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Home , Lisa Randall, Raman Sundrum

Interview with Interviewer: Shinji Mukohyama

Writing a Book Hoping Randall: It is really quite a lot People Change Their Way of time. It means giving up of Thinking about Science other things. I think I don’t Mukohyama: Thank you very do all other things as much much for making time for us. as I’d like to do. I am often Let me start by congratulating writing when I am traveling you on the publication of the ̶certainly at every available Japanese translation of your opportunity. Even I remember, second book.1 I really enjoyed I was sitting at the National helping in the translation of Academy of Science’s your book. meeting, which is a big deal, Randall: Thank you for doing and Bruno Zumino looked at that, it’s really important, me and said“, Are you writing because, as you know, it’s a your book?” I guess I was just dif cult thing. They try very shocked that I was. Basically I hard, and so it’s really good to try to do whenever I can, but have a physicist look at it. still it ends up taking quite a Mukohyama: Yeah. I noticed bit of time, and then I have that translating this book took this chunk of time and you a long time and lot of work. have to do this. Some of it is Writing the book really took very enjoyable, but some of it much more effort. is like a big purpose. To write Randall: Yeah, that’s true. a book with one idea is not Mukohyama: So how did you so hard. I think for me it is not nd time to do this? that interesting, so I try to put many ideas into the book, and then integrating them into a Lisa Randall is Frank B. Baird, Jr. Professor of Science at Harvard way that it all makes sense. University. She received her Ph.D. That becomes challenging. from in 1987. She became Assistant Professor in 1991 Each chapter was quite a bit, and Associate Professor in 1995 at and then guring out how to MIT. She held professorships at MIT (1998-2001) and

(1998-2000) before returning to 1 Harvard University in 2001. She is a Knocking on Heaven’s Door: How and Scienti c Thinking member of the National Academy Illuminate the Universe and the of Sciences (since 2008), European Modern World, ECCO Press at Academy of Sciences and Arts (since HarperCollins, September 2011; 2012), and many other renowned Random House, September 2011. institutes and societies. She was on Japanese translation: 宇宙の扉を the list of Time Magazine’s“ 100 ノックする, NHK Publishing, Inc., Most Inuential People” of 2007. November 2013.

12 Kavli IPMU News No. 25 March 2014 put all the stories together. So, Randall: I think some people yes, it took quite some time. get it. I think a lot of people Mukohyama: Did you start are very stubborn, and so they writing the second book soon have their way of thinking. after nishing the rst one?2 If you don’t say what you Randall: No. In fact, I didn’t are thinking, they don’t pay think I would write a book for attention or they think they a while. I think the original know it all. I tried very hard motivation was more about to speak to the middle, so sort of the frustration with the people could talk to each way science was presented, other. Some people appreciate more than just about the that. But, I think we have a physics, which of course I was long way to go. I think just in excited about too; the Large the terms the way things have Hadron Collider, , come out, people in America and all of that. After reading just like that argument much the newspaper, and following more, they don’t like to nd the debates, and traveling this middle ground as much. a bit, it wasn’t always clear But, I pursued it anyway, that even people interested in because I think it’s science understood really how important. I think it science worked. And I was will be a little while asked a lot of questions after before things change. my rst book. So, I realized But, maybe, it’s changing a this could be a very nice book, little bit. I think there was a and then I started writing. But, little bit more attention to it was some years later̶it thinking scienti cally in recent was few years at least. years than there had been Mukohyama: So do you think before. Maybe it’s helping. the second book changed Mukohyama: Yeah. We need Interview the way people think about patience. science? Randall: Yeah, I don’t know,

2 : Unraveling the Shinji Mukohyama is Associate Mysteries of the Universe’s Hidden Professor at the Kavli IPMU. He Dimensions, Allen Lane at Penguin, studies and June 2005; ECCO Press at Harper . He stayed at Harvard Collins, September 2005. Japanese University from 2001 to 2004. He translation: ワープする宇宙 ― 5次元 supervised the translation of Lisa 時空の謎を解く―, NHK Publishing, Randall’s rst book2 and the second Inc., June 2007. book1 into Japanese.

