E εσυ που ξέρεις καλά αγγλικα διάβασε ΓΙΑΤΙ Η ΚΒΑΝΤΙΚΗ ΜΗΧΑΝΙΚΗ ΔΕΝ ΜΠΟΡΕΙ ΝΑ ΧΡΗΣΙΜΟΠΟΙΗΘΕΙ ΓΙΑ ΝΑ ΔΙΚΑΙΟΛΟΓΗΘΟΥΝ ΜΕΤΑΦΥΣΙΚΟΙ ΙΣΧΥΡΙΣΜΟΙ:
A Quantum of Common Sense
By David Morgan
It seems these days there is no shortage of "quantum" machines, or "quantum" explanations that will cure all known ills, generate unlimited "free" energy, communicate with the dead, explain personal "reverse causality" or perform any other highly improbable thing you can think of. One might be tempted to be skeptical, except that it's just "science" isn't it? Doesn't quantum mechanics prove all these things to be true? Decide for yourself...
What is a Quantum?
The word "quantum" means nothing special in and of itself. It just refers to a unit of something. We might call a millimetre a "quantum of length". Although the term as used in the physical quantum theory is generally taken to refer to something fundamental and indivisible. The basis of quantum theory appeared around the beginning of the 20th century. Many scientists had tried to explain the unusual shape of the spectrum of radiation emitted by hot objects. Various attempts had been made to predict it by equation and all had failed. It was a scientist called Planck who introduced the idea that radiation was "quantized" into discrete units and finally managed to solve the problem.
This spawned a whole new area of science - the idea of "quantization" - nature operating in discrete units, revolutionised physics. But the idea only really came into its own in the context of the burgeoning science of atomic physics where scientists were for the first time, directly confronting objects so small that they were at the limit of detection. This area had problems of its own, few of them specifically related to the idea of "quantization". But it was the science of quantum mechanics that took on the burden and became inextricably linked with the exploration of the infinitesimal.
Many great scientists, household names, are associated with the early quantum mechanics. Nobody fails to recognise Einstein. Most have heard of Schrodinger, Bohr, Heisenberg etc. If all these great scientists were associated with it, it has to be something extraordinary. In many ways it is, and yet at the same time, it's not something so far fetched that it is beyond comprehension (although some may have an interest in making it appear that way!)
Many people will also have heard of some of the truly strange and incomprehensible things that are involved in quantum mechanics. Things like Heisenberg's Uncertainty, or Schrodinger's Cat. Except that none of these are all that weird at all! If anything, what is weird is the strange interpretations people can put on such things, and the way they can be misrepresented to confuse and mislead.
Let's take a brief tour of some major concepts behind the mysterious quantum mechanics and see if any of it makes sense. In particular let's see how quantum mechanics tells us how to do the strange things some people claim they can do with it - or not!
The Measurement Problem and Uncertainty
Consider how we see an everyday object. What we actually see is a stream of photons (light) reflected from the surface of the object. It follows then, that if we want to get a picture of something, we effectively need, in principle, to "bounce" something off it, and then in some way build a picture by analysing those "somethings" that bounce back to us.
For example, a blind man cannot directly see a car. But he could, in theory, build a perception of its general size and shape by simply throwing a ball at it, and by measuring the return time and angle for any given initial trajectory. He could gradually build a form of "mental picture" of the car. But the amount of detail in that picture would depend on the size of the ball that is used. The smaller the ball, the more accurate the picture.
In case that is not intuitively obvious, one only has to imagine throwing a tennis ball at a car. The tennis ball would hit the windshield at various different angles, the wheels, the doors etc., and bounce back at correspondingly different angles with different return times. The bounces of the ball would give us enough information to discriminate between a windshield and a wheel for example. If we now scale that up and instead use a huge inflatable ball which is of a size comparable to one of the major dimensions of an average car, let's say a ball 2 metres across, we would obtain much less information by throwing it at the car and observing the bounce back. The ball is far too big to bounce specifically off one wheel, or a windshield. And so we would obtain very much less information if we used a large ball. We would probably be able to tell very little about the actual shape of the car with the larger ball. But we could establish (roughly) the general position and size of the car.
If our experimenter is someone who has been blind from birth, then he would never have actually seen a car. Someone who has seen a car, and is already aware of the general size, shape and major characteristics of a typical car, could probably imagine a reasonably accurate mental "picture" of a specific car, from appropriately sized ball bouncebacks. For example, he could probably discriminate between a van and a Ferrari. But for a person who has never seen a car to begin with, that is much more difficult - some would say, impossible. That is very analogous to the state of play with regard to objects on the quantum scale such as an electron for example. Nobody has ever seen an electron. All information we have about it, is only based on what we have crudely measured by its interactions with other things (like the ball bouncing off the car), and what we have imagined, based on mathematical models which are in turn based on those previous measurements and interactions. And at the quantum scale, we don't have a "small" ball to throw. The objects that something like an electron interacts with measurably, are all of similar size to, (or much larger than) the electron. So, in effect, we know very little about the actual size, or shape of an electron. But we can at least get a general idea where one is.
