Interview with Arno A. Penzias


Arno A. Penzias, 1933-2024. Interviewed 23 January 1974 in Seattle, length of interview: 35 minutes.


Papers of Woodruff T. Sullivan III




Oral History


Sullivan, Woodruff T., III


Penzias, Arno A.


Original Format of Digital Item

Audio cassette tape


35 minutes

Interview Date


Interview Topics

His maser with Townes at Columbia (and Naval Research Laboratory). Early OH work; 3K background discovery (in detail), little on mm molecular lines, philosophy of Bell Labs vis-à-vis Jansky to Penzias.


The interview listed below was conducted as part of Sullivan's research for his book, Cosmic Noise: A History of Early Radio Astronomy (Cambridge University Press, 2009) and was transcribed for the NRAO Archives by TranscribeMe in 2023. The transcript was reviewed and edited/corrected by Paul A. Vanden Bout in 2024. Any notes of correction or clarification added in the 2024 reviewing/editing process have been included in brackets; places where we are uncertain about what was said are indicated with parentheses and a question mark, e.g. (?) or (possible text?). Sullivan's notes about each interview are available on Sullivan's interviewee Web page. During processing, full names of institutions and people were added in brackets when they first appear. We are grateful for the 2011 Herbert C. Pollock Award from Dudley Observatory which funded digitization of Sullivan's original cassette tapes.

Please bear in mind that: 1) This material is a transcript of the spoken word rather than a literary product; 2) An interview must be read with the awareness that different people's memories about an event will often differ, and that memories can change with time for many reasons, including subsequent experiences, interactions with others, and one's feelings about an event.


Working Files Series


Individuals Unit



Begin Tape30B

Sullivan 00:01

Okay, so talking with Arno Penzias at University of Washington on 23rd January '74. Now, you started, actually, at Columbia in radio astronomy. Is that--?

Penzias 00:13

Yeah, well, I started out in the Radiation Lab working for Charlie Townes in masers. And well, essentially, I worked in the Radiation Lab. I needed a thesis project. And Townes at that point had two fellows working on a 3 cm maser which was going to be used for radio astronomy. And he thought the next step would be 21 cm. And he offered me that project and I immediately did it, of course. The idea was to make a tunable maser to cover the redshifts. We were a little ambitious. Well, so I built this tunable 21 cm maser with a lot of other junk associated, took it down to NRL, and put it on their old 85 ft dish at Maryland Point, 84 ft I guess it was.

Sullivan 01:07

84. Yeah.

Penzias 01:08

And looked for hydrogen and clusters of galaxies. The project got sort of picked up by myself. The NRL guys really didn't have an idea of what they wanted to do with it. And got sort of indifferent results. It was very difficult to do. Ran out of antenna time.

Sullivan 01:23

Now, when is this? What year?

Penzias 01:25

This was finished in the end of 1960.

Sullivan 01:28

So, this was after Heeschen's research?

Penzias 01:31

Yes. I based this experiment, naively, on the 1958 Proceedings of the IRE article which said that there should be hydrogen clusters of galaxies. So, my thought was what I would just do is go make a survey of clusters. Because he was predicting 10 degrees for some clusters and others. And I thought that since I had this far tunable maser, I could make a survey, get a large number of these regions fairly quickly. Well, it turned out that the first one I looked at was the Coma Cluster. [?] result and didn't see anything. So, I called up Heeschen and he, much embarrassed, said, "Yes, there's nothing there." So, I said, "Well, in that case, what I will do is start with this most favorable cluster and set an upper limit." To my surprise, I found an extended source there at the red-shifted frequency. It turned out later that that was just a pair of unresolved galaxies, with a higher resolution antenna showed that there happened to be two galaxies with the same declination spaced by about half a minute of arc. So, the object looked like an extended source. And I originally attributed it to a line emission of some sort, but it turned out not to be the case. I only had a single-channel receiver.

Sullivan 02:39

This was the Coma?

Penzias 02:40

No, this was the Pegasus 1 cluster, which was his most favorable case. In the Coma Cluster, Heeschen had gotten a very good upper limit, and knew there was nothing there. Then I was a little dissatisfied with that experiment. So, I decided I would like to repeat it. And the easiest thing to do is to go to Bell Labs where they had this horn reflector antenna. And I could attach a maser to that very easily. They were set up for masers. I went there and rather than do that experiment, it turned out in the beginning, I did a few other things. And then the horn antenna was needed for satellite communication. So, I started out and did some OH line emission searches.

