When I was starting my PhD studies at King's College London, I had the opportunity to meet the famous physicist John Bell. His work established that quantum mechanics — and the bizarre kind of reality it entails — happens to be the way the world is. My conversation with Bell says a lot about how the physics community at large deals with the strange predictions from quantum mechanics. It's mostly with a combination of forced indifference and fear.
Things have changed surprisingly little in the intervening three decades, even if nowadays a growing number of scientists and philosophers grapple with what Einstein called "spooky action-at-a-distance."
In my second year, after passing the dreaded qualifying exam, I had to pin down my research topic. My advisor, John G. Taylor, was interested in unified theories using supersymmetry. This was the latest fashion in the early 80s, after Michael Green, now at Cambridge University, and John Schwartz, from Caltech, had shown that string theory, when married to supersymmetry (the origin of the famous "superstrings" that we hear so much about nowadays), offered renewed hope for a "theory of everything."
The idea was to explore how effectively string models describing the four fundamental forces in 9 and 10 spatial dimensions could be reduced to the usual three dimensions in which we live. The topic was fun, but not exactly what I was looking for. I wanted to do something else. (I ended up doing cosmology in higher dimensional spaces, which was a lot of fun!)
When I found out that John Bell was speaking at a conference at the Rutherford Appleton Laboratory (RAL) near Oxford, I rushed to catch a train and meet him. Bell was then working at CERN, the lab where the Higgs boson was found last year. Despite his excellent work in accelerator physics, Bell was famous for another reason, a theorem that had revolutionized our understanding of quantum physics.
In a nutshell, his theorem said something like this: our naïve expectation of "locality," that every effect has a local cause, independent of what happens elsewhere, is wrong. Two or more particles — and even larger objects — can coexist in states where one affects the other without an exchange of information or a cause.
It is as if twin sisters went to two parties in different countries and their actions were connected. If one sister danced the twist, the other would invariably tango, and vice versa. The sisters would always seem to "know" what to do, even without communicating. It would be as if they were a single unit, not two different people.
Particles in this kind of state are called "entangled." What Bell found was that, for entangled states, the whole is not just larger than the parts; the parts don't even make sense! And the "connection" is independent of the distance between the two particles. Accidentally, quantum physics has discovered some kind of wholeness in Nature.
Starting with my earliest days as a physics undergraduate in Rio de Janeiro, Brazil, I've been fascinated by quantum mechanics. Why were Einstein and Bohr, two of the great giants of twentieth-century physics, so much at odds with what it meant? I wondered if I should switch research topics and work on this question.
In his talk at RAL, Bell spoke about his 1964 theorem and how recent experiments by John Clauser in the United States and Alain Aspect in France had confirmed that quantum mechanics violated the assumption of locality. Einstein's spooky action-at-a-distance was a ghost that, as I wrote here last week, seemed to be real. The weird thing was that the "influence" between the two particles seemed to act instantaneously; or, at least, faster than the speed of light.
"Dr. Bell, my name is Marcelo Gleiser and I'm working with John Taylor on supersymmetric theories."
"Good, excellent topic of research."
"Yes, but the fact is, I've been interested in the foundations of quantum physics since I was an undergraduate. I even wrote to David Bohm asking if he would like to supervise my thesis work. But he said he wasn't taking students any more." (Bohm was then at nearby Birkbeck College, also in London.) Bell's eyes twinkled ever so slightly when I mentioned Bohm.
"Well, I find your interests laudable and rare for someone your age. However, I strongly advise you not to do your thesis work on such topics."
"And why not?" I asked, already guessing the answer.
"You should work on something solid first, that the community endorses. Until you have a solid reputation as a physicist, no one will listen to what you have to say about the foundations of quantum mechanics. And even then, it's not a sure shot, believe me."
"I understand," I replied, trying to hide my obvious disappointment. "Maybe later on in my career."
"Yes, that's what I did, at any rate."
So ended my encounter with John Bell. Nowadays there is a proliferation of books on the interpretations of quantum mechanics, some good and some very bad. The good ones* tell — with larger or smaller doses of technical material — how there are two types of physicists.
The pragmatists side with Bohr and don't ask questions about what's going on, content with using the success of quantum mechanics to go on with their research. They imagine that non-locality only entails with specially prepared quantum systems, that it is washed away in the everyday world by environmental disturbances. That is to say, the world we see is well described by classical physics, there is a clear separation.
The other group (much smaller) doesn't accept things so quickly. They believe that there is more to be learned, as did Einstein and Schrödinger. They believe that to unveil the quantum mystery is to open a door to unknown aspects of reality and how we interact with it.
I am glad John Bell gave me the advice he did 30 years back. If not for his nudge, I might have threaded a very different professional path. Who knows where I'd be now? The quantum ghost, however, continues to tease me. Its weirdness has traveled with me across the years, even as my research has focused on other topics.
Maybe it's time to give life to this disquietude and see where it takes me. If I wait too long I may end up like some physicists I know, only thinking about this stuff in retirement. By then it may be too late to fully grapple with something so challenging.
*Here are some books on quantum mechanics that I recommend: David Kaiser's How the Hippies Saved Physics; David Albert's Quantum Mechanics and Experience; Bruce Rosenblum and Fred Kuttner's Quantum Enigma; Louise Gilder's The Age of Entanglement. An excellent new one is: Quantum Physics for Poets, by Christopher Hill and Leon Lederman.)