94 Followers
67 Following
arbieroo

Arbie's Unoriginally Titled Book Blog

It's a blog! Mainly of book reviews.

Currently reading

Ursula K. Le Guin: Hainish Novels and Stories, Vol. 1: Rocannon's World / Planet of Exile / City of Illusions / The Left Hand of Darkness / The Dispossessed / Stories (The Library of America)
Brian Attebery, Ursula K. Le Guin
Progress: 292/1100 pages
Life and Letters of Charles Darwin - Volume 1: By Charles Darwin - Illustrated
Charles Darwin
Progress: 256/346 pages
Difficulties of a Bridegroom
Ted Hughes
Progress: 139/159 pages
Basics of Plasma Astrophysics
Claudio Chiuderi, Marco Velli
Progress: 47/250 pages
Ursula K. Le Guin: The Complete Orsinia: Malafrena / Stories and Songs (The Library of America)
Brian Attebery, Ursula K. Le Guin
Progress: 359/700 pages
A Student's Guide to Lagrangians and Hamiltonians
Patrick Hamill
Progress: 7/180 pages
Complete Poems, 1904-1962
E.E. Cummings
Progress: 110/1102 pages
The Complete Plays and Poems
E.D. Pendry, J.C. Maxwell, Christopher Marlowe
She Stoops to Conquer and Other Comedies (Oxford World's Classics)
Henry Fielding, David Garrick, Oliver Goldsmith
Progress: 76/448 pages
Gravitation (Physics Series)
Kip Thorne;Kip S. Thorne;Charles W. Misner;John Archibald Wheeler;John Wheeler
Progress: 48/1215 pages

Reading progress update: I've read 20 out of 1215 pages.

Gravitation (Physics Series) - Kip Thorne;Kip S. Thorne;Charles W. Misner;John Archibald Wheeler;John Wheeler

I'm on page 20 of 1215 of Gravitation: I couldn't help glancing into this before heading to the office this morning. 20p later I reluctantly dragged myself away. It's already provided a neat insight into co-ordinate systems.

 

People talk about needing multiple co-ordinate "patches" to cover a manifold. Why can't you just use one? Sometimes you can, e.g. a flat piece of paper. But what about a sphere? You can't wrap a flat piece of paper round a sphere (which is why map-making is such a pain). Any co-ordinate system you use on a sphere has a problem at two points (the poles) where all the lines of latitude meet and everything goes to hell in a hand basket ("Eveyerything goes to hell in a handbasket" is the practical definition of a singularity.) How do you get round this? Define TWO co-ordinate systems which don't have their poles overlapping. Now if you are at a singularity in one co-ordinate system, you just use the other system instead. You can do this for any co-ordinate singularity you find on a manifold. The system need only apply to a patch of the manifold, not necessarily the whole thing like with a sphere - hence "co-ordinate patches." You can invent as many as you need to cover all the singularities.

 

Topology joke my brother used to tell:

Q: How can you escape any prison cell, only using mathematics?

A: Simple! perform a co-ordinate transform such that the outside of the cell becomes the inside and vice versa - you are now free!