Is Quantum Electrodynamics relevant to every electromagnetic field?

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Is Quantum Electrodynamics relevant to every electromagnetic field?
 

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  • #2
PeterDonis
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Hi @Anne Ross and welcome to PF!

Quantum electrodynamics describes any scenario which involves only electrons (and positrons) and the electromagnetic field (or photons, if you prefer).
 
  • #3
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What about the electromagnetic field of the brain?
 
  • #4
PeterDonis
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What about the electromagnetic field of the brain?
Electromagnetic fields in the brain basically interact only with the electrons of the atoms in the brain (and in the electric currents flowing in neurons), so yes, quantum electrodynamics would be sufficient to describe them. In practice, however, quantum effects are negligible in the brain so classical electrodynamics works just fine for describing EM fields in the brain (and is much easier to use than QED).

Is there a particular reason why you are asking?
 
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Hi Peter, thanks for your answer. The reason I asked the question is that there is a theory of consciousness which claims that it is produced by the electromagnetic field of the brain. Intuitively I cannot understand how a field which is complex enough to produce all the phenomena of consciousness can be described classically. In particular one claim has been that what we see - the colours, shapes, depth etc is due to spatially patterned electromagnetic fields. It seems to me that the fields would have to be intricately patterned. Would this require quantum electrodynamics? Anne
 
  • #6
PeterDonis
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there is a theory of consciousness which claims that it is produced by the electromagnetic field of the brain
Can you give a reference?

one claim has been that what we see - the colours, shapes, depth etc is due to spatially patterned electromagnetic fields. It seems to me that the fields would have to be intricately patterned. Would this require quantum electrodynamics?
I don't think so, since none of what you describe appears to involve any quantum effects. There is nothing preventing classical EM fields from being intricately patterned.
 
  • #7
DrChinese
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I don't think so, since none of what you describe appears to involve any quantum effects. There is nothing preventing classical EM fields from being intricately patterned.
Anne: Here is an example reference related to what Peter is saying.

https://arxiv.org/abs/quant-ph/9907009

There have been a number of speculative attempts to connect consciousness to quantum fields. So far, none of these have really been convincing. Considering that there is no objective definition of consciousness in the first place (are ants conscious?), I would say this is an open question. ...With current consensus being that classical EM fields are adequate to explain the underlying interactions of neurons, axons, etc.
 
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In response to the OP: I noticed you were a cognitive scientist posting in a physics forum... I myself was trained as a physicist as well as a physician, so I am familiar with many aspects of cognitive science. Next to clinical practice, I do mostly interdisciplinary research, specifically applying concepts from physics and mathematics to other fields, often dabbling directly in cognitive science. Due to this I'm happy to talk to you more on a more honest and level playing field, instead of patronizing you by treating you as a layman/child, or playing hide the ball through mathematical obscurantism.

From your posts it seems you don't have a physics background, or at least haven't taken classical or quantum mechanics. The prerequisites for actually answering the questions you want to answer comprise at least the following: the entire undergraduate physics curriculum (in particular calculus, differential equations, analytical mechanics, electrodynamics, thermodynamics, complex analysis, statistical mechanics and quantum mechanics), undergrad courses in anatomy, physiology and pharmacology, a working conceptual understanding of dynamical systems theory, a graduate level grasp of biophysics, hydrodynamics and condensed matter physics.

Almost everyone who responds here knows physics, but has no idea about anatomy or physiology, let alone pharmacology. The level at which those need to be grasped is from the perspective of dynamical systems theory, i.e. basically as physical theories; these are essentially part of biophysics. Biophysics is a relatively new field and physicists not familiar with theoretical biophysics tend to severely underestimate the difficulty of the subject. The open questions in theoretical biophysics are mathematically speaking immensely complicated, generally severely much more difficult than in any of the other branches of physics (apart from perhaps some parts of mathematical and theoretical physics) and perhaps even more difficult than all of the other fields combined. In any case, I have yet to run into anyone on here who actually is a biophysicist, maybe you will be more lucky.

