Hitoshi Murayama, Ph.D.
Director, Institute for the Physics and Mathematics of the Universe, Tokyo University. Theoretical Physicist. Professor of Physics, University of California, Berkeley
Prof. Murayama received his Ph.D. in theoretical physics from the University of Tokyo in 1991. Subsequently, he was a research associate at the Department of Physics at Tohoku University, and came to the University of California at Berkeley as a post-doctoral fellow at the Lawrence Berkeley National Laboratory. Today he is the MacAdams Professor of Physics at UC Berkeley, and a member of the School of Natural Sciences at the Institute for Advanced Study in Princeton. Prof. Murayama assumed his current position at the IPMU in 2007. He specializes in particle physics.
Q. Could you first tell us about the organization and activities of the Institute for the Physics and Mathematics of the Universe?
IPMU research building. The spiral structure is seen on the side.
Offices are lined up in a spiral, and the doors are placed on the stair landings.
Galileo’s words on the pillar at the center of the communication space.
The IPMU was founded to integrate cutting-edge research in several disciplines to address the mysteries of the universe. What is the universe made of? How did it begin? What is its fate? What fundamental laws govern it? And why do we exist at all? Our aim is to address these five questions with the power of science.
We have two approaches to achieve this. One is to conduct research across and beyond specific fields. Questions about the universe are too complex to address with knowledge from only one particular field. This is why the IPMU brings in researchers from different areas - astronomy, physics and mathematics - to work on research together. For instance, Newton discovered the law of universal gravitation, and to explain the law he developed a new branch of mathematics called calculus. By creating new mathematics, he was able to explain the law of gravitation, why an apple falls from a tree, and why a planet orbits the Sun. Likewise, we aim to make discoveries through a marriage of different fields, including mathematics and physics.
Our second policy is to host scientists from around the world. Questions about the universe are common to all humankind, so research should be conducted not just by Japanese but together with colleagues from all over the world. At the moment, 60 percent of IPMU researchers come from overseas. In addition, the IPMU’s building has some innovations to facilitate communication between scientists in different fields and cultures. At the center of the building, there is a three-storey atrium, created to provide an area for researchers to mingle. All the offices are lined up around it in a spiral, so the space from the third to the fifth floor can function as one floor. This way, researchers naturally run into each other. Also, at 3:00 p.m. we ring a chime, and all the scientists gather in the common area under a skylight for discussions over tea. This three-o’clock tea time is mandatory to attend unless they are out of the office on business. At the center of the atrium, there is a pillar with words by Galileo Galilei, written in Italian: "Universe is a book written with the language of mathematics." This is the founding principle for research at the IPMU. Q. Reportedly, the IPMU is the first research facility ever to integrate different fields. What impact has this had?Globally, there are many cases of joint research done by collaborators from different fields - such as mathematicians and physicists, or physicists and astronomers - but there had never been a research institute like the IPMU before, where these fields were all put together in one place.
The merit of this is that a new discovery can be made through discussion with scientists in other specialties. A scientist pursues his or her own research, and works hard in the belief that it will lead him or her to answers. However, trying to explain your research to someone in a different field, you sometimes realize that you don’t know what you thought you knew.
For example, let’s say, I, as an expert in physics, try to explain my research to a mathematician. Mathematics is a study that demands a theory be developed extremely accurately and rigorously. On the other hand, in the world of physics, when we encounter something uncertain, we try to infer or speculate an explanation, even if it may be far-fetched. From the point of view of a mathematician, this is in some sense hand-waving.
So a mathematician will sometimes point out a hole in my explanation, and I then become aware that somewhere there is a gap in my thinking process, and that I am far from a solution, or that I need to think this way to be correct. And through discussions, mathematicians sometimes help me by suggesting a new approach. I am very thankful for this because it is good not only for refreshing my brain but also for closing gaps in thinking about a given problem. But at the same time, I am told that it is also beneficial for mathematicians to know that their knowledge is related to a certain physics problem, because it opens up their world, driving them to think about new directions of research.
