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About preskill

I am a theoretical physicist at Caltech, and the Director of the Institute for Quantum Information and Matter. Follow me on Twitter @preskill.

Universal thread

How many miles per gallon?

Thoughts while watching the Olympics …

My car gets about 30 miles per gallon of gasoline. Miles per gallon has the dimensions of inverse length squared, and the reciprocal of 30 miles per gallon is roughly the area of a circle whose diameter is 0.3 mm, or about 1/100 of an inch.

That means that when I drive my car, the fuel I consume has the same volume as a thin thread stretched along the road over the distance I travel, with a thickness just a few times the width of a human hair.*

That skinny little thread of gasoline is enough to keep my car going! Thinking about it reinforces one’s appreciation for the internal combustion engine.
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Two-trick pony

Steve Flammia wrote a flattering post on The Quantum Pontiff about a game we used to play, in which Steve would ask a question and I would have just a minute or two to prepare a 20 minute mini-lecture answering the question. Steve reports that “these were not easy questions.” But actually most of them were.

Steve gives an example: “Why do neutrinos have a small but nonzero mass?”
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Alesha

An excerpt from my notes (including a misspelling of “repetition”) taken at Alexei Kitaev’s seminar during his first visit to Caltech in 1997. That was a very exciting day.

In 1997, I had some disposable funding as part of a quantum computing project, and decided to seize the opportunity to bring an interesting visitor to Caltech. But whom to invite? Chris Fuchs, then a postdoc at Caltech who seemed to know everybody working on quantum computing, reported that Richard Jozsa, while attending a conference in Japan, had met a remarkable Russian from the Landau Institute named Alexei Kitaev.
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Sad about Sally

Sally Ride

I’m really sad about the death of Sally Ride. Aside from all her other achievements, she devoted herself to getting kids, especially girls, excited about math, science and technology. She was 61.

On April 28, 1994 (yes, I really know the date … I keep records), Sally spoke at the Caltech physics colloquium about the future of the US Space Program, and in particular about the case for building the International Space Station. The talk was remarkably frank about how ill suited the Space Station would be for scientific research.

My daughter Carina was 8, and I took her to Caltech after school to meet Sally. Carina brought her copy of Sally’s book To Space and Back, which Sally signed, “To Carina, Reach for the Stars! – Sally Ride”
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Supremacy Now?

Martin Zwierlein

In May 1994, Artur Ekert visited Caltech to give a seminar about quantum cryptography. Near the end of the talk, Ekert revealed an exciting new development — just weeks earlier, Peter Shor had announced the discovery of an efficient quantum algorithm for finding the prime factors of large composite integers, a problem for which no efficient classical algorithm is known.

Perhaps I’ve embellished the memory over time, but I recall being awestruck by this news. I spent the next month at the Isaac Newton Institute attending a workshop about quantum black holes, and though it was a very good workshop and I had some great discussions, I spent most of my time there secretly trying to understand Shor’s paper, which Ekert had emailed to me. This took some effort, because I knew little about algorithms or computational complexity at that time (even less than I know now), but by the end of the workshop I felt I understood the ideas behind Shor’s algorithm pretty well. I did not yet realize that I was in the midst of a career transition from particle physics to quantum information science.
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Closure

Frank Wilczek

There are two kinds of particle physicists: those who wanted the Higgs boson to be discovered, and those who wanted the Higgs boson not to be discovered.

At a conference last fall, I sat at the same dinner table with Frank Wilczek. Inevitably, the conversation came around to the prospects for discovering the Higgs boson in 2012. “It would be much more exciting if the Higgs isn’t found,” I insisted. Frank did not claim to disagree, but was adamant: “I want closure.”*

In the late fall of 1974, I had applied to graduate school, but did not yet know where I would be accepted. Roberta (then my fiance, now my wife) and I were in Boston for the day, so we decided to stop by Harvard to look around. We noticed Steve Weinberg was in his office, and though I had never met Weinberg and had no appointment, we barged in. I introduced Roberta and announced I was interested in coming to Harvard the following year.
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More to come

John Wheeler. Photo by the New York Times/Redux.

As a sophomore at Princeton I took a class called Honors Physics from a man named Johnny Wheeler. He wore a suit and tie to class, loved explosions, and created vivid art in real time with colored chalk. Implausibly old, he had worked on nuclear fission with Niels Bohr. He was 61.

The lectures were long on inspiration and short on information about how to do the homework. I was in awe of Wheeler. Some students thought he sucked.

One day I arrived late to find Wheeler conducting a poll. We were voting on the future of science: is there “more to come” or “less to come”? I don’t remember the count, but “more to come” won handily. Wheeler was pleased.

Later, at a student-faculty lunch, Wheeler seemed troubled. He had been asked to explain the essence of quantum mechanics in five words or less, and was stumped. Frank Calaprice, a nuclear physicist within earshot, interjected helpfully, “What we expect to measure?” I was silent.

The question was absurd. It was fascinating. I still think about it. I can’t answer it.

This year I taught a course on quantum statistical physics to Caltech sophomores. I wore khakis and always used the white chalk. Though I’m 59, few students seemed awed. Some thought I sucked. Maybe I did sometimes.

Johnny Wheeler never blogged. If he had, some readers would have been awed. Some would have thought he sucked.

But Johnny would not have reminisced about a class he took 40 years ago. He knew there was more to come.

Welcome to Quantum Frontiers! We hope that the posts to come will be long on inspiration, even if short on information about how to do your homework. Enjoy!