Sometimes, being an expert in one scientific field does not translate to another.

The ability to design a nuclear  reactor doesn’t make you qualified to dish out health advice… unless that  advice is to avoid eating uranium. But if you’re particularly  clever, you might find yourself making headlines for discoveries  in multiple scientific fields.

And today, we’re going to  talk about one such scientist: a particle physicist named Luis Alvarez, who investigated everything from atomic bombs, to Egyptian pyramids, to what  actually killed the dinosaurs. [♪INTRO] Luis Alvarez was born in  1911, which put him in a great position to contribute to the  newfangled field of particle physics. For example, that was the same  year that Ernest Rutherford proposed an updated concept of an atom, where most of its mass is concentrated  in a small, compact nucleus. But it was also two decades  before we knew that nuclei didn’t just have protons  in them, but neutrons, too.

Alvarez got a PhD in physics  from the University of Chicago before heading to UC Berkeley’s  Radiation Laboratory. And like any good scientist, he was constantly trying out new things and experimenting. So it’s no surprise that he was soon pulled into one of the biggest science experiments in history.

Life comes at you fast, and so did World War II. Alvarez started off working  in the microwave radar space. But eventually, he wound  up at the hottest place for scientists in the early  1940s: Los Alamos, New Mexico.

Working on …you guessed it… The Manhattan Project. You probably remember from history class… or the movie Oppenheimer… that the U. S. dropped two nuclear bombs on Japan.

But you might not remember that they were fundamentally different pieces of tech. Little Boy was a gun-type bomb  powered by the element uranium. That means that in order to  produce the necessary explosion… but only when you want it to… one  lump of uranium gets shot down a barrel super fast into another lump of uranium.

This would get enough uranium  atoms close enough together to achieve a runaway nuclear chain reaction, whose immense energy cannot be  contained by the stuff around it. But the Manhattan Project only had enough weapons-grade uranium for one gun-type bomb. So for the second nuke, Fat  Man, they turned to plutonium.

That element barely exists in nature, but it can be made in a nuclear reactor. There was a problem, though:  scientists quickly learned that the gun-type method  would not work for plutonium. Basically, the plutonium “bullet” would detonate before it could get fired toward its target, preventing the really big  boom the bomb-makers wanted.

Enter, Alvarez, who showed  up to Los Alamos in 1944. His job was to develop an  implosion method for Fat Man. It was very complex, involving a spherical core of plutonium surrounded by high explosives.

When those explosives were detonated, the resulting force would be directed inward, creating a shock wave that  compressed the plutonium core. Just like with the uranium before, this would set off a perfectly  timed runaway nuclear reaction, reversing the shock wave’s direction  outwards, into its surroundings. The results of Alvarez’s  work were obviously tragic.

Although unlike other  Manhattan Project scientists, he never regretted them. His work on Fat Man solidified his science career, but other projects would be a  bit tougher on his self-esteem. In the 1960s, Alvarez became  fascinated with the Egyptian pyramids of Giza.

Some had hidden  chambers, but others didn’t. Except Alvarez was convinced they actually did. He was inspired by Geiger  counters: electronic devices that detect and measure ionizing  radiation, like the stuff produced when certain radioactive elements decay.

His idea was to probe the inside of pyramids using short-lived subatomic particles called muons. They’re similar to electrons,  but over 200 times heavier. They’re also created in abundance during atmosphere collisions with cosmic rays.

In other words, they’re everywhere. Muons can travel through solids like rock, although how likely they are  to successfully make it through a bunch of solid rock depends  on how much energy they have. But if a massive, supposedly solid  object were hiding a secret room, Alvarez figured more muons would make it from one side of the object out the  other and into your detector.

He was certain that with the  proper experimental setup, all those naturally-occurring muons would help him unearth secret pyramid chambers. Spark chambers were super common  detectors in particle physics at the time, creating high  voltages between stacks of plates. As a particle passed through, you’d see a spark.