13 Mukohyama: I see. But for there are subtleties, as you other people it was too new know, about how it gets probably? communicated and“ Does the Randall: Yeah, I’m not sure. modulus5 carry information?” I don’t know. I think maybe in the mediation also because of duality, scenario; because we really people thought maybe it’s wanted to have a scenario just something that’s already where it really worked, where known. I think it took a you didn’t have the leading little while before people order terms. It was a tricky appreciated that we had really thing. We realized you had to done something different. I have working could be wrong, but that was on the other brane. But in maybe the sense I had. But, the process we were working we were certainly enthusiastic. out the geometry, we saw we don’t have time. There are make sure, because in some It was also a funny thing this exponential, which is too many things that have to sense we were really like, though, because we were remarkable for people like us be done properly. “Why didn’t anyone see this nishing up our paper on who have thought about the Mukohyama: Right. But before?” But, I think we were anomaly mediation and for years. I hope that the Japanese pretty excited. I don’t know sequestering.4 Of course you think about version of your book and your what we thought in terms Mukohyama: Right. that. But then, I was starting TV program and so on will of who pays attention. In Randall: So, we actually at the metric and I was change the way people think fact, in the beginning I don’t delayed these papers until we confused, because it looked about science and get more think people paid as much were done with that. like you could remove one of people interested in science. attention. Mukohyama: Oh, really? the branes, which was a very That’s what I hope. Mukohyama: Oh really? Randall: We were excited, but surprising thing. Randall: Oh, that would be Randall: People made it seem we wanted to nish the other Mukohyama: Yeah, it’s very nice. Thank you. I hope so too. like it was just another extra things. We also wanted to surprising. dimension modeling. We really make sure we understood all Randall: Certainly, when I Excited with the Idea of the had to make that clear. Raman aspects, and we also had the told people this, they thought Warped Extra Dimension gave a bunch of talks in the in nite extra dimension. So it has to be wrong, because Mukohyama: Now, let us talk beginning. Then I started to we had three papers that we we are not allowed to have about science. Your theory of give talks, and then I think were thinking about at the an in nite extra dimension the brane world scenario and people started learning. Also, same time. They were all very and because of theoretical warped extra dimension3 I think right then Mark Wise interesting. 3 is now very famous and is called it“ Randall-Sundrum” in Mukohyama: I agree. So, you Brane world is a physical setup in which matter and forces are con ned considered as one of the most his paper. It was very good for actually have three different to a surface called brane. Warped spacetime geometry is a spacetime promising scenarios beyond us, because it made it clear it models based on the similar that would be at except for an the . But, I was a different kind of model. setup. How did you come up overall scaling that varies with the position in a direction. Warped extra wonder what you thought Yeah, I think people didn’t with different ideas from the dimension is an extra dimension when you rst proposed this always appreciate right away similar setup at almost the along which the higher-dimensional spacetime geometry is warped. model with . that it was̶some people same time? It’s amazing. 4 Anomary mediation is Were you con dent that this did, but I am not sure it was Randall: Well, in some sense communication of supersymmetry model would get a lot of immediately known. the math came up with breaking by quantum effects. Sequestering is the physical attention? Mukohyama: I see. the ideas, because we were separation of different types in . Randall: I am never con dent Randall: But I think we knew working out the model for 5 about that. I thought it was that it was different, and we the sequestered scenario A modulus is a scalar eld whose potential energy function has a good idea. We wanted to were quite excited. and for this metric; because continuous families of minima.

14 Kavli IPMU News No. 25 March 2014 reasons, which it avoids in a be realized in theory. very subtle way. Actually, I think if I remember Mukohyama: Right. It was correctly, there was a kind of almost like a theorem before no-go theorem. At that time your work. what was your feeling? Randall: Exactly. People Randall: Well, I think I have thought it was a theorem, said this for a while. Although, in fact. You’re right. It’s very there is a lot of interesting subtle the way it avoids it, work that comes out of string and so there were a lot of theory, I think there is the subtleties there that we tendency to think that you wanted to make sure we are going to be able to gure weren’t missing something. it all out from rst principles. Mukohyama: Yeah. One of the reasons I think Randall: But it really worked model building is important ̶because the equations ̶in addition to matching things that I’ve said to people, astrophysical, and particle gave us the hierarchy, and experiment̶is because it but then you have to think physics measurements̶you then equations also pointed forces people to really think harder to see if they can work. certainly need to think about out that you could remove harder. In some sense, models are all of them to really pin down a brane. But then it became Mukohyama: Right. an incentive to push a little what is. As I’ll talk subtle to gure out what it Randall: Is it really true that harder and see“ Are there about today, we have a new meant. It wasn’t like we set they’ve gured everything out different ways?” I used to model of dark matter. I think out to do this, but because already, or could it be that draw this picture with people there were just a lot of ideas we were thinking about these there are some interesting working from the bottom, in dark matter that have yet big problems, it became clear things they’re missing? I doing model building, and to be explored and can make after a while. wasn’t very worried, because people working from the top, a difference for how people Mukohyama: I see. I thought the likelihood and you’re trying to nd a study it. That’s one of the Randall: As you know, when that they had gured out common ground. things. I also think whether you solve for MPlanck it’s everything that’s possible in we have one solution to the independent of the position was kind of low. hierarchy problem. I don’t What’s Next? of the second brane, roughly Also it wasn’t the point to know if it’s right. So there speaking. This is an incredibly derive in string theory. It was Mukohyama: I see. That’s are still issues to think about surprising thing if you’ve a model and we wanted to great. After having proposed there. thought about an extra see. But, I guess I do think that a possible solution to the What do you think about dimension. So, understanding there were many things that hierarchy problem, which these days? that was what took us to the could happen en-route from is really one of the biggest Mukohyama: I am still third paper. the Planck scale to the TeV problems in theoretical interested in the cosmological Mukohyama: Yeah, I see. scale, and it was unlikely that physics, what is your next aim constant problem. Now people think that everyone had worked out all in your research? What do Randall: Yeah. your scenario, the Randall- of them. you want to solve? Mukohyama: We worked Interview Sundrum scenario can be Mukohyama: I see. Randall: Right. We don’t together on the cosmological realized in string theory. I Randall: I mean they would know if that’s right and constant problem. We have think that the KKLT 6 is kind of also say that a positive there were many aspects some model and it addresses the string theory realization of cosmological constant is that we worked out, as you some important aspects, but... this warped extra dimension. impossible in string theory know. But, right now, I am Randall: It’s not a perfect... But at some point it was not before. thinking about dark matter, 6 clear whether this kind of Mukohyama: Oh, yes. because I think that the S. Kachru, R. Kallosh, A. Linde, and P. Trivedi, Physical Review D 68 (2003) warped extra dimension could Randall: There are many combination of cosmological, 046005