Now let's consider a different measurement. Let us try to measure how fast something is travelling - another car will do. But we are constrained by interactions at the quantum scale. Which means our measuring device for speed is also our large ball. How can we measure the speed of something, using only large "measuring" ball(s)? The most obvious way is as follows: we mark out some distance on a road, say 100 metres, and at each end of the distance marks we periodically throw measuring balls into the road. If the ball bounces back, then the car must be crossing the line at that moment (because the ball will only bounce back if there is a car there to hit and bounce from). In this way we finally get a measurement. At some point in time the car reaches the first line. A ball is thrown out just as it's crossing the line and bounces back. The observer at line #1 records the time when it happened. Some time later, the car reaches line #2, the same thing happens there. Now the two "blind" observers can compare their time measurements and get an idea of the average speed of the car, which is simply equal to 100 metres divided by time "t2" - time "t1".
But there is still a problem. Our measurements are quite crude and there are several possible sources of error. But if we ignore those for the moment, we still only have the average speed of the car. Why is this a problem? Well, if someone comes along and asks us where the car actually was at some moment in time between t1 and t2, it would appear that we could calculate that from the known measurements and our average speed. But we can't do that in practice! Why not? Because we don't know exactly what the car was doing between the ball bounces! The car may have driven a short distance past the first bounce point, stopped, waited for a while, and then started off again before reaching the second bounce point. Or the car may have speeded up after passing the first point and then slowed again before reaching the second. In other words, we have no way to establish whether the speed of the car was constant between the measurements. And if it wasn't, then we cannot possibly calculate the actual position at any given time between bounces! All we can say with any degree of certainty is that between measuring times, t1 and t2, that the car was somewhere between the two measuring points on the road. So when we know the average speed, we can't know the exact position of the car.
But now some clever person comes along and says that we can know the exact position of the car at the measurement points. Which is true. As the car passed the measuring points and the ball hit it, we did know that the car was there at those times. But we now have a different problem! At the points of measurement, we don't know the actual speed of the car, because we only have one measurement at each point! We need two measurements and a distance to work out a speed. The average speed doesn't help because it still doesn't tell us the actual speed at any given point.
So it seems our system of measurement suffers from a fundamental problem. We can know the average speed of the car within two points in time. And we can know the specific position of the car at two different points in time. But we can never possibly know both the exact speed and the exact position of the car at the same time! However, being clever experimenters, we can devise ways of making many more measurements, over much shorter distances, and we can get ever better approximations to the true speed and position. But eventually we hit a limit of possible accuracy. We cannot determine if our large ball bounces because it hits a point near the front of the car or a point near the back, all we can tell is that it hit somewhere on the body of the car at a specific time. And our measurement lines can never be closer together than the length of the car or the measurements are indistinguishable. So there is an absolute limit to the accuracy it is possible to obtain by this method. And this method is our only means of measurement in the quantum world.
This general principle is analogous to what is known in Quantum Mechanics as Heisenberg's Uncertainty Principle. In the late 1920's Werner Heisenberg presented a series of arguments that if we took the product of the position and the momentum of a particle, that there would always be some uncertainty in that figure by at least the amount of Planck's constant. So in other words, we can know the position of a moving particle at any given time. Or we can know the momentum of a moving particle at any given time. But we can never know both accurately at the same time. The more accurately we know the position, the less accurately we know the momentum - and vice versa.
And that is not the only problem. There is a different problem that adds to the confusion above. That is that our "measuring ball" usually has momentum of its own. In practise, compared to something like an electron, our measuring balls have similar momentum to the electron itself. That is rather like saying that in the examples above, our measuring ball is almost as heavy as a car! So if we throw one of these balls at the car, it won't just bounce off the car, leaving the car undisturbed. It will cause the car itself to bounce as well! Which means that we can work out precisely where the car was at the instant of collision with the measuring ball, but we also know for certain that the collision will have deflected the car from its original course as well! And therefore the precise position (and direction) of the car immediately after the collision is now unknown!
All the above are aspects of Heisenberg's Uncertainty Principle. We can call it, "The Measurement Problem". Stated simply, this says in essence that any measurement of a quantum system causes a change in the state of that system, and we can only measure to a limited degree of accuracy.
So to sum up where we have got to. Using an electron as an example, all we know is that the electron appears to be some vague fuzzy object in a cloud of mist that we can never see and which has never been seen. We can only detect or measure it by throwing things at it and seeing if they "bounce". And the things we can throw at it, are all quite big compared with it so we can never get any real details of it. And when we do that, we can work out at some instant what its position is, or its momentum, but never both precisely at the same time. And we also know that every time we measure one of these things, we change the very thing we are measuring, so the measurement itself is only valid for one instant! What a mess!
