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Credit: Haystack Observatory
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Interview of Alan E.E. Rogers by David Zierler on July 13, 2021,
Niels Bohr Library & Archives, American Institute of Physics,
College Park, MD USA,
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Interview with Alan Rogers, Research Affiliate and retired as Associate Director of the MIT Haystack Observatory. Rogers discusses his current work on the EDGES project and he suggests the possibility that this research will yield insights on the nature of dark energy. He recounts the circumstances of his birth in Rhodesia and the opportunities that led his family to the United States. Rogers discusses his education at MIT, his interest in radio astronomy, and his research under the direction of Alan Barrett. He narrates the origins of Very Long Baseline Interferometry and its application at the Haystack Observatory. Rogers explains geodesy and why the Mansfield Amendment changed the funding structure at Haystack. He describes becoming Associate Director of Haystack and how he became involved in cell phone infrastructure projects in the 1990s. Rogers explains how EDGES started, its value for measuring ozone concentrations, and he discusses his work for the Event Horizon Telescope. He explains his research contributions for the discovery of hydrogen in the early, cold universe and the value he places on the SRT telescope for educational purposes. At the end of the interview, Rogers explains his desire to expand understanding of low-frequency arrays, particularly in the SKA.
Okay. This is David Zierler, Oral Historian for the American Institute of Physics. It is July 13th, 2021. I am delighted to be here with Dr. Alan E.E. Rogers. Alan, it's so nice to see you. Thank you for joining me today.
Thank you, David, for inviting me. And I guess, thanks to Shep Doeleman for suggesting it.
That's right. Alan, to start, would you please tell me your title and institutional affiliation?
Well, my title really is just MIT Research Affiliate. I was, before I retired in 2006, an Associate director of MIT Haystack Observatory.
Alan, just as a snapshot in time, what are you currently working on, and more broadly, what is interesting to you in the field right now?
Well, I am working almost extensively on the EDGES project. I don't know if you know anything about that. It's basically a small antenna that we deploy in Western Australia. Western Australia, because we have to be in a radio quiet zone, and since we're operating in a frequency range which includes the FM radio band, we need to be in an area where the FM radio stations are very few and far between. Let's put it that way.
And what we're looking for is, in the early universe, you know you have the Big Bang, and the universe goes through this rapid expansion period. And of course, the temperatures are very, very high, and the particles eventually form atoms. The first atoms that are formed are primarily hydrogen atoms, and about 25% helium, and other atoms, but not the ones that we're made of. For example, deuterium is the next one in the abundance, and it isn't until the stars start to form that what we're made of, the other atoms -- oxygen, nitrogen and so on -- they're produced by stars. Well, before the stars actually form, this hydrogen gas emits radio signals -- either emits or absorbs radio signals.
In our case, we're looking at the absorption, if what we see is real. The absorption is of the cosmic microwave background, which I assume you've probably heard of, and is what's known as a spin transition of the hydrogen line, which has a rest frequency of 1,420 megahertz, or a wavelength of 21 centimeters. But because we're looking so far back in time, we're looking at a very large redshift. So, that frequency is moved all the way down, and again, if our observation is correct, what we see is the hydrogen line at around 80 megahertz, which is at the bottom end of the FM radio band. It's a very weak signal, so in order to detect it, we have to have a very, very well calibrated system. We claimed a detection and wrote a paper in Nature. The paper actually is led by Judd Bowman. Judd and I have been working on this for about ten years, really working on getting and building a system that is well enough calibrated to actually detect the signal.
To give you an idea of how weak the signal is, what we're seeing actually is a dip of half a degree kelvin. We're measuring signal strength in degrees kelvin. Half a kelvin out of the sky temperature at 80 megahertz is about 2,000 kelvin. So, it's a signal that's less than a thousandth of the signal from the sky. So, it's weak. What we claim to have detected is very exciting because if it's real, it's a marker. It really tells us when the first stars started to form. When this absorption goes away, as you go to higher frequencies, to lower redshifts, that's the time that the first stars form and when the first stars form the hydrogen is heated as it collapses into stars, and so now you don't see the hydrogen line in absorption as what's known as its spin temperature rises.
I should explain that a little bit. Hydrogen is made out of a proton and electron. It's the simplest possible atom. You can think of the proton and the electron as being like two little magnets. And you know, if you take two little magnets, they like to line up north-south. So, if you have them inverted the wrong way, they'll want to flip around to the lowest energy state. It's that energy difference that results in the frequency of 1,420 megahertz. It's what they call the spin flip transition. So, if the absorption we see is real, it is unexpected, not in redshift -- it's at about the expected redshift -- but it's a deeper absorption than expected for the current standard model of the cosmology. And what sets its strength has to do with the energy distributions between the upper and the lower level. If all those atoms were in the low-energy state, it would be a very strong absorption, but because the temperature is not absolute zero, the atoms are distributed between the two energy states, and that distribution depends on the temperature. The lower the temperature, the more atoms in the lower state, and the stronger the absorption. The absorption that we see would correspond to a temperature of about 3 kelvin, or maybe even a little bit lower, 2-3 kelvin, which is a factor of two lower than predicted from the standard model of cosmology.
So, if it's real, it could be completely new physics involving Dark energy and we don't really know what dark energy is. But it also could be just that the modeling of the evolution of the theory of the Big Bang, if you will, is not quite right somehow. And in fact, there is already at least one person who I think is fairly well-known, who's written a book, who does have an alternate model for the cosmology. But anyway, the important point, of course, is this has to be confirmed. And it's not an easy experiment to confirm because we've spent ten years developing not only what we think the right hardware is to do the job right, but also finding a good location, which has not only a low noise level, low signals from the various FM radio stations, but also has an infrastructure. This is the so-called MWA, or the Murchison Widefield Array. It's in Western Australia, north of Perth. And of course, it's also the area where they plan to have the low- frequency part of the SKA, the Square Kilometer Array. You've probably heard about that.
So, I personally am sort of a little bit on edge -- appropriate since it's called EDGES – because I keep wondering when and how this is going to get confirmed. Of course, especially with the COVID, plans, for example, for the Cambridge U.K. group to do something in South Africa are postponed. Given what's happening now with this new variant, I don't know when they'll be able to do anything. Furthermore, South Africa, to me, is a more difficult location. There are many more radio stations in that area than there are in this particular area in Western Australia. If confirmed, I think we have a very important result, and I'd like to make sure that our new equipment -- we have a new piece of equipment, which is different in that all the electronics is contained within the antenna itself. We feel, at least from tests we've done in the lab, that it's a little bit better calibrated. And it is different, but of course, we're not a different group. So, even if we get the same result—I should explain, we have gotten the same result from other versions of our original antenna. We started with an antenna that was about two meters long by one meter wide and one meter high, and we made it a little smaller, to what we called a mid-band antenna, and we still get the same result. And we've done things like changing the orientation of the antenna and done lots of different tests. But bear in mind, we're the same group, so we may be doing something wrong somewhere. So, another group has to confirm it.
That's great. Alan, a very general question about where the field is right now, especially in light of your interesting comment about there being something wrong with the Big Bang, where do you see observation leading theory in these cosmological and astrophysical questions, and where do you see theory leading observation?
