Active matter

{{Short description|Matter behavior at system scale}}

File:The flock of starlings acting as a swarm. - geograph.org.uk - 124593.jpgs acting as a swarm]]

{{microbial and microbot movement|collective}}

Active matter is matter composed of large numbers of active "agents", each of which consumes energy in order to move or to exert mechanical forces.{{cite journal |last1=Ramaswamy |first1=Sriram |title=The Mechanics and Statistics of Active Matter |journal=Annual Review of Condensed Matter Physics |date=10 August 2010 |volume=1 |issue=1 |pages=323–345 |doi=10.1146/annurev-conmatphys-070909-104101 |authorlink=Sriram Ramaswamy |arxiv=1004.1933 |bibcode=2010ARCMP...1..323R }}{{cite journal | last1=Marchetti | first1=M. C. | last2=Joanny | first2=J.F. | last3=Ramaswamy | first3=S. | last4=Liverpool | first4=T. B. | last5=Prost | first5=J. | last6=Rao | first6=M. | last7=Adita Simha | first7=R. | year=2012 | title=Hydrodynamics of soft active matter | journal=Reviews of Modern Physics | volume=85 | issue=3 | pages=1143–1189 | arxiv=1207.2929| doi=10.1103/RevModPhys.85.1143 | bibcode=2013RvMP...85.1143M}}{{cite journal |last1=Bechinger |first1=Clemens |last2=Di Leonardo |first2=Roberto |last3=Löwen |first3=Hartmut |last4=Reichhardt |first4=Charles |last5=Volpe |first5=Giorgio |last6=Volpe |first6=Giovanni |title=Active Particles in Complex and Crowded Environments |journal=Reviews of Modern Physics |date=23 November 2016 |volume=88 |issue=4 |page=045006 |doi=10.1103/RevModPhys.88.045006 |arxiv=1602.00081 |bibcode=2016RvMP...88d5006B }}{{cite journal |last1=Bowick |first1=Mark J. |last2=Fakhri |first2=Nikta |last3=Marchetti |first3=M. Cristina |last4=Ramaswamy |first4=Sriram |title=Symmetry, Thermodynamics, and Topology in Active Matter |journal=Physical Review X |date=11 February 2022 |volume=12 |issue=1 |page=010501 |doi=10.1103/PhysRevX.12.010501 |arxiv=2107.00724 |bibcode=2022PhRvX..12a0501B }} Such systems are intrinsically out of thermal equilibrium. Unlike thermal systems relaxing towards equilibrium and systems with boundary conditions imposing steady currents, active matter systems break time reversal symmetry because energy is being continually dissipated by the individual constituents.{{cite journal |last1=Najafi |first1=Ali |last2=Golestanian |first2=Ramin |title=Simple swimmer at low Reynolds number: Three linked spheres |journal=Physical Review E |date=16 June 2004 |volume=69 |issue=6 |page=062901 |doi=10.1103/PhysRevE.69.062901 |pmid=15244646 |arxiv=cond-mat/0402070 |bibcode=2004PhRvE..69f2901N }}{{cite arXiv |last1=Berthier |first1=Ludovic |last2=Kurchan |first2=Jorge |author2-link=Jorge Kurchan |title=Lectures on non-equilibrium active systems |date=7 June 2019 |class=cond-mat.stat-mech |eprint=1906.04039}}{{cite journal |last1=Cates |first1=Michael E. |last2=Tailleur |first2=Julien |title=Motility-Induced Phase Separation |journal=Annual Review of Condensed Matter Physics |date=March 2015 |volume=6 |issue=1 |pages=219–244 |doi=10.1146/annurev-conmatphys-031214-014710 |arxiv=1406.3533 |bibcode=2015ARCMP...6..219C }} Most examples of active matter are biological in origin and span all the scales of the living, from bacteria and self-organising bio-polymers such as microtubules and actin (both of which are part of the cytoskeleton of living cells), to schools of fish and flocks of birds. However, a great deal of current experimental work is devoted to synthetic systems such as artificial self-propelled particles.{{cite journal |last1=Howse |first1=Jonathan R. |last2=Jones |first2=Richard A. L. |last3=Ryan |first3=Anthony J. |last4=Gough |first4=Tim |last5=Vafabakhsh |first5=Reza |last6=Golestanian |first6=Ramin |title=Self-Motile Colloidal Particles: From Directed Propulsion to Random Walk |journal=Physical Review Letters |date=27 July 2007 |volume=99 |issue=4 |page=048102 |doi=10.1103/PhysRevLett.99.048102 |pmid=17678409 |arxiv=0706.4406 |bibcode=2007PhRvL..99d8102H }}{{cite journal |last1=Bricard |first1=Antoine |last2=Caussin |first2=Jean-Baptiste |last3=Desreumaux |first3=Nicolas |last4=Dauchot |first4=Olivier |last5=Bartolo |first5=Denis |title=Emergence of macroscopic directed motion in populations of motile colloids |journal=Nature |date=6 November 2013 |volume=503 |issue=7474 |pages=95–98 |doi=10.1038/nature12673 |pmid=24201282 |arxiv=1311.2017 |bibcode=2013Natur.503...95B }}{{cite journal |last1=Theurkauff |first1=I. |last2=Cottin-Bizonne |first2=C. |last3=Palacci |first3=J. |last4=Ybert |first4=C. |last5=Bocquet |first5=L. |title=Dynamic Clustering in Active Colloidal Suspensions with Chemical Signaling |journal=Physical Review Letters |date=26 June 2012 |volume=108 |issue=26 |page=268303 |doi=10.1103/PhysRevLett.108.268303 |pmid=23005020 |arxiv=1202.6264 |bibcode=2012PhRvL.108z8303T }} Active matter is a relatively new material classification in soft matter: the most extensively studied model, the Vicsek model, dates from 1995.{{cite journal |last1=Vicsek |first1=Tamás |last2=Czirók |first2=András |last3=Ben-Jacob |first3=Eshel |last4=Cohen |first4=Inon |last5=Shochet |first5=Ofer |title=Novel Type of Phase Transition in a System of Self-Driven Particles |journal=Physical Review Letters |date=7 August 1995 |volume=75 |issue=6 |pages=1226–1229 |doi=10.1103/PhysRevLett.75.1226 |bibcode=1995PhRvL..75.1226V |pmid=10060237 |arxiv=cond-mat/0611743 }}

