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Interview of Martin Schwarzschild by Bert Shapiro on 1977 September 27, Niels Bohr Library & Archives, American Institute of Physics, College Park, MD USA, www.aip.org/history-programs/niels-bohr-library/oral-histories/4869
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Discussion of Edwin Hubble in his later years; Hubble’s accomplishments and his wish to redo the deep count of galaxies on the 200-inch telescope. Schwarzschild’s relationship with Harlow Shapley and other astronomers (Walter Baade, Richard Tolman); work habits; Milton Humason. Thoughts on modern cosmology (astrophysics), quasar studies, the age of the universe (and erroneous estimates), the Big Bang, and an open versus a closed universe.
The circumstances under which you knew him and the, uh, uh… Did you have a project going with him?
I think it is rather important, uh, to emphasize at the outset that my getting acquainted with Hubble…
…was essentially in the later period of his life. In a certain way, uh, his life came to a magnificent climax with the publication of two or so papers. One, I think, by himself, if I remember right, or maybe Humason and, uh, as a collaborator, and one with Tallman. I do not, I’m very bad at remembering years, but I think it was around 1935 or 36 that those papers were published. I do not remember either the year of, uh, his book, which certainly is a milestone.
THE REALM OF THE NEBULAE?
That was…Well, uh the pocket edition was in 1935, so the first edition must have been earlier.
Right. It was approximately those years.
And the Sillman lectures at Yale University?
I see. I don’t remember that. I knew him much later. That is, essentially only when I started regularly every second year to spend half a year, mm, for a decade, at Pasadena, as a regular research opportunity as a Princeton professor. So that was starting essentially in ‘47, or actually I think ‘46 I went out for the first time. So, any of my comments regarding Hubble, uh, from a time in Hubble’s life which was not the time of the famous achievements.
The great period of the …
Yes. And therefore anything that might sound negative, uh, that I might say, uh, uh, about Hubble, it must be understood is not right in that period, not the very great one. Urn, one of the, um, characteristics of Hubble that somewhat surprised me and affected me personally to some degree was that the very big fight with Shapley he never could forgot. Neither could Shapley; since Shapley was, urn, for my personal life a magnificent figure in the sense that he found the means of giving me an opportunity to stay an astronomer since I had to leave Germany. He offered me a three-year post doctoral fellowship to come to Harvard. Quite irrespective of any other characteristics of Shapley’s, obviously my emotions were on his side, and the extremely violent attacks that I had to listen to from Hubble quite unprovoked I think for me, but if Hubble realizing, isn’t that right?
That you knew Shapley.
That I knew Shapley and that I had for entirely personal reasons, isn’t that right, a strong natural gratefulness to Shapley, were somewhat staggering that a man of that scientific size, uh, could not overcome, what must for both Shapley and Hubble have been apparently an extremely violent emotional experience and in their young years, isn’t that right, when emotions were up to high pitches. I tell this story to give a bit of a background why I might be a little improperly biased to Hubble in his later years.
Isn’t that right? Always with the emphasis that I really know nothing about Hubble in his great period. During those later years Hubble struck me to some extent as a, as a tragic figure. That might be a little overstated, but basically through the years that I knew him, urn, he seemed to be waiting for the completion of the 200” to redo — not that I could make out that much new ideas, but essentially redo much better and much deeper in space the same programs that he very much in collaboration with Humason, on whom he enormously depended on the observational side, urn, with the 200” after it was completed. The 200” got badly deferred in time, which for Hubble, of course, was really a tragic feature. In the meantime it also became clear that one piece on two periods of observations of his earlier work, namely the nebula counts as a function of their brightness, they are too inaccurate to be of, urn, pause, that important weight that Hubble initially and with him quite a number had expected from them. Indeed there came one extremely hard and critical decision, urn, time, when the 200” was just about going into operation It had to be decided whether Hubble was to be given nearly half the observing time from the 200” to repeat very deep counts of galaxies as a function of brightness. And for reasons that I do not know, Dr. Bowen, who was then the director of Mt. Wilson and Palomar, asked me to come to their afternoon meeting.
