students poured into universities around the U.S., many of them attracted to learning about technologies such as radar and nuclear power that helped win the war. This was one of the first eras of Big Science; spending on fundamental physics research was 20 to 25 times greater in 1953 what it had been in 1938. When Sputnik launched and set off the Space Race, the enthusiasm skyrocketed—the number of physics PhDs granted per year in 1967 was triple what it had been in 1959.

Obviously, something had to give, and that something was philosophy. With classroom sizes bursting, there was little time to have the kind of intimate and protracted debates that previous generations of scientists had engaged in. At the time, it was more important that students “shut up and calculate” rather than worry about the philosophical underpinnings of what they were doing.

Eventually, though, the exponential rise of physics degrees proved to be unsustainable, peaking around 1970. Funding dried up and, soon, many graduates found themselves unemployed, drifting, and aimless. In his book, How the Hippies Saved PhysicsKaiser traces how a group of underemployed new graduates found their way to Berkeley, California and—inspired by the strange counter-culture ideas floating around at the time—generated a new flowering in physics and philosophy.

Long, Tempestuous Relationship

The “New Physicists” of Berkeley. From left to right, Jack Sarfatti, Saul-Paul Sirag, Nick Herbert, and Fred Alan Wolf, circa 1975. Credit: Fred Alan Wolf

The Berkeley group’s work centered on a then-overlooked 1964 paper by physicist John Stewart Bell that had returned to the heart of the Einstein-Bohr debates. Working with two co-authors, Boris Podolsky and Nathan Rosen, Einstein had attacked one quantum mechanics’ fundamental ideas, the Heisenberg Uncertainty Principle, which states that no one can simultaneously measure a particle’s position and velocity. Einstein, Podolsky, and Rosen’s criticism centered on a pair of subatomic particles that were entangled, meaning that anything happening to one particle affected the other, no matter how far apart they are.

 ‘What does it all mean?’

After separating the two particles, a researcher could accurately measure the position of one particle while, at the same time, another experiment accurately measures the speed of the companion particle. Knowing both with so much precision would violate Heisenberg’s principle. The only way around this would be for the particles to communicate information faster than the speed of light and lower the measurements’ accuracies—which violates Einstein’s theory of relativity. In his 1964 paper, Bell restated this paradox in a more mathematically rigorous way and, to simplify greatly, showed that certain experiments on entangled particles could distinguish between Bohr’s version of reality and Einstein’s.

Though the experiments were exceedingly difficult, the Berkeley crew took to testing Bell’s ideas, and this interest eventually led to the development of many contemporary cutting-edge technologies such as quantum teleportation, quantum cryptography, and quantum computing. “We know about these things because of this colorful and enthusiastic group in the Bay Area who were trying to say, ‘Bell’s theorem is important, entanglement is weird and cool, and let’s give it all we got,’” says Kaiser. “And I think it’s part of the pendulum swings of what counts as philosophical engagement with modern physics. These folks weren’t doing philosophy like Neils Bohr and Albert Einstein, but they were inspired by those kinds of big questions, like ‘What does it all mean?’ and ‘How could reality be like that?’”

Of course, nothing lasts forever. Scientists and certain philosophers clashed during the 1990s period sometimes known as the Science Wars, in which humanities professors were accused of using post-modernist theories to argue that scientific truths were little more than social constructs. Cultural critics often invoked historian of science Thomas Kuhn’s ideas of scientific paradigm change—in which revolutions radically reshape scientific understanding—to bolster their interpretations. This era reached its peak with the Sokal Affair, in which physicist Alan Sokal managed to sneak a nonsensical paper titled “Transgressing the Boundaries: Toward a Transformative Hermeneutics of Quantum Gravity” into a prestigious cultural studies journal, embarrassing the liberal arts folks and leaving the scientists with a feeling of smug superiority.

It’s possible that this most recent bad blood is what soured people like Krauss and Tyson on philosophy’s importance to modern physics. In Chuck Klosterman’s book, But What If We’re Wrong?, Tyson is quoted as rejecting Thomas Kuhn’s ideas in their entirety, and implying that no major overhauls in scientific understanding have occurred since the 1600s Copernican revolution—an assertion not really backed up by empirical evidence.

But by and large, the needle has moved in the other direction. Applying quantum mechanics to cosmological theories such as the Big Bang have forced physicists to grapple with the outcomes of their ideas—if the entire cosmos can be described as a wavefunction, exactly what kind of an observer is causing its collapse? The multiverse, a major topic in physics today, is seen as one potential way of reconciling this inconsistency.

“Brian Greene [a multiverse proponent] is very much in the business of talking to philosophers and collaborating with them,” says Albert. “Steven Weinberg, one of the most prominent living physicists, has come around to saying the measurement problem is a serious problem.”

Physicists such as Sean Carroll have admonished their colleagues for saying silly things about philosophy. Bell’s theories continue to be tested; Kaiser and his colleagues have used distant starlight to probe certain aspects of entanglement. And a recent cosmology paper argues for the non-existence of dark matter and dark energy using philosophical ideas.

“When physics is in a period where it can make progress without paying attention to its foundations, the fields tend to be farther apart,” says Albert. “But when it arrives at a point where it becomes clear that in order to make further progress it has to reflect again back on its foundations, the interaction with philosophy becomes much more fruitful.”