Sullivan 03:16

Excuse me now, but you were hired to do radio astronomy?

Penzias 03:19

I was hired by Bell Labs to do radio astronomy.

Sullivan 03:21

Had they done any in the few years before that?

Penzias 03:24

No. No, they hadn't had any radio astronomers there since Jansky. But since they had this horn antenna, and since they had this satellite communications capability, they thought one fellow like me would be all right, especially since I had a hardware major sort of background. I could fit in well into the other things they were doing.

Sullivan 03:40

What was the horn antenna for?

Penzias 03:41

That was built for the Echo Project. This is this 20 ft aperture horn reflector.

Sullivan 03:46

The satellite Echo?

Penzias 03:47

Yes, the Echo satellite, the Echo balloon. It was launched by NASA, and it was a propagation experiment transmission at 2390 MHz from JPL, and the receiver was at Holmdel. This horn reflector with a 20 ft aperture had a maser in it at 2390 MHz. I even used it a little bit and tried to make some continuum measurements of Andromeda with it, but it was kind of half-hearted. And at that point, they then decided to go to an active satellite at 4000 Megacycles, Telstar. And so that the antenna was then needed for the Telstar operation. And I moved to a very small, fixed antenna with which I attempted to-- which I looked for general OH emissions from the sky, which I didn't find.

Sullivan 04:32

This is now when?

Penzias 04:33

Well, I came to Bell Labs in 1961. And I did this work toward the end of '62 and into '63.

Sullivan 04:46

This is just before it was discovered in absorption?

Penzias 04:48

Yeah. In fact, I was talking to the absorption guys at the time, and we both thought, well, we'd get a nice upper limit with the two I'd gotten, this emission upper limit. And they were expecting to get an absorption upper limit.

Sullivan 05:00

You never did publish that, though, did you, that search?

Penzias 05:02

Yeah. That search was only published as an abstract in the Bulletin of the American Astronomical Society.

Sullivan 05:10

I see.

Penzias 05:12

Then what happened was, as soon as the absorption measurement was found, the people at Harvard wanted to get on and check it and do some other work. So, I took my rig off the place I had it and brought it up to Harvard. And we worked at OH for a while, and we worked on finding some of the features in the Galactic Center that the Australians had missed. And we did a few things. Then about that time, the Echo Project was sufficiently far along that I could get the 24 ft horn reflector again, and we converted it for radio astronomy. I knew that the best, or at least my idea was, that the best use for this equipment was 21 cm. Because after all, we could do very well in sensitivity and calibration, but we had a very small area. So, we wanted to look at extended sources. And the best extended sources were the hydrogen clouds in those days. So, but among the experiments we wanted to do was galactic continuum at 7 cm. We started out to make cuts across the galaxy to get incremental information about the galactic spectral index.

Sullivan 06:20

And that frequency is only because

Penzias 06:22

that was where the Telstar frequency 4080 MHz.

Sullivan 06:27

Why did they use a horn, by the way, instead of a dish for these satellites?

Penzias 06:29

Oh, because you had a cab … two things. One, the side lobe level was very much lower. So that you could get-- at that time, a typical prime focused parabola had a 25 degree antenna temperature, where this thing had maybe a 2 degree antenna temperature. And then secondly, the focus is in a large cabin. And the masers in those days had permanent magnets and were very bulky. You couldn't possibly keep them full of helium during operation. So that's why I went there, because that antenna was so well suited to maser work. So, to convert this to radio astronomy. I started out by building a cold load as a reference.

End Tape 30B, Begin Tape31A


Sullivan 00:00

Okay, this is continuing with Arno Penzias on 23rd January, '74.

Penzias 00:06

So, I built this cold load. The idea was that I would build something which had the electrical properties I wanted at first, and then I would worry about the cryogenics second. And it turned out that I ended up buying an enormous dewar, I think of five imperial gallons of helium to cool, but it worked, and it was a very nice thing. And, of course, in retrospect, I was very glad I did because it probably is the most accurate, or among the most accurate cold loads ever built. I think later on, when people were looking at microwave background, that I did it in part because it was one of the ways of measuring the-- I needed it for calibration purposes. I wanted to measure the system temperature very accurately. One of the projects we set for ourselves was to make a very accurate absolute flux measurement for Cas A at this wavelength.

