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Interview of Maarten Schmidt by Paul Wright on 1975 March 10, Niels Bohr Library & Archives, American Institute of Physics, College Park, MD USA, www.aip.org/history-programs/niels-bohr-library/oral-histories/4861
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Growing up during World War II; early interest in astronomy; undergraduate studies in Groningen, Holland. Graduate school, Rijksuniversiteit te Leiden (Pieter van Rhijn, Jan Oort and Hendrik van de Hulst); Ph.D., 1956. Carnegie Fellow at California Institute of Technology, 1956-1958; assistant professorship at Caltech, from 1959; comparison between Leiden and Caltech then and now; interest in star formation. Review of published papers and discussion of research interests. Discover of the quasars; comments on exotic phenomena in astrophysics; Allan Sandage; collaboration with Martin Rees, Cambridge (Malcolm Longair and Peter Scheuer); the quasar PHL 957. Future research projects (Donald Weistrop), the original Dutch school of stellar statistics. Leisure time interests. Also prominently mentioned are: Adriaan Blaauw, John Bolton, Jesse Leonard Greenstein, Cyril Hazard, Malcolm Longair, Tom R. Matthews, Plaut, Peter Scheuer, and Sidney van den Bergh.
Dr. Schmidt, now would you tell us at length about your childhood, especially how events influenced your interests in astronomy?
I was born in Groningen, Holland in 1929 and I lived there until 1949. After high school I attended the University at Groningen and got my bachelor degree there. Then in summer of 1949 I moved to Leiden to attend graduate school in astronomy, also in Holland. After I'd been at Leiden for about a year, I went to do some astronomical work in central Africa which was a side activity. I could talk about it later or now if you want.
I think if you wouldn't mind mentioning a little more about your early childhood and your first interests in astronomy.
Right. My first interest in astronomy came I think during the war years in 1941 or 1942. I think it was 1942 that — I had been interested in doing chemistry and I had a small chemistry lab at home. But for some reason during that summer I got interested in lenses. And when I visited my uncle who was a pharmacist, who was an amateur astronomer, he showed me how with a couple of lenses of different focal lengths you could make yourself a small telescope. And when I came home at the end of the summer I tried it. One of the lenses came from my grandfather who was a house painter. A big, big thick lens about a half an inch thick, 4 inches in diameter and a small eye piece like biologists use to look at flowers and things like that. And I think that the connecting thing in between I used was a, the inner part of a toilet roll, which was cardboard. And I succeeded in seeing an image and I remember that I then wrote my uncle to say how could I test a thing like that because I had it now what could I do with it. And he said go to the library, find this or that book about astronomy and see whether you can split this or that double star.
So I went to the library and then of course I had to find my way around the heavens to find that particular double star in that particular constellation. And lo and behold, of course, what had happened was that my interest in astronomy originated right there and it grew. And I've built of course slightly larger telescopes than this short toilet roll affair. It was mostly an interest in astronomy then rather than one in optics. The interest took interesting forms in the beginning. As I remember that it was during the war years and I don't think that most of the books could he bought that I had from the library but I, in fact, copied one or two books just from beginning to end in a notebook, all the way, all the properties of Mercury, of Venus, copied everything including the drawings that I copied and so on. Amazing. The war years were of course an advantage.
We lived in the middle of the city, Groningen, it was dark, there was a blackout for a full five years. So it was easy to, from the middle of the city, observe the sky and look at double stars and as time went by sometimes a comet. Anyhow, this started it and I started studying astronomy at the university in 1946 and I participated just a little bit in the observing at Groningen Observatory. But then, of course, the war was over and the city was in plenty of light and it was not easy. Anyhow, my undergraduate years were mostly spent in the usual things, mathematics, physics and only a bit of astronomy. For my graduate education I went to Leiden, in 1949. I did what is in Holland called the "doctoraal" exam, which is a sort of candidacy exam, in 1953. That seems awfully late, but it was partly because of the year in central Africa which I'll come back to. And I got my Ph.D. In 1956. Now as I mentioned, during the first year of graduate school I went to Kenya to take part in an expedition that Leiden Observatory had undertaken to central Africa to observe positions of stars, to measure them from a point on the Earth's equator. And with a few other people from Leiden Observatory, I was there for just over a year.
We lived there on top of, what the natives called, a hill, 9,600 feet high in the Kenya highlands. Each clear night we observed positions of stars by a special technique. It was a very interesting experience. But it just didn't allow me to do an awful lot of astronomy. I was essentially an observing assistant for the main observer who was Van Herk who was interested in positions of stars. Anyhow, I came back late In 1951 Just before the Mau Mau started in Kenya and went back to work to study. My thesis work was on the distribution of mass in the Galaxy and I did that under the supervision of Professor Oort.
Certainly well known.
He was and is one of the most eminent astronomers. The other job I did before my Ph.D. work had to do with 21 centimeter radio astronomy and it was a determination of the spiral structure of part of our galaxy. Those were very exciting times because the spiral structure was delineated throughout the galaxy for the first time, mostly by us. Then in 1956 I went to America. Does this finish the Dutch part or do you want more of earlier history?
What I might do is just go back and just sort of touch upon a few of these and other things and go forward chronologically. I think that you've covered your early times quite thoroughly. How did you and your family live out the war?
We lived in Groningen, in the northern part of the country. It was away from the heavily populated western part of the Hague, Amsterdam, Utrecht, Haarlem, Rotterdam and so on. And that was an advantage during the last year of the war, after September 1944, when the Battle of Arnhem was fought and lost by the Allies. The Dutch railroad system went on strike to support the Allied landing. When the thing essentially failed, then they remained on strike and the Germans retaliated by taking out practically the whole railroad system, literally. And also they left the supplying of the population entirely uncared for and as a consequence starvation set in, which in the western part of Holland was very severe. In the northern part and the eastern part of Holland it was bad, but not very bad.
So we were somewhat lucky to live in that part of the country. To go back to the earlier years in the war, that's the thing I remember best. In the early part of the war I was about 12, 13 years old. It was at night the incessant droning sound of bombers passing over on their way from England to Germany. And not all the time would they pass over, sometimes they would bombard the city or they would get into an argument with the German anti-aircraft guns and they would bombard. It was very noisy at times and at times it was pretty risky too. I had a number of sleepless nights at that time. Often one would be awake in the shelters or at least in the lower parts of the house, from about eight to two in the morning or so, and then you get a couple hours of sleep and then went back to school. I also remember from that time that I once had the realization that it was all sort of exciting, that there was a restlessness and I wondered how one could really live in peacetime. [laugh] Things were sort of at a high pitch all the time and interesting. Well, I don't know whether you want to hear more about it. One can, of course, go on about the war years, but they aren't necessarily so interesting.
What was the occupation of your father?
My father was a government accountant and about 1956, I think, he finally became in The Hague the Chief Government Accountant. But we spent all our years in Groningen while he was there. So he was a civil servant. I also remember that during the war he was part of the civilian [this is a term I've never pronounced in English, you know] civil guard, to help people in case of bombardment and fire bombing and so on. For that reason, part of the war at least, whenever there was an alarm in the evening he had to go out and patrol the neighborhood and some.
Make sure there were no lights on, that sort.
Well, no, it was not against lights I think. It was mostly in case there was bombing or firebombing that he could alert the fire department. It was something that was organized by the civilian population quite independent of the Germans. They tolerated it and didn't mind. It was purely civilian in contrast to the German administration, of course.
What was your family's reaction to your interest in astronomy?
Somewhat guarded. My father, my family in general, was somewhat guarded. I mean, they liked astronomy as an activity for an amateur, you know, like I was in the beginning of course in high school. But later on when I went to the university and was studying physics and mathematics and astronomy they were somewhat guarded, they were not sure that there was any future in it. My father was rather narrow-minded at that time, but I do remember at that time in Holland there were only fourteen full time positions in astronomy in the whole country. Fourteen. And obviously that meant that every three years on the average, one of these positions would come open in Holland. And then you realize that some of them were professors at the university. Obviously not a job that you just jump into, as a young man. This was in the late 1940s, Sputnik had not arrived yet. Astronomy was, as compared to these days, really an ivory tower, dormant, no money science. Technically no money went into it. I remember that as a student whenever I went to a meeting either inside the country or sometimes to a neighboring country, I would never even think of asking the observatory to pay for my travel, that thought never crossed my mind. Money and astronomy didn't go together simply. I mean, since there were so few positions it was clear that the only good hope was to stay in astronomy, if you were very good, and if you were not, you could become a teacher in high school. Once that was sort of made clear, my parents didn't object anymore. One of my grandmothers, my maternal grandmother, was a little more insistent. She kept insisting until close to her death that it must be bad for my eyes to look through a telescope. I needed glasses rather young and she felt all the time that this wouldn't do them any good. So they were a bit worried and the general idea was that there wouldn't be too much of a future in it and that, in those times, was not unexpected. I can understand it.
