I think the best thing about this book is that it demands you never accept anything from anyone as absolute, not even from Einstein. Russell takes pains to explain what the theory of relativity is and what it means for you and our world while at the same time slowly destroying any concept of truth and reality that you may have. Which I suppose is what Einstein's theories, and quantum mechanics for that matter, do. Further, Russell makes you appreciate and understand the struggles of physics since Copernicus as "truth" is wrested from what we can observe and then represented as "laws" which may only be our best understanding eventually to be supplanted by even closer "truths". In the end Russell melds all this into philosophy, "What is matter?" he asks and in fact what is anything? The book bristles with wit as when discussing the u-bomb he thinks it's good for us that uranium can only explode at extremely high temperatures: "There is a further advantage: the supply of uranium in the planet is limited, and it might be feared that it would be used up before the human race were exterminated, but now that the practically unlimited supply of hydrogen can be utilised, there is considerable reason to hope that the race may put an end to itself, to the great advantage of such less ferocious animals as may survive". Priceless. Needless to say, I have now gone out to purchase more Russell books.