Study Maps The Odd
Structural Similarities Between The Human Brain And The Universe
One fascinating quirk of the Universe is that shapes and
patterns can be found in hugely different contexts: the Golden Spiral can be
seen in the human cochlea and the shape of a spiral galaxy; the fractal
geometry of veins echoed in the branching of lightning.
In a bold new pilot study, an astrophysicist and a
neurosurgeon have bumped it up a notch, using quantitative analysis to compare
two of the most complex systems in nature: the neuronal network in the human
brain and the cosmic network of galaxies in the Universe.
It's actually not that peculiar a comparison. You may have
seen an image that occasionally gets shared around, showing a human neuron and
a simulated galaxy cluster, side-by-side; the two look startlingly similar.
But there's a lot more to the human brain - and the Universe -
than how it looks.
So astrophysicist Franco Vazza of the University of Bologna in
Italy and neurosurgeon Alberto Feletti of the University of Verona in Italy
have spent the last few years investigating to determine if the similarities
are more than skin-deep.
Writing in Nautilus Quarterly in 2017 they explained:
"Galaxies can group into enormous structures (called
clusters, superclusters, and filaments) that stretch for hundreds of millions
of light-years. The boundary between these structures and neighboring stretches
of empty space called cosmic voids can be extremely complex.
Gravity accelerates matter at these boundaries to speeds of
thousands of kilometers per second, creating shock waves and turbulence in
intergalactic gases.
We have predicted that the void-filament boundary is one of
the most complex volumes of the universe, as measured by the number of bits of
information it takes to describe it.
This got us to thinking: Is it more complex than the
brain?"
The two types of structures differ in size by 27 orders of
magnitude (that's a billion billion billion). But the team's results suggest
that, while the physical processes that drive the structure of the Universe and
the structure of the human brain are extremely different, they can result in
similar levels of complexity and self-organisation, the researchers said.
The starting point was working out similarities between the
two. The human cerebellum has around 69 billion neurons; the observable cosmic
web contains over 100 billion galaxies. That's one.
Both systems are arranged in well-defined networks, with nodes
(neurons in the brain, galaxies in the Universe) connected via filaments.
Both neurons and galaxies have a typical scale radius that's
only a fraction of the length of the filaments. And the flow of information and
energy between nodes is only around 25 percent of the mass and energy content
of each system.
In addition, there are similarities between the composition of
the brain and the composition of the Universe. The brain is around 77 percent
water. The Universe is around 72 percent dark energy.
Both of these are apparently passive materials that permeate
their respective system and play only an indirect role in their internal
structures.
With these similarities defined, the team next undertook
quantitative comparison of the two, based on images. They obtained slices of
the human cerebellum and cortex at different magnifications, and compared them
to simulations of the cosmic web.
What they were looking for were similarities in the matter
density fluctuations between brains and the cosmic web. And they found that the
relative distribution of fluctuations in the two systems was amazingly similar
- although on much different scales.
A slice of cerebellum at 40x magnification (left in the second
photo) and simulated cosmic web at 300 light-years a side (right). (University
of Bologna)
"We calculated the spectral density of both systems. This
is a technique often employed in cosmology for studying the spatial
distribution of galaxies," Vazza said.
"Our analysis showed that the distribution of the
fluctuation within the cerebellum neuronal network on a scale from 1 micrometer
to 0.1 millimeters follows the same progression of the distribution of matter
in the cosmic web but, of course, on a larger scale that goes from 5 million to
500 million light-years."
But that wasn't all.
The team looked at other morphological features, such as the
number of filaments connected to each node. The cosmic web, based on a sample
of 3,800 to 4,700 nodes, had on average 3.8 to 4.1 connections per node. The
human cortex, for a sample of 1,800 to 2,000 nodes, had an average of 4.6 to
5.4 connections per node.
In addition, both systems showed a tendency to cluster
connections around central nodes. And both seem to have a similar information
capacity.
A recent study suggests that the memory of the human brain is
around 2.5 petabytes. Another recent study, by Vazza, suggests that the memory
capacity required to store the complexity of the Universe is around 4.3
petabytes.
"Roughly speaking," the researchers wrote in 2017,
"this similarity in memory capacity means that the entire body of
information that is stored in a human brain (for instance, the entire life
experience of a person) can also be encoded into the distribution of galaxies
in our universe."
That's not to say that the Universe is a brain, or capable of
sentience. But it does hint that the laws that govern the growth of the
structures of both could be the same.
According to a 2012 paper based on simulations, the causal
network representing the large-scale structure of spacetime in our accelerating
universe is a power-law graph remarkably similar to the human brain.
Studies such as this one, by Vazza and Feletti, could pave the
way to better understanding those laws.
"Once again, structural parameters have identified
unexpected agreement levels. Probably, the connectivity within the two networks
evolves following similar physical principles, despite the striking and obvious
difference between the physical powers regulating galaxies and neurons,"
Feletti said.
"These two complex networks show more similarities than
those shared between the cosmic web and a galaxy or a neuronal network and the
inside of a neuronal body."
The research has been published in Frontiers in Physics.
