|The Lazy Universe|
Author: Jennifer Coopersmith
OK, so it's a physics book - but it's a very interesting physics book.
I'm an ex-physicist and you know what they say - there is no such thing. A large proportion of programmers are STEM educated and so this is for you.
The first and most important thing to say is that this is neither a textbook nor is it a general reading book. It is something between the two and it is probably how textbooks should be written - in physics at least. It attempts to give you the reasons that are behind the mathematics, rather than just dump the math on you and then leave you to figure out what it all means.
The title of the book might not give you any idea what the subject matter is. For this you need to look at the subtitle, "An Introduction to the Principle of Least Action". This should provide the clue to it being about Lagrangian and Hamiltonian formulations of mechanics.
The idea is that because things take the shortest path through whatever they are moving in, this is a principle of laziness, i.e. least action. Personally I don't see it like this because finding the path with the least action seems to be a tough problem.
I have been interested in Lagrangian and Hamiltonian mechanics for a while, but can't say I ever really understood what was going on. I could use both, but I never felt confident that I understood why they worked. I have also encountered the idea of "least action" particularly in Quantum Field Theory, but again I never really thought I understood it enough to be sure of it. So this book promised to fill in the missing details in terms of the philosophy and motivation.
The author wrote the book based on the more advanced writings of Cornelius Lanczos, and you can think of it as a "popularization", but it is more than just a simple retelling. It is a history and a philosophy of advanced mechanics. It starts off with a fun look at the early days of Galileo, the Bernoullis, and so on. This is the part of the book that is most enjoyable; partly because the history is interesting and partly because of the engaging style. However, it might not be a style everyone likes. It is slightly academic and tends towards footnotes and references rather than keeping the flow going. There are also far too many appendices that give examples and expand on what is being explained. The body of the book is less than 100 pages, but there are over 200 pages of appendices.
Chapter 4 starts us on a quest to understand where the principle of least action comes from. First we look at the principle of virtual work. A strange idea when you first meet it, and to be honest no less strange after its explanation. Then on to D'Alembert's principle, which is slightly less strange for seeming so obvious.
From this point the book starts to be less rewarding. The problem is that in the early chapters it promises so much - an explanation of least action as a shortest path in some sort of abstract space, but we never really get the explanation. Instead Chapter 6 discusses Lagrangian mechanics, including the less well known version with Lagrange multipliers. Then we have an explanation of Hamiltonian mechanics. The problem is that these explanations leave a lot to be figured out. As the subject matter gets harder, the explanations become more vague and increasingly reference other material.
The book misses many opportunities to address issues that really throw the beginner and also fails to point out many things that would make things simpler. For example, the well known issue of why you can treat position and velocity as independent variables when they are clearly related is only touched on briefly. For me it is the key to understanding that the Euler Lagrange equations give you the equations of motion which supplies the connection between position and velocity.
Despite all my reservations this is an excellent book and I enjoyed reading it, even though it didn't deliver on its potential to make me see the unifying principles that make variational calculus so natural in a wide range of physical phenomena. It is clear that it is often something to do with finding the geodesic in some abstract space, but this generalization isn't precise.
I recommend this book if only because it will make you think harder about the way it all works. It doesn't give you the entire picture, but what it does give you is well worth it.
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|Last Updated ( Saturday, 07 July 2018 )|