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Does Some Deeper Level of Physics Underlie Quantum Mechanics? An Interview with Nobelist Gerard ’t Hooft

The views expressed are those of the author and are not necessarily those of Scientific American.


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VIENNA—Over the past several days, I attended a fascinating conference that explored an old idea of Einstein’s, one that was largely dismissed for decades: that quantum mechanics is not the root level of reality, but merely a hazy glimpse of something even deeper. A leading advocate is Gerard ’t Hooft of Utrecht University, who shared the 1999 Physics Nobel for helping to assemble the Standard Model of particle physics (for which, rumor has it, another Nobel will be awarded tomorrow). He and I chatted over a lunch of beef goulash and maize stew, and I thought you’d be intrigued by what he had to say.

’t Hooft thinks the notorious randomness of quantum mechanics is just a front. Underneath, the world obeys perfectly sensible rules. In the models he has toyed with, those rules govern building blocks even more fundamental than particles. You’d see them only if you could zoom into the so-called Planck scale, which, according to many modern theories, is the smallest meaningful distance in nature.

One point in favor of such an approach is that far-flung particles can act in a coordinated way, which you wouldn’t expect if they were purely random. Yet the idea of a deeper level is deeply troubled. In the 1960s, Irish physicist John Bell showed that the degree of coordination among particles is too exacting for any deeper level of physics to explain. Bell argued that particles actively need to communicate with one another, which ’t Hooft’s models don’t allow for.

When I first chatted with ’t Hooft for an article eight years ago, he told me he wasn’t sure how to evade Bell’s reasoning. Since then, he has sought to jump through a loophole known as superdeterminism. It’s a weird and downright disturbing idea. Only three other people I know support it, notably Sabine Hossenfelder of the Nordic Institute of Theoretical Physics, who blogged her views last week.

The sober way to put it is that physicists are never able to conduct a fully controlled experiment, since the experimental setup they choose is not strictly independent of the processes that created the particles. Even if the experimentalists (conventionally named Alice and Bob) live on Earth and the particles come from quasars billions of light-years away, they share a common past in the very early universe. Their subtle interdependence creates a selection bias, misleading physicists into thinking that no deeper level of physics could explain the particle coordination, when in fact it could.

The dramatic version is that free will is an illusion. Worse, actually. Even regular determinism—without the “super”—subverts our sense of free will. Through the laws of physics, you can trace every choice you make to the arrangement of matter at the dawn of time. Superdeterminism adds a twist of the knife. Not only is everything you do preordained, the universe reaches into your brain and stops you from doing an experiment that would reveal its true nature. The universe is not just set up in advance. It is set up in advance to fool you. As a conspiracy theory, this leaves Roswell and the Priory of Sion in the dust.

That said, one person’s conspiracy is another’s law of physics. Lots of things in the world seem conspiratorial at first glance, but are the result of well-established principles. The fact the moon spins on its axis at exactly the same rate it orbits Earth (thereby keeping the same face to us, or nearly so) is not the work of a cabal, but of laws such as the conservation of angular momentum. In the opening panel discussion of the conference, ’t Hooft speculated that some new law of physics might harmonize particles’ properties with humans’ measurement choices: “What looks like a conspiracy today may be due to a conservation law we don’t know about today.… It’s incredible until you find it’s mathematical necessity.”

What follows is an abridged transcript of our lunchtime chat.

GM: What’s the problem with quantum mechanics?

GtH: Quantum mechanics as it stands would be perfect if we didn’t have the quantum-gravity issue and a few other very deep fundamental problems. I want to understand what will happen to the Standard Model as we pursue higher energies, I want to understand what quantum mechanics is about, and I want to understand how gravity works. The suspicion is, probably, answers will come as a package. You can’t just solve one problem without touching the others; they’re probably related. Maybe you have to solve all problems in one giant stroke. If that’s the case, then you have a long fight ahead of us, because it’s going to be very difficult.

GM: Can you describe your theory?

