Cause, effect and time

In a previous post, about the book ‘The Idea of the World‘ by Bernardo Kastrup I wrote:

'A universe with only matter offers no explanation whatsoever for the fact that the detection of the slit that was passed, has an effect back in time. That is because the ultimate cause of the disappearance of interference – the manifestation of the photon in one of the slits – must have occurred before the moment of detection of the slit passage.'

A reader stumbled upon this piece of text and rightly so. In my reply to her message I promised to pay extensive attention to retrocausality, cause and effect, as manifested in delayed double-slit experiments. So here’s my attempt to clear things up.

Interference and the double slit

Double slit interference. © Joerg Enderlein

First, let’s look at the common double slit. Whether photons, electrons or buckeyballs of 64 carbon atoms are fired at it, the result is always interference. That’s because these objects pass, in the form of a quantum wave of a certain frequency and wavelength, through the double slit on their way to detection. In both slits, a separate but synchronous wave source is created for each passing object. Those synchronous waves coming out of those two slits will amplify or cancel each other out in certain places.

In Figure 1, the two waves will amplify each other along the dotted lines. The mathematical interpretation of a quantum wave is that those maxima represent the locations of the highest probability that the object will be found there during measurement. On the screen behind the double slits we observe a pattern of light and dark bands. This is not the result of one particle. To get such a pattern, you have to fire at least thousands of particles, where all of them have the same wavelength, at the double slit. This a pattern is the result of interference.

Figure 1 – Origin of the interference pattern behind the double slit.

Observing the slit

The wave therefore always passes through both slits. If we now set up the experiment in such a way that we can observe through which of the two slits each object passes, something remarkable happens. Each particle wave then adapts in such a way that it only appears in one of the two slits. The probability of finding the object in that slit on measurement has become now apparently 100% at the location of that slit. The wave will proceed now beyond the slit. A wave coming out of one slit cannot interfere with itself. Figure 2 show the result when we measure through which slit the object passes. In figure 2 the object passes through the left slit. But the probability of passing through the right slit is of course equal. Only one single wave for each individual object will now leave one of the two slits. The result on the screen is now a spread out spot right behind the middle between the two slits because the individual objects pass the slits alternately. What we see actually is the superposition of two spread out spots of light.

Figure 2 – Observing the slit – no interference. The particle manifests itself in one of the two slits. The pattern on the screen is the summation of the light received from the two slits.

Entangled photon pairs with shared information

Observing the photons at the slit is done by first entangling two photons and then sending one, the signal photon, through the double slit. I describe this experiment in my book in chapter 7 – The delayed choice experiments. Because of this two-photon entanglement, the state wave of the other photon, the idler, has information about the slit through which the signal photon passes. The idler state wave thus possesses information about which slit is being passed. When that information is irretrievably erased the result is interference fringes as in figure 1. If that information is not erased the result is a single spread out spot as in figure 2.

The quantum information eraser

Whether or not information is erased is done by sending the idler photon through a semi-transparent mirror. Passing or reflecting is a fundamentally unpredictable quantum process with a 50/50 probability distribution. When passing, the information is preserved, when reflecting, the information is erased. In the first case, information preservation, the experimental result of a beam of signal photons is indeed a spread out spot, in the second case, information erasure, we see a clear interference pattern.

So far, it’s already an important and hopefully now better understandable quantum experiment. Whether or not information is erased determines the pattern that appears on the screen behind the slits. The real interesting thing now is that we can place the semi-transparent mirror – the information eraser – so far away that the signal photon has already passed through the double slit long and wide, at the moment the idler hits the semi-transparent mirror where randomly is decided to pass (keep information) or reflect (delete information). Even in this set-up, the experimentally measured result is that the interference fringes either do or don’t appear, when the information is respectively either erased or not. This is even true if this random erasure happens in time after the wave of the signal photon has already passed the double slit. The causation of the interference pattern, the manifestation of two synchronous waves or of a single one, happens therefore in time after the slit passage.

Figure 3 – Time line for the two-photon quantum information erasure experiment. Information is erased in time after the moment of having either two waves or a single particle having manifested in the slits. Retrocausality?

