As the subtitle already mentions, the idea is that Einstein's relativity theory is explained in plain English without the mathematics. Well, almost without mathematics, because there are some formulas locked away in appendices, but even there, we find only the simplest ones. No proofs, no derivations, and whatever there is, is still simplified. This is quite an ambitious goal, but science writer Ira Mark Egdall has some experience by his teaching a lay course in modern physics at the Lifelong Learning Institutes at Florida International University, and when invited, he gives entertaining lectures about Einstein and time travel.
The main body of the text has two parts: the first on special relativity, E = mc² and spacetime; the second on special relativity, gravity, and the cosmos. This text has an abundance of notes. These are mainly references to sources but sometimes there is further explanation. All these notes are collected at the end of the book, numbered by chapter. Thus after looking them up for a number of times, the reader gives up and just goes on reading. No harm done. The notes can be checked afterwards of after a second reading.
The first part is really accessible for anybody, all you need to know is the notion of square root and the Pythagoras theorem, but who doesn't know that? You learn to know the notion of reference frame, Galileo's dictum on uniform motion, Newton's and Maxwell's laws (it is said what the latter are for, but they are never given). To solve some anomalies between mechanical and electromagnetic behaviour, Einstein came to the conclusion that light must have constant speed c, which then forced to introduce the Lorentz transformation for space and time. His famous formula was originally derived by Einstein in the form of m=E/c² which had to replace the m in Newton's equation.
In passing, we also learn some facts about Einstein's personal life and how he did much of this work and published his papers during his so-called `wonder year' 1905 while being a clerk at a patent bureau. We also learn that he was rebellious and had problems with authority. Although he was good in math and physics, the latter prevailed in his way of thinking. Physics came first, mathematics was second plan luxury. This is probably the reason that, notwithstanding that he had taken nine math courses of Hermann Minkowski during his Zürich Polytechnic (now ETH) years, it is Minkowski who worked out the geometry of the four-dimensional space-time geometry.
Egdall uses a pleasant and humorous style, inventing `short stories' and characters to illustrate the physical problems. Crash in his spacecraft crosses the classroom at half the speed of light. The twin girl Tina Tops is living on the top of a mount Neutron and her brother Sam Surface at sea level of planet Neutronium. They serve to illustrate the difference in gravitation. Some story happens in the year 2525, 'when men are still alive', and when the hypothetical planet Vulcan that should explain the perihelion shift of Mercury was not found, this is worth an apology to Spock. Remarks like that make you smile now and then. There are many graphical illustrations to visualize the physics explained in the text, also many pictures of the key characters (and of course many of Albert Einstein) and many citations (most of them are Einstein's) makes reading on fresh and light. Also the explanation is going through all the necessary steps. When progress is made and well established, some inconsistency is illustrated and a solution is worked out to solve the problem step by step, no hurrying, making sure all the readers have caught up with the guide. Once the theory is established, experimental evidence is described which leaves the reader totally convinced and at ease with the knowledge just acquired.
In the second part on general relativity, things get somewhat more involved since now it does not concern uniform motion squeezing space and time, but one has to deal with acceleration (in particular gravitation). Although Einstein got worldwide recognition by that time, he had a hard time solving this problem himself too as testified by these quotes
>>>> Grossman is getting his doctorate on a topic that is connected with fiddling around and non-Euclidean geometry. I don't know what it is. (A.E. in a letter to his first wife M. Maric, 1902)
>>>> Grossman, you've got to help me, or I shall go crazy. (A.E.)
>>>> I am now working exclusively on the gravitation problem and I believe that, with the help of a mathematical friend here, I will overcome all difficulties. (A.E. Oct. 2012)
>>>> Never in my life have I tormented myself anything like this... I have become imbued with a great respect for mathematics, the more subtle parts of which I have previously regarded as sheer luxury. Compared to this problem, the original (special) relativity theory is child's play. (A.E. in a letter to Grossman, Nov 2015)
He is strugling with the fact that gravitation cannot act instantaneously at a distance. That would contradict special relativity. Finally a mathematical solution was needed: spacetime geometry has to be curved under influence of mass and hence of energy. While it was relatively simple for the Lorentz transformation to make spacetime distance invariant, the invariance of the equations in the general theory is much more complicated. The Riemann curvature tensor is not a simple object to explain, and Einstein nearly gave it away to Hilbert when he naively explained his approach in great detail in his lectures in Göttingen, so that David Hilbert could work it out for himself and published his results 4 days before Einstein, but it turned out later that Hilbert's solution was not generally covariant. This saved Einstein, but he became more careful in communicating his unpublished results since then.
This general relativity theory changed our views on the origin and on the ending (if any) of the universe. Big bang, inflation theory, time travel, dark matter, dark energy, wormholes, black holes,... all topics that tickle the imagination of a general public and Egdall, bringing the reader to the point beyond general relativity, does not miss the opportunity to end his guided tour with a sparkling firework of these issues. The epilogue ends in a bit of a minor key with personal problems in Einstein's life at a later age, his disagreement with nuclear power, his disbelieve in quantum physics with what he calls `spooky action at a distance'. But to solve the holy grail of today's physics, i.e., quantum gravity and the grand unifying theory, we probably have to wait for another Einstein.
So you should not read this book for the mathematics, since Egdall does everything to avoid these, but it is an entertaining introduction for the layman, that brings the reader a very long way.