Back in July I
reviewed Jim Holt’s book,

*Why Does the World Exist?*(2012), where he interviews various intellects, including David Deutsch, who wrote*The Fabric of Reality*(1997), a specific reference point in Holt’s interview. I’ve since read Deutsch’s book myself and reviewed it on Amazon UK. I gave it a favourable review, as it’s truly thought-provoking, which is not to say I agree with his ideas.
I followed up Deutsch’s
book with John D. Barrow’s

*New Theories of Everything*(originally published 1990, 2^{nd}edition published 2007) with ‘New’ being added to the title of the 2^{nd}edition. The 2 books cover very similar territory, yet could hardly be more different. In particular, Deutsch’s book contains a radical vision of reality based on the multiple-worlds interpretation of quantum mechanics, and becomes totally fantastical in its closing chapter, where he envisages a world of infinite subjective time in the closing moments of the universe that, to all intents and purposes, represents heaven.
He took this ‘vision’
from Frank J. Tipler, who, as it turns out, co-wrote a book with Barrow called,

*The Anthropic Cosmological Principle*(1986). Barrow also references Tipler in*New Theories of Everything*, not only in regard to the possibility of life forms, or ‘information processing systems’, existing in the final stages of the Universe, but in relation to everything in the Universe being possibly simulated in a computer. As Barrow points out there is a problem with this, however, as not everything is computable by a Turing machine.
Leaving aside the
final chapter, Deutsch’s book is a stimulating read, and whilst he failed to
convince me of his world-view, I wouldn’t ridicule him – he’s not a crank.
Deutsch likes to challenge conventional wisdom, even turn it on its head. For
example, he criticises the view that there is a hierarchy of ‘truth’ from
mathematics to science to philosophy. To support his iconoclastic view, he
provides a ‘proof’ that solipsism is false: it’s impossible for more than one
person to be solipsistic in a given world. Bertrand Russell gave the anecdote
of a woman philosopher writing to him and claiming she was a solipsist, then
complaining she’d met no others. Deutsch uses a different example, but the contradictory
outcome is the same – there can only be one solipsist in a solipsistic
philosophy. He claims that the proof against solipsism is more definitive than
any scientific theory. However, solipsism does occur in
dreams, which we all experience, so there is one environment where solipsism is
‘true’.

In another part of the
book, he points to Godel’s Incompleteness Theorem as evidence that mathematical
‘truths’ are contingent, which undermines the conventional epistemological
hierarchy. Interestingly, Barrow also discusses Godel’s famous Theorem in depth,
albeit in a different context, whereby he muses on what impact it has on
scientific theories. Barrow concludes, if I interpret him correctly, that the
basis of mathematical truths and scientific truths, though related via
mathematical ‘laws of nature’, are different. Scientific truths are ultimately
dependent on evidence, whereas mathematical truths are ultimately dependent on
logical proofs from axioms. Godel’s Theorem prescribes limits to the proofs
from the axioms, but, contrary to Deutsch’s claim, mathematical ‘truths’ have a
universality and dependability that scientific ‘truths’ have never attained
thus far, and are unlikely to in the foreseeable future.

One suspects that
Deutsch’s desire to overturn the epistemological hierarchy, even if only in
certain cases, is to give greater authority to his many-worlds interpretation
of quantum mechanics, as he presents this view as if it’s unassailable to
rational thought. For Deutsch, this is the ‘reality’ and Einstein’s space-time
is merely an approximation to reality on a large scale. It has to be said that
the many-worlds interpretation of quantum mechanics is becoming more popular, but
it’s not definitive and the ‘evidence’ of interference between these worlds,
manifest in quantum experiments, is not evidence of the worlds themselves. At
the end of the day, it’s evidence that determines scientific ‘truth’.

Deutsch begins his
book with a discussion on Popper’s philosophy of epistemology and how it
differs from induction. Induction, according to Deutsch, simply examines what
has happened in the past and forecasts it into the future. In other words, past
experimental results predict future experimental results. However, Deutsch
argues, quite compellingly, that the explanatory power of a theory has more
authority and more weight than just induction. Kepler’s mathematical formulation
of planetary orbits gives us a mechanism of induction but Newton’s Theory of
Gravity gives us an explanation. It’s obvious that Deutsch believes that Hugh
Everett’s many-worlds interpretation of quantum mechanics is a better
explanation than any other rival interpretation. My contention is that quantum
rival ‘theories’ are more philosophically based than science-based, so they are
not theories per se, as there are no experiments that can separate them.

