Oral History Transcript — Dr. Gerson Goldhaber
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Interview with Dr. Gerson Goldhaber
Gerson Goldhaber; June 24, 2005
ABSTRACT: Gerson Goldhaber (1924- ). Early training at Hebrew University in Jerusalem (1942-1947). Graduate work at The University of Wisconsin. Research at Columbia University (1950-1953); memories of Rabi. Research at The University of California at Berkeley and at Lawrence Berkeley Laboratory (LBL). Took part in first experiment at Bevatron. Worked on K-mesons, the tau and theta mesons; measured the radius of interaction, and the difference between the behavior of like and unlike pion pairs; contributed to the design effort of SPEAR (Stanford Positron-Electron Asymmetric Ring) accelerator at SLAC; co-discovered, and named the Psi particle with George Trilling; Goldhaber found the naked-charm mesons; with colleagues, measured the lifetimes of a number of particles, including the tau lepton, the D mesons, and the B meson; at SLC (Stanford Linear Collider) did measurements of the mass and width of the Z particle, measuring how much of the Z decay went into neutral leptons. With colleague Robert Cahn, he wrote and published the textbook ďThe Experimental Foundations of Particle Physics.Ē Part of The Supernova Cosmology Project (SCP) since 1989. 2004, ĎGersonfestí held in his honor.
TranscriptSession I | Session II | Session III | Session IV | Session V | Session VI
Pavlish:It is Friday, June 24, 2005. We are sitting in Dr. Gerson Goldhaberís office in Lawrence Berkeley National Laboratory in Berkeley, California. This is Ursula Pavlish speaking. I am here today to interview Dr. Goldhaber. In the next hour or so, Dr. Goldhaber, I would like to ask you about your transition from particle physics to cosmology, particle astrophysics specifically, especially about your work in the Supernova Cosmology Project.
Goldhaber:Ok. We finished our work at SLAC. I had only discussed the work at SPEAR. But then after three years at SPEAR we went on to PEP which was a 12 GeV collider. Iím not sure of the number right now. Also, we built a better detector the Mark 2 detector, which was better in many respects. But the bountiful data that SPEAR gave us did not repeat. In this new energy region we did measure something of interest; we measured lifetimes. We measured lifetimes of the tau lepton, lifetimes of the D mesons, and particularly also the lifetime of the B meson. And those turned out to be quite long; 10^-12 seconds, which is long. Which has a very interesting consequence. This is what allowed one later on to study the B mesons for CP violation which is the experiment which is currently running at SLAC. It is called (b and b bar) BABAR. That went on for about six or eight years at this new collider PEP as it was called.
Pavlish:What is PEP short for?
Goldhaber:Positron Electron Something.
Goldhaber:And after that Burt Richter built a real collider where he collided positrons and electrons up to (what was the energy?), up to an energy high enough so that one could produce the Z which had been discovered by Rubia at CERN. And so we were able to do measurements of the mass of the Z, the width of the Z. How much decay went into neutral leptons. This showed for the first time that there are three types of neutrinos and not four. We already had suspected three types because of the neutrino which goes with the electron, the neutrino which goes with the muon, the neutrino which goes with the tau.
Pavlish:What was the fourth suspected one?
Goldhaber:Nothing was suspected but there could have been fifteen. So we showed that it was three. There was evidence from cosmological measurements but this really showed it clearly. At the same time the collider at CERN started working. They were able to produce much larger numbers of Z than we were able to produce. And so after a while we finished our experiment. That was the end of my work at SLAC, the end of our group at SLAC. That was the time, about 1989-1990, when the SSC was being considered; it was being built already. All my colleagues George Trilling, Gerry Abrams, John Kadike decided to work with the, at the SSC. However, I decided that the SSC was supposed to take ten years to complete and during those ten years one had to build detectors for the SSC. My colleagues decided to work on that. But I decided that I didnít want to work on building detectors. I was more interested in working with data. And it was going to take ten years, which was on my personal timescale too long, I thought. I decided that I was going to try to do something else. Now, it so happened that my wife, Judith, was writing a musical with Carl Pennypacker. Carl Pennypacker composed music and my wife wrote lyrics. They were working together at that time. I also went and discussed with Carl what he was doing scientifically. They had just started to look at distant supernovae. Carl Pennypacker, Rich Muller, and Saul Perlmutter who was at the time a postdoc in that group, had decided to look for high redshift Type 1A supernovae in order to find the fate of the universe. In discussing this with Pennypacker I got interested in this project and also felt that I could make contributions. Particularly, because in some sense because it was again a visual technique. This time you looked through a telescope instead of looking at emulsions, looking at bubble chambers, looking at computer reconstructed events. This was now looking at a telescope. I knew I could do this kind of work, I liked this kind of work. Also, I liked the project very much. It sounded very promising. So instead of joining SSC, which was still a going concern at the time, I joined Karl Pennypacker and Rich Muller to look for these supernovae.
Pavlish:How rare is this among particle physicists; Pennpacker, Muller, and Perlmutter, were they also particle physicists turning to cosmology?
Goldhaber:They had been particle physicists, yes.
Pavlish:Can you say perhaps a percentage of how many particle physicists decided not to join the SSC because at the time the SSC would have been the largest scientific enterprise in the world, right?
Goldhaber:These people already I mentioned, had decided to work on this Supernova search before even the SSC was going.
Pavlish:Would you say that was part of a trend towards cosmology?
Goldhaber:This was the beginning of a trend. Now there is a trend. It was the beginning. It was partly inspired by Louis Alvarez. These people had worked with Louis Alvarez. They had made a search for nearby supernova. They devised a method how they could find nearby supernovae. They were quite successful. They had found about twenty nearby supernova.
Pavlish:This was at which telescope?
Goldhaber:This was at a small telescope here at Loischner. Itís a University of California telescope just in our backyard. A 20 inch telescope. They had successfully found supernovae. Then they decided that it would be very interesting. This idea was known, A that supernovae might be standard candles and B that because they are standard candles you can measure distance with them. The idea is to find out how far the distant supernovae were. It was a question of measuring the redshift and the brightness of the supernovae. That told you then, placing those two numbers on a Hubble plot could tell you on what curve which was predicted from Einsteinís theory, what curve was the real one that the universe was on. There were different possibilities.
Pavlish:That is whether it is flat or?
Goldhaber:More than that. No, its what is the mass density of the universe. At first we thought, we are going to measure the mass density of the universe and this will tell us the fate. We were expecting the mass density to be large which meant that eventually the universe would recollapse, end up in a big crunch. That was our suspicion. We started out to measure the deceleration. Because of the mass, one didnít know anything about what is now called dark energy. So it was an attempt to measure a deceleration or the mass density of the universe. Now, it took us three years. At first we got a telescope in Australia, that we were able to do this work on, the Anglo-Australian telescope. There, the weather conditions were bad. Saul Perlmutter and others took a trip to Australia to take data at the telescope but then came back empty handed because the weather was bad it was raining at that telescope. This happened several times. Sometimes we did get some data. The end result was that for three years we did not see any supernovae. I joined this effort in 1989, started working, trying to find supernovae. At one point I got very excited because I found something but those turned out to be asteroids. I found asteroids in the data. The method is to take an image which we call a reference image. Three weeks later to take another image and subtract the two. If there was a supernova explosion, you would get a new point of light. If there was an asteroid then you also got a new point of light except that the asteroid moved. This new point of light didnít stay at a fixed location. It moved so thatís how you could tell the difference.
