Ultimate Explanations of the Universe Read Online Free PDF

which exists “of itself” and is “self-explanatory.” Einstein was quite open about his sympathy with pantheistic views of this kind. He, too, was fascinated by the “rationality of the universe” and often spoke of his “cosmic religion” in connection with this. No wonder, then, that the universe was “to explain itself”; the right cosmological theory should be the ultimate theory. 7
    Einstein immediately took up de Sitter’s suggestion that troublesome boundary conditions could be evaded by assuming that the universe was spatially closed. The logical enclosure of the universe, that is the idea that all of its explanations should be enclosed within the universe, found its expression in the geometrical enclosure of the universe. On finishing his paper Einstein had every reason to feel pleased with himself. There was only one solution to the gravitational field equations which met all of his philosophical criteria. That solution presented an eternal universe, spatially closed and obeying Mach’s principle.
    Einstein thought that the “cosmological problem” had been solved. I wonder what research problems he was pondering about after that?
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    2.5   An Expanding Vacuum
    The “universe’s rationality” is indeed one of its fascinating features. It certainly needn’t have been so that our minds would be capable of fathoming the mysteries of its structure. For we have managed to fathom so much. Einstein’s first paper on cosmology was undoubtedly a milestone on the road to understanding cosmic structure. As we think about this a disconcerting question comes to mind: are our brains advanced enough to allow us to completely solve the mystery of the universe? Or to put it in another way; does the structure of the universe have to correspond to our brain structure to such an extent as to allow us full access to discovering the way it works? On finishing his paper Einstein did not realise how far he still was from ultimate solutions. But he was soon to find out.
    Still in 1917 de Sitter published a paper presenting a new cosmological solution to Einstein’s equations (with the cosmological constant). 8 In this paper de Sitter embarked on a dispute with Einstein’s understanding of Mach’s principle and put forward his own interpretation. But this was not what proved fatal to the views of Einstein. The very existence of de Sitter’s solution put them to a difficult test. In de Sitter’s solution the density of matter is equal to zero. In other words de Sitter’s model is empty, and in spite of this the structure of space-time is still well-defined. Therefore it is not defined by means of a distribution of “material sources” and Mach’s principle (as Einstein understood it) is not obeyed in the general theory of relativity. Soon it turned out, thanks to the work of Georges Lemaître, 9 that although de Sitter’s world was empty, his space was expanding: if we were to put into this world two particles the masses of which could be ignored as negligible, so as to still be able to consider the model as empty, then those masses would begin to move away from each other.
    Meanwhile ever since 1912 Vesto Slipher had been measuring shifts in the spectra of galactic nebulae. In 1918, on the basis of his own and Slipher’s observations, Carl Wirtz expressed an opinion that the prevalence of red shifts in the spectra of nebulae could mean that these nebulae were moving away from each other. In the same year Eddington wrote in a letter to Shapley that the spreading out of the nebulae had been predicted in de Sitter’s model. 10 The recession of the nebulae came to be known as the de Sitter effect.
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    2.6   The Crisis of Einstein’s Philosophy
    From the theoretical point of view the situation was paradoxical. Einstein’s model had a non-zero density of matter but did not predict the moving away of the galaxies (spiral nebulae). De Sitter’s model predicted the moving away of the galaxies but had a zero