It was towards the end
of his book, before he took off in a flight of speculative fancy, that it
occurred to me that Deutsch had managed to convey all aspects of the universe –
space-time, knowledge, human free will, chaotic and quantum phenomena, human
and machine computation – into an explanatory model with quantum
multiple-worlds at its heart. He had encompassed this world-view so completely
with his ‘4 strands of reality’ – quantum mechanics, epistemology, evolution,
computation – that he’s convinced that there can be no other explanation,
therefore the quantum multiple-worlds must be ‘reality’.

In fact, Deutsch believes that his thesis is so all-encompassing that even
chaotic phenomena can be explained as classical manifestations of quantum
mechanics, even though the mathematics of chaos theory doesn’t support this. In
all my reading, I’ve never come across another physicist who claims that
chaotic phenomena have quantum mechanical origins.

Despite his emphasis
on explanatory power, Deutsch makes no reference to Heisenberg's Uncertainty Principle
or Planck’s constant,

*h*. Considering how fundamental they are to quantum mechanics, a theory that fails to mention them, let alone incorporate them in its explanation, would appear to short-change us.
Deutsch does however
explain the probabilities that are part and parcel of quantum calculations and
predictions. They are simply the result of the ratio of universes giving one
result over another. This implies that we are discussing a finite number of
universes for every quantum interaction, though Deutsch doesn’t explicitly state
this. Mathematically, I believe this could be the Achilles heel of his thesis:
the quantum multiverse cannot be infinite yet its finiteness appears open-ended, not to mention indeterminable.

Quantum computers is
an area where I believe Deutsch has some expertise, and it’s here that he
provides one compelling argument for multiple worlds. To quote:

*When a quantum factorization engine is factorizing a 250-digit number, the number of interfering universes will be of the order of 10*…

^{500}
Deutsch issues the
challenge: how can this be done without multiple universes working in parallel?
He explains that these

*10*universes are effectively identical except that each one is doing a different part of the calculation. There are also^{500}*10*identical persons each getting the correct answer. So quantum computers, when they become standard tools, will be creating multiple universes complete with multiple human populations along with the infrastructure, worlds, galaxies and independent futures, all simultaneously calculating the same algorithm. In response to Deutsch’s challenge, I admit I don’t know, but I find his resolution incredulous in the extreme.^{500 }
Those who have read my
post on Holt’s book, will remember that he interviewed Roger Penrose as well as
Deutsch (along with many other intellectual luminaries). Interestingly, Holt
seemed to find Penrose’s Platonic mathematical philosophy more bizarre than
Deutsch’s but based on what I’ve read of them both, I’d have to disagree.
Deutsch also mentions Penrose and delineates where he agrees and disagrees. To
quote again:

*[Penrose] envisages a comprehensible world, rejects the supernatural, recognizes creativity as being central to mathematics, ascribes objective reality both to the physical world and to abstract entities, and involves an integration of the foundations of mathematics and physics. In all these respects I am on his side.*

Where Deutsch
specifically disagrees with Penrose is in Penrose’s belief that the human brain
cannot be reduced to algorithms. In other words, it disobeys Turing’s universal
principle (as interpreted by Deutsch) that everything in the universe can be
simulated by a universal quantum Turing machine. (Deutsch, by the way, believes
the brain is effectively a classical computer, not a quantum computer.) Deutsch
points out that Penrose’s position is at odds with most physicists, yet I agree
with him on this salient point. I don’t believe the brain (human or otherwise)
runs on algorithms. Deutsch sees this as a problem with Penrose’s world-view as
he’s unable to explain human thinking. However, I see it as a problem with
Deutsch’s world-view, because, if Penrose is right, then Deutsch is the one who
can’t explain it.

Barrow is a cosmologist
and logically his book reflects this perspective. Compared to Deutsch’s book,
it’s more science, less philosophy. But there is another fundamental
difference, in tone if not content. Right from his opening words, Deutsch
stakes his position in the belief that we can encompass more and more knowledge
in fewer and fewer theories, so it is possible for one person to ‘understand’
everything, at least in principle. He readily acknowledges, however, that we
will probably never ‘know’ everything. On the other hand, Barrow brings the
reader down-to-earth with a lengthy discussion on the initial conditions of the
universe, and how they are completely up for grabs based on what we currently
know.

Barrow ends his
particular chapter on cosmological initial conditions with an in-depth
discussion on the evolution of cosmology from Newton to Einstein to Wheeler-De
Witt, which leads to the Hartle-Hawking ‘no-boundary condition’ model of the universe. He points out that this is a radical theory, ‘proposed by James Hartle
and Stephen Hawking for aesthetic reasons’, but it overcomes the divide between
initial conditions and the laws of nature. Compared to Deutsch’s radical
theses, it’s almost prosaic. It has the added advantage of overcoming
theological-based initial conditions, allowing ‘…a Universe which tunnels into
existence out of nothing.’

