In the
1990s, long before winning the 2020 Nobel Prize in Physics for his prediction
of black holes, physicist Roger Penrose teamed up with anesthesiologist Stuart
Hameroff to propose an ambitious answer.
They
claimed that the brain’s neuronal system forms an intricate network and that
the consciousness this produces should obey the rules of quantum mechanics –
the theory that determines how tiny particles like electrons move around. This,
they argue, could explain the mysterious complexity of human consciousness.
Penrose
and Hameroff were met with incredulity. Quantum mechanical laws are usually
only found to apply at very low temperatures. Quantum computers, for example,
currently operate at around -272°C. At higher temperatures, classical mechanics
take over. Since our body works at room temperature, you would expect it to be
governed by the classical laws of physics. For this reason, the quantum
consciousness theory has been dismissed outright by many scientists – though
others are persuaded supporters.
Instead
of entering into this debate, I decided to join forces with colleagues from
China, led by Professor Xian-Min Jin at Shanghai Jiaotong University, to test
some of the principles underpinning the quantum theory of consciousness.
In our
new paper, we’ve investigated how quantum particles could move in a complex
structure like the brain – but in a lab setting. If our findings can one day be
compared with activity measured in the brain, we may come one step closer to
validating or dismissing Penrose and Hameroff’s controversial theory.
Our
brains are composed of cells called neurons, and their combined activity is
believed to generate consciousness. Each neuron contains microtubules, which
transport substances to different parts of the cell. The Penrose-Hameroff
theory of quantum consciousness argues that microtubules are structured in a
fractal pattern which would enable quantum processes to occur.
Fractals
are structures that are neither two-dimensional nor three-dimensional but are
instead some fractional value in between. In mathematics, fractals emerge as
beautiful patterns that repeat themselves infinitely, generating what is
seemingly impossible: a structure that has a finite area, but an infinite
perimeter.
This
might sound impossible to visualize, but fractals actually occur frequently in
nature. If you look closely at the florets of a cauliflower or the branches of
a fern, you’ll see that they’re both made up of the same basic shape repeating
itself over and over again, but at smaller and smaller scales. That’s a key
characteristic of fractals.
The same
happens if you look inside your own body: the structure of your lungs, for
instance, is fractal, as are the blood vessels in your circulatory system.
Fractals also feature in the enchanting repeating artworks of MC Escher and
Jackson Pollock, and they’ve been used for decades in technology, such as in
the design of antennas. These are all examples of classical fractals – fractals
that abide by the laws of classical physics rather than quantum physics.
It’s
easy to see why fractals have been used to explain the complexity of human consciousness.
Because they’re infinitely intricate, allowing complexity to emerge from simple
repeated patterns, they could be the structures that support the mysterious
depths of our minds.
But if
this is the case, it could only be happening on the quantum level, with tiny
particles moving in fractal patterns within the brain’s neurons. That’s why
Penrose and Hameroff’s proposal is called a theory of “quantum consciousness”.
We’re
not yet able to measure the behavior of quantum fractals in the brain – if they
exist at all. But advanced technology means we can now measure quantum fractals
in the lab. In recent research involving a scanning tunneling microscope (STM),
my colleagues at Utrecht and I carefully arranged electrons in a fractal
pattern, creating a quantum fractal.
When we
then measured the wave function of the electrons, which describes their quantum
state, we found that they too lived at the fractal dimension dictated by the
physical pattern we’d made. In this case, the pattern we used on the quantum
scale was the Sierpiński triangle, which is a shape that’s somewhere between
one-dimensional and two-dimensional.
This was
an exciting finding, but STM techniques cannot probe how quantum particles move
– which would tell us more about how quantum processes might occur in the
brain. So in our latest research, my colleagues at Shanghai Jiaotong University
and I went one step further. Using state-of-the-art photonics experiments, we
were able to reveal the quantum motion that takes place within fractals in
unprecedented detail.
We
achieved this by injecting photons (particles of light) into an artificial chip
that was painstakingly engineered into a tiny Sierpiński triangle. We injected
photons at the tip of the triangle and watched how they spread throughout its
fractal structure in a process called quantum transport. We then repeated this
experiment on two different fractal structures, both shaped as squares rather
than triangles. And in each of these structures, we conducted hundreds of
experiments.
Our
observations from these experiments reveal that quantum fractals actually
behave in a different way to classical ones. Specifically, we found that the
spread of light across a fractal is governed by different laws in the quantum
case compared to the classical case.
This new
knowledge of quantum fractals could provide the foundations for scientists to
experimentally test the theory of quantum consciousness. If quantum
measurements are one day taken from the human brain, they could be compared
against our results to definitely decide whether consciousness is a classical
or a quantum phenomenon.
Our work
could also have profound implications across scientific fields. By
investigating quantum transport in our artificially designed fractal
structures, we may have taken the first tiny steps towards the unification of
physics, mathematics, and biology, which could greatly enrich our understanding
of the world around us as well as the world that exists in our heads.
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