Descartes’ world was, at best, dualistic (Matter and Spirit); at worse, Monistic Idealistic (Spirit is fundamental)! It has never been Monistic Materialistic (Matter is fundamental) as it became, after 4 centuries of overwhelming implementation of the scientific method that Descartes largely contributed to create!

Descartes never denigrated spiritual matters as some scientists do today. He struggled with other philosophers to develop the phenomenally successful method that was meant to help them accumulate reliable knowings about our universe, in a time when this knowledge burst out mainly from philosophers and theologians intellectual ratiocinations, instead from objective and reproducible observations and experiments.

On the night of November 10, 1619, Descartes discovers his future life’s objective through 3 founding dreams: to apply mathematical philosophy to the study of the material universe.

It is strange to discover that the most subjective experience – dreams – is at the origin of the most objective methodology – Science! As expected, Descartes’ dreams are clear only to himself; somebody else won’t understand the message: there is a fundamental relation between Nature’s laws and the laws of Mathematics; logical reasoning and critical analysis of every knowing in order to understand our world the best we can, with the help of predictive models. To gather objective observations then apply mathematical tools to build a model satisfying all the observations; a model that speaks to our imagination and, therefore, helps us understand the world we discover around us. A predictive model which suggests new observations or experiments whose results would confirm our new understanding of Reality. Or invalidate it and bring us to look elsewhere an indispensable confirmation in order to reach the goal of the scientific method: a personal and reasoned conviction that we understood something essential about the world in which we live!

Not only Descartes hasn’t denied a spiritual reality, he didn’t consider it less important – less real – that the material world. He didn’t look for a method able to give us new knowings about the spiritual, only the material realm. He left the spiritual questionings to philosophers and theologians. And Descartes wasn’t really cartesian (see next post please) in the sense we give today to this word! Only very careful in order to help his young philosophy to thrive. One can discover this intriguing facet of Descartes through his correspondence with Elisabeth!

How is it that we turned from a Cartesian Dualism to nowadays’ Materialistic Monism?

After 4 centuries accumulating huge successes, after daily evidences of the extraordinary predictive power we achieved out of our understanding of the material world that let us use the energy concentrated in matter, create new species, recover from some genetic disorders, conquer the Moon or Mars… due to unending questionings on the material world brightened by the scientific method, we forget the context in which it was created. The present paradigm: Materialistic Monism, is understood today as a fatality coming from the non existence of the spiritual realm; 4 centuries of materialistic successes make us forget the fundamental postulate: the artificial boundary Descartes built between the two realms.

But this barrier crushed down with the beginning of the 20th century. Lord Kelvin’s “little clouds” he saw in the blue sky of our material world’s understanding, at the end of the 19th century, became devastating tornadoes after which we must build a new look on material reality. A new paradigm in which we’ll have to add in the material reality well described by Physics, properties we considered until today as entirely immaterial!

We discovered in our equations, mysterious links between objects studied here and now and their a-local and a-temporal counter-parties.

Particles at the bottom of our material reality seem to acquire the properties we attribute to matter, from a realm where only mathematical equations describe waves that propagate, superpose and interfere. Objects we see as independent aren’t really independent; an action on one of them affects the other through a reality that transcends space and time, a mysterious reality which seems fundamentally unified: a realm of information more so than energy or mass. A realm from which our material reality seems to burst; a somewhat Ideal realm as Platon intuitively discovered long ago!

The simplest model which includes these discoveries, albeit the more radical one maybe, seems to be Simulism. Everett’s Multiverse or Brandon Carter’s Anthropic Principle which are the most popular alternatives are more complex to accept and both don’t answer the question of the origin. How to build a Universe from nothing?! With Simulism the only thing to do is to run the Program!


«Everything we call real is made of things that cannot be regarded as real.» Niels Bohr.

As soon as Physics began exploring the world of fundamental particles – the MICROCOSM – it had to change its ideas about reality’s nature, on what we can know about it. Niels Bohr was one of the first to accept this conceptual revolution:

« Isolated material particles are abstractions, their properties being definable and observable only through their interaction with other systems. » Niels Bohr.

His intuition led him to the mathematical formalism that will initiate the most precise and the most creative scientific model ever. Yet it remains the most incomprehensible one because of its conflicts with common sense and the Materialistic and Realistic paradigm common sense progressively imposed to our culture.

« Anyone who is not shocked by the quantum theory has not understood it! » Niels Bohr.

Physicists try to understand the many chocking anomalies accumulated since more than a century. They try to fit the experimental results to our consensual way to understand the material universe made out of particles with specific properties. A universe made out of particles whose properties can’t be changed without local interactions with them, particles with objective properties independent of the fact we’re observing them or not and that can’t change without being touched, heated, illuminated…

Serious problems appeared mainly when experimental results didn’t fit with one of the fundamental pillar of Cartesianism: the separation between observer and observed.

