My earlier discussion with Boda, and others, over quantum entanglement, has made me realise that I have
not made it explicitly clear, in my paper, "
A Direct Experiential Interpretation of Quantum Mechanics: How Madhyamika Philosophy Explains the Mystery of Quantum Physics," that Section 6 in my paper actually already deals with this issue. I have now amended this section of my paper to explicitly point this out.
So thank you, Boda, for making me realise this, and thus prompting me to add this explicit explanation into my paper. (The good thing about publishing papers on the internet is that you can still edit them long after they have been published!)
Since there appears to be a lot of interest (and it
is very interesting) in quantum entanglement at the present time (not just here on the forum, but elsewhere as well), I shall reproduce, here, the relevant section of my paper, which actually explains why we have the apparent "weird" effects of quantum entanglement, and how Madhyamika philosophy resolves the problem. (I will omit section 6.2 though because it only fills in the details of the delayed choice quantum eraser experiment, and is probably not necessary for understanding the "weirdness" of the experiment.) My apologies for it being very long, but I hope that this issue is interesting enough to warrant it.
6.1 The Delayed Choice Quantum Eraser and Quantum Entanglement
An innovative experimental set-up for the double-slit experiment, that is particularly appropriate for exploring the nature of the
quantum wave function, is an intriguing version of the experiment known as the delayed choice quantum eraser.
Recall that, in the basic double-slit experiment, a particle like a photon would pass through both slits if no measurement is made to ascertain which slit the particle went through. This is because, without a measurement being made, the
quantum wave function would not collapse, and the particle actually does not manifest as a single particle at a single position. The
quantum wave function would continue uncollapsed and represent merely a probability distribution of possible measurement findings
if and only if we make an actual measurement. Effectively, we can say that the particle is behaving like a wave and passing through both slits simultaneously, and would form an interference pattern on the screen, as a wave would do.
It is only the act of measurement—to ascertain which slit the particle passes through—that would cause the
collapse of the wave function and force the particle to manifest at one or other slit. If the particle did that, there would then not be an interference pattern on the screen.
Now suppose we do the measurement of which slit the particle passes through in an unusual and indirect way. First we can delay the choice of whether or not we make an actual measurement—that tells us which slit the particle passes through—until
after the original particle actually hits the screen. This can actually be done, and is what the phrase “delayed choice” refers to.
We can also do something even more unusual. Not only can we delay the choice of whether or not we actually make the measurement till after the original particle hits the screen, we can also delay the “choice” of whether or not the experimental set-up provides us, the observers, with the actual information of which slit the particle passed through. And this choice can also be made after the original particle has already hit the screen. This is the so-called “quantum eraser” part of the experiment, since the experimental set-up can act as though the “which-slit” information has been erased and cannot reach the observer.
The “delayed choice” and the “quantum eraser” aspects of the experiment can be achieved through the use of
quantum entanglement; in this case, through the use of entangled pairs of photons. Entangled photons have properties that are correlated in such a way that the
quantum wave function of each of the photons cannot be described independently of each other. Essentially they become one system. Because of this, a measurement of certain properties of one photon would provide information about the other photon.
In the delayed choice quantum eraser experiment, one of the photons in an entangled pair is called the
signal photon and the other is called the
idler photon. The basic strategy is to allow the signal photon to travel to the screen while directing its corresponding idler photon onto a different path. Then, only after the signal photon has already hit the screen, do we make a measurement on its corresponding idler photon in order to determine which slit the signal photon emerged from. That is how the
delayed choice aspect of the experiment can be implemented.
We can also arrange the experimental set-up such that some of the idler photons would encounter devices designed to “scramble” the information that it carries concerning which slit its corresponding signal photon emerged from. After this information has been scrambled, the observer can no longer obtain the “which slit” information from measurements made on the idler photon. This is the
quantum eraser part of the experiment.
This delayed choice quantum eraser experiment also illustrates the peculiar quality of
quantum entanglement, whereby the measurement of one of the entangled pair of photons actually appears to affect the other photon, as though a “message” has been sent between them, a “message” that is faster than the speed of light. In other words, the measurement made on one of the entangled pair of photons—in this case, the idler photon—appears to result in a “message” from the idler photon telling the signal photon that it has to now “decide” which slit it had passed through.