That said there are still some publications you might be able to read and understand as a non-physicist. Try for example Del Giudice et al. 1982. If you feel that this is too difficult to understand directly, then I suggest you start by gaining the prerequisites I named above.
Or more advanced Del Giudice 1985, 1986 which uses quantum field theory to do some biophysics. In any case, I will give you a hint: quantum electrodynamics (QED) is a quantum field theory (QFT), so forget trying to learn or read about QED and instead go for QFT; you will then quickly find that the prerequisites to being able to understand are basically the entire physics undergrad curriculum.
(deja vu:)
The frequency with which this outdated paper by Max Tegmark still gets quoted is a clear demonstration of intellectual inertia of physicists regarding prematurely settled matters (recall von Neumann's faulty proof before Bohm and Bell). The origin of this inertia clearly has poisoned the well w.r.t. the subject.

a) Shortly after this paper there was a reply to Tegmark in the same journal showing Tegmark was off himself by a considerable amount. https://arxiv.org/abs/quant-ph/0005025
b) Tegmark himself admitted in a debate in Oct 2013 that his theoretical criticisms of Orch OR in that paper weren't just numerically off but altogether somewhat premature given the direction both theory and experiment have moved since then. He however refuses to retract the paper seemingly in order to save face. This debate was filmed and is available here:
 
  • #9
DarMM
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Anne: Here is an example reference related to what Peter is saying.

https://arxiv.org/abs/quant-ph/9907009
I'm not discussing the "QM consciousness" thing at all, but just wondering something about Tegmark's paper. It seems to me it could also be used to argue that biological systems in general wouldn't use QM as the same approximate arguments that he gives in his paper work in general. However it seems plants do use Quantum Mechanics for photosynthesis, I always wondered where his approximations breakdown.
 
  • #10
A. Neumaier
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plants do use Quantum Mechanics for photosynthesis,
Only in the sense that every chemical reaction requires quantum mechanics for a correct description of the free energy expression governing the quantitative details. The more accurate a model the more detailed it has to be, the shorter the distances that need to be modeled, and hence the more quantum mechanics is needed.

Just like with everything else. For example, for use in engineering one can treat superconductivity as a macroscopic, classical phenomenological property of some materials. But designing a superconductor needs knowledge of small-distance features of the material and hence requires a quantum treatment.
 
  • #11
DarMM
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Only in the sense that every chemical reaction requires quantum mechanics for a correct description of the free energy expression governing the quantitative details.
I was more refering to the fact that chromophores seem to use entanglement. I don't know the details though, which is the reason for my question.
 
  • #12
A. Neumaier
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chromophores seem to use entanglement.
The formation of a water crystal does so, too - though in some approximation that only takes the potential energy surface from quantum mechanics (in which the result of the entanglement of the electrons is encoded) one can treat the crystal formation classically.
 
  • #13
DarMM
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True, but I was originally talking about Tegmark's paper where he argues there is no long lived entanglement in biological systems. I'm not really disagreeing with QM providing initial inputs to otherwise classical models.
 
  • #14
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The formation of a water crystal does so, too - though in some approximation that only takes the potential energy surface from quantum mechanics (in which the result of the entanglement of the electrons is encoded) one can treat the crystal formation classically.
Actually, a few years ago in the biophysics/physical biology community (particularly from the biology side, i.e. quantum biology), there were a few experimental results implying that the efficiency of photosynthesis is an explicitly QM effect, being more efficient than can be explained classically.

This was somewhat of a big deal back then, because this was an in vivo measurement occuring at room temperature, thereby falsifying the traditional point of view in physical biology that no quantum effects could be biologically important due to environmental decoherence.

Afterwards, some other researchers demonstrated both mathematically and experimentally that entanglement seemed to play a bigger role in biology than previously assumed due to the standard 'warm, wet and noisy' arguments. Here are a few of those publications:
Coherent Spin Transfer Between Molecularly Bridged Quantum Dots - Ouyang et al 2003

Efficiency in photosynthesis - Engel et al 2007

Entanglement in bird retinae - Gauger et al 2011

In-vitro demonstration of coherent effects in microtubules - Sahu et al 2013

There was a small revolution within the field due to such results and a few conferences were had, resulting in a few popular books written on the subject by many attendees of said conferences. These books are in particular Abbott et al., 'Quantum Aspects of Life' and McFadden et al., 'Life on the Edge'.
 
  • #15
A. Neumaier
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the efficiency of photosynthesis is an explicitly QM effect, being more efficient than can be explained classically.
there is no long lived entanglement in biological systems.
I don't know the details though, which is the reason for my question.
From Wikipedia's article on photosynthesis (where further links are given):
Wikipedia said:
A phenomenon known as quantum walk increases the efficiency of the energy transport of light significantly. In the photosynthetic cell of an algae, bacterium, or plant, there are light-sensitive molecules called chromophores arranged in an antenna-shaped structure named a photocomplex. When a photon is absorbed by a chromophore, it is converted into a quasiparticle referred to as an exciton, which jumps from chromophore to chromophore towards the reaction center of the photocomplex, a collection of molecules that traps its energy in a chemical form that makes it accessible for the cell's metabolism. The exciton's wave properties enable it to cover a wider area and try out several possible paths simultaneously, allowing it to instantaneously "choose" the most efficient route, where it will have the highest probability of arriving at its destination in the minimum possible time. Because that quantum walking takes place at temperatures far higher than quantum phenomena usually occur, it is only possible over very short distances, due to obstacles in the form of destructive interference that come into play. These obstacles cause the particle to lose its wave properties for an instant before it regains them once again after it is freed from its locked position through a classic "hop". The movement of the electron towards the photo center is therefore covered in a series of conventional hops and quantum walks.
Thus the quantum effect is extremely short-lived, but gives rise to a macroscopic effect through a classical hopping process. Same for cascading in photomultipliers through a classical branching process, etc..
I'm not really disagreeing with QM providing initial inputs to otherwise classical models.
Here QM provides initial input to an otherwise classical hopping model.
 
