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Can someone explain the quantum physics-consciousness connection? In the double slit or quantum eraser experiments, the system behaves as a whole, with some apparent time independent traits. Invoking some kind of time independent but still causal physics, the problem could be simplified. But to include consciousness in the picture, we need better evidence. So I'm going to propose the following version of the double slit experiment.

If consciousness was actually involved, a person could create or destroy the interference pattern by just looking at the slit measurement result even after it is recorded. To emphasize my point, imagine that the experiment is spread across 3 days. The first day experiment is done but the results are recorded into computer memory and no one looks at it. The second day someone comes in and just looks at the results of the slit detector. He/she could even encode some message by closing and opening his/her eyes while looking at the results. Since consciousness is involved, it should effect the interference pattern even after such an indirect and delayed measurement (by consciousness). Then on the third day a second person could just look at the interference pattern that was recorded two days earlier, and still see the interference pattern being created and destroyed and even read the encoded message by just looking at the slit measurements on the second day. Does this sound reasonable to you, or what am I missing?

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    $\begingroup$ As far as I can tell, there is no logical definition of consciousness that compatible with physics. $\endgroup$
    – Antillar Maximus
    Commented Jan 5, 2013 at 15:52
  • $\begingroup$ Hi @Anixx: A philosophy tag is not allowed, cf. this meta Phys.SE post. $\endgroup$
    – Qmechanic ♦
    Commented Jan 5, 2013 at 22:51
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    $\begingroup$ This question sounds like a misunderstanding of the theory. As far as I've been able to ascertain, the idea isn't that your conscious observation interferes, it's that on such a small scale, any observation physically effects a change in the system. When you are monitoring electrons, you have to "observe" them by bouncing photons off them with a sensor; this obviously interferes with their behavior. Watching it with your eye won't affect it, unless you're Superman. $\endgroup$
    – ArmedMonkey
    Commented Jul 19, 2013 at 14:06
  • $\begingroup$ "As far as I can tell, there is no logical definition of consciousness that compatible with physics". Fine. And what conclusion should one derive from this statement? A: Consciousness does not exist. B: Consciousness is something existing, yet outside the reach of physic (so probably not material). My choice is B. $\endgroup$
    – F. Jatpil
    Commented Feb 13, 2020 at 8:07
  • $\begingroup$ @ArmedMonkey in the double slit, if you track what slit it used, but you never save that information... then it doesn't collapse. So basically someone has to be able to figure out which slit it used. The sensor "knows" which slit used, but doesn't collapse the wave. Just the human collapses the wave. $\endgroup$
    – 07mm8
    Commented Mar 28, 2020 at 17:55

6 Answers 6

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Can someone explain the quantum physics-consciousness connection?

There is none.

There's a whole lot that can be said about this, but at a basic level, the explanation is that an observation in quantum mechanics is best thought of as an interaction with another particle (technically: a classical system). It doesn't have to involve a conscious observer. So in your example, storing the result into computer memory is equivalent to looking at it, and there will be no further effect on the recorded interference pattern.

If you could treat the computer memory as an incoherent quantum system (i.e. non-classical, so that storing into memory wouldn't collapse the wavefunction), and if I understand correctly what you're saying, the example you've proposed sounds pretty much like the delayed choice quantum eraser experiment. This experiment works like the double slit experiment with the difference that you can choose whether or not to detect which slit the photon went through after it has passed through the slits. The results are consistent with quantum mechanics in the sense that you still get the interference pattern if you don't identify the slit, and you don't get the interference pattern if you do identify the slit, despite the choice being made afterwards.

