Contemporary cosmological reflections

The standard Big Bang model has excellently passed many observational tests, also of the experimentum crucis nature. Cosmologists, however, are aware of its shortcomings.

These include, among others:

• A limited possibility of extrapolating the known laws of physics to the first fractions of a second after the Big Bang. Most physicists believe that we cannot get to periods earlier than approximately 10–33 s.
• The certainty that in the Planck epoch of 10–43 s., in which the Universe area connected causally becomes comparable to the size of elementary particles, the quantum gravity laws, which we do not know, ruled the Universe.
• The nature of the mysterious dark matter, constituting more than 90% of the mass of galaxies and clusters of galaxies (and generally about one-quarter of the mass of the Universe); we know only that dark matter cannot be a simple Baryon matter (ordinary atoms).
• The nature of an even more mysterious dark energy, accounting for approximately 70% of the Universe mass and having disturbing properties: negative pressure and a constant density, independent of its volume; it causes an accelerating expansion of the Universe.
• An amazing isotropy and homogeneity of the Universe (the problem of the horizon).
• The unsolved problem of the origin of primary fluctuations of the cosmic plasma density, from which later space objects originated (galaxies, galaxy clusters and superclusters).
• The unanswered question of why the Universe is described in Euclidean geometry (the problem of flatness).
• The unanswered question of the cause of the Big Bang, the dimensionality and topology of space, and the primordial singularity, of what was before the Big Bang.

There are, of course, theories, hypotheses, speculations or merely suggestions that go beyond the standard Big Bang model. These include, for example:

• The theory of cosmic inflation – a theory most mature from a theoretical point of view, attempting to explain the problems of the horizon, flatness, and the origin of the primordial density disturbances. There is still no confirmation of not only observational, but even unambiguous predictions, arising from this theory.
• Reflections on the basis of the string theory on what happened before the Big Bang. Here the problem consists in that the string theory has not yet been fully formulated; also, there are no observational predictions resulting from it.
• The concept of multiple worlds, which is just a loose collection of ideas. It is not supported by any reliable theory, let alone the results of observations, and many believe that it does not fit in the area of scientific reflection.