Well, of course, the theory of the Big Bang does go back quite a long way. Although, I should comment that when I came as a student back in the '60s, it was continuous creation, and people hadn't accepted the Big Bang. Even though, the Big Bang, of course, had been proposed much, much earlier. I think, actually going back as far as the 1930s. Of course, as you know, Einstein was deeply involved. But now, over the years, of course, more and more data has been coming in, particularly in the optical range. Also, of course, the cosmic microwave background has been measured pretty well now from satellites. So, your question really is where do we stand? There are lots and lots of different observations now, most of which agree with the standard model at some level. Although, there are some discrepancies in the news. This is not an area that I know much about but I should mention that Fulvio Melia -- you can look him up -- he's just come out with a book. I just got my copy of Cosmic Spacetime a few months ago, and he has what's known as the Rh = ct model for the universe, which he and his group claim that the discrepancies fit a lot of the observations better. And it is a simpler model. Simpler, in the sense that it does not require this super expansion at the beginning, which is called the inflation that's right at the very beginning. So, it's simpler. But look, I'm not a theoretician. I am primarily an engineer, and I've spent most of my time really doing the best engineering I can. Of course, nowadays, with semiconductors and most of the pieces of the system that we engineer are basically commercially bought pieces, and so on. But some of the circuitry is designed and actually built especially for it. But others -- for example, we're using a high-powered computer. It's not specially made for our experiment, but of course, the software is all special to our experiment.
Well, Alan, let's take it all the way back to the beginning for you. Let's start first with your parents. Tell me about them.
Oh, well, I had wonderful, wonderful parents. I was born in 1941 in what used to be called Rhodesia. I don't know if you remember the history of colonialism, if you will, within Africa. So, I was born in Rhodesia, and the reason I was born in Rhodesia is that my dad joined the Royal Air Force in the 1930s and became a flying instructor. That was part of his primary job. In fact, he actually wrote a little manual for the Civil Air Guard, which became the Women's Air Force. And my mother was one of his students. He was teaching women how to fly. The reason for that was the women were very deeply involved in flying transport missions during World War II. They were not flying fighter aircraft. My dad was sent to Africa to start pilot training because the Royal Air Force realized they weren't going to have enough pilots if they just relied on those they were training in the U.K. so they were training pilots at many places around the world, and Rhodesia was one of those. So, my dad and mom got married just before they went off to Africa, and I was born there.
Well, that's the beginning of the story. You asked about my dad, primarily. Actually, my dad, in the 1930s, was working on radio systems in aircraft so that aircraft could navigate. He was an amazing engineer. In fact, he built his own satellite radio tracking station. In fact, up on my bookshelf here, I've got a book about James Van Allen, and in front of me I'm looking at a picture of James Van Allen with my dad. My dad built this tracking station in Africa, and my sisters ended up recording signals from the very early satellites. Eventually, he was invited to join James Van Allen's group in Iowa, and my dad was project manager on one of the relatively early satellites that were designed by James Van Allen's group at the University of Iowa.
I was actually the first to come to the U.S. I was born in Rhodesia but my dad was ordered back to the U.K., so I traveled with my mom and dad in the middle of World War II back to the U.K. Fortunately, we made it. The ship that took us back to the U.K. had with us some survivors of the torpedoing of the battleship Barham, who had ended up in Cape Town, and they needed to get back to the U.K. But then I went to my very early school in the U.K. and after the war my dad decided that we should go back to Africa so I went to Junior school and High school, and then on to university in Rhodesia. I got my bachelor's degree at what used to be called the University College of Rhodesia and Nyasaland. I have a very nice picture, which I wish I could show you, which shows that despite the fact that everybody thinks that Rhodesia was entirely European dominated, white dominated, this picture shows that 50% of us were white, and 50% were black, and 50% were men, and 50% were women. It was a picture taken of the entire university because the university wasn't that big, which I'm very proud of.
And then, I should also mention, while we're talking about this, that I was planning to go to grad school in the U.K., and I had applied but I hadn't heard back from them. In those days, I should probably mention that both my dad and I were HAM radio operators. We were very much into HAM radio, because we liked to talk to friends around the world, and that was pretty much the only way you could do it back then.
Alan, what was your citizenship status when you were born?
Well, personally, I had a Rhodesian passport, but of course, Rhodesia, at that time, was a British colony still. It wasn't independent. Rhodesia declared itself independent while I was here in the USA. I did have a Rhodesian passport which was not valid so after I got married here in the U.S., and we went on our honeymoon, I did not have a passport. I had a green card, so I traveled on my green card. Actually, on the way back, I wanted to visit the U.K., because my grandmother lived in the U.K., and I found that I could only do that by actually getting a British passport. So, then, I did actually have to get a British passport when I came back. But then, fairly shortly after that, I became an American citizen, and obtained my U.S. passport.
Alan, do you have any memories of World War II from the Rhodesian perspective?
Well, from the African perspective, I have some–how shall I put it? I was too young during World War II to have any direct memory, but of course, I heard a lot about World War II. A huge amount. For example, my aunt joined the military, and she ended up being sent to Africa to be a secret cipher operator in Kenya. She actually married somebody in the British military in Kenya during World War II, and she ended up staying in Africa. Actually, she's quite famous. Have you ever seen the movie Out of Africa?
Okay, well, she was the old dowager that got up on the table and shot off a couple of guns, and said, "God save the King," or something. Ann Palmer was her name. Actually, Ann Palmer was secretary of the East African Women's League, and she arranged for a women’s conference in Africa, and Jackie Onassis came along, among others. She was pretty well-known for promoting women, especially in Africa, because I think, even more so than the U.S., Africans did not give much to the women. As far as World War II, of course, Rhodesians both white and quite a number of blacks that also served in World War II. But I don't know the statistics there.
So, the things that I remember about Africa are more to do with my mother, how she used to help out so much with the local native community. If somebody got sick, she would drive them into the hospital in the capital in the middle of the night, and so on. I had applied to university in the U.K., and I had actually received a Beit Scholarship. If you were Rhodesian, you typically wouldn't be a Rhodes Scholar, even though the country was formed by Rhodes. You might be a Beit Scholar. Alfred Beit was an engineer who worked with Rhodes, and I did receive his scholarship.
But I ended up talking to a HAM friend in Massachusetts here -- Phil Carter is his name -- and Phil said, "Since you haven't heard from the U.K., why don't you consider coming to MIT?" He said MIT because he actually went to Harvard, but he knew that my wanting to get my higher degree in engineering, I would be much better off at MIT than I would be at Harvard. And I said to Phil, "Phil, how do I get to MIT?" He said, "Well, my next-door neighbor, Gene Chamberlain, is the foreign students admissions officer for MIT." So, there you go. I pulled those tremendous strings, and I did get into MIT thanks to Phil.
I much appreciated that scholarship which I probably should not have accepted because in Alfred Beit's will, it really wanted Beit Scholars to either go to South Africa or the U.K. for their higher degree. So, quite a few years ago now I completely repaid all my scholarship to the Beit trust, which was much appreciated. I did communicate back and forth with the Beit trust, I don't know how much you know about Rhodes Scholars and Beit Scholars, but both Rhodes and Beit bequeathed money that primarily became used to educate people. Especially, from my perspective, the Beit Trust has done so, so, so many wonderful things in Africa. A lot of Beit Scholars, most of whom nowadays, of course, are Black, have gone to the U.K. I don't know how many have come to the U.S. I think because of the will, probably most of them have ended up either in South Africa or the U.K. I did get a little bit worried about a week ago when I read something I wrote about ten years ago showing all these pictures of all the great things being done by Alfred Beit trust, and I thought, wow, I sure hope they don't take Alfred Beit's statue down. I know there's a big argument now about taking down Rhodes's statute, especially the one in Cape Town.
Alan, when did you first connect with Alan Barrett?