In order to be reliable, results have to be reproducible by anybody who acquire the material and intellectual means to do so. They should not depend on the experimentalist, only on the observed object’s properties. It is necessary therefore to avoid any dependency of the results on the experimentalist’s subjectives faculties as intuition, personality… Yet the mathematical formalism created by the fathers of Quantum Theory includes intimately the experimentalist’s choices as can be seen with the experiment described below.


The famous experiment made by Stern and Gerlach is described in my book (chapter B.4) and here. It clearly showed we had to change our understanding of the nature of the fundamental reality: the one of the microcosm.

The main quantum postulate forces the fundamental reality’s properties to take well defined values, to be quantified. In our world a gyroscope can turn on itself with its axis pointing in whatever direction; in the undefined microcosm (when it is not observed) an electron can do the same with its spin that can be compared to a rotational axis; it can point in any direction: no one is forbidden. But when it is observed, when it interacts with an apparatus, the theory says it could take only one out of two values from an infinity of possible ones.

SternGerlach1 - copie

The magnet deviates magnetic particles. On the right: the expected result if the microcosm behaved like the macrocosm. At the left the actual experimental results.

A special magnet is disposed on the path of electrons whose spins could point a priori in any direction. If this was true then we should see a figure full of impacts like the one at right in which the electrons are deviated in relation to the direction where their spin points to. But it is not what we find when we do the experiment. The electrons are deviated on two lines only, as on the figure at left. We’re led to conclude the electrons are only of two types: half have their spin directed UP and the other half have their spin directed DOWN. No electron are found with other spin directions!

Stranger yet. If we turn the magnet 90° left or right we expect that no electron will be deviated because their spin were directed either UP or DOWN: no spin was seen as LEFT or RIGHT as we just discovered.

But that isn’t what we find. The result is once more a figure composed of 2 lines, but this time the electrons have their spin pointing either to the RIGHT for half of them or to the LEFT for the other half! How this could be possible since we found lately that all the spins were directed either UP or DOWN?!

Still worse! What happens if we place 3 magnets one after the other?

The first magnet separates the electrons on UP or DOWN paths. We place the second magnet on the path of the UP electrons but with a 90° angle with the first magnet. Like just seen, we find half of the electrons qualified as UP after the first magnet now deviated to RIGHT, the other half being directed to LEFT. Everything happens as if the UP electrons at the first magnet’s outlet change their property in order to acquire a RIGHT or LEFT spin instead of the UP one they expressed just before!

What happens now if we place a third magnet ofter the RIGHT outlet of the second and pointing in the same direction as the first magnet? We expect it should not deviated electrons to DOWN since we selected the UP electrons at the outlet of the first magnet before leading them to the second one. But this is not what is discovered! We observe once more half UP and half DOWN electrons. It seems that we create the electron’s property at the time of the measure since we discover DOWN ones after we eliminated them after the first magnet! It is exactly what Niels Bohr predicted beforehand:

« Isolated material particles are abstractions, their properties being definable and observable only through their interaction with other systems. »

We can’t anymore declare that an objective reality exists out there, whose properties are well defined in the microcosm after which our macrocosm is built! Only mathematical wave functions can give us some informations about what happens in the microworld when it doesn’t interfere with our apparatus. In this mysterious world particles exist only under their wavelike identity, they superpose, add or cancel… It is only when observed, when measured or when they interact with each other that the “wave function” collapses and they acquire a quantified, well defined property, compatible with the experimentalist’s choices! As an example, the intrinsic spin property of an electron will acquire its value which will be dependent on the angle the experimentalist chose for the magnet! Objectivity: this fundamental quality of the scientific method, is no more what it was! The experimentalist and his/her apparatus can’t be independent of the process and its results! The observer is an intimate feature of the experiment and its results!

It seems like if we’re confronted to a new dualism. A realm with wave functions only, another in which these waves are perceived as well defined particles!


The most difficult thing to do seems to accept the overwhelming strangeness of the microcosm!

«Not only is the universe stranger than we imagine, it is stranger than we can imagine» (attributed to Sir Arthur Eddington or to J. S. Haldane).

«Of all the theories proposed in this century, the silliest is quantum theory… the only thing quantum theory has going for it is that it is unquestionably correct.» Michio Kaku.

«We have to give up the idea of realism to a far greater extent that most physicists believe today» Anton Zeilinger

Some very simple experiments we could realise in any lab fitted to do optics, lead to a very strange world!

Let’s gather a laser, some mirrors and two photon detectors.

Interferometres1 - copie

The laser is set to deliver one photon at a time; M1 and M2 are classical mirrors while MS1 is semi-transparent: it reflects one photon out of two and transmits the other, at random. We expect the detectors D1 and D2 to click alternatively depending on whether the photon will be transmitted (D2 will click) or will be reflected by MS1 (D1 will click). For each photon emitted one or the other detector will click, never the two at once. It is what we find. The photon behaves like a particle and takes one path OR the other.

Let’s now modify our settings.

