The Fabric of Reality: The Science of Parallel Universes--and Its Implications

by David Deutsch

understanding does not depend on knowing a lot of facts as such, but on having the right concepts, explanations and theories.

Facts cannot be understood just by being summarized in a formula, any more than by being listed on paper or committed to memory. They can be understood only by being explained. Fortunately, our best theories embody deep explanations as well as accurate predictions.

Prediction – even perfect, universal prediction – is simply no substitute for explanation.

To say that prediction is the purpose of a scientific theory is to confuse means with ends. It is like saying that the purpose of a spaceship is to burn fuel. In fact, burning fuel is only one of many things a spaceship has to do to accomplish its real purpose, which is to transport its payload from one point in space to another. Passing experimental tests is only one of many things a theory has to do to achieve the real purpose of science, which is to explain the world.

The fabric of reality does not consist only of reductionist ingredients like space, time and subatomic particles, but also of life, thought, computation and the other things to which those explanations refer.

The heart of the argument is that single-particle interference phenomena unequivocally rule out the possibility that the tangible universe around us is all that exists.

They are called ‘planets’, from the Greek word meaning ‘wanderer’.

If, according to the simplest explanation, an entity is complex and autonomous, then that entity is real.

Occam’s razor (My formulation) Do not complicate explanations beyond necessity, because if you do, the unnecessary complications themselves will remain unexplained.

fiction is always an interpretation in the mind of the beholder.

The Turing principle It is possible to build a virtual-reality generator whose repertoire includes every physically possible environment.

Reasoning from the premise of one’s own existence is called ‘anthropic’ reasoning.

Richard Dawkins has coined the term meme (rhyming with ‘cream’) for replicators that are human ideas, such as jokes. But all life on Earth is based on replicators that are molecules. These are called genes, and biology is the study of the origin, structure and operation of genes, and of their effects on other matter. In most organisms a gene consists of a sequence of smaller molecules, of which there are four different kinds, joined together in a chain. The names of the component molecules (adenine, cytosine, guanine and thymine) are usually shortened to A, C, G and T. The abbreviated chemical name for a chain of any number of A, C, G and T molecules, in any order, is DNA.

So it seems that, as Stephen Hawking put it, ‘The human race is just a chemical scum on a moderate-sized planet, orbiting round a very average star in the outer suburb of one among a hundred billion galaxies.’

One could imagine another artificial non-replicator-based living organism that did the same sort of thing, taking every opportunity to recopy the knowledge in its genes onto the safest medium available. Perhaps one day our descendants will do that.

Life achieves its effects not by being larger, more massive or more energetic than other physical processes, but by being more knowledgeable.

meme An idea that is a replicator, such as a joke or a scientific theory.

Virtual reality — which can make one environment seem to be another — underlines the fact that when observation is the ultimate arbiter between theories, there can never be any certainty that an existing explanation, however obvious, is even remotely true.

When we say that our consciousness ‘seems’ to pass from one moment to the next we are merely paraphrasing the common-sense theory of the flow of time. But it makes no more sense to think of a single ‘moment of which we are conscious’ moving from one moment to another than it does to think of a single present moment, or anything else, doing so. Nothing can move from one moment to another. To exist at all at a particular moment means to exist there for ever. Our consciousness exists at all our (waking) moments.

But common sense also wants time to be a sequence of moments, with all motion and change consisting of differences between versions of an entity at different moments. And that means that the moments are themselves unchanging. So a particular moment cannot become the present, or cease to be the present, for these would be changes. Therefore the present cannot, objectively, be a single moment.

In Newtonian physics this four-dimensional geometrical interpretation of time was optional, but under Einstein’s theory of relativity it became an indispensable part of the theory. That is because, according to relativity, observers moving at different velocities do not agree about which events are simultaneous.

Relative to spacetime, nothing ever moves. What we call ‘moments’ are certain slices through spacetime, and when the contents of such slices are different from one another, we call it change or motion through space.

In reality, we make no choices. Even as we think we are considering a choice, its outcome is already there, on the appropriate slice of spacetime, unchangeable like everything else in spacetime, and impervious to our deliberations.

Physical reality is not a spacetime. It is a much bigger and more diverse entity, the multiverse.

If, aside from variants of me in other universes, there are also multiple identical copies

Time does not flow. Other times are just special cases of other universes.

Whenever we make a choice, we change the future: we change it from what it would have been had we chosen differently.

We do observe and understand the world through a collection of theories, and that constitutes a paradigm.

According to Thomas Kuhn, holding a paradigm blinds one to the merits of another paradigm and prevents one from switching paradigms. One cannot comprehend two paradigms at the same time.

The end-point of the gravitational collapse, the Big Crunch of this cosmology, is what Tipler calls the omega point.

But we know that the subjective duration of a virtual-reality experience is determined not by the elapsed time, but by the computations that are performed in that time.

Since the intelligences in the computer will be creative thinkers, they must be classified as ‘people’. Any other classification, Tipler rightly argues, would be racist. And so he claims that at the omega-point limit there is an omniscient, omnipotent, omnipresent society of people. This society, Tipler identifies as God.

we cannot predict what specific knowledge will be created in the future — because if we could, we should by definition already possess that knowledge in the present.