Cosmology, from its very birth, has been a science beset by insufficient data and ill-founded tenets. Faced with extreme difficulties in collecting observational data, it used to rely on simplifying working assumptions. Those assumptions had the tendency to evolve into dogmas or into elaborate theoretical constructs, immersed in which their practitioners all too easily forgot about these shaky foundations. It is enough to recall the original cosmological paper of Einstein from 1917, who, swayed by prevailing beliefs, was absolutely sure that the Universe must be spatially uniform and unchanging in time – so much so that he preferred to modify his freshly created theory rather than say that it contradicts the astronomical dogma. Another instructive example is the steady state theory. It had been very much in vogue for about 20 years, before it was proved wrong by a single discovery, that of the cosmic microwave background (CMB) radiation. It was glamorous and successful, in the eyes of its proponents, even though it relied on an assumption that is drastically at variance with laboratory physics (continuous creation of matter particles out of nothing).