Very soon. I think it was only like two weeks after I was a grad student, because he gave a class on radio astronomy. He talked about his detection of the OH molecule -- that's oxygen and hydrogen -- which he had detected in the interstellar medium. He detected it at the Millstone antenna, which is just about 5000 feet over in that direction from where I'm sitting. And at the end of his class, he said, "I'm looking for volunteers to come help me with the observations." And I volunteered. Well, I wasn't a citizen and they were very kind. They let me into Millstone -- of course, I had a red badge and they accompanied me into the control room.
Alan, what was Barrett’s research at the time you connected with him? What was he working on?
Well, his research right at that particular point was to look for other molecules that might be in the interstellar medium. He was very interested in the composition of the interstellar medium and understanding the interstellar medium. And the detection of the spectral lines from the OH molecule were part of that research. Back in the ‘60s, radio astronomy was in the electrical engineering department of MIT, as opposed to the physics department. It was only when Bernie Burke came along – Bernie came and joined the physics department at MIT. And then radio astronomy shifted more towards the physics department. So, I was always keen on astronomy. We had an astronomy club at Prince Edward School. That was my high school. It wasn’t radio astronomy; it was optical astronomy. We built our own telescope, and I was a member of school’s astronomy club. So, when I had the opportunity, even though my intention at MIT was primarily engineering, I was strongly drawn to radio astronomy because it was both engineering and astronomy combined.
And how closely related was your own thesis research to what Barrett was doing?
Well, my master’s degree was directly related to what he was doing, because what Alan wanted me to do was to make some calculations to see if I could work out what the expected excitation – this is similar to when I talked about the hydrogen atom and talked about the spin temperature. When you talk about the OH, we tended to talk about the excitation temperature. That is, the excitation temperature is again related to the ratio of the number of molecules that are in the low-energy state, compared with those in the high-energy state. So, the OH that Alan had detected was in absorption, which suggested that more of the molecules had their energy state for this particular transition, which was at a frequency of 1,667 megahertz along with other transitions at 1612, 1665, and 1720 megahertz. It suggested that most of the molecules were in the low-energy state for those spectral lines.
So, in order to calculate what you might expect, you needed to model the collisions that hydrogen would have with other particles. So, calculating the excitation temperature was my master's thesis. And then, when I went on to do my PhD, that was because a group in California had discovered that not only were the OH spectral lines in absorption, but some up there were in emission. But not just straight emission. They were in an extremely intense emission, as if they were a naturally occurring maser. And when this discovery was made, people like me, and Jim Moran, and a few other people, were speculating, well, maybe these are signals from extraterrestrials. How on earth do you make these signals to make them so strong?
But it was eventually shown that, in fact, they are naturally occurring masers, that occur under certain conditions that are what, in that field, you call pumping conditions. Other radiation that will come in and pump those molecules to put them into that higher energy state. And once there are more of them in the high-energy state than there are in the low-energy state, then you get this maser interaction. The key thing then was to try to understand physically, where these masers, these strong signals, are. And in order to do that, that was what I worked on primarily with other people here at Haystack to do interferometry in order to be able to locate, resolve, where they were in the sky, accurately. That eventually actually ended up, for us, doing very long baseline interferometry on these OH lines. I don't know if you know what VLBI is. Very Long Baseline Interferometry.
I do, yes.
Oh, okay. Well, of course, you know about the black hole and so on. Well, there were several groups in those early days. There was a group in the U.K.; there was a group in Canada; there was a group here at Haystack; there was a group at NRAO in Charlottesville, or Green Bank, I should say, probably. They all had developed and did some very long baseline interferometry. The Haystack group, of which I was a member, did the very first Very Long Baseline Interferometry on the OH emission, as opposed to the other groups which did the VLBI on quasars. Of course, later on, as I was telling you, when Shep Doeleman came along, not only on quasars, but on the center of the galaxy. Which, in a sense, is like a quasar, because there's a black hole at the center of our galaxy, and it's the black hole that's at the center of galaxies that are known as quasars. But these are much bigger black holes. Bigger, in terms of the number of solar masses in the black hole. And of course, much, much more powerful. For example, the EHT, which they got their first exciting results on M-87, which is a very strong quasar.
Alan, I'm curious how you saw your thesis research -- either at the time, or retrospectively -- how your interests fed into some of the broader questions in the field at that point.
Well, to be honest, for me personally, it started my interest in geophysics. The reason it did, primarily, was that when I was a student back in Africa as an undergraduate, I worked on a group of researchers during vacations primarily. They were doing something called paleomagnetism. With paleomagnetism, what you do is you go out and you find rocks and drill and make a core of that rock. And then, you spin that rock, and you measure the magnetic field in the rock. because the rock is magnetized, it generates electric fields in coils around the rock while spinning, and you use the induced voltages to measure the direction of magnetism in the rock. If you know where the rock came from, then what you can do is you can make a plot for a given age of rock of where that magnetism would predict where the north magnetic pole of the Earth would be.
And when the people in the paleomagnetic research area did this, they discovered that the continents moved, because they found that when they looked at rocks of the same age in different continents, they realized they would have to predict the same position for the north magnetic pole. So, the paleomagnetic group had come up with a very clear indication that the continents had moved. And when I came to the U.S. as a student, I mentioned this to several people, and they said, "No, there's absolutely no way. The continents can't move. You know they don't move." So, when VLBI came along, and Irwin Shapiro came and guided us, we realized the most important thing we could do would be to do highly accurate measurements of the Earth to see if continents do, in fact, move. And we did, eventually. The group, led primarily by Irwin Shapiro, showed that yes, indeed, the continents do move, and they're moving now.
So, using VLBI for earth physics, from my perspective at that time, was the thing that I was most interested in. And of course, it tied in with the paleomagnetic group, because when I received some kind of an award -- now I'm not sure I remember which one it was -- a member of that paleomagnetic group was actually there, and said, "Great, all that work you did --" because I had actually built part of the electronics that went with what they called the spinner magnetometer.
So, as the rock spun, it generated this magnetic field, and I had developed electronics to go with that device. That was my student project. This was, of course, in Africa as an undergraduate. This wasn't part of a master's or PhD. I wasn't really a big contributor. It was just that I happened to be into the electronics, and they needed somebody to work out the electronics of the spinner magnetometer.
Besides Barrett, who else was on your thesis committee?
That's a very good question. I think David Staelin who had been one of Barrett's first students might have been on the committee as well. You know, I don't remember. You know, you only see the committee when you actually present your thesis. Maybe MIT has a record of that somewhere. I'm trying to think who else would have been on that. Maybe a physics professor, but I can't really pull a name right now, to be honest. Sorry. That's what happens when you get up close to 80.
What were your decisions and opportunities to remain at MIT after your thesis research?
Well, you see, I was already effectively -- because I did my thesis work out here, the first interferometer we built out here actually was between Haystack and Millstone. And actually, for me, that was also done for radar. Radar interferometry, and the mapping of Venus. So, I was already here. I basically went from being a student doing a thesis out here at Haystack to becoming a staff member of MIT Lincoln Lab. It sort of happened naturally. I never had an MIT campus appointment other than being an electronics lab assistant helping MIT undergraduates for a while. I was a student at MIT, a thesis student working out here at Haystack, as many thesis students did. They didn't necessarily do their thesis work on campus. I did my thesis work here, and then after I finished my thesis in 1968, I basically just stayed on as a member of Haystack staff so there must have been a formal transition at some point when I was being paid by MIT Lincoln Lab.
