There’s
a quiet revolution underway in theoretical physics. For as long as the
discipline has existed, physicists have been reluctant to discuss
consciousness, considering it a topic for quacks and charlatans. Indeed,
the mere mention of the ‘c’ word could ruin careers.
That’s
finally beginning to change thanks to a fundamentally new way of
thinking about consciousness that is spreading like wildfire through the
theoretical physics community. And while the problem of consciousness
is far from being solved, it is finally being formulated mathematically
as a set of problems that researchers can understand, explore and
discuss.
Today,
Max Tegmark, a theoretical physicist at the Massachusetts Institute of
Technology in Cambridge, sets out the fundamental problems that this new
way of thinking raises. He shows how these problems can be formulated
in terms of quantum mechanics and information theory. And he explains
how thinking about consciousness in this way leads to precise questions
about the nature of reality that the scientific process of experiment
might help to tease apart.
Tegmark’s
approach is to think of consciousness as a state of matter, like a
solid, a liquid or a gas. “I conjecture that consciousness can be
understood as yet another state of matter. Just as there are many types
of liquids, there are many types of consciousness,” he says.
He
goes on to show how the particular properties of consciousness might
arise from the physical laws that govern our universe. And he explains
how these properties allow physicists to reason about the conditions
under which consciousness arises and how we might exploit it to better
understand why the world around us appears as it does.
Interestingly,
the new approach to consciousness has come from outside the physics
community, principally from neuroscientists such as Giulio Tononi at the
University of Wisconsin in Madison.
In
2008, Tononi proposed that a system demonstrating consciousness must
have two specific traits. First, the system must be able to store and
process large amounts of information. In other words consciousness is
essentially a phenomenon of information.
And
second, this information must be integrated in a unified whole so that
it is impossible to divide into independent parts. That reflects the
experience that each instance of consciousness is a unified whole that
cannot be decomposed into separate components.
Both
of these traits can be specified mathematically allowing physicists
like Tegmark to reason about them for the first time. He begins by
outlining the basic properties that a conscious system must have.
Given that it is a phenomenon of information, a conscious system must be able to store in a memory and retrieve it efficiently.
It
must also be able to to process this data, like a computer but one that
is much more flexible and powerful than the silicon-based devices we
are familiar with.
Tegmark borrows the term computronium
to describe matter that can do this and cites other work showing that
today’s computers underperform the theoretical limits of computing by
some 38 orders of magnitude.
Clearly, there is so much room for improvement that allows for the performance of conscious systems.
Next,
Tegmark discusses perceptronium, defined as the most general substance
that feels subjectively self-aware. This substance should not only be
able to store and process information but in a way that forms a unified,
indivisible whole. That also requires a certain amount of independence
in which the information dynamics is determined from within rather than
externally.
Finally,
Tegmark uses this new way of thinking about consciousness as a lens
through which to study one of the fundamental problems of quantum
mechanics known as the quantum factorisation problem.
This
arises because quantum mechanics describes the entire universe using
three mathematical entities: an object known as a Hamiltonian that
describes the total energy of the system; a density matrix that
describes the relationship between all the quantum states in the system;
and Schrodinger’s equation which describes how these things change with
time.
The
problem is that when the entire universe is described in these terms,
there are an infinite number of mathematical solutions that include all
possible quantum mechanical outcomes and many other even more exotic
possibilities.
So
the problem is why we perceive the universe as the semi-classical,
three dimensional world that is so familiar. When we look at a glass of
iced water, we perceive the liquid and the solid ice cubes as
independent things even though they are intimately linked as part of the
same system. How does this happen? Out of all possible outcomes, why do
we perceive this solution?
Tegmark
does not have an answer. But what’s fascinating about his approach is
that it is formulated using the language of quantum mechanics in a way
that allows detailed scientific reasoning. And as a result it throws up
all kinds of new problems that physicists will want to dissect in more
detail.
Take
for example, the idea that the information in a conscious system must be
unified. That means the system must contain error-correcting codes that
allow any subset of up to half the information to be reconstructed from
the rest.
Tegmark
points out that any information stored in a special network known as a
Hopfield neural net automatically has this error-correcting facility.
However, he calculates that a Hopfield net about the size of the human
brain with 10^11 neurons, can only store 37 bits of integrated
information.
“This
leaves us with an integration paradox: why does the information content
of our conscious experience appear to be vastly larger than 37 bits?”
asks Tegmark.
That’s
a question that many scientists might end up pondering in detail. For
Tegmark, this paradox suggests that his mathematical formulation of
consciousness is missing a vital ingredient. “This strongly implies that
the integration principle must be supplemented by at least one
additional principle,” he says. Suggestions please in the comments
section!
And
yet the power of this approach is in the assumption that consciousness
does not lie beyond our ken; that there is no “secret sauce” without
which it cannot be tamed.
At
the beginning of the 20th century, a group of young physicists embarked
on a quest to explain a few strange but seemingly small anomalies in
our understanding of the universe. In deriving the new theories of
relativity and quantum mechanics, they ended up changing the way we
comprehend the cosmos. These physcists, at least some of them, are now
household names.
Could it be that a similar revolution is currently underway at the beginning of the 21st century?