What a long, strange trip it would be

If you have read physicist Michio Kaku’s 1997 book “Visions,” in which he speculates about technology in the 21st century, then you already know that he has a penchant for futurology. And Kaku’s other books, such as “Hyperspace” (1994), testify to his passion for theoretical physics. In his latest book, “Parallel Worlds,” Kaku combines his interests in futurology and physics and pushes them to extremes by asking about the ultimate fate of the cosmos. In particular, he explores how the human race might survive if our own universe became uninhabitable.

To tackle this topic, Kaku covers a tremendous amount of material, including quantum physics, general relativity, time travel, black holes, the Big Bang, string theory and much more. These areas are discussed in a clear and lively way, and I particularly enjoyed the various detours into science fiction. (It is surprising how many valid scientific theories are adumbrated by episodes in fantasy novels.) However, the volume of material and the numerous side roads mean that readers need a certain level of patience to get to the meatier elements of the book, which essentially boil down to three key points:

First, the last decade has witnessed an astonishing revolution in cosmology. Since the late 1920s, it has been known that the universe is expanding in the wake of the Big Bang, and the assumption was that this expansion should be slowing because of gravity, which would eventually begin to pull all the galaxies back toward each other. However, recent observations indicate that the cosmic expansion is not slowing down but accelerating; in fact, the universe seems to be experiencing a runaway expansion.

This is bad news for the human race. As the universe increases in size, the matter and energy within it will become spread out, and space will become increasingly empty, desolate and lifeless.

While Kaku’s first point is rather depressing, his second point offers a ray of hope. Strange as it might sound, our universe might not be the only universe.

Cosmologists readily talk of multiple universes, which all come under the umbrella of the so-called multiverse. Each universe was created from its own Big Bang, and perhaps each Bang took place in one corner of an already-established universe. In this scenario, a mother universe effectively gives birth to an independent daughter universe. One way to picture this radical reinvention of the world(s) is to imagine each universe as a bubble -- and the multiverse as foam.

Many cosmologists like the notion of the multiverse, because it addresses some fundamental questions, such as why our universe contains life. The fundamental forces that govern our universe could well have taken on different strengths, but luckily they have just the right values to give life a chance. Some may think that the fine-tuning of the universe to enable life implies a Tuner.

However, believers in the multiverse argue that with an infinity of universes, it is not surprising that at least one of them is just right for life. And, of course, we live in one of those animated universes because we could not live anywhere else.

So, if we accept that our universe is expanding and evolving into a lifeless entity, and if we are prepared to believe in a multiverse, then Kaku’s third (and main) point is obvious:

If a species lives in a certain habitat and that habitat is degrading, then it can either die along with its habitat, or it can adapt to survive in the changing habitat, or it can find a new habitat. So if our universe is becoming inhospitable, what are the options facing the human race? Presumably we do not want to give up and become extinct, and any attempt at adapting is pointless, because the universe will eventually become so hostile that life will be impossible. We must, therefore, find a new habitat, which means a new universe.

This is where the book gets really interesting. If our universe is dying, then how can we find our way into a shiny, new, fertile universe?

As well as discussing wormholes, the cosmic phenomena that might serve as escape routes to another universe in the multiverse, Kaku spends time considering the stages of development that humankind would have to go through before being able to make such a trip. We all know that moving to a new house is expensive and stressful, so you can imagine the implications of having to move to a completely new universe.

For example, exploiting a wormhole would require vast amounts of energy. The Russian astrophysicist Nikolai Kardashev classified the energy resources of a civilization as follows: Type I civilizations have learned to harness all the energy on their planet, Type II civilizations have learned how to harness all the energy from a star, and Type III civilizations can tap into the energy of an entire galaxy. Only a Type III civilization could ever hope to move to a new universe, but at the moment we are not even at the Type I stage.

All this discussion of galactic energy sources, wormholes and the multiverse might seem utterly ridiculous, but the early section of “Parallel Worlds” takes a look at the development of cosmology and shows how the most bizarre ideas -- such as black holes and dark matter -- have been shown to be true.

Kaku points out that it used to be said, “There’s speculation, then there’s more speculation, and then there’s cosmology.” But he also shows that the latest astronomical observations have turned much that was previously speculative into hard fact. As the Scottish scientist J.B.S. Haldane once declared, “It is my supposition that the universe is not only queerer than we imagine, it is queerer than we can imagine.”

So “Parallel Worlds” might be more than just a tall tale. Do not let its bizarre contents put you off. After the physicist Niels Bohr had listened to a new theory proposed by Wolfgang Pauli, he stood up and said, “We in the back are convinced that your theory is crazy. But what divides us is whether your theory is crazy enough.” *