Limits of Physics
25 September 2009

Slobodan Perovic, one of our Postdoctoral Fellows this year, is going to give his talk in a few hours. Karen and I are standing in the door to his office, chatting. Then I notice on his computer screen that he is reading a paper by Patrick Grim. "You're reading a paper by Patrick Grim?! Did you know that..." I wanted to continue to tell him that Patrick had very recently been a Visiting Fellow and lived in the office next to Slobodan's. Before my speech could gain momentum, Slobodan said with telepathic prescience, "Yes, I know. It's amazing. He has the general theory of which my coming talk is a special case. It's really perfect!"

Then he told the story. Patrick had been passing through. He'd seen the abstract of Slobodan's talk posted. So he searched out Slobodan, found him in his office and announced to him "I have a paper for you!"

It was a great moment for me. These are the sorts of random, but immensely fruitful, connections we work so hard to see in the Center. Our Fellowship forms an extended community of scholars. Thinking together we can do much more than when we work alone. As I made my speech to Slobodan, I could see him thinking: "Here he goes again. Another speech. I hope he realizes I have a talk to give shortly."

It is the second morning of the G20 summit in Pittsburgh. We have weathered months of tales of impending disaster as the protesters and their angry hordes are predicted to sweep through the city, pillaging and destroying. In the event, it has been much quieter. I caught my bus downtown at the usual place and, since the streets were essentially deserted of traffic, arrived at the Center much faster than normally. At noon, the talk had a pretty good turn out. I guessed, most of us had the same experience.

Slobodan began by recalling for us the growing feeling among many critics that physics is suffering a decline. His first in a list of critics was Lee Smolin, who laments the impact of string theory. (This issue had been the topic of one of our workshops--Stringtime in Pittsburgh. Smolin had been present and made an impromptu speech from the floor.)

As the story unfolded, we heard of other skeptical worries and then passed through an anatomy of physics. We quickly arrived at what Slobodan felt was the culprit. There has been, he explained, a significant change in the way physics pursues experiments. In the early part of the century, in the glory days of the birth of quantum theory, the experimental tradition was "diverse"--the now popular term that Slobodan co-opted. He sketched out in general terms how this was so.

At this point, I'll admit to feeling a little skeptical and I suspect that same skepticism might have been shared in the room. "Give us some concrete details to back up the generalities," I was thinking. And then he did.

The next screen was a huge matrix that carved up the experiments of the heroic era in many ways. Slobodan began pointing at different rows and columns, filling in detail after detail.

One point especially impressed me. In this era, the experimentalists were also theorists. So overwhelmingly they were actually testing out their own theories, not just the theories of a few of the great names. That gave the experimental tradition its great diversity.

Slobodan now turned to the modern era, taking the history of Fermilab in Chicago as his example. There, over the decades, the initially open lab gradually narrowed its range to the longer term execution of just a few experiments, each of which required years to complete.

This was the change that Slobodan urged mattered. In the modern era, we no longer have many experiments driven by many questions from many perspectives. We now have just a few theories--or even just one--that delivers the questions for experimental investigation. Perhaps the experiments have answered those questions. But that does not mean that they have answered all the questions.

Is that really enough to explain the decline in recent physics? It was clear that this would be an energetic discussion. In the short break before question time, Nick Rescher secured his place at the head of the queue. Slobodan had mentioned his work and he needed to make a speech to set matters right. Then, as time ran short, I needed to handle questions wholesale. "We have 8 people in the queue and 21 minutes, so that makes less that 3 minutes each!" The back and forth was urgent and exciting. Slobodan's answer to the last question was terminated at the immovable stopping time of 1:30 pm by the ceremony of the presentation of the umbrella.

John D. Norton