I assume that you attended gymnasium in Groningen. What impressions did you have of your courses?
It was not actually a gymnasium, it was the, what they call an "HBS," which was a secondary school. It was a school that did not have Greek or Latin, but instead had more emphasis on the sciences and so there were two parallel high school possibilities in Holland at that time. These days there are four, I believe, very complicated. It was, in general, all right, but at times I remember I would get in conflict with the teacher of cosmography which was mostly descriptive, it was mostly a field of describing all the circles that you can think of in the sky, the meridian, right ascension, declination, the prime vertical, everything. And, it's amazing, they taught practically no astronomy. It was just, it was just all these circles that you can think of on a globe, you know. It was like an application of spherical trigonometry essentially, that was how it was applied. The man who taught was the director of the school and once in a while I would get in conflict with him because I honestly at times knew things better than he did and he wouldn't accept that very much. [laugh] I remember an incident that made him very angry, very unhappy. There were all these globes that you did have to draw, these half globes with the observers in the center and you have a north point, a south point on the horizon, east and west, the zenith, you know, everything. Well, he gave a good exercise which was how were all these things on different places on the earth? You know, if you were on the equator, if you were on the North Pole, and he drew a case where the observer was on the North Pole and yet he showed around the horizon that there was one point that was the north point of the horizon and opposite it was the south point on the horizon. Of course on the North Pole it doesn't make sense. Every direction is to the south, isn't it. It's somewhat esoteric, but I got into an argument with him about it. But in general, I was certainly not very clever in other fields. I mean I was a fairly reasonably good student but not very good. But of course in astronomy, in cosmography, I was very good.
You mentioned that you pursued a course of study at the University of Groningen in astronomy. What did you think of your courses there?
I should say that it was undergraduate school, of course, and it was mathematics and physics and astronomy. There was relatively little astronomy, the main thing was mathematics and physics. And that was very good. In astronomy I had Dr. Plaut, who at that time was what was called a scientific officer at the Observatory, because Professor van Rhijn, who was very well known, was quite sick and I had few if any contacts with him at that time. I was at that time often engaged in some student activities. I think I was president for a while of one of the student associations that had to do with having lecturers over in physics and astronomy. I was a fairly serious student and also I think at that time already my interests in astronomy had grown to such a degree that I wanted to get done with all this preparation. One of the difficult things for students who already know what they want, you have to go through an awful long time of preparation. In undergraduate school and so on, it takes a long time. It's somewhat hard to remain motivated all the time. By that time I was pretty sure I wanted to go into astronomy. Anyhow, the undergraduates school at that time at Groningen was relatively unexciting but I think it was a very good school.
Could you characterize the social and political climate at Groningen while you were there?
No, that's not very easy. The social climate. That's an interesting question. What have you exactly in mind?
Well, I think that at various times, say at Cal Berkeley about ten years ago, there was a Free Speech movement.
Yes. Well, that far back in time, seeing with that as an example, there was absolutely nothing that happened. No one even gave it more than one minute in four years of undergraduate school. So there was no clear political climate as far as it went. Students and politics did not come together. I mean their political interests or backgrounds from the family would all be quite different. Perhaps, I should remind you that Holland has a multiple political party system and before the war there were 55 political parties. In 1946-1949, while I was a student at Groningen, there were only on the order of 12. There is such a diversity that you regularly meet some people from political backgrounds that are very different and as a consequence it becomes relatively less important. Anyhow, students and politics did not go hand in hand, I'd say.
There's always been a spirit of toleration I think in Holland.
Yes, I know. But I know that these days that they are politically very much more active than they were at that time. So it's not just the matter of the Dutch being tolerant and therefore nothing apparently happening then, no nothing really happened in the 1950s, in the early 1950s or the late 1940s in the Dutch universities. Absolutely nothing! These days, at times, they practically have taken over. I mean soon after Berkeley things were very active over there too, with occupations and changes in the methods and representation, everything. And so at that time there was no thought of it. Nothing.
I think that period here was somewhat similar.
I think so, probably. So, it started here in 1960, no when was Berkeley, 1964?
About ten years ago.
1964, yes. Yes, before that time I think it was as I said. The social climate, again I don't quite know what you have in mind. But there were, a very important difference in that connection between an undergraduate school here and one in Holland. Over here the students have quizzes, mid-term exams, final exams. And every three months or four and a half months, depending upon where you are, the semester is over. You've got your grades, your new courses, I mean there is a constant finishing of things and the start of new things. Not so over there, the courses were all one year courses. So it took you from September to May. The exams were all almost always oral and individual, and there was no time limit for it. It could be done whenever you wanted. So for the first year you would just take course after course after course. You make notes and study some but in the meantime there was plenty of time for student activities. Then finally you started to take your exams, called "tentamens." You could do those exams whenever you wanted, so there were cases where I took the exam in the middle of the third year of a course I had taken in the first year. You'd call up the professor and he would say, "okay, come around Tuesday afternoon at 3:30" and he'd come into his office to give the exam. If you didn't make it, he'd give you so many months, which means you could come back after that many months to do it again.
So as a consequence, lots of people were in the university as students at that time who had hardly been tested as yet as to their ability to do well at examinations or even to pass them. So life was rather more careless there as a student. We could sort of goof off for a whole year and then perhaps you'd be in school for five years rather than four years, but there were no committees that you had to petition to stay a year longer in undergraduate school. Some people took seven years for their undergraduate studies. It was very, very free, and that in a sense, I think, probably is the best description of the background against the social climate to be seen. Relatively carefree and you could be in a number of student clubs and associations and even be a president or vice-president of one of them and so on, spend lots of time and lots of things and yet you might make it. Many didn't, of course. It was a somewhat wasteful system you know. And these days they're changing all that to quite a degree because every student costs a lot of money. Those were state universities, by the way. I mean the universities, all but one university in Holland are, you cannot say federal, but rather state universities. So the social climate was very good in fact. Lots of student activities and balls and festivities. Really very nice. [laugh] I think compared to that it's rather dull for a student here.
At Cal Tech?
Certainly at Cal Tech; Pasadena has nothing to write home about, I think.
You mentioned that you, at the University of Groningen, there was an observatory there…
and you doubtlessly did some observing.
Yeah, I helped a little.
What type of instrumentation did they have there?
That's a good question, what did they have there? It was a reflector of about fifty centimeters in diameter and it stood on the roof of the observatory building which was next to the University in the center of the city. I took spectra of blue stars, spectra of stars to study the effects of dust in between the stars and us, there is dust floating around the galaxy. And van Rhijn, whom I mentioned before, the director, had been very interested in the properties of that dust for his studies on the statistics of stars and how you derive from that the structure of the galaxy. And he found it necessary that the little observing that was done at Groningen would contribute to the understanding of the properties of the dust. So they took spectra of stars that are the same, are of the same general properties.
Primarily blue stars?
Blue stars, which are intrinsically bright, these are stars that you can see far away. You would choose one star whose light would be reaching us through quite a bit of dust and another in a relatively dust free region. From the difference in discoloration that it caused, because the star seen through the dust becomes redder compared to the dust free case, we tried to study that effect. I'm not so sure these observations were successful. It was sort of fun and interesting too, to see a real telescope at work and to assist Plaut who was taking all these exposures. It was sort of romantic, too, of course I mean it was still pretty carefree for me because he had the responsibility for the whole program but I stayed part of the night. I would go from the house on my bicycle and go to the observatory and he'd let me in and we'd work for a number of hours. That observatory, being in the middle of the city, they had a funny system that was hardly ever used, I think, but they had gotten the municipality to require that every building that had roof top advertisements in lights would take care that there was a switch at ground level that could be handled with a particular key so that if any observer found it necessary to observe low in the sky in the direction, he would get a bike, go to that part of the city, go to that particular part and turn off that darn light. [laugh] I think we once used it or never did it. I have the inkling that we once did it and I felt very guilty, you know, these advertising lights. It was in the late 1940s. That privilege one doesn't have any more. We'd have a heck of a time going around Los Angeles. [laugh]
Did your family support your aspirations sympathetically and financially?
I've already mentioned that they were slightly worried about whether there was a future in astronomy but one step was settled, or at least had become clear, that I could become a high school teacher. They did support me and certainly financially through the years. My father was essentially middle class and we had no particular financial difficulties. That went quite well. As a matter of fact, once I became more and more interested, they were happy about it.
Would you care to relate any additional anecdotes about your lab work at Groningen?
No, I don't think so, I don't think so. I think that's about it.
During your graduate work at the University of Leiden you continued your work in astronomy. Who were the professors who particularly impressed you there?