Pavlish:That asteroid would be in our?
Goldhaber:In our galaxy, yes. Itís an object in our galaxy. Now, Pennypacker later went into education. He has this project called Hands On Universe and he made use of these asteroids. He gave high school students the chance to find asteroids, which is a real astronomical object. So it was very exciting for them. They were able to use our data also to find asteroids. Anyway, our first supernova was found in 1992, a distant supernova. At that time it was the highest redshift supernova ever seen.
Pavlish:That was the first supernova?
Goldhaber:First distant supernova. We looked for distant supernovae.
Pavlish:So from the beginning you were looking for the furthest supernovae?
Goldhaber:Yes, we were looking the furthest we could go and we found one. At that time there was another experiment which also tried to do this. They had a very hard time but they did find a supernova at redshift of 0.3 while the one we found was at redshift 0.45.
Pavlish:May I ask, how does one configure a telescope to observe distant supernovae? Was that something that was new?
Goldhaber:What was new in this business is that the CCD (Charge Coupled Device) has been developed and has been in use in telescopes. You no longer take pictures on photographic film, but you use these devices which are now in all the cameras, the CCD cameras.
Pavlish:The digital cameras?
Goldhaber:Yes, itís the same device. That made all the difference that you could start making quantitative measurements. So in that sense it was relatively new. And that really allowed one to make these measurements. It wouldnít have been possible, you couldnít have done that with film.
Pavlish:So itís something like many tiles, and then you measure the light intensity?
Goldhaber:At each point, yes.
Pavlish:So when youíre looking for more distant supernovae versus closer ones are you looking for a certain wavelength?
Goldhaber:Weíre looking for very dim supernovae. The thing is that, if you look out into space, youíre more likely to find a distant supernova than a nearby one. Because the telescope looks at a fixed solid angle. Nearby, thatís a small amount of sky coverage. As you go farther away, youíre looking at a bigger and bigger volume of sky. And so thatís why you can find distant supernovae. In the earlier work, they looked at specific galaxies. A supernova is an exploding star that is in some galaxy. So they looked at a series of galaxies over and over again and then they found the nearby supernovae. But here, we were looking just out into space, mostly randomly. We selected a region of space which had very few stars. You donít want to look at stars they are too bright. I can show you some of these things. Letís seeÖ itíll take a little time to come up. So you do find distant supernovae. Ok letís take a look at this.
Pavlish:So thatís some solid angle of the sky? ?
Goldhaber:Itís some volume or area of the sky.
Pavlish:And those are stars, those little white dots?
Goldhaber:The green dots show that this is a subtracted image where the subtraction has noted that something is there.
Pavlish:Ok, so what do the little white dots mean in the subtraction?
Pavlish:Oh, ok. Theyíre green.
Goldhaber:It means that there was a residue after the subtraction, there is something left over above a certain threshold. You have to put in a certain percent increase. So let me show you. Letís go here. This is what all the subtractions look like. I can immediately kill all these because thatís a bad subtraction.
Pavlish:How do you know that?
Goldhaber:Because it should look something like this or like this. Or maybe even like this. This is probably also bad. Youíll see in a moment. This is bad. These others are possible. I go to the tiles. Now, here what you see, thereís a galaxy and then you subtract it and something is left over. This is the subtraction. It should be a nice, solid form. This form means that itís a bad subtraction. Let me look at another one.
Pavlish:So does a bad subtraction mean that there is something else like reflected light?
Goldhaber:No, it just means that the two images are not a perfect match. So sometimes you get some light coming through. That one is also bad. Let me go on. Here again thereís a galaxy and light is coming through but itís not a point of light. A supernova is a point of light and this is a big mess.
Pavlish:So is that understood what that mess is?
Goldhaber:It is just that the two images donít match perfectly. If we did a more careful job. Ah, here take a look at this. This is the original image and this is the new image. What do you see?
Pavlish:Thereís blackness and then a little point.?
Goldhaber:Thatís a supernova. In fact I have to write that down.
Pavlish:So this is new data?
Goldhaber:Itís not exactly new data. We are scanning toÖ 1060. Here it tells me that the brightness increased by 124%. So let me go on. So thatís a supernova. So youíve seen, thatís how you find a supernova.
Pavlish:So is that also it, when you see a little dot on the side?
Goldhaber:Yes, this is the original reference image and this is the new image. This is the subtraction. You take away the old image from the new image and you see something is left over. So let us also look at it here. Look at it in greater detail. I can magnify this. I did something wrong. Now this is magnified, this point. And then I magnify it some more. And then I magnify it some more. And now some more. Ok, now actually one more.
Pavlish:So by now weíre seeing the individual CCD pixels?
Goldhaber:Youíre seeing the CCD pixels, yes. You see. Now I can look at the reference image. This is what this looks like. Thatís the galaxy. And now I look at the new image and you see there it is, there is something new there.
Pavlish:How is it possible that it is so bright? You have a whole galaxy with how many stars?
Goldhaber:The supernova is as bright. The galaxy is 1012 stars, typically. And the supernova is as bright as or brighter than the whole galaxy.
Pavlish:Wow, and how is that possible?
Goldhaber:Because itís an explosion which burns up an entire star within seconds.
Pavlish:Because its dying, the star?
Goldhaber:Yes, the star is exploding which is basically like a hydrogen bomb. Itís not hydrogen. Its carbon and oxygen but you get Fusion. With Type 1A supernovae the whole object burns up. Ok, so now you saw a supernova. Now I can go, next.
Pavlish:So are these images from the Australia telescope or are these fromÖ
Goldhaber:No, no, fortunately we went to other telescopes. This is actually from the Hubble space telescope.
Pavlish:Is that your current source of supernovae?
Goldhaber:Yes, we are currently working with the Hubble space telescope. Before that, we worked with a telescope in Chile. Most of our work when we discovered the dark energy was with a telescope in Chile. Ok so this one is junk, this one is junk, this one is junk. So this has just one supernova.
Pavlish:So how rare is that?
Goldhaber:Now in five minutes thereís a talk. You may want to go to it. I have my lunch along. Iím going to eat my lunch. Maybe after the talk you can go to lunch in the cafeteriaÖ technical detail. What was your next question?
Pavlish:I was wondering, how rare is that, what we just saw? The original snapshot you brought up is one image of one area of the sky, to actually find a supernova in that image?
Goldhaber:In these exposures we find one supernova in two or three images. Because the Hubble Space telescope is looking at very distant supernovae. These are very distant supernovae. Not just distant but very distant. They have redshifts greater than one.
Pavlish:May I just clarify again what that means. Redshift, that means how far away it is but when you say greater than one, if I translated that to light years?
Goldhaber:Yes, if you translated that to light years, itís about nine to ten billion light years.
Pavlish:z=1 is 9 billion light years
Goldhaber:Now, the whole universeís age is about 14 billion light years So if we are looking two thirds of the way to the big bang.
Pavlish:And what is the most distant supernova that you have ever discovered?
Goldhaber:We have discovered up to 1.2 z, now maybe 1.3 with some other work Iím doing. The other group has seen them up to 1.7.
Pavlish:Now what other group is that? Theyíre doing similar work?