Sullivan 00:56

I see.

Penzias 00:56

Again, the most accurate that anyone ever made. And there were several calibration methods, and one of them required a very precise knowledge of system temperature, which required two very precise termination temperatures, and so I overdid it, but I just built the best thing I could. In part, we were hardware sort of people. We wanted to just show other people how radio astronomy could be done if you really worked at it very-- there's not a question of doing anything very sensational, but just very, very carefully. Another thing we wanted to do, there was another experiment which we didn't want to use as cold load for, and that was we felt that we would-- when we did our Galactic spectral index work at 21 centimeters, there will be enough of a component perpendicular to the plane that we could make an absolute measurement. The best absolute measurement-- the highest frequency anyone had done one was 400 MHz, Shakeshaft and his coworkers. So, we thought, though, because people in the past have had troubles with horn reflectors, two other groups had used horn reflectors in the past and one was six GHz, where they found their residuum was sort of three degrees higher. That is, they measured the system temperature, and then they knew what the components were supposed to be, and the components turned out to be about 10% lower, which amounts to about three degrees or so, or a little-- and so they kind of buried this result. And another guy did the same thing for the Echo satellite at 2390 MHz and he, again, measured a system temperature which was two or three degrees higher than his components, but he said that his measurement error was 10%, and his knowledge of individual components was 10%, so the value is probably in between the two. And in fact, his result is in his paper, and I quote it, I think, in the memorial to George Gamow[?].

Sullivan 02:39


Penzias 02:40

I referred to that particular comment that he showed careful engineering.

Sullivan 02:44

What about the other one? Is there a published reference for--?

Penzias 02:46

That is a public reference in the proceedings, but they actually took their three degrees and buried it a little bit that is there were two groups that did this, and two guys will work on the antenna and two on the maser. And the antenna guys asked the maser people, essentially, "Well, how much could you be off?" and they said, "No more than one degree." All right. Then you get one and we get two degrees. And they said, well, maybe they're-- and then in their diagram, they have two degrees from the back lobes of the antenna, which adds up, and then they add up-- and they have the maser component that's one degree higher than they really thought it was to make it come out even. So, what happened, both those references to those papers are-- both those papers are referred to in our original 7 cm paper.

Sullivan 03:30

Oh, they are?

Penzias 03:30


Sullivan 03:30


Penzias 03:31

That was a problem, by the way, since in one case the residuum had been referred to and the other case had been buried. So, we were very careful in what we said about the two groups. We didn't want to-- of course, in their defense, in both cases, all they wanted to do was know what the system temperature was. They weren't out to do radio astronomy the way we were.

Sullivan 03:48

But maybe they really did have 10% error, so this may have been, coincidental also [crosstalk].

Penzias 03:50

Their errors I think were-- well, I think, in both cases, the errors were probably-- those were generous estimates on the errors. There really could be very much better. They had very good IF attenuators. I don't think they could be off by as much as 10% of half dB. They wouldn't have been offering anything like that.

Sullivan 04:07

By the way, you were saying, we now. Who is we working in this?

Penzias 04:10

Well, at this point, about the time I finished my OH work, Bob Wilson joined the Bell Labs. And he started helping me re-instrument the horn reflector for 4GC work. And he measured the gain of the antenna very carefully using a helicopter-borne source while I made the cold load. And we combined this tend to make the absolute flux measurements of Cas A. And we started a number of projects like the-- at 4GC, we took these cuts across the Galactic plane to get some idea of the spectral index. Well, since there were problems with the antenna, we felt that any residuum we got, that 21 cm would not be believed as becoming from the sky. So, I thought, at least, this was my idea, that we should really first do it at seven. We should really do a good job at 7 cm, and really make sure that we get a zero there. Because after all, we don't expect a Galactic contribution. So, we ended up being like the biologist who cures a control group with a more serious disease.

Sullivan 05:15

But no, you said you were interested in the spectrum of the Galactic radiation. You were going to combine your 7 and 21 cm data, or you were going to use [crosstalk]?

