What happened to Schrödinger’s philosopher cat, the most famous experiment in quantum physics?

Harald Ritsch/Science Photo Library

Harald Ritsch/Science Photo Library

The development of atomic physics questioned the image of the real that modernity erected on classical mechanics.

He established that deterministic explanatory models, which worked with perfect precision in the macro world, became inconsistent when the understanding of the micro world was delved into.

Thus, in establishing his famous indeterminacy or uncertainty principleWerner Heisenberg discussed the possibility of closed, mechanical causality in the realm of physics.

This dramatically broke with any closed explanation, in terms of unidirectional causes and effects, of the world.

How bad is uncertainty

The principle, formulated in 1925, indicates that the more precise the knowledge of the position of a particle, the more imprecise is the measurement of its mass and its speed, and vice versa.

Thus, the accuracy with which it can be measured is limited.

This does not depend on the apparatus used, which could be hypothetically perfect, but on the fact of measuring itself, because the measure of something depends on the way it is measured and not on the object measured.

Distance, for example, is indifferent to whether it is measured in kilometers or miles because this does not change it, but the result varies if one method or another is used and, with it, the valuation of it.

This does not nullify the validity of classical physics, but it qualifies its accuracy: classical mechanics it intends to work with perfectly measurable magnitudes, so it assumes that the exact measure of whatever it is can be known and in any of its aspects. Thus can postulate a deterministic and invariant view of the real.

The idea that the uncertainty principle actually overrides determinism has been questioned, but this implies the acceptance of a somewhat strange idea: that in reality there are no positions, masses or velocities of particles, only waves that are perfectly quantifiable through complex functions.

In this way, the indeterminacy of any system would only be apparent.

The idea, however, does not modify the intuitive problem of altering a system by measuring it.

Furthermore, the change from particles to waves does not solve the question of the epistemological closure of physics, as raised Erwin Schrödinger, who devised the well-known cat thought experiment in 1935.

Here is a cat locked up

Let’s imagine animal inside an opaque box equipped with a device consisting of a glass vial containing a volatile poison, and a hammer held on the vial, so that if it falls on it it will break it, causing the poison to escape.

To guarantee the self-sufficiency of the system, the hammer, in turn, has been connected to an alpha particle detection mechanism, so that if it is hit by one of them, it will activate and fall.

Next to the detector we place a radioactive atom with a 50% probability of emitting an alpha particle in the course of an hour. The box is closed and it is expected.

At the end of that hour, one of two possible events will have occurred: either the atom has emitted an alpha particle and activated the poison trap, or it has not emitted it.

In consecuense, the cat will be alive or dead. The interesting thing is that you cannot know what has happened without opening the box.

A conscientious scientist determined to ensure the predictive quality of what he does will want to develop a model that allows him to anticipate what has happened to the cat before seeing it with his own eyes. He will then resort to a formulation of the problem in the key of quantum mechanics.

A) Yes, the cat will be described by a complicated wave function that will be the result of the superposition of the two possible states combined at fifty percent:

A) Live cat.

B) Dead cat.

Applying quantum formalism something happens that leaves us perplexed: the cat would be alive and dead at the same time.

What is done then is to resort to the only positive way to find out what has happened: the box is opened. But when carrying out this check —measuring— the system is altered, since the superposition of states described in the function is broken.

At this moment is when, my savior, the blissful determinism imposed by common sense appears to indicate that, as the cat could not be alive and dead at the same time, it must already be alive or dead before.

But nevertheless, quantum mechanics is informing us of something more perverse: as long as no one opens the box, the cat will be in an undefined state, made up of the superposition of the two possible states: A or B.

This simply means that it is the form of control that is applied to a system that alters and determines it, because it modifies it.

There are multiple interpretations of this mental model.

The most basic is that the quantum interpretation shows that it is not as “obvious” as common sense indicates that the ultimate certainty about something can be reached, since there is an ungovernable probabilistic component.