At that meeting, besides Dr. Bowen himself and of course Hubble, were invited Baade and Minkowski, both experts in related fields, but not in the specific field, and Tallman, the theoretician and very close and extremely fine friend of Hubble’s. I’m not that sure whether Humason was there, and I may not remember one more person or so, but it was a very small session. Actually I think in Hubble’s house, and the afternoon, the discussions were extremely difficult and the final decision was against Hubble getting the necessary, very large amount of 200” observing time for that program. I felt then, and ever since, that the decision was right, hut I truly realized that for Hubble this was an unbelievably hard afternoon, one in which he behaved extremely dignified. Mmm. I think that in my mind the hero of that, on the personal side, really treacherous afternoon, uh, was Tallman, who understood, uh, the reasons why, in fact, there was a severe doubt in everybody else’s mind of the value of repeating this major piece of observations. It was a question of achievable accuracy at that time being insufficient in the judgment of pretty wD11 everybody but Hubble.
The distribution of galaxies in deep space.
Yeah. The distance from us.
With distance from us.
Right, right, right. Um. And Tallman had that afternoon just understood how to put it in a way to Hubble so that it took some of the edge off and that Hubble could go through that afternoon, uh, uh etc. in a fine personal manner. That was impressive for me as by far the youngest of that group, uh, to see a man like Hubble being essentially defeated, but helped by a real great character, uh, namely Tallman, isn’t that right, a close friend, in these difficult circumstances. Pause. I have heard about Hubble’s observational skills in a somewhat negative way from various sources. In fact, the inaccuracies, particularly of this part of the early work of Hubble, I even then was taught uh, um, by a teacher in Germany, who understood both general relativity and the observational side very well, Professor Heckmann. In that sense I became somewhat prejudiced against that part of the work, not the Hubble diagram itself, which is of velocity distance relations, not rightly just the other cornerstone of Hubble’s work at that time. And also my wife and I became very good friends of Mr. Humason and his, uh, wife, and also we learned to know the, uh, uh, the professional photographer at Mt. Wilson very well personally, and to judge from them only second hand, Hubble’s art of photography was not the standards that ? or Humason had, and Baade, obviously. But Baade was just extremist; in a certain sense Humason too. Extreme of carefulness and beauty of photographic observations. Hubble came really with quite a different, uh…He was a very different man. In whole style is not right and the question of personal dignity played a big role. He was extremely attached to sort of the English style, even though to the best of my knowledge he had no English background himself. But the way he lived, his house, and all of it was of, mm, mm, of course in a sense very much more formal than certainly Baade and Minkowski, who had no touch of formality in them by nature, and Humason, who came from an extremely poor and completely uneducated background. You know, he had no schooling at all. So, for Hubble, I think, the collaboration with Humason was entirely decisive to achieve the scientific goals. But Humason could not make any contribution to the interpretation of the results, so I do not want to shift that achievement away from Hubble in any sense. Pause. I think that, uh…
…my main impressions as far as…
That was very tragic just that one incident, or other incidents that were…
As a matter of fact, you see, he did not live long enough to exploit the 200” in any other way, uh, uh, either, and in that sense somehow after the great results of the mid thirties, scientific life was sort of standing still. And there seemed very little natural drive, and then this one major decision, isn’t that right, made from then on obviously it must have from his emotional point of view made look the future very less bright.
How much time was he allotted on the instrument as opposed to half the time? What were the alternatives to half?
Well, the main point was that he got ample time for his other programs.
Yes, but, it was also…I do not remember that very well, but he was very much interested in what became the Hubble Atlas, that is to really document is not right, but modern means the Classification, what he had introduced prior to the mid thirties. Quite a number of projects, all of importance but not essential(?), uh, in nature.
I see. What do you think that his main objective would be distance in velocity out to greater and greater and greater distances? Was that not his main…?
That was one of the two major problems, exactly as ho had done with the 100”.
Only farther out. That were the two main programs, isn’t that right? The velocity distance one…
And the other one was the counts.
And both of these he was cut back…
No, no. No, no.
Just in the counts?
In the counts. But the counts were the ones that would take far larger observing time than the velocity. The velocity one everybody was enthusiastic about, there was no question about that. Still, when all is said and done, isn’t that right, Hubble is a man who had a great time in the purely scientific fruitfulness sense to a point, and then something like sort of standing back and waiting and being to some degree cut out.