GtH: The theory is that you have something classical underlying quantum mechanics, obeying totally classical laws of nature—classical, meaning it looks like solving the classical planetary system or billiard balls or anything large-scale—except that ordinary classical theories are based on the real numbers. I’m not excluding real numbers as a good basis for a classical theory, but I’m also considering other options, such as the integers or, even better, numbers that form a finite set. I think I need finiteness at all levels of an ultimate theory.

GM: That’s motivated by Planckian discreteness?

GtH: Yes. At the Planck scale, it’s likely that you only deal with Boolean variables and integers, because that’s what the holographic principle of black holes seems to be telling us—that the amount of information on the black hole horizon is actually finite.

GM: Last night, you gave an example of your underlying classical model as almost like a chessboard.

GtH: That’s just an example of a problem where the question is a perfectly classical question, the answer is a perfectly classical answer, but the way to get the answer is by using quantum mechanics. Quantum mechanics is just a tool—and an extremely useful tool. That’s the way I think quantum mechanics has to be looked at.

When I consider a classical theory, and I give it a quantum wavefunction just because I use quantum mechanics as a tool, that wavefunction automatically collapses when I do a measurement. When you do a Schrödinger cat experiment, the outcome of the cat will be either alive or dead, but never in between.

GM: So, in this sense, superposition is a mental construct, whereas the real world doesn’t really have that. We created a problem by our choice of this convenient tool of quantum mechanics to do our statistics for us.

GtH: Yes, there’s no superposition. The only superpositions are in our way of describing what’s going on. For very good reason: we can make transformations such that we can describe the vacuum as a single state. In reality, the vacuum is probably a very complex, fluctuating mode. If you make superpositions, you can make a single state look like the vacuum.

GM: I was quite taken by the examples you gave of how you can get apparently quantum behavior from a classical system. Do you think that our universe is governed by extremely simple laws that then become complicated because there’s so many degrees of freedom?

GtH: Well, that’s the hope. There’s no guarantee that it’s true. Nature’s laws seem to be so universal, with such a sense of internal logic in them, that maybe the ultimate law is very simple and straightforward.

GM: Do you think the very simple law should be a local law?

GtH: Basically yes. I think locality will be an essential ingredient. You have to understand why things happening here are independent of things happen there. If you don’t assume such a thing, then it gets a lot harder to understand how laws of nature are working. Then nature’s bookkeeping system seems to be complex again. I want a bookkeeping system that tells you what happens here just depends on a few bits of information right here.

GM: Apart from locality, what other basic principles are really vital?

GtH: Well, causality—the fact there’s a strict separation between cause and effect. I want a theory in which everything that happens has a cause. The decay of an atom is caused by deterministic laws. Today, we only know its statistical laws, but ultimately you should be able to point at a definite cause: this is why the atom decayed today. Something in its environment happened.

GM: Ordinarily, we think that Bell’s theorem would rule out a classical model. So, how do we overcome that issue?

GtH: Yes, that’s not easy. I do not have the complete answer, because whatever answer I think of, I am always the first to criticize. The only answer I can come up with today is that there are correlations all over, presumably because the entire universe started with a single big bang. Everybody in our universe has a common past, and so they are correlated. The photons emitted by a quasar are correlated with the photons emitted by another quasar. It’s not true those quasars are independent.

That could be the answer to Bell. You can do the exercise. You can ask about a source emitting photons and the ancestors of Alice and Bob. While the source emits photons, Alice and Bob have not yet been born. They are many, many light-years away from each other. Those ancestors—the atoms in them—eventually cause Alice and Bob to make their decisions. Those atoms are correlated with the atoms of the source. Everything is correlated with everything else—not a little bit, but very, very strongly.

GM: Did you ever meet John Bell?

GtH: I think it was in the early ’80s. I raised the question: Suppose that also Alice’s and Bob’s decisions have to be seen as not coming out of free will, but being determined by everything in the theory. John said, well, you know, that I have to exclude. If it’s possible, then what I said doesn’t apply. I said, Alice and Bob are making a decision out of a cause. A cause lies in their past and has to be included in the picture.