Goldhaber:Yes, as I mentioned we started this in 1988 and finally we found about 7 supernovae. In 1995 we had more but we were ready to publish seven supernovae. And there was a conference in Spain that we went to and at that conference another group decided hey this really works. They originally thought this wasnít going to work but then they saw that this really works so they said that they would also independently look for these distant supernovae. Very soon after we came up with evidence for dark energy they also came up with evidence for dark energy. So basically, its always said that there are two groups that have observed this. They like to say they found it first, we like to say we found it first.
Pavlish:Is this the Bob Kirshner and —?
Goldhaber:Bob Kirshner yes and particularly Schmidt, Brian Schmidt and also Adam Riese. Anyway, they have seen some distant supernovae a little further out than we have, so far.
Pavlish:They use the same telescopes or different?
Goldhaber:With the Hubble Space telescope, yes. But now weíve gotten a very large commitment from the Hubble Space telescope and we hope to find many more distant supernovae. So what I was showing you here was a practice in finding these by using the data which we already know but just to see how well we can find these. You see how clear they are when you find one.
Pavlish:Itís very evident. Thatís really neat.
Goldhaber:I think itís probably time to go over to the talk. So where did we end up?
Pavlish:We were just talking a little bit about Kirshner, about how they said that they had found it first, maybe I asked a question about that.
Goldhaber:It was all within a week or two. Ok, I still am not clear what we were discussing. We were discussing the observations of the dark energy.
Pavlish:Yes, and you were still helping me with the science of it. About the universe being 14 billion years old. About the different zís, how far the zís of the supernovae that you have discovered are. That now youíre using the Hubble telescope but that you were using a telescope in Chile.
Goldhaber:Those discoveries were from a telescope in Chile.
Pavlish:And did you yourself go out to the telescope in Chile?
Goldhaber:No, I did not. But we had people going out. Unfortunately some doctor said that I shouldnít go to the high altitudes so I havenít gone. Iíve gone to telescopes earlier on, I went to a telescope in the Canary Islands. But I did not go to Chile.
Pavlish:For the work that youíre doing you didnít need to go.
Goldhaber:Somebody needs to go. I was working on analysis of the data as were many of my colleagues of course.
Pavlish:I had a lot of questions about the scientific papers.
Goldhaber:Yes, sure. What questions did you have? Letís try that for a while.
Pavlish:Iím not sure about Omega M and Omega Lambda.
Goldhaber:Omega M is the mass density of the universe in certain units. In units of the critical density. Whatís called the critical density? Omega Lambda is the vacuum energy density, again in those same units. And now for a flat universe, the sum of those two is equal to one. After we did our work, there is evidence from the asymmetries in the cosmic microwave measurements that the universe is flat. That the sum of those two should be one.
Pavlish:Thatís a constraint on the equation that allowed you to find that there must be some dark matter or dark energy.
Goldhaber:Yes. Thatís a constraint that came afterwards. We didnít have that constraint when we made the measurements. Letís see. So the original measurements were simply what was the best value between Omega Mass and Omega Lambda. We had some value there, with large errors, an error ellipse which also included the flat universe. There was a prejudice, a theoretical suggestion called inflation which predicted a flat universe. Now we have experimental proof for a flat universe. If you have a flat universe you get this Omega Mass about 0.3 and Omega Lambda about 0.7.
Goldhaber:No, experimentally. It is called a concordance, how they agree. For a flat universe the sum of the two ought to be one, then the supernova result gives 0.3 and 0.7.
Pavlish:Ok, let me just back up a little bit. How do you get from the supernova to these values?
Goldhaber:To these numbers.
Pavlish:Is it very complicated?
Goldhaber:Iíll have to go to the papers and look at the, show you the relationships. So this is our paper. We studied 42 supernovae and we get a relationshipÖso what we first measure is we plot the redshift. We plot the magnitude which we find which is the brightness. We plot brightness against the redshift. And then here we have a curve, this one here which is labeled 1.0 which is the, which would be if there were zero cosmological constant and a mass density of one. See, thatís the solid line here. So the observation was that the data points did not fall on that line, they fell somewhere above it, in other words the evidence was that the supernovae were dimmer than was expected from this line, than what you would have gotten for Omega Mass=1. They were dimmer. Now, when theyíre dimmer, this means they were further away. So then the question is how do they get further away. They get further away if thereís not just the standard expansion of the universe but there was some acceleration of the expansion. Then they got further away. And that was the evidence that there must be Omega Lambda which means that there must be dark energy. So they were clearly further away than expected from a standard universe of total Omega=1 but 0 cosmological constant. The two of them add up to one. This then is expressed by, letís see if we have one plot here, is expressed like this. So we have a 99% probability that the answer is somewhere in here. But then if Omega total=1, or itís a flat universe, then it lies down here with .7 and .3. You see? What we determined is that it lies somewhere in here. If the universe is indeed flat then it comes out 0.7 and 0.3. This was the evidence for a cosmological constant, or what we now call dark energy. It wasnít called dark energy at first.
Pavlish:So how did it get named? Was it elsewhere that it was named? What did you call it at first?
Goldhaber:Only at a later time did the asymmetries, about two years later, the asymmetries in the Cosmic Microwave Background showed that the total Omega was one. So the equation is total Omega = Omega Mass +Omega Lambda. When thatís equal to one, we get Omega Mass= 0.3 and Omega Lambda= 0.7. At the time we already knew that this was an interesting possibility because Inflation predicted that total Omega=1. So when we set out, we didnít know, we thought there was only an Omega Mass and that could be anywhere between 0.1 and 2. We were expecting it actually to be probably greater than one, in which case there would be a deceleration. In fact we were measuring the deceleration, only we found that the deceleration was negative. So it was an acceleration. Does that explain it?
Pavlish:That does help.
Goldhaber:That helps. Ok, fine.
Pavlish:What you actually did in this project is very important and itís related to your earlier work in particle physics. I think in this one you mentioned that the curve you saw was like a resonance curve. I would just like to ask you to tell the story of that.
Goldhaber:I was analyzing it in the way I was accustomed to from particle physics to find out what the answer was, what Omega Mass was. I made the assumption that the total Omega was equal to one which wasnít known at the time, it was an assumption I made. When I did that I found that Omega Mass came out to about something like 0.2 so that there had to be something else, omega Lambda about 0.8. This was a quick and dirty analysis of the data, and this I presented to my colleagues. They made a much more careful analysis and indeed they found that it is about 0.3. They convinced themselves. It is not that I convinced them. This was an indication. I got an indication and they analyzed it with much greater care, taking into account some corrections and came out with a consistent result. So, I didnít do the complete measurement, I did a rough measurement using methods which I used in particle physics. I saw that peak thatís in this paper. To me it looked convincing. This, I presented to my colleagues. They were not convinced because I said it, they convinced themselves. They measured it themselves and found that it was very similar to what I said.
Pavlish:And these are the notes from the meetings, right. Did you have a secretary?
Goldhaber:One of our colleagues, Rob Knop, took careful notes.
Pavlish:And this here it says for 38 supernovae, so thatís a large sample.
Goldhaber:By the time we published it, it became 42 but at that point it was 38.
Pavlish:Your group was ahead of the other group, right, because they only had something like seven?
Goldhaber:They had ten.
Pavlish:You originally had seven.
Goldhaber:Those seven actually indicated something different. On those seven we had close to Omega Mass = 0.9 or something. So the first seven didnít indicate this. Itís only with a larger sample that we got this result, in fact inconsistent with the first seven.
