Parallel Worlds by Michio Kaku

We are going through a golden age of science writing (at least in physics/cosmology and in paleontology, the two areas I most read about). When I was growing up in the 1960s and early 1970s, there were of course some good books. George Gamow’s books on modern physics were always good, there were some nice dinosaur books (I remember reading some of the books of Roy Chapman Andrews – an overrated paleontologist but a pretty good writer), and so on. And of course, there were the science writings of SF writers like Isaac Asimov, whose non-fiction output, like his fiction output, was frankly overrated. There were some good books there (especially a few of his books on biology and organic chemistry), but most were rather pedestrian.

Today, however, there are a number of very good books coming out every year. I have an entire shelf of good books on paleontology and several shelves of books on physics, cosmology, mathematics, and astronomy. Moreover, the sciences themselves are going through and incredible phase right now – especially in physics and cosmology as we learn more and more about the universe and its early history. Late last year, I read Brian Greene’s superb Fabric of the Cosmos, perhaps the best book on this topic. This week, I read Michio Kaku’s Parallel Worlds, which is also very good (though if you only want to read one book on the topic, Greene’s is better).

Kaku is not only a very good physicist, he is an engaging writer who does a good job of explaining physics to a lay audience. Parallel Worlds, like his earlier Hyperspace, discusses cutting edge physics and cosmology (string theory and M-theory, general relativity, and so on) in a way that’s both easy to follow and usually insightful, such that the reader does come away knowing a good deal about his topic. (I do think there are a couple of places where he glosses over things just a bit, and I think the book would have been even better if it were perhaps 5 or 10 percent longer, but that’s a quibble about an otherwise fine book).

Twenty-five years ago, the standard theory of the universe was the rather simple model of the big bang that most of us knew. The universe started as a single, hyper-condensed mass and exploded outward to produce what we have today. Over time, gravity would slow down the expansion, and one problem in cosmology was whether the universe would expand forever or whether there was enough mass that gravity would eventually overcome the outward motion and pull everything back together gain into a big crunch.

At the same time, the rest of physics was explained by the two great theories of the twentieth century: general relativity, which explained gravity and the macro universe, and quantum theory, which explained the world of the very small to an incredible level of precision. But, despite many attempt, physicists had been unable to unite these two theories in a consistent way.

But out knowledge of the world changed. The model of the big bang become much more complex and strange, both as a result of theoretical physicists applying new theories to our understanding of the universe (string theory and M-theory, in particular; a bit more on these later), but also due to experimental evidence and some niggling problems in the old standard big bang theory. Most shocking, perhaps, was the discovery that the expansion of the universe wasn’t slowing down – it is speeding up! An “anti-gravity” force (dark energy) is making the universe expand more rapidly than it had just after the big bang.

And the big bang itself – well, perhaps it wasn’t an ultra-massive kernel that expanded outward. It may have been as little as an ounce of material in a multiverse that suddenly – by simple quantum chance – expanded into our universe.

Much of what we know understand is being driven by the evolving theory of everything called string theory or M-theory (a similar theory that involves not just strings but membranes of various dimensionality). The basis of string theory is that the “elementary” particles we are familiar with – electrons, quarks, and so on – are not really point particles. Instead, they are really manifestations of the vibrations of much tinier “strings.” The difference between the particles is simply that they are different “tones” or vibration modes of the strings. It’s a very beautiful and elegant theory, which manages to overcome many of the problems of unifying general relativity and quantum theory. It’s also immensely strange, involving a universe that’s not the three or four (if you count time) dimensions that we’re familiar with, but one that involves ten or eleven dimensions, some of which are rolled up much smaller than an atom, so that we don ‘t see them. It’s a theory that allows for other, parallel universes a millimeter away from our own.

Kaku does a good job explaining the history of these theories and their basic concepts. He conveys the true strangeness of the universe, and even engages in some speculation about not only the future of the universe but the future of intelligence in the universe (or, more accurately, the multiverse, since looks at whether intelligence can survive the death of our universe by moving to another).

He also doesn’t shy away from some philosophical and even theological speculation. For example, he looks at the idea of our living in a “Goldilocks zone” and what that implies. Most people know we live in a planetary orbit that is “just right” – farther away, and it would be too cold and water would freeze, close in and it would be too hot. But, from an astronomical perspective, it’s even more complex than that. If our solar system didn’t have a planet like Jupiter to help, over time, clear out asteroids and comets, constant asteroid strikes on the earth may have prevented life from every developing. If we didn’t have a moon as large as the one we have (which helps stabilize the earth’s orbit), again, life may note have developed. And so on. And from a physics perspective, the whole universe falls into this. If the strong nuclear force were a bit stronger or a bit weaker, stars might not form at all or might form but burn through their fuel so fast that life wouldn’t form. If other fundamental constants were a bit different, higher elements (beyond lithium) might not form, or the universe might collapse soon after it formed, or expand too fast, and so on. So amongst all the possible universes that could have formed after the big bang, we are in one that allowed galaxies, stars, and us to come into existence. Is this a proof that God exists? Is it just chance? Do all these possible universes actually exist? Kaku discusses all these views. (He doesn’t – and can’t in such a general books – go into great detail, since this topic alone could take up a much longer book. But he has enough to stimulate a lot of thinking about the topic.)

Kaku is also a science fiction reader, who likes to refer to works of writers like Bear, Asimov, and so on in his discussions. For an SF fan like me, this adds to enjoyment of the book and it does, I think, help solidify some of his examples.

In the end, if you only plan to read one book on the topic (there’s so much to know and it’s all so interesting that I’d recommend reading many more than one), I’d recommend Brian Greene’s Fabric of the Cosmos. But if you read two, this is the one to read next.