TY - JOUR

T1 - Physical basis for the symmetries in the Friedmann–Robertson–Walker metric

AU - Melia, Fulvio

N1 - Publisher Copyright:
© 2016, Higher Education Press and Springer-Verlag Berlin Heidelberg.

PY - 2016/8/1

Y1 - 2016/8/1

N2 - Modern cosmological theory is based on the Friedmann–Robertson–Walker (FRW) metric. Often written in terms of co-moving coordinates, this well-known solution to Einstein’s equations owes its elegant and highly practical formulation to the cosmological principle and Weyl’s postulate, upon which it is founded. However, there is physics behind such symmetries, and not all of it has yet been recognized. In this paper, we derive the FRW metric coefficients from the general form of the spherically symmetric line element and demonstrate that, because the co-moving frame also happens to be in free fall, the symmetries in FRW are valid only for a medium with zero active mass. In other words, the spacetime of a perfect fluid in cosmology may be correctly written as FRW only when its equation of state is ρ+3p = 0, in terms of the total pressure p and total energy density ρ. There is now compelling observational support for this conclusion, including the Alcock–Paczy´nski test, which shows that only an FRW cosmology with zero active mass is consistent with the latest model-independent baryon acoustic oscillation data.

AB - Modern cosmological theory is based on the Friedmann–Robertson–Walker (FRW) metric. Often written in terms of co-moving coordinates, this well-known solution to Einstein’s equations owes its elegant and highly practical formulation to the cosmological principle and Weyl’s postulate, upon which it is founded. However, there is physics behind such symmetries, and not all of it has yet been recognized. In this paper, we derive the FRW metric coefficients from the general form of the spherically symmetric line element and demonstrate that, because the co-moving frame also happens to be in free fall, the symmetries in FRW are valid only for a medium with zero active mass. In other words, the spacetime of a perfect fluid in cosmology may be correctly written as FRW only when its equation of state is ρ+3p = 0, in terms of the total pressure p and total energy density ρ. There is now compelling observational support for this conclusion, including the Alcock–Paczy´nski test, which shows that only an FRW cosmology with zero active mass is consistent with the latest model-independent baryon acoustic oscillation data.

KW - cosmological observations

KW - cosmological parameters

KW - cosmological theory

KW - gravitation

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U2 - 10.1007/s11467-016-0557-6

DO - 10.1007/s11467-016-0557-6

M3 - Article

AN - SCOPUS:84962360841

SN - 2095-0462

VL - 11

JO - Frontiers of Physics

JF - Frontiers of Physics

IS - 4

M1 - 119801

ER -