Pioneers in Science and Technology Series: Luis Alvarez

              
ORAL HISTORY OF DR. LUIS W. ALVAREZ
Interviewed by Clarence Larson
Filmed by Jane Larson
March 13, 1984
 
DR. ALVAREZ: …San Francisco, right there across the bay in 1911. My father was a physiologist who used to work in San Francisco, downtown as a clinician in the afternoon to make a living. His fees went up as he got more and more proficient, he spent less and less time in the office and more in the laboratory. My introduction to science was through my father’s laboratory. I found that his biological work was of no interest at all to me, but I did enjoy the electrical equipment that he had, and I learned how to run a weak stone bridge and make all kinds of electrical measurements when I was in high school.
MR. LARSON: Yes. Well perhaps I might ask you here as I remember when I was growing up I used to read a column in the paper by Dr. Alvarez. Was that your father who wrote for so many years?
DR. ALVAREZ: That was my father, Walter Alvarez.
MR. LARSON: I think that orients me.
DR. ALVAREZ: Dad was invited to join the staff of the Mayo Clinic in 1926. So at age 14, I moved to Minnesota in the middle of the winter where it was cold and I had never been in snow or ice before. It was quite a shock. Then after Dad had done a few years of medical research, physiological research, the Depression came a long and Mayo Clinic couldn’t afford such a big staff in the laboratory, so he went back into clinical work. Then when he retired as you said earlier, he found some measure of fame as a syndicated medical columnist. So I am always asked if I was related to Dr. Walter Alvarez. Nowadays, they ask if he’s my son because I’m working actively with my son who is a geologist named Dr. Walter Alvarez. 
MR. LARSON: That’s fine. Three generations of famous people then.
DR. ALVAREZ: I took chemistry and physics in high school and I liked them very much. When I went to the University of Chicago, I majored in chemistry because I had never heard that there was such a profession as a physicist. I had never heard of anyone who was a physicist. I had read lots of books on the great achievements of the chemists, but physics was a new world.
MR. LARSON: That’s a very interesting point because that has been brought out in at least three people that I have known who were very interested in physics, but decided they couldn’t make a living on physics so they took their degrees in chemistry. Dr. Wigner, Dr. Teller, and actually Linus Pauling also. It was a rather common thing at that time.
DR. ALVAREZ: That’s right. I remember I use to go to cocktail parties after I had my doctor’s degree and people would ask me what I did and I would always say I was a chemist because it was too complicated to explain what a physicist was and what he did. At least in college I did discover physics. I wasn’t a very good chemical student. I did discover physics and I found that I was good at it and enjoyed it tremendously so I switched over to become a physicist. My first work in the research department was with Arthur Compton. Arthur Compton had won the Nobel Prize for discovering the Compton Effect in x-rays and he had just changed fields and he was working on atomic rays. He suggested an experiment to find the sign, electrical sign of the particles that make up the cosmic rays. I built the apparatus and took it down to Mexico City where I made the measurements and we published a paper together about 1933 and surprised everybody that the cosmic rays were positively charged. 
MR. LARSON: Oh yes. That was really a significant discovery there.
DR. ALVAREZ: Then I did a few other things that didn’t amount to much and I had the fortunate circumstance that my sister was Ernest Lawrence’s secretary. Ernest offered me a job here at Berkeley at the laboratory and I have been here ever since, except for five years during the war. I was, told people that I got my job here because of my sister, but I think I kept it because of myself. I don’t think I would have kept it for almost 50 years on the basis of my sister’s recommendation. 
MR. LARSON: Well you have had a long career. You probably have almost been here longer than anyone else.
DR. ALVAREZ: Well, on the active staff. 
MR. LARSON: Fine. Yes, well then after you joined the, Dr. Lawrence’s staff then, what phase of the accelerator work did you become interested in. 
DR. ALVAREZ: Well the first day I got here, Ernest said to me, “Well, I just got some money to build a big cyclotron. I want you to design the magnet for it.” I said, “Well, Professor Lawrence, I have no experience designing magnets. I don’t know anything about it.” He said, “You’ll learn.” And I did. I made lots of model magnets and shaped the pole pieces on the lathe and made the measurements and eventually came up with the design of what turned out to be the 60-inch cyclotron.
MR. LARSON: Oh yes. The 60-inch.
DR. ALVAREZ: It turned out to be the largest magnet in the world. Then I got into nuclear physics and spent four years or so full-time doing a lot of interesting things. Probably the first interesting, useful thing I did was to discover a new mode of radioactivity called K-electron capture, K-capture.
MR. LARSON: Oh yes. And what system was that on that you…
DR. ALVAREZ: Well I made the radioactive materials on the 37-inch cyclotron. This was a mode of radioactive decay that had been predicted by Enrico Fermi.
MR. LARSON: Oh yes.
DR. ALVAREZ: But nobody had observed it. Then I found the properties of helium-3 and hydrogen-3. At that time, everybody believed that hydrogen-3 was radioactive, excuse me, that hydrogen-3 was stable and helium-3 was radioactive. That’s what it said in all the books and I found that it was just the other way around.
MR. LARSON: What year was that?
DR. ALVAREZ: That was ’38, I would guess.
MR. LARSON: 1938, oh yes.
DR. ALVAREZ: And so tritium is of course now a famous material, that’s hydrogen-3, its radioactivity is frequently in the newspapers and of course that’s the material that is used to make hydrogen bombs.
MR. LARSON: Yes, well of course that…
DR. ALVAREZ: That was the last thing in my mind of course at that time. Nobody thought of any kind of bombs, let alone hydrogen bombs.
MR. LARSON: During the war, at Y-12, Dr. Oliphant came down several times and I some of the times I discussed some of the things about tritium at that time with him.
DR. ALVAREZ: Well, him and [Ernest] Rutherford discovered hydrogen-3 and helium-3 as high speed ions, but they didn’t know what happened to them afterwards. Just like somebody discovering the alpha particle which is quite a different discovery than the discovery of helium.
MR. LARSON: Yes. 
DR. ALVAREZ: They are closely related, but if you discover the alpha particle, you don’t know anything about helium.
MR. LARSON: That’s correct. That’s a very good analogy there. Fine. Well then so, those must have been very exciting times with all those different radioactive elements becoming available on the cyclotron and your discovery of some of these things related to that. So it must have been a very active time here at the laboratory.
