Ultimate Explanations of the Universe Read Online Free PDF Page A

terminology used today) in space.
    But then what boundary conditions should be applied? Somewhat earlier the Dutch astronomer Wilhelm de Sitter had hinted at a solution. In Einstein’s theory we do not have to insist on a flat space: we know that gravitation distorts its geometry. So we may do away completely with the “boundary,” and hence with the need to adopt any kind of boundary conditions. Such a situation would hold if space were spherical in shape, analogous to the surface of a sphere (if we move along it, nowhere do we encounter an edge). Einstein calculated that there was a solution to the field equations which had these properties.
    There was just one remaining problem, the one that had troubled Newton – the question of gravitational instability: why would the stars in a spherical universe not collapse into a single point? To obviate the difficulty, Einstein did what von Seeliger and Neumann had proposed earlier with respect to Newton’s theory of gravitation: he augmented his equations with a component entailing a constant the purpose of which was to stabilise the model. This constant – Einstein named it the cosmological constant – is an exact counterbalance of the attracting gravitational force. That is how the first cosmological model based on the theory of relativity was constructed. Today we call it Einstein’s static model.
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    2.4   The Universe and Philosophy
    Let’s not be led astray by appearances, however. True enough, Einstein’s paper is an example of a fine piece of research opening up new horizons while at the same time addressing the old problems. But his aim went much further: it was precisely to reach the ultimate explanation. Naturally, such intentions are not to be disclosed in a research paper submitted for publication in a scientific journal, although they may often inspire many an author. On the other hand we have to admit that Einstein cared far less about conventions than many of his colleagues. The attentive reader will quite readily identify a certain philosophical motif in his 1917 paper: “In a consistent theory of relativity,” he wrote, “there can be no inertia relatively to ‘space,’ but only an inertia of masses relatively to one another.” 5 Again this sounds technical, but it’s fairly easy to decipher what Einstein was thinking of. The inertia of a particular body with respect to space, which would have to be something like Newton’s absolute space, would mean that the body’s mass, which is a measure of its inertia, would be its absolute property, something with which the body was endowed a priori. But the world should be a “closed system,” all of its justifications should remain within it, not assumed a priori. The only sensible solution to this situation was to assume that the mass of a particular body was as it were induced in it by all the other bodies in the universe. Hence there would be no inertia with respect to space, only with respect to other masses. Einstein took this idea from the writings of the physicist and philosopher Ernst Mach, and in his honour called it Mach’s principle. The intention to create a theory of physics incorporating Mach’s principle was one of the main motives behind Einstein’s efforts which eventually led to the emergence of the general theory of relativity. No wonder that this motive is clearly visible in his first paper on cosmology.
    But Einstein’s philosophical inspirations went even further. Ever since his young days he was interested in the life and work of Baruch Spinoza, a seventeenth-century philosopher. Spinoza was so fascinated with instances of rationality in the world that he identified the world with God. “By God,” he wrote, “I understand a being absolutely infinite, that is, a substance consisting of an infinity of attributes, of which each one expresses an eternal and infinite essence.” 6 Understood in this way, God is identical with the universe; hence God is the “substance”