| Not only at very high temperatures and densities we cannot be certain about the properties of matter, but there exists absolutely no evidence that can justify the extrapolation of the evolution of the universe towards such temperatures and densities. The properties of the observable universe are consistent with an initial state where the temperature was so high that the protons and neutrons were free, not bound in atomic nuclei, like today. This means that the temperature corresponded to a kinetic energy of several tens of MeV per particle. At such a temperature, the state of the matter is a plasma composed only of protons, neutrons, electrons, positrons, photons and neutrinos. At this temperature, the matter has the simplest possible composition. At lower temperatures the particles become bound in nuclei, atoms and molecules, which become more and more complex with decreasing temperatures. At increasing temperatures, the higher the temperature is, more and more mesons, baryons and heavy leptons are generated and the plasma composition becomes more and more complex. However, at that temperature where the matter has the simplest composition, any traces of its former evolution have been practically erased and we do not have any rational reason for making suppositions about it. Perhaps the matter was indeed even denser and even hotter, but there is no basis for this extrapolation except some philosophical belief that is not based on any scientific observation. An extrapolation towards greater temperatures and densities could be justified only if we knew boundary conditions around the universe, which we do not know. In conclusion, what can be known with reasonable certainty about the Big Bang starts from a moment in time when the temperature corresponded to a kinetic energy of several tens of MeV per particle, and all extrapolations to times before that moment are hypotheses that are not based on any experimental data, so they can be neither verified nor falsified. The supposition that the Universe may have started from a single point is something that has nothing to do with science, but it may be a valid religious belief. |