The Fabric of Reality: Towards a Theory of Everything (Penguin Science)

by David Deutsch

Changing the past means choosing which past snapshot to be in, not changing any specific past snapshot into another one. In this respect, changing the past is no different from changing the future, which we do all the time.

Einstein’s equations certainly permit the existence of pathways into the past; many solutions with that property have been discovered. Until recently, the accepted practice has been systematically to ignore such solutions. But this has not been for any reason arising from within the theory, nor from any argument within physics at all. It has been because physicists were under the impression that time travel would ‘lead to paradoxes’, and that such solutions of Einstein’s equations must therefore be ‘unphysical’.

Typical candidate versions of a quantum theory of gravity not only allow past-directed connections to exist in the multiverse, they predict that such connections are continually forming and breaking spontaneously. This is happening throughout space and time, but only on a sub-microscopic scale.

Future-directed time travel, which essentially requires only efficient rockets, is on the moderately distant but confidently foreseeable technological horizon.

if the future development of fundamental physics continues to allow time travel in principle, then its practical attainment will surely become a mere technological problem that will eventually be solved.

knowledge creation and biological evolution are physically significant processes. And one of the reasons was that those processes, and only those, have a particular effect on parallel universes – namely to create trans-universe structure by making them become alike.

The multiverse will never be a free-trade area because the laws of quantum mechanics impose drastic restrictions on which snapshots can be connected to which others.

Time travel may or may not be achieved one day, but it is not paradoxical.

Popper’s The Myth of the Framework.)

Kuhn’s theory suffers from a fatal flaw. It explains the succession from one paradigm to another in sociological or psychological terms, rather than as having primarily to do with the objective merit of the rival explanations. Yet unless one understands science as a quest for explanations, the fact that it does find successive explanations, each objectively better than the last, is inexplicable.

You need only attend a research seminar in any fundamental field in the ‘hard’ sciences to see how strongly people’s behaviour as researchers differs from human behaviour in general.

not true in the soft sciences

Even though the history of quantum theory provides many examples of scientists clinging irrationally to what could be called ‘paradigms’, it would be hard to find a more spectacular counterexample to Kuhn’s theory of paradigm succession.

We need not concern ourselves here with the arcane details of the Copenhagen interpretation, because its motivation was essentially to avoid the conclusion that reality is multi-valued,

Unfortunately, in the generation between the Copenhagen interpretation and Everett most physicists had given up on the idea of explanation in quantum theory.

generations of physicists have found it sufficient to regard interference processes, such as those that take place for a thousand-trillionth of a second when two elementary particles collide, as a ‘black box’: they prepare an input, and they observe an output. They use the equations of quantum theory to predict the one from the other, but they neither know nor care how the output comes about as a result of the input.

(An artificial intelligence is a computer program that possesses properties of the human mind including intelligence, consciousness, free will and emotions, but runs on hardware other than the human brain.)

The possibility of artificial intelligence is bitterly contested by eminent philosophers (including, alas, Popper), scientists and mathematicians, and by at least one prominent computer scientist.

It is not the fittest species variant that survives (Darwin had not quite realized this) but the fittest gene variant.

the intricate and apparently purposeful design that is apparent in living organisms is not built into reality ab initio, but is an emergent consequence of the operation of the laws of physics.

Although we do not know what consciousness is, it is clearly intimately related to the growth and representation of knowledge within the brain.

knowledge can be understood as complexity that extends across large numbers of universes.

thanks to the multiverse character of quantum reality, free will and related concepts are now compatible with physics.)

individually, all four theories have explanatory gaps that can make them seem narrow, inhuman and pessimistic. But I suggest that when they are taken together as a unified explanation of the fabric of reality, this unfortunate property is reversed.

Copenhagen interpretation of quantum mechanics An idea for making it easier to evade the implications of quantum theory for the nature of reality.

Many computer scientists have been so impressed with recently discovered connections between physics and computation that they have concluded that the universe is a computer, and the laws of physics are programs that run on it. But all these are narrow, even misleading perspectives

people’s minds will be running as computer programs in computers whose physical speed is increasing without limit.

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.

With one second, or one microsecond, to go, they will still have ‘all the time in the world’ to do more, experience more, create more – infinitely more – than anyone in the multiverse will ever have done before then.

At some stage human beings would have to transfer the computer programs that are their minds into more robust hardware.