Retrocausality? Or an observer effect?

This therefore appears to be an effect with a retroactive effect in time, retrocausality. Study the timeline in Figure 3. Another interpretation, which is the one I prefer, is that the quantum wave of the photons becomes entangled with the measurement setup and that the real quantum collapse, the manifestation of the measured object, only happens when the observer sees the view results. See figure 3 again and consider what it is implicating.

Missed opportunity?

This experiment, Random Delayed-Choice Quantum Eraser via Two-Photon Imaging, was done and published in 2007. The results confirm the apparent retrocausality. However, what I did not find in the description of the experiment is the idea of moving the information-erasing semi-transparent mirror further away so that the signal photon has already been detected as the idler hits the mirror. The event of the photon hitting the detector, conform either the interference pattern or the spread out light spot, would already exist before the idler hitted the mirror. That would confirm even more convincingly that the quantum collapse is ultimately an observer effect and that it is not an effect of the measurement set-up. A missed opportunity.

Cause, effect and time thus become something created by the observer.

I hope this has made the cryptic text at the head of this blog text a lot more understandable. Comments are always welcome, they are the source of clearer texts.

A reaction on a reader comment.

What is information? What is observation?

Those are the hard questions in quantum physics:

What does it mean to observe? When is something observed? What is an observer?

What is information? When do we ‘have’ information?

They seem simple words used and understood by everyone. Apparently they are not.

As far as I’m concerned, everything that enters my consciousness as experience is an observation. Whether I do that directly with my physical senses or whether I use on the other hand a giant instrument like the Large Hadron Collider in Geneva for my measurements, in both cases I receive information about the world. And ultimately always through my physical senses. Only when that information manifests itself in my consciousness can I say that I have been given information and that I understand what it means. In the same process, history is recorded, and time.

In the case of the described experiment above, the information about the result will be stored on a hard drive in a computer. These bits are processed by a computer program so that it can be displayed on a screen. The experimenter observes the result on his screen as little dots of light. Or it can be printed on paper, after which the experimenter views the results. In both cases, only then the information does enter the consciousness of the experimenter and becomes history that can be shared with other observers.

When is information irretrievably lost?

Now what does it mean when we say that the information is lost? If that information has already been observed, then as far as I am concerned, it has not been lost, even when the information has been erased from the hard disk after being observed. In this type of experiment it is a requirement that the information present in the entangled and unmanifested quantum wave is so irretrievably lost that the probablity that it can ever reach an observer somewhere in the future is absolutely zero.

In all the experiments I’ve read about it, the information is lost before the quantum wave will reach the detector. A semi-transparent mirror is very suitable information erasure device. It can be set up in such a way that:

  • only when the quantum wave passes it, the wave will reach the detector.
  • when reflected the information, that was contained in the unmanifested quantum wave, gets lost, erased.

The erased information can then never reach the observer. If, on the other hand, the wave passes the semi-transparent mirror, the information is still contained in the entangled wave. This wave reaches the detector, which in fact also consists of a complex of quantum waves. So, the detector and the quantum wave become entangled. That entanglement then extends to the computer to which the detector is connected and only ends with the observation by the experimenter. Only then will the information contained in the – now with the instruments entangled – quantum wave enter consciousness as an experience of the experiment. This is in fact John van Neumann’s projection postulate that – despite its inherent mind-matter duality – I still find the most plausible explanation for the so-called quantum collapse. Apart from the idealistic interpretation of quantum physics.

If we want to know for sure that it is by the information that eventually reaches the observer that the quantum collapse occurs, irrevocably destroying it can of course also be done by ensuring that it does not end up on the hard disk of the computer. Or immediately and irretrievably deleted. That seems also pretty irrevocable to me. I describe such an experiment in my book Chapter 13, Falsifiability of the Consciousness Model, section ‘Adapted Quantum Eraser’. Or look on this website: ‘A true quantum information eraser‘.

Quantum Physics is NOT Weird – Available now on Amazon

After a year of translating and editing efforts the Enghlish edition from my book is published. It is now available at I’m quite proud of it.