Pavlish:I would like to ask you a bit about that. I donít know how easily it is communicated to a lay audience, but your work to make sure that the data is statistically significant or that the analysis is, well itís so rigorous. Even after the talk this afternoon, everything is so precisely checked and rechecked.
Pavlish:I was wondering how the work that you did in particle physics carried over to this workÖ Did you have specific methods that you used?
Goldhaber:I sort of convinced myself when we had the larger sample that there seems to be some acceleration of the Universe. But there were many checks which had to be made which I did not do, did not make. Then my colleagues started working on it. Obviously, at first nobody was convinced of what I said. Only me, only I was convinced. Slowly then the group started working on this, and carefully evaluated everything and basically came to the same conclusion.
Pavlish:So this was really the very first indication that the universe is accelerating, the expansion of the universe.
Pavlish:And since then there have been other confirmations.
Goldhaber:Thereís been much more work, much more work. First of all, thereís been confirmation from the other group.
Pavlish:Ok, themselves also looking at supernovae.
Goldhaber:Looking independently at different supernovae. They had a smaller sample, but by that time, the measurements were getting better. You see, we had included earlier data for which the measurements were still more primitive.
Pavlish:You mean by measurements, the CCD camera?
Goldhaber:How accurately the supernovae were measured was not as accurate. Also one needed information from more than one filter which for the first few we didnít have that information. For the first few we didnít have that information. So their ten supernovae had the color information so they were more accurate. They were more like our later supernovae. But taking the total sample of 42, first it was 38 and then we kept adding a few more. By the time we published the data it was 42. So, anyway by the time it was all analyzed and carefully checked, it was a clear indication.
Pavlish:Since then, is there a bank of supernovae? You had 42, are there now 100?
Goldhaber:Yes, there are a lot more and they confirmed what we found. Particularly, we published another 11 which were measured by the Hubble space telescope. The Hubble space telescope gave us much more accurate measurements. We had another paper, later on, which confirmed. There were two important papers. One, with the Hubble space telescope which confirmed the data. Then there was another paper from our group which measured in detail, what kind of galaxy was involved. We identified the galaxies that gave the supernovae. We found there that elliptical galaxies have less dust. This was a paper by Sullivan et al which identified the individual galaxies. We found then that there was less scatter. You see these points which I showed you before, had a lot of scatter.
Pavlish:I think that thereís a picture of these similar to what you showed me on the computer.
Goldhaber:No, yes thatís a picture of a supernova.
Pavlish:Thatís different than what youíre talking about.
Goldhaber:Yes, Iím talking about many supernovae. Here, I will show you the paper here. This is the paper by Sullivan. Heís the first author but this is from our group, which identified the supernovae, the galaxy from which the supernovae came. And showed that if you have elliptical galaxies, then you have less scatter of these points. You see here, you have a lot of scatter. The elliptical galaxies give a more precise measurement. This is the same original data. Then we have another paper, Rob Knop et al which had 11 new supernovae which were measured by the Hubble space telescope. They confirmed the data with more accurate measurement. We have the same distribution here only with smaller uncertainty. Then there was a paper from the other group also using the Hubble space telescope and going to higher redshift. This went up to redshift of 1.7. Our redshifts at first were below z=1. Later on we began to find something of higher redshift. Now the higher redshift is interesting. Higher redshift means earlier, when the universe was younger. Then it turns out that for the younger universe, it was much denser, much smaller. Much smaller volume, so the gravitational force was bigger than the cosmological constant. And so you were in a decelerating phase. It showed evidence that this acceleration that we measured only came in the last 3 to 5 billion years. Not in the early universe. And that would happen if the repulsive force is constant, but the gravitational attraction depends on the size of the universe, on the distance between galaxies.
Pavlish:And what indicated that, again, about the supernovae? What about the supernova tells you that?
Goldhaber:The supernova stays on the same curve that I showed you. For that curve in an earlier time, the gravitational force was bigger. The force wasnít bigger, but the distances were smaller. The universe was smaller; separation between galaxies was smaller so the attractive force was bigger than the repulsive force. So there was actually deceleration. The early universe decelerated It is only in the last 3 to 5 billion years that we have acceleration.
Pavlish:Were the points lying under the curve?
Goldhaber:They were still on the same curve but the effect was that there was first deceleration and then it goes over to acceleration.
Pavlish:So how does dark energy come into this?
Goldhaber:Dark energy is the vacuum energy. First of all, we donít know yet what it is. There are hundreds of theories about what it could be but we donít know. So, whatís called dark energy is an effect of the vacuum energy density. At least one interpretation, letís say, which we know is true that the vacuum has energy. You know in quantum mechanics (youíve had quantum mechanics?) you get pair production. You get virtual pairs and then they get reabsorbed. This effect gives rise, it would give rise to a repulsive energy. Only, when you calculate it, it is an enormous repulsive energy. There wouldnít be any universe if that were true.
Pavlish:According to quantum mechanics?
Goldhaber:Yes, well, if that were the effect thatís there. So there is something else that tones it down by many orders of magnitude. In other words if you calculate the effect of virtual particles, you get repulsion which is the effect of 10 to the 120 too big.
Pavlish:Wow. Wait, can you tell me that again? So you have the vacuum energy..
Goldhaber:You have the vacuum energy. If you do a calculation on how big that effect is it gives you a repulsion which is 10 to the 120 too big. That couldnít be. The universe wouldnít be stable if that were true. Thereís something that reduces it by a factor of 10 to the 120 to a finite value, to a value which we observe. We donít know what it is. This is a big mystery of particle physics. What is the effect? But now its coffee time so we have to stop.
Goldhaber:You want to know people I have known, people I know. Letís see. In Wisconsin it was Ray Herb, when I was at Wisconsin, and Richards. They are not that well known. Ray Herb built the electrostatic generator. The high energy I was working at was 5 MeV. Then when I went to Columbia yes, there was Rabi, there was Kusch, there was Townes. And then I worked with Lederman, and there was Steinberger. Mel Schwartz was a student of mine. Those three got the Nobel prize. Mel Schwartz took classes from me. He was in my class. Leon Cooper was my teaching assistant when I was at Columbia. You know who he is?
Pavlish:Of Cooper pairs?
Goldhaber:Yes. So it was a good bunch. I mentioned already Bernadini was a visitor there. Ok, thatís it Columbia.
Pavlish:With all these great personalities together, was thereÖ
Pavlish:Yes. Like Rabi must have been veryÖ
Goldhaber:Rabi had the last word on everything, yes. Then there was, when I came here to Berkeley, I joined Segre in his group and then Segre and Chamberlain. Chamberlain is still here. Unfortunately he is sick. He has Parkinsonís. Then there was Louis Alvarez. Ernest Lawrence was still alive. He lived until í58 I think, and I came in Ď53.
Pavlish:Was he very dynamic?
Goldhaber:Yes, very much so. He was very pleasant, very nice to new PhDs. Then, at Columbia there was also Rainwater. Iím mentioning people who got the Nobel Prize. Rainwater was working there. Also, Val Fitch was a student when I was there. Here in Berkeley Iíve gone through those. Then I know also here Steve Weinberg was an assistant professor here. Then he left for Harvard and so on, MIT, and Texas. Shelly Glashow was also an assistant professor, maybe an associate professor here. And he left for Harvard.
Pavlish:You were close friends with him.
Goldhaber:Yes, with him I was close. Particularly the connection of working on charm. When I go east, when I go to Boston, I visit him. Who else do I know?