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  • #16
DarMM
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From Wikipedia's article on photosynthesis (where further links are given):

Thus the quantum effect is extremely short-lived, but gives rise to a macroscopic effect through a classical hopping process. Same for cascading in photomultipliers through a classical branching process, etc..

Here QM provides initial input to an otherwise classical hopping model.
However still far longer than Tegmark claims it should be, my main concern is what was wrong with Tegmark's model.
 
  • #17
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From Wikipedia's article on photosynthesis:

Thus the quantum effect is extremely short-lived, but gives rise to a macroscopic effect through a classical cascading process. Same in photomultipliers, etc..
The fact that there were explicitly quantum effects with macroscopic consequences occuring within living systems at all was in itself the big discovery.

This is because everyone (both in physical biology as well as in biophysics) simply assumed - largely bolstered by Tegmarks paper - that such a thing was explicitly physically impossible - living systems being far too warm, wet and noisy, leading practically immediately to decoherence, and certainly too fast for biological systems to make use of it if it even occurred.

Nevermind the fact that this occurs in a process essential to all multicellular life, that is almost an afterthought. The important thing due to the experimental demonstrations was that this opened a large can of worms, because many phenomena that biologists once considered to be completely understood may need to be reanalyzed together with physicists/applied mathematicians.
 
  • #18
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However still far longer than Tegmark claims it should be, my main concern is what was wrong with Tegmark's model.
Max Tegmark's model was somewhat specific to microtubules, but then again it wasn't. The problem is Tegmark incorrectly interpreted Penrose' model as a tubulin soliton seperated from itself by about a tubulin length. This is in the order of a few nanometers instead of - as Penrose claimed - an atomic level seperation in the order of femtometers. This resulted in completely wrong numerics of ##10^{-20}## s to ##10^{-13}## s; the corrected results were of the order ##10^{-4}## s.

The corrected results were still off from the needed ##10^{-2}## to ##10^{-1}## s to be consistent with EEG phenomenology. Here it should be noted that the corrected calculation was based on a highly preliminary toy model of Penrose' hypothesis pretty much assuming that no other serious interactions occur which influence the microtubule.

More serious biological versions of the model which actually take account of neuronal and biological synchronicity - which of course only a theorist would even dare to ignore - pretty much immediately showed that through the correct dynamical descriptions using beat frequencies it was trivially easy to achieve consistency with EEG phenomenology.

Moreover, afterwards it was shown experimentally that there actually seems to be coherent effects in microtubules, which also have a fractal pattern over a large ranges of frequencies. The researcher in question who demonstrated this, A. Bandyopadhyay, is currently doing more experiments at MIT, I believe, but he may have gone back to his original lab in Japan.

There is a larger theme in the practice of theoretical science here where theoretical calculations done using highly preliminary models of some hypothesis, prior to any experiment being done/possible, leading to very strong claims against some particular hypothesis.

These claims then often later turn out to be incorrect due to them resting on mathematically seemingly trivial assumptions, which actually are conceptually - i.e. if understood correct physically - clearly unjustifiable. The problem is then that a hypothesis can be discarded prematurely due to taking the predictions of the toy models at face value; this seems to occur when a toy model is an idealization which is actually completely inaccurate w.r.t. the actual hypothesis due to the nature of the idealization itself.
 
  • #19
atyy
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I'm not discussing the "QM consciousness" thing at all, but just wondering something about Tegmark's paper. It seems to me it could also be used to argue that biological systems in general wouldn't use QM as the same approximate arguments that he gives in his paper work in general. However it seems plants do use Quantum Mechanics for photosynthesis, I always wondered where his approximations breakdown.
http://condensedconcepts.blogspot.com/2016/11/photosynthesis-is-incoherent.html
Photosynthesis is incoherent
Ross McKenzie
"I do not find the 60 fsec timescale surprising. In 2008, Joel Gilmore and I published a review of experiment and theory on a wide range of biomolecules (in a warm wet environment) that suggested that tens of femtoseconds is the relevant time scale for decoherence."