Logically, a book on
‘theories of everything’ must include string theory or M theory, yet it’s not
Barrow’s strong suit. Earlier this year, I read Lee Smolin’s

*The Trouble With Physics*, which gives a detailed history and critique of string theory, but I won’t discuss it here. Of course, it’s another version of ‘reality’ where ‘theory’ is yet to be given credence by evidence.
As I alluded to above,
what separates Barrow from Deutsch is his cosmologist’s perspective. Even if we
can finally grasp all the laws of Nature in some ‘Theory of Everything’, the
outcomes are based on chance, which was once considered the sole province of
gods, and, as Barrow argues, is the reason that the mathematics of chance and
probability were not investigated earlier in our scientific endeavours. To
quote Barrow:

*…it is possible for a Universe like ours to be governed by a very small number of simple laws and yet display an unlimited number of complex states and structures, including you and me.*

Of all the
improbabilities, the most fundamental and consequential to our existence is the
asymmetry between matter and antimatter of one billion and one to one billion. We know this,
because the ratio of photons to protons in the Universe is two billion to one
(the annihilation of a proton with an anti-proton creates 2 photons). It is
sobering to consider that a billion to one asymmetry in the birth pangs of the
Universe is the basis of our very existence.

The final chapter in
Barrow’s book is called

*Is pi really in the sky?*This is an obvious allusion to mathematical Platonism and the entire chapter is a lengthy and in-depth discussion on the topic of mathematics and its relationship to reality. (Barrow has also authored a book called*Pi in the Sky*, which I haven’t read.) According to Barrow, Plato and Aristotle were the first to represent the dichotomy we still find today as to whether mathematics is discovered or invented. In other words, is it solely a product of the human mind or does it have an abstract existence independently of us and possibly the Universe? What we do know is that mathematics is the fundamental epistemological bridge between reality and us, especially when it comes to understanding Nature’s deepest secrets.
In regard to
Platonism, Barrow has this to say:

*It elevates mathematics close to the status of God... just alter the word ‘God’ to ‘mathematics’ wherever it appears and it makes pretty good sense. Mathematics is part of the world, and yet transcends it. It must exist before and after the Universe.*

In the next paragraph
he says:

*Most scientists and mathematicians operate as if Platonism is true, regardless of whether they believe that it is. That is, they work as though there were an unknown realm of truth to be discovered.*

Neither of these
statements are definitive, and it should be pointed out that Barrow discusses
all aspects of mathematical philosophies in depth.

I think that
consciousness will never be reduced to mathematics, yet it is consciousness
that makes mathematics manifest. Obviously, some argue that it is consciousness
alone that makes mathematics at all, and Platonism is a remnant of numerology
and mysticism. Whichever point of view one takes, it is mathematics that makes
the Universe comprehensible. I’m a Platonist because of both the reasons given
above. I don’t think the Universe is a giant computer, but I do think that
mathematics determines, to a large extent, what realities we can have.

Despite my criticisms and disagreements, I
concede that Deutsch is much cleverer than me. His book is certainly
provocative, but I think it’s philosophically flawed in all the areas I discuss
above. On the other hand, the more I read of Barrow, the more I find myself
aligning to his cosmological world-view; in particular, his apparent attraction
to the Anthropic Principle. He makes the point that the probability of the
critical Nature’s constants’ values are less important than their necessity to
provide conditions for observers to evolve. This does not invoke teleology - as
he’s quick to point out – it’s just a necessary condition if intelligent life
is to evolve.

You’ve no doubt noticed that I don’t really
address the question in my heading. Deutsch’s multiverse and String Theory are
two prevalent, if also extreme, versions of reality. String Theory claims that
the Universe is actually 10 dimensions of space rather than 3 and predicts 10

^{500}possible universes, not to be confused with the quantum multiverse. 20^{th}Century physics has revealed, through quantum mechanics and Einstein’s theories of relativity, that ‘reality’ is more ‘strange’ than we imagine. I often think that Kant was prescient, in ways he could not have anticipated, when he said that we may never know the ‘thing-in-itself’.
It is therefore apposite to leave you with
Barrow’s last paragraph in his book:

*There is no formula that can deliver all truth, all harmony, all simplicity. No Theory of Everything can ever provide total insight. For, to see through everything, would leave us seeing nothing.*

Barrow loves to fill
his books with quotable snippets, but I like this one in particular:

*Mathematics is the part of science you could continue to do if you woke up tomorrow and discovered the universe was gone.*Dave Rusin.