Penzias 05:23

Well, no, we wrote a paper. We wrote a paper on that. We combined it with a lot of other people's. The reason that was very good to do at 7 cm was we had three-quarters of a degree beam. And that turns out to be the same as the antenna that Westerhout used for his 21 cm survey. Also, the 90 ft by Wilson and Bolton at 960, and the Jodrell Bank antenna at 404. All had the same beam size. So, what we did was we took cuts across the plane with the same beam at places which was set to avoid discrete sources.  And that particular experiment on galactic spectral index is, in fact, the-- it may even be referred to-- if it isn't referred to in our first reference paper, it's certainly referred to in one of the others. It's in the ApJ in December of '66, I think.

Sullivan 06:13

But you were willing to combine with other measurements that hadn't been [crosstalk]?

Penzias 06:15

Yeah. sure. Oh, no, no, no. No, the 7 cm cuts across the plane were not absolute. They were relative. The absolute measurement we would make at 7 cm was merely to get a zero. It was not a question of combining with anything else. It was the thought that if we get a zero here, then that means the antenna is fine. We were in, some sense, trying to fix the antenna or checking the antenna, but we had an astronomical motivation. It had nothing to do with the satellite communication. Certainly, the satellite equipment had all been removed, and we had put in a switch in a cold load. And it was purely a radio astronomy receiver. You couldn't be able to do satellite imaging with it anymore.

Sullivan 06:51

[crosstalk], yeah.

Penzias 06:55

So then what happened was essentially very simple. We found the result starting in the fall of '64.

Sullivan 07:05

Maybe this is a good place to break off because it's--

Penzias 07:09

In the fall of 1964, when we hooked our entire receiver together, we found that the temperature from the sky that we were getting was indeed almost four degrees hotter than we had expected. Because, we, unlike the previous workers who were measuring the system temperature, in which any of the components in the system could cause the problem since we had a cold load right next to the antenna, one of the two ports of an extremely low loss switch, we knew that it had to be in the antenna or outside it. So, we couldn't exclude the antenna itself because it was possible that it was lost in the throat. One possible explanation was due to a pair of pigeons which used to come up into the throat and warm their feet. The throat of the antenna extended to a heated cab.

Sullivan 08:05

I see.

Penzias 08:05

And they stayed in this cab to warm their feet. But unfortunately, they didn't mind what they were stepping in because soon the entire throat of the cab was coated with a white dielectric material. We didn't do anything about that because we had calibrated the antenna in this condition, more or less, with the helicopter-borne source for the absolute flux measurement. Well, in about December of '64 or January '65, we finished with the absolute calibration, the absolute flux measurement. And so, then we took the antenna apart, we took the throat apart, captured the pigeons, mailed them off to Whippany. They flew back and we got rid of them permanently the second time. Cleaned out the antenna throat. And we found, in fact, that the temperature decreased from something under four degrees to something over three degrees.

Sullivan 09:00

Now the whole cleaning was to try to get rid of this four degrees or [crosstalk]?

Penzias 09:03

Yeah. Well, the point was to make sure that there wasn't a gap, there wasn't just some lossy gap in the throat section where sheets of aluminum, which then went down to a place where it was sort of bolted together with aluminum to finely machined pieces. And the thought was maybe one of those joints could have a 1% loss in it, which would account for the whole thing. Well, we checked that and it was all right. And then we took a very special-- it was a conductive tape that you put over the joints which makes them act just like pure aluminum. And that didn't change the loss at all. So, we thought there was no loss then at all in these joints and those were fine. Then we knew it was outside the antenna for sure. Other antennas like this had had their backlobes checked very carefully so we knew there was nothing in the far field. But we still were checking. And we decided to take a transmitter around the field in which this antenna was located and actually measured the near field loss to the ground. This was to make absolutely sure that no radiation from the ground could ever get in the antenna when the antenna was pointed up. And, indeed, that was the case. We did this at many different spaces. About this time, we had the problem of what to do with this result. And my inclination was to add it to this absolute flux measurement paper because--

Sullivan 10:20


Penzias 10:22

Yes, because papers, after all, can't be wrong if it has the right result in it. Then there can be something in the paper which is incorrect or is found afterwards. It's only when you write a paper on a subject which is completely nutty if you stick your neck out. On the other hand, we were sure of the result. We just didn't have any explanation. And we could just record the fact that we couldn't imagine it having solar system origin because we checked it for a whole year. We didn't think it was galactic in origin because it had no galactic dependence.

Sullivan 10:52

No dependence of anything in fact.

