The key ideas

Parallel Worlds: A Journey Through Creation, Higher Dimensions, and the Future of the Cosmos

Michio Kaku, 2005

A satellite took a baby picture of the universe and showed that everything stars and we ourselves are made of is only about four percent of what it contains. Physicist Michio Kaku leads from this puzzle to the boldest ideas of modern cosmology: bubble universes, eleven dimensions and an escape from a cooling cosmos. We will sort out where the book offers tested observations and where it offers hypotheses and the author's own dream.

Who it is for

For anyone who looks up at the starry sky and wants to understand what the science of the universe knows for sure, what it assumes, and what it can so far only dream about.

The mind of God is cosmic music, the music of strings resonating through eleven-dimensional hyperspace.

What the book is about

In 2003 the WMAP satellite sent back to Earth a detailed map of the faint heat left over from the early universe. Michio Kaku calls it a baby picture of the universe. According to the data the author cites (as of 2005), this map was used to estimate the age of the universe, about 13.7 billion years, and what it is made of.

And then came a surprise. Ordinary matter, the stuff that stars and we ourselves are made of, makes up only about four percent, according to these data. So what is everything else made of?

From this question, theoretical physicist Kaku leads on to even bolder ones. Is our universe the only one? Does it have neighbors? And could we ever escape from it? Let's be honest from the start: the book mixes three layers. They are tested observations, hypotheses that have not yet been tested, and the author's dreams about the future. Kaku writes about all of it with the same delight, so from here on we will mark which layer is which.

Idea 1. Pigeon droppings and the echo of the beginning

How can we know that the universe had a beginning? In the late 1940s, George Gamow and his colleagues reasoned like this: if everything started from a hot, dense state, then the cooled-down heat of that time should still fill the sky. Their opponent Fred Hoyle, a supporter of an eternal universe, called this idea the “Big Bang” on a radio program. The name stuck.

In 1965, Arno Penzias and Robert Wilson were working with a large radio antenna and could not get rid of a faint hiss that came from every direction in the sky. They even cleaned pigeon droppings out of the antenna. The noise remained. It was that very cooled-down heat, the cosmic microwave background. They later received the Nobel Prize for this discovery.

An image to aid understanding, not a proof. You walk into a room where a stove was burning in the morning. The fire is gone, but the warm walls tell you it was there.

The Big Bang rests on a trace that can be measured. That sets it apart from many of the ideas in the book's later chapters.

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About the author

Michio Kaku is an American theoretical physicist, a professor at the City College of New York and one of the founders of string field theory. He is a well-known popularizer of science and the author of “Hyperspace,” “Physics of the Impossible” and other books.

All books by this author: Michio Kaku

Terms from the book

  • Inflation
  • Dark energy
  • String theory
  • Cosmic microwave background
  • Multiverse: The hypothesis that our universe may be one of many. It arises in some models of inflation and in string theory; it has not yet been tested.
  • Anthropic principle: The idea that we can only observe a universe in which observers are able to appear. One possible explanation of fine-tuning, not a tested law.

All terms

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