Q. Could you explain the cutting-edge research at the IPMU?
XMASS experiment facilities (courtesy: Kamioka Observatory, Institute for Cosmic Ray Research, University of Tokyo)
The research is related to one of the questions from earlier: what is the universe made of? We learn at school that everything is made of atoms, and as a matter of fact, scientists did not doubt it, either. But about 10 years ago it became evident that that we know only about 4% of all the energy (i.e. atoms) in the universe, and that most of the universe is in fact not made up of atoms. It is thought that the rest is about 23% dark matter and about 73% dark energy. No one knows what they are, nor has anyone seen them. IPMU’s primary research is to find this invisible dark matter.
To do this, we have three research projects:
- The XMASS experiment is using a detector 1,000 metres underground. Dark matter makes up almost a quarter of the universe, so a large quantity of it must exist around us even though we cannot observe it. We are waiting for dark matter to hit the detector in the quiet environment deep underground. The XMASS detector was built in the Kamioka mine, in Gifu prefecture, and observation is scheduled to start this September. This detector is 100 times more sensitive than any others, so we think we have a higher chance of discovering dark matter. This is a joint experiment with the Institute for Cosmic Ray Research at the University of Tokyo.
- The second project uses something called the gravitational lensing effect, which is one of the predictions of Einstein’s general theory of relativity. It is a phenomenon where gravity bends light rays as if they are traveling through a lens. By measuring the degree of curvature of the light, we can calculate how much gravity exists in a particular spot, and how much matter it takes to produce that gravity. For instance, let’s say there’s a spot in the universe where dark matter clusters. If you observe a galaxy behind it, the light from the galaxy is pulled and bent by the gravity of dark matter. As a result, the galaxy looks distorted. So when we find a galaxy with a distorted shape, we can map the dark matter that exists between that galaxy and us. This is a project with the Subaru Telescope at the Hawaii Observatory of the National Astronomical Observatory of Japan.
- Finally, there is data analysis of particle accelerator experiments. The universe began with the Big Bang, and dark matter is thought to have been produced then. So if you have energy as intense as the Big Bang, it may be possible to produce dark matter again. In Europe, scientists are using the Large Hadron Collider to simulate Big Bang conditions by accelerating and colliding tiny particles. Our goal at the IPMU is to devise calculations with which to analyze experiment data that could prove the existence of dark matter.
I think these three projects will show that the IPMU’s integration of different fields is highly beneficial.
Q. What results have been achieved so far at the IPMU?
A map of dark matter superimposed on the image of a cluster of galaxies observed by the Subaru Telescope. The image is about seven hundred million light years across. (courtesy: Masahiro Takada (IPMU))
Although the IPMU was launched only in October 2007, many interesting results have already been achieved. For example, associate professor Masahiro Takada has observed clusters of galaxies, using the Subaru Telescope to study the existence of dark matter and the way it clusters. His observations make use of the gravitational lensing effect, and he has shown not only that there is a large quantity of dark matter within the galaxy clusters, but also that its distribution has an oval shape, and that it’s denser at the center than at the edges. More interestingly, the observation results were similar to predictions made with computer simulation. According to the most advanced simulations, by IPMU associate professor Naoki Yoshida, dark matter in a cluster of galaxies would be not round but an elongated oval. It is wonderful to be able to confirm a theory with observation.
Also, principal investigator Prof. Ken’ichi Nomoto and his research group have used the Subaru Telescope to measure the light of a supernova. That supernova had been observed with the naked eye by the Danish astronomer Tycho Brahe in 1572. A supernova is an extremely bright phenomenon from a massive explosion that happens at the end of the life of a star. It’s so bright in part because light from the explosion bounces off accumulated dust in the galaxy - the same principle as the echo you hear when you shout in the mountains. Prof. Nomoto measured the supernova light of an explosion first detected more than 400 years ago, and traced what kind of explosion it was.
