Unknowns and unknown unknowns: from dark sky to dark matter and dark energy

TL;DR

This paper discusses the fundamental unknowns of dark matter and dark energy in cosmology, emphasizing the importance of astronomical observations and ongoing projects like SuMIRe to uncover their nature and pose new questions.

Contribution

It highlights the shift from known to unknown questions in cosmology, emphasizing the role of observations and presenting the Japanese SuMIRe project as a means to explore these mysteries.

Findings

Dark matter models are numerous and potentially detectable.

Dark energy lacks a widely accepted theoretical framework.

Astronomical observations are crucial for understanding dark energy.

Abstract

Answering well-known fundamental questions is usually regarded as the major goal of science. Discovery of other unknown and fundamental questions is, however, even more important. Recognition that "we didn't know anything" is the basic scientific driver for the next generation. Cosmology indeed enjoys such an exciting epoch. What is the composition of our universe? This is one of the well-known fundamental questions that philosophers, astronomers and physicists have tried to answer for centuries. Around the end of the last century, cosmologists finally recognized that "We didn't know anything". Except for atoms that comprise slightly less than 5% of the universe, our universe is apparently dominated by unknown components; 23% is the known unknown (dark matter), and 72% is the unknown unknown (dark energy). In the course of answering a known fundamental question, we have discovered an unknown, even more fundamental, question: "What is dark matter? What is dark energy?" There are a variety of realistic particle physics models for dark matter, and its experimental detection may be within reach. On the other hand, it is fair to say that there is no widely accepted theoretical framework to describe the nature of dark energy. This is exactly why astronomical observations will play a key role in unveiling its nature. I will review our current understanding of the "dark sky", and then present on-going Japanese project, SuMIRe, to discover even more unexpected questions.