Quantum Spacetime and Emergent Geometric Structure
​​​Welcome to the EAAS workpackage 1!
short description?
(original) description of WP: emergent phenomena in physics typically deal with the collective behaviour of microscopic matter constituents living and interacting on a fixed “background” spacetime. We will go one step further and ask how spacetime itself could have emerged from a fundamental, microscopic quantum state at the beginning of our universe. Our research will address a key open challenge in quantum gravity, namely, to provide a dynamical explanation for the origin of spacetime and gravity. The gravitational nature of the interactions raises the intriguing possibility that the universal features of geometric emergence we will find are very different from those governing matter systems. We will model coarse-graining mechanisms (i.e. hydrodynamic or continuum limits) that extrapolate between microscopic, random-geometric building blocks and macroscopic Lorentzian or Riemannian spaces (related by Wick rotation) and study their effect on geometric and curvature observables. Of particular interest for early-universe cosmology are emergent de Sitter-spaces and their global symmetries. An overarching objective is to quantify fluctuations that emerge alongside the classical background and can serve as primordial seeds of cosmic structure formation or drive inflation.
Symmetric preferences, asymmetric outcomes: Tipping dynamics in an open-city segregation model
​​By: Fabio van Dissel, Tuan Minh Pham and Wout Merbis [arXiv:2602.09795]
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Cities can become segregated even when people do not have a strong preference to live among their own kind. This puzzling effect was famously shown by the economist Thomas Schelling, who demonstrated that mild individual preferences can still produce sharply divided neighborhoods.
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In this work, we revisit that question from a new angle and uncover a surprising result: even when two groups have exactly the same preferences, one group can suddenly come to dominate a city.
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Instead of assuming that people consciously optimize their happiness or follow strict rules about when to move, we model residential change as a stochastic process, similar to chemical reactions. People move in or out of neighborhoods at certain rates, influenced by who already lives nearby, but without making deliberate “best” decisions. Vacant homes play an essential role by enabling movement, much like empty seats in a game of musical chairs.
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Using this framework, we find three key behaviors:
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Mixed neighborhoods where different groups are well integrated.
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Segregated neighborhoods where people cluster with similar neighbors, but both groups remain equally represented overall.
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A tipping point where, beyond a critical strength of in-group attraction, the city suddenly shifts to a state where one group dominates, even though both groups follow identical rules.
​
​This tipping point behaves much like phase transitions in physics, similar to how a magnet suddenly becomes magnetized when cooled below a critical temperature. However, careful analysis shows that this transition does not fit neatly into any well-known physical universality class, suggesting genuinely new collective behavior.
​
The broader message is important for urban policy and social science: both large-scale segregation and neighborhood tipping into a dominance of one type can emerge from simple and symmetric rules between individuals.
​
Because our model is based on measurable movement rates rather than hidden personal preferences, it also opens the door to closer connections with real housing and mobility data. This makes it a promising framework for understanding, and possibly anticipating, sudden shifts in urban demographics.
Symmetric preferences, asymmetric outcomes: Tipping dynamics in an open-city segregation model
​​By: Fabio van Dissel, Tuan Minh Pham and Wout Merbis [arXiv:2602.09795]
Symmetric preferences, asymmetric outcomes: Tipping dynamics in an open-city segregation model
​​Cities can become segregated even when people do not have a strong preference to live among their own kind. This puzzling effect was famously shown by the economist Thomas Schelling, who demonstrated that mild individual preferences can still produce sharply divided neighborhoods.
​
In this work, we revisit that question from a new angle and uncover a surprising result: even when two groups have exactly the same preferences, one group can suddenly come to dominate a city.
​
Instead of assuming that people consciously optimize their happiness or follow strict rules about when to move, we model residential change as a stochastic process, similar to chemical reactions. People move in or out of neighborhoods at certain rates, influenced by who already lives nearby, but without making deliberate “best” decisions. Vacant homes play an essential role by enabling movement, much like empty seats in a game of musical chairs.
​
Using this framework, we find three key behaviors:
-
Mixed neighborhoods where different groups are well integrated.
-
Segregated neighborhoods where people cluster with similar neighbors, but both groups remain equally represented overall.
-
A tipping point where, beyond a critical strength of in-group attraction, the city suddenly shifts to a state where one group dominates, even though both groups follow identical rules.
​
​
​
​​
​
​
​
​
​
​This tipping point behaves much like phase transitions in physics, similar to how a magnet suddenly becomes magnetized when cooled below a critical temperature. However, careful analysis shows that this transition does not fit neatly into any well-known physical universality class, suggesting genuinely new collective behavior.
​
The broader message is important for urban policy and social science: both large-scale segregation and neighborhood tipping into a dominance of one type can emerge from simple and symmetric rules between individuals.
​
Because our model is based on measurable movement rates rather than hidden personal preferences, it also opens the door to closer connections with real housing and mobility data. This makes it a promising framework for understanding, and possibly anticipating, sudden shifts in urban demographics.