Yes, and the reason he was waiting was for the 200” telescope.
That was my impression.
Your impression, and were there any other reasons that were… Was he running any other…
No. For example here he never participated, and that was really not his character, in the consequences of Baade’s discovery of stellar populations, isn’t that right, he was, he was not a man who easily teamed up, except with Humason, who started far, far inferior, isn’t that right, to him.
It was not a relationship of equals really in an intellectual sense.
No. Right, right. And there was no question in Humason’s mind…
Was he competitive with Baade at all?
It’s very hard to know. Not the two men, both great ones, in spite of the enormous difference in character and approach, did manage to keep on good terms, but to the best of my knowledge not in the sense of real scientific collaboration. But their styles were impossibly different.
Did Hubble ever discuss his objectives, uh…all one gets out of the scientific journals are distances and velocities, but as far as the implications, as far as the cosmological and religious implications, did he ever discuss those with you?
Did he ever discuss them with anybody else you knew of or…
I’m quite sure with Tallman.
I mean, I would be fantastically surprised, because they were so — they were much nearer in character and uh, and of course Tallman had the theoretical background with Hubble did not have. I mean, Tallman was really a first-class relativist. I would be very surprised if Hubble did not discuss these broad aspects, and Hubble was enormously aware of the…
Of the broad aspects. And yet there isn’t anything in his writing about it that one can…
Well but, at least as far as the possibility of general relativity not being right, isn’t that very explicit in, in his 1936 paper?
Uh, I don’t know. I’m not…I really don’t know. I meant not the broad aspects of the theory of relativity but the broad aspects of, uh, the theory about creation or about the religious, the spiritual religious implications. Did he ever discuss religion or spiritual implications of expansion.
Not with me, but I mean, in a way it would have been very surprising if he had because, uh, in his mind I was too much identified personally with Shapley, isn’t that right, which made it hard. Also my temperament is very different, isn’t that right. I don’t think I have any trace of formal dignity (laugh) in me and therefore…
What are your age differences?
My wife and I felt always ill at ease when we were at the Hubble’s house, and that was only a very few times. The whole style was just, you know, like being in an English nobleman’s castle, and not knowing the right people; I’m exaggerating obviously to bring the point out.
Yes, but that’s what other people have said exactly. What did Hubble say about Shapley specifically?
Oh, he accused him of, I mean in front of me, of straight dishonesty and real crookedness. And I don’t remember the details at all. It was so…
Did he say anything about him making capital of the fact that Hubble was away at war or something. There was one story like that, that when Hubble…
No, I don’t remember that. Of course, it’s quite true that their political aspects grow during World War II quite different also.
Shapley was much more progressive, and Hubble was more conservative?
If you want to put it that way, right, I mean for Shapley it was natural, isn’t that right, to worry about refugees like myself. I don’t think it would have struck Hubble as a natural activity.” And for Hubble it was very natural, isn’t that right, to go into direct active, uh, work for the army.
Yes. He also made statements for the press and made speeches in Pasadena about defending the English; the war effort, at least as far as his public statements are concerned, had to do with the war effort and supporting the English and the British.
That would fit. He was extremely English by…
Isn’t that inconsistent with his personality to stay away from public issues generally even though he was in favor of the English (laugh) and wanted to win his…
I think it is very…
…for isolation. There are a couple of other inconsistencies.
Yes, but on this particular I think for Hubble, instead of making speeches, to go to Aberdeen, to the ballistic laboratory and do his national service there, it seems to me entirely in character.
Yes. Oh, yes, but not the speeches and not the public statements. I have a lot of those collected from the newspapers.
And that, you know, because he leads a very isolated life.
So far as his science he kept to himself, his only collaborator was Humason, who was, he didn’t discover very much with obviously, except for technical details of the work, and yet on the issue of the war, and we can explain at least part of it, he was very…he made public statements, speeches, and uh, it seemed…
Excuse me, do you want to stop here? I think it was quite right, but as you described it in some sense as an inconsistency for Hubble to express himself so strongly about Shapley in the one instance that I…well, more than one instance, but only twice or three times, but he would become so sharp. But I think it was more that his idea was that of an English gen1eman. He had an underlying lively temperament, too…
Why for example was…
What do you think he held against Shapley really? What were his bones of contention?
