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Interview of Allan Sandage by Alan Lightman on 1989 January 11, Niels Bohr Library & Archives, American Institute of Physics, College Park, MD USA, www.aip.org/history-programs/niels-bohr-library/oral-histories/33964
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Parental background; early interest in science and experience looking through friend's telescope in the fourth grade; feeling of compulsion as a child to go into science; sense of duty inherited from parents; early reading in science; pleasure of solving problems in science; education at Miami University and influential teachers there; experience in the Navy in 1944 and 1945; education at University of illinois; learning observational techniques from Robert Baker; getting into Caltech; attraction of the new 200-inch telescope; attraction of Edwin Hubble and Walter Baade; Sandage's intention of being an apprentice; Sandage's childhood feelings that the world was spirit and magic and the disappearance of those feelings upon entering Caltech; education at Caltech; equations became reality at Caltech; the mystery of science; Ph.D. work with Baade on finding and fitting main sequences in globular clusters; history of motives of work with Martin Schwarzschild on dating globular clusters; apprenticeship with Hubble on the 200-inch telescope; Sandage's later monopoly of the 200-inch after Hubble died; Sandage's feeling of responsibility to carry on Hubble's work; objections to the steady state model; learning about the big bang model; limits of Hubble's understanding of the big bang model; influence of theoretical papers by Mattig; influence of Fred Hoyle; introduction to and early attitude toward the horizon and flatness problems; change in cosmology from finding out what galaxies are like to how galaxies originated; Sandage's change in attitude toward the horizon problem; attitude tow.ard the grand unified theories; Sandage's gradual appreciation for the "new" cosmology, involving particle physics; change in attitude toward the flatness problem; attitude toward dark matter and missing mass; openess to the value of omega; problem of consistent ages in cosmology; many forms of evidence for the big bang model; reaction to de Lapparent, Geller, and Huchra's work on large- scale inhomogeneities and importance of similar work done earlier by Gregory, Thompson, Rood, Chincarini and Tifft; relation between theory and observation; science is not the discovery of absolute truth but only an approximation to reality; lack of good observations at the frontiers of science; the change in cosmology from asking only "where" and "what" to also asking "how;" outstanding problems in cosmology: dark matter and value of omega; ideal design of the universe; question of whether the universe has a point.
I want to start with your childhood and to ask you to tell me a little about your parents.
My father was raised on a farm in Iowa, and my mother was raised in a small farming town. My mother was born in the Philippines, of American parents. She had traveled across the Pacific six times before she was six years old. My grandfather on my mother's side was the Commissioner of Education in the Philippines, under President Harding at the time. He had spent 8 years there and came back to the U.S. with 3 daughters to Lamoni, Iowa to become president of Graceland College, which is the church school of the Reorganized Church of latter Day Saints. My father was one of four children who were raised on a farm by his father, who had not finished the eighth grade — that's my grandfather on my father's side. My father was the first in his family to go to what was called academy at that time, which is the equivalent of high school now" and then from academy to college. He went to Graceland College, and then on to the University of Iowa for a Ph.D. So he went from farming, on what was almost the western frontier in the 1910s, to a Ph.D. He married the daughter of the president of the college in Lamoni. He's still alive at the age of 87. I was raised in an academic atmosphere. My parents were connected with some university for all the time I was living at home.
Were either of your parents interested in science, either as a hobby or as part of their career?
Not in any serious way. They didn't know very much about science. My mother was trained in music and my father in economics and the theory of the free enterprise system. I became interested in science during a two-year period spent in Philadelphia when my father, on leave from Miami University in Oxford Ohio, was connected with the Census Bureau. I became interested because of a childhood friend (Bruce Olsen), who had a telescope. Upon looking through this telescope in the suburbs of Philadelphia, it became clear that I had to be an astronomer.
You think that that's when your interest began looking through this telescope?
Yes. No question. It happened overnight.
How old were you at this time?
I was in the fourth grade.
My daughter is in the third, so you must have been about 9 years old?
Yes, between nine and ten. Every weekend, I would go down to the Franklin Institute and to the planetarium. James Stokely, who was head of the Fels planetarium, was my early hero. That and the childhood friend [were the beginning of my interest in science]. I was always interested in numbers, but I didn't know much about mathematics at the time. I more or less learned science as a hobby after that, and it became a very strong passion. All of science became a great interest.
At this early age, when science grabbed you, was astronomy particularly strong in your interests?
Yes. My friend was primarily interested in astronomy, and he knew a tremendous amount. It was astronomy, rather than science in general, that occupied most of our projects.
Did you have any idea at that early age that you might want to become an astronomer?
Yes, I knew right then that that was what I had to do.
You say had to do.
Had to do.
Why do you say "had?"
Compelled. Out of a sense, not so much out of duty, but there was just nothing else that seemed as worthwhile. I have been fortunate in my life in knowing, in general, what I have had to do. Now, when the neighborhood children come to our house and I ask them what it is they want to do with their life, they have no compelling idea. Even through college, some of them have not yet found their goal, their vocation. I've never been in that state, yet it has not always been so comfortable to be so driven.
And you think you were driven at the age of nine?
Yes. It seemed required that I must learn everything about everything. Otherwise, I thought that I was not doing things properly. I felt guilty at not knowing.
You felt guilty?
It developed into a sense of duty, yet I can't tell you where that sense of duty has come from. I still have it as a requirement, something like a permit, to do research.
Do you think it came from your parents?
Yes, because it's in the chemistry. It must have come from my parents, in the 3 genes and therefore in my chemical makeup — not in the training, I think. There is this compulsion in other family members on my father's side. My father has it. Several of my cousins have it.
At this age, were there any books that you read about science or about astronomy that you can remember?
Yes, there were many popular books. I read a great deal. One was called The Romance of Astronomy. These were books for children. One was called The Stars for Sam. I expect that I still might have those two books. I was self-educated in astronomy. I never have taken undergraduate courses in astronomy. I read Baker's third edition of his textbook in astronomy when I was 11 or 12 and knew then what the harvest moon was like, why at some times during the year the ecliptic is much more steeply inclined to the equator than at others. Many of the celestial-sphere situations I had taught myself, from about the age of 9 or 10.
Before you went off to college, did you read any books that dealt with cosmology?
Yes, the books by Eddington, such as The Nature of the Physical World and Space, Time, and Gravity, but these were quite difficult at the time.