But most physicists refuse to consider that as an essential element, and I very well understand why. Once you have a physical theory, that tells you the outcome of a physical measurement based on what Alice and Bob decide to measure. If they measure this or they measure that, our theory should tell us what they will see. Our theory should not bother about why Alice and Bob make this or that measurement. That is perfectly natural for today’s physics. But then you will not be able to answer the question of what quantum mechanics is. You must realize that Alice and Bob are not making that decision out of free will. That free will is actually embedded in the complexity of the atoms in their brains. The world is so complex that nobody can predict what their decision will be, but nevertheless, whatever their decisions will be, they will be a consequence of the laws of nature.

GM: Most people can accept that our experimental decisions are determined, but the degree of freedom that determine them are usually taken as independent from the degrees of freedom of the system we’re studying.

GtH: Then you’re stuck not only with Bell’s inequalities, but more generally with the whole quantum picture of reality. So, I think you have to assume that Bob has made a decision not out of free will, but by some predetermined correlation.

In quantum physics, there’s a notion of counterfactual measurement. You measure what happens if I put the polarizer this way, and then you ask, what if I had it that way? In my opinion, that is basically illegal. There’s only one thing you can measure.

GM: What’s the current direction you’re taking in your research?

GtH: First of all, I’m writing things down. What I discover is, when I write things down, it forces me to think about things much deeper than I did in the past, and I get new ideas. Things I have in my mind sound very simple, but when you attempt to write them down, they become more complicated and force me to think about them.

Right now, I work on two projects. One is quantum mechanics; the other is quantum gravity. Conformal symmetry [insensitivity to absolute scale] is a much more important symmetry with quantum gravity than people usually think. So, I’m trying to build conformal symmetry into a theory of quantum gravity, and while doing so, for a moment I’ll forget the quantum mechanics problem. The reason we have scales today is because conformal symmetry is spontaneously broken. That’s why atoms have sizes and clocks have rates at which they tick.

For instance, the universe must have had a period of inflation—that was a period when conformal symmetry was working very, very well. The universe looks like it was in a mode when it was conformally symmetric for a while. How do we embed that in a proper way in the rest of our understanding of nature?

GM: As a student, you learn the full mathematical machinery of quantum mechanics and the usual interpretation that goes along with it. What caused you personally to begin to question that? So many students don’t question that.

GtH: I’m asking questions all the time. One of the questions I’m asking all the time is: Are we doing things right? Am I doing things right? The books that I read, are they correct? Maybe I’m wrong in some basic way. I know that I’m not entirely correct because I haven’t got the correct theory. But I continue asking questions.

George Musser About the Author: is a contributing editor at Scientific American. He focuses on space science and fundamental physics, ranging from particles to planets to parallel universes. He is the author of The Complete Idiot's Guide to String Theory. Musser has won numerous awards in his career, including the 2011 American Institute of Physics's Science Writing Award. Follow on Twitter @gmusser.

The views expressed are those of the author and are not necessarily those of Scientific American.





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  1. 1. gs_chandy 9:50 am 10/7/2013

    The ’cause’ of some effect or occurrence in a complex system is very difficult for our limited minds to discover (with any degree of certainty). It is generally quite possible to find out, to a *reasonable* extent, the factors that may have “CONTRIBUTED TO” to the effect or occurrence.

    It strikes me that physics should now start thinking in terms of “CONTRIBUTORY FACTORS” rather than only “CAUSATIVE FACTORS”.

    –GSC

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  2. 2. vladimir tamari 10:59 am 10/7/2013

    It is refreshing to find someone of Dr.’t Hooft’s standing question the weirdness and unrealism of Quantum Mechanics to seek a deeper order. But explaining Bell’s results and entanglement may not need going out on another spooky tangent: Although I am far less qualified, I have long been considering the concept of sub-atomic building blocks, a self-assembled universal lattice of dielectric nodes out of which everything, space, matter, radiation and dark matter and energy is made.

