Modal Realism and the Possibility of Island Universes: Why There are no Possible Worlds

In this article, I defend Lewisian modal realism against objections arising from the possibility of ‘Island Universes’ and other similar cases. The problem comes from Lewis’ claim that possible worlds are spatio-temporally isolated. I suggest a modification of Lewisian modal realism in order to avoid this family of objections. This modification may sound quite radical since it amounts to abandoning the very notion of a possible world, but as radical as it may sound it in fact remains well in the spirit of Lewis’ original view.

Topics in Modern Cosmology

This chapter recounts the discovery that the spiral nebulae are galaxies of stars and coequals of the Milky Way, which led to the exploration of a new level in the hierarchy of structure in the physical universe called the realm of the spiral nebulae. It details how cosmology has grown to include the study of other systems, such as the radiation backgrounds and the gas cloud, but common luminous galaxies comparable to the Milky Way remain the centerpiece. It also highlights some of the ways people came to see that the spiral nebulae as island universes of stars and discusses some elements of the systematics of the structures and spatial distribution of the galaxies. The chapter reviews the luminosity of the Milky Way galaxy that had been estimated from star counts and statistical estimates of star distances by 1920. It mentions Ernst Öpik, who put the ratio of the mass to luminosity.

Awe

By awe, philosophers and psychologists mean the sensation that overcomes someone in the presence of something simultaneously vast, powerful, and, when compared to humans, strangely humbling. The chapter begins with a review of amazing discoveries such as island universes, the expanding universe, and the Big Bang that altered the understanding of the universe and made the solar system “seem but a speck of dust in infinite space.” It then turns to other sources of awe, or the Depression sublime: the Empire State Building; Jesse Owens’s record-setting long jump at the 1936 Berlin Olympics; the moral heroism of the Joads in John Steinbeck’s The Grapes of Wrath; and James Agee and Walker Evans’s deification of tenant farmers in Let Us Now Praise Famous Men. Whereas most accounts of the sublime involve the vastness of nature overwhelming human beings, during the Depression human beings themselves became a source of the sublime.

ANTI-DE SITTER ISLAND-UNIVERSES FROM 5D STANDING WAVES

We construct simple standing wave solutions in a 5D spacetime with a ghost-like scalar field. The nodes of these standing waves are "islands" of 4D anti-de Sitter spacetime. In the case of increasing (decreasing) warp factor, there are a finite (infinite) number of nodes and thus a finite (infinite) number of anti-de Sitter island-universes having different gravitational and cosmological constants. This is similar to the landscape models, which postulate a large number of universes with different parameters.