The Fabric of Reality David Deutch

particle and, like a photon emitted from a torch, it travels in different
directions in different universes. So when a cosmic-ray particle strikes a
DNA strand and causes a mutation, some of its counterparts in other
universes are missing their copies of the DNA strand altogether, while others
are striking it at different positions, and hence causing different mutations.
Thus a single cosmic-ray strike on a single DNA molecule will in general
cause a large range of different mutations to appear in different universes.
When we are considering what a particular object may look like in other
universes, we must not look so far afield in the multiverse that it is
impossible to identify a counterpart, in the other universe, of that object.
Take a DNA segment, for instance. In some universes there are no DNA

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molecules at all. Some universes containing DNA are so dissimilar to ours
that there is no way of identifying which DNA segment in the other universe
corresponds to the one we are considering in this universe. It is meaningless
to ask what our particular DNA segment looks like in such a universe, so we
must consider only universes that are sufficiently similar to ours for this
ambiguity not to arise. For instance, we could consider only those universes
in which bears exist, and in which a sample of DNA from a bear has been
placed in an analysing machine, which has been programmed to print out
ten letters representing the structure at a specified position relative to certain
landmarks on a specified DNA strand. The following discussion would be
unaffected if we were to choose any other reasonable criterion for identifying
corresponding segments of DNA in nearby universes.
By any such criterion, the bear’s gene segment must have the same
sequence in almost all nearby universes as it does in ours. That is because it
is presumably highly adapted, which means that most variants of it would not
succeed in getting themselves copied in most variants of their environment,
and so could not appear at that location in the DNA of a living bear. In
contrast, when the non-knowledge-bearing DNA segment undergoes almost
any mutation, the mutated version is still capable of being copied. Over
generations of replication many mutations will have occurred, and most of
them will have had no effect on replication. Therefore the junk-DNA
segment, unlike its counterpart in the gene, will be thoroughly
heterogeneous in different universes. It may well be that every possible
variation of its sequence is equally represented in the multiverse (that is
what we should mean by its sequence being strictly random).
So the multiverse perspective reveals additional physical structure in the
bear’s DNA. In this universe, it contains two segments with the sequence
TCGTCGTTTC. One of them is part of a gene while the other is not part of
any gene. In most other nearby universes, the first of the two segments has
the same sequence, TCGTCGTTTC, as it does in our universe, but the
second segment varies greatly between nearby universes. So from the
multiverse perspective the two segments are not even remotely alike (Figure
8.1).
Again we were too parochial, and were led to the false conclusion: that
knowledge-bearing entities can be physically identical to non knowledge-
bearing ones; and this in turn cast doubt on the fundamental status of
knowledge. But now we have come almost full circle. We can see that the
ancient idea that living matter has special physical properties was almost
true: it is not living matter but 
knowledge-bearing matter that is physically
special. Within one universe it looks irregular; across universes it has a
regular structure, like a crystal in the multiverse.
So knowledge is a fundamental physical quantity after all, and the
phenomenon of life is only slightly less so.
Imagine looking through an electron microscope at a DNA molecule from a
bear’s cell, and trying to distinguish the genes from the non-gene sequences
and to estimate the degree of adaptation of each gene. In any one universe,
this task is impossible. The property of being a gene — that is, of being
highly adapted — is, in so far as it can be detected within one universe,
overwhelmingly complicated. It is an emergent property. You would have to
make many copies of the DNA, with variations, use genetic engineering to

