Late in the summer of 1971 a symposium on applied and laser physics was held in Esfahan, Iran. Among the physicists and engineers who attended the meeting were two Nobel laureates, Charles Townes and Alexandr Prokhorov, and at least three future laureates, Nicolaas Bloembergen, John Hall, and Arthur Schawlow.

That a major international science meeting was held in Iran might seem odd at first. But the Iranian revolution, which toppled Shah Mohammad Reza Pahlavi and precipitated Iran’s diplomatic isolation, was eight years in the future. From what I can tell, Esfahan is a fine place to hold a meeting. In late summer, the air is warm and dry. The ancient city is full of centuries-old Islamic architecture.

History of a different kind was recorded in Physics Today‘s issue of March 1972. On page 23, you’ll find the transcript of a panel discussion that took place at the Esfahan meeting. Here’s a snippet from the introduction.

The symposium was held on the campus of Esfahan University in Esfahan, the second largest city of Iran, under the auspices of Arya-Mehr University of Technology and with the support and cooperation of Esfahan University and the Massachusetts Institute of Technology. Ali Javan (MIT) was director of the symposium, which was sponsored by the International Union of Pure and Applied Physics.

The panel discussion reported here was moderated by Arthur Schawlow of Stanford University. In his introduction to the discussion, Schawlow invited each of the eight panelists to speak for a few minutes on some aspect of lasers or laser applications, scientific or otherwise. He particularly requested them to talk about the future and to be “as wild as possible!”

You can read the article yourself and form your own opinions about the panelists’ remarks and predictions. Most of the panelists looked forward to extending the reach of lasers into new parameter regimes, such as shorter, more powerful pulses and new wavebands. The goal of making an x-ray laser was notably popular.

I was struck by the remarks of Ray Kidder of Lawrence Livermore National Laboratory. Kidder wrote about an application that he thought was exceedingly important yet perhaps was the farthest-off: “The production of useful power from thermonuclear fusion.”

Kidder was one of several Livermore physicists who developed the concept of using powerful lasers to initiate nuclear fusion in pellets made of deuterium and tritium. In September 1972 his colleagues John Nuckolls, Lowell Wood, Albert Thiessen, and George Zimmerman published a Nature paper outlining the idea and Livermore’s National Ignition Facility was built to realize it. Later this month, if all goes to plan, NIF’s 192 lasers will zap a DT pellet in an attempt to free more energy in nuclear fusion than was imparted by the laser beams.

Having urged his fellow panelists to be wild, Schawlow was not especially ambitious in his speculations, unlike Kidder or Boris Stoicheff of the University of Toronto, who thought that lasers and masers could be used to find space aliens.

Schawlow did recognize, however, that an efficient, visible laser would be needed for everyday uses, “like cutting metals, communications, photography and, if the cost was low, perhaps even typewriter erasers!” He guessed that a high-density gas, rather than a liquid, would provide the active medium.

Evidently, Schawlow hadn’t heard that Zhores Alferov and his colleagues at the Ioffe Institute in Moscow had succeeded in 1970 in making a laser diode that works continuously and efficiently at room temperature. But given the myriad uses of laser diodes—among them barcode readers, laser printers, and DVD players—Schawlow deserves credit for anticipating lasers’ spread into our everyday lives.

Charles Day

I joined Physics Today‘s editorial staff in June 1997. Back then, one of the first adjustments I had to make was to edit and write articles for all kinds of physicists, not just for the astronomical community I used to belong to.

As you can imagine, part of the adjustment entailed watching out for specialist jargon. Astronomers know what BL Lac objects and P Cygni profile are, but most other physicists don’t. Biophysicists, geophysicists, and other groups of physicists have their own jargon. My fellow editors and I strive to explain or eliminate it.

Jargon is usually easy to spot—especially if it’s unfamiliar to the editor. But there’s another verbal barrier to smooth communication among physicists: the specialized usage of seemingly nonjargon words and phrases.

I’m not referring to the particle physicists’ flavor, charm, or strangeness, which are almost never misleading in context. Nor am I referring to words like stress and strain, which have precise and distinct meanings in physics and engineering, even though the two words are synonyms in everyday parlance.

No, the words I find treacherously misleading are more subtle. In accelerator physics, “luminosity” means what you might expect: the number of particles per unit area per unit time—except when the particle physicists implicitly integrate over time and use the term as a measure of accumulated events. In its renewed quest to measure the mass of the Higgs boson, Fermilab’s Tevatron isn’t really becoming more luminous; it’s running for longer.

Another tricky usage is astronomers’ “hot gas.” Stellar coronae, galactic winds, and supernova remnants—to name just three examples—contain hot gas. Fine. But the gas in those objects is nearly always ionized and is more properly called plasma.

Does it matter whether you say the Sun’s corona is made up of hot gas or plasma? Yes. Because plasma particles are charged, the physics is far more complex that it is for a collection of neutral gas particles. Just how the Sun’s corona is heated to temperatures far higher than the chromosphere beneath it remains a mystery—despite decades of detailed observations. To refer to another star’s corona as “hot gas” is to brush that complexity, which all stellar coronae more or less manifest, under the metaphorical carpet of self-deception.

That said, most astrophysical plasmas are neutral overall. Some calculations, such as James Jeans’s 1902 estimate of how massive a cloud must be before it collapses under its own gravity, work just as well for neutral gas as they do for plasma.

Still, I think it’s wise to refer to hot astronomical gas as plasma, if only as a reminder of the complexity that might be lurking inside. And if you’d like more than a flavor of the challenging complexity of astrophysical plasmas, I recommend taking a look at the recently published report of a workshop held in January in Princeton, New Jersey.

Incidentally, the report is what gave me the idea for this post. Thanks, Hantao!

Charles Day