The Big Bang model assumes that the Universe expands by continuously changing the relationship between the metrics of space and time. However, the relationship between space and time could remain constant during the cosmological expansion and all cosmological locations in time and space could be equivalent, if the metrics of both space and time expand. The Expanding Spacetime theory accurately models the universe we observe and offers simple and direct explanations for several cosmological enigmas.

About 240,000 optical observations of the Sun, Mercury and Venus accumulated during the era of classical astrometry from Bradley up to our days are incorporated to analyze the secular variations of the longitudes of innermost planets. A significant discrepancy between modern ephemerides and optical observations is discovered. The possible sources of this discrepancy are discussed. The tidal acceleration of the Moon has been revised to conform the lunar theory to the ephemerides of the planets. The offset and residual rotation of the Hipparcos-based stellar system with respect to the dynamical equinox is determined. Interpretation for this rotation is given.

The Pioneer 10 acceleration anomaly might be explained by tired light redshift of cosmological origin. Not only would this explain the constant acceleration term but also its annual variation.

The observed magnitudes of distant supernovae Ia (SNe Ia) explosions are lower than expected. This has been interpreted as accelerating cosmological expansion. However, this interpretation relies on the assumption that there is cosmological time dilation as well as redshift. However, if there were no time dilation the theoretical predictions would agree with the observations. The observed light-curves from SNe appear to be stretched out in proportion to the factor (1+ z), which has been interpreted as evidence of time dilation. The possibility that this observational phenomenon is a selection bias effect due to magnitude limiting is investigated.

Schwarzschild's exterior solution, which implies the possibility of Black Holes, relies on the assumption that the vacuum energy-momentum tensor is zero. If this is not the case the solution might not exist. Einstein¹s General Relativity relations are applied to the spherically symmetric case assuming a vacuum energy momentum tensor with zero equivalent mass density but non-vanishing components. This is the vacuum energy-momentum tensor for an Expanding Spacetime proposed by the author, where all four dimensions expand. I show that the Schwarzschild type external solution does not exist in without modifying the vacuum energy-momentum tensor. However, this modification implies that the gravitational field cannot extend all the way in to the event horizon, which rules out the existence of Black Holes. Freely falling particles in the Expanding Spacetime never reach the event horizon. An object of maximum possible energy density might be formed instead of a Black Hole.

Very high frequency, small amplitude, temporal excitations in the metrics of the Minkowski spacetime modeled in general relativity generate spatial modulations of the metrics that satisfy wave equations. De Broglie type matter-waves are shown to result from spatially confined motion of metrics oscillating at the Compton frequency. The momentum relation of Bohm and de Broglie follows directly from the geodesic equations of general relativity. A clear physical explanation for the double-slit interference experiment is given. Setting part of the Ricci scalar equal to zero gives a covariant wave equation and the Schrödinger equation becomes part of a more general solution that also models quantum jumps. This possible link between general relativity theory and quantum theory explains the particle-wave duality and suggests that the quantum mechanical wave functions are amplitude and phase modulations of very high frequency oscillations in the metrics of spacetime.

Optical observations in the solar system suggest that the planets might accelerate relative to their computed ephemerides. However, no evidence for this acceleration has been detected in modern ephemerides primarily based on radar ranging between the planets and the Earth and laser ranging to the Moon. It is suggested that this disagreement between optical observations and the ephemerides might result from a cosmological spacetime that is locally curved.