DR. ALVAREZ: It really was. One of the other things that I did that was probably important was the, Felix Bloch and I made the first measurement of the radioactive magnetic moment of the neutron.
MR. LARSON: Oh, yes.
DR. ALVAREZ: That took about a year. I’m going to be talking next month at the physical society in Washington at a memorial session for Felix Bloch on that subject, so I’ll have to start thinking about it. 
MR. LARSON: Yes, I hadn’t realized that that was done that early.
DR. ALVAREZ: ’39.
MR. LARSON: Yes. That’s a very significant advance there to work that out. Fine. Well then as, when you got through with that contribution, what was your next field that you went into.
DR. ALVAREZ: Well one day in 1940, Ernest Lawrence called Ed McMillan and me in and told us what the British scientists were doing in the defense work, told us about radar. That was the first time we heard about that and said that the United States was setting up a laboratory in Cambridge, Massachusetts, to work on radar particularly with the newly invented cavity magnetron that was invented in Mark Oliphant’s laboratory.
MR. LARSON: Oh yes.
DR. ALVAREZ: By [John] Randal and [Harry] Boot. That was the thing that made microwave radar possible. 
MR. LARSON: Yes, without that, of course, you’d have no high power source.
DR. ALVAREZ: That’s right.
MR. LARSON: You’d have very short radio waves.
DR. ALVAREZ: At that time magnetrons typically gave two or three watts and all of a sudden Randal and Boot had 50,000 watts in their very first attempt and then inside of a year they were up to a million watts. It was enormous improvement in technology that made radar possible. 
MR. LARSON: That’s astonishing. That must have been a very short time then between that invention and the actual practical use of it.
DR. ALVAREZ: Oh yes. It was used very, very quickly. 
MR. LARSON: So, then you, you went then to MIT to work on the radar project.
DR. ALVAREZ: That’s right.
MR. LARSON: Fine. Well of course in addition to all of the work that you did there in making radar possible for the defense of England and later on the defense of our own Armed Forces, do you remember any particular outstanding events during your stay there.
DR. ALVAREZ: Well probably the most significant event was one day when I was watching the first automatic radar that could follow an airplane, before that time, if you wanted to follow an airplane you had to turn some cranks toward some needles and this was a system in which a radar antenna automatically kept pointing at an airplane and following it, no matter where the airplane went.
MR. LARSON: In other words, could lock…
DR. ALVAREZ: Lock on.
MR. LARSON: …and follow it.
DR. ALVAREZ: That’s right. And several mechanisms, the first ones I had ever seen. It suddenly occurred to me that if you could locate an airplane well enough to shoot it down, it would speed up the three coordinates, the angles and the distance, then you ought to be able to feed that same kind of information into a friendly pilot, help him when he was up in the clouds and get him back down on the ground. 
MR. LARSON: Oh yes.
DR. ALVAREZ: That was the basic concept of GCA, or Ground Control Approach.
MR. LARSON: Oh yes.
DR. ALVAREZ: So, in those days if anybody had an idea and people thought it was a good idea, then you just immediately started working on it. You didn’t have to write proposals and have peer reviews and all that other stuff. So within a day or so I was working on GCA, put together a team of people and we thought we could use this so called gun-laying radar system, directing anti-aircraft fire. But the difficulty was when the antenna pointed down close to the ground, half the time it would look into the runway and see the reflection of the airplane above the runway. The runway was a good mirror so that was kind of a useless thing if you were going to track somebody down, you wouldn’t want to tell them you were 25 feet under the ground, you want to fly up to get under the runway. We had to go back to the old drawing board and I invented a new kind of antenna that made it possible to distinguish between the airplane itself and its reflection on the ground. 
MR. LARSON: Oh yes. So that made possible then the practical use in bringing airplanes down through clouds which would have never been made possible.
DR. ALVAREZ: And all during the war and after the war, in the Berlin Airlift, GCA was the only way of landing aircrafts in bad weather. Nowadays we use a thing called ILS, instrument landing system. It wasn’t available until several years after the war. 
MR. LARSON: Yes, I believe that came much later after the war. 
DR. ALVAREZ: Yeah, it was in development, but they couldn’t use it at Berlin because it had trouble with reflections from buildings. It would bend the beams and the runway coming into Tempelhof Airport in Berlin ran right between a couple of apartment buildings. GCA did the job just fine and they brought in all the coal and food. 
MR. LARSON: Well that’s a very fascinating story of the development of that because modern airplane travel without the applications of radar would just be utterly impossible.
DR. ALVAREZ: But the radar is all on the ground. 
MR. LARSON: Now, of course.
DR. ALVAREZ: The radar that is carried now by commercial airplanes only is for weather.
MR. LARSON: Oh yes.
DR. ALVAREZ: You’re looking for thunderheads and things of that sort.
MR. LARSON: But the radar on the ground is able to guide the plane. 
DR. ALVAREZ: Actually it’s not so much radar as it is transponder assisted radar. You don’t get a reflection directly from the skin of the airplane. But the pulse from the radar sitting on the ground triggers off an instrument in the airplane called a beacon, or transponder. That sends back a much louder signal and in fact identifies the airplane and tells its altitude. So the radar has been enormously improved. As a matter of fact I have the fundamental patents on radar transponders.
MR. LARSON: Oh yes.
DR. ALVAREZ: I worked on those.
MR. LARSON: That would be one of the very classic patents that…
DR. ALVAREZ: Long ago run out.
MR. LARSON: Oh yes. Run out, but as far as the history of science and technology is one of the important things.
DR. ALVAREZ: It is quite an important thing.
MR. LARSON: Now let’s see. We solved those problems. I gather you weren’t content to merely solve the problems of radar, but you also then entered into the Manhattan Project.
DR. ALVAREZ: Yes. Robert Oppenheimer had been trying to get me to leave the radar business and come out to Los Alamos and I finally finished up the three big jobs that I did at MIT. I only talked about one of them, but I had two other radar systems that I essentially invented and developed. I went over to England in the spring of 1943 and demonstrated GCA to the RAF [Royal Air Force] for about three months. We landed all kinds of airplanes. Every kind of airplane that the RAF had and we landed every pilot from sargent to Air Chief Marshall in all kinds of weather and demonstrated that it was a really good system. It really did work. Then I came back and I had planned to go directly to Los Alamos, but I had a telegram cable from Robert Oppenheimer when I was in England, would I mind working with Enrico Fermi for a while because Enrico wanted Emilio Segre to leave Los Alamos and come work with him. So Robert Oppenheimer apparently traded a bird in the bush for one in the hand, so to speak. I went to Chicago and worked with Fermi for six months which is hardly a fate worse than death for a nuclear physicist. It was a delightful experience for me and I learned a whole new way of doing physics. 