Penzias 10:54

Yeah. It was isotropic, unpolarized, and free from seasonal variation, as we said. So, we didn't know what it was and we assumed it could be some weird solar system effect that we didn't know about. But it didn't have a day-to-night variation, for example. But there was a high-altitude nuclear test that year and there might be some peculiar particle radiation that we knew nothing about. On the other hand, two different people had gotten their two other wavelengths so certainly, we had a very funny spectrum. We thought we knew the spectrum of radio sources. In those days, people didn't know about variable radio sources or [their ?] spectra very much. But we didn't think that the integrated sources could do it. So, we just didn't have an explanation. But that wasn't our job. Our job, we felt, was to measure things. And indeed, we had.

Sullivan 11:40

So even before you had the explanation, you knew about these previous experiments. You said--

Penzias 11:45

Oh, the other two measurements were both done at Bell Labs and of course we knew about them, people that worked with us.

Sullivan 11:50

So, you immediately said, "Well, they had it, but they didn't realize it." Yeah.

Penzias 11:53

Well, we knew that they-- well, the point was, of course, they hadn't, that is their errors were larger, their residuals were the same. There wasn't enough evidence to base it on the point was their residuals were the same and that was persuasive evidence that it was the same at all those frequencies. About three years earlier, I wrote a paper on a LaTeX citation, and I have a copy of it in the NEREM Record. You know what NEREM is?

Sullivan 12:13

Yeah. Yeah. I have a [crosstalk].

Penzias 12:14

And in the NEREM Record, I put in the excitation for OH. This was before I found the emission. And one of the things in there is the contribution of radiation. I said it's two degrees. And why did I say the radiation contribution was two degrees? Well, I was talking to George Field about OH excitation because he's done 21 cm excitation. And I said, "Well, look, George, we have two bits of evidence about what the radiation is. And one is that these experiments at Bell Labs, which come up with a couple of degrees high." And then the second thing is I saw this in Herzberg about the CN being high. And then the thing that really shocked me-- the thing that really shocks me now is that when I did the microwave background, I completely forgot that I had known about the CN business. And then I saw George Field in December of '66 just after he had published a paper talking about the CN excitation-- no, December of '65. Sorry, at Berkeley. December '65. And he said, "Oh, now I understood what you were talking about all those times." And of course, I had the opportunity I suppose if I could bribe enough other witnesses saying that I pursued the background radiation relentlessly for four years before I found it, but that wasn't the case. It's the watertight compartment of the line. You're just taking something else. And it never occurred to me that this CN was related to it because I didn't realize that the transition was actually within the black body spectrum. So, it was something. But it is interesting - George Field is a witness - that I was talking to him about CN excitation.

Penzias 13:59

And when Bob Dicke and I and someone else went up to see Pat Thaddeus, and Pat Thaddeus said to us, "There's another way of doing it." And I saw it was a copy of Herzberg over on another table. I felt like such an idiot. I just wanted to bang my head against the wall. I said, "Of course, I can show you the page." But by that time, of course, it'd be foolish for me to take it away from those people who, of course, had Nick Wolf, who thought of it. Lots of people thought of it. And George Field thought of it independently, apparently. But back to the basic idea. My understanding was that Bob Dicke, in looking at multiple bang Universe, gave people the job of seeing what sort of temperatures would be necessary in the condensed state to burn all the elements back to hydrogen, and then would there be an observable consequence. And Dicke's big contribution was to look for an observable consequence, to suggest an observable consequence. People went through this and found this relation that was well known to Gamow, Alpher, and Hermann. But there is a funny thing there, in that, when we say it's Gamow’s theory when papers were with his other workers, whereas in this case, the theory belongs to more people, I suppose. Not to take anything away from these experimenters, who are very clever and done pioneering and very important work in this area. But it seems kind of funny that people always mention this in the same way. The contributions were really very different. Roll and Wilkinson did an experimental job. Peebles had the theory, and Dicke basically had the idea. And the real contribution was the question of looking for observable consequences on Dicke's part. So that's all kind of merged together.

Sullivan 15:43

[crosstalk] I never thought of he just gave the statement.

