Welcome to Our Blog on Philosophy of Cosmology
Welcome to our blog on philosophy of cosmology. Herein you will find discussions of issues in philosophy of cosmology, developments in cosmology and fundamental physics, and more generally philosophy of physics and philosophy of science and sometimes discussions about what it all means. The Bloggers are members of a group of philosophers and physicists (see main page) who are involved in a 3 year project supported by the Templeton Foundation and whose research includes cosmology, string theory, philosophy of physics, metaphysics, philosophy of religion and related fields. In addition there will be invited guest bloggers and commentators whose work and interests appropriately intersect with our group. We are aiming to produce lively, informed, and philosophically interesting discussions.
Among the questions in philosophy of cosmology which we are interested in addressing are:
1) Does the low entropy condition of the universe at the Big Bang (what is often called the “past hypothesis” or “PH”) require explanation? How successful are attempts to explain it?
2) Was there anything “before” the Big Bang?
3) Is our universe one among many? What scientific and philosophical reasons are there for “many universes” and “bubble universes” hypotheses?
4) What does the apparent fine tuning of the laws and initial conditions of the universe imply about the origin of the universe and about the existence of many universes?
5) What is the meaning and metaphysics of probability in the context of fundamental physical and cosmological theories?
6) How should the cosmological constant and dark energy be understood?
7) What are the connections between cosmology, statistical mechanics, and time’s arrows?
8) Does “the wave function of the universe as a whole” make sense? What is its “ontological status?”
9) How do the interpretational problems in quantum mechanics (“the measurement”) interact with issues in cosmology? How should the non-local influences found in QM be understood?
10) How does the physical description of the universe relate to the physical states of its constituents? Is there support for a Spinozistic conception of the universe on which the whole is metaphysically prior to the parts?
11) Does the uniqueness of the universe pose special epistemological problems especially regarding the nature of probability and statistical reasoning?
12) What are the metaphysical natures of fundamental laws and fundamental chances?
13) Why is there something rather than nothing?
I imagine that all of these will be discussed during the course of our project. However, I suggest holding off definitively answering question 13 until our grant has expired.
I would like to start our discussions off with question #1 above since I know that our group represents various views about it.
Roger Penrose has said that the question of what, if anything, explains why 13.7 billion years ago the universe was in a very special state (“the Big Bang”) is one of the most important and puzzling questions facing the foundations of physics. In a recent article our colleague Tim Maudlin remarked that ‘This question of accounting for what we call the “big bang state” is probably the most important question within the philosophy of cosmology”.
The BB state is “special” (quite unlike the universe we see around us now) in that its volume was tiny, and its density, pressure and temperature immense. But according to Penrose what makes it especially in need of explaining is that its entropy was incredibly low. The low entropy of the BB state is a conclusion of inferences based on observational astronomy and also a hypothesis that grounds (and seems to be required to ground) the second law of thermodynamics and arguably also is implicated in various other temporal asymmetries (the asymmetries of records and influence). How that works or is supposed to work will be discussed and argued over in future blog entries. The low entropy of the BB state means that the set of micro states that realize the BB condition occupies a minute portion of the phase space of possible states; so small that were we to suppose (as Penrose suggests) that the actual state was selected at random from the set of all physically possible states (given the mass energy of the universe) the chance of selecting a state with the Big Bang conditions is, Penrose calculates, 1 over 10^10^123. Penrose thinks that since the BB state is so unlikely it cries out for an explanation. Among the suggestions one can find are
1. The universe was created in the BB state by a designer.
2. The universe is infinite and unbounded in both temporal directions and is typically in equilibrium. The BB state came about as a very unlikely fluctuation. While it is very unlikely to find the universe in a low entropy state in any finite temporal interval it is very likely (probability 1) that in the infinite history of our universe that there are such (infinitely many in fact) such fluctuations. (Boltzmann might suggest this.)
3. Multiverse hypotheses. For example, Sean Carroll has proposed an account which roughly says that our universe was cleaved off from a “mother universe” whose state is typical and which produces “baby universes” in BB like states.
4. The intuition that the BB state “cries out” for explanation is based on a mistaken use of probability. There is no more need to explain the low entropy BB state than to explain the dynamical laws. (Of course this is not to reject the possibility of explaining the BB state).
1 and 2 are probably non-starters for well known reasons (1 since it really isn’t an explanation and 2 for reasons that Feynman and others have pointed out). It is unclear how to me whether Carroll’s account works or even if the fundamental laws are as he hopes it works. Here is a link to a very nice talk he gave to Google (the company) that explains it. I am interested in developing 4 since it goes along nicely with the Lewisian account of laws and objective probabilities that I like. But even after persuading myself of that account (I am sure we will discuss and argue about the nature of chances and laws in future blog entries) there still feels like there is an itch that needs scratching. Anyway, I am curious what you all think about Penrose’s problem.