TY - JOUR

T1 - How isotropic is the Universe?

AU - Saadeh, Daniela

AU - Feeney, Stephen M.

AU - Pontzen, Andrew

AU - Peiris, Hiranya V.

AU - McEwen, Jason D.

PY - 2016/9/23

Y1 - 2016/9/23

N2 - A fundamental assumption in the standard model of cosmology is that the Universe is isotropic on large scales. Breaking this assumption leads to a set of solutions to Einstein's field equations, known as Bianchi cosmologies, only a subset of which have ever been tested against data. For the first time, we consider all degrees of freedom in these solutions to conduct a general test of isotropy using cosmic microwave background temperature and polarization data from Planck. For the vector mode (associated with vorticity), we obtain a limit on the anisotropic expansion of (σV/H)0 < 4.7×10-11 (95% C.L.), which is an order of magnitude tighter than previous Planck results that used cosmic microwave background temperature only. We also place upper limits on other modes of anisotropic expansion, with the weakest limit arising from the regular tensor mode, (σT,reg/H)0 < 1.0×10-6 (95% C.L.). Including all degrees of freedom simultaneously for the first time, anisotropic expansion of the Universe is strongly disfavored, with odds of 121 000:1 against.

AB - A fundamental assumption in the standard model of cosmology is that the Universe is isotropic on large scales. Breaking this assumption leads to a set of solutions to Einstein's field equations, known as Bianchi cosmologies, only a subset of which have ever been tested against data. For the first time, we consider all degrees of freedom in these solutions to conduct a general test of isotropy using cosmic microwave background temperature and polarization data from Planck. For the vector mode (associated with vorticity), we obtain a limit on the anisotropic expansion of (σV/H)0 < 4.7×10-11 (95% C.L.), which is an order of magnitude tighter than previous Planck results that used cosmic microwave background temperature only. We also place upper limits on other modes of anisotropic expansion, with the weakest limit arising from the regular tensor mode, (σT,reg/H)0 < 1.0×10-6 (95% C.L.). Including all degrees of freedom simultaneously for the first time, anisotropic expansion of the Universe is strongly disfavored, with odds of 121 000:1 against.

UR - http://www.scopus.com/inward/record.url?scp=84990236829&partnerID=8YFLogxK

UR - https://nottingham-repository.worktribe.com/

UR - https://discovery.ucl.ac.uk/id/eprint/1493640/

U2 - 10.1103/PhysRevLett.117.131302

DO - 10.1103/PhysRevLett.117.131302

M3 - Article

AN - SCOPUS:84990236829

SN - 0031-9007

VL - 117

JO - Physical Review Letters

JF - Physical Review Letters

IS - 13

M1 - 131302

ER -