MR. LARSON: Yes, that must have been a wonderful experience to work with Fermi, directly with Fermi.
DR. ALVAREZ: It was. I ate lunch with Fermi just about every day for six months. It really was an exciting time. I felt that I was completely disconnected from the war. I had been living with guys who were out fighting the war. I had been having all of my meals in England with RAF pilots who would go out at night, fly over Germany, drop bombs and very often not comeback. They wouldn’t be there the next day. Very often they were dead. I really felt that there was war going on and I didn’t feel happy just playing around in nuclear physics.
MR. LARSON: Oh yes. So it was shortly after that then that you went to Los Alamos. 
DR. ALVAREZ: Robert invited me to come and this time it was clear that I should go and I did go. You mentioned a few minutes ago something about fission and binary fission. You said you should drop the word binary. I’ll just mention that at Chicago the only thing I did that had any importance or any reason to remember it was that I discovered trinary fission. The fact that one percent of the times approximately instead of just having two fission products come out when a neutron hits uranium, an alpha particle also comes out. So there is a three-way fission.
MR. LARSON: Oh yes. 
DR. ALVAREZ: I would have forgotten about that if you hadn’t used the word “binary fission”.
MR. LARSON: I’m glad that was brought out. I had forgotten entirely about that.
DR. ALVAREZ: It wasn’t a world shattering discovery.
MR. LARSON: About one percent of the time that that happens? That’s a very interesting point there. Well, fine. Then you went on to work with Oppenheimer and his group there.
DR. ALVAREZ: My main job there was something that made possible the development of implosion bombs. You probably know that plutonium had originally been proposed to be shot the way uranium was out of a gun. Then the discovery of spontaneous fission made that impossible and then the implosion method which had been originally proposed by Seth Neddermeyer was the only way that plutonium could be detonated. The difficulty was, well, there were three things wrong with it. Three problems that had to be solved, one of which had to do with the simultaneity of detonation of electric detonators. 
MR. LARSON: Yes, that’s amazing. By simultaneous that means to a microsecond.
DR. ALVAREZ: Oh no, much better than that.
MR. LARSON: Much better than a microsecond?
DR. ALVAREZ: At that time, the best simultaneity you could get out of detonators was about one millisecond. Those were the so called SS, seismic detonators that were used in the oil prospecting business. The standard detonators had a time space of about two milliseconds. We needed about a tenth or a hundredth of a microsecond so there was an enormous improvement that had to be made. I suggested a way to do that and my colleague Larry Johnston implemented it. The first time he tried it I think he hit the half a microsecond. It was a sudden breakthrough and I worked on that a good many months during the war. The job was done.
MR. LARSON: That of course must have been a devastating discovery that that spontaneous fission of plutonium would cause this problem.
DR. ALVAREZ: It absolutely turned the laboratory upside down. I have never seen such a sudden drastic change in any program in my life. When Joe Kennedy was in charge of the Chemistry Division there and his main job as far as I could tell was to purify plutonium to get rid of the light elements like lithium, boron, beryllium and things like that so that the alpha particles from plutonium would not make too many neutrons. But when you find that you were living in a rainstorm of neutrons, that job just disappeared. They completely dismantled that whole section of the chemistry department and turned them to things having to do with high explosives.
MR. LARSON: Well that was a brilliant solution to that problem and such a short time frame.
DR. ALVAREZ: It really wasn’t that short. It took quite a while to do it. 
MR. LARSON: Now how long did it take to…
DR. ALVAREZ: Well it was certainly more than a year.
MR. LARSON: More than a year?
DR. ALVAREZ: Very hard work.
MR. LARSON: But it was such a devastating problem when it came up. 
DR. ALVAREZ: It really was.
MR. LARSON: It could have seemed to some people to take decades to solve it ordinarily.
DR. ALVAREZ: Now, the detonators are one of the ways, one of the things that made it possible and the explosive lenses which have never been described in the open to the best of my knowledge, are the other contribution. 
MR. LARSON: But at any rate, it proved to be a resounding success in the first test. 
DR. ALVAREZ: Right.
MR. LARSON: Well, fine. After you worked on this and that problem was solved then I guess you went on to still other problems. 
DR. ALVAREZ: Well Robert Oppenheimer said, you know, well I guess I went to him and said, “Look, Robert, I would like to have a new job. I’m through with my other one, I would like to have a new job that would get me overseas.” I had been overseas in the European Theater with radar and I thought it would be interesting to get out in the Pacific. He said, “Well, as a matter of fact, we have a job that I think just fits you.” This, normally when you develop a new weapon like a new bomb or anything of that sort, new rifle shell, you take it out to Aberdeen test grounds and you test it, and test it, and test it, learn all about it. Learn how well it shoots and how much energy it releases. So we hadn’t got as many test devices to choose to do that kind of a program, so we are going to have to take the proving grounds over enemy territory, make the tests when the bombs are dropped in combat. So he said, “Will you figure out some way to measure the yield of the bombs that we will drop on Japan?” So I figured out a way to do that using the acoustic method. We eventually, very quickly I should say, very quickly designed and built a pressure measuring device that could be dropped out of an accompanying airplane on parachutes which would essentially put, dropping slowly as the two airplanes made approximately 180 degree turns to “get the hell out”. The acoustic pressure measuring device in the parachute cages would then radio the signals back to the airplane where they would be recorded on cathode ray tubes. 
MR. LARSON: So you got a recording of the response then.
DR. ALVAREZ: We got the recording. Well we got the pressure versus time curve and then using theory and knowing the distances and the altitudes you could calculate the pressure. Now the difficulty with this is that nobody paid a speck of attention to our measurements because before we had a chance to reduce our measurements President Truman announced that the yield of the bomb was 20,000 tons of TNT. That was one of the projected yields and he didn’t know that. He just thought it was a number and so he released that and for, I don’t know, 25 years that was the “standard” of the Hiroshima bomb. People at Los Alamos couldn’t make those numbers agree with what they measured in Hiroshima, with the intensity of the burning and various other indicators of pressure that they had made it look like it was somewhat less. Somebody remembered that we made some measurements and I got, started getting letters from Los Alamos saying, “Could we see your records?” They didn’t even have our records. I had them in my personal files. So I made Xerox copies of them and sent them to Los Alamos and they analyzed them and said it looks more like 13 kilotons. That is now the excepted number and that is now being used in place of the old standard 20 kilotons as the Hiroshima number.