Pavlish:You mentioned Teller before.
Goldhaber:Yes, Teller was here and Teller was helpful in us getting our clearance. He pushed it forward. Letís see who else was here? Well, those are the main people. Then of course my brother was at Illinois first but then he moved to Brookhaven.
Pavlish:And he was the director there.
Goldhaber:Later he was director there, yes. Then of course I knew a lot of people who were not at the places where I worked. I knew Oppenheimer, but in his later years.
Pavlish:When he was already at the Institute?
Goldhaber:When he was at the Institute, yes. I knew Oppenheimer. I worked with Bram Pais, also at the Institute; you may have heard his name. We wrote a paper together.
Goldhaber:About this GGLP effect. Heís the P in GGLP. He helped us understand. We got the experimental result and he was a theorist and he helped us understand what it means and how to formulate it properly. So we wrote that paper together.
Pavlish:So when you did that, did you go over to New Jersey?
Goldhaber:As a matter of fact yes.
Pavlish:Specifically to work on this?
Goldhaber:Yes, for a couple of days. Not a long time. When we started, he was here as a visitor. Then I went to Princeton and stayed over. I donít think I stayed at his house but we were working at his house.
Pavlish:And thatís when you also met Oppenheimer?
Goldhaber:No, Oppenheimer I met at conferences. There was a conference in Miami where Oppenheimer was there. I have some pictures.
Pavlish:Did he strike you as amiable?
Goldhaber:Thereís a funny incident which illustrates his methods. I was giving a paper at the conference and he was chairman of that section. I forgot what it was at the time. But what I do remember is he got very interested in what I was discussing and as chairman he decided to cancel lunch. So we could go on. I donít know how much the other people appreciated that. He said, letís just go on. I mainly met him at conferences. I had no other contact with him. And of course I know Dirac, again I met at conferences.
Pavlish:Any interesting stories with Dirac?
Goldhaber:No, nothing special.
Pavlish:Was he rather reserved?
Goldhaber:I met him briefly. Also, Schwinger I knew a little better. We were at a summer school in Hawaii together. [opens filing cabinet] That was my brother and I.
Pavlish:This is at Brookhaven?
Goldhaber:Yes, that was at Brookhaven. That was one of his anniversaries. This is Sula, my first wife.
Pavlish:Was he director at this time?
Goldhaber:Possibly. I donít remember. This is Sula and Yuval Neíeman.
Pavlish:Should we put this back in there?
Goldhaber:Yes. This is Oppenheimer and myself. This is Meshkopf.
Pavlish:What event is that?
Goldhaber:This was at the conference in Miami. It doesnít say the year.
Pavlish:That was the conference where he canceled lunch.
Goldhaber:Yes. That was the occasion. I thought I had some other ones. But anyway. There was a picture also with George Zweig. I donít see him here. Oh, this one. Itís a bad copy. Well, anyway.
Pavlish:Did you ever meet Feynman?
Goldhaber:Oh yes, I knew Feynman well. He was at our house. And Gell-Mann. I forgot: Feynman, Gell-Mann.
Pavlish:Any funny stories with Feynman?
Goldhaber:Not really. For Gell-Mann in the early days he visited here often because he was working on the subject of what we were working on. Who else? I told you I knew Heisenberg.
Pavlish:And many people knew you!
Goldhaber:Some people knew me, yes.
Pavlish:You can choose not to answer this if you would like not to. But in this paper you write, ďI have never hidden data and I was not about to startĒ when discussing this little controversy. I think thatís a very honorable. If you chose not to answer thatís fine. In retrospect, do you believe that overall this is a good policy for a scientist, never to not even hide dataÖ to keep it private for a while so that other people donít get to a discovery first?
Goldhaber:For a while yes.
Pavlish:Is there a kind of operating code that all physicists follow that you follow also? Are you a little more open with your results than others?
Goldhaber:I tend to be open with my results. It is hard to say. It is individual. Some people like to keep their data longer. I tend to talk about it. I am usually told not to.
Pavlish:Told by others in the group.
Goldhaber:I donít like to keep data hidden. Ok, what else?
Pavlish:I have a lot of technical questions from these papers. I was wondering what R-band, B-band, Z-band filters are.
Goldhaber:Those are filters, different color filters which one uses on the telescope. Usually, mostly you donít just take the light as it comes. You put it through different filters. Thatís all it means. R is red. B is blue.
Pavlish:In particle physics — itís a controlled environment, you have manmade conditions whereas in particle astrophysics, or cosmology, you have the whole universe there as your laboratory. Does it make the experiment more complicated or simpler? How have you found the data analysis to be in these very different conditions? Are you surer of things when you know all the components of the experiment?
Goldhaber:Iíve found it rather similar. At least, what I do. Other people may find it quite different. Basically, you do an experiment. Say on the Bevatron, we did experiments, we took bubble chamber film, we measured the particles in the bubble chamber and we calculated some result from it, say a resonance for example. And in astrophysics, you take different images. You take images, but finally you have data on these supernovae in our case and you perform all kinds of manipulations of this data. And at that level, it is very similar. Of course you have to understand whatís going on. You have to understand what youíre doing. What you actually do is look at a graph, finally, and draw some conclusions from it. At least thatís the kind of thing Iím doing. Other people are doing other kinds of work.
Pavlish:Do you have a feeling about the results coming in in cosmology and astrophysics? Do you think that thereís so much more to be discovered using telescopes?
Goldhaber:Iím sure that thereís a lot more to be discovered, yes. People who think that the field is over, like the beginning of the century people were thinking all thatís needed is a few more decimal points. And that was pretty wrong. I think that thereís more to be discovered, lots more. Particularly, the thing that always intrigues me is that we now know that baryonic matter which is what we are made of, is only 5% of the universe. In fact, what we are made of is really even less. The stars are only 1%. The other 4% is gas which actually is hard to see. And look at the complexity of this 1% of the universe. What is the complexity of the other 99%? And we donít know anything about that. We donít know what the dark matter is, we donít know what the dark energy is. When we find out what they are then what is all the complexity that we have in our 1%? So, thereís a lot to be discovered.
Pavlish:Do you think there might be other forces too?
Goldhaber:I donít know. Thatís in the realm of theory. Iím an experimentalist.
Pavlish:The data would have to giveÖ
Goldhaber:Yes. The data would have to convince me about something. It is not obvious. As to other forces, people can speculate. Until thereís evidence, I wonít go for that.
Pavlish:I was wondering, in addition to the supernova measurements, what are other ways of determining cosmological parameters?
Goldhaber:There are lots of other ways which are now being explored. One thing is, that you can measureÖ one is gravitational lensing. Gravitational lensing means that mass deflects light. So you have several effects. Thereís strong lensing where you actually see a new image, you can actually see double images or fourfold images of an entire arc. Thatís been seen. Then, there is microlensing, which means that the lensing changes the shape a little bit. Instead of a round galaxy, it becomes distorted. From this distortion, people are also able to get at the cosmological parameters. Then, there is whatís called concordance. Let me see if I can illustrate that for you. Letís see. Here, this is our webpage. You should know of the webpage. Its ďsupernova.lbl.govĒ and then here we have all kinds of figures. Iíll show you one here. This blue here is the result you get from the supernova. This is the plane Omega Lambda, Omega Mass plane. Then the CMB, the Cosmic Microwave Background measurement says that the answer must lie along this curve. This is the curve of the flat universe. And then there are measurements on clusters of galaxies which tell you something about the mass density of the universe. And you see how you get concordance. They all intersect at some point more or less. There you see, you could take just those two measurements, clusters and CMB and you would come up also with the 0.3. This came later, this confirmation of the dark energy.
