  The coherence of the interaction of light with a collisionless gas (Einstein
1917) founds the theory of gas lasers. It is, for the understanding of
universe, a simpler and more powerful tool than the big bang which requires
questionable supplements (dark matter, MOND, etc..). The Impulsive Stimulated
Raman Scattering (ISRS) redshifts gradually light pulses which cross excited
atomic hydrogen H*, so that the redshift is a measure of the column density of
H*. Thus, the distance of the hot stars, surrounded by much H*, is exaggerated
by the use of Hubble's law. Local exaggerated distances create voids in the
maps of galaxies which become spongy. The interpretation of spectra of quasars,
the periodicity of galaxy redshifts introduce an experimental "Karlsson's
constant" exactly computed by ISRS. The need for dark matter comes from the
exaggeration of the distance, therefore the size of galaxies. Without dark
matter, celestial mechanics provides a reliable distance of spiral galaxies.
Coherence also introduces superradiance and mode competition that explain that
only the limbs of Str\"omgren spheres are visible as circles maybe punctuated
by an even number of dots: Too numerous, the figures assigned to gravitational
lenses can be such limbs. The coincidence of the ignition of the rings of
SNR1987A with the extinction of the star is due to a multiphoton coherent
scattering of star light, which amplifies the superradiant emission of the
rings.. A blueshift of microwaves crossing H* resulting, between 10 and 15 AU,
of the expansion of solar wind, explains the "anomalous acceleration" of
Pioneer probes. All is obtained without any change in theories of standard
spectroscopy.