Alvarez came up with the idea  of placing detectors in and around pyramids to measure  muons as they passed through. He basically x-ray-ed a pyramid. Specifically the Pyramid of  Khafre, the second-largest in Egypt and one believed to  have no chambers inside it.

Now, Alvarez had reasons to feel cocky. In 1968, he won the Nobel Prize for his work with elementary particle physics. But what goes up must come  down, including Alvarez’s ego.

His team counted over a million muons, and found that the center  of the pyramid was solid. Alvarez said the results were the  biggest surprise of his scientific life. But he learned a lot about pyramid construction, and his work with muons would be super useful down the road for future scientific efforts.

For example, in 2017  researchers announced they had used muons to find a hidden  chamber in the pyramid of Khufu. Which is next door to Khafre’s. That’s a bit of a Sliding Doors moment for you.

Like, “Which of these two pyramids right next to each other should I look at  to test this ground-breaking new scientific technique? One that will depress me at my failure, or the one that will actually discover something in 2017?” The pyramids may have felt like  a “coming back down to Earth” moment, but an actual coming  to Earth moment wasn’t far off. Remember, Alvarez was a physicist by training.

So when his son Walter went  into geology, he was baffled. Rocks?! Really Walter?!

Walt Alvarez became an expert on plate tectonics and mountain formation, with a  big interest in the K-T boundary: the geological layer that marks the end of the Cretaceous period and the  beginning of the Tertiary period. Just so you know, this would eventually get renamed the K-Pg boundary, with the Pg standing for “Paleogene”. Whatever your call it, this  geologic boundary has loads of dinosaur fossils, suggesting a  lot of them died off very quickly.

But there was also an absence of limestone, which usually comes from  bodies of tiny sea creatures. Walt got really curious about  what might have caused all this. Eventually, he reached out  to his rock-indifferent dad.

Luis, whom I’m now tempted  to call Alvarez the Elder, soon grew curious about an external killer: something that could’ve come from space. A researcher named Malvin  Ruderman had once suggested such a quick mass extinction could  come at the hands of a supernova. A massive stellar explosion,  assuming it was sufficiently close to our solar system,  could have bathed our planet in enough radiation to destroy  our protective ozone layer.

And in 1978, the father-son duo and other team members tested rock samples from the ocean floor. They found 30 times more  iridium than they’d expected. A supernova could have deposited  a bunch of excess iridium.

But it also would have delivered  a particular kind of plutonium. And when they searched for an  excess of that, they came up empty. But iridium can come from other  things in space, too.

Like asteroids. So if rocks in the K-T boundary  around the world had way more iridium in them, that could be a sign that  a very large space rock crashed into the planet around the same time  that most of the dinosaurs died. Alvarez the Elder ran the  numbers, and concluded an asteroid would eject debris and block out  the Sun, like at nuclear test sites.

The team couldn’t find an  asteroid-sized crater to match, but they went ahead and  published their findings in 1980. That was the year I was born.  I remember this being a debate! It was like, people didn’t know,  and now it’s pretty much settled.

Paleontologists hated it. The  asteroid theory threw the scientific community into a tizzy, leading to  years of back-and-forth and fighting. In the midst of this scientific civil  war, Luis Alvarez died of cancer.

But in 1991, only three years later,  researchers published their findings on the Chicxulub crater underneath  Mexico’s Yucatán Peninsula. And in 2010, a group of 41  scientists concluded the asteroid that created this crater also probably triggered the mass extinction of the dinosaurs. Sorry to all the paleontologists back then who disagreed, but the physicist-geologist duo won that round.

But you’re free to take your  skills, pull your own Luis Alvarez, and upend another field if you’re able. And if you do, SciShow will get to  cover your accomplishments as well. This video was inspired by Collisions,  a new book by Alec Nevala-Lee.

It’s a biography of Luis Alvarez, and tells the story of the many fields he revolutionized. If you’d like to check it out,  head to the SciShow Bookshop page. That’s right!

We have a Bookshop page. There’s so much good science writing out there, and we want to help promote it. This video was made possible by  the Alfred P.

Sloan Foundation. [♪OUTRO]