Edwin Hubble's Realm of the Nebulae?
No, I read that later. I had read that, however, before I went to Caltech. I read it at a moderately early age, but that moderately early age was 15 or 16, probably. I remember reading [James] Jeans, and I do remember reading about Rutherford and the splitting of the atom. I was in the science club in junior high school and would attempt to explain the nucleus of the atom to other members of the science club, but, of course, that is not particularly unusual.
You said you read The Realm of the Nebulae at 15 or 16. Did you have any preference for any particular cosmology at that time, or did you think about cosmology at all? Did you think about the universe as a whole?
No. I simply wanted to be a practical astronomer, not a cosmologist. I wanted to do proper motions and parallaxes and all that good stuff. I got thrown into cosmology quite by accident. I became Hubble's assistant by the circumstances of events, and the compulsion forced me, out of some sense of duty, to do the extragalactic distance scale after I was on my own. I suppose now that I would have rather done parallaxes, radial velocities, and proper-motions of stars. [Sandage laughs.] It would have been a lot less controversial. It would have been a smoother road to travel.
It might not have been as interesting.
Oh, I don't know. Somehow, the setting of a problem and solving it, of and by itself, is enjoyable — to develop the methods of solution and then to go and do it and then to write the paper. It doesn't quite matter what the subject is as long as the problem requires detail. It's getting the thing done. The value of the Hubble constant not being done, in other people's minds, is a thorn, although I think it's done, and I think we know the answer for sure. I also think we know why other people have gotten the wrong value. But the fact that the problem is controversial and not solved is not a happy situation — psychologically. I don't mind being wrong. But what is disturbing is to listen to presentations where I truly believe there are fatal flaws in the opposing argument, such as neglect of observational bias in the samples. You must have the same feeling in your work in globular clusters. You know the dynamics, and yet it must be disturbing to see conclusions being made from inadequate analysis.
Well, with globular clusters, the real systems are sufficiently complex that I'm not sure whether the simple dynamical models that have been worked out have enough realism to be applicable to the observations. So that's not really a clear-cut situation there.
I certainly feel the same way about determinations of the value of omega, but not about the value of H0, [the Hubble constant] or the distance to the local calibrators, for example.
Those are things that I would like to come back to later.
Tell me a little bit about your undergraduate education at the University of Illinois.
I first went to Miami University, where my father was on the faculty of the business school. Knowing I must become an astronomer, I started in physics and had a tremendous grounding there by the hard taskmaster, Professor Ray Edwards. He was the one-man physics department at Miami. He was so inspirational that something like 80 eventual Ph.D's went through his hands on their way to first class graduate programs throughout the country.
That is extraordinary.
Professor Edwards received the Oersted Medal of the American Physical Society, for outstanding teaching at the undergraduate level. I may have talked about him in an early interview with Spencer Weart some years ago.
You said some of this.
Another teacher of great influence was Professor Anderson of the mathematics department at Miami. These two men were good to me, but they demanded much. I did not have a naturally analytical mind [to which] things come easy. So I had to work hard to understand the material. I remember that I didn't understand calculus or differential equations until the next courses up. I expect that's normal for some, but many of my classmates had more native intuition and problem solving ability during those Miami years. Then the war came, and the two years away in 1944 and 1945 were crucial to the maturation process.
You were in the Navy?
In the Navy, yes. There I was in a situation that was difficult because it was practical- the repair of electronic gear. The training was to find something that was broken and to fix it under pressure. Many people in the program later became astronomers. Art Code was there for one, as was Albert Wilson (later to become the principal observer on the Palomar Sky Survey, and then a mathematician and cosmologist at the Rand Corporation).
When you then went back to the University of Illinois, were there any particularly influential experiences or people there?
Yes. I knew that I had to major in physics as an undergraduate. The pressure and the competition to complete the courses and to do well was strong. [My] analytical mechanics professor (Robert Becker) was important, as was [my] modern physics professor Gerard Kruger, and the professor of optics (Professor Almy). Robert Baker, the only astronomer at Illinois, permitted me to do a junior and senior thesis. He taught me observational techniques. Had I not had these experiences in real research, as a junior and senior — and I was happy beyond words in this work — if I hadn't been taught these techniques by Baker, I would not have reached Caltech with the experience that came to be crucial in later being sent up to the Mount Wilson offices and becoming Hubble's assistant at the age of 24. So everything worked in a linear chain. To get into Caltech, I went to see the head of the physics department at Illinois to ask him for a letter of recommendation. The department head was F. Wheeler Loomis, a very famous physicist who had made important contributions in electronics at the MIT radiation lab during the war. He hadn't a clue as to who I was, but he called for my transcript of grades and saw a good report. How I did that, I still don't know. Well, yes, I suppose I do know. It was the 70 hour weeks trying to solve the impossible problems. I sat in Loomis's office while he dictated a letter to Lee DuBridge — a letter of recommendation to admit me to Caltech. [Loomis] didn't know me from scratch, but I was in his department, he saw my record, and I suppose I looked enough beyond the pale to have a chance at Caltech.
And he dictated while you were sitting there?
Yes, while I was sitting there.
Professors don't do that too often, do they?
I suppose not. But he did then.
It's good that he only had good things to say about you. If you had had a few Bs and Cs on your transcript...
It would seem so. I applied in physics because there was no astronomy then at Caltech. But that was the year the astronomy department began, with Jesse Greenstein as the one-man department. I eventually got a letter from the admissions office at Caltech saying that I had been admitted in the first class in the new department of astronomy.
They must have known you had an interest in astronomy.
I had written a letter of application saying that I wanted to be an astronomer, and I was applying to CalTech to be associated with the new astronomy that was happening.
When you said the "new astronomy that was happening"...
Well, I knew [about] the 200-inch [telescope] and I knew that Mount Wilson was the greatest observatory in the world. I would expect you to say it was Harvard but...
Harvard didn't have a 100-inch telescope.
No, nor Edwin Hubble or Walter Baade. And they didn't have l of the spectroscopists.
You knew about Hubble then at that time.
Oh, I had read Realm of the Nebula, and it had gotten into the seed of my soul. Also, the 200-inch project had been common news since the 1930s, and I wanted desperately to be near that telescope.
But you say that you still wanted to do classical astronomy as opposed to cosmology?