I do not know the details, but they were both very aggressive, roughly contemporary, brilliant men. At the same time at the same observatory, isn’t that right, and it doesn’t mean to… That may be enough (laugh), isn’t that right, to make it impossible? I do not want to imply that I feel that Shapley was all that balanced about the early affairs here. To the end of his life he had a very severe grudge against indeed Mount Wilson as a whole. Have you any theories about the conflict? Is this between the East and the West Coast?
No, no. No, no. It was again an entirely personal.
From the time that Shapley was in, uh, in Mt. Wilson.
And you had no theories about it or suspicions or…
What it exactly was about I do not know and, I mean that, I’m not by heart a historian so I never went into it, but I’m not that sure you know whether the particular things that make two people with strong energies, isn’t that right, and marvelous capabilities, isn’t that right, as young brilliant stars, isn’t that right, collide, I think the particular causes are quite irrelevant. In the characteristics of the two working at the same observatory may be really much more the basis than any particular event, for all I know.
Yes. Uh, in doing a story about cosmology, we wanted to treat a story of cosmology that is an evolution of the subject matter, but there’s also an evolution in the approach.
Right. That is, pause, I think it may not be too exaggerated to say, and I’m hesitant saying anything because cosmology as a whole is not my field of expertness, but we might well describe what was understood and practiced as cosmology up to the early 40’s probably was essentially what Hubble described as cosmology. But it was straight Einsteinian relativity on the theoretical side and essentially the key work largely, but not only, initiated and done by Hubble and his immediate collaborator, particularly Humason. That means the direct study of galaxies and really their aggregate behavior in space, mainly through these two main tests: the velocity expansion and the number behavior: the counts. It was, I think, and I realize obviously very strong work, but, uh, only at the advent of Baade’s stellar populations and soon following with the theory of stellar evolution, new input scan, initially of course the fields of stellar populations and stellar evolution, they’re quite separate from cosmology. But these fields contributed reasonably fast two items that were of clear, feed to cosmology. One was the age determination of the older stars in our galaxy, with much fumbling and terribly wrong numbers, which I helped to produce at the beginning that slowly got corrected. And another one which in a sense sprung much more from Baade’s population discoveries but then got tied very soon into stellar evolution, and that is the discovery that the very oldest stars in our galaxy did not have anything like as much of the heavy elements in them as the younger stars, so that the possibility of starting our galaxy, which very well may be a typical one, with mostly hydrogen and deuterium and very little heavy elements, isn’t that right, arose, and that obviously would then be a condition that the cosmology had to fulfill. And that was something that then was picked up and with great vigor by Gamow and other people in the big bang. In the detailed, astrophysical part of the big bang.
So, that I think was the first big period of astrophysics entering and supplying from completely different areas of astrophysical thought, import and conditions, but cosmological theory had to apply. Then jumping again a big distance, obviously the discovery of variation background was a key milestone as an addition, as a matter of fact, to cosmology, providing one of the key, new items and most recently, you may have heard already from Dr. Oestreicher much more, where a question largely invented I think by Dr. Peebles, how much can we learn regarding the early phases of the universe from the present observed fact that the galaxies are not statistically distributed over the sky, but seem to be clumped in a very complicated but very interesting manner. This is an idea for which the observational material is quite old, indeed one of the major inputs came from Professor Shane, but there were earlier inputs, the Shapley-Ames catalogue of galaxies already had provided a beginning. But the idea, I think, is really only a very few years old, and the moment promises, has not yet to the best of my judgment, but promises to be a major new input, into cosmology. There we are back, using galaxies, isn’t that right, as the major entity, but studying something quite different than the main features that are, that Hubble studied in his cosmological work. For very broad steps…
… that is my picture of the development of cosmology, but does not say that any of the old features have been thrown out; particularly the question of the expansion by the velocity-distance relation and the precise calibration of that relation is still outstandingly important a question and a variety of new tools and astronomical objects are being used for it, but the character is not all that different from what Hubble did. On his second major part accounts, nobody has tried to repeat them again, and the quasars were invented, there was a furor of excitement of using that particular tool over again and in that case it failed abruptly. It took less than a decade to make it quite clear that the quasars had peculiarities of a type that made them even worse among galaxies, for that purpose, but these same characteristics make quasars extremely exciting from an astrophysical point of view.