And then in 1969 the year of the Mansfield amendment, when it was realized that only research out here could be funded by Lincoln Laboratory if it was defense related our former director, Paul Sebring, who passed away fairly recently, obtained support for the astronomy staff from MIT directly. Paul had formed an organization called NEROC, the Northeast Radio Observatory Corporation, which gathered together the local university community here, interested in radio astronomy, to apply to the National Science Foundation for funding for radio astronomy out here. Because prior to the Mansfield amendment, Lincoln Lab had some extra funds which they were allowed to spend on non-defense related items. At that point, my salary came from MIT, as opposed to Lincoln Lab.
Alan, I'm curious, in the late 1960s, with all of the protests about the Vietnam War, and specifically, concerns about the Defense Department's relations with university research, specifically Lincoln Labs, if you got involved in any of that, or thought about those issues at all.
I registered for the DRAFT in late October 1967 like all the other students, many of them got called up. But there was an age thing. I was just over 26 so I didn’t get “called up.” Does that resonate with you?
I certainly would have gone but I was just a little bit too old to go. I was just so fortunate always to be sort of in the right place at the right time. For example, me and my parents got on that ship to go from Africa back to the U.K., and it just happened to be just exactly almost at the same time that the women at Bletchley Park had started to decode the messages going to the submarines, and so the British realized that they shouldn’t put their ships in a convoy. They should keep them out of the convoy, which we did. So, we made it all the way back to the U.K. without being torpedoed. Then, of course, somehow, I got to talk to Phil Carter and Gene Chamberlain, and got into MIT. It has just been – amazing to me that I’ve been so fortunate to be, I guess, in the right place at the right time. Very, very fortunate.
What was your initial title when you joined Haystack in 1968?
That’s a very good question. I went from a research assistant position as a student with a S.M. degree to a Senior Research Scientist when I received my Ph.D.
It was not a postdoc. It was a full-time position.
No. I was actually never a postdoc. I still have a Lincoln badge, and – I’m still associated with Lincoln in some sense in that I had been involved in doing something called holography. What happened here at Haystack, the original antenna was designed for eight gigahertz. Actually, we managed over the years by making adjustments to it to get it to work at higher and higher frequencies. But then, there became a point when the defense community wanted to go to higher frequencies, and they decided they were going to replace the whole Haystack antenna with a new antenna. With the old antenna, I had helped developed something called holography, where what we would do is we would look at a TV satellite with the antenna, and we would scan the beam back and forth making a grid on the satellite position. And we would have a small reference antenna. We would use that to make a map of the antenna beam that not only contained the amplitude of the beam, but also the phase of the beam. And from that, we were able to determine by Fourier transforming the deviations in the surface of the antenna. And that’s what allowed us to keep improving the antenna by adjusting it. When the new antenna was installed, they started to do a similar thing, but trying to do it with lasers. That didn't work out, so they asked me to get involved to do it with the radio technique using a TV satellite. So, that holography was used to adjust the new antenna.
Alan, what were some of the early technical challenges in developing VLBI technology, Very Long Baseline Interferometry?
Well, the big technical challenge was getting a good enough quality of what we call the local oscillator. When you build an interferometer at least for the high frequencies we were going to do the interferometry -- let's say, doing it for example at a frequency of 8 gigahertz, we would have to convert that 8 gigahertz down to a lower frequency so that we could actually record the signal, in those days, on magnetic tape. We couldn't record an 8 gigahertz signal on magnetic tape. There was just no way you could do that. So, we would convert the frequency down to a lower frequency where it could be recorded.
In VLBI, you have to record the signals from each antenna, and then you bring the data together, and you cross correlate it in software. But in order to down convert the signal, you have to have a very precise local oscillator, and the frequency of that has to be extremely accurate. It has to be accurate to better than parts in 10^12, because if it isn't, the data that you get from one antenna will not correlate with the data from the other antenna, because they'll be mismatched. And in order to get that very high-quality local oscillator, what you have to do is to start with a frequency that comes from an atomic clock. That atomic clock has to be a very good atomic clock. Typically, what we use is a hydrogen maser atomic clock, which generates a very precise frequency, and also a very stable frequency.
So, one of the big technical challenges was to get the very best conversion, if you will, or synthesis might be a better word, of the 10-megahertz reference frequency that came from the hydrogen maser to the higher frequency which would be used to do the down conversion. So, that was a challenge, and in fact, especially at the much higher frequency -- so, when Shep Doeleman and I, for example, went out to try to get other antennas to work well at 3 millimeters, frequencies of around 100 gigahertz or so, that was even more critical. So, what we would do is we would have a little test oscillator system that we would then inject into the receiver in order to measure the performance of this down conversion system. And in many cases, of course, we had to improve that. And then we also had what we call a phase calibration system where we would deliberately inject a synthesized signal all the time in order to take out, if you will, any instabilities or changes in the local oscillator frequency itself. I'm sort of explaining this in very simple, crude terms, if you will.
Alan, beyond astronomy, what other field saw value in the development of VLBI?
Well, certainly, of course, geodesy, but the geodetic VLBI also does very accurate measurements of the earth’s rotation and orientation. Bear in mind that GPS does a good job of navigation, and so on, here on the ground, but the GPS systems are not in inertial space. They're in orbit, and their orbits have to be determined. The only way you can get a very, very precise determination of the earth's rotation and its orientation is by using quasars, which are far enough away that they form an inertial system, if you will. So, that's really the most important. I mean, without using the quasars in what we call the geodetic mode, which has a lot of electronics in it that have to be extremely accurately calibrated, and is run routinely to determine not only the continental drifts, and so on, but also the rotation rate, the time if you will. And also, the earth's rotation pole wanders around. It's not perfectly stable. And of course, you get effects of the environment, for example. If the atmosphere speeds up, the earth’s rotation slows down, and so on. There's a lot of geophysics in that.
I wonder if you can explain for our broader audience what geodesy is, and why this technology is important for it.
Well, as I say, it's important because it provides an inertial reference frame. Without that, what reference frame would we have? You can put things into orbit, and so on, but you then have to refer their positions to some stable frame. What stable frame are you going to use? I mean, before using radio for doing this, of course, it was done with optical observations like at Greenwich, for example, even starting back in the 1700s. They used to make very precise position observations of optical stars.
Alan, in what ways was Haystack connected with the larger world of observation? Or was it essentially, were you working more or less on an island unto yourself at that point?
Well, of course, VLBI, you're not ever in an island to yourself, because you have to combine it with some other antenna. The V in there stands for Very long, so typically -- for example, most of the early geodetic measurements were made from Haystack to an antenna in Sweden. Nowadays, of course, there's a network of antennas around the world. I'm not that much involved now in the geodesy part of it. Occasionally, questions come up on some of the electronics, but it's a well-maintained system. It's essential to providing this inertial reference frame. You've got to have a good reference frame. And the quasars are far enough away that they actually form this good, accurate reference frame. The problem with optical objects is typically they're not that far away. If they're individual stars, especially, they're typically even within our galaxy. Of course, they have motions of their own. So, they don't form a very stable reference frame.
What were some of the key funders of Haystack at that point, in the late '60s and 1970s?
Well, before the Mansfield amendment, Haystack was funded entirely by the money that came from the Defense Department to Lincoln Lab. The Mansfield amendment did allow some fraction of the money to be spent on more general things. Following the Mansfield amendment, I would say the U.S. Naval Observatory, primarily for the geodesy work, and NASA combined. Both of those organizations. And then for the radio astronomy, like EDGES and so on, National Science Foundation.