Oort, of course, and Oosterhoff, van de Hulst. Oosterhoff, he did work on variables, variable stars especially in globular clusters. Van de Hulst did work on zodiacal light and the interstellar dust and who also predicted in 1944 that neutral atomic hydrogen should emit spontaneously a little pulse of 21 centimeter radio radiation. In the middle of the war he predicted that, and Oort was also involved with that while in hiding, because during those last few years of the war, all men between eighteen and forty-five had to work in Germany. So that a very considerable fraction of the population went underground and Oort also went underground. I don't know about van de Hulst, he may also have been underground. Anyhow, it was while he was underground that he made this prediction that neutral atomic hydrogen should emit 21 centimeter radio radiation. And there's one place in nature where you were likely to observe it, namely in our own galaxy, because every atom would emit so little of the stuff that you wanted to have an enormous line of full emitters, and that is what you get in the galaxy when you have a couple of thousand light years of this stuff all in a row, in the plane of the galaxy where we live. And indeed the radiation was discovered in 1951 by three groups within a few months. The Russian, Shklovsky, independently of van de Hulst because communications were bad, of course, predicted that it should exist, also in 1944. Shklovsky is still very active, eminent astrophysicist. Then there was also Professor Blaauw who was at Groningen at the time. He was not a professor yet, but he was to become one later on. And I would say that Oort and Blaauw probably influenced me most and van de Hulst to quite a degree. Well there is no doubt that Oort is the one that really had the most influence on me. He is very eminent, has an enormously broad knowledge of what is going on in astronomy. He has insight, very deep. He's not necessarily one of the best teachers and in a sense you learn from him perhaps by…
What is almost like osmosis.
Yes, by seeing him in action, by just experiencing him. He would not necessarily often explain things very well, yet his ideas and his insights were so deep that if you manage to sort of break through the initial barrier it becomes an enormous inspiration. That is still what he is for me at the moment. In fact, it's quite amazing. I see him perhaps about once a year and in perhaps one or two hours or so I think we discuss about as much as I would with other people in twenty hours. We range over most of astronomy, there is no need for an introduction, we just say a few words to each other about things and he says something that gives me an idea and I say something and he discusses it and within five minutes we have done with a topic that otherwise with other people would take an hour or two. And then we go to the next one. You see that very effective tuning in is obviously the way he has affected me that has done this. Oort, of course he was the one who discovered the rotation of the galaxy, who was involved in a number of other things in astronomy, and he's the one who is really responsible for the present eminent position of Dutch radio astronomy. They have an antenna array and that is doing beautiful work and with which very interesting new things are being found. Those were the three or four people that influenced me most, I think.
Would you care to relate any anecdotes about your lab work with one of these professors there at Leiden?
Oh, perhaps indirectly. It was very much the idea at this time, this doesn't exist there anymore I think, that all the students would do observing, that they would really get their hands dirty. There were several telescopes at Leiden Observatory, again it was in the middle of a city, the city is somewhat smaller than Groningen, and I started to specialize in comet observing. Also Oort and I, before that in 1951, we both became involved together in the study of the properties of certain comets and we discovered that certain comets had behaviors that are different from others and we managed to link that to the shape of the orbit. We even thought we understood why those things were linked. I mention this because it is interesting that recently when Comet Kouhotek was about to come through, you may remember that quite a hullabaloo was created about how bright it should become and what was to be the century spectacle. I hardly paid notice until in one of the announcements I saw that the orbit had been determined for the first time. And it turned out that the orbit was exceedingly elongated, almost parabolic.
Then something clicked because I realized that Oort and I had found in 1951 that comets that have these very elongated orbits, when they approach the sun from the outside, that their brightness goes up much slower than other comets. So I sat down and looked at our old papers from 1950 and I computed on that basis that Comet Kouhotek should be, should have a maximum brightness of about +1 or 0 or something, just like the brightest stars. And that was at a time that the prediction was that it should be -10 which is 100 times brighter then Venus. I never fully publicized this because you can never be sure, comets are idiosyncratic things. And I'm sure that if I had announced it that the thing shouldn't become that bright, it would, you know, just to spite me, so I didn't say much. I made it known a bit over here and, in fact, I mentioned it to the astronauts' office since they were going to go up for it. But again, it was very interesting because several months later Oort wrote me a letter, we write each other every few months, and in a postscript he said… No, no, my father wrote that Oort had written an article in a Dutch newspaper after the whole thing was over in which he had indicated that it was not to be expected that the thing should be that bright, as it had not been, because he and a student of his, Maarten Schmidt, now at Palomar in California, had found in 1950 that and that. [laugh] So even without me checking with Oort he'd had exactly the same idea.
That was on comets, but I also did some observing to try and check some of these findings we had on newer comets and to do the observations in a better way. That actually was rather interesting, not easy because comets are faint characters usually and to see them in the middle of a city and to find them at all, I think I observed some ten or twelve comets or so in the years I was there and got a few useful observations. Of course, when you take them you hope they are all useful. But there were a few that were quite useful and interesting. As I said, everybody was supposed to observe whenever it was clear or the telescopes were busy and once in a while Oort would come out of his house because he lived right on the Observatory grounds, and he would go around the telescopes to check to see if everybody was really observing. [laugh]
Not asleep, or something.
No that's right, that's right. I don't think anything terribly funny happened but it was sort of amusing. Completely gone out now, I mean, 21 centimeter astronomy has taken over to quite a degree there that it can be done in day time, you don't check observing at night anymore. Sometimes it would be rather, well, the weather in Holland is so unpredictable, it's almost like this [cloudy day in California], that knowing whether you would have to stay over for the weekend or not, often it was very difficult. Usually the weather would be so bad you just go in the weekend whenever you wanted to go in Holland. But, of course, it's Saturday afternoon at four o'clock, suddenly everything would clear up. There would be a blue sky and you would wonder whether you had to go back to Leiden to observe. Which in a number of cases I did and had to. Not only that but often during the week itself if it was your turn to observe you would have to leave social gatherings or whatever meetings just to go back and go to the telescope. That's something that we don't have over here, because the facilities are so far away that you either are there specially and you sit out at night locally or you're here and just don't bother about the weather. It's rather different. Yeah, whether there was anything else that I should mention about the years in Leiden.
What instrumentation did they have there?
I used a photometer at the telescope to measure the brightness of the comet in different color bands. And some of these, with interference filters, they were aimed at certain cyanogen and carbon bands to try and see the variation of these bands as the comet got closer to us or was receding.
You mentioned that there were a number of telescopes. What were the sizes?
In addition to the twenty inch telescope, there were other telescopes, refractors, not reflectors. One was a thirty-three centimeter telescope with which people like Pels Muller and Blaauw would take exposures to study proper motions or angular motions in the sky of stars in the Hyades cluster. And then there was a ten inch telescope on top of the building with which double star observations were done to measure the separation and the position angle of double stars so as to study their orbits, to get periods and the separation, to derive the mass of the stars that way. They were the main programs going on over there.
Prior to Baade's work on Population II stars, the Hubble constant was in conflict with certain geological data. Do you recall any of your professors' perspectives of this timescale paradox?
Not too clearly. I do remember, the main thing that I remember from that time was in 1952 I think it was, it may have been 1953, Fred Hoyle coming through Leiden and giving a talk on this subject. The thing I most clearly remember, I was still a student of course, was that he said he was on his way to California to resolve the matter with the 200 inch. I remember as a young student that I piped up at the time and said how was he going to resolve it with the 200 inch. I mean, I was already a bit distrustful, that you could just go to the telescope and resolve it. And it wasn't awfully clear about how that would be done and he talked himself out of it. [laugh] And I guess I'm still arguing with him. But people like Oort and Oosterhoff all were super critical, not in a bad sense, but any such statement implying that the two timescales didn't agree, they would simply not accept at face value and I think I've inherited such an attitude also. But they would say well how sure are you about the one timescale, how sure are you about the other and so on. Is this a real necessary consequence and so on. And for that reason it may well be that there was much less interest at that time in the issue simply because I had mentioned that they hardly believed that these timescales were that way around.
Somebody like Oort with his insight understood that distance scales in astronomy are something tremendously difficult. That you couldn't believe them to the required accuracy. But of course you're quite right that timescales were the wrong way around at that time and that of course is how the Steady State started. My own personal regret is that, when the timescales then readjust themselves, the Steady State still exists. One should be able to switch it on and off. [laugh] I shouldn't become personal. Anyhow, it was not a big issue, at the time there, but I must admit that I do not remember very clearly any statements about it. I think that, I'm almost sure that Oort simply would not have believed it, would have taken a wait and see attitude.
How did you perceive astrophysics before you decided to make contributions to the field?
