The Effect of the Quantum Zeno Effect

Zeno of Elea (born 495 BCE) had been a thinker like few before and after him. Undoubtedly one of the most underappreciated philosophers of our recorded history, Zeno’s work has been effectively plagiarized by the likes of Isaac Newton and Albert Einstein — okay, not really, but his paradoxes have lived on through time (ironically) as a testament to the fact that time itself (as well as motion through time) is truly an illusion.

QZE, simply put, details the idea that the evolution of a quantum system can be slowed due to repeated measurements; similarly, other quantum theorists will and do apply this concept to the collapse of wave functions. It emanates from one of nine surviving paradoxes of Zeno of Elea which, together, sought to break down our understanding of time by revealing how illusory our motion through it really is.

But, more than anything, QZE epitomizes the endless dance between mind and matter — between consciousness and the physical world around it. Sadly, it harshly reiterates the fact that we humans are exceptionally limited in our perception and understanding of the world around us. 

And so I was more than happy to have the chance to pick the mind of someone who is well steeped in this discussion —physicist and author of Decoherence and the Appearance of a Classical World in Quantum Theory, Erich Joos.

The brief Q&A (presented below) served to affirm two points for myself: a) I’m in way over my head trying to discuss intricate concepts with physicists and b) we can’t really know what any of it means — which, I’ll happily admit, is somewhat of a relief under the shadow of the first point.

Here’s the truth of the matter —  as I see it: We’re not supposed to be able to zoom in close enough to see the odd happenings of quantum mechanics, but technology has superseded our abilities of observing the natural universe around us; consequently, it has led us to witness some of the most counter-intuitive and nonsensical occurrences that, try as we might, we can’t explain. 

And so what do we do? We guess. Mystics and spiritualists will try to squeeze such ‘spooky happenings at a distance’ into their interface of reality to signify that consciousness can influence matter or possibility; that we can entangle ourselves mentally or quantum tunnel through life’s obstacles to achieve unrestrained success. Similarly, technologists will use these findings for whatever digitized purpose they see fit (quantum computing, for instance, or highlighting simulation theory); astrophysicists will possibly see these happenings as cosmically fractal in nature when overlaid upon the macro-celestial world and physicists, like Erich, will simply see more questions than answers. 

We know one thing from quantum science — the observer effect is real and, in the realm of this discussion, it’s no less of a substantial element in the overall equation. This means something, we just don’t know what it means. 

In fact, the one thing that remains comically consistent is the fact that a true understanding of time itself remains so outrageously elusive. Time remains the enigmatic force that will maybe never show its face, causing us to wrestle with both its subjective and objective natures or taunting us to try and outsmart it by liberating ourselves from its perceptive clutches.

Well, this is where Zeno’s parables come in to say that, even after 2500 years, even with all the technology and mathematics and instruments of science, with our novel and modern understandings into spacetime or gravity or dark matter or quantum physics — we can’t. 

While it makes for a good kick in the pants of every generation throughout our evolution, it’s something that Plato, Immanuel Kant, Bertrand Russel and countless others since have come to acknowledge: we humans are tremendously limited in our ability to understand the nature of our reality — especially through sensory experience.

The QZE is a can of worms that I had been happy to open for the sole fact that it reiterated to me the limits of our understanding. Maybe the mystics are right, or maybe this all means nothing. Consciousness, time, matter — we should never get comfortable enough to think that we can even begin to understand how these all work and, especially, how they interact. 

Sometimes, we just have to acknowledge that we can’t know everything.

Q. Does the quantum Zeno effect convince you, yourself, that time (and our motion through time) is really illusory? As the philosopher Zeno sought to do with his paradoxes, are you convinced that our limited perception of time is inherently unable to understand time’s true nature? Or does this all mean something different to you under the umbrella of decoherence?

E.J.: Understanding the “nature of time” is an endless journey, where everyone starts from a different shore. In order not to be lost, I prefer to concentrate on a few aspects from a physicist’s perspective.

The “quantum Zeno effect” is a special physical situation where a “system” is “observed” very “intensively”. From a physical point of view, this means there is a strong interaction between the considered system which another one, which is usually called “measurement device”, but could be anything which interacts in a certain way. Then, from the very structure of evolution (in time!) in quantum theory (formalized by the Schrödinger equation), it follows that the normal evolution of the system may be slowed down and completely stopped in the limiting case of “indefinitely strong observation”. Of course such a limit cannot be achieved in the real world and is only a mathematical idealization. In a sense, the quantum Zeno effect is the limit of strong decoherence.

Not all objects are sensitive to the quantum Zeno effect. Of course — after all we see an evolving world around us. Staring a my pencil as it drops from my table will not stop it from doing so. It turns out, that in particular what we call “macroscopic objects” escape this effect, while typical “quantum systems” (nowadays called qbits) are very sensitive.

So from a physical standpoint there is nothing mystical about the quantum Zeno effect.

In this framework, time is still an external parameter (the Newtonian sense). If one wants to deal with time itself as a dynamical quantity, one enters the field of quantum gravity. There is no Zeno effect for time, but no time either in the equations (at the beginning). It takes some work, to find conventional “time” via decoherence in quantum gravity. 

As an anecdote, John A. Wheeler suggested the term “watchdog effect” a long time ago. Today “Zeno effect” is more commonly used.

Q. In a paper that you had written two decades ago regarding decoherence (Elements of Environmental Decoherence), you conclude that: “we should not be surprised, however, if it finally turned out that we do not know enough about consciousness and its relation to the physical world to solve the quantum mystery”.

You arrive at this conclusion after comparing two variable interpretations: An altered approach of the Schrodinger equation and a variant of the Everett Interpretation, noting psycho-physical parallelism as playing somewhat of a fundamental role in either case.

I’m curious to know if you’ve expanded on this conclusion and these interpretations since you’ve published this paper; if so, I’d like to know about how you currently perceive the psycho-physical parallels to exist and, if not, do you think that we’ll ever be able to know enough about consciousness and its relation to the physical world to, as you say, solve the quantum mystery?

E.J.: Soon, after the proceedings you mentioned, an important paper by Max Tegmark appeared. He studied decoherence in the brain and showed that decoherence is very strong for typical processes in the nervous system. This led to chapter 3.2.5 in our book about “decoherence in the brain”. I think this is one of the most important chapters of our book.

You will find there also some important quotations from von Neumann (about psycho-physical parallelism) and Einstein (in a discussion with Heisenberg).

One consequence of all this is that — as long as our subjective experience is “parallel” to certain brain states — under normal circumstances there is no chance of any “non-classical” experience, since all such states would be very unstable under decoherence and therefore could not be part of our experience. This is the same argument which shows that we will never find a true Schrödinger cat.

So it seems clear that the final “cut” between observer and observed can indeed be shifted deeply into the subjective observer without running into inconsistencies.

A still controversial part of the theory remains, however: this is the meaning of the Born probability rule. Is it a part of the “external world” or rather on the side of “subjective experience” of a branching observer? A traditional approach would be to change the Schrödinger equation, for example by adding some nonlinear terms to reach the Born probabilities. But this is not so simple as it appears to be, as any non-linearity easily leads to superluminal information transfer — not a thing we would like to allow.

My present feeling about these matters is that the old question about the meaning of probability, already an issue before we knew anything about quantum theory, is still with us.

Perhaps this question will finally be understood at the same time, when we will understand the meaning of quantum physics.

Erich Joos is a physicist and author of Decoherence and the Appearance of a Classical World in Quantum Theory