MR. LARSON: Yes. Well, I…
DR. ALVAREZ: Harold Agnew probably told you all that. 
MR. LARSON: No, he didn’t quite tell us the end of that story. That those are the measurements which finally clarified the discrepancy there. Good. I’m glad to get that additional piece of information. Well that is a fascinating story and incidentally one of the things that I have heard is, and I would like to have you just make a brief mention of it that your idea of trying to get a message to the emperor through one of these parachutes. I’m not sure how if this is apocryphal or if this is fact to that story.
DR. ALVAREZ: No, it is an absolute true story. Harold Agnew and I, as he probably told you, flew over Hiroshima, but neither of us flew over Nagasaki. But the same pressure gauges were in the airplane that accompanied the bomb dropping airplanes in Nagasaki. 
MR. LARSON: Oh yes. 
DR. ALVAREZ: And Larry Johnston that I mentioned earlier and a couple of sergeants from the Los Alamos SED group were in the plane and dropped the gauges and got the measurements. So we got a good measurement over Nagasaki as well. I didn’t go along, and Harold didn’t go along. But the night before I did get this idea that it would be interesting to get a message to the Japanese high command and so I sat down and wrote a letter out longhand to my friend Dr. Sagane who was at the University of Tokyo and who had spent a year and a half or so in Berkeley before the war.
MR. LARSON: Oh yes. 
DR. ALVAREZ: I knew him quite well and I addressed it to Dr. Ryokichi Sagane, from three of your former colleagues at the Berkeley Radiation Laboratory. I had enlisted the encouragement and support of two of my friends Bob Server and Phil Morrison. So they, none of us signed our names, but at least there were three of us instead of just one. I wrote the thing out by hand and they approved it. Then we made carbon copies, in fact, back when I wrote the original letter I made two carbon copies and we put then in envelopes and taped them onto the pressure gauges and they were dropped out over Nagasaki.
MR. LARSON: Oh yes. 
DR. ALVAREZ: I have actually seen the report of the naval officer who opened those envelopes who probed around in the pressure gauges. I’ve always thought he must have had a lot of courage because the newspaper reports in this country at least said that the bombs were dropped on parachutes. So he must have thought that it was a good chance he was probing around with an atomic bomb. 
MR. LARSON: Yes. That’s fascinating. I guess the fact that those instruments were dropped by parachute confused people. 
DR. ALVAREZ: That’s right. There was never any mention of the instruments, it was just that parachutes were seen coming down. The interesting thing there is that I have in my files at home, both, one of the letters that went down in Nagasaki. Dr. Sagane sent it to me after the war. I sent him a full set of physical reviews from the whole war period. I had to do that surreptitiously because General McArthur didn’t want any intercourse between the Americans and the Japanese in the field of physics. You know he destroyed the 60 inch cyclotron.
MR. LARSON: Yes, I remember that sad occasion. 
DR. ALVAREZ: So I got these to Sagane sort of by a [inaudible] route. As a favor in return, Sagane sent me the letter. In fact he had already given it to Arthur Compton’s brother Wilson Compton who was then president of Washington State College. But to my suggestion, Sagane wrote President Compton asking if he would give this letter to me, which President Compton did during halftime during a football game here at Cal Stadium when Washington State College was playing Cal. I had an appointment to meet Wilson Compton and he gave me the letter. So I have the letter in my files. The one that actually came down and I also have the pressure gauge. 
MR. LARSON: Oh, yes. That’s fascinating. Incidentally are their copies of that letter in any of the archives of the nation?
DR. ALVAREZ: I know there is one in the museum in Hiroshima. 
MR. LARSON: There is one in Hiroshima, but none in this country?
DR. ALVAREZ: I don’t know that there are any. There probably are. It’s been reproduced a lot of times.
MR. LARSON: It has been reproduced.
DR. ALVAREZ: There was an article written about it by Lowell Thomas in the Saturday Evening Post one time. It was entitled “Under Separate Cover, One Atomic Bomb”.
MR. LARSON: Oh yes.
DR. ALVAREZ: The other thing that’s probably important is that I learned that that letter did get to the high command essentially immediately. They took it seriously and the fact that they offered to surrender the next day. Whether that had anything to do with it I don’t know, but I like to think it did. 
MR. LARSON: Well, I think that’s a story which is, that needs to be told and I’m certainly delighted that we were able to get the first hand story from you. 
DR. ALVAREZ: I had another letter which is interesting, as long as we’re talking about letters of that period. On the way back from Hiroshima to Tinian, I wrote a long letter to my son who at that time was five years old, telling him about my experiences, what it’s like to go into combat for the first time, and the whole thing. It’s a long letter. I wrote it out long hand. It’s also been reproduced a few times, but it’s a fairly personal letter. 
MR. LARSON: Oh yes. Well, that’s a really touching thing there. Well. After that experience, it’s hard to imagine other things that could be nearly as exciting, but this is just the start of many exciting things that you have done. What would you consider was the next thing, chronologically? 
DR. ALVAREZ: Well, chronologically, the next thing I did when I came back to Berkeley was design and led the team that built the first proton linear accelerator. 
MR. LARSON: Oh yes.
DR. ALVAREZ: Ernest Lawrence asked me and Ed McMillan and Glenn Seaborg to all come back to the laboratory. We all had been his young kids, so to speak, when we went away we all did important things by ourselves and he knew that we would get offers of good jobs other places. He went out of his way to assure us that if we came back we would have a chance to do whatever we wanted to do and he would support us. I told him that I wanted to build a proton linear accelerator which nobody had ever done before. So he said fine and backed me to the hilt. It was built very quickly and was running in less than two years from the time we started. On that team I enlisted the aid of Pief [Wolfgang Kurt Hermann; W.K.H.] Panofsky, a very famous particle physicist who had already signed up to go to the Bell Laboratories, if I hadn’t asked him to come join the laboratory here at Berkeley he would have probably been one of the co-discoverers of the transistors at the Bell Labs. As it was, it was strange, he was about the smartest person that I met during the war, but he was completely unknown because he wasn’t either at Los Alamos or at the Radiation Laboratory or any of the other big laboratories. He was working on a tiny little project with his father-in-law Jessie Dumont. I happened to know him, meet him because he was the one who built the microphones that we used in our pressure measuring gauges. So he came up to Los Alamos and helped us with our work. He was flying with Harold Agnew and me over Alamogordo on the B-9 flight. As soon as Ernest told me I could build a proton linear accelerator and that I could hire any five people that I wanted. I said the first guy I’m going to hire is Pief Panofsky; he’s the smartest guy I met all during the war. Of course Ernest had never heard of him. He’s done very well for himself as you know. 
