TY - JOUR

T1 - Isotropic and semi-isotropic observations in cosmology

AU - Maartens, R.

AU - Matravers, D. R.

PY - 1994

Y1 - 1994

N2 - We investigate the geometric consequences for dust universes of isotropies within the set of idealized galactic observations - -area distance, number counts, proper motions and image distortion. Anisotropy in the Hubble parameter is shown to indicate non-zero proper motions. If the proper motions and distortion are assumed to be zero (semi-isotropic observations), then the vorticity vanishes, the Hubble and deceleration parameters are isotropic, and Einstein's equations strongly constrain the area distance and the number counts. These constraints allow limited anisotropy, and in principle they provide indirect tests for the presence of proper motions and distortion. If, further, we assume isotropy of the area distance and number counts (isotropic observations), then we prove that Einstein's equations force the spacetime geometry to be isotropic. With the Copernican principle, this leads to an observational proof of the standard FLRW model.

AB - We investigate the geometric consequences for dust universes of isotropies within the set of idealized galactic observations - -area distance, number counts, proper motions and image distortion. Anisotropy in the Hubble parameter is shown to indicate non-zero proper motions. If the proper motions and distortion are assumed to be zero (semi-isotropic observations), then the vorticity vanishes, the Hubble and deceleration parameters are isotropic, and Einstein's equations strongly constrain the area distance and the number counts. These constraints allow limited anisotropy, and in principle they provide indirect tests for the presence of proper motions and distortion. If, further, we assume isotropy of the area distance and number counts (isotropic observations), then we prove that Einstein's equations force the spacetime geometry to be isotropic. With the Copernican principle, this leads to an observational proof of the standard FLRW model.

UR - http://www.scopus.com/inward/record.url?scp=21844495671&partnerID=8YFLogxK

U2 - 10.1088/0264-9381/11/11/011

DO - 10.1088/0264-9381/11/11/011

M3 - Article

AN - SCOPUS:21844495671

SN - 0264-9381

VL - 11

SP - 2693

EP - 2704

JO - Classical and Quantum Gravity

JF - Classical and Quantum Gravity

IS - 11

M1 - 011

ER -