  Before 1998 the universe expansion was thought to be slowing down. After 1998
the universe expansion is thought to be accelerating up. This change of the
belief is motivated by the observed brightness of the high redshift supernova
Ia fainter than expected. In this paper it is argued that this change of the
belief is not necessary. There is a more reasonable explanation for the
observed brightness of the supernovae Ia fainter than expected. That is: the
universe space filled with the tenuous ionized gas; the Thomson Effect of free
electron in the ionized gas caused the observed brightness of the high redshift
supernova Ia fainter than expected. The observations of Warm-Hot Intergalactic
Medium (WHIM) support this explanation. The universe space filled with tenuous
ionized gas explanation will lead to the puzzle of the dark matter and dark
energy disappeared simultaneously