MR. LARSON: Yeah. He’s never left the accelerator field and has done tremendous things.
DR. ALVAREZ: It’s probably the most important thing I did after the war, was to get Pief out of the Bell Labs.
MR. LARSON: That’s a fascinating story there. Well of course the linear accelerator was immediately a tremendous tool for nuclear physics. What are some of the outstanding things that came out as a result of the…
DR. ALVAREZ: Oh I don’t think any great physics came out of the linear accelerator. The reason we built the linear accelerator was that if you plot the cost of an accelerator as a function of its energy, the cost goes up as the cube or the square for a magnetic machine and only goes up linearly for a linear accelerator. So if you plot these on log paper, some of them are going at a steeper slope and are going to be at a higher value at some energy than the linear accelerator. So the theory was if you went up to a high enough energy, the linear accelerator would always win out. The difficulty with that theorem which is absolutely correct is that the magnetic guys kept changing their design. So you’re going from a cyclotron that was a solid pole piece, they cut out the center and made things called proton synchrotron, they went to strong focusing, and every time the proton linear accelerator curve was about to be lower than the magnetic curve, then the magnetic guys would change their design parameters and they always won out. So the linear accelerator is largely used as an injector into magnetic machines, although there is a very large almost billion volt linear accelerator at Los Alamos. It’s turned out to be a very useful machine, but it was not the world beater that we thought it was going to be.
MR. LARSON: Well, yes. I think simply just the development of the strong focusing was a tremendous thing at reducing the costs there. 
DR. ALVAREZ: As a matter of fact the very first accelerator that had strong focusing in it was our 32 million volt proton accelerator. As soon as we heard about strong focusing, my colleagues and I put it into our accelerator and showed that it worked.
MR. LARSON: Oh yes. So you immediately adapted that principle. Well, very good. Well, as they say, those are the… Incidentally, what year did you finish up the proton accelerator?
DR. ALVAREZ: 1947.
MR. LARSON: 1947. So…
DR. ALVAREZ: Another interesting thing there, it will sound very conceited to say it, but we went from nothing, not knowing how to build a proton linear accelerator, to having and operating one in just under two years. Then one day Ernest came, about two, three years later, Ernest came in and said, “Oh by the way, Louie, did I ever tell you I gave your linear accelerator to USC.” I said, “No, but that’s fine with me.” I wasn’t using it very much then. So the USC people came up, learned how to run the thing, moved it down to Los Angeles with all the technicians who had run it. It took them over three years to get it running down there. 
MR. LARSON: That’s amazing. 
DR. ALVAREZ: So Pief Panofsky and I kind of patted ourselves on the back after that experience. 
MR. LARSON: Well, that’s a fascinating story concerned with doing things directly and having, knowing what to do…
DR. ALVAREZ: Well we really didn’t know what to do. We were flying blind most of the time.
MR. LARSON: Plus, of course, in so many things in science, you can’t account for the intuition which leads for the right thing to do at the right time. I guess Pasteur originally remarked about that. Well, fine. After the linear accelerator where did your attentions go? 
DR. ALVAREZ: I probably, probably the next thing of any real importance was the bubble chamber. That started, Don Glaser of course was the inventor of the bubble chamber. He made little bubble chambers about this big with hydrocarbons like ethane and when I first heard about that in 1953 I immediately decided that if we were going to make any use of bubble chambers they had to work with liquid hydrogen because liquid hydrogen has all of its target nuclei protons as in carbon, hydrocarbons, you have 12 protons and neutrons all in a big glob. It’s a very, very unattractive thing to a nuclear physicist or a particle physicist. So I said, I learned about the invention of the bubble chamber in Washington at the American Physical Society meeting in 1953 from Don Glaser. I told my two young friends in Washington that, by golly, we are going to go right home and build liquid hydrogen bubble chambers and that’s going to be the greatest detecting device that’s ever going to be seen. So we did do that and very, very quickly went from a one inch chamber, we saw the first tracks in hydrogen in my group. A young chap named John Wood who built the first liquid hydrogen bubble chamber that showed tracks. 
MR. LARSON: What size was that bubble chamber?
DR. ALVAREZ: I happen to have it right here. Here it is.
MR. LARSON: Oh God.
DR. ALVAREZ: Nice souvenir to have on your desk.
MR. LARSON: That’s fascinating. If you could just hold that up to the camera. Can you see it alright?
MRS. LARSON: We got it.
MR. LARSON: We got a good picture.
DR. ALVAREZ: That’s the only early bubble chamber that I have. The next one was two inches in diameter and probably the most important thing that was discovered in this period in our group was the fact that you didn’t have to have smooth glass walls to make a bubble chamber work.
MR. LARSON: I know it didn’t have to be optical, perfect or anything.
DR. ALVAREZ: Well you had to be able to see through it. You could have gaskets. Don Glaser pointed out and was very emphatic on the point that you had to have very, very smooth walls because you had to be able to reduce the pressure on the liquid and not have bubbles form at the walls.
MR. LARSON: Oh yes. 