I think that the grandness of the cosmological dream was something completely beyond me. I didn't think I was capable of working in that ephemeral realm. It was something that you did only after you had seen if you could succeed in Peoria somehow. You had to do an apprenticeship before you could enter the gates. But also, classical astronomy had the precision (then and still) that holds its own immense satisfaction. I yearn yet to have been a meridian circle astronomer working, for example, on the FK4.
It sounds like you took it seriously, though.
Oh, very seriously.
You took cosmology seriously.
It was like going to a cathedral. I had the feeling that the world was magic. I went to Caltech still feeling as I had as a child that the world was magic, and that it had enchantment. Everything I had looked at from the time I was a child was enchanting and I had to grab it somehow. Then I went to Caltech, and that was a very hard experience. The magic disappeared, in the understanding of what was required to do real research.
What do you mean when you say the "world was magic?" Can you tell me about that?
I can't. It's gone. But I can remember something of what the child did feel.
When I think of magic, I think of rabbits coming out of hats.
No. The world was spirit. I expect a great deal centered around the mystery of existence. I would go into the woods and see flowers and simply become overwhelmed. It was a continual experience of surprise, joy, and amazement that there is something rather than nothing. By magic, I suppose I mean mystery.
To see what there was.
Yes, although the day-by-day world of people was harder than the world of nature. I couldn't wait for night to come and for the stars to come out. I would stand in the backyard and look at the appropriate time and identify the stars as they became visible out of the twilight. It was like being, I suppose, in a sort of heaven. I can't explain it in words even today. I had that internal feeling about everything - about physics, about the way the world works, and about why we are.
You are referring to the natural world?
Yes, the natural world. The world of people was a world to be avoided because it was more difficult than the world of things.
I think that a lot of people who go into science do it for that reason.
It was not conscious. I simply had to go into science. Yet the apprenticeship that is required... When I finally went to Caltech and realized that to become an astronomer you had to become an analytical machine, it was something of a crushing blow.
This didn't jive with your poetic sense of the natural world?
You couldn't be an amateur and accomplish anything. Although that's not quite true, because at Illinois I took plates, and I measured them. I counted a million stars. I learned to solve the fundamental equation of stellar statistics to derive stellar densities. I knew how to do that from Bok's book on the distribution of stars in space. It was all apprenticeship, and it was still magic at Illinois. The pressure was my own; the competition was not so fierce. Caltech was considerably more difficult than I had imagined. And the magic disappeared. It became a requirement to do the apprenticeship, so as to qualify for a vocation.
Has the magic come back?
No. It never has. It is difficult after all these years to explain what it was as a child that I felt, but I know that after the first year at Caltech, my life fundamentally changed. The magic of existence was replaced by the mysteries in the text books. The childlike awe was replaced by the awe of the enormous complication and order of the world of physics that was to be learned.
It reminds me of what some people have said about reading poetry. When you analyze it too closely and you try to take a poem apart and try to understand its structure, you lose the poem.
Yes, that's a good analogy.
So you were learning these analytical techniques at Caltech, and somehow that made the poem disappear?
Yes and no. Something replaced the magic. By doing science in the Caltech way (I.e. in the problem solving curriculum of the physics tradition), the world, in fact, became more mystical, in the sense that the interconnection of all of physics with mathematics became so beautiful but also so difficult. Throwing everything into those years at Caltech, I came to believe that reality was the equations. Reality was the interconnection between them. At the deeper levels is where you get the connectivity, and it's quite a mystical experience, one that takes enormous preparation. A different kind of mysticism — much deeper than I had as a child. So this magic was replaced by mystic.
You said that although the magic never returned, this state of mysticism...
Became stronger and stronger.
That has remained?
It's not really mysticism in the way that word is generally used. There is only one solid way of doing solid science. You cannot do [science] in a mystical way, but only in a rationalistic, reductionist fashion. It is in the way that man has imposed a system on the world, called laws, and believes that he has some understanding. Yet there is no real understanding.
But this connection between nature and mathematics...
Why do differential equations describe the world? You give yourself a state now and you give yourself the first derivative and a recipe for, say, the second and third derivative, and then just with a Taylor series, you predict the next state. No one understands how the world knows to work like that, but it does. What is action-at-a-distance in Newtonian gravity? Or what is the curvature of space in Einstein’s alternate description of the gravitational force? One mystery has been traded for another, and yet we still do not understand. And take quantum mechanics - the modern way that the observer himself changes the situation is not our early intuitive notion of cause and effect. The philosophy of modern physics, in the sense I mean the word, is mystical. With its virtual states, non-empty vacuums, the universe created by a random fluctuation out of nothing, and so on, modern physics has become non-scientific in [terms of what] we would have considered scientific a hundred years ago.
Now you can't even give the position and the first derivative anymore.
And according to the views of Schrodinger, John Wheeler, and others, the situation depends upon whether you exist somehow. I took my first and only quantum mechanics under [Richard] Feynman. He was just inventing the path integral method. That's not the way to learn one's first course in quantum mechanics. I had had no undergraduate course in quantum mechanics, and so I could not adequately appreciate the new philosophy of QED. It was a matter of rote to do the Hamiltonians and the perturbation theory etc. It has been clarified in the last 15 or 20 years, to see the way that quantum mechanics shows the fantasy of reality.
The thing about Feynman... I was a graduate student at Caltech.
Goodness me! When?
I got my Ph.D. in 1974 with Kip Thorne.
Well, you must know what I'm talking about then concerning the mental state induced when the equations become the living thing. One begins to believe that they are the reality rather than being simply an ingenious invention of the human mind.
I know what you're talking about. I wanted to ask you about some of your work early in your career. In your work with [Martin] Schwarzschild in 1952, on dating globular clusters, do you remember the motivation for that work, as far as you personally were concerned?