Research in active matter combines analytical techniques, numerical simulations and experiments. Notable analytical approaches include hydrodynamics,{{cite journal |last1=Toner |first1=John |last2=Tu |first2=Yuhai |last3=Ramaswamy |first3=Sriram |title=Hydrodynamics and phases of flocks |journal=Annals of Physics |date=July 2005 |volume=318 |issue=1 |pages=170–244 |doi=10.1016/j.aop.2005.04.011 |bibcode=2005AnPhy.318..170T |url=http://eprints.iisc.ac.in/3397/1/A89.pdf }} kinetic theory, and non-equilibrium statistical physics. Numerical studies mainly involve self-propelled-particles models,{{cite journal |last1=Vicsek |first1=Tamás |last2=Czirók |first2=András |last3=Ben-Jacob |first3=Eshel |last4=Cohen |first4=Inon |last5=Shochet |first5=Ofer |title=Novel Type of Phase Transition in a System of Self-Driven Particles |journal=Physical Review Letters |date=7 August 1995 |volume=75 |issue=6 |pages=1226–1229 |doi=10.1103/PhysRevLett.75.1226 |pmid=10060237 |arxiv=cond-mat/0611743 |bibcode=1995PhRvL..75.1226V }}{{cite journal |last1=Chaté |first1=Hugues |last2=Ginelli |first2=Francesco |last3=Grégoire |first3=Guillaume |last4=Raynaud |first4=Franck |title=Collective motion of self-propelled particles interacting without cohesion |journal=Physical Review E |date=18 April 2008 |volume=77 |issue=4 |page=046113 |doi=10.1103/PhysRevE.77.046113 |pmid=18517696 |arxiv=0712.2062 |bibcode=2008PhRvE..77d6113C }} making use of agent-based models such as molecular dynamics algorithms or lattice-gas models,{{cite journal |last1=Bussemaker |first1=Harmen J. |last2=Deutsch |first2=Andreas |last3=Geigant |first3=Edith |title=Mean-Field Analysis of a Dynamical Phase Transition in a Cellular Automaton Model for Collective Motion |journal=Physical Review Letters |date=30 June 1997 |volume=78 |issue=26 |pages=5018–5021 |doi=10.1103/physrevlett.78.5018 |arxiv=physics/9706008 |bibcode=1997PhRvL..78.5018B }} as well as computational studies of hydrodynamic equations of active fluids. Experiments on biological systems extend over a wide range of scales, including animal groups (e.g., bird flocks,{{cite journal |last1=Ballerini |first1=M. |last2=Cabibbo |first2=N. |last3=Candelier |first3=R. |last4=Cavagna |first4=A. |last5=Cisbani |first5=E. |last6=Giardina |first6=I. |last7=Lecomte |first7=V. |last8=Orlandi |first8=A. |last9=Parisi |first9=G. |last10=Procaccini |first10=A. |last11=Viale |first11=M. |last12=Zdravkovic |first12=V. |title=Interaction ruling animal collective behavior depends on topological rather than metric distance: Evidence from a field study |journal=Proceedings of the National Academy of Sciences |date=29 January 2008 |volume=105 |issue=4 |pages=1232–1237 |doi=10.1073/pnas.0711437105 |pmid=18227508 |pmc=2234121 |arxiv=0709.1916 |bibcode=2008PNAS..105.1232B |doi-access=free }} mammalian herds, fish schools and insect swarms{{cite journal |last1=Buhl |first1=J. |last2=Sumpter |first2=D. J. T. |last3=Couzin |first3=I. D. |last4=Hale |first4=J. J. |last5=Despland |first5=E. |last6=Miller |first6=E. R. |last7=Simpson |first7=S. J. |title=From Disorder to Order in Marching Locusts |journal=Science |date=2 June 2006 |volume=312 |issue=5778 |pages=1402–1406 |doi=10.1126/science.1125142 |pmid=16741126 |bibcode=2006Sci...312.1402B }}), bacterial colonies, cellular tissues (e.g. epithelial tissue layers,{{cite journal |last1=Trepat |first1=Xavier |last2=Wasserman |first2=Michael R. |last3=Angelini |first3=Thomas E. |last4=Millet |first4=Emil |last5=Weitz |first5=David A. |last6=Butler |first6=James P. |last7=Fredberg |first7=Jeffrey J. |title=Physical forces during collective cell migration |journal=Nature Physics |date=June 2009 |volume=5 |issue=6 |pages=426–430 |doi=10.1038/nphys1269 |bibcode=2009NatPh...5..426T |doi-access=free}} cancer growth and embryogenesis), cytoskeleton components (e.g., in vitro motility assays, actin-myosin networks and molecular-motor driven filaments{{cite journal |last1=Keber |first1=Felix C. |last2=Loiseau |first2=Etienne |last3=Sanchez |first3=Tim |last4=DeCamp |first4=Stephen J. |last5=Giomi |first5=Luca |last6=Bowick |first6=Mark J. |last7=Marchetti |first7=M. Cristina |last8=Dogic |first8=Zvonimir |last9=Bausch |first9=Andreas R. |title=Topology and dynamics of active nematic vesicles |journal=Science |date=5 September 2014 |volume=345 |issue=6201 |pages=1135–1139 |doi=10.1126/science.1254784 |pmid=25190790 |pmc=4401068 |arxiv=1409.1836 |bibcode = 2014Sci...345.1135K }}). Experiments on synthetic systems include self-propelled colloids (e.g., phoretically propelled particles{{cite journal |last1=Palacci |first1=Jeremie |last2=Sacanna |first2=Stefano |last3=Steinberg |first3=Asher Preska |last4=Pine |first4=David J. |last5=Chaikin |first5=Paul M. |title=Living Crystals of Light-Activated Colloidal Surfers |journal=Science |date=22 February 2013 |volume=339 |issue=6122 |pages=936–940 |doi=10.1126/science.1230020 |pmid=23371555 |bibcode=2013Sci...339..936P }}), driven granular matter (e.g. vibrated monolayers{{cite journal |last1=Deseigne |first1=Julien |last2=Dauchot |first2=Olivier |last3=Chaté |first3=Hugues |title=Collective Motion of Vibrated Polar Disks |journal=Physical Review Letters |date=23 August 2010 |volume=105 |issue=9 |page=098001 |doi=10.1103/PhysRevLett.105.098001 |pmid=20868196 |bibcode=2010PhRvL.105i8001D |arxiv=1004.1499 }}), swarming robots and Quincke rotators.{{cite journal| journal=IEEE Transactions on Industry Applications|title= Quincke Rotation of Spheres|date=July 1984|volume=IA-20|issue=4|last1=Jones|first1=Thomas B.}}

Concepts in Active matter

• Active gels
• Dense active matter
• Collective motion
• Collective animal behavior
• Collective cell migration
• Motility induced phase separation
• Schooling, flocking and swarming
• Active stress
• Disordered hyperuniformity

Active matter systems

• Biological tissues
• Subcellular and cell mechanics
• Crowd behaviour
• Self-propelled particles and colloids