Pavlish:Wow, thatís very neat.
You asked, so there are other methods. And you heard today at the end he talked about cosmological parameters based on those measurements. So there are now beginning to be a lot of different measurements which can lead to the cosmological parameters. We are planning, our group, largely Saul Perlmutter who is the head of the group and Michael Levy are planning a telescope on a satellite. Whatís it for? It is to study supernova. Also, this gravitational lensing will be done. The idea isÖ now why do we need it? We already have measured this. The reason is, thereís one basic question. [continuing with afternoon session] SoÖ
Pavlish:So is the cosmological constant, constant in time?
Goldhaber:Is it constant or is it changing with time. How do you see change the time? You look backwards in time. You can only look backwards in time. We canít look forward yet.
Goldhaber:The idea there is to get something like a few thousand supernovae, and with very accurate measurement and control all the systematics and ask this question, is it constant or is it changing in time. When we have the answer that should help in understanding what it really is. I mean, whatever theory explains it must explain this behavior. The aim is to understand more about dark energy. In the meantime, people are looking for dark matter.
Pavlish:Are the two related? Are dark energy and dark matter related?
Goldhaber:As far as we know, theyíre not related. I wouldnít be surprised if some theory claims that they are related. To the best of my knowledge, theyíre not related. But there are experiments which try to measure the dark matter, that try to find the particles that are dark matter. Possibly when this new collider goes into effect at CERN, one might be able to find those particles, produce those particles. Ok, whatís your next question?
Pavlish:Ok, so my other questions all would have to do with these papers. Really just, when I look at these plots, a lot of these, I have trouble understanding them. Or, however you prefer to use the time because we donít have that much time. Or to finish up this book? Or for you to talk about things we havenít talked about yet. Or your ideas for how you might be able to make this book into a popular version.
Goldhaber:These papers you donít need to understand. Well, thereís one thing I worked on which Iím proud of. That is to show that the universe is really expanding. Going back some. Because as soon as Hubble found the expansion of the universe, there were people who said that maybe thereís a gravitational effect that gives you redshift, that the redshift we observe is not expansion of the universe but that itís some gravitational effect. Or that itís the effect of tired light. Tired light means that somehow the photonsÖYou see, what we observe is that they are redder, they have lower energy, so if they scatter somehow then you would also lose energy and they would become redder. The experiment that I did was to show that the supernovaeÖ You donít need to understand this one, so donít bother with it. Actually, I could give you an extra copy of this paper.
Pavlish:I could probably just get it from online if you donít have extra copies.
Goldhaber:I have lots of copies. So here I plotted, the blue dots are nearby supernovae and the red dots are distant supernovae. As you can see, itís a wider curve for distant supernovae. This effect is an effect of time dilation. In other words, this distance here is something like three weeks for the supernova light to be sort of halfway. For the nearby its three weeks but for the distant ones itís more like six weeks. This is the effect of time dilation. Time dilation only occurs if you have an expanding universe. So, in other words, at this side, this light comes off from the supernova and we observe it, but then we come back six weeks later and we observe this light here, but in the meantime the supernova has moved away from us with the expansion. The expansion of the universe has gone by six weeks. And so this light takes longer to come to us and that difference is the time dilation. This experiment proved the expansion of the universe. Let me get you a copy of this paper.
Pavlish:And this was your experiment?
Goldhaber:Yes. This was a part of our experiment, yes. Hereís a copy of that.
Pavlish:Thank you so much. So these are the same supernovae?
Goldhaber:No, they are different supernovae. The red ones are distant. Redshift of a half say, on average. And this is close to a redshift of .01, something like that, so essentially zero.
Pavlish:How is the six weeks? These are not the same supernovae?
Goldhaber:They are different supernovae. The supernovae are all say, letís say identical. Itís not completely true but they are very similar to each other. And so if you consider them as identical, the difference between this curve and this curve is that I divided by one plus z. One plus z is the expansion of the universe. And that brings them all together. But you see, they are not perfect. There is some individual, what we call stretch, from one supernova to another. Theyíre slightly different. When you take that factor out then you really fall on top of each other.
Pavlish:Iím trying to piece this together. First you have Hubble. Then Einstein proposed the cosmological constant and then it kind of went out of favor, right?
Pavlish:Then the evidence came out again with your work.
Goldhaber:Actually, Einstein first proposed the cosmological constant and when Hubble found the expansion of the universe then Einstein considered this his greatest mistake, his greatest blunder as he put it. And what we find now is that maybe it wasnít such a big mistake. That there is something like a cosmological constant.
Pavlish:And this was, when Einstein proposed it, was it within general relativity or?
Goldhaber:Yes. But he had the following reason, which is very logical. At that time, which was I guess 1917, it was believed that the universe is static, you know, not moving. If it is static, then we know that gravity pulls everything in. So he felt, how can you have it static? It should collapse because of gravity. He said well, to keep it static, I have to add another repulsive force to make it static. Now, because his equations were showing either it should expand or collapse. So he made it static with the cosmological constant. But then when Hubble discovered that itís actually expanding, he felt that he could have predicted that but he didnít. So that was his blunder.
Goldhaber:Now, that cosmological constant is not the one we are finding, that value. He wanted a value to make the universe static. What we are finding is quite different; much smaller and so forth. Well, itís different. But donít say I found it.
Goldhaber:Our group found it. I happened to point it out to the group first that thereís evidence forÖ
Pavlish:But you think that they would have, sooner or laterÖ
Goldhaber:Sure. Anything that somebody can find, the lucky one finds it first. Otherwise its found three weeks later or six months later. You knowÖ
Pavlish:Thatís what itís like inÖ
Goldhaber:The data is there. Like, I found charmed mesons. But so would anybody else have found it.
Pavlish:You think so?
Goldhaber:Yes, itís there. Itís in the data.
Pavlish:But still there are things in science that if one person hadnít come up with itÖ
Goldhaber:Then it would take a couple of years longer. Because, if something is real, then itís obvious in the data. So if somebody doesnít notice it early then it will be noticed later on.
Pavlish:So thatís an interesting contrast with your artwork, for example, which nobody else could have produced exactly as you.
Goldhaber:Probably so, yes.
Pavlish:Do you think?
Goldhaber:No, well, sure. Somebody could have produced drawings. I have this particular style. I donít think of it that way.
Pavlish:You donít think of science versus art that way?
Goldhaber:I think of art as recreation, as recreational work as opposed to serious work.
Pavlish:I would be interested actually in what your ideas are for the; youíve mentioned the popularization of this book. If you would rather just finish up with explaining the last chapters or...
Goldhaber:Well, this book really explains all these experiments, brings out the details in all these experiments. And what I was thinking is one could describe all these experiments for the layman and make a book out of that. A popular book. It still would be ďThe Experimental Foundations of Particle Physics .Ē
Pavlish:Maybe with some pictures
Goldhaber:Yes, pictures of the people involved. And a simpler explanation. Now, the other book Iíve been thinking of is based on all the lectures which Iíve given, which I gave to you. Make that the basis of a book. So those are two different possibilities.
Pavlish:Perhaps to tie together the themes of going to higher and higher energies.
