Double slit experiment interpretation

Part 2 - Interpreting the Double Slit Experiment

What is Light?

Variations on the double slit experiment have been done a great many times in numerous labs and in multiple ingenious configurations over many years and the results are very reliably established, verified and repeatable. Recent experiments have even eliminated the last of any very unlikely alternative explanations for the results and there is no real dispute over the observations. Some of the apparent contradictions the experiments show are:

Light can be interpreted as both a particle and a wave.

Observing the particle changes its behaviour.

A sequence of single light particles sent separately still display interference as though interfering with each other.

Observation of an effect at a greater distance and later time can change an earlier result as if time is being re-written.

Entangled particles affect each other instantaneously over any distance.

Don't break Causality

To interpret these results and draw some initial conclusions many of our assumptions about reality will have to be adjusted, but there is just one axiom that we can keep, which is that causality cannot be violated. Without causality flowing in the correct direction genuine paradoxes could exist and not be solvable. If things can happen before the event that caused them then anything is possible and nothing has to exist for a reason, i.e. with a history. That would break any understanding of reality and make no sense. Even in a multi dimensional universe, or extreme versions of space time, for causality to be reversed would seem to break the most fundamental logic. Chronology protection conjecture

So it must be an instantaneous event?

The experimental results suggest that a later event can have an effect on an earlier event, even if that effect is seemingly unmeasurable until later, intriguingly keeping causality intact. We need a solution where the earlier event cannot be affected by the later event even though the results seem to show that to be the case. There is only one solution to this conundrum, and that is that the events do not happen consecutively, but happen simultaneously. This has to be correct logically. Put simply, if the time from the laser to the screen is x and the time from the laser to the distant detector is y and logic demands that y cannot be greater or negative without breaking causality, then the only solution is that both x and y are equal to zero. Although counterintuitive because we always expect motion to take time, it is the only possible answer. With more evidence, it can be shown that it is likely to be correct.

Consider the passage of light. We know from special relativity that the faster something travels the less time it takes, and also that if something is travelling at the speed of light (speed of causality) the time it takes is zero. It can also be shown similarly that from the light’s point of view the distance travelled is also zero. In the delayed choice experiment the choice is seemingly ‘delayed’ by the fact that the detection is being made at a distance greater than that of the initial effect - the interference pattern. But that distance is being travelled at the speed of light, the speed of causality, so from the point of view of the photons, from leaving the laser to hitting the screen and also hitting the more distant sensors, no time has passed at all. Light is emitted at a source point, travels through space without any interaction, and can be detected at a destination. It does this from its own point of view taking no time at all and covering no distance.

The Speed of Light is NOT About Light | Space Time | PBS Digital Studios

Is light a simultaneous thing?

It seems that the particle's ‘wave function’ exists as a discrete event at a fundamental level where time hasn’t condensed out of a more basic reality. Could it be that for the photon, the events we perceive as separate are actually occurring in some way simultaneously - they are all a single 'thing'? Maybe time and space follow on from that ‘thing’ and we are making a mistake by interpreting it the other way round? If that is the case, then for the light beam it’s not any sort of logical problem for it to appear to react to the existence of the more distant sensors, the ‘observation’. The problem is only seemingly a illusion for us because we exist in a space where time is part of our reality - spacetime. Maybe the experiment is a glimpse into a deeper more fundamental reality, or perhaps an extreme dimension of our reality.

It seems a logical conclusion, and possibly the only conclusion? If we agree that causality cannot be violated and we also agree that the later ‘observation’ appears to us to occur at a later time, then there has to be an error in how we are perceiving that later time interval. For something with zero mass travelling at the speed of light/causality no time passes at all. Maybe even for photons travelling from a distant galaxy, they exist as a single event for which time doesn’t happen? Time perhaps is something that only happens outside their reality when matter moves much slower and has mass, our normal experience. It is well established in relativity theory that there is no ‘now’ for any point in spacetime. (The instant we perceive as ‘now’ in our own frame of reference cannot directly correlate with any other point in the universe. If you try to relate ‘now’ to a point in another galaxy, it can change by centuries simply through the effect of the relative motion of your timeframe.) So although unintuitive, it's possible that a photon can appear to travel across the universe in our perception of time but in zero for its own time and still not break causality in our reality. That would also suggest that time and space are not fundamental phenomena but are something that is condensed out of a more basic reality.

