radiosources, objects believed to be extremely distant. Counts of these The influence of Copernicus sources indicate that their number density is different at large distances on physics from what it is here. Or we may put it differently : the number density of B. Paczynski, Institute of Astronomy, Warsaw radiosources was different a long time ago from what it is now. This is in This month sees the 500th Anniver tific one, and there are some perils contradiction with the strong cosmo sary of the birth of Copernicus. To associated with it. logical principle. Also, the Universe mark the occasion, Europhysics News Why should we not make the cos seems to be filled with a black body has invited B. Paczynski, Polish Board mological principle more perfect ? microwave radiation which has, at member of the EPS Division on Phy Once we say that the Universe is the present, the temperature of 2.7 K. It is sics in Astronomy, to write this article. same everywhere, should we not also almost certain that this radiation was say that it is the same at all times ? produced about 1010 years ago when Once we have decided our place is the Universe was very dense and hot, Copernicus shifted the centre of and matter was in thermal equilibrium the Universe from Earth to the Sun, not unique, why should the time we live in be unique ? In fact such a with radiation. Such conditions are and by doing so he deprived man vastly different from the present kind of its unique position in the Uni strong cosmological principle has been adopted by some scientists. It situation and this is another obser verse. That action had the most pro vational evidence against the strong found impact on scientific thinking. It leads directly to steady state cosmo logy. I believe this is the most extreme cosmological principle. We can no is likely that the philosophical con longer belive that the Universe was sequences were even more important extension of the Copernican idea. We live in the century when cosmo always more or less the same. But this than the purely scientific value of the conclusion is difficult to accept for new model proposed for the solar logy is becoming a science. Cosmo logical principles may be verified many people. Therefore, a model of system. The Copernican model helped the oscillating Universe has been de people to look at the Universe from a observationally. Observations of dis tant galaxies indicate that the Uni veloped. Perhaps we live at some new point of view : we may consider specific phase of the present cycle of ourselves to be just a part of the verse expands on a time scale of 1010 years. Therefore the density of matter the oscillating Universe, but there was, Universe which can exist without us and there will be, an infinite number just as well, rather than to think that decreases with time, contrary to the strong cosmological principle. To of cycles, and our cycle is not really we are the very central and the most unique in an way... Isn’t this another important part of the Universe. I think save this principles, we have to postu late a continuous creation of matter. extreme extension of the Copernican we should make a distinction between idea ? the scientific achievement and the This raises some philosophical pro philosophical consequences. blems. We either have to accept the As there seems to be disagreement hypothesis that matter is created now, between the strong cosmological prin The Copernican model of the solar or we have to agree that our times ciple and the observations, we have to system, with some improvements due are unique and the Universe was to Kepler, is still valid after four and be more modest in extending the way entirely different some 1010 years ago. of thinking initiated by Copernicus. a half centuries. There are not many It is very fortunate that this is no scientific models created in this cen Perhaps we should ask ourselves if it longer a matter of philosophy only, is really justified to assume that the tury which are likely to survive for so but is a problem that may be the Universe is more or less the same long. The heliocentric theory, once so subject of observational studies. It is everywhere. Isotropy of the back radical, today belongs to the esta now possible to observe very faint ground 2.7 K radiation indicates that blishment. As time has passed by the Universe is homogeneous on a mankind has moved further and further very large scale, over the distance of away from any place that could be 1010 light years. But there is not too considered to be a centre of anything. much observational evidence for the It is surprising to notice how this ex homogeneity on a scale of say 109 tension of Copernican thinking has light years. What should also be kept become a dogma of modern science. in mind is that we have no observa Let us consider cosmology. Almost tional evidence for the existence of all cosmological theories adopt the so any extraterrestrial life, intelligent life called cosmological principle: the in particular. The very important pro Universe should look more or less the blem of whether we humans are alone same everywhere. This is a simple in the Universe has not yet been solved extension of the idea that can be by science. The answer one is willing traced back to Copernicus. If Earth to give to this problem depends mainly does not occupy a special position, on one's philosophical convictions. I then there is no reason for the Sun believe that most scientists are willing to be a unique star, and as a matter to think that mankind is not unique. of fact the Galaxy we live in should Ultimately it is so because most of us not be a unique galaxy. The cosmo cannot accept the possibility that the logical principle is basic for the theory, Earth could have a central position because it makes this theory suffi from any point of view. Copernicus ciently simple to study. It is a philoso N.COPERNIC was most efficient in moving us away phical principle rather than a scien Nicolaus Copernicus 19 February 1473 - 24 May 1543 from any kind of centre.
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