belousov.tel

CBB Unit Seminar

Biology for Physics

Roman Belousov

Erzberger Lab | EMBL EMBL, Heidelberg

🙏 Many thanks!

Erzberger group

  • Sabrina Savino
  • Valentina Barletta
  • Samuele Massimi
  • Michele Lupini
  • Jenna Elliot
  • Tim Dullweber
  • Ian Estabrook
  • Patrick Jentsch

EMBL EMBL

  • Quail group
  • Cuylen group
  • Dey group
  • DB/Hiiragi (former)
  • DB/Petridou
  • DB/Graf

🌍 External: Gulbenkian Institute, Politecnico di Torino, University of Turin, Utrecht University

Publications

  1. Repulsive particle interactions enable selective information processing at cellular interfaces. Elliott et al. Physical Review Letters (2025)
  2. Shape switching and tunable oscillations of adaptive droplets. Dullweber et al. Physical Review Letters (2025)
  3. Feedback between microscopic activity and macroscopic dynamics drives excitability and oscillations in mechanochemical matter. Dullweber et al. Physical Review E (2025)
  4. Coupling of cell shape, matrix and tissue dynamics ensures embryonic patterning robustness. Moghe et al. Nature Cell Biology (2025)
  5. Nuclear deformability facilitates apical nuclear migration in the developing zebrafish retina. Maia-Gil et al. Current Biology (2024)
  6. Poissonian cellular Potts models reveal nonequilibrium kinetics of cell sorting. RB, Savino et al. Physical Review Letters (2024)
  7. Embryo‐uterine interaction coordinates mouse embryogenesis during implantation. Bondarenko et al. The EMBO Journal (2023)

Quantity changes into quality (Hegel)

  1. From action principle to thermodynamics of elastic and viscous soft matter. Barletta et al. In preparation
  2. Microcanonical ensemble out of equilibrium. RB, Elliott et al. Physical Review E (2026)

Physics is NOT Mathematics

Mathematics is a language of Physics!

Draco ignivomus

Kingdom
Animalia
Phylum
Chordata
Class
Reptilia-ish
Order
Squamata-adjacent
Family
Draconidae
Genus
Draco
Species
D. ignivomus

Common Fire-Spitting Dragon is a large, volant, hexapedal reptiloform organism distinguished by keratinized cranial horns, extensive patagial wings, reinforced thoracic rib architecture, and a highly expressive glare suggestive of territorial contempt. Adults are typically found in mountainous regions, volcanic slopes, and anywhere livestock are left suspiciously unattended.

What is physics, then?

⟲ Wired up with first principles!

Describing complex systems

“In physics, interpretability means using concise equations that reliably explain phenomena” [Tan et al. SymTorch (2023)]

🥴? ψ(x)=tanh⁡(exp⁡(cos⁡(sin⁡(λx)))) \psi(x) = \tanh\Bigg(\exp\bigg(\cos\Big(\sin\big(\lambda x\big)\Big)\bigg)\Bigg)

Desirable, but not sufficient... Interpretability requires a context!

Biology needs phycisal models

(Draco ignivomus)
Interpretable as parts of the whole coherent theory of life, to fit all our work together!

Example: sorting by differential adhesion

Epi & PrE sorting
Epiblast and Primitive Endoderm in the inner cellular mass from a mouse blastocyst.
Simulations
Poissonian cellular Potts model at T0=37 ∘CT_0 = 37\ ^\circ\mathrm{C} and above...

Example: sorting by differential adhesion

Martian mouse
😏?
Simulations
Effective temperature TT vs. active fluctuations η\eta

Ensemble theory of active fluctuations

Ensemble theory
NN walkers on a lattice (Nℓ=1,2,...LN_{\ell=1,2,...L} at site ℓ\ell): each walker exists in one of MM energy states

Lagrange multipliers

Traffic
Traffic ∑ℓ≠mNℓm\sum_{\ell\ne m} N_{\ell m}
Thermodynamic β=(kBT)−1\beta = (k_{\rm B} T)^{-1}
conjugate to the total energy EE
Current affinity η\eta
conjugate to the traffic (generalized current)
Pℓm=Nℓm/NmP_{\ell m} = N_{\ell m}/N_m is the faction of particles jumping from mm to ℓ\ell

Principle of maximum (micro-)caliber

CPM interface
Random walk of an interface between cells in CPMs

Poissonian dynamics: P(x±dx∣x)∝exp⁡(−βΔE−η)P(x\pm dx|x) \propto \exp(-\beta \Delta E - \eta)

Active mobility: μ(0) kBT0<μ(η) kBT0\mu(0)\ k_{\rm B} T_0 < \mu(\eta)\ k_{\rm B} T_0

Maximize path entropy

Nℓ(t+dt)=∑mPℓm(β,η)Nm(t)N_\ell(t+dt) = \sum_m P_{\ell m}(\beta,\eta) N_m(t)

Norton ensemble
fix traffic
Thévenin ensemble
fix β\beta and η\eta

Summary

  • Biology is complex, but we can still make sense of it with interpretable physical models!
  • Biology urges physics to (finally) establish the missing first-principles:
    • ☑ Ensemble theory of nonequilibrium thermodynamics;
    • ☐ Action principle for viscoelastic materials and their thermodynamics;
    • ☐ Ensemble theory of phase-separation phenomena and pattern formation.

Thank you for your attention!

Principled cat & Martian mouse

Questions?