From the back of the cover

The materialistic Newtonian model of the world is an excellent and extremely powerful scientific tool. However, when it is the only tool that we allow in our search to understand the universe, it becomes a confusing stumbling block. If you allow a hammer as your only tool, everything you encounter will start to look like a nail. In a lot of articles and books popularizing physics by ‘hammering’ physicists and physics writers it seems obvious that Newton’s objective material reality is still unrefuted in their way of thinking, and often precisely when it concerns quantum physics. This leads to literally incomprehensible statements, like particles being also waves and traveling physically every possible path. Trying to preserve Newtonian materialism as the only allowed description of reality ensures misinterpretation and clouds our minds in quantum confusion. Notably when the mind of the observer enters the stage. All the important interpretations of quantum physics are treated extensively in this book, either materialistic or consciousness oriented. It is up to the reader to make his or her own informed choice between them. No mathematics needed.

For a quick look at the contents: Quantum Physics is NOT Weird; The Contents

The Idea of the World, according to Bernardo Kastrup

After we came out of the church, we stood talking for some time together of Bishop Berkeley’ ingenious sophistry to prove the nonexistence of matter, and that everything in the universe is merely ideal. I observed, that though we are satisfied his doctrine is not true, it is impossible to refute it. I never shall forget the alacrity with which Johnson answered, striking his foot with mighty force against a large stone, till he rebounded from it – ‘I refute it thus.’

James Boswell: The Life of Samuel Johnson

Kastrup’s book is not for easy reading. Each sentence must be mentally uncompressed like a zip file. You really need to have a few concepts from philosophy at the ready. However, when you persevere, his reasoning proves crystal clear and it is not easy to find fault. I think it is worth discussing his arguments here because they are surprisingly close to my idea of the world and to my interpretation of the message of quantum physics. At the end of my book I arrive at the same view of the world as Kastrup. I champion the idea there of ​​a cosmic consciousness that ‘dreams’ this universe with us as actors in it, just like we can dream complete worlds in our sleep that are usually experienced as ‘real’ when in the dream state. Comparing Kastrup’s book with mine, in my book I do slowly peel away all the layers of the way we were taught that reality is put together, eventually arriving at Idealism. Kastrup however, goes straight to the heart of the matter – Idealism – starts from that position and then argues why that is a better and more fruitful view of reality than Physicalism.

The idea of a dreaming cosmic consciousness is essentially identical to Bishop Berkeley’s Idealism. Kastrup argues that Idealism provides the best explanation, needing the fewest ontological assumptions, for a large number of phenomena for which Physicalism is unable to provide any explanation. There are also various phenomena that even contradict Physicalism.

Any interpretation of the world, both Idealism and Physicalism, is ultimately based on a number of unprovable metaphysical assumptions. The less assumptions, the better seems to be a good starting point for a sensible choice between the two. Let’s take a look at the pros and cons for both systems and immediately register whether we can somehow be sure whether the premise is correct or not and whether it is consistent with experimental findings.

Physicalism, the problems

According to Physicalism, the world exists objectively and permanently. There exists only matter. Everything has ultimately a material cause. Our consciousness has to be a product of matter, an emergent epiphenomenon. But how can we actually justify that view with hard evidence? Remember that, without exception, the world presents itself to us as experiences appearing in our consciousness. Only at the exact moment they appear in our consciousness, those experiences become real to us. Experiences that appear in our consciousness are the only phenomena where we can unequivocally say that they are real. However, we can in no way assure ourselves that the source of our experience existed objectively and physically before it appeared in our consciousness as experience.

Samuel Johnson’s experience of his foot hitting the large stone is an experience within his consciousness. Not outside. So, it proves nothing. The fact that we agree with other people that something occurs in the world seems an argument for its objective physical existence but that is ultimately also an experience within our consciousness and thus cannot prove its objective existence. In a dream someone in your dream can confirm that he also sees what you see. But his confirmation turns out to be empty when you wake up.