Yes. I had done my Ph.D. research with [Walter] Baade, who had posed the following problem. He had not gotten the things he had expected in Andromeda (M31) with the first plates of the 200-inch. The magnitude and a half discrepancy in the level of the RR Lyrae variable stars (the story is in all of. the textbooks) was on his mind, and he then did not know whether the difference was in the absolute magnitude of the classical Cepheids or whether the RR-Lyrae star absolute magnitudes were wrong. So he said, "If we can go faint enough in a globular cluster and find the main sequence" — which he firmly believed was there but which had not been discovered — "and fit that main sequence to the nearby stars, we can determine the magnitude of the RR-Lyrae stars." That was the problem he posed for me for a Ph.D. thesis. So, when we had found the main sequences in M92 with Arp and Baum, and in M3, Schwarzschild came to Mount Wilson on one of his annual visits. I remember running up the stairs at the Mount Wilson offices where I was making the measurements — that is, Santa Barbara Street — and meeting Baade and Schwarzschild in the hall. I had the first diagram of the main sequence turnoff in the H-R diagram, and I showed this to Baade, and I blurted out to Schwarzschild, "See, observations are better than theory." A young person, shy as anything, volunteering that... Schwarzschild then invited me to come back to Princeton to work on an explanation that he had. He was doing non-homogeneous stellar models to attempt an understanding of red giant stars. It was his motivation to explain what happened in the H-R diagram after the Chandrasekhar-Schonberg limit, when a star has burned about 10% of its hydrogen into helium. This limit was already known in 1942.
Did either one of you think about getting ages at that time?
I don't think so at the beginning. The attempt was to see whether we could go through the barrier in the models, where no equilibrium configurations were known. I didn't know very much about [stellar] interiors then, and I learned from the work with Schwarzschild. [It was his motivation] to see whether he could push the calculations through the limit of homogeneous models that Chandrasekhar and Schonberg had developed, and he realized that a difference of mean molecular weight would cause the fitting of the core and the envelope to produce large envelopes. We knew that's what had to happen for stars to go off the main sequence, as the new globular cluster data had shown directly. The age came as a dividend of that. I can't remember exactly how that came about, but it kind of was a flash of insight that occurred within a week or so by fitting the' model turnoff with the observations. It suddenly fit, and we knew that we could identify the C-S limit with the globular cluster main sequence turn off and thereby date the cluster, knowing that 10% of the fuel had been burned at that stage.
I had wondered whether the age determination was motivated at all by the discrepancy between the geological age and the Hubble time.
No. The motivation was to explain with stable models how you could get stars to move off the main sequence and explain the globular cluster observations themselves. You know that up until that time, it was thought that a star moves 'Up the main sequence because it's entirely convective and mixed, and therefore there is no chemical inhomogeneity. Gamow, in his famous 1938 book The Birth and Death of the Sun, has the track of the sun going up the main sequence. Everyone thought that. It was really Schwarzschild's insight that led to the series of results that changed that idea. The three students and the one expert in numerical analysis who were involved with Schwarzschild were Oke, Rabinowitz, Richard Harm, and me. I just happened to come to Princeton at the right time. We all attempted to find the path of the stars off the main sequence instead of up it.
Let me ask you about your work on the 200-inch. When you were there in the early 1950s, you and a small number of people had a really unusual...
... monopoly on the most powerful tool in astronomy. Did that make you feel a sense of responsibility about what projects you should work on?
Absolutely. I was told what to work on in the first three years upon being sent up to Santa Barbara Street from Caltech to observe for Hubble. I had worked for Hubble in the summer of 1950 on bright, variable stars in M33, but then he fell ill with his first heart attack. Dr. Bowen then employed me to get the plates for him on his large Palomar program, just begun. After Hubble came back to the Mount Wilson offices in 1951, we would sit each week and he would tell me what to do. So, the first three years as a student, when I was the observer for Hubble, I was working to his direction at Palomar.
What about after that?
After that, I felt a tremendo.us responsibility to carry on with the distance-scale work. He had started that, and I was the observer and knew every step of the process that he had laid out. It was clear that to exploit Baade's discovery of the distance scale error, it was going to take 15 or 20 years, and I knew at the time that it was going to take that lo.ng. So, I said to myself, "This is what I have to do..." If it wasn't me, it wasn't going to get done at that period of time. There was no other telescope; there were only 12 people using it, and none of them had been involved with this projects. So I had to do it as a matter of responsibility. But I believe now that I was more interested in stellar evolution and following up the globular cluster work. The whole of the explanation of the H-R diagram seemed to fall into place in such a remarkable way in about three years, and that had been the center of my Ph.D. work. I then thought I knew how the H-R diagram came about, the explanation of the giants, the bifurcated luminosity function, etc. But, later on, the two subjects came together by necessity, because without evolution you canno.t understand the universe at large red shift. It was fortunate, again in a linear way, how everything was forced into the same stream that, until about 1955, had moved in two separate rivers. Hubble and Baade's fields had developed separately until it became evident that they had to merge.
Let me ask you, before we go on, about another project that you did. Do you remember during this period of time, in the early 1950s, whether you had a preference for any particular cosmological model?
It was very clear to me from the beginning that steady state was wrong. There was never a question in my mind, because having been a student of Baade's and then understanding the age dating of the globular clusters and the connection between globular clusters and elliptical galaxies; it was obvious that all galaxies were the same age in their oldest stellar content. And that could not be a steady state universe.
What about within the big bang theory? Did you have a preference for, say, open or closed or flat?
No, that was a matter of direct observation. At the time, I didn't deeply understand the theory of the Friedmann models, nor did many others who were connected directly with the observations. Humason, Slipher, Mayall, and probably Hubble did not entirely appreciate the details of the Friedmann models, the collapse above a critical density and the explicit (i.e. closed form) equations relating density to space curvature. Papers were never written explicitly as to what...
... qo was…
Yes, qo. It took me about ten years to understand, and out of that self-education of the models came the 1961 paper on the ability of the 200-inch to discriminate between cosmological models. I had taught myself cosmology out of Heckmann's book, called The Theory of Cosmology; there was a book called The Expansion of the Universe by Couderc, translated by Sedgwick — that held the key to many of the central ideas; and there was the wonderful book by Gamow called The Creation of the Universe. Out of those — I probably read them five or six times — I finally understood what the papers in the earlier journals were saying, and I put it together in the way that I could understand. It turns out that that's the way other people of my generation could understand it also. All I did was make explicit what an observer should know so as to do practical cosmology.
But you say that Hubble didn't appreciate all of this.
Well that I don't know for sure. He wrote nothing on the second order term [involving q0] that was explicit, that was spelled out. It was Heckmann and then Robertson who made the explicit series expansions, in 1942 and 1955.
Hubble said nothing to you?
Nothing concerning the theory or the implications of the redshift for the curvature of space.
When you started working on your program to determine qo, do you remember what the motivation was, or how you came to decide that was something you wanted to measure?
There were two crucial papers in 1958 and 1959 by Mattig, in Astronomische Nachrichten. Mattig was a student of Heckmann's, and Mattig later said that these were merely class exercises, but if you read those two papers, they are the first papers in the literature where the solution of the redshift-distance relation is given in closed form.
