Institute of Astronomy

Zero Active Mass in FRW Cosmologies

SpeakerTalk DateTalk Series
Fulvio Melia, University of Arizona11 June 2015Institute of Astronomy Colloquia


The standard model of cosmology is based on the Friedmann-Robertson-Walker
(FRW) metric. Often written in terms of co-moving coordinates, this elegant and
highly practical solution to Einstein's equations is based on the Cosmological
principal and Weyl's postulate. But not all of the physics behind such symmetries
has yet been recognized. We invoke the fact that the co-moving frame also happens
to be in free fall to demonstrate that the FRW metric is apparently valid only for
a medium with zero active mass. In other words, the application of FRW appears
to require an equation-of-state rho+3p = 0, in terms of the total energy density
rho and total pressure p. Though the standard model is not framed in these
terms, the optimization of its parameters brings it ever closer to this constraint
as the precision of the observations continues to improve. For example, the
latest high-precision BAO measurements rule out the standard model at better
than the 99.95% C.L. if the zero active mass condition is ignored.


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