DR. ALVAREZ: When we first started building what was then called dirty bubble chambers where they automatically started boiling at the walls because there were gasketed seals between the glass windows and the metal bodies they were called dirty chambers. We didn’t like that name, but pretty soon all the chambers that anyone was building were dirty chambers. The clean chambers never amounted to anything.  They never did any physics. So the most important discovery probably was made in my group. Well two of them: one was that you could use liquid hydrogen and see tracks and secondly that you could use metal gasketed to glass windows so that permitted us to go to very large chambers. We made a four-inch chamber that worked quite well and then a 10-inch chamber. That was the first one done on a drawing board by an engineer. All the ones before had just been hacked out with the metal in a machine shop with no drawings at all. Maybe just a sketch. The 10-inch did some really beautiful physics down at the Bell Laboratory. Before that was running, we had the plans for the 72-inch and that’s an interesting story how that came about. I went to Ernest Lawrence and said, “You know Ernest, I think we should have a big bubble chamber here.” He asked me how big should it be. I said, “Well we got one planned for 72-inches long and 20-inches wide and 15-inches deep.” He said that seems pretty big, how big is the biggest chamber that is now working. I said, “Four inches in diameter.” He said, “That’s too big an extrapolation for my taste.” I said, “Well we’re building this 10-inch chamber and if that works and I’m pretty sure it will, then the 72-inch is guaranteed to work because our expansion system is such that the 72-inch can be thought of as a whole bunch of square 10-inch chambers expanding outward and several on top of each other and two side by side for the whole 72-inch length.” I said, “If we can’t make the 10-inch work we will give the money back to the AEC. If we can make it work, we’ll be well on the way to making a 72-inch chamber work.” So he said in his characteristic way that you know very well, said, “I don’t believe in the 72-inch chamber, Louie, but I believe in you so I’ll go to Washington and work to get that money for you.” Shortly after that, we went to Washington together and one morning we called on three of the Atomic Energy Commissioners, Johnnie von Neumann, Lewis Strauss, and Bill Irving and that afternoon they said they had a meeting that afternoon and quoted you the money. That’s the way things went then.
MR. LARSON: Yes.
DR. ALVAREZ: My young friends can’t believe that now because they know about writing proposals and peer review and all that sort of stuff. They can’t believe that in one day, less than one day, talking in morning and going to a cocktail party in the afternoon and finding out that we had the money. 
MR. LARSON: Well it takes longer now to write the proposals and the peer reviews than it would take you to build it. 
DR. ALVAREZ: Of course then we had the money, and then we had to make the thing work. Nobody else got into the business, the large bubble chamber business until our chamber was working. I think a lot of them expected us to fall flat on our face. We had a pretty good chance to, but we did make it work and as soon as the 72-inch chamber was working then Brookhaven started an 80-inch chamber which took five years to come on and Saran started a 2-meter chamber which is very nearly the same size, and that took six years. So we had the field all to ourselves for several years.
MR. LARSON: That’s a marvelous tool for nuclear physics that was available.
DR. ALVAREZ: At that time it was by far the best tool. 
MR. LARSON: So, but the extrapolation from that tiny chamber to 72 inches is…
DR. ALVAREZ: I learned that extrapolation from Ernest Lawrence, you know.
MR. LARSON: He had no inhibitions.
DR. ALVAREZ: He got a little more faint-hearted as he got older.
MR. LARSON: Well that’s fascinating.
DR. ALVAREZ: He certainly did a good job of extrapolating and talking business.
MR. LARSON: Well fine. Incidentally, along that line, there were so many of these contributions that you made to nuclear physics, would you care to mention about the, how do these relate to the citation, the Nobel citation perhaps.
DR. ALVAREZ: Well the citation was for discovering a lot of new particle resonances, which came out of the, really out of the 15-inch chamber and then later out of the 72-inch chamber.
MR. LARSON: Oh yes.
DR. ALVAREZ: And the citation went on to say that these were accomplished through the development of liquid hydrogen bubble chamber and data analysis techniques. So it was a very long citation. 
MR. LARSON: Well, of course it was directly related to the development…
DR. ALVAREZ: It was all related to the machine because one of the things we had to do with the bubble chambers was to make data analysis equipment that would keep up with the enormous number of nuclear events that were seen in the chambers.
MR. LARSON: Oh yes.
DR. ALVAREZ: Before that time, people used cloud chambers. The density of the cloud chamber gas was maybe one percent or less than that of the material in the bubble chambers. So there weren’t very many things happening. So they could take all day or half a day to analyze an event, but in my original write up on the 72-inch chamber I said that if we didn’t have this developed in time to use these data analysis technologies which we did develop, then the bubble chamber would simply be an expensive toy because then one day we could produce enough interesting events to keep the whole cloud chamber fraternity worldwide busy analyzing the events. They never would have gotten them all analyzed. So we did all this work of automatic measurements of the films, automatic track followings, which came out of my radar observations, and then using computers to fit a smooth circle through the tracks, the points on the track and then take the circles on the two films, combine them to give a smooth track in three dimensions because you always take stereos, pairs, or triads. Then we had to analyze those afterwards. It was a very big development to get the data analysis techniques going without them, as I said; the bubble chambers would simply have been an expensive toy. 
MR. LARSON: Oh yes.
DR. ALVAREZ: I think that’s what the Nobel citation recognized, that it was not just the development of the chambers, but also the analysis technology.
MR. LARSON: Yes, the associated analysis technology was almost equally important. 
DR. ALVAREZ: Oh certainly it was equally important. 
MR. LARSON: Yes, well fine. I guess chronologically, what was the next problem you, some of the other miscellaneous problems you worked. 
DR. ALVAREZ: I did some work in cosmic rays using high altitude balloons, super conducting magnets, nothing world-shaking came out of that, but it was a lot of fun. Then I got the idea to x-ray the pyramids of Egypt using cosmic rays. Spent a few years on that.
MR. LARSON: Yes. I can, I was very fascinated by that because I have been interested in the history of Egypt and we visited the pyramids and so on. Which pyramid was it?
DR. ALVAREZ: The second pyramid that’s the one right next to Cheops Pyramid, was built by the son of Cheops. The earlier pyramids, Cheops pyramid as you know has three big chambers in it above the ground level. The pyramids that were built just before that had two chambers in them and ones before that had one chamber. So with the numbers of chambers increasing in number, I was convinced that Khafra’s chamber, Khafra’s Pyramid built by the son of Cheops would have three or four chambers in it and you might ask why they hadn’t been discovered. The answer was that as each pyramid builder built his pyramids, he got a little more clever at hiding the chambers from grave robbers.
MR. LARSON: Oh yes. 
DR. ALVAREZ: The original chambers, the original pyramids all had their entrances in the middle of the north face. So if you knew that all you had to do was get a battering ram and get some people with metal spikes and start drilling in on the center and you would run right into the chambers.
MR. LARSON: When we visited we climbed up to one of the chambers of the Cheops.