In closed form without a series expansion?
Without a series expansion. This was 1958. Hubble had died in 1953. Nobody McVittie, Robertson, Heckmann, Tolman — had put those equations in closed form. They were always in series expansions. Once you had the equations in closed form — the Mattig equations between luminosity, redshift, and q0 — then you saw the nature of what happened at the large redshifts. These two Mattig papers, I think, changed the subject of practical cosmology.
But couldn't you also see that in the series expansion? Couldn't you still see it up to z's [redshifts] of 0.3 or 0.4? You would still be able to measure a q0 possibly with a series expansion.
Not z of 3 or 4.
I said 0.3 and 0.4. Wouldn't you be able to still get q0 from a series expansion?
The equation that the space curvature is H20(2q0 - 1)?
Oh, that equation, of course, is an exact result.
I didn't know that equation until [Fred] Hoyle came over from England and gave a course to the students at Caltech while I was still a graduate student. Hoyle's understanding of everything and teaching it to the students was the cornerstone from which I then began to work. So it was not true that I taught myself entirely from the books. I had understood parts of Hoyle's lectures, and out of that then came the 1961 paper, distilled into a language of the observers.
You think that is when you decided that you wanted to determine q0?
Hubble had tried to find what he called the "deceleration," by the second order term in a series expansion, as he mentions in his Rhodes lecture, "Observational Approach to Cosmology" in 1938. However, if you read this in detail, it is evident that he has the sign wrong as to whether deceleration has occurred. But there the statement is made that by going to high enough redshifts, you're looking far enough back in time to permit a measurement of a deceleration. You see a change in the distance-reshift relation caused by a change in redshift, which can indicate either an acceleration or a deceleration. Hubble never really emphasized what the cosmic significance of the redshift was concerning a creation event. When [Milton] Humason would come down from the mountain with an ever larger redshift, there would be a press conference, in which Hubble was asked for the significance of the observations. He would simply say that they were trying to carry the [Hubble] law to as far as they could. He did not emphasize the time scale, nor did he talk about the curvature of space from the redshift measurement. He talked about the curvature of space from the galaxy counts — that he well understood, because in 1936 he had done the experimental geometry of whether the volumes increased more or less rapidly than r3. But he did not emphasize the dynamics that come directly from the Friedmann equation.
And you were turned on to all of that by Hoyle and Mattig?
Yes, and also by H.P. Robertson. He was my professor in mathematical physics. I couldn't have a better background for the problem that we later carried out. Baade was my thesis advisor; I worked for Hubble; H.P. Robertson was the leading theoretical cosmologist at the time.
I'm sorry for changing direction here, but I want to move to the recent present, the mid-1960s and on. Do you remember when you first heard about the horizon problem?
Only much later than probably everybody else had heard about it, and quite a bit later than it first appeared in the literature. I probably didn't hear about the horizon problem until five years ago.
When you did hear about it five years ago, how did you hear about it? Did you read about it, did someone talk to you about it?
I didn't go to meetings often. When Dicke stated the problem that parts of the universe could not communicate with each other, yet the 3 degree radiation is so uniform, I had not appreciated its significance until sometime later. The thrust for the distance-scale problem, which is a purely technical undertaking, was taking all my efforts and seemed far removed from the philosophical theory of flatness, etc. These subjects, which are now the modern cosmology, seemed at the time to be simply conjecture. I also thought that talking about such things was unusually speculative. When the grand unification idea came, there were some five years when statements like, "The universe can be made from nothing, from a vacuum fluctuation" appeared in papers in Nature. I thought this work was crazy. It was not the nuts and bolts type of cosmology that I grew up with these ideas were picked up again by a kind requiring the type of observations I could make that would be useful in measuring the Hubble constant, for example.
When you heard about the horizon problem five years ago...
Perhaps ten years ago would be closer.
You say you didn't pay much attention to it for a while.
You mean by the horizon problem the communication problem and the question of delta T over T in the microwave background?
Yes, the communications problem — that there are regions of the universe that appear to [have been] separated by more than [their horizon at the time that they achieved equal temperature].
And tell me what the significance of that is to an observer whose responsibility was to determine relative and absolute distances to galaxies?
I can't tell you what the significance is.
I didn't care at the time how galaxies were formed, because we knew that galaxies did form. And, as an astronomer, not a "new" cosmologist, it was crucial to study what galaxies were like, not how they were made. As an astronomer, I wanted to know how they can be used to mark the space, not how they are formed. I thought, until about five years ago, that cosmogony was the worst subject you could go into.
What happened five years ago?
It then dawned on me that ELS had something to say about the formation of galaxies.
Who is ELS?
Eggen, Lynden-Bell, and Sandage.
Then, when I was compelled in the 1970s and 1980s to add to the material on the velocities and chemical compositions of the stars in the galaxy to try to find out how the galaxy formed — simply to finish up that problem to a point that could be seen — I had to understand a bit about the collapse phases. I still think that there is a large separation between astronomers and astrophysicists who are trying to explain how it happened. I want to know, after it happened, what is it like now? So, in a sense, I was a geographer. Many cosmogonists, instead, are trying to understand why the continents did what they did. I was trying to find out what was on the continents. The difference between cosmology and cosmogony is that one accepts the universe; the other wants to know why and then how.
What is your view of the horizon problem today?
Now I think it's the most important problem in the Held. I have become a devotee of modern cosmology — the question of delta T over T; why you can't find the fluctuations. I am as worried as anybody at knowing that each galaxy is a little Friedmann universe and, having understood that from the point of view of the universe itself, that if you can't find these "fluctuations out of which the galaxies are supposed to have been made, then maybe the whole thing is wrong.
The whole big bang model? Do you mean more than the big bang model when you say the whole thing?
If one requires fluctuations to form galaxies out of gravity — and that seems to be what Laplace told us about the formation of the solar system, in what was once so speculative a theory, but of course the solar system was formed through a situation something like that — then we had better find with COBE [the cosmic background explorer satellite] the fluctuations, or one has a terrible problem. (The detection limit of COBE is expected to be at least 10 times fainter than the minimum fluctuation signal needed to make the galaxies.) I have become terribly interested now because of the quite beautiful grand unification [theories].
I was going to ask you specifically about the inflationary universe model.
