It is believed that a PhD student should not touch some scientific problems even with the very tip of a long spear - this applies in particular to the gaps in the foundations of quantum theory. These tasks are so complex that there is not the slightest chance of progress. These tasks are so vague that there is not the slightest chance to convince anyone to pay attention to progress. An example of such a task is Role
of quantum physics in shaping consciousness.
Disclaimer! From the translator: I translated this post in an attempt to understand the idea. The concept itself is quite controversial, and not all points are clear (or insufficiently complete) in the original. I do not take responsibility for the original and leave the post as a starting point for your thoughts and discussions.
Habré already had a post about the idea of Fisher, but it’s always interesting to hear explanations from the actors (authors). Some places are adapted, links added.
In fact, we know that quantum physics precisely plays a role in our mind: the laws of quantum physics allow atoms to remain stable, and decayed atoms just cannot influence consciousness.
But most physicists are convinced that the useful quantum entanglement
cannot exist in the brain. Entanglement manifests itself in quantum correlations between quantum systems, which are stronger than any achievable in classical systems. Entanglement disintegrates very quickly in hot, humid and noisy environments.
And the brain is just such a medium. Imagine that you put entangled molecules A
in someone's brain. Water, ions and other particles will collide with these molecules. The higher the ambient temperature, the greater the collisions. The particles of the medium will be entangled with the molecules A
through electromagnetic interaction. The more A
gets entangled with the medium, the less A
can remain entangled with B
. In the end, A
will be slightly entangled with the many particles of the medium. And such weak entanglement cannot be used for some useful calculations. So it seems that quantum physics can hardly have a significant effect on consciousness.
Don't touch it
However, my supervisor, John Presquill
, suggested that I consider whether it would be interesting to work on this topic.
Try a completely new topic,
- he said, take a chance. If it doesn't work, well, okay. All the same, there is not much waiting for graduate students. Did you see the Matthew Fisher article about quantum consciousness?
is a theoretical physicist at the University of California, Santa Barbara. He is praised and honored, especially for his work on superconductors
. A couple of years ago, Matthew became interested in biochemistry. He knew, of course, that most physicists doubt the participation of quantum processes in the formation of consciousness. But what if this were not true, he thought, how could they participate? I thought - and in 2015 I wrote article
in the Annals of Physics, in which, with the help of reverse engineering, proposed a variant of quantum consciousness.
A graduate student in no case should concern such tasks, even a three-meter radio antenna, asserts common sense. But I trust John Preskill as no one else on earth.
I'll look at the article
, I said.
Matthew suggested that quantum physics can affect consciousness as follows ( an article on Habré
). Experimenters have already made quantum computations using one hot, wet and random system: at nuclear magnetic resonance (NMR)
. NMR is used in magnetic resonance imaging
(MRI) for imaging the human brain. Standard NMR system consists of liquid molecules at high temperature. Molecules, in turn, consist of atoms whose nuclei possess a quantum property called spin
. The spins of the nuclei can encode quantum information (CI).
Matthew argued: what can prevent the nuclear spins from storing quantum information in our brain? He compiled a list of things that could destroy quantum information, and came to the conclusion that hydrogen ions pose the greatest threat. They can get tangled with their backs (and lead to decoherence
) via dipole-dipole interaction
How can spin avoid this threat? For example, a spin of
will reset the electric quadrupole moment of the nucleus, quadrupole interactions will not result in decoherence of such spin . And in which atoms in our body does a spin equal
? In hydrogen and phosphorus. Only hydrogen is exposed to other sources of decoherence, so Matthew came to the conclusion that phosphorus atoms can store CI in our brain, while the spins of the phosphorus nucleus work like qubits (quantum bits).
Phosphorus is protected from electrical interactions, but what about magnetic dipole-dipole interactions? Such interactions depend on the orientation of the spins relative to their position in space. If phosphorus is part of a small molecule dangling in a biological fluid, the position of the nucleus changes randomly, and on average the interaction will be zero.