So, before the Mansfield amendment, what was the reporting structure between Haystack and Lincoln? Did the director of Haystack report to Lincoln Labs?
When that changed, did your day-to-day change at all? Did that make a difference from where you sat?
No, not really. When I was working in radar astronomy, that was before the Mansfield amendment and it wasn't really defense work. I did get involved for many, many years in developing location systems for cell phones, but that was funded privately. There was a company called True Position that came to MIT for help. Actually, came to MIT campus for help. And Chuck Counselman, who was an MIT professor, decided that he would get Haystack involved with this problem of being able to measure the location of cell phones. But that was all funded by industry. It was used to develop what's currently used for the 911 system. The 911 system also uses GPS as well nowadays.
But there are still things like, for example, locating the phone that belonged to the owner of the car that Boston bomber Tsarnaev highjacked, for example, happened to be left in his car. I wish I knew whether the owner of the vehicle had deliberately left his phone in the car, because when that phone registered, it was located using the True Position system just from the signals that came from the phone. In fact, there's a NOVA program about that. I'm not in the NOVA program, because the bombing in 2013 was a few years ago after my work on the True Position system. But clearly, once we had cell phones, there was a need to locate them. And at least, in the early days, and even now today in New York, you really can't always do a good job to locate a cell phone with GPS, because there are too many buildings in the way. You don't have the sky coverage. So, systems like the True Position system which use the first arrival time of the signals from the phone are critical in being able to locate a phone.
What interactions did you have with NASA after the Mansfield amendment, when it became more invested in Haystack?
Well, to be honest, I never did a lot of work writing proposals. Actually, interestingly enough, when Irwin Shapiro got the Whitten medal award he gave talk, and I have a copy of his talk, which I just read again recently because I was trying to refresh my own memory on certain things. I don't think he did a lot of proposal writing at that time. I think, people like me have to thank people like Paul Sebring and Tom Clark, for example. He wasn't here at Haystack, but he already worked for NASA. So, we had good connections with NASA. Let's put it that way. And yes, the proposals, most of those were fairly straightforward proposals. Much shorter back in those years than proposals are nowadays. And they would come primarily from people like our directors here, whereas nowadays things are different and many of the current proposals here at Haystack are written by individual staff members.
Alan, moving into the 1980s, what were some of the key technological advances that were relevant for your research, in terms of computation, instrumentation, those kinds of things?
Yes, well, certainly, for VLBI, the key thing was to be able to record wider and wider bandwidths. That was the key thing. In the very earliest VLBI, we used IBM computer tapes, and we were able to record, literally, only a fraction of a megahertz. But then we moved to developing our own high-density tape drive recording systems. And more recently, of course, everything now is recorded on computer disc. And because the amount of data we have to record is so huge it cannot be sent via the internet, especially for the EHT for example, it gets recorded on computer disc and then transported. Some of them now are solid state, but some of them also are the old-style rotating computer discs. They fit into a module, and that module gets shipped.
For example, when the EHT does an experiment, we can't get the data back from the South Pole, for example, until it has been shipped all the way from the South Pole. So, typically, that's a three-month or longer delay. Several months delay to get it back. And in addition to that, nowadays, the correlation that we use in order to correlate the data for EHT and for geodesy -- geodesy is also recording much wider bandwidth -- uses 3,000 cores. A big computer system with 3,000 computer cores in it, and so on. If you go back ten years ago, in order to get the correlator we needed, we actually had to design the individual correlator chips that would do the correlation. Now, we don't do that. All the computing is done in standard, commercially available hardware. But the commercially available hardware, now, is so incredible that it can do the job, whereas if you go back to the very first VLBI that was recorded on tape, that was correlated by a 1-bit correlator that was physically built out of transistors by Sandy Weinreb here at Haystack, for that job. But now, of course, a little bit later than that, that same sort of correlator was put into a chip. Of course, now, we don't develop any special chips anymore because the chips that are developed for computers now all do exactly what we want. You can program them to do exactly what you want. So, that kind of technology is still moving along with Moore's law, as you know.
Moore's law continues.
Yes, continues. Every time you go by a laptop, well the first one, you probably were lucky if you got storage of 100 megabytes. Now, you're talking about gigabytes or terabytes in your laptop.
Alan, what opportunities have you had at Haystack to work with students?
I've actually had quite a lot of opportunities over the years. There's two types of them. One is, people like Shep Doeleman, who was Bernie Burke's student, and Bernie sent him out here to Haystack to work on VLBI. And the same thing with Judd Bowman. He was Jacqueline Hewitt's student, and he came out here to work on the EDGES project, and so on. So, I've had a few of those occasions where an MIT PhD student has come out here, but I was not their advisor. I was not Shep's formal advisor. Bernie Burke was Shep's formal advisor. And Jacqueline Hewitt for John.
And the other is a program called REU, research opportunities for undergraduates. And until this year -- this is the first year I have not had an REU student. I've just felt sort of overburdened with things. I don't have a student this year. But I think for over 20 years, I had an REU student each year, and they worked on different things. For example, I had an REU student that worked with me on testing out one of the early versions of the EDGES system. We took it up to a relatively quiet radio site up in Maine. West Forks, Maine is relatively free of interference, although no longer. They've just installed more equipment out there.
But the thing that I've spent probably more time than anything else on, which has just changed, really, starting this year, I developed something called a Small Radio Telescope. You can google it if you want. SRT, Small Radio Telescope. It was suggested by Irwin Shapiro. Irwin told me one day, "Students said that they can go out, and you can get a pretty nice optical telescope, but if you want to do something like looking at the hydrogen line in our galaxy, and measuring the galactic rotation curve, how do you do that? Alan, you should work on developing a low-cost, small radio telescope." Well, I did that. The early version of that, I built a prototype, but then a company came along, run by a professor, Mike Cobb of Southeast Missouri State University, as sort of a garage operation. It was called Cassicorp.com. So, I did the design but then this company would actually build it.
Cassicorp ended up building more than 800 of these small radio telescopes. They were sold around the globe. Anyway, I now put on the web all the information on how to build a Small Radio Telescope using parts that you can purchase, but you have to put the thing together, but you can purchase all the parts. And most universities now, and a lot of private people also, put together their own Small Radio Telescope. Primarily, as far as the universities, in doing the course on radio astronomy -- of course, I happen to be grabbing this because her picture's right here. Here's Vera Rubin. She was the one that measured the galactic rotation curves optically. Okay, well, you can measure the galactic rotation curve using the Small Radio Telescope. That's a very neat project for students to do and is part of most radio astronomy or astronomy classes that are given at most universities around the world.
Until, starting maybe the beginning of this year, I was still getting maybe one email a week from somebody somewhere around the world who needed some kind of help with a small radio telescope. Either they had had it so long, something had broken or worn out, or there was some software thing that they needed to change, or whatever. But I have passed that -- a younger person is taking this over. I wrote everything in C. Now, of course, everybody uses Python, and now, there's a younger person, John Swoboda, who's taking on the Small Radio Telescope. It's not fully up on the web yet, but it's close. So, I think it's an important thing. It would be nice if an industry grew, like Mike Cobb's company would just make something available that you could just buy. But I think the problem is the market is not big enough that any company has considered doing that. So, if you want a Small Radio Telescope, I think your only option really is to pretty much build it yourself, but by buying the standard pieces. For example, you can buy the motor drives and some other parts from a company up in Canada.
Alan, tell me about your decision to become Associate Director of Haystack in 1993.
Oh, you looked that up.
It's right there on your CV.
