The holidays are coming to an end, so expect a return soon to the usual somewhat irregular posting frequency.
Over the past week or two, one thing that I did was get a chance to read new books by two of the most prominent physics bloggers around: Chad Orzel (who has been blogging since 2002, now at Uncertain Principles), and Sean Carroll (since 2004, now at Cosmic Variance).
Orzel’s new book is entitled How to Teach Physics to Your Dog, and he has a website with all sorts of material about the book here. I guess it’s generally agreed that a cute dog improves just about any sort of material. While Brian Greene in his Elegant Universe Nova special introduced general relativity by trying to discuss it with a dog, concluding that “No matter how hard you try, you can’t teach physics to a dog”, Orzel takes a very different tack, structuring his book around conversations with his dog about quantum mechanics. The dog ends up with a solid intuitive understanding of quantum physics and presumably the idea is that the reader should be able to do as well as the dog. The book is a quite good, non-technical, exposition of some of the paradoxical aspects of quantum mechanics, emphasizing the subtleties of the relationship between the quantum and classical views of reality. His expertise in experimental atomic physics gives him an excellent understanding of these issues, and he does a good job of conveying some of this to the reader.
Among the best features of the book are enlightening treatments of the quantum Zeno effect, quantum tunneling, entanglement and quantum teleportation, as well as careful treatment of some crucial subtleties of the subject. If you want to go beyond the usual explanation that the uncertainty principle is about how measurements must change the state of a system, and find out how one can use quantum mechanics to measure a state without changing it, this is a good place to start.
By the end, I observed myself ending up in a linear combination of two possible states describing my feelings about the dog thing: about equal amplitudes for charming and annoying. Even now that we’re in a different decade, I haven’t yet collapsed into one state or the other.
The other new blogger-book is Sean Carroll’s From Eternity to Here, which has its own website here. I confess to being somewhat mystified by this book, and a bit surprised by its contents. Carroll is a very smart guy, with a serious dedication to making the wonderful science of his professional field (cosmology and particle physics) accessible to the general public. Given this, my expectation was that the book would be mainly devoted to telling the conventional scientific story of some part of our current understanding of these subjects, with perhaps a more positive take than mine on the possibility of exciting new discoveries in the near future. I also expected him to include some material on his highly idiosyncratic ideas about the arrow of time.
It turns out though that this rather long book is heavily oriented towards making the case for unconventional claims about physics, with essentially no discussion at all of what is happening on the experimental side of the subject. The LHC appears only in a footnote explaining that it won’t destroy the earth, and there’s virtually nothing about the hot topics of dark matter, gravitational waves, or the cosmic microwave background. In a final footnote, Carroll explains that he decided not to write about these experiments because
it’s very hard to tell ahead of time what we are going to learn from them, especially about a subject as deep and all-encompassing as the arrow of time.
Carroll’s problem is that the questions that he has chosen to highlight in the book may be “deep and all-encompassing”, but they’re of a sort one might describe as “philosophical” rather than scientific. Much of the book is devoted to arguing that in order to understand the local (in time) question of why entropy increases, one must understand the global puzzles pointed out by Roger Penrose associated with gravitational entropy, the Big Bang and inflation. More succinctly, the explanation for why an omelet doesn’t turn into an egg somehow involves understanding the Big Bang. Even after reading the book, I remain unconvinced that the global problem has to be solved to explain the local problem, and unfortunately there’s no scientific way to resolve my difference of opinion with the author. No conceivable experiment can provide evidence one way or another about which of us is correct.
After making the case that one needs to understand the low entropy of the early universe to understand everyday physics, Carroll goes on to propose his own theory, the “Ultimate Theory of Time” of the book’s subtitle. It’s a version of the usual “multiverse” argument: one explains some mysterious distinctive feature of the universe by positing that we live in a multiverse without this distinctive feature, which just occurs as a dynamical accident in our particular universe. The problem is that this particular explanation is not a conventional scientific one, since it is immune to experimental investigation, and, as far as I can tell, few physicists take it seriously. Carroll’s one scientific paper on the subject, (written in 2004 with his graduate student Jennifer Chen) received a lot of publicity on the internet and in Scientific American, but doesn’t seem to have yet been published, despite being listed on his CV as submitted to Phys. Rev. D.
The book seems likely to get a lot of public attention, but I’m not sure this is a good thing for the public understanding of science. It raises fundamental issues in physics, which naturally attracts people’s interest, but then addresses them in a rather post-modern yet pre-scientific manner, avoiding contact with either mathematics or experiment. Probably the best way to think of From Eternity to Here is as an extended essay in the philosophy of science, and as such I’d be curious to hear what philosophers expert in the subject make of it.
Update: Scientific American has an interview with Carroll, in which he addresses objections like mine as follows:
The following statement is very true: To understand the second law of thermodynamics, or how the arrow of time works in our everyday lives, we don’t need to ever talk about cosmology. If you pick up a textbook on statistical mechanics, there will be no talk about cosmology at all. So it would be incorrect to say that we need to understand the big bang in order to use the second law of thermodynamics, to know how it works. The problem is, to understand why it exists at all requires a knowledge of cosmology and what happened at the big bang.
Once you assume that the universe had a low entropy for whatever reason, everything else follows, and that’s all we ever talk about in textbooks. But we’re being a little bit more ambitious than that. We want to understand why it was that way—why was it that the entropy was lower yesterday than it is today?
To understand why the entropy was lower yesterday really requires cosmology. And I think that if you sit down and think about it carefully there is absolutely no question that that is true, yet a lot of people don’t quite accept it yet.
After having sat down to think about it carefully, I still don’t quite accept it…