I don't know whether or not that's a very good question, because it's difficult. What did I think of it? I don't know, before you start to understand the field better, everything is sort of amorphous, isn't it. It's sort of like a jelly. I remember for one thing that I could hardly understand how people could think of new things to do in astronomy. That is, the less you know about a field, by ignorance, the simpler it looks, I could hardly understand why these people always keep busy and seemed to get new ideas to do new kinds of observations, to make new discoveries, how is it possible. Yet, of course, the field in reality turns out to be much more diverse.. I mean there's lots of detail, design…in it and yet there is a grand design and all that together makes things infinitely complex, really. Until you enter a field and penetrate into it, you just don't know things like this. So I'm afraid it seemed rather amorphous and I don't know why I was then interested in it if I couldn't see through things yet. I think often in young people you will find that their interests are based on things that cannot be quite explained. That's why I would guess if somebody's rather interested in the field one shouldn't try and investigate too closely by questioning him why he's interested. Just let him be interested, that's better, you know. It's great to be interested in something although sometimes the reason is superficial, dreamy or unrealistic, but who cares. So I honestly don't know why I became interested. And as I said, in the beginning the field was fairly amorphous to me, totally unlike what I now see.
You mentioned the science office in connection with the University of Groningen, I believe.
I should say scientific officer, it is one rank in the civil service, Scientific Officer. Those you'll find in Australia, for instance.
Were you a scientific officer at Leiden?
Well, when I came to Leiden I was first an assistant and I stayed an assistant until 1953 when I think I was made an Adjoint Scientific Officer. It was the most junior post one could think of. And then some years later, 1953 and I think in 1954 or 1955, I became Scientific Officer. That was before my Ph.D. And then very soon after I got my Ph.D. I left for this country so there was no particular reason for an advance at that time.
That was in 1956?
That was in 1956, right. I got my degree in April 1956 and I think in May we left for the United States to take up a Carnegie Fellowship, here at Santa Barbara St., at the Mount Wilson Observatory.
Can you tell us about your duties at Santa Barbara Street?
I was entirely free. These fellowships are intended just like a typical post doctoral research fellowship. For people to essentially round out their education, to get experience with research programs on large telescopes and so on. It was very pleasant and relatively carefree time, as a Carnegie Fellow, and I was there from 1956 to 1958. Actually the observing that I did, it was the main thing, the observing I did was never very successful, it was never even published. In fact, I don't think I'll ever publish it. And while I was doing that I became interested in star formation and especially in the consequences of star formation. When you have a galaxy that consists of a lot of gas, interstellar gas floating around and stars, the stars form from the interstellar gas and something is happening that is irreversible. The gas loses some of its mass and the total star population is increased.
Then the star blows up at the end of its life and you have gas again and a star less. But it's not necessarily the case, and I became interested in the secular changes in stellar systems that occurred as a consequence of star formation. So I think from that time this half-theoretical work had probably more lasting value than the observations I did at the telescopes that didn't turn out too well for reasons that, well actually I might have been too critical. I remember I was doing observations of one cluster, NGC 6939, and I found that the absorption that I determined from the photometry on the sixty and 100 inch telescopes for the dwarf stars and the giant stars didn't agree with each other. I remember about a year later that other people discovered things in photometry of clusters that led them to believe that clusters have different metal abundances. I think I was essentially affected by the same thing. But the star formation thing had really sort of become much more interesting. I was a fellow until about May or so, 1958, it was a period of two years, and in the last few months they had asked me here at Cal Tech whether I would stay on as Assistant Professor, which I decided not to do, so I went back to Holland.
Coming back to Holland was perhaps a bit of a shock because after you've been in this country for a number of years it turns out that Holland is relatively small. Somewhat packed together, you know, and I think we were back only on the order of a half or three quarters of a year, when I realized that perhaps I should reconsider the offer from Cal Tech. So negotiations were opened again and it was successful. Then it was a matter of getting me out over there. I had been on the first visit, I had been out on an exchange visa. There happens to be a law that says that in such a case you have to stay out of the country for two years before you may re-enter as a permanent immigrant. So it took a rather lot of effort on the part of certain individuals to get that law waived, which they finally managed to do. So we came back in late 1959. And I'm still here.
Your research interest seems to be initially centered on distribution of radio and optical objects in our Galaxy. How did you come to be interested in this area?
This is radio and optical objects in our Galaxy.
That statement is a bit, perhaps slightly incomplete. My initial interest in radio astronomy had to do with 21 centimeter and that was from interstellar gas. And there I did one of the first determinations of spiral structure in the Galaxy, my interest in the distribution of optical objects in the galaxy was not an effort that, I don't think that it was actually the case. My thesis was on the distribution of mass as a whole in the galaxy. You have to sort of from the gravitational effects you see to infer how much mass there is but you cannot all see it. I'm thinking about whether I'm overlooking some things because it's so easy. It so happens that just over the last half year I've gone back to very local optical objects in our own Galaxy. And this is something I'm rather excited about, at the present, but at that time I think my interests were in masses distributed in the galaxy, spiral structure in the galaxy as determined by radio observations, comets, the effects of star formation. Yes, I think those were the main different things that I was interested in before I started radio galaxies and quasars, but those I suppose are outside our galaxy, right.
I was referring to a paper you did for the Journal of the Astronomical Society in Canada in August of 1961.
Right. Yeah. Right. Yes. Yeah, that was a review paper. I was certainly interested in those things, but I did not so much original work in there, although I must admit that a few years later I did study with Kraft the distribution in our neighborhood of cepheids which are variable stars in our own Galaxy.
In connection with the rotation…
In connection with the rotation properties, determination of the Rotation Constant A. Yeah.
That anticipates my next question. How did you and Kraft come to write that paper?
Well, that must have happened as follows: he had been involved in trying to calibrate the period luminosity law for cepheids which was discovered by Shapley and Miss Leavitt in the Magellanic clouds. For in the Magellanic clouds you see that stars of a certain period have a particular brightness and then you see for increasing periods that the brightness is larger. It's beautiful, but the one thing that remains unknown is the distance to the Magellanic Clouds. In that case you would know what the absolute brightness, the intrinsic brightness of a cepheid of a particular period. And that's been the so-called problem of the zero point of the period-luminosity law. Kraft had been working on that on the basis of cepheid that had been found in the second half of the fifty's, in galactic clusters, in star clusters in our own Galaxy. Since with star clusters we can determine distances rather reliably, if we see a cepheid in the middle and it's a member of a cluster, we know it's distance too. So he had been working on that and he was then planning to, with the new zero point he had, and the new ability to determine distances, he was then wanting to study the properties of cepheids in our neighborhood. Since I was very interested in the rotation curve at that time, the constant A, we decided to team up. I was then working here, and he was working at Santa Barbara Street, which is the other half of the Hale Observatories. So it was as easy as anything to join up, to team up. And to do this jointly. That must have been just about the last paper I wrote, I think, on things that had nothing to do with quasars or radio galaxies, from what I remember. That was in 1963.
In your paper on the rate of stellar formation of stars of different mass you indicate that in the past relatively more bright stars were formed. The implications of this paper, to stellar evolution, would appear to be great. How did your interests come to shift into stellar evolution?
Well, I mentioned a while ago, it is this rate of star formation business which I started to work on as a Carnegie fellow here. I think strangely enough my interest was started by an article by Sidney van den Bergh, who happens also to be a Dutchman too, was at that time already at Toronto, I think, although he may have been elsewhere. Sidney van den Bergh who had written a paper in which he said, first, star formation is taking out of the gas certain bits and making them into stars at so and so a rate. Then he said there is so and so much gas at the moment. And he divided one into the other and found that we had 500 million years to go and then we'd be out of gas, literally [laugh] And that seemed atrocious to me. So it was a little bit in opposition and protestation that I started to work on it. I said, look here. It must be wrong to say that the rate of star formation is always the same when you have less stuff to form stars from it must go slower. So I then said suppose the rate of star formation is proportional to the amount of gas that you have, because it's from the material you make it from.
Then I started to look into the consequences and well it became a whole investigation and soon I realized that perhaps there were reasons to believe that it went even with a higher power of the gas density. And that essentially started me off. Now I should say that these findings that I had later on in 1963, that at earlier times that relatively more bright stars must have formed, that at the moment I simply don't know whether that result still holds. There have been, in the meantime, a number of investigations by other people, quite a number, and they have pointed out other alternatives by which you can explain certain paradoxes that I tried to explain at the time. And having an extra fraction of the stars in big stars, early on, is now to be considered as only one of the solutions. There are three other types of solutions around. And I think that the solution I proposed is probably not doing too well at the moment. But it's an interesting speculation anyhow. Moreover, that speculation was done twelve years ago, where most of these other solutions that I mentioned were about five years old.