Along the way, one must force oneself to understand the wonderful physics of quarks, gluons etc. While all this was going on at Caltech, I failed to heed [Murray] GellMann, to heed the very complicated eight-fold formalism and the working out of the hadron resonances. It seemed that once five or six fundamental particles began to proliferate, physics and astronomy got further and further apart. Cosmology at the telescope became practical, while physics, with its chromodynamics, had become speculative. I disappeared to the mountain and read very little of this business. [I had no] curiosity because I first thought it was too speculative. And only finally, very late, after reading Weinberg's book The First Three Minutes, did it seem to gel. Now [particle physics and modern physics] are so central to cosmology. This is the modern cosmology. Although I am still a nuts and bolts engineering cosmologist, I did begin to learn about that, and of course it's exciting and perhaps even convincing.
What is your opinion of the inflationary universe model?
I'm taken philosophically with [Robert] Dicke's original problem of the flatness. That seems more important than the horizon [problem], although they clearly are related. Why is q0 so close to 1/2 or omega so close to 1? I knew in 1961 that [the universe] comes out of the big bang with q0 equals 1/2, regardless what it develops into, and so this far away from [the big bang], why is it still so close to 1/2? Observations set limits between 0 and about 1, 1/2 being the exquisitely tuned, just flat, condition.
Do you remember when you first heard about the flatness problem?
Perhaps only about ten years ago. When did Dicke come out with it — 20 years ago?
He first posed it in 1969, in a little-read book that was not very widely known.
Mao Tse Tung's little red sayings. That's the way — I felt about that whole business then. One needed redshifts, distances, and number counts for a direct attack on the geometry, rather than a method that simply used Eddington's arm chair — so I thought at the time.
I guess it got more publicity when his article with [James] Peebles came out in the Einstein Centennial volume in 1979. When you first heard about the flatness problem, whenever it was, did you take it seriously?
No, not at all. I thought, "Omega has the value it has and philosophy doesn't make one wit. Let's go out and still try to measure it." [It was] philosophy, not physics, that omega has to be close to 1. It was the reasoning that then developed into the anthropic principle, and the fine-tuning problem. I didn't try to speculate back that way. Rather than speculate, it seemed to me that those with telescopes should try to see what is there, as a geographer, by direct measurement.
Do you still feel that way?
The beauty of omega equals one has been growing on me. I am trying to see whether I can reconcile the time scales as a test. Clearly the two time scales, one from the expansion age and the other from the age of the galaxy from stellar age dating, have to be determined independently. I know now what you are going to ask: Is my low value of the Hubble constant motivated by philosophy to make the time scales agree? No.
No, I wasn't going to ask you that. I was going to ask you about your saying that the idea of omega equals one has been growing on you.
As a beautiful [idea], because grand unification is so satisfying.
When you say grand unification, I assume that you mean the inflationary universe model as part of that.
Yes. But, of course, one can get flatness in other ways, such as an appropriate value of the cosmological constant.
If the idea of omega equals one has been growing on you, how do you reconcile that with the required factor of 10 more matter needed?
My thinking about dark matter has changed in the last three years. I thought that the evidence for dark matter was not at all proved, and certainly whenever I read that the rotation curves of galaxies are flat, showing dark matter, you're not going to find there the factor you need to close the universe. You need a factor of 100 [between visible matter and the amount of matter required by omega equals one]. There is not even a factor of 10 from the flat rotation curves (first discovered by Horace Babcock in his Ph.D. thesis using M31, in about 1938, but ignored and now uncredited). Interesting as they are, they are not relevant to the cosmological problem per se.
Yes, that doesn't give you enough.
Because the light gives you an omega of 0.01.
And the dark matter that is observed from rotation curves gives you an omega of 0.1.
So then you need another factor of 10. How do you feel about that other factor of 10?
I'm open on the problem now, and I guess I have been seduced in some way by going to the first CERN conference, and to an Erice conference of particle physicists and astronomers, where these things were married. That's where I began to take grand unification quite seriously.
You say you have gotten seduced by it?
Yes. It's so beautiful that you think it has to be true.
It is remarkable that an observer would find a theoretical idea so beautiful, that he is willing to accept it even when it [conflicts with the observations].
I haven't accepted it. I haven't rejected it. It does not conflict with observations if we require 100 times more matter than can be directly seen, but nevertheless feel via cluster dynamics, as Zwicky proposed. And we need not reject observations. The time scale argument permits a direct measurement of omega. We should keep an open mind and try to sharpen the observations until there can be no doubt.
The word you used was "seduced."
It is said that on the morning after seduction you feel awful.
Has the morning after come yet?
In cosmology? No, it's still the middle of the night. But, you see, physicists are the cleverest people in the world. Some people are going to spend their life trying to find this stuff by building detectors that can detect single high energy particles, for example Leo Stodolski, who was at the Erice Conference. He is using quantum detectors that are factors of thousands more sensitive. To spend one's life in this way takes faith in the things unseen.
And these [detectors] are to find some of the hypothesized particles that could [make up the missing mass]?
Yes. I sit listen to the theoreticians talk, and they're in a magic world. I want to think they are crazy. But science has gone far beyond string and sealing in believing in the reality of things unseen, rather than in the assurance of things simply hoped for. They have become Bishop Berkeleyites.
Do you think they're right?
There is no way for me to tell. The crucial thing is experiments.
Well, if experiments are the crucial things, then why are you willing to at least entertain this other factor of 10 of mass?
It's clear that the jury is out. Until recently, I thought for sure there was no way that omega could equal one on the time scale argument. Forget the arguments on the mass-to-light ratio because matter could be dark, but for the time scale, the universe feels all the matter. I don't believe the Hubble constant can go any lower than 40 [kilometers per second per megaparsec], and I was entirely convinced that the age of the globular clusters was at least 18 billion years. Then this fantastic discovery came that the oxygen does not track iron as the iron goes down in the oldest stars. I'm sure you know why this is. It's because the oxygen is made by explosive nucleo-synthesis in stars greater than 20 solar masses, in the very earliest star formation. That means that the initial mass function had to be peaked at 20 solar masses in the very early days of the galaxy. That's an amazing statement, but as an observer, that's a solid piece of evidence. Then, once you know that oxygen is overabundant relative to iron in the oldest stars, 250 times more abundant than iron, you realize that the ages calculated on the basis that the real metali city is due to iron are dead wrong. The ages have to be decreased at least by a factor of 1.25. That takes the age of the globular clusters and the halos of our galaxy down to about 13 billion years. We have only realized this in the last year. If then H0 = 42, 1/ H = 23 billion years, which is larger than the 14 billion year age of the universe by the magical factor 3/2 [corresponding to omega equals one and k = 0].