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create many bear embryos for each variant of the DNA, allow the bears to
grow up and live in a variety of environments representative of the bear’s
niche, and see which bears succeed in having offspring.
FIGURE 8.1 
Multiverse view of two DNA segments which happen to be
identical in our universe, one random and one from within a gene.
But with a magic microscope that could see into other universes (which, I
stress, is not possible: we are using theory to imagine — or render — what
we know must be there) the task would be easy. As in Figure 8.1, the genes
would stand out from the non-genes just as cultivated fields stand out from a
jungle in an aerial photograph, or like crystals that have precipitated from
solution. They are regular across many nearby universes, while all the non-
gene, junk-DNA segments are irregular. As for the degree of adaptation of a
gene, this is almost as easy to estimate. The better-adapted genes will have
the same structure over a wider range of universes — they will have bigger
‘crystals’.
Now go to an alien planet, and try to find the local life-forms, if any. Again,
this is a notoriously difficult task. You would have to perform complex and
subtle experiments whose infinite pitfalls have been the subject of many a
science-fiction story. But if only you could observe through a multiverse
telescope, life and its consequences would be obvious at a glance. You
need only look for complex structures that seem irregular in any one
universe, but are identical across many nearby universes. If you see any,
you will have found some physically embodied knowledge. Where there is
knowledge, there must have been life, at least in the past.
Compare a living bear with the Great Bear constellation. The living bear is
anatomically very similar in many nearby universes. It is not only its genes
that have that property, but its whole body (though other attributes of its
body, such as its weight, vary much more than the genes; that is because,
for example, in different universes the bear has been more or less
successful in its recent search for food). But in the Great Bear constellation
there is no such regularity from one universe to another. The shape of the
constellation is a result of the initial conditions in the galactic gas from which
the stars formed. Those conditions were random — very diverse in different
universes, at a microscopic level — and the process of the formation of stars
from that gas involved various instabilities which amplified the scale of the
variations. As a result, the pattern of stars that we see in the constellation
exists in only a very narrow range of universes. In most nearby variants of
our universe there are also constellations in the sky, but they look different.
Finally, let us look around the universe in a similar way. What will catch our
magically enhanced eye? In a single universe the most striking structures

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are galaxies and clusters of galaxies. But those objects have no discernible
structure across the multiverse. Where there is a galaxy in one universe, a
myriad galaxies with quite different geographies are stacked in the
multiverse. And so it is everywhere in the multiverse. Nearby universes are
alike only in certain gross features, as required by the laws of physics, which
apply to them all. Thus most stars are quite accurately spherical everywhere
in the multiverse, and most galaxies are spiral or elliptical. But nothing
extends far into other universes without its detailed structure changing
unrecognizably. Except, that is, in those few places where there is embodied
knowledge. In such places, objects extend recognizably across large
numbers of universes. Perhaps the Earth is the only such place in our
universe, at present. In any case, such places stand out, in the sense I have
described, as the location of the processes — life, and thought — that have
generated the largest distinctive structures in the multiverse.
TERMINOLOGY
replicator An entity that causes certain environments to make copies of it.
gene A molecular replicator. Life on Earth is based on genes that are DNA
strands (RNA in the case of some viruses).
meme An idea that is a replicator, such as a joke or a scientific theory.
niche The niche of a replicator is the set of all possible environments in
which the replicator would cause its own replication. The niche of an
organism is the set of all possible environments and life-styles in which it
could live and reproduce.
adaptation The degree to which a replicator is adapted to a niche is the
degree to which it causes its own replication in that niche. More generally, an
entity is adapted to its niche to the extent that it embodies knowledge that
causes the niche to keep that knowledge in existence.
SUMMARY
Scientific progress since Galileo has seemed to refute the ancient idea that
life is a fundamental phenomenon of nature. It has revealed the vast scale of
the universe, compared with the Earth’s biosphere. Modern biology seems to
have confirmed this refutation, by explaining living processes in terms of
molecular replicators, genes, whose behaviour is governed by the same
laws of physics as apply to inanimate matter. Nevertheless, life 
is associated
with a fundamental principle of physics — the Turing principle — since it is
the means by which virtual reality was first realized in nature. Also, despite
appearances, life 
is a significant process on the largest scales of both time
and space. The future behaviour of life will determine the future behaviour of
stars and galaxies. And the largest-scale regular structure 
across universes
exists where knowledge-bearing matter, such as brains or DNA gene
segments, has evolved.

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This direct connection between the theory of evolution and quantum theory
is, to my mind, one of the most striking and unexpected of the many
connections between the four strands. Another is the existence of a
substantive quantum theory of computation underlying the existing theory of
computation. That connection is the subject of the next chapter.

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