In molecules there are other atoms besides phosphorus. The nuclei of these atoms can interact with the spin of phosphorus, and destroy its quantum state. This will not happen only in one case: when all the spins of these nuclei are zero. In which atoms in the human body the spins of the nucleus are zero? In oxygen and calcium.So phosphorus will be protected from interaction with other atoms in molecules with calcium and oxygen.
Matthew proposed his own version of a molecule that would protect phosphorus from decoherence. And then he discovered that such a molecule is indeed described in the scientific literature. The molecule
called the Posner cluster
or Posner's molecule
(I will call her Posner for short). Posters can exist in artificial bioliquids — liquids created to imitate the fluids inside us. Posners are believed to exist in our bodies and participate in bone formation. Matthew estimates that Posner can protect the backs of phosphorus from decoherence for 1-10 days.
(image courtesy of Swift et al .
But how can Posners affect consciousness? Matthew offered the next option. Molecule adenosine triphosphate
(ATP) is an energy source for biochemical reactions. "Triphosphate" means that there are three ions in it phosphate
consisting of one atom phosphorus and three oxygen atoms. Two phosphates can separate from the ATP molecule, remaining connected to each other.
A pair of phosphates will drift until they meet an enzyme called pyrophosphatase. This enzyme can divide a pair of phosphates into two independent phosphates. At the same time, as Matthew suggested, along with Leo Rajhovsky
, the backs of the phosphorus nuclei are projected into the singlet state
, which is a state with maximum entanglement.
Imagine the many phosphates in biofluids. Six phosphates can combine with nine calcium ions and form a Posner molecule. Each Posner can have six common singlet with other Pozner - this is how the whole clouds of entangled Posner molecules are formed.
One clot of Posner can fall into one neuron, while another clot into another neuron. Posners can be transferred across cell membranes with VGLUT
(BNPI) protein. So the two neurons are also entangled. Imagine two Posners, P and Q, converging in the neuron N. Quantum Chemistry Calculations
show that these Posners can unite with each other. Suppose P
was entangled with Posner P ’
in the N’
neuron. If P
merged into the neuron N
, the entanglement between P
and P '
will increase the likelihood of combining P '
United Posners will move slowly - they will have to overcome water resistance. Hydrogen and magnesium can replace calcium in pozner, breaking molecules. Phosphates with a negative charge will attract positively charged
, just like phosphates attract
.Calcium released will fill the N and N ’neurons. Increasing the concentration of calcium leads to the emergence of a chemical potential on the axon and the release of neurotransmitters that transmit a signal between two neurons. If two neurons N and N ’are entangled through Posner molecules, two neurons can light up simultaneously.
We do not know whether the mechanism proposed by Matthew works in our brain. However, last year Heising-Simons Foundation identified
Matthew and colleagues 1.2 million dollars to experiment.
John Preskill told me: let's say Matthew's idea is at least partially correct, and Posner molecules can really store quantum information. Quantum systems process information differently than classical systems. How quickly will Posners be able to process quantum information?
I threw out my spear in the fifth year of graduate school, and left Caltech for a five-month internship, refusing to return with an article answering John's question. And I did: the article was published in the Annals of Physics
Fortunately, I was able to interest Elizabeth Crosson
in my project. Elizabeth, now an assistant professor at the University of New Mexico, was then working as a postdoc in John's group. We both were engaged in the theory of quantum information, but our qualifications, abilities and strengths were different. We complemented each other, having the same stubbornness, which forced us to continue to send letters and exchange messages day and night.
Elizabeth and I translated the ideas of Matthew from the language of biochemistry into the mathematical language of CI theory. We divided Matthew's narrative into a sequence of biochemical steps, and figured out how each of these steps would transform the CIs recorded in the phosphorus nucleus. We presented each transformation in the form of an equation and a block diagram element (block diagram elements are images that can be put together to create working algorithms). We call this set of transformations Posner operations.