Anticipate, not predict

An attempt has been made to overcome this paradox, in order to advance towards the idea of ​​a predictive model that allows us to know what is going to happen to the cat.

The most recent has been contributed by Zlatko Minev, a member of the team led by Michel Devoret at Yale: the “Quantum leap”, that is, the moment in which it is decided whether the cat lives or dies, it is not as abrupt as thought.

Although it was not observed experimentally until the 1980s, the idea of ​​the quantum leap is due to the Danish physicist Niels Bohr, being what happens when the quantum information of an atom or molecule is measured –called bit or qubit—.

In making this measurement, the atom “jumps” from one energy state to another and these jumps are known to be unpredictable in the long term.

What the Yale team has established is that, although it is not possible to make exact predictions about changes in a system, it would be acceptable to have a monitoring device that provides an early signal that a quantum leap is going to occur.

This would give physical coherence to any system under study and, ideally, could anticipate the death of the cat and even reverse it before it occurs (which, by the way, is paradoxical enough in itself).

In reality, this finding does not invalidate the usefulness of Schrödinger’s paradox, since it does not break with the quantum dogma that the future is random, nor does it alter the foundation of the indeterminacy principle.

It only indicates – and it is not a little – that it is possible to have a means that warns that a change is going to take place in the system under study.


Nobel Foundation
Danish physicist Niels Bohr.

Something similar to what happened to the fish on dates prior to the eruption of the volcano on the island of La Palma: Fishermen reported that catches had been dramatically reduced before the eruption because the fish had simply disappeared from normal fishing grounds.

Not that the animals knew there was going to be a volcanic eruption.

They simply anticipated danger by perceiving early signs, such as low-intensity tremors or subtle changes in the temperature and composition of the water, that are beyond human perception.


All this, and here comes the philosophy, opens new interpretive paths as far as the mind-body problem is concerned, they invalidate the presumption that dualism is necessarily a false, anomalous, or dispensable approach.

In fact, compared to what the supporters of reductionism postulate, neither is it absurd to be a dualist nor, in fact, it can be said that being one lacks scientific sense.

Schrödinger himself advanced some ideas in 1944.

Attracted by the enormous complexity observable in living matter, he proposed that, in relation to the behavior of this living matter, it was necessary to seek some different answer, since it should be accepted that, perhaps, it worked in an irreducible way to the ordinary laws of physics.

This does not imply that new physical laws must be discovered to explain the functioning of the living, but that the different superimposed systemic levels of which any organic activity is constituted modify, alter and alternate the deterministic and probabilistic processes that function regularly in inert matter.

How to explain consciousness then?

One can begin by accepting the existence of an immaterial soul as a symbolic-rational response to the fact of the plurality of manifestations of the conscious.

Historically successful solution, but with serious theoretical difficulties. And if not, ask René Descartes.

Another alternative would be to understand that consciousness is in intimate connection with the physical state of a limited region of matter, the body, on which it depends, and that, since there is a great plurality of bodies, there would be a plurality of consciences or minds, as many as people.

But this would get us into the problem of subjectivism and relativism.

That is, how would it be possible that people could agree on something with others, if we live trapped in our own conscience?

Unless, of course, an alternative compromise proposal was proposed, such as the so-called systemic emergentism (which we are going to leave for another day).

Schrödinger opted, third option, for a monistic-materialist stance when approaching the case, understanding that the mental was a mere epiphenomenon.

But this type of explanation is not entirely functional either, insofar as it requires a psychophysical determinism that its own paradox questions, since it prevents the anomaly inherent in psychophysical laws from being explained.

Turns out, her cat wasn’t just dead and alive at the same time.But he was also a philosopher.

* Francisco Pérez Fernández is pProfessor of Criminal Psychology, Crime Psychology, Anthropology and Criminal Sociology / Researcher, Camilo José Cela University.

* Francisco López-Muñoz is pTenured Professor of Pharmacology and Vice-Rector for Research and Science of the Camilo José Cela University, Camilo José Cela University.

BBC Mundo


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