In early 1963, you were the first to discover the extreme redshift of the spectrum of 3C273. I've discussed this event with Dr. Sandage and Dr. Greenstein. In view of the significance of this discovery to the history of astrophysics, I would appreciate it if you could describe at length how you came to be interested in these objects, and your perceptions and reminiscences of the situation before and after the discovery.
That's a big question. I must have started during my work on radio galaxies. Tom Matthews, who was working in the radio astronomy group here in 1960, on the basis of accurate radio positions of objects in the sky, determined with the Owens Valley Radio Interferometer, had been plotting these positions on maps of the sky and had been identifying galaxies that way. And I was involved, starting in about 1960, late 1960 or 1961, I had been involved in taking spectra of those galaxies to get their redshifts and I did that for a number of years. Now the first finding of a quasar I was not involved in at all. Nobody knew, of course, it was to be a quasar. But I think it was in October of 1960 that Matthews identified an object, one of the radio sources, 3C48, with a star. I guess the position at that moment was already quite accurate. So he found that it had to be identified as a 16th magnitude star. Since I was not involved in that, what I have to say here doesn't carry too much weight. I think it was Guido Munch, in fact, I think Guido Munch probably took the first spectra of the thing and these were not understood. They showed some lines and it was not clear what they were. And I think at a later stage that Alan Sandage, it may have been that Sandage first got the object from Tom Matthews and measured the colors. And I also know that Jesse Greenstein became involved in and took some spectra. He may have been last. I don't know. And John Bolton was also involved. He was the Director of the Radio Observatory. He was much involved in the identification work. But I think it was actually done by Matthews.
If there is any discrepancies exactly about who did what at that time, since I was totally out of it and happily working on the radio galaxies, you know, I wouldn't be too sure. Anyhow, apparently the results were communicated In the December meeting of the AAS and that was that. Now in Tom Matthews' further work of identifying radio sources by plotting on sky maps with optical objects, we encountered further stars and I think that the first one of those stars was 3C286. And I took spectra of it and I found that it had one emission line. And I remember that I published a note about this object, a half page note in the Astrophysical Journal which had a complaining sort of tone, it sort of said there was one emission line, perhaps another absorption line but not certain. It didn't look like this, nor that, nor that, nor that, and it was sort of the end of the story. Yet historically, I think again without knowing it this was the first publication I think, original publication in the astronomical literature of a description of a quasar. Well, Tom was just identifying and identifying; he gave me more and more of these objects. I'm not absolutely sure about the order, there was also 3CI47 and 3CI96. Now 3CI96 is not too clear in my mind because I never found a line in it, no emission lines, no structure. Much later lines, very weak lines, were found in it and finally identified. I never got those at first. In 3CI47 I had six lines, five or six lines, but some of them I wasn't too sure of. And I remember that I discussed those lines at a symposium at the Goddard Space Institute in some skyscraper in Manhattan. Goddard Space Center or so. It was a conference about radio galaxies and I discussed the spectrum of this particular object, 3CI47, again a quasar to be.
I suspected that the lines were variable but I wasn't sure, and I gave a possible explanation of some lines but it was all very unclear, very unsatisfying. Now that was in December 1962, probably a few days later I went to Palomar and I did some work then on number five, 3C273, of these stellar objects of Matthews 3C48, 286, 196, 147 and 273. It must have been after Christmas 1962 then that I took a number of spectra. This was a very bright object with a jet. The jet was very faint and the star was very bright and when Tom showed me this object which he had in fact gotten from Cyril Hazard in Australia, from the occultation I immediately thought that the Jet had to be the interesting object. But it was exceedingly faint so during that run I thought I might as well take a spectrum of the star. I had no idea that it would be of any major interest but just to get the star out of the way. The first exposure was very much over exposed, a 13th magnitude star. I usually worked on 18th magnitude galaxies and I over exposed it, really badly. It looked already a bit odd. I thought I saw one or two structures in the spectrum that looked odd but I didn't give it much attention and the next night, or the night after that, I took a number of exposures. Those exposures showed, I think, four emission lines. And I measured them and I told my colleagues about them. I think Bev Oke must have come up to Palomar to work with the multichannel spectrophotometer, probably in early January. It sticks in my memory that not very long after that time that we knew about the existence of yet another line in the infrared near 7600 Angstrom. And in hindsight, I sort of treated this material almost with abandon because I freely showed everybody where the wavelengths were and told everybody would they please try and identify it. [laugh] Instead of locking the door and trying to do it and discover it myself. So a number of people in fact were cooperative and gave me suggestions of what it could be but things never fitted exactly.
There were always one or two important lines missing and things were never satisfactory. It was under those circumstances that I got a letter from Bolton in Australia who said that Hazard and the others who had been involved in the occultation were writing an article for Nature, would I perhaps write a brief companion article to describe the spectrum of this thing because I'd kept Bolton informed about what I found. So it was on the 5th of February in 1963, it was a Tuesday afternoon and I sat down in my office over there where Jim Gunn now is, and I sat down to write it down for Nature and I had a spectra next to me and I was looking at the spectra once in a while to make sure that I was writing down everything I should. I realized at a certain moment that out of the six lines that were known, if I left out one in the red, one in the very far blue at the end, then the remaining four lines seemed to be fairly regular. In order to investigate this regularity, what I did was entirely foolish. I tried to construct an energy level diagram, which is something I'd never done before. In hindsight it is not reasonable to do that. So I tried to do that, determined frequencies and differences of frequencies for the four lines that seemed to be regular. When I did this things didn't work out.
So I got a slight bit frustrated, look here, it is regular isn't it, I said to myself as it were. And in order to prove that, I decided I would take the ratio of the wavelength of the lines to the nearby balmer line because they are spaced regularly, one, two, three, four, five. So I did that and that's when the discovery came because the first ratio was 1.16, between the first line and the nearest balmer line. And then the next line and the nearest balmer line gave 1.16 again and the third was 1.16 and the last one was 1.16. Then I suddenly realized that if I took the balmer spectrum and increased it by 16% wavelength that I could explain four of my lines. That included Oke's line in the red and three of the lines I had here. Then I immediately checked the other two lines. If those were also 16% shifted up, where did they originally come from? The one came from 2800 Angstroms and I was vaguely familiar with Magnesium II and that's what it turned out to be. The other one gave me about 5,007 which is the strongest line of the well known OIII doublet which is often seen.
The only thing was that it was somewhat faint in this case but except for that it was quite reasonable. So I, in about an half an hour or so, suddenly had all the lines identified with a redshift of 16%. A redshift of 16% is not so large because a redshift of 46% was known for a galaxy. But this was a bright star and not an excessively giant galaxy and that was the astonishing thing, that a bright star could have a big redshift. Well, I opened my door, I think I saw Jesse walk by or I went to his office and said could he come in my office for a moment, I wanted to tell him something. So he came to my office, then he sat down and he got pale when he heard it. He said perhaps we should look at 3C48. Now a funny thing had happened, again in hindsight it was funny a week before we went through this discovery process, Jesse had finished a thick paper about the spectrum 3C48 with what afterwards appeared to be a no good explanation of a spectrum. He himself was not necessarily very convinced, yet he put a lot of work into it because he found the things should be explained. And I remember that the week before this all happened he came to my office, he'd thrown the thing down on my desk, somewhat frustrated, and said well, if you don't have any remarks within a week, I'm going to send it off. So in hindsight, this whole thing was in order to… Alright, we looked at the spectrum of 3C48 for awhile and we soon found, suddenly our eyes were opened, we were willing to try big redshifts, that is it had a redshift of 36 or 37% and the interesting thing is we got again Magnesium II that way. Magnesium II from 2800 so we now saw in two different quasars that they both had Magnesium II emission. That was of course a mutual confirmation. So it seems quite promising at that moment. S
o we got a redshift of 36 or 37%, we then spent quite a bit of time on the derivation of whether this could be perhaps due not to a redshift at all, whether we could think of highly ionized light atoms, iron, with only one electron remaining in that outer shell that would give a balmer type spectrum but shifted. So we spent on the order of half an hour on my blackboard to try and work this out. And our initial impression was that it could not be done. Because of all the activity in my office, Bev Oke was attracted and we discussed the thing for another while and I think it must have been 5:30 when we adjourned to Jesse's house where we had a couple of drinks. Then Naomi his wife was just flabbergasted because we never do that kind of a thing. We just entered there and we discussed things for another while and then I went home and I told my wife that, I think I said something like, something terrible happened at the office today. And I proceeded to tell her. And I remember that night, in the evening, in the living room I paced up and down like a caged tiger for probably hours. Because it all became clear, already at that moment, although it was yet to come what it meant, what the future held in this case. Because if you see very bright objects with such large redshifts then somewhat fainter ones must have much bigger redshifts. I think I also spent that evening on finishing the work we'd done on my blackboard to see if there could be hydrogen-like ions. Although we never published it, I think we could convince ourselves easily on the basis of that proof that it couldn't be. As soon, of course, as you have two or three very different redshifts you'd have to invent a different ion for each of them. So that was fruitless anyhow. There was in the beginning, certainly with me, a deep worry that we were missing something completely, that we were being fooled somehow. And that, and I remember that was the main worry with me certainly for two or three weeks.
