We Don't Make the Rules: Professor Geoffrey Penington

Well, the numbers don’t lie. Patrick Hayden, Penington’s advisor at Stanford, is a pioneer in the field that combines physics, math, computer science, and information theory that is about to explode: Quantum Information Science (QIS). He uses black holes as illustrations of highly efficient quantum information processing. The way they scramble information shows how quantum computers might manage large-scale quantum data and the fundamental limits of this kind of computation. How can this be tested? “It’s unlikely that anyone is going to make a black hole,” Penington drily observes. 

If experimentalists can’t rig up a test, what to do? Penington may have the solution and, of course, it involves more math. Physicists can see what is happening at the edge of black holes but no one can look at what is going on inside them. Mathematicians can make a model, though, poke around inside it, and then read the results back into the original. This is good work, but like a lot of advanced math it gets very arcane very quickly. Here’s how Penington starts this modeling project off: “By studying the entanglement wedge of highly mixed states, we can understand the state dependence of the interior reconstructions. A crucial role is played by the existence of tiny, non-perturbative errors in entanglement wedge reconstruction.” 

This analysis is not just advancing our understanding of the composition of galaxies and the evolution of the universe, thus improving fundamental physics, but also providing potential methods for “accomplish[ing] otherwise impossible communication and computing tasks.” Penington and his colleagues are looking at the most out of the way phenomena using the most remarkable equations and magical spells and what they are finding may become incorporated in how you secure the financial data on your desktop or receive personalized medical treatments at the local clinic in the not-so-distant future. What we find over the horizon can improve how we spend our days at home. 

UC Berkeley’s position as a research university closely affiliated with the Berkeley National Lab (LBNL) means our faculty combine pioneering fundamental investigation with high quality teaching at an unmatched scale. How does Geoff Penington get this material across to aspiring scientists? With a wonder and enthusiasm that belies his buttoned-up British upbringing. Today’s quantum physicists don’t dismiss the vintage understanding of fundamental forces and particles; they look at Newtonian theory as “controlled approximations” or “somewhat simplified accounts” of what’s down there. We have measuring and sensing capabilities now that can catch more of the specifics. Penington points at the coffee table in his office for an illustration: in the quantum world you get a spooky result if you measure the width and then measure the length, because if you measure the length first, you’ll get different results. Worse than that, your results will vary according to certain probabilities such that sometimes the differences will appear and sometimes they won’t. Think of the Newtonian story as a courtroom artist’s sketch and the quantum version as eyewitness testimony from different bystanders. They both help you prosecute the case. 

It is important to Penington that the general interest reader does not take away from this a sense that investigators are somehow making this all up or imposing some arbitrary framework on a mushy disordered reality. Far from it – the testing that is available proves that Quantum Field Theory is accurate “out to something like 20 decimal places, so we are not making up these rules!” 

There is another apparent binary distinction that Prof. Penington also rejects: faith vs. doubt. Repeatedly in his career, Geoff has had an intuition, or he might say an instinct, about how a problem will conclude that turned out to be right when the plodding calculations were finally done. He’s not the kind of theorist that can talk in complete, ordered paragraphs but his gut tells him that we will likely find a grand unification of physical theories and when we do it will be natural, sensible, in accord with what precedes it, rather than some shattering breakthrough. His enthusiasm for the heavens shows when he counsels “Why limit your thinking to areas that experiments can check on? Explore every choice.” 

The PhD at Stanford with Patrick Hayden served as another kind of bridge to help Penington make the transition from the UK to the USA. As a “mild-mannered Canadian,” Hayden eased the jolt from British understatement to American hyperbole. Penington learned that there is a middle way between Oxbridge self-effacement and Silicon Valley braggadocio. Hayden’s mentoring was quietly effective, a less-is-more approach where he always contributed le mot juste at the right moment. Penington took this in for his own teaching style, with the warning that “less can be more, but you have to get the less right.” The Berkeley CTP is known both for its accomplishments and for the sense of community among the researchers. So Penington sees Berkeley as a step up in more ways than one. A great place to encourage exploration in his students and to continue pushing his own.