Oh, it is? Oh, it wasn't my decision. If you'd been around a long time, and you'd been a staff member, typically staff members get promoted into the director's office. The director has to have some help and needs to appoint an “Associate director,” or whatever. That's how it works. It wasn't my decision.
What were some of your administrative responsibilities in this new role?
Well, evaluation of proposals. Maybe a little bit more proposal writing, but also attending director's office meetings where we could make decisions. Like right now, I don't make any decisions, really, that affect everybody. Colin, our director, especially with the COVID thing, he had to worry about meeting all the requirements that MIT has for COVID, and we still have to wear masks everywhere. There's a huge amount of work that has to be done by the director's office. It's a big job. We have a fairly big staff, too.
How did you get involved in working with the cell phone industry?
Well, the founders of True Position, Bill Berkman and associates knew they needed to and wanted to develop a system for locating cell phones, but there were technical questions they wanted help with, so they came to MIT campus and Charles Counselman, who is now an MIT Professor Emeritus, got us, me primarily, involved. And it was more than me in the end. I put together huge numbers of memos and things, but I was primarily looking at processing. How do you – when you get a signal from a cell phone, not only does it come to you – well, it hardly ever comes to you completely directly. It mostly comes to you because it reflected off a building, or a tree, or all sorts of reflections.
So, what you need to get the best result, is you need to be able to identify the very first arrival of that signal, because that’s going to be the shortest path to that phone. And you then also have got to get that signal from several cell sites in order to actually compute the location. If you just get the signal from one cell site, and you measure that delay, you only know that it’s located in some circle around there. If you had two, then it’s the intersection of two circles. And then if you have three, then you actually get a location. You can see all of this on the NOVA: Manhunt Boston Bombers program. So, they wanted me to work on developing the algorithms and the software, but some of the technicians here helped with the trials in some cities, and tests and so on, and I was only a little bit involved in those. I was involved in analyzing the data to some extent, but I didn’t go down to roam the streets of Philadelphia, which apparently, in some places, were not that great.
Tell me about your work measuring deuterium abundance in the interstellar gas.
Well, that was an opportunity that came up because of this work on cell phones, because this company gave us $310,000. They didn’t pay my salary or anything when I was doing this, but they ended up giving us money. And we used that money to build an array of Antennas right here, close to Haystack. We were very fortunate, everything just worked out just right. The technology had just moved to the point where, with a single computer, we could process all the signals from one group of antennas that were what we called a station of antennas, and it was all cheap. Everything was low-cost. We only had those few hundred thousand to build the whole thing. So, we were able to do it.
And we were also very fortunate because the frequency, 327 megahertz, is a protected band around the world, generally. But here in the U.S., it actually belongs to the Defense Department. But the Defense Department doesn’t use it in this area. So, we were able to have a pretty clear channel at deuterium line frequency, and we were able to – it took us a lot of averaging. I just gave you the EDGES signal – a half a kelvin out of 3,000 kelvin. For the deuterium line, we were looking at a few thousandths of a degree kelvin strength of the actual deuterium line. So, it’s a very, very weak line. But it is also relatively, compared with the EDGES hydrogen line, because it's just coming from our galaxy, it is relatively narrow in frequency. So, it doesn't cover a wide frequency range, and that narrower frequency range makes is easier to detect. I spent and a lot of time finding sources of interference -- for example, I would go out and find there was some interference coming in from some kid who had some computer game on some particular piece of hardware that was generating interference. I was able to buy him another one which didn't generate interference.
And then, a couple of places, I ended up going to the door and knocking on them, and saying, "Look, you're generating a signal that's interfering." She'd say, "Oh, no problem. It belongs to some old telefax machine that I can shut off. I'd forgotten, I left it turned on all those years." She just pulled the plug, and the interference was gone. So, I spent a lot of time going around and getting rid of interference, and we also had interference from the power lines because of leaking insulators, which is something I was familiar with from my days in Africa. When you get an insulator on the power line that is broken or damaged, you can get an electric arc that discharges across there and produces a huge amount of interference. And all you have to do is to identify this with the power company, and they'll fix it for you because it's wasting energy, and they want to fix it anyway. But you have to go around with a radio to identify problems. So, I did a lot of going around and identifying interference. So, it was a very nice project, and of course, it wasn't me alone. It was a fairly big system. You can check it out on the Haystack webpage.
Now, was the timing of your decision to retire influenced by your interest in the EDGES project, that you needed more time to focus on that?
You know, to be honest, I think it was a little bit influenced on the fact that about that time -- I forget what the circumstances were exactly -- there was some pessimism about continuing to get funding for radio astronomy, and I was a little bit concerned that I might have to move into something that was not really science related. I just felt I enjoy what I'm doing. Why should they pay me for it? I guess. I don't know. I'm not the P.I. Colin, now, is the P.I. on the EDGES project. I typically write the proposal, but he puts it together and submits it and so on. Some people retire and go play golf all the time, or do something else. But I've never -- some of the things that I might have been interested in doing -- for example, after I was married, we went back to Africa for a year, where I was a lecturer in physics at the University of Zimbabwe as it was now called and I worked on putting radio collars on warthogs as part of a nature study research project. I was interested in developing radio collars, and doing that kind of thing, which I thought I might enjoy. I had done it a little bit, but I became more and more into the important astronomy questions as opposed to the important environmental questions. Or, well, you know what I'm trying to say.
For example, one of the engineers I admire so much, Sandy Weinreb and his son Glenn who has a small company working very, very hard on technology for improving energy efficiency of buildings. He's actually got something called a Manhattan II project. He's pushing very, very hard to do things that are going to solve the global warming issue. All I can do at this point is, my son and I decided to go as much solar as we could. We had 100 trees cut down. We put in freestanding solar array up, the biggest area that we could put. Unfortunately, the town -- I don't understand this -- they limited the amount that we could put in. But it's doing fantastic. We get free electricity. Between my son and I, we get several hundred dollars a month now.
Wow. What were some of the values of the EDGES collaboration for measuring ozone concentration?
I'm sorry, you want to talk about ozone now?
Yeah, the value of EDGES for measuring ozone concentration in the mesosphere.
No, there's no connection between the system that I worked on for ozone and EDGES. I mean, there's a little commonality in some of the hardware involved, but very little. The ozone system is a spectrometer. I guess, in some sense, that is common, but it's developed using satellite TV antennas, and it's made to be very low-cost. And it was part of an REU development project. I had student help developing it. And we were getting a lot of very good data, but you know, certainly what's happened is that ozone frequency of 11.72 GHz is now being taken over by more satellite communication on location.
So, now it's very hard, except for some locations around the world, like the South Pole, to actually find a good place to put the ozone spectrometer. I have discovered here that I have moved the ozone system that we have here at Haystack so that it's shielded by the building. The signals that are causing interference are coming from the geosynchronous satellite orbit, so if you could block those signals, you could get the ozone data. But for example, when we had a collaboration with the high schools, we had to install some of these ozone systems. For example, we had one at the Chelmsford High School. That's up on the roof, and there's no way of protecting it from the interference we're getting now. Sadly, you probably know that there's a lot of concern now from both optical and radio astronomers about all the stuff that's being put up into space.
Right, space junk.
Yeah. Well, some of it's junk, and some of it's obviously useful, but it's also a limiting factor for some radio astronomy and atmospheric monitoring.
Now, what was your involvement at the creation of the EHT, when it was launched in 2009? Where were you in that?