So that's already pretty close to omega equals one.
Yes, but only if the Hubble constant is low and if you're not willing to put the cosmological constant in. And I was taught not to [put the cosmological constant in], or, better, my psyche still says not to do it. But if you eventually have to do it, you will have to do it regardless of the psyche. [Cosmology] is not as satisfying as parallaxes and proper motions because it's too fuzzy. I heard George Smoot talk here yesterday, saying that five years ago at meetings such as this, you go to a cosmology session and there were not very many people, and everyone else thought that these were the way outs who weren't doing science. But cosmology has taken over astronomy and become respectable. Physicists now call themselves astronomers, which clearly makes them respectable despite their claim that 99% of the universe is unseen!
Do you agree with that?
And you were there at the modern beginning.
I was already old at the beginning, being a practical (i.e. an engineering) cosmologist. The subject has become respectable because of the detailed measurements of the cosmic background radiation. I should say something else. I didn't think that the discovery of the cosmic radiation was very important in proving the Friedmann model because we already knew that the universe had a beginning, based simply on the linear form of the Hubble law and the agreement of the time scales. What has struck me so clearly during the past 25 years is that three time scales agree within a factor of 2. Those are: [first], the [Ernest] Rutherford nucleosynthesis time. Rutherford had that already in 1909.
The geological dating?
No, the uranium half-life. The work was not concerned with geology, but with the age of the element; themselves.
[Second], the age of the globular clusters, and [third] the value of the Hubble constant. That we knew already in 1958 or so, and the time scale arguments were so strong, together with the linearity of the Hubble law, that there was no question concerning the validity of the evolutionary Friedmann model. The only velocity field that permitted a singularity was linear. We knew that the law was linear because of the major part of the early work at Palomar from 1950 to 1960. So, when the three degree radiation came and everybody thought that the discovery was the proof of the expansion, for me, the agreement of the three time scales had [already] been the proof that there surely was a creation event. Now, that argument is not convincing, and the three degree radiation is, of course, crucial. What has turned out to be so convincing is that [the cosmic background radiation] really is almost a black body, it's everywhere, and it shows the relative, large-scale motion of the galaxy, a motion that is the right order of magnitude for the random motions as we know them.
And it also gives us a number, [the cosmic temperature today].
Yes. But then Gamow, Alpher and Hermann had it all. Everything that has happened in intermediate cosmology — not grand unification but in that intermediate [epoch] — was in Alpher's Ph.D. thesis, and then it has all been rediscovered, as if it were new, as if Alpher, Herman, Gamow, and Follin had never worked. I think that makes this Gamow et ale creation such a fantastic story, supporting the ultra-modern cosmology of which grand unification is but the logical next step. Then also there is the calculation of the helium abundance. It all now has become physics instead of speculation. So, I suppose that's where the seduction came in.
Let me ask you about another recent discovery — that's the discovery of some of the large-scale structure by de Lapparent, Huchra and Geller.
They did not discover it.
I mean the lineage of work.
I guess somewhere around there. There has been a travesty of justice done in the reporting of the discovery of the voids and the bubbles and the sheets. The discovery was made by Gregory and Thompson, Rood, Chincarini and William Tifft.
The void in Bootes was discovered by [Robert] Kirshner, [Gus] Oemler, and Paul [Schechter] around that time too, wasn't it?
The Gregory and Thompson discovery was several years earlier than that, and they feel as badly about the rewrite of the history as Alpher and Herman feel about the similar neglect of their prediction of the three degree radiation.
I'm glad you said that.
Anyway, what is the question?
The question is — has this sequence of discoveries, beginning around 1980 onward, surprised you?
I guess it finally made my mind capitulate to their existence. By that I mean that the Shane-Wirtanen counts showing regions like in Hercules and Corona Borealis had hinted at [such large-scale voids and structures]. Then when the Peebles's map came showing the filaments, I tended not to believe that. Yes, this was the crucial thing that finally made me try to understand why Hubble had gotten 0.6 m in his log N(m) counts. Hubble did four central things, one of which was to show that the galaxy counts, log N(m), go as 0.6 m. That discovery showed homogeneity on the large scale. And his 1934 paper, which was one of the most elegant in science, showed that the galaxies were distributed [homogeneously]. For that [picture of a homogeneous universe] to collapse then, having been brought up essentially by Hubble, took all of this stuff we have just talked about.
Has it shaken you faith in the standard model at all?
The standard model is a good tangent model to reality. You still get 0.6 m at low redshifts, and the appropriate smaller number at large redshifts, if you integrate over a large enough solid angle. So on the small scale you have what [Harlow] Shapley always said — nonhomogeneity. On the large scale, you have what Hubble said. Tyson's counts and everybody else's counts is about 0.6 m.
You have mentioned the relationship between theory and observation a little bit so far, but I wanted to ask you how well do you think that theory and observation have worked together in the last ten or fifteen years in cosmology?
What kind of theory? Friedmann models?
Well, let's say the theory of galaxy formation or the theory of the early universe.
All right, cosmogony. The theory of the early universe, for example.
Okay. That subject had been rather devoid of anything in the old cosmology, except, of course, the expansion. [In the] old cosmology, you gave yourself the field of galaxies and asked what the motion of the universe was. For me, the most astounding fact in science is that the redshift exists and is linear with distance. That doesn't need very much theory to understand what that implies. When the Penrose theorem showed the requirement for a singularity, I said so what?
You already believed it.
