All_About_Space_-_Issue_94_2020

groupofscientistshascreateda

computersimulationoftheuniversein

ordertotestoutanalternativetheory

toAlbertEinstein'stheoryofgeneral

relativity.Theirstudyfoundthatgalaxiessimilarto

ourownMilkyWaycouldstillformintheuniverse

withmodifiedlawsofgravity,suggestingthatthe

theoryofrelativityisnottheonlywaytoexplain

gravity'sroleintheevolutionoftheuniverse.

PhysicistsfromDurhamUniversityinEngland

createdthecomputersimulationsusinga leading

alternativemodelforgravitycalled‘f(R)gravity’,

alsoknownas‘ChameleonTheory’,whichalters

thebehaviourofgravityaccordingtothe

surroundingenvironment.Thesimulations

showedthatthemodifiedgravitymodelcould

stillleadtogalaxyformation.

A

"Modifiedgravitytheories,includingChameleon

Theory,hadbeenstudiedbythecommunity

fora while,anda lotoftheirpredictionswere

known,"BaojiuLi,a physicistattheInstitutefor

ComputationalCosmologyatDurhamUniversity,

toldus."However,themajorityoftheseprevious

studieswereconductedwitha criticalsimplification

• theassumptionthattheuniversecontains
  onlydarkmatter,andnoluminousmatter."
  Oneoftheunansweredquestionsincosmology
  isthereasonthattheuniverseisexpanding,
  Lisaid,andothermodelshavetriedtoanswer
  thatquestionbyintroducinganunknownforce
  calleddarkenergy.Thisconstantforceinthetheory
  ofgeneralrelativitycanaccountfortheexpansion
  oftheuniverse,butdoessobyincludinga vast
  amountofdarkmatterthatremainsunconfirmed.

Scientistsbelievethataround 68 percentof

theuniverseismadeupofdarkenergy,while

darkmattermakesup 27 percent;normalmatter,

whichincludesbodiesthatarevisibletoussuch

asplanets,starsandgalaxies,makesuparound

fivepercent.

"However,alternativestoa cosmologicalconstant,

whichexplaintheacceleratedexpansionby

modifyingthelawofgravity,likef(R)-gravity,are

alsowidelyconsidered,givenhowlittleisknown

aboutdarkenergy,”Liadded.

Thestudyalsolookedattheeffectofmodified

gravityonsupermassiveblackholes,whicheject

heatandmaterialthatburnsawayatthegasneeded

toformstars.Theenergyemittedfromblackholes

alsofeedsnucleifoundingalaxies,andtherefore

playsa majorroleingalaxyformation.

This

computer-

generated

imageshows

a discgalaxy

ina modified

gravity

simulation

IN COOPERATION WITH

©Christian

Arnold/Baojiu

Li/Durham

University.

CHAMELEON

THEORY

Testing an alternate method to

Einstein's general relativity

Reported by Passant Rabie

Chameleon theory