"What is life?" --This is the title of the famous book written by Erwin Schrödinger, one of the inventors of quantum physics. The book contains influential ideas to understand life as physical phenomena. Actually, it did inspire the pioneers of molecular biology.

Although about 70 years have passed since the challenge was taken on by Schrödinger, the fundamental question "What is life?" has not been exhausted at all. I was one of the newcomers involved in the attempts to answer this question during the Modeling Origins of Life (MOL) workshops held at ELSI and at RIKEN last summer.

I am a mathematical physicist working at Nagahama Institute of Bio-Science and Technology. Piet Hut --my mentor in interdisciplinary studies and my student in basic category theory (a mathematical theory of systems of "arrows": processes, operations, functions,...,etc.)-- invited me to visit ELSI. At first, I did not understand the reason exactly, but I found why he did so as soon as I started having some discussions with researchers involved in the MOL project. The discussions gave me many insights.

For instance, the discussions made me interested in "Allometry relations", universal power laws, e.g. "metabolic rate is proportional to (weigh.)^(3/4)". There were many interesting explanations for those laws, but I wonder if this "universality" is a logical consequence of "a definition of life" --"What is life?"-- or not.

There are many related questions. Did this allometry relation also hold at the beginning of life on Earth? How about for "life" on other planets? How about for many kinds of models for life? I believe that ELSI is the best place to challenge such kind of "universal" questions about life, and hope to collaborate with interested people at ELSI. I myself have a background for noncommutative probability, which provides new methods to analyze "growing networks". I consider the concept of "growing networks" to be essential to solve these questions, as well as other questions in physics, chemistry, biology etc.

Back to the original question: What is life? It is not only a metaphysical question. The good "answers" will work as a working hypothesis. Actually, in the discussion with ELSI people I have come back to the question many times. There should be many kinds of biological, chemical, informational or mathematical answers. I believe that there should not be a "necessary and sufficient" definition of life, but that it is fruitful to investigate the "system"of necessary or sufficient conditions (that is, the mutual theoretical or experimental relationships between definitions of life).

Of course, there is a clear, but in a sense essential, FACT, not depending on particular answers: "I am an example of life". So the question "What is life" is inevitably related to a deep philosophical question, "What is me?". This fact makes the original question more difficult, and at the same time, more attractive.