I recently finished reading Sean Carroll’s new book, From Eternity to Here. Peter Woit opined that the book was “an extended essay in the philosophy of science” and was curious to know what philosophers would think of it, so I thought I’d give it a shot. While the questions that Carroll addresses are questions that are discussed by philosophers of physics, the book lacks good arguments for the conclusions that Carroll draws. He makes many sweeping claims, many of which have been disputed by philosophers, but he makes no engagement with those disputes. The arguments he provides are not new in the literature and are much better defended elsewhere. So it’s certainly not a new contribution to the philosophy of physics literature, and if it is philosophy of science, is philosophy of science badly done.
First, a short sketch of Carroll’s argument. Carroll essentially takes David Albert’s line that the tension between the time-asymmetric second law of thermodynamics and the time-symmetric laws of classical mechanics can be resolved by postulating low-entropy initial conditions for the universe — a postulate that has come to be called the Past Hypothesis in the philosophical literature. On top of that, Carroll argues that those initial conditions themselves need explanation, and the explanation he favours is a multiverse that buds off little “baby universes” that start off with low entropy initial conditions, We, Carroll suggests, are in one of those baby universes.
Carroll often makes a major philosophical point without sufficient justification and without addressing some obvious objections. Most but not all of the following instances where he does this are points are important for his main argument.
- Explanation of “special” initial conditions of the universe. Craig Callender objected in his review of Carroll’s book to Carroll’s assumption that “special” initial conditions have to be explained at all. Callender himself argued this with more detail in a paper, and the issue of whether explanation is needed in this case is a matter of debate in philosophy of science. But Carroll doesn’t justify his assumption at all.
- The Past Hypothesis. As mentioned, Carroll’s argument for the Past Hypothesis is basically David Albert’s. This argument has been criticized in various places. To his credit, in this case Carroll does mention the existence of those criticisms, in footnote #142, where he admits that the status of the Past Hypothesis is “not uncontroversial”. However, he does not engage with those criticisms.
- The Past Hypothesis as a law of nature. Carroll states that there is a distinction in physics between laws and initial conditions, and that since the Past Hypothesis is an instance of the latter, it is not a law of nature. But this does not address the reason supporters of the Past Hypothesis think the Past Hypothesis is a law of nature. The reason David Albert, Barry Loewer and a few others think that the Past Hypothesis is a law of nature is because they hold a Humean, Mill-Ramsey-Lewis view of what the laws of nature are, and think that the Past Hypothesis would appear in the system of statements about the world that forms the best balance of simplicity and informativeness.* Carroll’s statement about laws versus initial conditions completely ignores the [prima facie, not unreasonable] view of laws of nature held by these people. Carroll’s objection to calling the Past Hypothesis a law of nature is premised on a different view of what the laws of nature are, a view that is neither articulated nor justified.**
- The relation between information theoretic entropy and thermodynamic entropy. Carroll repeats Landauer and Bennett’s arguments for equating information theoretic entropy and thermodynamic entropy. These arguments have been criticised, and Carroll does not mention these criticisms. The equation of those two kinds of entropy is put forward as unproblematic when it is not.
- The different arrows of time. Carroll frequently conflates the different arrows of time and makes big, unsubstantiated claims based on those conflations. A series of such claims is presented with hardly any support on pp. 40-41. Among the claims are:
- The arrow of time*** “explains” why we remember the past but not the future.
- The fact that our memories of the past are reliable is explained by the monotonic increase of entropy with time.
- “We distinguish past from future through the relationship between cause and effect.” (Isn’t it the other way around?)
- From the previous point, he thinks it follows that “part of the distinction we draw between ‘effects’ and ’causes’ is that ‘effects’ generally involve an increase in entropy”. (I don’t understand. How do causes not generally involve an increase in entropy? How are causes somehow exempt from the second law of thermodynamics? And what does he mean by “involve”?)
- “Our notion of free will… is only possible because the past has a low entropy and the future has a high entropy.”
Overall, I think it’s a nice pop science book to read for laypeople who want to get their feet wet in some of the issues in the foundations/philosophy of statistical mechanics, but for those already familiar with the ins-and-outs of that field, and for philosophers in general, Carroll’s book is too sloppy to be of much help.
*See for example this paper by Loewer.
**It seems, among other things, to be a non-Humean view.
***It’s not clear at this point even what Carroll means by the arrow of time.