Here, the apparent “message” being sent to the signal photon, by having a measurement made on the idler photon, is even more dramatic than being faster than the speed of light. The “message” appears to have been sent backwards in time! This is because we have already allowed the signal photon to hit the screen before a measurement is made on the idler photon. That, in the first place, is why it is called a “delayed choice” experiment.
The measurement made on the idler photons, nonetheless, still appears to affect the pattern the signal photons leave on the screen, even though the measurement on each idler photon was made, every time,
after the corresponding signal photon had already hit the screen. So if we consider that a message has been sent by the idler photon to its corresponding signal photon, it could only have been sent backwards in time!
6.3 The Two “Weird” Things About the Double-Slit Experiment
A simple way to obtain an overview of the delayed choice quantum eraser version of the double-slit experiment is to look at the two “weird” things that would arise
if we were thinking along the lines of a mind-matter duality—i.e., where the object (the photon) is distinct from the mind (the observer).
It is important to realize that there are actually two things that are “weird” about this experiment. One weird thing is that, although the photon displays the properties of a wave (like producing an interference pattern), we only see a photon as a particle whenever we make an actual observation. This, as we know, is the
collapse of the wave function. To reiterate, before the observation, the
quantum wave function provides us with a probability distribution of where the photon may be found
if and only if we make an actual observation. When we actually make an observation, however, the photon is only found in one place. This is one of the two weird things about the double-slit experiment.
The second weird thing is this: If we now place a detector so that we can tell which slit the photon went through, the interference pattern disappears. It is as though, having a detector there, forces the photon to choose which slit it goes through. Now here’s the real peculiarity concerning this: we do not actually have to make an observation for the interference pattern to disappear. Just having the detector there will cause the interference pattern to vanish. It is as though the photon knows that we can spy on it if we want to, and that is enough for it to stop performing the “interference pattern trick.” All that is required is an experimental set-up that enables the observer to make an observation
if he wants to, and the interference pattern disappears. No actual observation at the slits is required. Also, if we remove the detector at the slits, the interference pattern reappears. So it is the experimental set-up that determines the result.
To make this phenomenon even more intriguing, we have the
delayed choice quantum eraser experiment, whereby the information on which slit the photon went through can only be obtained
after the photon hits the screen (this is possible through the use of
quantum entanglement). This does not seem to make any difference to the result, i.e. as long as there is the ability to tell which slit the photon went through, no interference pattern occurs. It is as though the photon realizes that we can determine which slit it went through after it hits the screen, and that is already enough to stop it from performing the interference-pattern trick.
To make things still more intriguing, if we now insert another device (this is the eraser part) so that it now obscures the information concerning which slit the photon went through, the interference pattern reappears. Now, it is as though the photon has found out that the information from our detector (that allows us to see which slit it went through) is now being scrambled by another device so that we can no longer obtain this information. That being the case, the photon is now happy to perform its interference-pattern trick again.
So what actually is going on? It almost appears like the photons know what we are able to do in terms of spying on them, and that these photons are conspiring to thwart us in our quest to determine how they are performing their tricks! Of course, no one actually thinks that the photons are sentient beings involved in an elaborate conspiracy to trick us, but that really appears to be what is happening. This is the second weird thing about the double-slit experiment.
All this sounds extremely strange, and that has, in fact, been the central mystery of quantum mechanics for over a century now. However, remember that, here, we have considered the findings of the double-slit experiment
in terms of a mind-matter duality. It is actually this mind-matter duality that led to these two so-called “weird” effects in the double-slit experiment.
Let us now, instead, consider the findings of the delayed choice quantum eraser version of the double-slit experiment in terms of a
direct experiential interpretation of quantum mechanics.
6.4 The Nature of the Quantum Wave Function
Keep in mind that there are two key effects about the double-slit experiment that involve the observer:
1. The
collapse of the wave function upon measurement by an observer.
2. Changes in the probability distribution of the measurement results that depend on whether or not the “which slit” information can reach an observer.
Both these effects point to an observer effect in quantum physics. This means that any claim to a solution that negates the observer effect must account for
both these effects.