DR. ALVAREZ: I know exactly where you went. I’ve been there dozens of times. In fact you went into that pyramid through an entrance way that’s called Ma’mun’s Tunnel. Ma’mun was the caliph of Cairo in the, I think, 12th century and he got the idea that it would be nice to find out where the pharaoh was buried because there was probably a lot of gold in there. So he sent his tunnelers to work on the middle of the north face and told them to dig straight south. They dug for about 100 feet and if it hadn’t been for an unusual accident, they would have dug for another 300 feet and come out on the far side of the pyramid. After they had gone 100 feet, they had no gunpowder of course, they were just digging with tools, and they heard a noise off to their left. What they had done was dislodge a block from the roof of a long descending passageway that went down way, way, way down into the basement and that block went tumbling down and they could hear it. A rock is a pretty good transmitter of sound. So when they reported this to the caliph, he said there’s got to be something to the left, so turn your tunnel to the left. You probably didn’t notice it when you went in Ma’mun’s hole. You went in 100 feet and then turned sharply to the left and you ran into the descending passageway. 
MR. LARSON: Oh yes.
DR. ALVAREZ: The descending passageway intersected the ascending passageway at that point. And it was a block that was covering up that juncture that had dropped down to the bottom of the pyramid. So then they went around some big granite blocks and went up the ascending passageway into the grand gallery and then into the king’s chamber and the queen’s chamber which is just below that. That’s how it was found. Had it not been for that lucky accident they would have gone right through to the other side and said, “Sorry fellows, but there are no chambers in this pyramid.” 
MR. LARSON: There are no chambers. 
DR. ALVAREZ: So my theory was that now that people had stopped being allowed to probe around the pyramids, that probably there were three or four chambers up in Khafra’s pyramid and nobody had found them and we would find them using cosmic rays. It would be like taking candy away from a baby because we had these fancy tools, namely cosmic rays which would go right through the pyramid to the other side. So I enlisted the aid of some people in Egypt, some good Egyptologists, and physicists. We got money from the Atomic Energy Commission. One of the interesting things there was that Glenn Seaborg was head of the Atomic Energy Commission and an old friend from radiation lab days and I got the best Egyptologists to show him around through the pyramids. I found out that he was going to be at an Atomic Energy meeting in Japan and he was coming back to Washington through Egypt. So I intercepted him, had him intercepted and shown the pyramids and he was turned on by them just as I had been and gave us the money. We set up our equipment under, there’s a room underneath the second pyramid, and we put our cosmic ray equipment in there. In fact there is a picture of it right up there. 
MR. LARSON: Oh yes. 
DR. ALVAREZ: You see a couple of Egyptians operating it, up there in the upper right. See the pyramid, satellite photograph of the Delta. There is the second pyramid down to the left. The sphinx is a part of the pyramid complex as you see in the upper photograph. A lot of people don’t think that the sphinx is somehow related to Cheops pyramid. It’s not related at all. It’s a direct part of the…
MR. LARSON: It’s a part of the complex.
DR. ALVAREZ: It’s a part of the acropolises of Khafran. His burial chamber, his burial place and his sphinx. So we proved that the second pyramid was solid. A lot of people say to me, “Louie I hear you didn’t find any chambers in the pyramid.” I said it wasn’t that we didn’t find any; we found that there weren’t any. 
MR. LARSON: You found that there were none.
DR. ALVAREZ: There were none. Quite a different statement. You never found any chambers in the pyramids, most people didn’t find any, but that didn’t prove anything. We found there weren’t any chambers.
MR. LARSON: That’s a fascinating application of nuclear physics.
DR. ALVAREZ: Well, it’s the only thing that cosmic rays have been used for in a practical sense that I know of. 
MR. LARSON: Well fine. Well following this, what other applications to history and science and so forth, have you worked on?
DR. ALVAREZ: Well for the last five years I have been working with my son who’s a geologist, that’s Walter and with Frank Asaro and Helen Michael who are nuclear chemists and we have been combining our various expertise in the solution of the problem of what killed off most of the life on earth 65 million years ago. We now have a theory that is believed by almost everybody. There are two or three holdouts, but a few people don’t believe quantum mechanics and there are a few people who don’t believe plate tectonics so the fact that there are a few people that don’t believe the impact theory, extinctions, is…
MR. LARSON: There are a few people that believe the flat earth theory.
DR. ALVAREZ: So I will say at the moment, it is the theory. Nobody else is a serious competitor and it explains everything that I know and the idea is that a large chunk of extraterrestrial material, either a comet or an asteroid hit the earth 65 million years ago. It was about 10 kilometers in diameter, came in at about 25 kilometers per second and threw up an enormous cloud of dust. In fact the dust went outside the atmosphere and was transported around the globe worldwide by ballistic orbits and then fell down through the atmosphere and by falling down through it made day into night, stopped photosynthesis and we are now beginning to understand just how the killing was done. Our original proposal was that the darkness which stopped photosynthesis, cut off the food chains, killed the animals that ate the plants, killed the animals that ate the flesh because there wouldn’t be any animals to eat. That’s getting stronger every day. In fact I just heard today that a very good young paleontologist has correlated the kinds of animals that went out whether or not they ate live food or dead food. 
MR. LARSON: Oh yes.
DR. ALVAREZ: The correlation is quite good. That just came out this morning. Now that the paleontologist really believe us, they kind of dug their heels in for several years, but now that they believe it, they are going to jump in and explain everything by this new theory. That happened precisely that way in plate tectonics, you know [Alfred] Wegener got the idea that the continents drifted around, Africa and South America seem to fit neatly together. He said they pulled apart. Everybody said, “Oh you’re out of your mind.” The paleontologists had all kinds of evidence that this wasn’t so. Once there was good geophysical evidence for it then the paleontologists came in and wrapped it up. They came in with all kinds of evidence that proved it was right. So we’ve been expecting that in this case, paleontologist dug their heels in at first…
[Phone rings]
DR. ALVAREZ: Can we have a breather for a second?
MRS. LARSON: Sure.
