M-Theory

In the history of science we have discovered a sequence of better and better theories or models, from Plato to the classical theory of Newton to modern quantum theories.

Will this sequence eventually reach an end point, an ultimate theory of the universe, that will include all forces and predict every observation we can make, or will we continue forever finding better theories, but never one that cannot be improved upon?

We do not yet have a definitive answer to this question, but we now have a candidate for the ultimate theory of everything, if indeed one exists, called M-theory.

M-theory is the only model that has all the properties we think the final theory should have.

It is the theory upon which much of this book is based.

M-theory is a whole family of different theories, each of which is a good description of observations only in some range of physical situations.

It is a bit like a map.

As is well known, one cannot show the whole of the earth’s surface on a single map. The usual Mercator projection used for maps of the world makes areas appear larger and larger in the far north and south and doesn’t cover the North and South Poles.

To faithfully map the entire earth, one has to use a collection of maps, each of which covers a limited region. The maps overlap each other, and where they do, they show the same landscape. M-theory is similar.

The different theories in the M-theory family may look very different, but they can all be regarded as aspects of the same underlying theory. They are versions of the theory that are applicable only in limited ranges—for example, when certain quantities such as energy are small. Like the overlapping maps in a Mercator projection, where the ranges of different versions overlap, they predict the same phenomena.

But just as there is no flat map that is a good representation of the earth’s entire surface, there is no single theory that is a good representation of observations in all situations.

We will describe how M-theory may offer answers to the question of creation.

According to M-theory, ours is not the only universe. Instead, M-theory predicts that a great many universes were created out of nothing.

Their creation does not require the intervention of some supernatural being or god. Rather, these multiple universes arise naturally from physical law.

They are a prediction of science.

Each universe has many possible histories and many possible states at later times, that is, at times like the present, long after their creation.

Most of these states will be quite unlike the universe we observe and quite unsuitable for the existence of any form of life. Only a very few would allow creatures like us to exist. Thus our presence selects out from this vast array only those universes that are compatible with our existence. Although we are puny and insignificant on the scale of the cosmos, this makes us in a sense the lords of creation.

To understand the universe at the deepest level, we need to know not only how the universe behaves, but why.

Why is there something rather than nothing?

Why do we exist?

Why this particular set of laws and not some other?

This is the Ultimate Question of Life, the Universe, and Everything.