http://www.pnas.org/content/114/32/8493
Nature does not rely on long-lived electronic quantum coherence for photosynthetic energy transfer
Hong-Guang Duan, Valentyn I. Prokhorenko, Richard J. Cogdell, Khuram Ashraf, Amy L. Stevens, Michael Thorwart, and R. J. Dwayne Miller
 
  • #20
DarMM
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http://condensedconcepts.blogspot.com/2016/11/photosynthesis-is-incoherent.html
Photosynthesis is incoherent
Ross McKenzie
"I do not find the 60 fsec timescale surprising. In 2008, Joel Gilmore and I published a review of experiment and theory on a wide range of biomolecules (in a warm wet environment) that suggested that tens of femtoseconds is the relevant time scale for decoherence."

http://www.pnas.org/content/114/32/8493
Nature does not rely on long-lived electronic quantum coherence for photosynthetic energy transfer
Hong-Guang Duan, Valentyn I. Prokhorenko, Richard J. Cogdell, Khuram Ashraf, Amy L. Stevens, Michael Thorwart, and R. J. Dwayne Miller
I've read the paper just there and a few follow up articles, from a general review by Philip Ball "Still seeking coherence" it seems it's genuinely an open issue as to what is happening in these cases, there is some evidence of quantum coherence, but there may be other ways of modelling the effects. Duan et al.'s paper does not conclusively close the issue.

Does anybody know about what is currently thought of entanglement in other biological systems?
 
  • #21
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http://condensedconcepts.blogspot.com/2016/11/photosynthesis-is-incoherent.html
Photosynthesis is incoherent
Ross McKenzie
"I do not find the 60 fsec timescale surprising. In 2008, Joel Gilmore and I published a review of experiment and theory on a wide range of biomolecules (in a warm wet environment) that suggested that tens of femtoseconds is the relevant time scale for decoherence."

http://www.pnas.org/content/114/32/8493
Nature does not rely on long-lived electronic quantum coherence for photosynthetic energy transfer
Hong-Guang Duan, Valentyn I. Prokhorenko, Richard J. Cogdell, Khuram Ashraf, Amy L. Stevens, Michael Thorwart, and R. J. Dwayne Miller
This experiment only looked at FMO proteins and chromophores in water solution, i.e. this is an in vitro experiment, not an in vivo argument - completely disregarding both known and unknown naturally occurring biological rhythms. Disregarding these things is a form of experimental simplification - analogous to mathematical toy models and idealization - the full experiment requiring far more advanced research techniques.

I have by now read over a thousand papers like this and the first thing one can always conclude is that such in vitro experiments do not easily generalize to in vivo; this is why eg. promising in vitro medical treatments in the large majority of cases turn out not to work in actual practice. I'd need to see at least a systematic review based on meta-analyses of all experiments done so far to draw a proper conclusion.

Therefore, the conclusions of Duan et al. should definitely be taken with a grain of salt. Even worse, generally speaking purely due to the in vitro nature of the experiment it would actually even usually be discarded out of hand by both physiologists and clinical practictioners.

There is in fact plenty of extant phenomenological experimental evidence which can be directly pitted against these particular conclusions - known and understandable to anyone who has taken high school biochemistry and biology - namely the existence of decoherence free regions in chemical molecules and reactions where superposition is shielded from the outside environment.

A popular example is when you try to dissolve amphipathic molecules - which have a hydrophile and hydrophobe end - in water. The hydrophobic ends will clump together, making up hydrophobic pockets in water, while the hydrophilic end make up the outer surface of the pocket that is in direct contact with water. For those that do recall high school chemistry, the reason for the clumping of the hydrophobic ends is that they are attracted to each other by van der Waals-forces.

Essentially this example also accounts for an empirical phenomenon known and recognizable by almost everyone - even primary school children - namely that oil and water do not mix and oil drops coming together and floating on top of water. The same applies to organic molecules, such as benzene. Benzene is a molecule that can exist in superposition of two resonance states:
p2p7n6.jpg

Benzene dissolved in water will also form hydrophobic pockets. These pockets represent decoherence free subspaces wherein benzene can remain in a superposition of resonance states, which oscillate in the terahertz frequency (~##10^{12} \mathrm {Hz}##). The same thing goes for thousands of organic biomolecules including amino acids and proteins, including microtubules in neurons.

In many experimental biomedical disciplines (biology, neurophysiology, pharmacology and anesthesiology) there are many theoretical models which depend on molecules (such as therapeutic pharmacon) which depend on the resonance between molecule and some biological sensor (such as a cell membrane receptor). If I remember correct, it has even been demonstrated that fruit flies can sense -through smell - differences in electron resonances between certain odor molecules.
 

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