One felt that there might be a big trap. That you might feel after you had published it and somebody came up with a simple way out that showed that things were not so extraordinary at all. As if you'd been sort of taken, as if you'd been taken in, that you proved that you're so gullible that you really thought the star of 13th magnitude could be at a distance of two billion light years, ha ha ha. Who could ever believe that. And yet, we thought as hard as we could and we told our colleagues and we simply couldn't think of anything that was really a way out. Now we thought also very briefly about gravitational redshifts, in other words not motions. But basically we thought that these were redshifts just like the Hubble Expansion. Therefore, if you saw a 16% redshift for these things, it had to be just as far away as galaxies at 16% redshift. In other words, the Hubble constant applies to them. Although we did briefly think about gravitational redshifts, we didn't initially give much, as much idea that they could be the cause of these redshifts. So anyhow, it wasn't too long after that I finished writing in Nature article which took a rather different tone. Jesse and Matthews had a 3C48 discussion right next to it and Bev Oke came with a description of the red spectrum of the 3C273. So together with the Australian paper we got four papers in a row in Nature which must have happened in March or April, I think, 1963. So that was how it happened, I think.
I think it was quite interesting you giving some of your insights as to the agonizing experience it was for you.
Yeah. At that time it was real agonizing about science. Later on there came agonizing about publicity, you know, just publicity to such a degree that it became enormous pressure. At that time it was simply a matter of knowing that Nature forced you to say something. You couldn't keep quiet and you had to say something and it better be good because it was clear it was an occasion. So it was to be an occasion and whatever the explanation was, it was to be a rather remarkable event in astronomy. That was really what was, of course, going through my head when I was pacing up and down that night. Boy, I'll have to say something, what do I say, do I believe it, is there a way out, what does it mean for astronomy? It is sort of interesting because, I would say that indeed it was, in a sense, the birth of the present era of exotic phenomena, exotic and explosive phenomena in astronomy, with the quasars, the pulsars, the x-ray binaries, the black hole, the 3° background radiation. I mean all these things were yet to come. The quasars suddenly started it and since then just about every two years there has been a major development of another discovery. Astronomy in an accelerated development that is just unbelievable. I mean before 1963 things were so unlike after 1963, there was no way to compare it. So in a sense the agony and the pressure of making a good on-the-spot scientific judgment just in one day essentially, the fifth of February, was a very interesting one. Because we had not been subjected to this yet. Later on it was much easier for people to accept extraordinary things in astronomy because we've seen it as I said every two years we've seen them. This has come on with about five to six, even with seven different types of phenomena including the gamma ray bursts that you may have heard about. Fantastic things. You never heard things like it in astronomy! And if they came, it was one a lifetime… So it was the beginning of an era that, of course we didn't know at that time, we couldn't help but realize that the quasars would play a very important role from then on, it was clear enough.
Your interests appear to have shifted slightly in the classification of extra galactic radio sources into weak and strong sources. Why did your interests shift into this area?
Well, that question is not entirely correct, but I'm sure you don't mind if I point it out. My interest is still mainly with the quasars, but two years after the discovery of the quasars, those that were found through radio radiation, Alan Sandage discovered that there are a whole lot of such objects around that do not carry radio radiation and, in fact, there seem to be many more of those. They seem to be the more common. These days, I think that we call the phenomena as a whole the quasars. They can talk about the radio quiet quasars like Sandage's object, and talk about radio strong or radioactive, or whatever you want, quasars like 3C273. To my mind they are all one class. They're all one type of phenomenon and so I've been studying both kinds since, for quite a number of years, and my main interest at the moment is in their statistics, their distribution in the universe when you look back in time, because these things are so far away. At the very large distances we see them, light has been traveling for more than half the age of the universe. So you look back in time and you look at large distances and thanks to the statistical studies done, it's been possible to show that at these earlier times there were very many more quasars than there are these days, by an enormous factor. But, of course, I should qualify all this by saying that I'm just adopting here this point of view that they are indeed cosmological, in other words, that the redshifts indeed are caused by the same basic thing that causes the redshift of galaxies.
Therefore, the distances of galaxies and quasars of the same redshifts are the same. But since you've been talking to Burbidge it must be clear to you that at least some people do not necessarily believe that. So I have not so much shifted my attention to other things as well as that it is very fruitful to consider the quasars of all sorts of radio properties including where you cannot detect it. It is true that I have probably gone into the statistical study of quasars because the study of individual, the careful study of individual quasars has not yet gained a lot of insight into what they really are. Insight into what they really are is still very sadly lacking. It's been my own program over the last five or six years to one, extend the total knowledge of quasar spectra simply by taking as many as I could because certain types of spectra are very rare. And you can only encounter them if you take spectra of a lot of different quasars. In the second place, to combine this approach with the statistical investigation by doing the first thing that I mentioned in taking further quasars, spectra of further quasars, by doing that in a very systematic fashion, by making sure that over a particular area of the sky I take every quasar brighter than magnitude 19 or 18 or whatever it is and of certain radio properties. It turns out if you do that, if you set up the work that way, that what you get is an extra bonus. That you can study the distribution of the quasars in the universe in depth or back in time. It's out of that that this enormous density increase with time backward resulted. So it's certainly paid off tremendously because the quasars as yet are the only object in the universe for which we see clearly an evolution. That they change their properties as a whole with cosmic time. There is no other object for which we know that! We can guess it, galaxies must do it, simply because they convert their gas to stars. So we know that our Galaxy, five billion years ago, looked systematically different, different from what it looks now. But we don't know how much. We can argue that galaxies must evolve slowly and change their properties. We know they do. I mean, that's how confident we are that this general line of thinking is quite right. For the quasars, we've seen it, actually. And that's rather interesting.
You collaborated with Tom Matthews to write several articles. Do you have any anecdotes you would care to share about Tom Matthews?
I don't, I can't think of any. I may be overlooking one or two. Anecdotes don't happen all the time of course. [laugh] I mean, no, I don't think so. I can't remember any.
In 1966, your interests ranged into the lifetime of extra galactic radio sources in which a distribution was presented for the elliptical galaxy in the mean radio phase to which mean radio phase lasted about one billion years. How did you come to be interested in these space densities?
I can hardly remember. I honestly don't quite remember, but I should say that it was a particularly deep thing to do. It's a well known technique in, certainly in physics, and I'm sure in other fields, that if you know that particular types of objects are connected in an evolutionary fashion, that the numbers you see in the various evolutionary stages must be proportional to the lifetime in that stage. You can translate this to the human population, roughly at least. Although there are certain effects that make this invalid. But roughly the number of people between fifty and sixty years is half as much as between thirty and fifty years, simply because the one interval is twice as long as the other. Now if you think hard about it, there are certain corrections that ought to be made because of death and because of change in the birthrate. But very superficially you don't expect that there are ten times as many people in the thirty to fifty age range as between fifty and sixty, or the other way around. So I don't quite know how I got to it, that was a fairly simple and straightforward consideration. That a lifetime of the radio phase of the ellipticals had to be on the average that long, and it was more in the nature of an idea that seemed not to have been expressed in the astronomical literature is why I wrote it down. Nothing wrong with it by the way, I mean, it appears to be a good idea, it's not been deflated, but it was not a major investigation. It was some insight that I realized had not been expressed.
In 1967 you offered evidence supporting the contention that cosmic rays do not originate with extra galactic radio sources. How did you come to be interested in the origin of cosmic rays?