15 Mukohyama: It’s not the real because we don’t have that institutes. of seminars and so on. solution. much room. We've already Randall: What are these other Randall: Yeah, it’s still lively. Randall: Right. gone to 8 TeV and now we’re institutes? And here is it very interactive? Mukohyama: I want to pursue only going to 13 or 14. Mukohyama: The next Mukohyama: Yeah. this direction, but at the same Mukohyama: Right. building is for the Institute for Randall: Very good. time... Randall: It’s a concern. But, Cosmic Ray Research (ICRR), Mukohyama: Do you have Randall: What other directions of course it would be very and the other building is for any message for young do you have? exciting if something is in this the Institute for Solid State people in Japan? Mukohyama: I am not sure machine and tells us what’s Physics (ISSP). Randall: Just to be excited at this moment; it’s kind of going on, whatever it is. I Randall: Do you have any about science, to be happy a longstanding purpose of mean, of course we hope that interactions with them? about thinking for themselves, my research to attack the they’ll nd something. Mukohyama: Sometimes and of course not to the problem of the cosmological some members attend exclusion of understanding constant. At this moment I am Message to Young People in seminars over there, and what other people are doing, now interested in dark energy. Japan people also come here from but to get inspired by the Randall: Which is similar, yeah. Mukohyama: Okay. I think there. Some people at ICRR amazing things that are Mukohyama: Right. They this is your third or fourth visit are af liated with Kavli happening. Also I hope things are related to each other. In to Japan, and your rst visit to IPMU. Also, we have some go well in Japan in the future. the end, we have to solve Kavli IPMU. interactions with Physics Mukohyama: Thank you very the cosmological constant Randall: Yes. Department which is located much. problem, and then attack the Mukohyama: What is your on the down town campus of Randall: Okay, great. Thank dark energy problem. impression about science in the University of Tokyo. you. Randall: Maybe. Japan? Randall: Is it a bit far? Mukohyama: That’s my gut Randall: There are some quite Mukohyama: Yes, a bit far, feeling, but it’s still too dif cult good people here. There are but I usually attend a seminar to attack the cosmological some quite good people who there on every Monday. constant problem at this come to the States, even Sometimes people come moment. My attitude now is temporarily like you did. I here, and sometimes we also to think about dark energy hope to see it stays strong. In have joint seminars among for a while. terms of my books, it’s very different institutes in the Randall: Okay. nice that people were really greater Tokyo area. I think Mukohyama: Now, back to interested at least in my rst there was something similar the LHC̶it found the Higgs book, with the second one, in Boston. Boson, so people are looking not yet in the stores, just Randall: Yeah, there was. for new physics beyond the coming out; it was one of the Not much any more. I think Standard Model. What is the most scienti cally interested they are busy. There are so most exciting scenario from audiences, so I think that’s many seminars here. Do you your point of view? very good. hear seminars from Japanese Randall: Well, of course I Mukohyama: Scienti cally I’m people or foreigners? would love them to nd this enjoying being here, especially Mukohyama: I think half and kind of . I do worry at the Kavli IPMU. Here, half. Maybe more people from that the machine might have people in different elds can abroad. And all seminars are too low energy and eventually communicate. given in English. we want to have much higher Randall: Is this the only Kavli Randall: OK, very good. energy machine, because IPMU building? Mukohyama: I remember at just statistically it’s not that Mukohyama: Actually, we Harvard the every-day likely that the new physics have the second building, a atmosphere was very would be in the next machine, building shared with other stimulating, and we had a lot

16 Kavli IPMU News No. 25 March 2014