Interferometres2. - copie

We added a second semi-transparent mirror MS2. In theory we could continue to expect half of the photons on D1 and the other half on D2. A photon that crossed MS1 could in theory, cross also MS2 and let D2 click, or it could be reflected on MS2 and let D1 click.

But it is not the results we find! This time only D1 clicks to 100% of the photons emitted by the laser and D2 doesn’t click at all! The only way to understand this result is to accept that the photon crosses the apparatus with its wave nature and not as a particle! It is the only way to build a constructive interference on D1 and a destructive one on D2. The wave arriving on D1 would have had the same number of reflexions/transmissions whether it has been transmitted or reflected by the mirrors (1 transmission and 2 reflexions: they will be in phase on D1 and will add)

construct - copie

When the wave arriving on D2 undergoes 2 transmissions and one reflexion if it takes the upper path, or 3 reflexions if it takes the lower one. This time the waves aren’t anymore in phase and will cancel each other.

destruct - copie

These experiments are clear illustrations of the wave/particle duality: the photon travels with its wave nature and expresses its particle nature only when detected on the counter. But where is this wave? In which realm does it travel? Not ours: the one where matter expresses the properties as we perceive them, with its mass, its limited speed rate…


Even if this conclusion was implicit since the origin of Quantum Theory, only recently did it arouse interrogations followed by experiments. Quantum Theory is so strange to our consensual paradigm that it remained ignored and often is ignored today.

Einstein struggled in order to demonstrate that the Theory was incomplete because it predicted results he considered as impossible: like a “spooky influence” of a particle upon another one, even if their remoteness banned any communication between them! But Einstein was wrong. Alain Aspect’s experiments showed it since 1982!

We just understood why only D1 clicks and never D2. This shows that they are correlated. And we would see exactly the same features if D1 and D2 were separated by huge distances, even if they were separated by whole the Galaxy! The following experiment stresses even more the strangeness of these conclusions.

Interferometres3. - copie

We added the mirrors M3 to M6 such that the UP path could be extended in relation to the DOWN one. As we extend the UP path we’ll see less and less clicks on D1 correlated with more clicks on D2! At some time only D2 will click and no photon will be detected on D1. While extending progressively the UP path we see COORDINATED reactions on D1 and D2: when one clicks less, the other clicks more until it reaches 100% then diminishes until 0% and so on.

This is a logical result if we accept that the photon travels at once on the 2 paths according to its wave nature, then adds or subtracts the 2 waves’ amplitudes when reaching the detectors, according to the phase differences. The results aren’t anymore 100% or 0% as before, but vary gradually between these two limits since we can change progressively the difference in the UP and DOWN paths. We could for example find 30% on D1 and 70% on D2 (see below a measure taken with a phase difference illustrated by the vertical line “B”); there is a correlation between the 2 detectors.

Interferometres4. - copie

When we change the distance followed by the UP ray thanks to the mirrors M3 to M6, we change the phase of the UP wave related to the DOWN one; one goes, for instance, from the situation where the 2 waves are in phase (line “A”), to the one showed with the line “B” where D1 will react about 30% and D2 for 70% of the time. The 2 detectors always remain coordinated, whatever the distance between them!

Again, this result will remain the same even if the distance between the detectors is so great that no communication could travel between them. A mysterious link joins D1 to D2 outside the world we perceive as real because the objects in it have mass, a place in space and react only to events mediated by energy transfer. But the photons with which we imagined our experiments seem to travel instantly across the space between D1 and D2 in order to secure a coordinated result and obey one of the most fundamental laws of Physics: Energy Conservation. If a photon has been emitted by the laser, then a photon must be detected! It looks as if matter’s properties that are, for us, at the origin of all objective reality, are intimately linked to mysterious properties that we can’t access outside mathematical formalism: wave functions notably. The wave functions expand across an immaterial realm since objects behave as if they weren’t submitted to imposed restrictions coming from physical parameters as we perceive them in the material realm.


Our material world is made of particles, most of which have mass, that are local (detected in a precise place in space) and linked to time (they eventually change their location in relation with time’s flow). But this world seems to be mysteriously linked to another one, a realm in which the particles’ properties seem to follow the waves function’s mathematical formalism out of which they “collapse”! In this mysterious world space and time aren’t the same as in ours. There is a dualism: a material world that we perceive, linked to another one, immaterial since matter isn’t in its particle nature and has no mass-energy.

Now we can analyze and compare these two Dualisms; Descartes’ one and the other, brought by Quantum Physics. It will be the subjects of a later post.

A video from the physicist Antoine Suarez explains the experiments that underly this new Dualism. But he doesn’t name it like that! Another video from Antoine Suarez describes the experiment that showed that the realm of waves is a-temporal.

Bibliography: Andrew Truscott et Roman Khakimov published: A. G. Manning, R. I. Khakimov, R. G. Dall, A. G. Truscott. “Wheeler’s delayed-choice gedanken experiment with a single atom.” Nature Physics, 2015; DOI:

An explanation of this experiment can be found here.

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