Departmental Overviews (Physics): The Enjoyment of Discovery and the Wonderfulness of the Unknown - School of Science, the University of Tokyo
Mar 11, 2019

Departmental Overviews (Physics): The Enjoyment of Discovery and the Wonderfulness of the Unknown


-The Department of Physics -


Professor Satoshi Yamamoto (Head of the Department of Physics)


Physics is an experimental science that faces nature and investigates various phenomena from a broad range of substances and properties in nature. The field is strongly related to mathematics and has developed through both theory and experimentation. In particular, since the 19th century modern physics has supported the study of not only the origins of matter and the universe but has also built the foundation for all academic research through providing an understanding of microscopic views of substances and their related fundamental theory, which in turn has helped to form our present-day civilization based on the full use of electronics and information technologies. This role has remained the same to this day.

In science, gaining an understanding of something causes more mysteries to emerge. When looking back at scientific advancement over more or less a century, I wonder what kind of developments are waiting for us in the next 100 years. Even in the field of physics, our observations of nature will undoubtedly undergo massive changes and developments, and I believe that the ones to accomplish this may be you.

The three strengths of physics

As shown in Figure 1, physics covers a range of fields that is so wide that it is impossible to describe each one within the limited space in this article. Based on these many fields, I will introduce three strengths of physics. Please visit the Department of Physics homepage or laboratory pages to read about each field in depth.

Figure 1. An overview of the fields in physics. The Department of Physics is divided into nine sub-courses (A0-A8) according to these fields.

1: The ultimate challenge

A characteristic of physics is to thoroughly and ultimately investigate an object regardless of what it is. To achieve this, we are conducting research using the most refined technologies and methods. Let’s look at some examples.

Our pursuit of the origin of observable matter has us enter the invisible worlds of atomic nuclei and elementary particles. In contrast to the diversity of matter, the world of the elementary particles that form matter is simple and beautiful. Modern physics is experimentally approaching the origin of matter by conducting high energy accelerator experiments and searching for very rare events such as proton decay (Figure 2).

The detection of the Higgs boson, which is responsible for the origin of mass, has recently been attracting increasing attention. Even in theoretical research, the construction of theories that surpass the standard model, such as those using supersymmetry, as well as theories aimed at unifying quantum gravity, for instance superstring theory or M-theory, are advancing alongside mathematical physics. Research on elementary particles is strongly tied to the origin of the universe, through inflation theory, dark matter, and the origin of dark energy, and has become the ultimate frontier of exploring space-time and matter.

Figure 2. The ATLAS detector at the LHC accelerator located in Geneva, Switzerland, which discovered the Higgs boson. The diameter is 22 m and the length is 44 m. This is an example of state-of-the-art measurement in physics.

(Photo by Professor Shoji Asai)


Recently, gravitational waves have become a popular topic of discussion. Gravitational waves are said to be the last homework assignment left by Einstein and were predicted by the general theory of relativity. A gravitational wave emitted from the coalescence of black holes and that of neutron stars was recently detected using a detector with state-of-the-art laser technology. Persistent advanced technological developments over more than 30 years made supersensitive measurements that detect the displacement of a single hydrogen atom over the distance between the Earth and the Sun possible, which then led to the detection of gravitational waves.

A new world is also emerging in the field of quantum informatics. Beyond classical information and communication technology, we are now realizing technologies that use properties of quantum systems. Research is now being conducted in terms of how to use these extreme technologies for actual communication and what we can ultimately gain from these technologies. In our current “information society,” information is also a subject of exploration in physics.


2: Understanding diversity

Another strength of physics is that it explores diversity. Diversity is not just about collecting and examining various things but also deepening our understanding of nature by deriving fundamental laws that govern diversity. In particular, thermodynamics and statistical mechanics have played a key role in elucidating diverse systems consisting of various materials on various scales, which in turn has developed rich fields such as condensed matter physics, non-equilibrium physics, biophysics, and quantum informatics.

