Top-Down cosmology and model-dependent realism: A philosophical study of the cosmology of Stephen Hawking and Thomas Hertog

Within the domain of history and philosophy of cosmology, I have investigated the cosmological work of Stephen Hawking and his collaborator Thomas Hertog between 2006 and 2018. In 2006, Hawking and Hertog put forward a new framework called top-down cosmology. This approach starts from the present (―at the top‖), with the properties of the universe as we can observe it today, and works its way back to the past (―down to the bottom‖). What makes top-down cosmology uniquely stand out, compared to many other competing approaches, is Hawking‘s attempt to scaffold his cosmological work by means of his philosophy of model-dependent realism. This philosophy claims it is meaningless to ask whether a theory is real, only whether it agrees with observation. When two competing, even mutually incompatible, theories agree with observation, it is impossible to say one is more real than the other. From a philosophical point of view, model-dependent realism is seriously flawed. However, from a cosmological point of view, it gave Hawking and Hertog a practically unconstrained liberty to play with the concepts and tools of different branches of physics to construct their cosmological models. I claim that model-dependent realism is not a brazen and failed attempt at philosophising, but a well thought through strategic move with cosmology which definitely has its merits for science, provided that it would be worked out in a more systematic way. I defend the position that model-dependent realism could be very helpful in preventing scientists of letting themselves get ―held back‖ because the theories they are working on are ―too far away‖ from our common sense view of the world. To support this claim, I examined the relationship between top-down cosmology and model-dependent realism. I also claim that Hawking‘s and Hertog‘s approach to cosmology is indicative for a gradually changing attitude about what counts as ―the scientific method‖ within the scientific community of fundamental physics and cosmology. The characteristics of this changing attitude are a more lenient view towards falsifiability and a stronger focus on non-empirical theory assessment.