# HEP/Astro Seminar, Wednesday 13th January 1999

##
Implications of Cosmic Repulsion for Gravitational Theory

## Philip Mannheim (U. Connecticut)

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### Abstract

With the recent emergence of the fact that $\Omega_{M}(t_0)$ is
apparently less than one, standard cosmology now faces two particularly
unpalatable alternatives: either there exists another source of energy to
precisely bring $\Omega_{tot}(t_0)$ back to one, or else the spatial
curvature $k$ of the universe is non-zero. In the standard
Einstein-Friedmann cosmology neither of these options is achievable
without a fine tuning of the early universe above and beyond that already
provided by inflation; and, moreover, if inflation is correct, the large
value inferred for $1-\Omega_{M}(t_0)$ would then entail after
generations of work, and after an almost 20 year long conviction that
$\Omega_{M}(t_0)=1$, that the cosmology community apparently does not
have all that clear an idea as to the primary content of the
universe. Given the severity of this situation, it is legitimate to
ask if the problem lies not in unknown astrophysics, but rather in
the assumed validity of standard gravity itself, with all of the
problems which cosmology currently faces being readily traceable to
one single source, namely the Einstein-Friedmann cosmological
evolution equations themselves. In order to address this question
we present a general, model independent analysis of the recently
detected apparent cosmic repulsion, and discuss its potential
implications for gravitational theory. In particular, we show that a
non-flat negatively spatially curved universe acts like a
diverging refractive medium, to thus naturally cause galaxies to
accelerate away from each other. Additionally, we show that even
though such a negatively spatially curved universe is not natural
in standard gravity, it does nonetheless have a natural origin
within conformal gravity, a fully covariant candidate alternative
to standard gravity. In conformal cosmology the flatness, horizon,
universe age, cosmological constant, and cosmic repulsion problems
are all resolved, and no need is found for dark matter.
(References: astro-ph/9803135; astro-ph/9804335, Phys Rev D58, 103511,
1998.)

## 3:30pm, Smith Lab 4079

Francesco Antonuccio (
anton@pacific.mps.ohio-state.edu),
last updated 15-SEP-97.