I already believed it because a linear field is the only field that permits a singularity. You show that just by geometry. And the timescale argument. The timescale argument was so central to everything, plus the form of the law being linear, proved to me, without any theory, that the big bang was right. So, you asked earlier whether I ever thought there were two [viable] theories like steady-state [in addition to the big bang theory]. The steady-state was out from the beginning on two grounds: the grounds we just talked of, and the fact that all galaxies were the same age, via the evolution argument. Of course, both of those positions are now known to be fuzzy. At any given moment, you think you know something, but ten years later you know that foundation was less strong than assumed, and I'm sure that happens now. Science is not the thing I thought it should be as a child. It is not the discovery of absolute truth. I had thought that science was the way to find truth. Science is not the way to find truth, but only probable truth. You get only an approximation that always changes and there are no absolutes. That is an unusual thing to say for a pragmatist, and I suppose Newton's laws or Einstein's laws are as close to [truth] as we know. But you don't read a physics textbook written 300 years ago to learn about physics, and I expect that 100 years from now, you're not going to read the Astrophysical Journal to learn about astronomy. Science is the only self-correcting human institution, but it also is a process that progresses only by showing itself to be wrong. As a boy, I thought I was after absolute certainty in reality by going into science; now that belief has collapsed. What bothered me for some 10 or 15 years is now the reality that we live in a world that is continually doubtful, that we can never know fully, and whose existence is still a mystery. I am at peace with a world that is not absolute.
How do you reconcile that philosophy with your feeling that you really think you understand what the value of the Hubble constant is?
That's like asking "Do you know the value of the charge of an electron?" That's a measurement.
I see. So when you say that there is no absolute truth in science, you are talking about something deeper than just the values of things.
Oh much deeper — an understanding. There is no question that the charge of an electron is a number, to be sure, with a measuring error affixed.
And when you are talking about revisions of science, you mean ...
You mean in changing its understanding.
Its foundation, yes.
I think in the Weart interview you referred to a statement by [Hermann] Bondi saying that when there is a conflict between theory and observation, the observations are usually wrong. Do you believe that?
I do now. At the time, I thought it was the second most outrageous statement ever heard in science. I will tell you what the first is in a minute. I was still under the belief that observations are always right, that theory is much more suspect than good observations. But it is clear that there are hardly ever any good observations at the frontier, is the way I would say it now. Further, the statement should (and probably did) include the words "well established theory." Bondi's first most outrageous statement was "don't do anything today because you can do it so much better tomorrow."
Let me ask you about your view of the outstanding problems in cosmology today. I remember that in 1970 you wrote an article in Physics Today which had the title "Cosmology...
"The Search for Two Numbers."
Do you think that things have changed since then?
[Now] is the new cosmology. That was the old cosmology. That is when I didn't really care how the galaxies formed, and I didn't care how the chemical elements formed. I thought then that both were topics probably beyond the realm of science. Friedmann cosmology is still the search for two numbers, but the field has expanded to ask questions which I thought science was not permitted to ask. Of the three questions "where? what? and why?" I believed that science was only permitted to ask "where" and "what." The new cosmology is trying to ask, at the deepest levels, "why?" "Why is there matter?" Now the modern cosmologists have been terribly successful. What really was a revelation to me was the discovery of the W and Z intermediate vector bosons. I've asked people like [A.] De Rujula and John Ellis and 'others, were they surprised, and they say "Oh, no, it had to be there. It simply had to be there." I asked [Abdus] Salam that, and he said, "There is no question. The theory was just so beautiful, that if they hadn't found them, it was the experimenters who were wrong." So, they had such a foundational belief, just like my belief that steady state was wrong for reasons which were so strong to me.
What do you think are the outstanding problems in modern cosmology now?
Omega and the dark matter. That's been forced upon us by the beauty of the theory. So you see I have kind of changed from a pure observer, hoping to see the absolute, to a mystic believer in beauty. Does that make any sense?
Yes, it does.
It's called maturation, I suppose.
I want to end with a couple of philosophical questions. I'll have to ask you to put your natural scientific caution aside perhaps. If you could design the universe any way that you wanted to, how would you do it?
[Sandage laughs.] Do you ask everybody that?
If I were present at the creation, would I give the Creator better advice, and you are asking for that better advice?
Well, you don't have to give that answer.
That's posing your question in different words: what advice would I have given the Creator, or the creation? How would I like the creation to be different than it is?
I would like my DNA and RNA not to cause such chemistry in the brain to cause grief, in the attempt to answer the unanswerable. Not grief exactly. I would like to be more at peace with the world. Put differently, it's so hard to understand anything. What, in fact, is life? The mystery... I wouldn't want to destroy all the mystery, as we do in reductionist science. The greatest mystery is why there is something instead of nothing, and the greatest something is this thing we call life. I am entirely baffled by you and me. We were both there near the beginning. The atoms in our bodies were made then, yet their sum now, in a living thing, is greater than the whole. And we are extremely complicated. You ask how I would create the world differently. A better question would be, "What would you like to know in science?" I would like to understand the meaning of life. More to your point, perhaps, the universe is the only way it can be for us to exist. If that's true, to ask to create a different universe is to ask to enter into genocide. Now that's the anthropic principle, but the more I think about how everything is so finely tuned, [the more that principle makes sense]. Everything that you and I need to live is given to us on this earth. You go out to dinner, and you find everything you need and you need everything you find. Of course, you could say that if that weren't true, then we wouldn't be here in the first place. That's begging the question. Maybe the universe cannot be any different than it is now for us to exist. So my answer to your question would be that I wouldn't change a thing if I want to live and be the same as I am now.
Let me ask you one more question, which you have touched on in the last question. There is a place in Steve Weinberg's book The First Three Minutes, which you referred to earlier, where he says that "the more the universe seems comprehensible the more it also seems pointless."
I think that's a silly statement because the answer is not known. "Pointless?" The universe is so mysterious in being tuned the way it is that I am willing to keep the option open and not ask for an absolute answer, which, I suspect, can never be gotten anyway. I would not have said it this way 15 or 20 years ago, but to end up like Nietzsche, sitting by a window for 7 years rocking, not talking to anybody because of his nihilism, is not the way — even if we don't know the path. Nihilism finally ends up in insanity, at least in Nietzsche's case in Basel. To avoid that, I'm quite willing to believe there is a purpose. But it is a belief. Weinberg, in his sentence, also states a belief, and why he's driven to that is probably as complex as why I am driven to the opposite pole. But I am not willing to be a Nietzsche nihilist, because I think that is much more pointless.
I think that is a good place to end the interview.
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 Meeting of the American Astronomical Society, Boston, January 9-12, 1989
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 R.P. Kirshner, A. Oemler, Jr., P.L. Schechter, and S.A. Shectman, "A Million Cubic Megaparsec Void in Bootes?" Astrophysical Journal Letters, vol. 248, pg. L57 (1981)
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 See Ref. 7.
 A.R. Sandage, "Cosmology: A Search for Two Numbers," Physics Today, vol. 23, pg. 34 (1970)
 See Ref. 23., pg. 154