I started working with Shep Doeleman back in the 1990s. This work concentrated on VLBI at 3mm wavelength. We published results of the small scale structure of Sagittarius A* in 1994. I continued to support this millimeter wave VLBI through 2013 through technical developments and trips to the Kitt peak and CARMA sites so I was very active in the technical development in this area when the EHT was formed. After 2013 Shep and others were the major people involved and within the last few years, I've had very little involvement. And actually, since we published the Nature paper, I've had medical issues and I've just spent virtually all my time either on EDGES or trying to keep some of the other things going, the ozone system a little bit.
And what has been some of the ongoing work for EDGES?
Well, we're going to have a big discussion on where we go from here. The plan was to deploy the new system we have right here at Haystack. The prototype was tested in Oregon at the end of 2019, and we found that the Oregon site was not good enough because there's too many -- the problem with the FM is complicated. What's happening is that the little micro meteorites are coming in. You know, the Earth is moving in space. There are little micro meteorites that are coming in and hitting the atmosphere all the time, continuously. And whenever one of these little particles hits the upper atmosphere, it burns up and forms a little ionized region. And that's at a height of about 100 kilometers up. Have you ever tried using your radio on FM out in some remote location?
Doesn't work very well.
Well, have you ever noticed that you occasionally get like half a note, or a few words? That's because a micro meteorite burned up, and the signal came from the antenna, and it was reflected off the micro meteorite down to your radio. And the problem is that because it's 100 kilometers up, an FM station has to be 2,000 kilometers away from you to not have that availability of that path. So, if you go to Oregon, yes, up to 100 miles away, probably there's no FM stations. But within 2,000 kilometers, there's still a huge number, thousands of FM stations. If you go to Western Australia where the current EDGES is, there are only like 20 or so FM stations within 2,000 kilometers. So, that's just a matter of degree. There's like more than -- I would say almost 100 times more FM stations within that radius in Oregon. So, you're subject to almost this sort of continuous blast of the reflections from the micro meteorites.
And we knew this, but we just thought, you know, we should try it. And we were hopeful that maybe we could still get a result. But after making that visit, we realized, no, we wouldn't. So, the plan is -- we took the prototype there. We know it works. We don't know for sure that it works well enough to detect -- we think it does based on the data that we got in Oregon. We've now made a copy of that, so we have two of them. And the plan is to go send at least one of those, deployed at the MRO in Western Australia. And we're looking at the possibility that while we probably can't go, because of the restrictions on travel, we could perhaps hire an engineer or get a collaborating engineer there so they could do everything, or it could be installed remotely. And we wouldn't have trouble then. But we're having a telecon sometime, or a zoom sometime later this week, to try to firm this up.
We have another idea that we have talked about occasionally, and that is, not going to Western Australia, but going to MARS. Not the planet Mars, but McGill has the McGill Arctic Research Station. That spells MARS. And we think the number of FM radio stations within the radius is fairly low. We don't actually have a hard number, but it's certainly much, much better than Oregon. But in terms of traveling there, they're all, quote, booked up, because they're doing important Arctic research as well. At least, through this year, so it wouldn't be until next year. So, we don't know when we're going to deploy.
Alan, you mentioned the Nature paper. I wonder if you can explain a little bit more about the earlier evidence about hydrogen in the universe, and how cold the early universe was. How did all of this research come together?
Oh, my gosh. Well, you know, most of it comes from -- well, from the measurements that were made early on of the Hubble constant. Are you familiar with the Hubble measurements? Astronomers measured the redshifts of distant galaxies, and they tried to estimate their distances, and so on. And then, of course, the other key piece of evidence is the CMB, the Cosmic Microwave Background. And as far as understanding the temperatures and everything, my understanding is that based on the satellite measured the fluctuations in the CMB.
WMAP. You got it. It's just WMAP, and there's going to be a successor, too, right?
Are you thinking of the European Planck Mission as the successor to WMAP?
Planck of course. That was 2009 to 2013. And then, WMAP 2001-2010
Okay, the various parameters that they get that are needed in the standard cosmology model come from combination of the data from these probes, and from the redshift measurements of galaxies. And now, if you google around, you'll find that they've found some discrepancy. Now, they think that the Hubble constant may depend on time. In other words, it's not a constant. They're beginning to find things that may not agree with the standard model, so I don't know whether that means the standard model has to be modified, and so on. And as I explained, the standard model is not the only model out there. We've got this one that I just mentioned as an example, Melia's model, which is called Rh = ct. He's going to be visiting Haystack. He did explain a little bit to me that cosmology is a complicated thing. Yeah, Rh = ct universe without inflation. Melia put out a paper very recently expressing great hope that the EDGES result was going to be verified because it happens to fit the Rh = ct cosmology. He sounds like a good guy to me. I don't think he's somebody who isn't knowledgeable. He's written this very comprehensive book, which not only has very, very clearly written, and a very good section on the standard model, but it also includes all the different tests. You know, the comparison with Planck, and so on and so forth. Of course, there's a huge number of people working in cosmology and I don’t know if many think the Rh = ct cosmology is viable.
To bring the conversation closer to the present, you mentioned it earlier, but I wonder if you could talk a little bit more about the development of the SRT, and in particular, some of its value for educational purposes.
Well, I think I did explain that it's the only relatively low-cost, simple instrument that's available for a class to use for radio astronomy. I mean, you could use it to, for example, look at the sun. You can point it and you can determine the radio strength of the sun, which actually is quite variable depending on the activity that's going on. So, some people, for example, some universities would use the SRT to monitor the sun and look at its variations. And then, using it to look at the hydrogen line, and actually, to measure the galactic rotation curve, which you could do with the SRT. It's just a very, very good teaching project. In fact, I think if you -- Physic Today, various places, they have references to the SRT and its use for the galactic rotation curve, for example.
I wonder if you can talk about the relationship between measuring the galactic rotation curve, and detecting the presence of dark matter.
Well, yes. I mean, it gives a simple formula. It explains that if it was normal physics, you'd expect the centrifugal force due to the galactic rotation to be balanced by the gravity force, and the gravity force, of course, depends on 1 over the distance squared. But the centrifugal force depends on the velocity squared over the distance. I hope I'm saying this right. So, you'd expect that as you look at the rotation velocity as a function of the distance from the center, you'd expect it to drop off with the square root of the distance. But it doesn't. It stays flat. And the only way you can understand that is to have additional matter, which is called dark matter, because you don't see it. Am I giving you the right picture? I mean, you can just write down the formula which equates the centrifugal force to the gravitational force you'll find the velocity depends on 1 over the square root of the distance away. Whereas in reality, when you make the measurement, it doesn't drop with distance. It stays more or less constant. I'm sorry, I should be sharing the screen or something, and putting the math out for you. But you can certainly google that one. And of course, I always try to mention Vera Rubin when I give a talk about the dark matter. Of course, I'm talking about just doing it for our galaxy. With the SRT, you can only do it for our galaxy. You can't do it for another. You'd need a much bigger telescope to do it for Andromeda.
Well, Alan, now that we've worked right up to the present, for the last part of our talk, I'd like to ask a few retrospective questions, and then we'll end looking to the future. So, first, I wonder if you could take a broad view about the development of VLBI. How it started, its original motivations, and the extent to which those early days are more or less relevant today, or the field has really gone in different directions.