Solid-state physics clarifies the various collective properties of matter at the atomic level. For example, superconductivity is a cooperative phenomenon caused by the interaction between electrons and nuclei in crystals. Solid-state physics also experimentally and theoretically elucidates various interesting phenomena, such as topological quantum phases, correlated electron systems and quantum magnetism, based on the mutual interaction among constituent particles and fundamental laws of physics. Such a cooperative phenomenon is also seen in the structure of nuclei, although the energy scale is much different from those in the above examples. When protons and neutrons create many exotic nuclei, an interesting property develops and overturns what we thought we knew, which is garnering attention as one of the frontiers of quantum many-body systems.

Figure 3. Advanced laser technology is used to investigate physical properties of matter. (Below) A terahertz spectroscopic device, which is used to investigate the optical properties of copper oxide high-temperature superconductors.

(Photo by Professor Ryo Shimano)


Diversity in the universe is also the subject of physics as no two galaxies, stars, solar systems and planets are alike (Figure 4). In recent years, research on planetary systems outside of our solar system is rapidly advancing, and is revealing that these planetary systems are completely different from our own. Factors that govern this diversity are being explored using both observation and theory to address how the Solar System was born and why at least one planet within it has life.

Physics also includes the study of biology. In biophysics, organisms are regarded as a system and are reduced to the cellular level, and even further to the molecular level, in order to capture mutual interaction. In this way, we are approaching the application of physics methodology to the essence of biological phenomena behind biodiversity.


Figure 4. The universe is also an important target of physics research. The image above is an optical image of a cluster of galaxies taken by the Subaru telescope (Credit: HSC Collaboration) and below is a three-dimensional distribution map of dark matter derived from the optical image.

(Photo by Assistant Professor Masamune Oguri, The University of Tokyo Theoretical Astrophysics Laboratory)

3: A broad range

In addition to the two strengths mentioned above, physics also has wide applicability. Physics covers a broad range of fascinating areas aside from the ones previously discussed, such as photon science, plasma physics, and active matter. What’s more, physics is the basis of the basic principles that support the study of all natural sciences. It can be applied to anything as long as it is a natural phenomenon. In fact, physics contributes to astronomy and earth and planetary science as well as chemistry, biological science, information science and engineering, and further develops these fields by forming boundary areas.

The broad range of physics is further demonstrated by the various paths taken by graduates of the Department of Physics. Many students continue on to careers in academia at universities or research institutions in Japan and abroad, as well as find employment in industry. In modern society, we face challenges we have never experienced before. We have to analyze them in depth in order to establish the problem and work towards a solution. This method is the same in research. In particular, physics not only observes phenomena but also cultivates the power to think back to fundamental principles. Therefore, companies have high expectations for our graduates regardless of whether they have Master’s or Doctoral degrees.

The organization of the Department of Physics

There are many other departments related to physics at the University of Tokyo, such as the Department of Applied Physics in the School of Engineering, the Department of Multidisciplinary Sciences in the Graduate School of Arts and Sciences, and the Department of Complexity Science in the Graduate School of Frontier Sciences; however, the Department of Physics at the School of Science is the largest and covers the most fields. In addition to the faculty members in the Department of Physics, the Graduate Department of Physics also includes faculty members from the Institute for Solid State Physics, Institute for Cosmic Ray Research, Graduate School of Frontier Sciences, Kavli Institute for the Physics and Mathematics of the Universe, Japan Aerospace Exploration Agency (JAXA) and the Institute of Space and Astronautical Science and High Energy Accelerator Research Organization (KEK). In total, there are 131 faculty members who are conducting cutting-edge research in almost all fields of physics. We are proud of being one of the world’s largest graduate schools in physics. Our research and education are of the highest standard in physics and has produced four Nobel laureates in Physics: Dr. Leo Esaki for his discoveries regarding tunneling phenomena in semiconductors (1973), Distinguished Professor Masatoshi Koshiba for the detection of neutrinos from a supernova (2002), Dr. Yoichiro Nambu for the theory of spontaneous symmetry breaking (2008) and Distinguished Professor Takaaki Kajita for the discovery of neutrino oscillations (2015). Approximately 60% of Master’s students continue on to the Doctoral program and every year 60 to 70 students acquire Doctoral degrees, start work in academia and are active in every part of society as members who have strong problem-solving abilities.

