Physics can be like a universal tool kit for solving mysteries. It doesn’t come with instructions, but if you figure out how to use it you’ll find that it comes equipped with everything you need to discover whether or not an ancient pyramid has hidden chambers, how to explain discrepancies in the JFK assassination footage, or find substantial evidence that a meteor impact killed the dinosaurs. And for those who don’t know how to use the tool kit, be sure you get a detective like Luis W. Alvarez.
As reported by Phil Schewe in this week’s Physics News Update (http://www.aip.org/pnu/2007/split/847-2.html), a paper by Charles G. Wohl, published in the November issue of the American Journal of Physics reflects admiringly on the career of a true physicist. Luis W. Alvarez won a Nobel prize in 1968 for his work in elementary particle physics, but his other work stands out for it’s application to classic mysteries.
The Pyramid Burial Chambers:
The two largest pyramids ever built are in Cairo, in honor of Cheops and his son Chephren. With over 13 acres of floor space hardly being used, it boggled archeologists why there weren’t more rooms in Chephren’s pyramid. It was highly hypothesized that there were hidden chambers in the pyramid, but no clear way to find them. Luis Alvarez knew that if you pass waves or particles through a dense substance (like X-rays through your body) you can gather information about the interior structure of that substance (the X-rays bounce off your bones but penetrate flesh). If there were chambers in the pyramids, sending particles or waves through them might reveal where. Alvarez realized that X-rays would be no good through the very dense rock. So instead of blasting particles up through the pyramid, he had the idea of letting the particles come from above.
Cosmic rays in our galaxy are responsible for a shower of relatively large particles called muons raining down on us constantly. Our bodies have adapted to the barrage so as to keep us from sprouting holes. Muons are strong, but they can be partially stopped by rock. In other words, fewer muons will make it through a wall of rock than started in. Alvarez’s team put a muon detector in the main room, in the center of the lowest part of the pyramid. If there was a hidden chamber in the pyramid, more muons would show up on the detector because they met less resistance: a gap in the rock, or chamber, would allow more of them to pass through. Somewhat sadly, Alvarez’s team found no sign of hidden chambers. From Wohl’s paper:
It was a disappointment to find no burial chambers and no mmarvelous treasures. But the use of “rays” provided by nature together with the new tool of spark chambers was ingenious. And the mystery was solved. People would say to Luie, “So you didn’t find any chambers.” “No,” Luie would reply, “We found that there are no chambers.”
The JFK Assassination Video Tapes:
The immediate wave of conspiracy theories in the murder of John F. Kennedy in 1963 were often based on one seemingly disturbing fact: video footage of Kennedy being shot showed his head bucking forward, in the direction of the bullet, and then back toward the shooter. Intuition told people that his head should only move in the direction of the bullet, and that it’s motion backward suggested a second shooter somewhere on the scene that day.
Having also explored the physics of photography (what hasn’t he studied?) but really only needing basic mechanics, Alvarez thought he could explain the puzzle in the video. If a bullet strikes an object and sticks to it perfectly, the motion of the combined object-bullet will only be in the initial direction of the bulle. The bullet’s momentum has to be conserved. But the energy of the bullet is changed into heat and damage to the object: so in the case of a human head, the bullet causes jets of blood and brain matter (pardon the gore) to also move in the direction of the bullet (away from the shooter). These jets also have momentum that must be conserved. So, the jets push the head back toward the shooter, causing a seemingly counterintuitive motion. It may seem hard to believe, but both mathematics and demonstrations (they used melons wrapped in filament tape) illustrated Alvarez’s point.
Alvarez did additional analysis of the film, but nothing to settle the conspiracy theories or bring us any closer to really understanding what happened that day. The paper emphasizes that even if a bullet from one direction were responsible for the motion of JFK’s head, it can’t actually tell us the number of shooters at the scene. Such mysteries may remain unsolved.
The Extinction of the Dinosaurs
This may truly have been Alvarez’s biggest achievement and one that set off a chain reaction of discoveries. Alvarez’s son, Walter, is a geologist. In the 1970’s Walter showed his father a slice of clay, a centimeter thick, in he middle of a tall wall of limestone in Italy. The clay was known as the KT boundary, marking the end of the Cretaceous period. The limestone below this line of clay is full of fossils, but the limestone above it is scarce. Geologists knew that whatever happened to put that layer of clay there, also caused a mass extinction and wiped out nearly half the species on earth, including the dinosaurs. What they didn’t know was why.
At this point, the paper notes that there were many, many wrong turns, dead ends, and unsuccessful attempts at solving this mystery. You’d expect as much for such a huge puzzle.
Alvarez knew that during Earth’s formation, heavy particles like iron, platinum, and iridium (to name a few) sunk through the molten layers of the newly forming planet and came to rest in its core. Thus there is very little of any of these elements in the Earth’s crust. But rocks in space haven’t gone through this process of separation, and carry with them a mixture of elements including these heavy metals. Meteorites burning up in our atmosphere leave a light but constant sprinkling of these heavy elements on the surface of the Earth. An increased level of one of these elements would imply that a larger than usual amount of rock from space had come to rest on the Earth’s surface. Alvarez focused on iridium. The amount of iridium in the soil is less than parts per billion, which means it is only detectable using techniques of nuclear chemistry. This would explain why geologists didn’t noticed what Alvarez and his son found.
The levels of iridium in the KT boundary clay were through the roof compared to the rock around it. In a very short period of time, a large amount of an element known to be present in meteorites was deposited on the Earth’s surface and a significant amount of clay was deposited before limestone could form. Most importantly, these deposits coincided with a mass extinction. The father and son raced to get samples from other parts of the world. If their theory was correct, the deposits should be everywhere on Earth, since the proposed impact would have to have spread around the world to do the kind of damage they were suggesting. And indeed, over a hundred sites showed the same results. Further analysis of the clay showed that other materials were present that supported the meteorite theory including soot (suggesting much of the vegetation burned) and microscopic diamonds (created from intense heat and pressure), among others.
The work done by Alvarez and his son of course led to further investigation into the theory that the mass extinction was caused by a meteorite impact, and after Alvarez’s death scientists found what they think is the crater left over from the impact.
For a more in-depth portrait of Luis Alvarez’s discoveries, see the paper by Charles G. Wohl, cited below.
Adventures in physics never fail to amaze me. Answers literally falling from the sky! Physicists like Luis Alvarez are truly geniuses for their combined discipline, ingenuity, and creativity, using the fantastic tools given to us by the natural world.
1. Wohl, Charles G. “Scientist as detective: Luis Alvarez and the pyramid burial chambers, the JFK assassination, and the end of the dinosaurs.” American Journal of Physics. 75 (11), November 2007.