Physicalism and quantum physics

Physicalism , according to its material premise, has to assume logically that consciousness is a product of matter because there is only matter. An emergent phenomenon of neural activity. However, consciousness as an emergent phenomenon of the brain does not explain the puzzling discovery of quantum physicists that observation does influence the outcome of observation. Even back in time. This is the logically inescapable conclusion of the so-called delayed-choice experiments, such as those by Scarcelli, Zhou, and Shih in 2007. For a detailed description of their experiment and the logical conclusions, I refer to my book, Chapter 7, Delayed Choice Quantum Eraser – 2007 version.

A universe with only matter offers no explanation whatsoever for the fact that the detection of the slit that was passed, has an effect back in time. That is because the ultimate cause of the disappearance of interference – the manifestation of the photon in one of the slits – must have occurred before the moment of detection of the slit passage.

Time line for the two-photon quantum information erasure experiment. Information is erased in time after the moment of having either two waves or a single particle having manifested in the slits. Retrocausality?

And that is by no means the only experiment where Physicalism is incapable of explaining. All Bell experiments to date have shown with increasing confidence that the measurement on particle A – although the location of that measurement is still far removed from the location of the measurement on particle B – fixates the result of the measurement on particle B. That happens before the measurement on particle A the state of neither A nor B existed. You cannot claim seriously that the particles existed already, however without their properties. Therefore I speak deliberately of measurements and not of particles flying apart, since we cannot speak of a propertyless existence of a particle before the measurement. Something that exists has by definition properties, right? Physicalism does not offer a solution.

On top of that, the quantum collapse, the appearance in the measuring instrument of the particle that immediately before the measurement existed as a coherent probability wave is still an unsolved mystery for which a really fundamental explanation has not yet been found by Physicalistic theories. Quantum decoherence offers no real explanation for the quantum collapse but offers on closer inspection just another label for this phenomenon. It explains nothing. It also does not explain how a non-physical probability wave remains coherent. Coherence – coherence – is a phenomenon that is pre-eminently explained physically. How probabilities – numbers – can form a coherent wave is still not explained.

Physicalism also involves non-contextuality. This means that the outcome of an observation should not depend on the way in which other observations are made at the same time. Non-contextuality is contradicted by the Bell experiments too. An experiment to examine non-contextuality was conducted in 2019, the provisional result of which again appears to have violated non-contextuality. For more on this I refer to my post: ‘The consensus problem in quantum physics‘.

Apart from those physical experiments, there are countless phenomena in the world that cannot be explained properly or not at all with Physicalism. These are therefore often considered impossible and written off on the basis of fantasy, illusion, deception, faulty research, anecdotal evidence and what more. The near-death experience (NDE) is a good example of this way of ignoring evidence. Incidentally, The NDE can be perfectly explained with Idealism, in fact, it predicts it.

The objections to Idealism

Idealism says this: there is only a universal consciousness in which reality as we experience it takes place in the same way as when we dream. Obviously within consciousness. The materiality and permanence of the perceived world is an illusion. Kastrup lists the main objections:

  1. The experienced concreteness of the world.
  2. The personal private character of consciousness.
  3. Does only perceived reality exist?
  4. My consciousness is incapable of adjusting the perceived reality.
  5. If the world is a dream how come we share it?
  6. What is the origin of the laws of nature?
  7. That phenomena take place outside our personal psyche is equally well explained by Physicalism. Why another explanation?
  8. How is it that what goes on in our psyche correlates with the observable processes in our brain?
  9. Why is it that, shortly before we make a decision, brain activity already increases? (Libet)
  10. Where is that immaterial consciousness when we are unconscious?
  11. Isn’t Idealism the same as solipsism?
  12. How did the Big Bang come about without consciousness?
  13. When I look at the universe, I see no consciousness there.