    I found that in such a physically realistic and linear model randomness emerges through the diffusion of a wave pattern of angular momentum transferred from node to node within lattice. Beautiful Universe Theory: http://www.ne.jp/asahi/tamari/vladimir/beautiful_univ_rev_oct_2011.pdf Fix Physics! : http://fqxi.org/community/forum/topic/essay-download/1323/__details/Tamari_FQXI_2012_ESSAY_July.pdf . Ironically Einstein’s own concept of a point photon has created a false particle-wave duality, and Eric Reiter has recently experimentally proven it wrong: unquantum.net

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  3. 3. satchito 12:29 pm 10/7/2013

    Amazing!! Great interview, makes me wonder the degree of our connections with everything else.

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  4. 4. Aiya-Oba 1:08 pm 10/7/2013

    Great work on Nature’s stem logic. Wavefunction, superposition, and superconductivity all reflect absolute (nonlocality) state of Space-in-itself.
    Equator of self-contradiction, eternal oneness of pairness (superposition), is Nature’s absolute logic.
    Spacetime is simultaneouly relative and absolute as singularity of locality and nonlocality. Aiya-Oba (Philosopher and discoverer of Nature’s absolute logic).

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  5. 5. ilduche 7:20 pm 10/7/2013

    I have been trying to explain to my kids for years that it is entirely possible to control (on some level) the dice on a crap table. There are after all good shooters and bad shooters. This guys explanation of Bells Theorem covers it beautifully. Wonderful interview, thank you!

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  6. 6. CharlesRKIss 9:07 pm 10/7/2013

    I find the idea of a conservation law, that would preclude perfect knowledge, say of the Fundamental Law of Nature, very intriguing! And have never thought of such a correlation before, but had always imagined perfect knowledge as a contradiction; a redundancy perhaps. Anyway, to go no further on the topic, I’m surprised ‘t Hooft would believe what he says,

    ” For instance, the universe must have had a period of inflation…”

    This seems just far off, and an arbitrary belief to have. The enormous background dependence in cosmology really discourages me from believing in almost all the cosmological “musts”.

    I even fail to accept the Big Bang Hypothesis, since a universal origin seems to me the ancient relic of the Old Testament. This logic that demands an origin over an infinite time scale; what is it?

    Anyway, I digress. I’m just surprised at “Inflation” as a “must.”

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  7. 7. geojellyroll 10:08 pm 10/7/2013

    This is one of the better written and most intriguing articles on Scientific American this year. Thanks you.

    An aside. I’m a geologist and know little about physics at this level. Forgive my naivity.

    I’ve wondered (based on pure speculation) if in the near future if we may find evidence of life ‘elsewhere’ in the Universe not from signals gathered by radio astronomy but by channels of communication that may be taking place at a quantum level between various ‘intelligent civilizations’. Just perhaps a symetrical non-random underpinning of quantum happenings is the network for quadrillions of other intelligences. We may be on the verge (at least within a few decades or millenia) of being literally dumbfounded by what we are about to discover.

    Then again…perhaps there is nothing left to learn that is within the grasp of human understanding even in theory. Our physical senses and grey matter just can’t ‘get it’.

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  8. 8. geojellyroll 10:14 pm 10/7/2013

    RE the above. the quadrillion is a low number…not proposed by myself but a cosmologist that pointed out that if one in a million star systems in the Universe has intelligent life….that’s a quadrillion. Too spread out for much chance of any contact at a macro level.

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  9. 9. CharlesRKIss 10:27 pm 10/7/2013

    This is true.

    ” …if I put the polarizer this way, and then you ask, what if I had it that way? In my opinion, that is basically illegal.”

    And fascinating.

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  10. 10. Satya Narayan Tiwary 3:36 am 10/8/2013

    EPR paradox has proved that Quantum Mechanics is incomplete. In Quantum Mechanics, the most fundamental, basic, beautiful and powerful principle is known as
    Principle of Superposition. According to this principle, Quantum Mechanics is complete and incomplete both at the same time. It covers truth and untruth both simultaneously, hence it is weird, mysterious, bizarre and shocking. No body understands Quantum Mechanics.
    S. N. Tiwary, Director

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  11. 11. dadster 7:17 am 10/8/2013