The Illusion of Time - How 'Now' is Relative

The Geometry of Causality | Space Time

It's ironic that if we never knew about the delayed choice interference effect but for some reason we theorised that photons might behave in this way - making connections outside our perception of time - the experiment we might design to prove the theory could be the double slit experiment. This concept needn’t lead us to suppose that we are in a deterministic universe though. Without finding a way to manage the concept of something outside time, we haven't got any logical framework to work back and use it to rule out randomness and freedom of choice inside.

The Interference Pattern - the Probability Wave

Experiments show that even single particles create an interference pattern when the data for many transits has been amalgamated. This is puzzling, but if the wave for a single particle is a probability wave of all its possibilities, (The Copenhagen interpretation visualises a probability wave travelling through space) the interference pattern must be being being caused by the particle wave interfering with its own possibilities. By observing or detecting, therefore terminating the probability wave on path A, the observation eliminates any probabilities from path B so the second slit is no longer available for the wave path and so the interference pattern disappears because none of the probabilities can use that path to interfere when the wave collapses. This concept is only difficult while we think of the photon as taking time to transit. If we see the transit as a single instantaneous event the paradox disappears. In every experiment, it can be shown that the interference pattern is the result of interference between only the possibilities that are available at the 'moment' of the transit event. If a detection has occurred on a particular path only the paths that were valid probabilities for that photon can and will interfere.

and a probability wave function combination with the probability wave driving the motion of the particle. But why even hold on to the concept of an actual particle if it is not needed? Suppose the creation point and the destination detection/observation point for a single photon are connected by the wave function which is a discrete event outside space time? The starting point of the wave function is the source and when it meets any non-transparent or non-reflective matter it terminates. For the wave function to continue its path it can traverse through transparent material or it can be reflected by a non matt surface, but at some point it interacts with matter that has neither of those properties and at that point the wave function associated with that particle terminates/collapses. It can be visualised as similar to the way in which ionised air molecules reach a charge point where a lightning bolt can track across; the wave function establishes the possibilities from the probability wave, defines a single path through space and time and as it does so the photon is observed/detected at the destination point. If the destination is not totally light absorbent, a new photon/wave function is emitted and this destination point now becomes the starting point for a new probability wave. This seems a logical way to reconcile the fact that light can be interpreted as both a particle and a wave. It would also explain the observations in more complex double slit experiments where several paths exist, but only one is actually used, yet subtle effects from the other paths can still be detected in the resulting detection. (PhysicsWorld.com: Physicists ask photons 'Where have you been?') So long as any path is valid, i.e. possible for the photon path, the resultant wave can have properties affected by interference from all potential paths as the probability wave will explore all of them but collapse on a single one. This creates the interference pattern, as all the possibilities of the probability wave are distributed according to their probability potential of condensing into reality.

Observation is the same as Detection

Despite confusion, there is nothing special about observation; it is the same thing as detection. You cannot observe a photon without interfering with or collapsing the wave because it is a fundamental phenomena, and so by definition there cannot be any related phenomena that can be detected, only the wave itself and so there cannot be any way of detection without interference. It is a misunderstanding to imagine you could observe a photon without interaction. For example, you could detect a train passing on a nearby railway line by sight, sound, vibration and many means without having any effect on the train itself, but suppose you had to detect the train and the only available method was by putting another train on the railway line? The concept that conscious observation may change the outcome of the experiment is just an illusion caused by our tendency to imagine incorrectly that we can observe the photon without interference, and also to assume that the later observation is somehow influencing an earlier event. Both these assumptions are incorrect.