[Break in video]
DR. ALVAREZ: I was explaining that the original theory that the 65 million year ago extinction that wiped out the dinosaurs was triggered by the impact of an asteroid or comet. That theory is now almost universally accepted, but just two or three months ago a new feature was injected which is very exciting to everybody and that is two people at the University of Chicago, David Robb and Jack Stankowski, have found that the extinctions in the last 250 million years are periodic with a period of about 26 million years. So, the paleontologists have gone from not believing that any extinction were due to the impacts of extraterrestrial bodies, to now believing that all of them are and they come at regular intervals of 26 or 28 million years. We had a meeting here at Berkeley just 10 days ago at which all of the players in this new round which we might call a periodic comet shower theory they were all there and it was extraordinary for me to hear one paleontologist say to another, one said, I should say first of all that in addition to the extinctions being found to be periodic, my son Walt and one of his friends have shown that the craters on the earth are also periodic with that same period and that ties the craters which are made by impact, ties the impacts to the craters, ties the craters to the extinctions and shows that they are all periodic. Something that nobody would have guessed five years ago. In fact when somebody first suggested it a couple of years ago everybody thought he was out of his mind and now we found that most everybody at this meeting now believes it. I think the evidence is overwhelming. So another one of my young friends has come up with an explanation for this and that is that the sun is not a single star the way most everyone has assumed, but is part of a double star. In the past it has been strange to find that the sun was a single star, because most stars are parts of multiple systems. More than half of them are. So now if the sun has a companion that’s in a 26, 28 million year orbit so it goes out about two and a half light-years when that companion comes back close to the sun it can inject a shower of comets from the so called port-clog which is a reservoir of comets and shower about a billion comets in a sudden pulse right into the earth’s orbit. So some of them will crash into the earth and make the craters. The craters make the dust in the sky, the cold, the darkness, and it all makes the extinctions. It all ties together beautifully. Now the question is where is that star. It’s got to be out there. I’ve spent a good amount of time in the last two months searching through catalogues of stars, looking for that star, learning everything I can about astronomy and a kind of astronomy that nobody really knew about before. We’ve got a lot of people working on it. I’m convinced that in another year we’ll know where that star is and people will be able to see it and say that guy has been going around with the sun for the last few billion years and that’s what’s allowed us to be here, because it wouldn’t be any people on the earth if the last, not the last one, but the major extinction 65 million years ago hadn’t been triggered by a comet shower. We’ve now given up on the idea of single asteroids for multiple comets. We always said we couldn’t tell what kind of a chunk of rock it was that hit the earth, it was either a comet or an asteroid, and I’ve said several times in lectures that I doubt that if anybody would be able to tell whether it’s an asteroid or a comet. Now I’m sure we know it’s a comet. Not one comet, but more than one comet. So, I’m sure we’ll find that star and people will say that’s the guy that made it possible for us to be here because if that star had not sent in the comet shower that killed the dinosaurs, we wouldn’t be here. The mammals could not live in an environment where the dinosaurs ran the world. There is no way for the little mammals to develop and grow and turn eventually into people. 
MR. LARSON: So the mammals came essentially right after the dinosaurs really.
DR. ALVAREZ: They were there before the dinosaurs, but they were only about the size of rats. Immediately the dinosaurs disappeared, the mammals grew in size and grew in complexities and abilities and branched out, radiating is the word used by paleontologists. They radiated into all the little niches in the environment and we are the result of that. We couldn’t have developed if the dinosaurs were still here. 
MR. LARSON: A few million years after this catastrophe then the mammals were, began to increase in size and take over the world.
DR. ALVAREZ: The dinosaurs had to be cleaned out first. That’s what the comets did and the comets were triggered I believe by the solar companion, which has been named even before it’s been seen. My young friend calls it Nemesis. Well you already got the name for it, now you got to find it. Kind of like we had the names for uranium and neptunium before they were discovered.
MR. LARSON: A very good analogue there. Fine. Well that’s apparently, almost as we talk here, there are more developments. It’s one of these tales that’s going to have a continuing thing. So I will be looking forward to finding that companion star, although it baffles my imagination, you know the needle in the haystack analogue. It’s sort of like finding the needle in the haystack the size of the world.
DR. ALVAREZ: It’s been my business for the last 25 years, finding needles in haystacks taking millions of bubble chamber pictures and finding one event to discover one particle. It’s been our business. That doesn’t scare me a bit. 
MR. LARSON: Well those are fascinating contributions you’ve made here. I was wondering if there were any other thoughts you would care to leave. As I mentioned we are planning to put these in the archives. We already have arrangements with the University of California, and I have some interest by MIT and presumably we are working on better ways of preserving this other than tape. As a matter of fact laser disks and so on for permanence. So I was wondering if there were any other thoughts you might care to add.
DR. ALVAREZ: My main thought is you ought to get somebody like me much sooner. Science is a young man’s game. It always bothers me when you take pictures of someone that is 72 years old like I am say he somehow or other is going to be some sort of a role model for people so they will know how science is done. You may notice over on my desk, I have a picture of Einstein when he was really Einstein. He didn’t have any long white hair. There he is standing at his little desk. That’s Einstein when he was doing relativity. That’s what he looked like. 
MR. LARSON: Yes. He was very young.
DR. ALVAREZ: Very young. When he got old and had white hair and couldn’t do science any more, then people use to interview him and take pictures of him and make statues of him. I always say that’s the guy who use to be Einstein. 
MR. LARSON: Yes. 
DR. ALVAREZ: That fellow standing at the desk, he’s Einstein. So I really think you should get young people like my young friend Rich Muller who I was talking about, my son Walt, get them when they are in their 40’s when they are really doing the most important science they are ever going to do. I have the good fortune to still be doing good science at this advanced stage, but most of the people that you are going to interview my age, most have stopped doing physics many, many, many years ago. I’m not being critical of them. It’s just a very fortunate circumstance that I can still do it.
MR. LARSON: Yes. Well you have a very good point there and something that I will give some real thought to. Perhaps stimulating another group to do that exact sort of thing. I think you raise a very important point there. 
DR. ALVAREZ: I’m always outraged when I go to the Academy of Sciences and I see that statue of Einstein. That’s the guy that use to be Einstein, that statue. It’s not Einstein.
MR. LARSON: It’s certainly a very good point there. 
DR. ALVAREZ: I can’t think of anything that turns people off more than thinking you have to look like Einstein to be a good scientist. 
MR. LARSON: Einstein was what, 25 when he came out with his theory of relativity.
DR. ALVAREZ: He was fabulous. He was the greatest scientist this century has seen in my opinion, but the pictures that you see of him are not of that particular person. That’s the person that he developed into.
MR. LARSON: Well I think that you have raised a very good point there and if I am successful with this, I think I will try to get something started like this, because this is a marvelous new tool and people are quite amazed that this is so easy to do and the effect is almost as if the person was in the same room with you.
DR. ALVAREZ: That’s right.
MR. LARSON: Which it gives you, I think it’s a good educational, as well as archival tool there. Fine. I just want to thank you very much Luis, for this marvelous exposition of all of the contributions that you have made. I am looking forward to running this again and digesting some of the thoughts you had. 
[End of Interview]