Accelerated expansion
In 1997, the High Z supernova research project and subsequent independent teams probing deeper than ever by means of type 1A supernovas, arrived to a surprising discovery, the Universe was not only expanding, but the expansion rate was actually accelerating.
Surprising as it was, the discovery came in handily to solve the "age crisis", for when the Universe's history is plotted back taking into account acceleration, numbers begin to fall in place and they point to about 13 billion years, consistent with the independent and well accepted determination of about 12 billion years for the age of the oldest stars.
Acceleration also could not be accepted easily for in case of being correct, then some unknown form of energy must be assumed in order to counteract and overcome gravitation, just as dark matter had to be postulated to explain galactic disc dynamics. The discarded Cosmological Constant or "dark energy", whatever the name, had to be assumed again though no hints of its nature were - or are - known, to account for the apparent springiness of empty space. There is, for some respected researchers, far too much dark stuff to assume.
On the other hand, respected voices who were previously in disagreement with the Hubble constant value obtained by the Key project, and who had alternative theories for accounting with the age crisis, suspected supernova 1A findings were not conclusive and could be explained by alternative phenomena like obscuration by intervening dust and gas clouds which, by dimming of starlight, could mimic a larger than actual distance. It should take further work on independent lines to settle the point.
Echoes from the Big Bang and the largest structures in the Universe
Two additional independent lines of observation, confirmed with excellent consistency the acceleration of universal expansion, the power spectrum of the Cosmic Microwave Background Radiation anisotropy size, and the mapping of large scale structure of matter.
In 1966, two researchers from Bell Labs stumbled upon an annoying microwave noise. Watson and Penzias, determined after careful verification that this noise was coming from the sky itself, and that it was remarkably uniform. They were not aware of the Big Bang theory which predicted the existence of just such microwave "glow" as the echoes from the primeval fireball, red shifted all the way down to the radio spectrum of wavelengths. Its experimental finding was the first observational confirmation of the Big Bang hypothesis.
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