Well, the suggestion for being able to do interferometry over very large distances, radio interferometry over very large distances by recording the signals and then correlating them was actually made by the Russians a few years before any VLBI was actually done. So, actually, after that suggestion had been made, I think I already mentioned there were several groups around the world who developed their own VLBI systems. There was a group in Canada, a group here at Haystack, the one at NRAO, and the group in the U.K., they all used slightly different systems. For example, from what I recall, the group in Canada and the U.K., which I think were maybe more like part of one group, but they used a video recorder -- remember the video recorders from years ago? VHS video recorder, big machine like this. And we used a digital system, and we recorded on magnetic tape. I don't know if you remember the old IBM -- well, you may have never seen one -- big reels of tape. And the NRAO group, they also used a video recorder, but they used it digitally, whereas the Canadian/U.K. group did their correlation basically in an analog fashion by playing back the analog signals.
So, after it was demonstrated that you could get, quote, fringes, which is what interferometry -- when you have an interferometer, what you're looking for are, quote, fringes. If you don't get fringes, either something's wrong, or the object that you're looking at is too big. If you think of the fringe pattern that's in the sky, if that object covers many fringes, then you're going to get a low correlation. So, let's see. You wanted -- okay, so that was -- once the concept had been demonstrated, and once it had been demonstrated that there were two sets of objects which were very interesting to study, one of which being quasars, or black holes. Quasars and black holes, from my perspective, are really sort of the same thing. Although, most likely every galaxy -- I'm not sure this is proven -- has a black hole at its center. And some black holes are more active than others, because it depends on the size, the mass of the black hole and the size. Bigger black holes draw in more material and create a stronger signal, and so on. Or you could use a VLBI to look at things like the OH masers. And of course, one of the really neat things you could do with that, because masers are a strong signal, you could look at masers not only in our galaxy, but in lots of other distant galaxies, and so on.
So, since those separate groups, there's been more of a unification of the equipment, so that it's more universally compatible. For example, the equipment to do geodesy VLBI is now more uniform around the world. It may not be identical, but it has to be compatible. There are specifications, for example, for how the data should be written, and so on. So, the people who are interested in the geophysics can use the data from stations around the world. And the same thing for the astronomy. It does more unification. And standards, of course, and you have to have groups involved, and they have to collaborate. You can't, sort of, come up with your own system, unless you own all the dishes around the world that are involved. So, it's a very collaborative venture. Of course, in recent years, it's gained a lot more interest especially because of the possibility of being able to understand in detail what's going on in the center of our galaxy. And it's because our galaxy -- the black hole is so close, relatively speaking, from the center of our galaxy, and it's a much smaller black hole, it's actually changing in time much more rapidly. So, there's a much better chance that you'd actually be able to see the dynamic changes, whereas the dynamic changes that are occurring at M-87 are at a much longer scale. You'd have to observe it for years, whereas if we could get good results on the black hole at the center of our galaxy, and get fringes on timescales of even the shortest fraction of an hour, we'd be able to see lots of interesting things which could be connected with the modeling of what's going on. Everybody's looking for this new video of a black hole at the center of the galaxy. It's a great new project. I'm probably, realistically, getting to the point where -- you've already seen me struggling to write down a simple formula, and so on. As long as I'm around, I'll try to keep an interest, but I don't think I'm going to be that deeply involved.
Alan, of course, the field recognized you first with the Dellinger Medal in 2008, and with the Grote Weber in 2010. I wonder, in what ways, that made you reflect on your broader contributions in radio astronomy.
Well, I haven't really thought about it. I certainly think I have tried to move in the direction of things that are -- I guess, I'd put it of great interest. I'm not sure quite how to answer this question. Can you phrase it again a little differently?
You were recognized by your peers in the field for all of your contributions. How have you seen your own contributions? How have you reflected on this?
Well, I guess, only in the sense that I like to keep working as hard as I can, and particularly, have I made a mistake somewhere? Did I calculate something incorrectly? Can I correct it? I don't know how to put it. Currently, I do write a lot of memos. I find them useful, because I like to document what I'm doing. But to be honest, in the last couple of years, I have contributed to some papers, but I have not been writing papers myself. Anyway, I think, realistically, I'll be fortunate if I've got a few more years at least to be able to keep up with what's going on. And I am trying to pass things on. John Barrett, whose office is here at Haystack. He's a young fellow, and he's going to be around. I need the younger generation to take over. I should say something now about the SKA, the Square Kilometer Array, right? And yet, you know, the SKA was proposed by Bernie Burke. Did you realize that?
I did not, no.
Bernie actually proposed the SKA. Yes, he did. I am concerned that, at least for the low-frequency part of the SKA, maybe not enough study has been done yet. It's just been announced that it's been funded. They're going to start construction. Now we're talking multi billions of -- are you aware of that?
You are, okay. I would hope that there would be a stronger link that the U.S.--I'm a little bit mixed up in my own mind, to be honest, about what the role of the U.S.A. is in this. So, I'm a bit concerned. It needs discussion. I am concerned about it. I am also kind of concerned that the SKA hasn’t verified their design. For example, they have a prototype in Western Australia, which I think is complete. They ought to demonstrate that they can verify the deuterium line detection that we made years ago. It's supposed to go up to 327 megahertz although, they haven't actually used it up to 327 megahertz. So, I don't know.
Alan, of all the things that you've worked on, what stands out in your memory as giving you the most intellectual, or scientific satisfaction?
Oh, my gosh. Because there's so much uncertainty, I'm pretty certain that what we've seen with EDGES is correct, but I can't be absolutely 100%. So, I guess, I would say the deuterium detection, and what we did there was very satisfying to get a nice result and be able to work out all the problems with the interference, and get it fixed. But on the other hand, I also enjoy working with the students, contributing to SRT. I occasionally even think about those days when I was working on the spinner magnetometer. Actually, not much. Your communication with me had me digging back into my past.
Alan, last question, looking to the future. For however long you can and want to remain active, what do you want to accomplish personally, and where do you see the field headed?
Well, I'd like to continue to work on understanding the low-frequency arrays, particularly in the SKA, for example, that's going to be built. And probably doing some modeling. I've done a lot of modeling using this electromagnetic code that's -- actually, primarily, the best code is available from this company called FEKO in South Africa. I think a lot more modeling needs to be done, and I'd like to -- I don't know whether I should write a book, or whether I should try to put a lot of the material that I have in memos into some kind of a book. You know, a very close friend of mine, Jim Moran-- do you know Jim Moran?
He worked very hard on that very, very great book on radio astronomy. Particularly, for VLBI, it's a really, really good book. I think I would have to collaborate with somebody to put together a book. At this point, I don't know for sure whether it warrants a book, but I think especially if the result is confirmed, I think it does warrant a book. There's a lot of material that needs to be put together that I think will be useful. I think there hasn't been a good enough understanding of modeling for the low-frequency. The low-frequencies are very tricky, in my opinion. Because the sky is so bright, you've got lots of signal to detect, but what you have on the ground is very complicated. You can get all these complicated scattering issues. Almost like the cell phone problem. You get the signals from the sky. They not only enter your antenna, which is what you want, but they also get reflected off the other antennas, and the bushes around, and all the rest of it. It's complicated. It's very analogous, actually, to a multi-path that you have in cell phone location. Needs to be fully understood, and we've got work to do to make it work.
So, we'll see. But my capabilities, I'm afraid, are not what they were when I was younger but I'm doing okay. I don't think I have Alzheimer’s, but I definitely have some memory issues.
All the more reason why it's so important that we were able to do this today.
Yes, thank you, thank you, thank you.
I'd like to thank you so much for spending this time with me. I'm so glad that I was inspired to get in touch after I interviewed Shep Doeleman, and it's been a pleasure spending this time. So, thank you so much.
Well, you've spent a lot of time on this. Thanks again.