Goldhaber:Yes, a book could be partly about me but itís also about particle physics. I donít know. Those are some ideas. Now there are things in here which may be too difficult to explain to the layman but I think much of it can be explained. Now letís see, where were we? I think we finished with charm.
Pavlish:Can I actually ask you, do you ever think about; for your children or your grandchildren do you ever explain these difficult concepts in a way that can be understood easily?
Goldhaber:I sometimes try, yes.
Pavlish:Do you off the top of your head?
Goldhaber:My son is interested in what I do. I sometimes try to explain it. Heís a businessman so heís not in physics. Yes, I think so.
Pavlish:But off the top of your head?
Goldhaber:And of course Iíve explained it to my students. For several years, the basis of this book was a course, as I mentioned to you. Now letís see. Sorry, you had some other questions.
Pavlish:I was just wondering if anything off the top of your head comes to you as a particularly good way of elucidating some of the ideas.
Goldhaber:I have to think about it. Well, yes I think the strong interactions are now explained in terms of the quarks. So one can explain quarks and gluons. In fact this chapter now is quarks, gluons, and jets. Well, the first evidence was from scattering electrons off protons which gave the evidence for quarks. Gave the evidence that somehow there was something inside the proton. It wasnít a solid particle. Just like Rutherford scattering showed that there was something inside the atom. Similarly here. So the ideas are that there are quarks that are held together by gluons. The strong force is the force of gluons holding together the quarks. Thereís this funny concept of, that when theyíre close together the forces are small and when they get farther apart the forces get strong. So you canít pull them apart. You canít pull out the quark from the nucleus, from the nucleon. Asymptotic freedom is what itís called.
Pavlish:So how is that, so the gluon is a force particle? Is that only for the strong force?
Goldhaber:Yes, for the strong forces. For the weak forces you have the Znot and the W, the W and the Z are the weak force. Since I deal in evidence. Thereís evidence that one gets jets coming out. Then there was direct evidence that you get threeÖ this isnít very convincing. I have one here. That you get sort of three jets coming out where one of those two are the quarks and the third one is a gluon jet. There was this very characteristic three objects coming out when the electron hits hydrogen for example. But the theory is that theyíre held together by the gluons. The gluons act like a rubber band. When youíre close together thereís no force or very little force. As you pull it apart you get stronger and stronger and stronger. Finally the rubber band breaks. Youíd think youíd get a gluon out. But no. As it breaks, you make a pair of pions and this goes off as a rho and this remains as it was originally. So you cannot get the quarks to come out. People have tried. There have been many experiments where people have tried to see the quarks. Ok, next chapter. Chapter eleven is the fifth quark. Remember before we had up, down, strange, and then we found charm. The fifth quark is the bottom quark. Leon Lederman is associated with this work. Thereís an interesting story there. He thought heíd found a bump in this, looking at two muons in some interaction, two muons coming out and he plotted the mass of those two and he thought he saw something at about 6 GeV. Well, we also worked in that region and we did not see any such effect. He called it the Upsilon. So, then it was called ĎOops Leoní. But then he went on. He persisted and he did find finally, that there was an oops, he still called it the Upsilon, but he found it at 12 GeV instead of at 6 GeV.
Pavlish:So itís really something else that he found. He just renamed it.
Goldhaber:The other one was a false alarm, Iím sorry itís about 9.5 GeV instead of 6. So the 6 was a false alarm but there was such an object higher up. That is the equivalent to the psi. The psi is the charm and the anticharm bound. Here this is a b and an antib bound (b, bbar). Then they found also the equivalent of the charmed mesons which I found. Here they have the equivalent. Mesons which contain a b quark. Ok, thatís what this chapter is about. That was chapter 11. Letís see. What is chapter 12?
Pavlish:By now it wasnít quite as revolutionary because it had been already...
Goldhaber:Thatís right. It was sort of a carbon copy of what we had found there. Interesting, but not quite the same level of excitement. Now the B mesons are very interesting. They changed the PEP machine to run at this energy and sit there and make B mesons. And the B mesons you can study CP violation, and they found CP violation for the B. Now, you asked me yesterday why donít we find it for charm. Iím not completely sure. This is a theoretical argument. For one thing the B has a much longer lifetime than the charmed particleÖ but Iím not sure. The answer is known but at this moment it escapes me. There was this prediction that you wouldnít find it for charm. Now it may have something to do that the charm is an up quark while B is a down quark. See, the CP violation was found for the strange quark which is a down quark and now also for the B which is a down quark. But charm was an up quark. Iím not sure if that is the explanation. There is some known explanation though not to me at the moment. Ok, that gets us to chapter 12. And this is the discovery at CERN of the heavy bosons: the W and the Z. And, again, I have personally nothing to do with this or with the B mesons, with the B particles, except that we did measure the lifetime of the B. So thereís the Zzero here you see. You calculate the mass of two electrons and then you find the distribution here and then you find suddenly a bump. This is what I mean by a resonance bump. You get such a bump. What I found here looked similar. That in my mind made me believe that itís real. And they also measured the W. These particles were predicted from the weak interaction. We have different particles which are the force particles. The photon is a force particle. One used to think that the pions hold the nuclei together but thatís not true. Itís the gluons are the strong interaction. Then the force for the weak interaction, thereís the charged one which is the W and the neutral one which is the Z. And both of these were discovered by Rubia and coworkers at CERN. They really specifically designed an experiment to measure these. They knew from the weak interaction theory from Weinberg, Salam, and Glashow, it was known where to look for these. That was a very major discovery.
Pavlish:Confirming the theory.
Goldhaber:In this case confirming the theory while our psi discovery was totally something new. There was no theory. Hey, we finished the book. There is an epilogue. Now, my colleague Bob Cahn, who is here at LBL, is working on the second edition of our book. Iíll be working with him also.
Pavlish:When do you expect that to come out?
Goldhaber:Any year now. Itís very late. We should have had it for a long time because people were clamoring for this book. Where did you get it, from Amazon?
Pavlish:Online, I think from Amazon used. They have used copies but they say some of them are like new.
Goldhaber:How much do they charge for those?
Goldhaber:Well, there should be a new book out maybe it will also cost one hundred I donít know. This one was more like fifty when it first came out. Now this is really only the particle physics up to 1990 or so. Since then there have been developments which are not discussed here. Of course they hadnít been found when we wrote this. One of which is CP violation. Then thereís a lot of new data on neutrinos. Neutrinos turned out to be very exciting. There are three kinds of neutrinos. Each one goes with one of the three leptons. Thereís the electron, muon, and the tau. Each one of them has a neutrino associated with it. Sort of a dublet. Electron neutrino, mu neutrino sub mu, tau neutrino sub tau. Originally one thought the neutrinos have zero mass but actually they can mix and that implies that they have a mass.
Pavlish:Why is that, according to the theory?
Goldhaber:According to the theory, yes. So, one is now making measurements on neutrinos to find out the details of how this works. Thatís the current experimental question. Then, there were these large detectors, water detectors built to measure proton decay. The theory predicted the proton should decay. But so far they only found a limit to proton decay. Itís longer than 1033 years or so.