    To assume or to seek a cause for everything and to every event or to every phenomena that you sense, is the most difficult path of enquiry any rational mind can take. It’s much simpler and easier to ascribe phenomena to the realization of spontaneous probabilities and random uncertainties under certain temperature presenter conditions and points of view and then carry on from that platform building up further. That’s Occam’s razor at work. Perhaps to get at the cause might be one complicated way but if it could be done by quantum tunneling ( or thought tunneling ) and arrive at the same shores that we would have , had we taken the boat of causation , then why grudge the tunneled out route? It’s like Kasparov arriving at the right move in a chess situation through his own intuitive reasoning and a computer arriving at the same move in that situation after going through all possibilities at the speed of light . Why should Kasparov bother or fault his intuition just because he took a short cut route to arrive at the same point !

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  12. 12. srbeck13 2:30 pm 10/8/2013

    With respect to “nature’s laws seem to be so universal, with such a sense of internal logic in them, that maybe the ultimate law is very simple and straightforward”: our logical thinking, like everything else about us, comes from evolution, in other words from the environment, in other words from nature. If a gene arose that made us come to a logical conclusion that did not conform to nature and we acted on that conclusion and if that action were harmful in our environment, the gene would not be passed to our offspring and that gene would be removed from the genome. So, logic doesn’t determine nature; nature determines logic. That is why nature seems logical.
    This also means that what seems logical is determined by the environment that we happen to have evolved in and not by some universal absolute. As far as I know no evolutionary adaptation is perfect. So even though most faulty logic would be harmful and not survive in our genome, some of our logic might be false and there might be no way to know.

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  13. 13. PacRim Jim 2:39 pm 10/8/2013

    Why assume that the universe consists of levels?

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  14. 14. Wayne Williamson 7:44 pm 10/8/2013

    Excellent…I hope it is pursued…I love the concept that everything is the point of origin(read big bang)

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  15. 15. neutrinoman 1:54 pm 10/9/2013

    We have to be careful about trying to scientifically study the actual sequence of events in the Universe. Modern Western science has been so successful in part because it works with idealized, repeatable types of situations in controlled experiments. Without that control, repeatability, and idealization, we’re trying to predict the actual events. This is why weathermen, financial analysts, and astrologers get no respect; they can’t deal scientifically with what they’re studying, at least not directly. They’re inside the system, or they can’t repeat in a controlled way — the difference between academic psychology (a science) and clinical psychology or psychiatry (a branch of medicine, always a art in the end).

    Quantum mechanics is not random, not at a basic level. I give you the initial state of the “state vector” or “state function” in a Hilbert space, you apply the time-dependent Schroedinger equation and predict how the state evolves. Nothing random there.

    It’s only when we try to extract “classical” information from the state vector (a classical measurement, say) that we run into trouble. Then “the wave function collapses,” and probabilities, based on the wave function, appear. This “collapse of the wave function” is some kind of mapping from the basic, deterministic quantum world to something else, a partially classical framework. If the quantum of action (h) is small enough, that mapping-to-the-classical turns into a different kind of determinism, the determinism of Newtonian mechanics or something similar, like classical field theory.

    Perhaps ‘t Hooft is proposing a nonlocal (or multilocal) determinism as a starting point. Breaking off a local piece, divorced from the whole, we get something that looks random, but isn’t.

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  16. 16. MrReality 4:11 pm 10/9/2013

    The truth that we have been seeking to explain the cosmos is much simpler than
    one might think. In order to understand the formation of particles and matter, we must come to understand exactly what space-time is. Albert Einstein assumed that the speed of light was a constant. He was wrong. The speed of light is merely a function of the medium through which it passes; just as the speed of sound is a function of the temperature and density of the atmosphere. The resulting logic dictates that space-time has a much higher energy state than the solid matter which exists within it. Space-time not only expands, but it also contracts. The fact that our planet exists within an expanding string of space-time skews our spectrographic analysis of the expansion theory. Our current assumption that space-time expands volumetrically is incorrect. Deep space mapping shows this effect. Most galactic formations occur along streams of space-time and resemble a neural network. In addition, all the dark matter which we observe from our telescopes only forms around vortexes in space-time we currently refer to as black holes, not a densely packed core of protons and neutrons. I hope you find my comments enlightening and thought provoking.