Well that happened, as far as I know, on the spot at a conference. I was In Noordrijk, Holland at an IAU symposium and a discussion was going on between various people and I'm sure that Burbidge was involved, and I expect that Ginzburg or Shklovsky or both were involved, about what fraction of cosmic rays may be coming from extra galactic sources. I think it was either Shklovsky or Ginzburg who had a very involved, complicated derivation which suggested that it could not be all from extra galactic sources, that a substantial part had to be from our Galaxy. The derivation was lengthy and very involved. And the more lengthy and involved something like that is the more uncertain it must be. While I was sitting there I thought up on the spot a way you could essentially prove the thing much more elegantly, I thought, in about one minute, rather than this very lengthy one. Since that was a very short derivation its weaknesses and strength could be seen clearly. So I was still thinking it out when the discussion of the paper ended and then there was coffee. And while I was shuffling in the line to get to the coffee, I presented the idea to Lo Woltjier who said, yes, he saw nothing wrong with it. So immediately after I presented the idea and that was the birth of that. Actually I didn't write it down for a long time because I am not in the field of cosmic rays, you know, I mean it's not my area. But then I think I was at another conference where I think Ginzburg spoke where this thing was almost repeated. I realized I ought to publish it, because it was a nice simple argument. [laugh] So I just went out and published it. It's rather closely related to the idea of the lifetimes of the elliptical, it was the same kind of thing. It was actually quite straightforward. So I guess I stepped outside the quasars once in a while if I feel that something should be said and it is particularly simple. But that again didn't take any substantial time or effort. And it was just an idea. But that idea is still valid, too, I believe. I'm not sure it's fully appreciated by the cosmic ray physicists. [laugh] I still think it's not fully appreciated by them, but it's a very good idea, if I may be immodest.
You began a project about this time to determine the distribution of quasars with distance and luminosity. Would you care to comment on your perception of the significance of this work to astronomy in general and cosmology in particular?
As I mentioned, if you do the observations and the statistics in this very systematic fashion then you can investigate the distribution in depth or distance or time back. You then find that at these large distances the long times back that there were many more quasars than now. The most reasonable explanation or background idea that I have there is that indeed quasars may well have to do with the birth phenomena of galaxies. That in the nucleus of galaxies in formation that in the beginning things are especially violent, for what exact reason, of course, we don't know yet. For that reason we see so many of the quasars at very early cosmic times. There are reasons although they are not very strong by themselves, but there are reasons to believe that most galaxies formed in the early part of the early stages of the universe and if you now see that the quasars mostly occurred in the early part of the universe, it is effective to link the two together. Obviously that will be tremendously important for cosmology itself because it can tell you for instance what the birth rate of galaxies is. It would tell you that galaxies still formed at quite a rate even a couple of billion years after the universe started its expansion. I might say that is perhaps something that is somewhat unexpected. I think that most cosmologists would have thought ten years ago all galaxies, or almost all galaxies formed in the first, were born in the first, oh perhaps a few hundred million years or so. Yet on the basis of this work it would look more like it's been a few billion years. Anyhow, I think that the link of the quasar phenomenon with the birth of galaxies is a very attractive one but to be sure it is unproven. It's just a very effective idea to have in the back of one's mind.
Your interests in spectroscopy of radio galaxies have been of long duration. In your paper you proposed the possible variation of fine structure with time. How did you come to write this paper?
It must have been the paper with Bahcall, I think. I should say that we did not propose that it changes with time but rather we said that it seemed that the thing hadn't changed with time. We were reacting to a proposal by Gamow who said that all these redshifts that astronomers see might be due to the fact that the electric charge changes, the unit electric charge changes with time, such that E4 is proportional to time. Now it so happens that the electronic charge, E, is involved in the line splitting of certain lines that we see in quasars. Doublets that are quite close to each other, a few angstroms apart. The typical system of those lines is determined by the so-called fine structure constant of which E is a part. It is a combination of Planck's constant and the velocity of light. If E was really variable the way Gamow wanted it, then the fine structure constant ought to also be variable. We tried to check whether the fine structure constant had been constant and we found that at a redshift of two it seemed to be within 5% or so of what it's present day value is and that seemed to rule out Gamow's proposal. That led to quite a bit of correspondence with Gamow, he was a very amusing, original man. Very, very nice one, too.
Do you have any anecdotes about your relationship with him you might care to share?
No. I haven't met him personally. It was all by letter and I still have some of those letters, I think. But those always turned up in a rather fantastic fashion with lots of side remarks and scribbles at the top. He was a fantastic man.
From your work on the V/VM ratio has for quasars, would you comment on what implications of this paper the evolution of QSO?
I should say that is actually what I was talking about a little while ago, the distribution in depth of quasars. The method I used there was one that is described as the V/VM method. I invented it to study the distribution in depth of quasars from a given sample, that is complete over a particular part of the sky, complete within a certain radio and optical limit. I had to do that because with radio quasars there are two limits involved that you have to adhere to at the same time. The thing, as long as you talk about radio quasars, the thing has to be in the radio catalog and that means that it's brighter than the radio limit. At the same time the thing has to be visible. For it to be visible it has to be brighter than some optical magnitude. So there are two limits that the sample must obey at the same time and there didn't exist in astronomy, to my knowledge, any method with which you could investigate distribution in depth of objects that are from a sample that is subject to two limits at the same time. One limit yes, a magnitude limit yes, but never two limits at the same time. And it took many months before suddenly this method of V/VM came about. It is very powerful and it is extremely elegant and it can be used with great generalities, it's really very nice. The V/VM method is probably for me the most satisfying method that I developed ever in astronomy, I think. I have, as a side issue, I've just recently used it, over the last half year, to determine the local density of fast moving stars in the galaxy which had never been done before in the galaxy. The local density of fast moving stars, faster than 250 kilometers per second. Again it turned out that I had to adhere to two limits at the same time for reasons that I won't explain. And here the V/VM method was ready and it could just be applied like that without further thinking necessary. Just great. So that was a brain storm that I'm most happy about. It hasn't been used much yet and I think it can be used all over the place. It yields the enormous density increase of quasars towards earlier times. And I've just mentioned that this is probably to be related hopefully with the birth of galaxies. So this question came somewhere in between the others.
You've worked with M.J. Rees on some papers. Could you offer any anecdotes from your work together?
Yes and no. What really happened was, when I had applied this V/VM method for the first time, a couple of English radio astronomers, Malcolm Longair and Peter Scheuer, found it necessary to write an article in the Monthly Notices of the Royal Astronomical Society in which they tried to argue that there was nothing new with the method, that source counts of radio sources had already shown everything that I had derived in that paper in which I had used V/VM method. That paper was quite unfortunate and rather damaging. I didn't at first quite know what to do about it. It was atrocious really. Partly I didn't know what to do about it because nobody was too familiar with it. Then Martin Rees came here from England, also from Cambridge, on a visit and the first thing when he got into this building and saw me, he said, "Did you see that article by Longair and Scheuer, isn't that terrible?" And I said I think so, too, why don't we write up something together. So while he was here we wrote up something together and we came with an impressive array of arguments which, by the way, clarified to me my own method. You know, it's very good to be sort of attacked so that you have to defend yourself.
Forces you to clarify your own method.
That's right and Martin Rees, who is one of the most clear thinking persons in astronomy, was enormously helpful. He had a number of ideas. I've never heard any critical comments from those two gentlemen again.
You co-authored several papers on the QSO PHL 957. Besides the determination of this object being one of the most luminous known, what are your perceptions of the importance of this work?
Not excessive. It's at the moment one of many. It did have the largest redshift for a while, up to 1975. But at the moment I think that there are probably five or six that have larger redshifts already. I have, I think, one of them. But there are a number of other cases in which other people have larger redshifts than I have for any quasar. Why I am unable to hold on to the distance record, the redshift record, at the moment is totally a matter of luck. Because you simply cannot predict the redshift of a quasar without observing its spectrum. It happens that I've been taking a large number of quasar spectra over the last four or five years and my largest redshift has been upward of 2.8 or so, or 2.7, on that order. There are at least three quasars with larger redshifts all by different other people. Why I cannot get the largest I don't know. I'm not particularly after it but since I take a large number of quasar spectra, I don't quite see why I don't have it. [laugh] But anyhow, this PHL 957 was interesting because it was the largest for a little while. It has a very large number of absorption lines in which we managed to identify quite a large number of redshift systems and that means the very stuff in front of the quasar at smaller redshift that is ejected by the quasar. It perhaps belongs to the fifteen quite interesting quasars. And as you mentioned there, it is one of the intrinsically brightest. It may, in fact, be the intrinsically brightest perhaps. But as I say, no deep or great significance.
You also wrote papers on the statistical study of the evolution of extra galactic radio sources. Since that paper, do you have any additional direct evidence for the evolution of radio galaxies?
No. The evolution of radio galaxies, distinct from quasars, right?
The evidence for radio galaxies I have there was indirect because you can look at the source counts, the number of radio sources of different strengths, you can estimate the radio source counts due to quasars, subtract that and be left with a supposed radio galaxy count. In those papers that you mentioned, I then tried to see whether those remaining counts could possibly be generated by a radio galaxy population that was uniform throughout the world. That turned out to be impossible, so there had to be evolution. I think that in the meantime that there has been direct confirmation of this on the basis of work done by Longair and Readhead. Readhead is a research fellow in our group here and also from Cambridge, England. They've looked at a particular type of radio galaxy, those that have small nuclei and therefore will scintillate in the interplanetary medium. They found that their numbers would go up again from the V/VM method which they now applied. That there appears to be a strong evolution for these objects. So at least for part of the radio galaxies it has been confirmed. It's rather encouraging.
