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The international workshop “Concepts of Quantum and Spacetime” was held at KEK from 9 to 12 March 2026 as a joint event organized by KEK Theory Center and RIKEN iTHEMS.

 

The two fundamental questions, “What is quantum?” and “What is spacetime?”, are deeply intertwined. The workshop discussed the question “How can quantum theory and spacetime be understood in a consistent manner?” from a fundamental and broad perspective and shared various ideas with open minds, to find directions guiding quantum theory over the next 100 years. The topics were diverse: foundations of quantum theory, quantum gravity, emergence of spacetime, formulation of semi-classical gravity, experimental aspects of fundamental properties in nature, and foundations of quantum many-body systems and thermodynamics.

Around 90 researchers from various countries, generations, and fields came together. (Around 40% of these were from overseas.) The 14 keynote speakers shared their visions on quantum theory and spacetime. (The talk slides are available in the website.) The 13 selected short talks and the 22 poster presentations were of a high standard, leading to lively discussions.

Interestingly, the disagreements and confusion arising from differences in their expertise and viewpoints actually gave rise to new discussions and ideas. This was likely due to the open atmosphere of sincere engagement that emerged because the thema was not confined to specific methods or theoretical frameworks.

Furthermore, small yet significant touches—such as providing boxed lunches to keep the lively atmosphere of the lecture hall going during the lunch break, and setting up whiteboards in open spaces to encourage discussion—proved effective. These efforts fostered constant, natural interaction and lively discussion throughout the venue. Participants did not merely listen; they truly shaped the workshop.

Many participants commented that it was an interesting and wonderful workshop. We also received feedback such as, “I gained ideas for future research,” and “This provided valuable insights for organizing future workshops.”

 

Yuki Yokokura, chair of the organizing committee and assistant professor at the KEK Theory Center (now at Kochi University of Technology), reflected on the workshop:
“These are the result of the deep curiosity shared by all participants regarding fundamental questions, “What is quantum?” and “What is spacetime?” It is precisely such curiosity that will naturally give rise to new ideas and collaborative research and connect the world. I hope that workshops embodying a similar spirit will be held around the world on a variety of themes in the future. “