Penzias 15:45

Well, he never thought it could be observed. The only one that did, Shücking in New York, told me that he once went to an observatory director and asked him if it could be measured because he had noticed an in some paper, other that people are measuring smaller antenna temperatures and radio sources or comparable ones or something. And the guy said, "No, because how would you point? Only if we could point away from it." Apparently, this particular guy didn't know about absolute measurements at all. But it was interesting that Shücking apparently thought of looking for observable consequences. In addition, a couple of guys in Russia, Novikov or Sunyaev or something, they're in Thaddeus’s review of the microwave background. He talks about those people.

Sullivan 16:33

Which review is that?

Penzias 16:34

There is something in Annual Reviews, volume 10, I think.

Sullivan 16:37


Penzias 16:39

Novikov or some such name I really don't know. So anyway, what happened about the time I was going to bury this result in another paper, I was mentioning my troubles to Bernie Burke, who said, "Oh, he had a preprint from some guy at Princeton who said there would be at least 10 degrees at X-Band. I said, "Well, if that could be 10 degrees at expand, it certainly can be 3 degrees at C-Band." I said, 3.5 by the way, the result was we got a result which was like 3.4, but I purposely rounded it off to 3.5 to give people a better feeling for the crudeness of the measurement. I tried to communicate something there. I think it always grates my teeth when people talk about the 2.68 degree fireball a little bit.

Sullivan 17:30

Implying it is close to -0.1.

Penzias 17:33

No. Whether it applies, it really-- it communicates as people had said 2.7 or 2.8 or 2.6 or whatever number it communicates a little less certainty than probably isn't even intended. There is an error, after all, which is quoted in all the papers. But when one puts it on a curve, of course, you don't and so it looks a lot more accurate than it really is. Personally, I like the name 3 degrees much better. And in fact, it may really be the-- a lot of measurements are really much higher than 2.7 or more accurate ones. The ones with higher claimed accuracy are a little lower, but there's a perfect lot of valid measurements of higher values.

Sullivan 18:18

But I don't quite know. Now Roll and Wilkinson, you haven't said exactly that they were set by--

Penzias 18:25

Then Dicke once-- as soon as people said predicted-- as soon as Peebles had predicted 10 degrees, Dickey thought this is an easy thing to measure, let's do it fast, let's not put a graduate student on it. We'll just take two PhDs to work very fast and do this in a few months. Well, they started working, and by the time-- it took them much longer to get started, and then by that time I had called Dicke, and then Roll and  Wilkinson were added to the paper because by that time we're very generous on Dickey's part they were part of his group after all. But the work was really Dicke and Peeble's.

Sullivan 18:58

But really it wasn't easy to measure. I mean--

Penzias 19:00

It wasn't easy.

Sullivan 19:02


Penzias 19:03

No. But 10 degrees is a lot easier to measure 3 degrees. You can measure it to a 3 degree error. A 2 or 3 degree error is not hard to do.

Sullivan 19:10

Okay, so on Dicke's ideas, it would have been easy to measure.

Penzias 19:15

Relatively easy, not enormously easy. But physicists think they can do these things fairly-- you don't understand the problems until you try it.

Sullivan 19:23

So that's how it came out to be a joint thing there.

Penzias 19:26

Well, it wasn't in the sense that then we decided to publish simultaneously because we didn't want to take any credit for the theory. In fact, there's no reference to the theory in our paper except to say that a possible explanation may be in the accompaning paper. But we were very careful not to take away anything from the Princeton people.

Sullivan 19:47

It's interesting to me that this happened at Bell Labs, which of course is where radio astronomy started. Do you have any thoughts on-- is that just a coincidence or--?

Penzias 19:56

It's hard to know. It has to do to some extent with the Bell Lab's mentality of wanting to do things very carefully. It probably has something to do-- it's certainly more than a coincidence, but I would have a hard time phrasing why I felt that way. That's what we were trying to do, after all, was make the most … that the cold load I made was supposed to be the best in the world, most accurate. And the Flex measurement was supposed to be the most accurate.

Sullivan 20:28

It was for the sake of accuracy, almost.

Penzias 20:31

Well, it was for the sake of uniqueness in that the Bell Labs was not in the business of doing radio astronomy, and isn't to this day, to some extent. And generally, what we try to do is work at universities where other people can't. That is, we only do things that other people are not likely to do. So, we do some far-out things or things that require a little more care, something to take advantage of our technology. Mostly, I think, in the case of the background measurement, there was a question of taking advantage of their antenna technology to make very careful radio astronomy measurements in the same way. In fact, Jansky worked in the same group that I did, as I mentioned to you. And that same group was doing radio measurements at a much longer wavelength.

