Posted on July 23, 2004

Soapbox Seminar #3

Two Guys name of Jackson and Ryan

The inside story of how the Jackson-Ryan Hypothesis came to be.

It was summer of 1973, sixty-five years to the day, give or take, from the Tunguska Event itself, that two young American physicists from the University of Texas at Austin, my old alma mater, sent the British science journal Nature what had to be one of the crazier ideas ever submitted to that respectable publication (which is saying a bunch!). Because A. A. Jackson IV and Michael P. Ryan, Jr. came right out and asked the question—

“Was the Tungus Event due to a Black Hole?”

Meaning what? That it was a black hole went and hit the earth back in 1908? But how could the earth have survived that kind of a collision? Wouldn’t it have got itself torn to pieces and gobbled up?

Nope, you’re thinking of the big black holes, twice the mass of the sun and then some. Jackson and Ryan had something a lot smaller and more manageable in mind.

Seems that, a couple years earlier, in 1971, Stephen Hawking had come up with the notion that real little black holes — only a trillion tons or so — could have been created in the Big Bang (we’ll see how later).

— So now, we’ve got one of these “primordial black holes” (PBHs) plowing into the earth?

Kind of makes you wonder who thinks this stuff up, doesn’t it? Well, meet A. A. Jackson IV, Ph.D. — Al, to his friends. Al comes from a long line of Dallas Jacksons. The family goes way back in those parts, so far back that the place where the late billionaire H. L. Hunt built his mansion was named, you guessed it, Jackson Point.

Al’s an astrophysicist by trade. He taught all over the place before returning home to Texas. There he’s working for NASA, training space-shuttle pilots and helping come up with the Nemesis hypothesis for the extinction of the dinosaurs. He’s a Fellow of the Lunar and Planetary Institute. And he’s dreamed up some pretty good science fiction in his time, too (more on that here).

In fact, that’s what his detractors say he was doing the day he came to Mike Ryan in the spring of 1973 with a crazy idea ...

The way Al tells it, it all started thirteen years earlier, at the 1960 World Science Fiction Convention in Pittsburgh. It was there that Al, just a college freshman, ran into a living legend: science popularizer Willy Ley.

It had been Willy’s Conquest of Space book that had gotten Al interested in science in the first place. And now, here’s Al, sitting on the banquet-room floor, hanging out with one of his boyhood heroes, in the middle of the WorldCon costume ball (which back then was not much of a ball, and most people weren’t wearing costumes ). And Willy’s talking about an article he’s working on for Galaxy science fiction magazine, an article about someplace Al’d never heard of — Tunguska.

Willy proceeded to tell Al all about the Tunguska Event, about Kulik’s failure to find a crater, most of all about Aleksandr Kazantsev’s loony idea that the explosion must have been caused by an alien spaceship whose reactor went critical. And about how the whole Tunguska-Crashed-Spaceship thing had become as big in Soviet UFO circles as Roswell was becoming here.

Needless to say, it made an impression. Al never forgot Willy Ley’s Tunguska stories, and thirteen years later he shared them with his friend Mike Ryan, a postdoc at the University of Texas where Al was a grad student. About that same time, Al came across Stephen Hawking’s first paper on primordial black holes, and, with Tunguska still on his mind, he casually mentioned to Mike “what about the Tunguska Event being due to a PBH”?

Mike said maybe they should do some calculations. It was pretty easy to see how much energy would be deposited in a shock wave due to a gravitating body moving through the atmosphere faster than the speed of sound. Sure enough, about an asteroid’s worth of matter in a molecule-sized package would do the trick. Weighing in at a quadrillion tons or so, the PBH would produce all the observed Tunguska effects — bright blue “tube,” massive explosion, total devastation — through gravitational interactions alone.

Figuring what would happen after that was trickier. Once the thing hit, it should keep on going. With its tiny diameter and enormous mass, the PBH would slice through solid rock like it wasn’t there. It should’ve plowed straight through the earth and come rocketing up out the other side and gone sailing off into outer space again.

But not before producing the same sorts of effects at the exit as at the original point of impact. In fact, as Al and Mike wrote, “This exit provides a check for the whole hypothesis” — all you had to do was look for a second set of shockwaves and earthquakes shortly after the first.

But look where? Where would the thing come out?

The way Mike tells it, “Al and I used the best azimuth we could find, calculated the distance through the Earth for the angle of entry, then used the sophisticated method of stretching a string ... on a globe someone had in their office.” Sort of like a low-budget remake of that scene in Close Encounters of the Third Kind, where the NASA guys roll this big globe down the hall and use it to find the latitude and longitude of Devil’s Tower, Wyoming. But it worked, gave them the answer they were looking for: The exit event would have been out in the Atlantic, northwest of the Azores. To test the theory, just check the shipping records.

By this time, spring semester was over, and Mike was packing up to spend a summer at Oxford. Before he left, he and Al talked about the Tunguska idea a couple more times, and Mike suggested Al write it up.

By June of 1973 Al had done just that: sat down and worked out the calculations and sent them off in a letter to Mike. Mike spruced the paper up and sent it along to Nature just to see what would happen. Next thing Al knew he was getting phone calls from Time magazine — he hadn’t even known the paper was going to be published.

So, happy ending, sort of. And, to cap it off — No, let’s let Al tell that one in his own words:

[Stephen] Hawking came to U of T in the fall of 1974 for a visit before the Texas Relativistic Astrophysics Conference of that year. At that conference I walked up and introduced myself to Hawking. Alas, this was at the time when he needed his graduate student assistant to “translate” for him, before he had his computer [speech synthesizer]. The student had gone to the bathroom. [Hawking] seemed to recognize my name, motioned me down and said something to me.

I didn’t understand a word. He obviously knew of the paper, but I don’t know if he said “that was an interesting paper” or “what a piece of crap!” To this day I have no idea what he said! (My own guess is it was positive, since he loves crazy stuff!)

But, if Al’s crowning moment with Stephen Hawking ended up kind of ambiguous, the reaction of the physics community at large would be anything but. And “what a piece of crap!” would be the least of it!

[Notes and Further Reading]

Stephen W. Hawking, “Gravitational Collapsed Objects of Very Low Mass,” Monthly Notices, Royal Astronomical Society, vol. 152 (1971), pp. 75-78

Albert A. Jackson IV and Michael P. Ryan, Jr., “Was the Tungus Event due to a Black Hole?” Nature, vol. 245, September 14, 1973, pp. 88-89.

Special thanks to Al Jackson and Mike Ryan for sharing their personal reminiscences of how their Tunguska paper came to be.

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