Imagine that you can perform Posner's operations, preparing molecules, trying to connect them, etc. How can you handle CI with these operations? Elizabeth and I found applications in quantum messaging, quantum error recording, and quantum computing. Our results are based on one assumption — perhaps erroneous — that Matthew made the right conclusions. We have characterized what can be achieved by Pozner if they are actively managed, although random effects would direct them in biofluids. But this is at least a good starting point for further research.
We found several KI effects that can be realized with Posner molecules. First,
CI can be teleported from one Posner to another, but there is noise. His nature is in an effective dimension that Posners perform on each other when combined. This dimension transforms the subspaces of the Hilbert space of the two Posners through the coarse dimension of Bell. The Bell measurement gives one of four possible outcomes, or two bits. If one of the bits is discarded, the measurement result will be gross. Quantum teleportation requires a Bell measurement, and the coarsening of this measurement leads to noise.
This noisy teleportation is also called super-dense coding
. A bit is a random parameter that accepts one of two values, and “trit" is a random parameter that can take one of three possible values. A trit can be effectively teleported from one Posner to another using entanglement if one bit is directly transmitted between them.
Matthew argued that Posner’s structure protects CI from decoherence. Scientists have developed programs Correction and Error Detection
to protect CI from decoherence. Can Posners implement such programs in our model? It turns out that yes: Elizabeth and I (with the help of a former post-doc from Caltech Fernando Pastavski
) have developed an error detection program that can work on poznerov. One Posner encodes a logical qutrit (the quantum version of trit), and the code detects any error that occurs in one of the six qubits in Posner.
how complicated can a quantum state be that can be prepared using Posner's operations? Quite complicated, as we discovered: suppose you can measure this state locally so that the results of previous measurements will affect measurements in the future. You can do any quantum computation. That is, Posner's operation allows you to prepare a state that can be used to create Universal Quantum Computer
we found a numerical estimate of the effect of entanglement on the speed of combining Posners. Imagine that you have prepared two Posners P and P ’, which are only entangled with other particles. If Posners converge with the correct orientation, the probability of their unification in our model is equal to 33.6%. And if every qubit in P is maximally confused with a qubit in P ’, the probability of combining increases to 100%.
Elizabeth and I present the process described by Matthew in a 2015 paper as flowcharts.
I was afraid that other scientists would laugh our work like crazy. To my surprise, she was received with enthusiasm: colleagues praised the riskiness of research in a new direction. In addition, our work is not mad at all: we do not claim that quantum physics affects consciousness. We base ourselves on Matthew’s assumptions, noting that they may be erroneous, and examine the consequences of his assumptions. We are not biochemists, and not experimenters, so we confine ourselves to statements in the theory of CI.
Perhaps Posners cannot maintain coherence long enough to use quantum effects in information processing. Will Matthew's mistakes put an end to our research? Not. Posner prompted us to ideas and questions in the theory of CI. For example, our quantum schemes illustrate the interactions (unitary gates) and the measurements made by combining Posners. These schemes have partially become the motivation for the emergence of a new field of research that emerged last summer and is now gaining momentum. Take the random unitary gates interspersed with measurements. Unitary interactions confuse qubits, and measurements destroy confusion.Which of the influences will be more significant? Will the system go from “largely confused” to “largely not entangled” at a given measurement frequency? Researchers at Santa Barbara
; MIT; Oxford
; Lancaster, UK
; Berkeley; Stanford
; and Princeton
addressed this issue.
Aspriant physicists, as is commonly believed, should not touch the quantum consciousness even by the Swiss guard's halberd. But I'm glad that I tried: I learned a lot, made a contribution to science, and it was an adventure. And if someone disapproves of such audacity, I can blame John Preskill.
The Quantum Information in the Posner Model of Quantum Cognition article can be found here . The arXiv version is here , and here is an article report.