Sullivan 21:25

[inaudible] in the '60s.

Penzias 21:28

Yeah, I was there in the '60s but I mean, the same group existed in the 1930s. A lot of the same people were still there. It's in the same place. This is the radio research department. The question comes up, I guess, in the attitude at Bell Laboratories, which is a researchy kind of thing, where people want complete answers. This is different from a place that requires research on some schedule that's a product that has to be turned out and you have to slap it together. Although there is some of that, too, that is, the people who are doing the system temperature satellite communication work, or they wrote it down carefully, did have less interest in pursuing it. Well, it did take the fact that there was enough time for them to hire a radio astronomer. I really don't know. I think maybe if Jansky had never been there, radio astronomy might not have occurred for them. Although it probably would have, because the guy who was running the places, Rudi Kompfner, was the type of person who liked science and liked things and knew about astronomy and radio astronomy. In fact, the way I heard about the job at Bell Labs was that Rudi Kompfner invited Charlie Townes and a group of his students down to see the place that we're building this antenna for all. It's a major group. You ought to know about it. And it's kind of a recruiting thing.

Sullivan 22:57

Yeah, that makes sense.

Penzias 22:59

Yeah. In fact, this is one of the reasons why we do radio astronomy. One of the other justifications is recruiting in the sense that people like to work in a place where more fundamental things are going on.

Sullivan 23:09

Yeah, now the molecules is past the end of mine when I'm just personally interested. Is that really the same sort of thing? Would you say that you have a technology that--?

Penzias 23:20

Well, we started out that way in the sense that we introduced millimeter astronomy as there was some-- excluding Gene Epstein, we provided the first millimeter mixers to NRAO when they built their 36 ft at 85 GHz. In fact, we left them there. We donated the mixers and then also through Charlie Burris's good offices, helped the fellow Mattauch from the University of Virginia build diodes so we could transfer the technology to them. In addition, what we were trying to do was exploit the technology ourselves for some radio astronomy things that we were interested in. And at the time, we did a little bit of continuum work but we weren't terribly interested in it. I'd been somewhat interested in molecule back from the days when I [threw away ?] but then I went ahead and said, "Well, this was a good opportunity again. We could build a millimeter line receiver and doing it in the RG 138 band, all three of the simple diatomics without hydrogen and CN all have the J=1-0 transition in that band and we can look for all three. And then by working at millimeter waves we could do a systematic study of molecules rather than a coincidental accidental lambda doubling transition or something that happens in other molecules, happened in the earlier molecules, because almost all molecules have a rotation spectrum called a millimeter. So, it seemed like an attractive enough project. We had the advantage of very good technology at Bell Labs. So, we just built such a thing and went out and did it. And just to say well, it has proven a little bit a lot of people decide to get into this just judging from the fact that when we started, we asked Dave Heeschen for two months on 36 ft. It just wasn't very heavily used. But now it's hard to get.

Sullivan 25:28

So now it appears to me that it's more of an ongoing program rather than it's not going to be like Jansky where there's a shot.

Penzias 25:35

Well, in Jansky's case well, the main thing was, since there was no university response in Jansky's case, that's the important thing. There is no customer. I think part of the thing is the feedback that since the work we do is appreciated by universities, the fact that I'm here giving the [inaudible]. It is the sort of thing that is a way that they can judge whether it's a good thing to do or not. It's very hard for someone to judge whether-- it's very hard for a manager, after all, to judge whether something is good or not. I mean, tenure committees and universities have to do somewhat the same thing. And in part, if it's a history department and they have only one sort of Marxist in the department, nobody else that knows anything much about that. What they have to do now is they want to see if the other guys who are publishing on Marx for this particular guy. And so, in the same way, these people at Bell Labs have to see if the astronomical community thinks the work is good either by copying it or talking about it or quoting it, then it seems reasonable work. And if it's good work and we can do it, then there's some justification for doing it.

Sullivan 26:47

Okay, well, thank you very much. Okay, we got it all done. That was the end of the interview with Arnold Penzias.



Papers of Woodruff T. Sullivan III, “Interview with Arno A. Penzias,” NRAO/AUI Archives, accessed July 20, 2024,