It will go too far here to go into all these objections. I refer to Kastrup’s book, part III: Refuting objections. But I will go here into objections 1 to 4:

  1. The concreteness of the world is also ultimately an experience within consciousness. A good definition of consciousness is ‘That which experiences’. By that definition, there is no way to experience the objective world without the involvement of consciousness.
  2. That we all experience a personal private consciousness is completely possible if every private consciousness is an independently functioning part (subroutine) of the universal consciousness, but which can only communicate with that universal consciousness to a very limited extent.
    • A technical example: Virtual computers within computers. The virtual computer has no direct connection to the hardware and cannot control it directly. I myself have a fully functional — and legal — Windows 10 running in a virtual environment on an Apple computer.
    • A human example: Dissociative Identity Disorder (DID – formerly MPS). Several personalities can reside in one person. An excellent example is the case of a woman who has both blind and sighted personalities. When the blind personality takes control, the visual brain centers are demonstrably no longer active. They become active when a non-blind personality takes control. Read: Sight and blindness in the same person: Gating in the visual system.
  3. That the moon only exists when I look at it, that’s impossible, it cannot be! However, what do we mean by “the moon exists”? When I look at the moon, I see it because a number of photons manifest themselves on my retina. Those are not the identical photons that someone else sees. The other person who notices with me that the moon is in the sky receives his own photons, not mine. The moment that seeing the moon is needed within my experiences, the universal consciousness will ensure that I receive the correct photons according to the image of the world that universal consciousness is constantly creating and according to patterns that we recognize as laws of nature. Think of VR glasses, if I put them on and look around (move my head) the VR projects the corresponding image. The image that corresponds to what should be behind me is not projected into the glasses yet, it does not ‘exist’ yet.
  4. If consciousness creates the world, why can’t my thoughts create the world the way I want? The simplest answer to that is that I – what I currently experience as I – am a split off part of the universal consciousness. So I’m a case of DID. That split fragment that I am is incapable of influencing the total picture of the world with an action of the will. That is shielded from my mind. Incidentally, it has been shown in countless parapsychological experiments that the mind of the observer influences reality. Also think of what is often reported when people are dreaming and start realising that they are dreaming but are not able to alter their dream very much. Still a dream is viewed as something that is created by individual consciousness.

For the other objections against Idealism I have to refer to Kastrup’s book. I can tell you that he convincingly deals with all of them.

Idealism versus Physicalism

Idealism makes metaphysical unprovable assumptions. You cannot avoid that. According to Kastrup:

  • Universal consciousness is primary. It is the ground of everything.
  • Universal consciousness must have the capability of self-excitation, like a string that spontaneously enters a state of vibration.
  • This self-excitation must be the source of every experience.

Defenders of Physicalism often point out – in the spirit of Samuel Johnson – that Physicalism does not require any metaphysical assumptions. Everything is already available. But this is not true. Where do the physical laws come from? Why does matter behave according to mathematical laws?

Quantum physics phenomena are explained by physicalists with the assumption of the quantum field. That is a field of potential that pervades the entire universe, constantly active at every point with virtual particles appearing out of nowhere and quickly disappearing into nothingness again unless it transforms – unpredictably – into a non-virtual – observable – particle.

  • The quantum field is primary, it is the ground of everything.
  • The quantum field has the capability of self-excitation. It continuously produces spontaneously virtual particles that are able to become objectively real.
  • That self-excitation is the source of every observation.

When you compare quantum physics with Kastrup’s idealism, what would be the most parsimonious hypothesis in this, thinking of the phenomena which Physicalism cannot explain?

Nothing but benefits

If you consider it for a moment, Idealism appears to offer excellent explanations for a number of phenomena where Physicalism goes astray:

  • The NDE
  • The surprising aptitude of mathematics to describe the phenomena in the world while mathematics is pre-eminently a product of the mind.
  • The fact that space and time depend on the position of the observer. That space can be curved. This indicates that space and time are a product of the mind.
  • Synchronicity. Events that have no causal connection but have a common meaning for the person experiencing the synchronicity. Stopping clocks at the time of a family member’s death is one that happens quite often.
  • The surprising precision with which the physical constants are aligned so that life is possible. A slight deviation from that would result in a universe without any life as we know it.
  • The quantum coherence in living systems that persists much longer than is thought possible.
  • The quantum efficiency of metabolic processes.
  • Etc.

And last but not least. Idealism also offers a significantly more hopeful message than Physicalism. The end of the physical body is not the end of consciousness. The universe is far from meaningless.