From your many years of study of the evolution of extra galactic radio sources, could you give us your perceptions of the present state of our understanding of these objects?
Well, that's too awfully hard. In a sense, unlike a number of other people who are active in the field, I am able to work for a long time without having a very clear idea of what the object I'm looking at actually is like. Perhaps in my case it's just as well. Some people have to always have some speculative idea that they then roughly believe in about what they see. They will think up an immediate explanation for every phenomenon. I find that quite possible to do without that. So even if I see the evolutionary effects of quasars and also radio galaxies, I can be satisfied to think not much more than that, yes, it might well be correlated with the birth of galaxies. I don't know whether that's a weakness or strength, it's strange. You might say, hey, what about your scientific curiosity. Of course I'm tremendously curious what these things really are, but on the other hand I feel that we've been hit so hard by fantastic phenomena that even just filling it in with "explanations" as it were, just for your own satisfaction, would be so much work that I refrain from that. So for long times I can work in a subject and try to do the phenomenology of it and yet refrain from thinking too deep about what it actually is. I think to a degree as far as I'm concerned it's a safeguard or my mind would be too full to see the simple relationships that once in a while can be found in the sky. Because to my mind is one of the most fun parts of a field like this, that things can be done in a way that are so incredibly simple that you don't understand why either you or nobody else had thought of it.
That to my mind is tremendously satisfying because the field, as any other field, is full of very complicated derivations, groups, formulae. I mean, if you want to go into detail and be specific and also very hypothetical, things can be made so incredibly complicated. Yet it's great fun to see once in a while that certain of the relationships are basically so simple. I guess perhaps that's a greater reward than to have a deep insight into what your thing really is, because when you have these exceedingly simple relationships you feel that you're probably close to real nature. As Einstein said, God could surely not be malicious, and I think similarly many scientists would feel that on the contrary indeed, when you really come down to it, science must be exceedingly simple. That things ought to be very, very simple. For that reason the satisfaction out of the sometimes exceedingly simple relationships like the V/VM method which is really simpler than anything I've ever done. I mean it's so simple if you explain it to somebody also in astronomy that people in general won't understand it, because it seems a hollow statement, self-proof, something that they already knew.
Yeah, self-evident, why bother. It's an extra real power of the method, it's that simple. [laugh] Anyhow, I don't quite know what's behind it, I don't quite know what the objects are, I have vague ideas and I feel no strong urge to go too deep into that.
From your study of quasars associated with Abell clusters you found that the ratio of the bright QSOs to bright galaxies in the clusters is not more than about ten times that ratio in the field. Could you comment on what possible implications of this work to cosmology?
No. It's, it was a purely observational result which was dictated very much by what we could do and there's no particular clear implication for cosmology from that. I would again rank that perhaps as one small piece in a puzzle of which you get a solution because you simply happen to see that one of the pieces happened to fit right over here, but it doesn't mean as yet that you really know what the whole thing is about. You just saw that things fitted together, you saw the possibility to do that. I think that that piece sort of ranks as one incidental puzzle piece that could be placed, could be fixed, but it does not have a deep significance somewhere yet. It may soon.
We have reviewed most of your papers up to the present time. In the present and future do you foresee additional work in the distribution of extra galactic radio sources or do you see yourself moving in the direction of, you've mentioned already fast moving local stars and such things as that, or your interests generally shifting away from these distribution studies into something new?
They do a slight bit, yes. I'm by no means finished with the quasars yet. I'm still working on the statistical study, this time of six centimeter catalog quasars and these I think will be very helpful in illuminating certain problems that exist at the moment in the statistics. I mean even though the way we've discussed it it seems pretty straightforward perhaps, there are lots of problems. Both at high frequency, that is at small wave lengths, six centimeters and also for quasars without radio radiation, more statistical work ought to be done. I'm sorry to say that the statistical work goes so slowly at the telescope, it really takes many years before you get results. But nonetheless, in the meantime, partly through thesis work of a student of mine about four years ago and recently through work on these fast moving local stars. I've become more interested and active again in work in our own Galaxy. In effect, having to do with the make-up, the stellar make-up of our own immediate neighborhood. In other words, if you go out by a hundred light years, very close to the sun, what do you encounter, how much gas do you encounter, how many stars of different properties do you encounter, and also, if you add it all up, how much mass do you get per unit volume, per cubic parsec.
As far as the latter goes, we already know how much that should be roughly from certain dynamical arguments and we've been very interested over the last few years to see whether that, let me put it this way, over the last fifteen years there always seemed to be missing mass. In other words, that stars had to exist or gas that filled up this local neighborhood to the total masses that we knew existed, because the existing stars and gas, the known stars and gas didn't do it, didn't fill the bill. In this thesis that I mentioned from a student, Donald Weistrop, who is now at Kitt Peak, it looked indeed as if we had found the missing mass component as very faint, small…dwarfs of a fifth of a solar mass which appeared from her (his?) work to be much more numerous than we had ever thought in our neighborhood. Now in this recent study of fast moving stars, I used what, as I mentioned the V/VM method to get the local density of these stars and I think that it should be possible to even do this for stars in general.
So I have hope that in a few years we can attack the whole problem of the make-up of the Local Neighborhood anew and do a much better determination of what is called the Local Luminosity Function, how many stars with particular property per cubic parsec. It's a long standing problem in astronomy which actually goes all the way back, that problem, the Local Luminosity Function, to the Groningen School where I started after all. Van Rhijn, who was mostly sick when I was a student there, had succeeded Kapteyn who was a famous astronomer who once made a model of the Galaxy that in the 1920s was known as the Kapteyn Universe. He spent all his life trying to get the Luminosity Function in our Neighborhood. He spent practically all his life on it and did eminent work in it, but it never got entirely solved. Van Rhijn then spent his whole life on it. Even then remarkably enough, in my student's thesis about five years ago we managed to make a major addition to that work by Kapteyn and van Rhijn in the form of these dwarfs that they had, that somehow they had missed for reasons that are clear now. That had to do with the fact that you have to be able to work very faint, in order to see enough of them. That is what our 48 Schmidt telescope at Palomar succeeded in giving us. So I may be making a slow circle and I may be coming back to my forefathers or rather the original Dutch school of stellar statistics to which Oort also really belonged in the beginning, until he blossomed out into other things. Blaauw, whom I mentioned, also belonged. And by golly, I think I'm sort of returning slowly in that field which is a classical Dutch field of stellar statistics. But with new methods of course, it's now modern.
I have read that your leisure time interests include music and hiking.
Yes. Both I do too little. [laugh]
Would you care to elaborate on how you pursue these?
Yeah. I think I said already most about it, mainly I do too little. I play a little violin and I play a little piano but neither of them well enough to really be proud of. In fact, I play neither of them hardly at all anymore. Certainly the violin sounds terrible. You should keep up violin though, or not touch it. The hiking I, well the hiking I used to do in summer in the late 1940s in France and Switzerland. But here I've done less, but I still love to do it and usually here it's not mountain hikes but just sort of local in the foothills here with my children. So they're not hobbies that are really all consuming. In fact, I find that I'm spending less and less time on those things and more and more time on astronomy. It's really very, very bad! But somehow I find recently that astronomy is not tiring me very much, so I seem to be able to stand a lot of it. I know the real reason of that, I mean, the reason that I have a nice office here is because I do so much administration. But for that same reason I do practically no astronomy in the office at all anymore. So when I come home I take up my things and I start to work on astronomy and enjoy it. It's too bad I have to do it at nighttime, but it seems to happen to many people, eventually. They get locked up in administration. I'm doing much more of it than I wish to do.
I had a conversation with Robert Richardson, who you may know. He used to be on Mt. Wilson staff.
And he said that he felt that administration was, should be handled by a separate administrator and it takes too many very fine researchers away from their work.
That's, it is probably true to a degree, but so many of the things that have to be decided require quite a knowledge of the people and of the field and so on. I do have an able administrator downstairs and yet there is a lot that has to be done. In other words, I do nothing in the administration itself, you know, the books and so on nothing of that kind.
I guess maybe he was referring to an instance where this qualified researcher, who had to pick the shade of linoleum for the kitchen at Mt. Wilson.
Yeah. That certainly would be a shame. He seems to be writing children's books at the moment. Isn't that right?
On science or non-science?
I think both.
On both, yeah.
He seems to be very happy with that type of work.
Dr. Schmidt I certainly want to thank you for the time you've given me.
Oh we certainly went a little over, didn't we. [laugh]
I really appreciate you taking your time and it's been extremely interesting to me and I think it will be interesting to others also.
Thank you, and you are welcome.