A Most Incomprehensible Thing: Notes Towards a Very Gentle Introduction to the Mathematics of Relativity
This book is astonishing, really. A non-physicist decided to teach himself relativity theory, using some text books and the full range of publicly available online resources. That's no mean feat. But then he did something really brave - arguably crazy as all truly brave acts are - and wrote a book for other people who are attempting to do the same thing.
If you've followed my status updates you might be thinking it's just a catalogue of errors but that would not be fair; most of the mistakes I found are simple slip-ups, probably typos in several cases. That type of thing occurs alarmingly often even in texts by professionals that have been checked by professionals. The trouble here is that they may cause more trouble for the intended audience than they would for people with considerable mathematical/scientific training.
More worrying are the small number of errors that show lack of understanding of the physics and/or maths, as these are likely to confuse and mislead the intended audience. I suggest that readers keep an eye on the online errata page, which the author has successively updated in the light of reader comments.
I feel that anyone without a physics degree but wanting to learn relativity theory in all its mathematical glory should read The Special and the General Theory by Albert Einstein before attempting this book and perhaps following up with a professional introductory text on the General Theory if sufficient interest remains.