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  17. 17. egbegb 8:02 pm 10/11/2013

    As a Ph.D. in quantum physics (retired and long not a practicing quantum mechanic) I am interested in your views. There are much simpler things in life to aim your theories at. The first physical issue I can think of is the three-body problem. Another non-physical issue is “chaos” theory — or mathematical chaos as identified by Mandelbot. Both issues seem unpredictable forever. Irrational numbers also come to mind.

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  18. 18. tamir 12:01 pm 10/14/2013

    Ever since I encountered the transactional interpretation of QM and the notion of weak measurements, I felt a lot better about the theory as I find the Copenhagen interpretation to be problematic on many levels.

    Weak measurements are becoming a reality in labs around the world. As more evidence builds up for the physical reality of the probability function, the notion described in the article would have to somehow provide an explanation to its existence rather than dismiss it as a mathematical tool used for ease of notation and calculations.

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  19. 19. Wilhelmus de Wilde 5:50 am 10/16/2013

    The deeper layer of quantum mechanics is treated in my essay “THE QUEST FOR THE PRIMAL SEQUENCE” http://fqxi.org/community/forum/topic/1810.
    Gerard ‘t Hooft sais : “The cat is dead or alive” I assume that in between this two extreme states there are still a lot tones of grey.
    When we go down one layer after QM we enter at the Planck length and time, where there is no longer “before” or “after” so we are entering a non causal “dimension”, that I call TOTAL SIMULTANEITY, there everything is correlated with everything else, not a little bit but very very strong.

    Wilhelmus

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  20. 20. MrReality 9:49 pm 10/29/2013

    This will be my final entry on the subject at hand. The model of the universe that I have shared with you is not written in any current science books. Nor will you find it at your neighborhood bookstore. This is a new approach to understanding the world and universe around us. Mainstream physicists will have difficulty accepting that they have been led down an erroneous path. The next great discovery in quantum theory and particle matter will not be born out of a particle accelerator. Einstein was correct in stating that matter cannot be accelerated to the speed of light. However, matter can be energized to a higher kinetic energy in a static state. As I stated above, all solid matter is in a state of compression. All matter can be decompressed. It will require the construction of a new type of matter resonator. Here are the basics. Utilizing a super conducting resonating magnetic field based on the molecular structure of the object to be decompressed, the nuclei of the bonded molecules will reattach to their constituent electron fields given sufficient excitation. The bonding effect will render the object invisible to all instrumentation. It will have become space-time or “E” state matter. Once in this state, it will exhibit simutanieity and can exist in any location within the universe. Deenergizing the resonating field will again separate the electrons from their nuclei and restore the object. As always, there is more to the story. If you think you are ready to accept more revelations as to the inner workings of our universe, google the name “c.r.boretsky”. Prepare to be enlightened.

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  21. 21. David Brown 2:25 pm 03/28/2014

    “… ‘t Hooft speculated that some new law of physics might harmonize particles’ properties with humans’ measurement choices …” Could such a law be related to the explanation of the flyby anomaly?
    Does the Rañada-Milgrom Effect Explain the Flyby Anomaly?

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  22. 22. David Brown 5:31 am 04/22/2014

    “Quantum mechanics as it stands would be perfect if we didn’t have the quantum gravity issue and a few other very deep fundamental problems.” I conjecture that there are 2 basic possibilities for the physical interpretation of string theory: (1) As measurements approach the Planck scale, spacetime becomes higher dimensional and the Heisenberg uncertainty principle should be replaced by a more complicated uncertainty principle involving both hbar and alpha-prime. (2) Measurements are not options that approach a limit. Instead, measurement is a natural process that separates the boundary of the multiverse from the interior of the multiverse. Under all circumstances in which time, space, and energy are measured, the Milgrom-corrected Einsteinian field equations are empirically valid on average. In terms of measurement, the Heisenberg uncertainty principle is never replaced by a more complicated uncertainty principle.

    Link to this

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