Entanglement

It is possible to send photons through a BBO crystal that causes it to split into two separate paths creating particles with entangled properties. Perhaps what is happening is that it doesn't collapse the wave function but it forms a 'Y' junction? The energies of the two resultant waves are lower but they are still part of that single discrete wave function, so when it collapses/terminates it does so instantaneously for both paths and imparts the properties we observe. In effect, a probability wave collapses from multiple dimensionless possibilities into a single outcome which we observe as our reality, but for entangled particles the wave has several outcomes. For existing particles that are forced to become entangled experimentally what may be happening is that their wave functions are being merged and so become an extended part of the same wave function. It's no more difficult to imagine the collapsing wave to be a connection between three or more points then it is for two. This would explain how entangled particles have an instantaneous connection despite being apparently unconnected over any distance. It also explains how we use Qubits in quantum computers by uploading the many possibilities of computations into entangled probability waves to compute the results while in effect temporarily stepping outside time.

Quantum Entanglement & the Great Bohr-Einstein Debate | Space Time | PBS Digital Studios

that some details were left out for brevity. There wasn’t a screen, but a detector D0 being driven by a stepper motor. (Note the lens to focus.) Also, the phase shift of the two complementary interference patterns corresponding with detections at D1 and D2 is explained in the original paper as being due to the 50% beam splitting mirror: “... caused by the transmission-reflection unitary transformation of the beamsplitter BS”. This is due to the Hong–Ou–Mandel effect: “Physically, the beam splitter transformation means that reflection off one surface induces a relative phase shift of −1 with respect to reflection off the other side of the beam splitter”)

The coincidence counter monitors the detectors to decide which signals to associate with the same event and correlate the data. If the light path is to either D1 or D2 that would be an exclusive path that can only pass through one or other slit so there is no interference pattern. But if the light path is to either D3 or D4, it has a choice of path through either slit via the beamsplitter BSc so the probability waves interfere over both paths. That result seems to suggest that the source, destination and route are all a single event, and that seems to be a possible way to interpret it; the source emits, the destination is the collapse point, it occurs as a single event which we perceive as happening over time, but perhaps time is a consequence of these events and not a parameter within which they occur?

single universe which we inhabit. Every possible variation need not result in an outcome of every possible reality. So although there may possibly be infinite different universes, there is no need to theorise ours to be a many-worlds universe of continually evolving outcomes from every moment in which we exist. Just one may be sufficient. Perhaps even Wheeler's 'one-electron' universe might make sense if the electron doesn't have the necessity to loop both ways through time, but can weave a single timeless course?

Conclusions:

Light is not simply a phenomena within our reality but is something that creates the fabric of it.

A photon is not a particle but a wave.

The probability wave causes the interference pattern and its collapse resolves the possibilities into a single location. It does this as a single event not as a sequence of events.

It is all simultaneous. Light that travels from early in the life of the universe and terminates in the future is concurrent outside our perceived dimensions.

Observation and detection are the same thing.

Entanglement is the state of two or more particles sharing the same probability wave and its collapse is a single simultaneous event with multiple outcomes / locations.

Space and time are not fundamental. They are emergent from a more fundamental timeless reality.

The Many-Worlds Theory is redundant.

Perhaps it’s all the other way around?

The concept of light passing from point to point, emitting and terminating and doing it in multiple places and times, all apparently simultaneously is complicated. But by imagining it outside of what we know as reality, it actually becomes much simpler. If we turn our conceptualisation of reality inside out, we can view light not as something existing within our reality, travelling through space, but as something that is helping give rise to it.

Light and all other EM radiation could actually be existing as a timeless 'primordial fizz' and it is much more than simply a phenomena relating to, and inside of, our reality but is actually something more fundamental from which our reality emerges. Reconciling QM and GR is hard because of the difficulty of seeing the photons as fast moving particles in a slow moving universe. Perhaps this fizz is what is actually writing space and time and matter, through the framework of relativity? From the perspective of the fizz there are no fast moving particles, our entire universe and all of time is just a simultaneous event, a blink in infinity.

