I have worked in astrophysical cosmology, both theoretical and observational, over the last two decades. Around 1987 I began to study the thermal history and consistency tests of the Friedmann model of the Universe. In particular, I was concerned with the cosmological constant Λ, the need of which I realised when I worked on the galaxy number count, which witnessed significant progress with the advent of charge coupled devices. A non-zero Λ was also consistent with the view I obtained from the work to assess the determination of the Hubble constant from nearby galaxies. I raised the issue of the cosmological constant being non-vanishing, but this was an anathema at the time, something that should be avoided at any rate, and I was subsequently strongly criticised by all.

While I tried to assemble observational data, I realised that there was a serious lack of data that could be used for cosmology. Having felt that we could not make progress without more extensive observations, I became engaged in observations. While I was carrying out observational programmes, I was invited by my friends in the US to join a digital sky survey project they conceived (later named the Sloan Digital Sky Survey: SDSS). Having organised a group of Japanese astronomers, and having secured necessary funds, we joined the project in 1992 as its fifth initiating member and worked for this and preparation for photometry. After completion of the instrument in 1999, I worked mainly on galaxy science and cosmology deduced from the survey. It took 15 years to reach fruition, but the results seem rewarding. The most important results are the verification and advancement of the cosmological model based on the ΛCDM universe, and the data themselves, which can be used for a multitude of precision astrophysical sciences for many years to come.　

Along with work for SDSS, I also worked on theories and observations with the Subaru telescope. My most recent work, still under way, is to make an inventory of all energies present in the Universe and study transactions among the entries. This is a synthesis of the data and knowledge obtained over many years, and it shows the accuracy of our knowledge in many different astrophysical processes and observations.