Yes. There was another question about Hubble, if you don’t mind. Was Hubble troubled by his, uh, did he talk to you or did yo8 know that he was troubled by the, uh, age of the universe that was implicit in his constant, that his constant directed an age, or that if one used his constant that the age of the universe was therefore 1.8 billion years? Which was far less than the age of the oldest rocks, far less than the crust of the earth. Did that trouble him?
I do not remember…
That it troubled him and I’m not that sure it troubled any of us that hard, because I think from…it became…I mean…the uncomfortable part is that the, all the other age determinations, of which were age of the rocks and the earth; was one of the earliest, hut still on very unsafe grounds. As a matter of fact the accuracy since then has…and their, the thought basis of it has increased enormously, and we shouldn’t look at…even though the values haven’t changed all that much in that case, we shouldn’t look at it with a certainty with which we now look at it at that time, and other ages both coming from reactive isotopes and then coming later from stellar evolution. We all erred on the small side. Discrepancies were nothing like as bad as if you now took the original Hubble constant and its corresponding age and the present determinations coming for older items datable by radioactivity or the best estimates now available for the oldest stars in our galaxy. I mean that contrast never was there because the Hubble constant changed in the meantime. At the very beginning the oldest stars were, were only 3 billion years. Sandage and I published the first age, and it was that low, that long. So the discrepancy never was, I think, sufficiently striking for…we always worried a little about it, always kept it in mind and worked…but it never seemed that I can remember an obvious discrepancy. I…I know of no discussion…
With Hubble that would have…that he was more troubled than other people.
He did look back that way, though. He used the look back time in the same way that people are using it today.
Oh yes. No, there was no question that the interpretation was clear, and clear in his mind, but the discrepancy I don’t think, at least I am not aware of anybody — everybody always watched it very carefully and we discussed that at long length, it’s not right, but always I think most of us ended up by saying the uncertainties in all values are sufficient, but we don’t have to go to violent…
There is now described as a standard story of creation, called The Standard Story, uh, do you agree with this story and do you agree with the present age of being around 18 billion years? I mean, do you think there are enough certainties there to talk about it with confidence and with…or do you feel the uncertainties are still very great, so great that, uh, that the age of the universe is still a mystery, uh, that the story of an explosive beginnings is still a very tenuous one. What’s your confidence in those stories?
First with regard to the age, as either defined by the Hubble constant, or defined by, uh, isotropic abundance considerations, or defined by the oldest stars in our galaxy, all are of that same general order of magnitude. But having lived through so many erroneous estimates, I would rephrase your question, how big an uncertainty do I give? And I would, I would say that I would be surprised if it was a factor 2 off in both directions. But only surprised; I would not want to exclude that it might be as much as a factor 2 off. As I say, if it was that much off in either direction as a factor 2, but has half or twice, I would be surprised. So, if you ask me in that broad magnitude range fairly convinced, if you ask me, is it eighteen or fifteen, I would say nobody knows. And to regard the big bang theory as a beginning, the new data most importantly, the two items: radiation background and the lack of, the very small amount of heavy elements in the earliest born stars, I think has added to a theory which was well founded in general relativity long before these observations and discoveries. So in that sense, isn’t that right?
I think that raises the level of confidence in to that picture. But I would also like to say my level of confidence in the history of the universe from the point of the big bang till now may be fairly high. As to our predicting whether, how it will go in the future, or more specifically whether it is now an open or closed universe, that question, which is a very fundamental one both scientifically and philosophically, isn’t that right, I think is completely unsettled. That is, I don’t trust any correction.
Is that the largest and most exciting question open today then therefore?
I think from the overall point of view the question of open versus closed universe on the basis of general relativity, isn’t that right, provides a correct foundation, because only with that foundation is this a well-posed question. On that basis, I think for cosmology that is the most exciting open question.
There’s one thing…