These conclusions might be considered as a ranging shot on the problem, but they are logical and probably not too far off target. They don't try to contradict any know facts, or invent any radical new theory, but simply are an attempt to analyse the evidence to find a rational perspective that might eliminate paradoxes, and to suggest that might be possible without the complications of retrocausality or invoking the many-worlds theory. For those still reading, let’s move on and explore if this hypothesis might correlate with other evidence. The interpretation and attempt at logical conclusions of the double slit experiment so far are based on sound observational evidence, but part 3 is more speculative and explores if the conclusions of part 2 might be extrapolated to offer possible explanations for other anomalies.

Credit: Wikipedia - Patrick Edwin Moran

The Delayed Choice Quantum Eraser

Wikipedia - Delayed Choice Q Eraser

In 1999 an experiment was carried out demonstrating that the interference pattern could be altered by a detection at a time later than that of the creation of the interference pattern, suggesting that time was seemingly being re-written, causality was being broken. It seemed that a later action erased the knowledge of which slit the particle had passed through. This is described in the PBS YouTube videos 3 & 4 listed previously. (It should be noted

Light

Causality

Simultaneous

Interference

Instantaneous

Duality

Observation

Entanglement

Delayed

Many Worlds

Particles?

Conclusions

Wrapup

Credit: Wikipedia - Christian Schirm

The Many-Worlds Theory is not needed

The Many-Worlds Theory is invoked to solve the causality paradox. If a later detection apparently changes an earlier event, the theory proposes that every possible outcome does actually occur and we find ourselves in the universe that contains the outcome we see. But if the events are actually simultaneous that idea becomes redundant as there is no paradox. Just as all the molecules and currents in a sea create one single ocean we can sail on, the oscillations in the primordial fizz could be writing the

Particle Wave Duality

Consider a photon. It is created at a light source and it is detected at another point in space but there is zero evidence of it in between. There cannot be or the detection/observation point would be the destination. The word photon is used as a convenient metaphor to interpret the observations by ascribing them to a particle, but an alternative model that fitted the observations could also be valid. Classical theory suggests that the photon is a particle that moves through space, but that cannot be correct as a single particle would not make an interference pattern as it could not interfere with itself. Pilot wave theory suggests that what might be making the connection is a particle

Credit: Wikipedia - Jean-Christophe BENOIST

Do we need Particles at all?

If this applies to photons, perhaps it applies to all particles, and if a particle can be interpreted as the collapse point of a probability wave - the point at which a new wave is created as a rebound of its energy - perhaps the particle isn't needed at all in the concept? After all, we never see particles; anything we know about particles is from observing the interaction with other particles. Maybe all matter is simply the transition point of infinitely looping collapsing and rebounding waves? Could everything we think of as particles be oscillating probability waves? Theory suggests that all ‘particles’ could be interpreted as energy waves. Mass, energy and gravity can all be explained relativistically in terms of massless particles and the particles can themselves be interpreted as waves.

When Time Breaks Down | PBS Digital Studios - Confinement gives matter mass and time

Even whole atoms can be shown to exhibit similar interference patterns but the effect disappears as mass increases. This is because their probability waves amalgamate the possibilities to a mean and so the positional uncertainty approaches zero. Quantum tunnelling demonstrates this uncertainty about position. The probability wave defines the possible positions in space over the path of the particle, but there is always uncertainty about position in the direction of travel as well as laterally, so for the occasional particle, its transit path can include the extreme positional probabilities of existing first on one side of a thin barrier, and next on the other side. (Imagine a game of snakes-and-ladders where you have to throw a one followed by a six to pass a run of snakes.) This gives the impression that it has penetrated through the barrier but it hasn’t, it’s just that two of the contiguous possible positions it can exist happen to have been on different sides and have become part of an improbable but valid path. This is strong additional evidence for the particle not being a particle at all, but a wave - a wave of positional possibilities.

Is Quantum Tunneling Faster than Light? | Space Time | PBS Digital Studios