The Department of Physics is a very large department and in terms of operation is divided into nine sub-courses from A0 to A8 in which related fields are grouped together (Figure 1). When students take graduate school entrance examinations in the Department of Physics, they can specify their first and second sub-course choices, and written examinations are common.

A free and open-minded atmosphere

Anyone has the chance to make a breakthrough in physics by finding a new phenomenon or methodology. Professors and students are equal in front of nature and even those who are young can have great success. The Department of Physics has an open-minded atmosphere in which supervisors guide students while respecting their independence and do not participate in evaluating their student’s doctoral defense. The number of foreign students has also been increasing recently. The number of professors from countries outside of Japan are still small (three out of 131); however, we are progressing towards internationalization. Almost all laboratories are conducting international collaborative research, and there are many students who are involved in these international activities.

A welcoming environment for female students

Alongside internationalization, we are aiming for a department where women are active in the field. At the moment, the proportion of female faculty members and students in the Department of Physics is unfortunately small. In the Graduate Department of Physics, the proportion of female students is 5.6% (27 out of 480). The number of female faculty members is gradually increasing; however, it is still quite low in comparison to other countries. One reason for this seems to be that Japanese society still mistakenly refers to physics as “a man’s field.” However, the study of physics and research of nature is neither male nor female. About half of those who attend physics-related Open Campus or Public Lecture events are women. There is also no difference in the proportion excellent male and female students. Provided this, I would like more women to join the Department of Physics if they have an interest in the field. If the ratio of female students surpasses 30%, this will instigate a huge change that will undoubtedly strengthen the Department.

The enjoyment of discovery and the wonderfulness of the unknown

There are no limitations when it comes to topics that physics tackles as anything can be challenged using physics. That is why physics is the foundation of every discipline regardless of its basic application. Physics is also characterized by strength and flexibility. If a law of physics is unknown, we find the law by not only organizing the phenomena but also extracting the underlying factors that govern them and/or capturing their universal properties by using statistical analysis. If the present laws are inadequate, or wrong in extreme cases, we should be willing to go back to the beginning and rewrite them.

In these ways, physics has elucidated systems in nature one by one since long ago. This has accumulated a vast amount knowledge that supports modern society and greatly influences how we view nature, the world and life, and has also benefited culture as well.

How much, then, do we truly understand nature’s systems? There are so many textbooks containing so much information that it is impossible to read it all. However, our acquired knowledge is only a very small part of understanding nature. Based on this small amount of knowledge, we believe we are enjoying a fulfilling life but this way of thinking is arrogant. When something unexpected happens, we think it’s surprising but it is merely a reflection of our lack of knowledge regarding nature.

Nature is something that is more profound than what we believe we understand. This is why despite the long history of physics, nothing is ever finished and there is no end. There are also times when the end result is a complete surprise. For instance, we first began to understand the essence of light with Newton’s corpuscular theory of light, which was followed by Thomas Young and Augustin Jean Fresnel’s wave theory, and right after we believed everything was clarified by Michael Faraday and James Clerk Maxwell’s equations of electromagnetism, it was found that quantum mechanics was based on both particle and wave properties. I wonder what kinds of developments are waiting ahead? Even if new discoveries haven’t become a big story yet, they often overturn previous notions. This is what makes research in physics so interesting and exciting.

You may feel moved when you tackle undiscovered phenomena in physics and elucidate systems in nature that have never been thought about. However, once you understand your discovery, it becomes a well-known truth, and then a new problem immediately emerges. For example, the detection of gravitational waves presents new problems in not only the field of astrophysics but also in nuclear physics. Science never puts an end to mysteries; instead, it creates new mysteries. Understanding things is, of course, fascinating. However, there is also greatness in things we do not understand because the possibilities are endless. The endless challenge of what we do not understand is the essence of physics and science.

Are you up for the challenge?


▶︎ For more information, please visit the Department of Physics homepage:


This article is from the 2018 "Departmental Overviews in the School of Science" series in The Rigakubu News ―


Translated by Kristina Awatsu, Office of Communication

― Office of Communication ―

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