The second effect, though, does not require an observer to be physically present and actually noting the results
at the time of the experiment. What this tells us is this. If the experimental conditions enable us to tell which slit the signal photon passed through (if we wanted to find out), no interference pattern would emerge on the screen. If the experimental conditions were such that we cannot tell which slit the signal photon passed through (even if we wanted to find out), then an interference pattern would emerge on the screen.
The key factor is whether or not the “which slit” information is available to the conscious observer. If the information is available, no interference pattern forms. If the information is not available, an interference pattern forms.
This result provides us with very important information concerning the nature of the
quantum wave function. What it means is that the probability distribution for the measurement results changes upon altering the experimental conditions, even when the experiment is conducted without any conscious observer being present to note the results directly at that time. In other words, we can alter the
quantum wave function just by altering the experimental set-up.
Note, however, that this does not mean that the
collapse of the wave function can occur without the observer actually reading the results. All that has happened, without the observer present, is that the probability distribution of possible results has changed. No
collapse of the wave function has occurred in this process.
In other words, while we know that there is a change in the probability distribution of the possible results—concerning where the set of photons end up on the screen—we still do not know where any one particular photon ends up. We still only have a probability distribution of possible results, and not the actual results, if the observer does not make an actual observation of the results. In other words, the
quantum wave function has changed but it has still not collapsed.
So what does this tell us about the
quantum wave function? It tells us that the crucial factor in determining the form of the
quantum wave function are the possible
experiential events that the experimental set-up would allow the observer to have. In other words, the set of possible
experiential events determine the
quantum wave function. If we change the set of possible
experiential events by changing the experimental set-up, the
quantum wave function would change accordingly to reflect this new set of possible
experiential events that the observer could encounter.
Note that this mechanism is akin to a change in the
preferred basis depending on what the observer chooses to measure. In other words, a change in the possible set of
experiential events—which, of course, would change when a different property is being measured—would lead to the
quantum wave function being altered to reflect this change in the set of possible
experiential events.
All this means that it is the
experiential events—that are the acts of observation involving both the particle and the conscious observer—that are the primary reality that the
quantum wave function provides information on. A change in the possible set of
experiential events changes the
quantum wave function, even without an observer being present at the time. Nonetheless, an actual act of measurement by a conscious observer is still required for the
collapse of the wave function.
A
direct experiential interpretation of quantum mechanics thus explains the two so-called “weird” effects of the double-slit experiment. These effects are actually only weird in terms of a mind-matter duality. If we adopt a middle way approach—as provided by Madhyamika philosophy—without positing a mind-matter dichotomy, and consider instead that the
experiential events are the
primary reality that quantum mechanics deal with, we can arrive at a consistent interpretation of the double-slit experiment that is free of contradictions.
Note that if we consider the
experiential events to be the primary reality, rather than the particles (in this case, the photons) themselves, it also explains the peculiar property of a “message” being sent faster than the speed of light—or in this case, even backwards in time—in cases involving
quantum entanglement. In other words, this idea of a message being sent, between an entangled pair of particles, only arises
if we consider the particles to be inherently existing entities, that are independent of the conscious observer, in the first place.
In the Madhyamaka view of reality, these particles (the photons) do not inherently exist, independently, on their own right, or from their own side, but are only dependently arisen. Their very existence depends on causes and conditions, and on the mind of the observer that apprehends them. In other words, it is the
experiential events that form our reality, and not the photons themselves, independent of the observer.
Now, if it is the
experiential events that actually constitute our reality, we do not need to posit a “message” being sent between the idler photon and its corresponding signal photon. What we need to realize is that a measurement made on the idler photon changes the set of possible
experiential events in the experimental set-up, and this changes the
quantum wave function accordingly. As already mentioned, this process is akin to a change in the
preferred basis upon changing the
observable we choose to measure.
Thus a
direct experiential interpretation of quantum mechanics not only explains the two so-called “weird” effects of the double-slit experiment, it also explains why, in cases of
quantum entanglement, apparent “messages” can be sent faster than the speed of light, or in our case, even backwards in time. All these “weird” effects arise only because we have been inappropriately trying to fit the formulation of quantum mechanics into a philosophical framework that posits a mind-matter dichotomy, or more specifically, into a framework of materialism. The correct philosophical framework is actually that provided by Madhyamika philosophy.