Goldhaber:But what they did find is there was a supernova explosion and not the Type 1A which we have but the Type 2 emits a lot of neutrinos and they were able to detect the neutrinos from the supernova explosion. In two places on earth, one was in Japan; the other was in Ohio, in a mine in Ohio. My brother is associated with that experiment. Itís called the IMB. B is Brookhaven. I am something. M is Michigan. Anyway. So they observed the neutrinos arriving from the supernova. Thatís an interesting thing. The neutrinos arrive before the light arrives, not because they are faster but because they get out as soon as the explosion occurs. Because they have such a low cross section. The photons rattle around and take some time to get out. So the neutrinos arrive a few hours before the light arrives.
Pavlish:They have a smaller cross section does that mean they take up a smaller volume?
Goldhaber:They only interact by the weak interaction and this gives them a very small cross section while the photons interact electromagnetically which is longer. Itís less than the strong interaction but bigger than the weak interaction. The funny thing is that you donít see the explosion but you detect the neutrinos from it. This occurred I think it was 50 kiloParsecs. It was a supernova in the large magellanic cloud, 1987A. But then one has observed the neutrinos from the sun. The burning of the sun involves neutrino emission, thatís been observed. There are a lot of neutrino experiments now. Thatís the current hot topic. Iím not involved in that at all. So you see thereís a lot of particle physics Iím not involved in.
Pavlish:Since youíve joined the cosmology project.
Goldhaber:Yes, but also aside from that.
Pavlish:Can I ask actually, what it was like for you since you didnít join the SSC. And when it was canceled. Was a difficult time for your colleagues?
Goldhaber:Very difficult. Some people moved to Texas and bought houses. Yes, it was a very difficult time.
Pavlish:Did you find yourself providing support for them or it was that they had to figure it out for themselves what they were going to do next.
Goldhaber:They had to figure it out.
Pavlish:Did you have anyone join your project?
Goldhaber:Not ours, but some people came back to Berkeley and joined the Babaar project because the other one didnít go. Yes, it was a difficult time for them, thereís no question, particularly if they bought houses and sold houses, retired from their jobs to take up something in Texas. It was a very major perturbation. I did not gloat that I didnít go there. Ok, do you have any other questions?
Pavlish:This is technical. What is the difference between Type 1A and Type 2 Supernovae? Can you just see it, the difference?
Goldhaber:They have a different spectrum; they have a different light curve. Thatís enough. They act differently. Let me tell you what type 1A is. Type 1A happens like this. You have a star and you know that it burns hydrogen to carbon. That is the basic source of energy for the star. Thatís how our sun works. Now, what happens when you use up all the hydrogen? When it keeps burning, finally you use it up. Thatís a very catastrophic effect. The star suddenly collapses and becomes a white dwarf. This is for stars about the mass of our sun. That will happen to our sun in 5 billion years or so. We have to prepare accordingly. So now you have a white dwarf. What a white dwarf is, is carbon and oxygen nuclei and electrons. It changes from the size of the sun to something the size of the earth. The white dwarf is about the size of the earth. What keeps it from collapsing further is the free electron gas, the electron gas pressure, thatís what holds up the white dwarf. In principle it could stay that way forever. Now, there are some white dwarfs which have a companion star. Many stars have companion stars. So when one of them goes into a white dwarf the companion is still there. If the conditions are right, you can have mass transfer from the companion star to the white dwarf. So the white dwarf is getting heavier and more massive.
Pavlish:Mass transfer, what mass is being transferred?
Goldhaber:Hydrogen is transferred from the star to the white dwarf, mainly hydrogen. Now the white dwarf is getting heavier. And when it reaches the Chandrasekhar limit, which is 1.4 times the mass of the sun, as it gets heavier the force of gravity gets larger and larger on the inside of the star. It pulls in stronger and stronger. When it reaches the Chandrasekhar limit, the gravity overcomes the, the electron gas pressure has a certain maximum pressure, it cannot get bigger than that value. Then it just collapses the white dwarf. That is the supernova explosion. And that takes two seconds. In two seconds the white dwarf collapses and as it collapses it heats up inside and starts a fusion reaction, only now itís a fusion of carbon and oxygen nuclei. They fuse together to make heavier elements all the way up to iron. It is this fusion which then explodes the white dwarf. It explodes. It is this explosion which is the Type 1A supernova. Then, what you have is what is called a photosphere, it goes over into gas, expanding gas. The expansion is up to 30 km per second, the expansion of the gas.
Pavlish:Is the neighbor star unaffected?
Goldhaber:It probably is affected, we donít know. Maybe pushed away, but we donít observe that.
Pavlish:How close is the neighbor star?
Goldhaber:Several radii, several solar radii, the size of the sun. So itís fairly close. Now, letís see. So now what is the light that you see? The energy of the explosion goes all into kinetic energy. It just explodes this thing. It doesnít produce any heat, any light. But in the process it makes radioactive substances in the fusion process. In particular it makes Nickel 56. In fact one gets something like 0.6 of a solar mass of Nickel 56. A big chunk of nickel. And Nickel 56 is radioactive. It emits gamma rays. And it goes over to Cobalt 56. Nickel 56 has a six day half-life. But Cobalt 56 has a seventy day half-life. If youíre going to quote numbers youíll have to check this precisely. And then Cobalt 56 decays to Iron 56 which is stable. Now, itís the energy of the radioactive decay which gives the light. That heats up the photosphere and that is the light we see. So we donít see the light of the original explosion, we see the light through the Nickel 56.
Pavlish:So might you see several, like when it goes from Nickel to Cobalt you see light, and then when it goes from Cobalt to Iron you see light again?
Goldhaber:Yes, but all this is mixed together. The lifetime determinesÖthe time to maximum light is about twenty days. And then it gets dimmer because the radioactivity begins to decay away. So these two lifetimes determine the shape of the light curve of the supernova.
Pavlish:And thatís what youíre measuring.
Goldhaber:Thatís what we measure. We see the light.
Pavlish:And that light gets red shifted then.
Goldhaber:We see the red shifted light. Thatís exactly it. And people are doing calculations to try to match the data. Theyíre not perfect yet. They can get the general trend of whatís going on. Itís very complicated. There are hydrodynamic effects. What you see is the outer shell of the photosphere that keeps expanding at one tenth the velocity of light. Thirty km per second is one tenth the velocity of light. Why these are standard candles, the explanation is because the explosion occurs when you reach 1.4 solar masses, the Chandrasekhar limit. That is in common to all the Type 1A supernovae and so thatís the expansion, thatís the light that we observe. Now a Type 2 supernova is quite different. First of all itís much heavier, itís a star of maybe 50 to 100 solar masses. See this was a star of maybe 1 solar mass, same as our sun. These are much heavier. Here when the hydrogen gets used up the star collapses and then the core gives rise to the Type 2 supernova. It has quite different properties, completely different properties, just that theyíre both supernovae.
Pavlish:This has no companion star?
Goldhaber:No companion star and it itself explodes right away when it reaches this stage of using up the hydrogen.
Pavlish:Is this more common? Is one more common than the other?
Goldhaber:Theyíre about the same, actually becauseÖ well, thereís no because. The many solar mass stars have a much shorter lifetime. They burn up faster while the solar mass has a longer lifetime. But it happens, thereís no physical law that they have to be the same, but it happens that theyíre quite comparable. The type 1A supernovae are usually brighter. That also makes them easier to see at a large distance. But people are trying now to use type 2 supernovae as quasi standard candles. Now, I suggest that we go over to our house and have a drink and then maybe go out to dinner somewhere.
I would be quite honored.Session I | Session II | Session III | Session IV | Session V | Session VI