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  • $\begingroup$ Question is not whether delayed choice quantum eraser is in accordance with quantum mechanic, but whether it has implications for consciousness. And yes, it does! It implies macroscopic objects (photographic plates) are in superposition until an observer does (or does not) measure the corresponding entangled particle partners (maybe years later?). And if macroscopic object can be in superposition, than our eye, our brain can be..... hmm... but we do not observe superpositions in real world.... well, there has to be some limit. $\endgroup$
    – F. Jatpil
    Commented Feb 11, 2020 at 14:43
  • $\begingroup$ @David Z: You say "you don't identify the slit" basically that "you" doesn't mean consciousness? If there is no "you", then there is no collapse of the wave. For example if you store that information in a way a human can't figure out, then it will not collapse the wave. And the reverse is true. What if you put a cat inside a box and show the result only to the cat inside the box? It will collapse or not? What if you remove the cat? (Note that nothing can see the result from outside the box) $\endgroup$
    – 07mm8
    Commented Mar 28, 2020 at 17:47
  • $\begingroup$ @07mm8 It's been a long time but I believe I was referring to the measurement apparatus, not a conscious observer. $\endgroup$
    – David Z
    Commented Mar 28, 2020 at 21:29
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No, quantum physics doesn't need consciousness, Hydrogen atoms were radiating their discrete line spectra long before consciousness evolved. The products of those emission events are only just reaching us now.

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  • $\begingroup$ Thanks all. So you're saying the consciousness connection is an oversold aspect of the theory. Perhaps shows the incompleteness or a lack of understanding of what's lies beyond our common sense. But I still don't see why well known scientists are making a big deal of it. By doing this, they just let the thing be hihacked by the religious. $\endgroup$
    – user17498
    Commented Jan 5, 2013 at 18:25
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    $\begingroup$ @user17498 Consciousness is not an oversold aspect of quantum theory, is not an aspect of it at all. I think 99 % of all sane physicist consider "quantum consciousness" as part of the crackpot domain I'm afraid. The logic is explained well in the introduction of this article: rationalwiki.org/wiki/Quantum_consciousness $\endgroup$
    – Heidar
    Commented Jan 5, 2013 at 19:51
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    $\begingroup$ Yes, quantum physics does not need consciousness; but IMHO consciousness needs quantum physics desperately but no one seems to be interested. $\endgroup$
    – Creator
    Commented May 9, 2017 at 21:26
  • $\begingroup$ How do you know that??? Atoms maybe did something and when we first observed the sky then the reality collapsed into state "atoms with excitation spectra and photons". $\endgroup$
    – F. Jatpil
    Commented Feb 11, 2020 at 14:37
  • $\begingroup$ @F.Jatpil strictly, I'm not aware of any experiment which has ruled out a rule of consciousness in QM. However there is also no reason to believe that consciousness does have anything to do with QM, as the results from QM can be understood without ever referring to "consciousness", which is a very ill-defined concept to begin with. (Is a virus conscious? A bacteria? A fish? There is no natural boundary here). There also has been no experiment which rules out the possibility that the wave function collapses whenever someone takes a poo. So you should believe just as strongly in consciousness. $\endgroup$
    – don't train ai on me
    Commented Feb 11, 2020 at 15:05
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In addition to David's answer I observe the following:

Too much emphasis is placed on the simple double slit experiment as far as the possibility of defining a wavefunction and the probabilities arising thereof. IMO the destruction of the interference pattern is due to the Heisenberg uncertainty relation, taking into account the slit separation and the measurement errors.

In a modified experiment with two slits

In a quantum mechanical two-slit experiment one can observe a single photon simultaneously as particle (measuring the path) and as wave (measuring the interference pattern) if the path and the interference pattern are measured in the sense of unsharp observables. These theoretical predictions are confirmed experimentally by a photon split-beam experiment using a modified Mach—Zehnder interferometer.

A similar experiment with electrons:

electron double slit modified

Electron buildup over time

These show in my opinion that the wave function, even if it is a complicated one, is truly a probability distribution for the statistical appearance of a particle, nothing esoteric about it.

