Professor Leonard Susskind cut his lecture short last night so we could all attend a presentation by Joachim Stohr about the birth of the X-Ray Laser. Susskind was not entirely thrilled about going, but his position at Stanford comes with certain responsibilities, and he had gotten in trouble before for failing to attend presentations by fellow faculty in the physics department. So off we went.
Joachim Stohr, Professor of Photon Sciences and Director of the world’s first x-ray laser, the Linac Coherent Light Source (LCLS), gave an excellent presentation aimed at the layperson, explaining the nature of light, how it consists of photons that behave like particles or waves — depending on how you study them — and how photons come in a variety of wavelengths. The shorter the wavelength, the higher the frequency and overall energy.
While scientists have found ways to align and compress low-energy photons into coherent laser beams, attempts to do the same with very high energy photons — x-rays — had met with failure. In fact, many felt it impossible. But researchers at Stanford, using a good portion of SLAC, figured out a way to jostle x-rays repeatedly — akin to jostling passengers on a Tokyo bus — coaxing them into a compacted alignment. The result? An x-ray laser.
An x-ray laser is much different than an x-ray machine. An x-ray machine is like a scattergun; it bombards an object with random x-rays, and from the scattering one can deduce the shape of large objects. An x-ray laser — because the beam is so compact and coherent — can define very small objects, even down to the atomic scale, and with astonishing precision. For comparison, an x-ray laser can give a trillion times the definition of photos taken with top-of-the-line high-speed/bright-flash cameras used to freeze the beating of hummingbird wings. What can one do with an x-ray laser? Study the knitty-gritty details of matter. Two examples. Water is a mystery. We know it is composed of H2O, but nobody understands the mechanics underlying its behavior. Just how do the bonds shift about, and how are electrons exchanged, as water “flows?” How does it all unfold? Another example is photosynthesis. How exactly does it happen at the particle level? As Joachim explained it, by zapping samples of water, or chlorophil, with an x-ray laser and observing the resultant scattering, one could capture a movie of what is going on.
At the end of his presentation, Joachim Stohr took questions, and before very long Professor Susskind’s hand shot into the air. “Forgive me for introducing a note of skepticism into all of this,” he said, “but how can you possibly create a movie of activities at the atomic level? How do you account for quantum effects?” Joachim responded haltingly that it wasn’t necessary to take those into account, and that much like x-ray diffraction one could get a picture of what was happening. “So we can ignore quantum effects,” Joachim concluded. Susskind retorted that you CAN’T ignore quantum effects, that they ARE the reality at that level. Joachim may not have heard him, or if he did, he chose to move things along. He called on someone else and the subject was dropped.
Suddenly Susskind was up out of his seat and squeezing past people in his aisle, shaking his head in disgust. At any moment I expected him to turn and point a glary finger at Joachim, shouting, “Release the quantum!” But he didn’t. And soon he was out the door.
Who was right? I suspect both were. To communicate with nonscientists, Joachim had chosen to use the concept of a movie. He talked as if one could “film” the ongoing activities at the atomic level. That just isn’t possible due to quantum effects. What I believe one could do — and what I think he meant — is that one can capture, in great detail, an instant in a reaction, using an x-ray laser burst. By performing this experiment over and over again, countless times, one could — statistically — glean a process at the atomic level. Still, this amounts to creating a stack of random photos and afterwards trying to arrange them into chronological order — which strikes me as daunting.
Susskind prides himself on communicating with non-scientists in ways that do not distort the reality. He also prides himself on thinking on his feet, being able to tackle any question at a moment’s notice. His lectures are marvelously fluid in this respect, incorporating whatever additional explanation becomes necessary based on student questions.
Joachim, on the other hand, meticulously prepared and presented his powerpoint slides, and though it was a great presentation, his skills at thinking on his feet, and addressing unanticipated questions, are clearly not on a par with Susskind’s.
The clash was unfortunate, but intriguing. I look forward to next Monday’s lecture when Susskind will no doubt give us his candid opinion of just what the x-ray laser is and is not capable of doing.