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    $\begingroup$ Well, maybe a "little" esoteric, in that amplitudes for different alternatives interfere :-) $\endgroup$
    – twistor59
    Commented Jan 5, 2013 at 8:45
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As stated by @AnnaV @DavidZaslavsky and @Twistor59 there is none. In fact, you can formulate quantum mechanics without needing any observer. And this is good because, for instance, the interference pattern will be recorded by instruments even when there is no physicist at the lab. I recommend a modern textbook on quantum mechanics such as R. B. Griffiths' Consistent Quantum Theory. Some relevant excerpts:

Measurements play no fundamental role in quantum mechanics, just as they play no fundamental role in classical mechanics. In both cases, measurement apparatus and the process of measurement are described using the same basic mechanical principles which apply to all other physical objects and physical processes. Quantum measurements, when interpreted using a suitable framework, can be understood as revealing properties of a measured system before the measurement took place, in a manner which was taken for granted in classical physics. See the discussion in Chs. 17 and 18. (It may be worth adding that there is no special role for human consciousness in the quantum measurement process, again in agreement with classical physics.)

[...]

Both quantum mechanics and classical mechanics are consistent with the notion of an independent reality, a real world whose properties and fundamental laws do not depend upon what human beings happen to believe, desire, or think. While this real world contains human beings, among other things, it existed long before the human race appeared on the surface of the earth, and our presence is not essential for it to continue.

The idea of an independent reality had been challenged by philosophers long before the advent of quantum mechanics. However, the difficulty of interpreting quantum theory has sometimes been interpreted as providing additional reasons for doubting that such a reality exists. In particular, the idea that measurements collapse wave functions can suggest the notion that they thereby bring reality into existence, and if a conscious observer is needed to collapse the wave function (MQS state) of a measuring apparatus, this could mean that consciousness somehow plays a fundamental role in reality. However, once measurements are understood as no more than particular examples of physical processes, and wave function collapse as nothing more than a computational tool, there is no reason to suppose that quantum theory is incompatible with an independent reality, and one is back to the situation which preceded the quantum era.

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  • $\begingroup$ "there is no physicist at the lab" but the wave will collapse when the physicist goes to the lab, right? $\endgroup$
    – 07mm8
    Commented Mar 28, 2020 at 17:52
  • $\begingroup$ @07mm8 There is no wave and there is no collapse. $\endgroup$
    – juanrga
    Commented Mar 28, 2020 at 20:30
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The above answers are correct, in that arbitrary physical apparatuses will effectively measure the system under consideration via entanglement (which becomes decoherence in cases of uncontrolled entanglement) but they leave out something worth noting.

Namely, the only reason we have a "measurement problem" at all is that we are forced to answer the question "why do I see only one result, given that there are multiple branches?" MWI answers this by saying "hogwash, the various copies of you together see all of them." Collapse interpretations answer it with a collapse.

But regardless of which formulation you favor, it's useful to notice that the reason we're asking this question is because in some hard-to-define sense, it seems like you experience one outcome. If you try to make precise what you mean by "I experience one outcome," you will discover that you're trying to make sense of what (if anything) it means to be conscious.

One popular answer is that it's nonsense. Another approach is to take a look around and simply ask yourself: doesn't it sure seem like something is happening? Whether or not anything is actually happening (or it's just a trick of your brain), if it seems like anything, that's consciousness. Nonsense or not, you can in some useful sense be more sure of that than of anything else (including the existence of physical reality).

That's why many prefer to leave it to philosophy.

Ed Witten:

"I’m not going to attempt to define consciousness, in a way that’s connected with the fact that I don’t believe it will become part of physics. … And that has to do, I think, with the mysteries that bother a lot of people about quantum mechanics and its applications to the universe. … Quantum mechanics kind of has an all-embracing property, that to completely make sense it has to be applied to everything in sight, including ultimately, the observer. But trying to apply quantum mechanics to ourselves makes us extremely uncomfortable. Especially because of our consciousness, which seems to clash with that idea. So we’re left with a disquiet concerning quantum mechanics, and its applications to the universe. And I do not believe that disquiet will go away. If anything, I suspect that it will acquire new dimensions."

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It does not matter whether the observer looks at the observed system or not. This is because even if he does not look at it, technically he already observed the result because he is connected to the measurement apparatus via external medium (such as air of the atmosphere).

Only of the observer thoroughly isolated from the external medium, he can affect the experiment by looking at the result.

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