It is very important to realise however, that just because the electron appears to be a "fuzzy, misty, vague" thing, that in reality we have no way of knowing whether it really is vague and fuzzy/misty etc., or whether it is actually a precise well defined object that simply lies beyond our measurement capabilities.
Failing to realise the latter is usually the first step to misunderstanding or misrepresentation of quantum mechanics.
A Leap of Faith
Heisenberg himself opened the door to widespread misunderstanding when he introduced a philosophical view of his own into the matter. Heisenberg was convinced that quantum states were separate discrete states with nothing in between. To Heisenberg, when a quantum object changed state it simply "jumped" directly from one state to another without passing through intermediate states. This is the famous "Quantum Leap". But this is often confused with the states between measurements which is a different thing entirely. For example, when the car crosses the measurement lines in our example above, it is in a specific "state" at the instant of crossing. While it is travelling between the measurement points, we have no idea what the car is doing, and Heisenberg extended this to say that while we couldn't measure something, it didn't actually exist! Applying the example to our car implies that the car only exists at the instants it is being measured!
Before going any further it is important to note that this is a theoretical assumption, one which was essential to a system of mathematics (called matrix mechanics) that Heisenberg had personally developed. Heisenberg's system never really caught on as it was widely considered too difficult and awkward, and it was superseded by a simpler system developed by Schrodinger. It is not possible to determine at the quantum level whether Heisenberg's idea is true or not, therefore it remains simply a theoretical assumption. It is also worth noting that Heisenberg himself was inconsistent on this point. At times he seemed to be saying that the object did not exist whilst it wasn't being observed. At other times he seemed to be saying that because we couldn't know anything about the state of something that we couldn't see, we could treat it as though it didn't exist (but that it may exist nonetheless).
To many, the very idea that something ceases to exist whilst we are not observing it is absurd! For others, it is the foundation stone of a new "faith". In reality, the situation is complicated and not at all as simple as it seems. Firstly it is absolutely essential to realise that Heisenberg's statements were confined to the "quantum realm". There is an apparently obvious argument that if macroscopic objects, the objects of our everyday world and experience are built of "quantum components", then whatever applies to the quantum world also directly applies to the macroscopic objects built from quantum objects. This argument is false. The "weirdness" we observe at the quantum scale does not directly translate to the macroscopic world. Before considering that in any detail, let us take a closer look at the idea of whether an object exists only when it is being observed. In particular, it is worth looking at a popular argument often quoted in connection with quantum matters, which is that, "if a tree falls in the forest when nobody is looking, does the tree actually exist and actually fall?".
The Observer Problem
The corollary to the above question is of course, that if we find a tree in the forest that has fallen, does it simply come into existence at the moment we see it? The answer is no. The tree fell when nobody was looking and has been there all along, we simply discovered it when we entered the forest and saw it. You may be tempted to ask how I can be so certain about that. The answer is really quite simple and depends on the definition of "observed" and "observer".
In quantum mechanics the word "observed" has a different meaning to what we mean when we talk about observation in an everyday sense. We have already seen above, that when we "see" something in the everyday world, what actually happens is that we observe a pattern of photons that bounce off the object and travel to our eyes. However, we can infer that if a pattern of photons bounces off an object, then that pattern will contain information about the object regardless of whether anyone sees it or not. The "pattern" of photons (a light image) exists from the moment the photons interact with the object, it makes no difference whether anyone actually "sees" it or not. How do we know that? Easy. We can set up a camera or other recording device and it will capture that image and record it. There doesn't need to be an actual human present in order to "see" the image.
This then begs the question of what constitutes an "observation" and what constitutes an "observer"? From the example above, it is fairly easy to see that an "observation" is simply an event in which something interacts with a system in such a way that the "something" in question acquires information about the system. In the above example, the "something" is photons of light. An "observation" occurs when the light interacts with the thing being observed. In other words, an "observation" is not something that explicitly depends on the presence or attention of a human being.
Taking the earlier example, the act of bouncing a ball off a car constitutes an "observation". The observation occurs the moment the ball hits the car, it doesn't matter whether there is any person present to catch the ball afterwards.
So who exactly is "the observer"? Well, the observer is a more nebulous object. It can be argued that an observer is a person who sees the pattern of light, or it could also be the camera that records the image. In essence though, it doesn't matter. The real question is, whether or not the presence of an observer is essential to the existence of the object observed?
In the case of the tree in the forest we can make certain inferences. We know that all physical systems continuously interact. A tree has a gravitational field (an extremely weak one) as does any material object. The tree will have certain distributions of electrical charge within it. It will also have energy. The earth itself is moving all the time so the tree will have momentum (any object with mass that is moving has momentum). And so on. All these properties of the tree will interact with other objects. For example, the gravitational field of the tree will affect other trees around it, and even a person on the other side of the planet (albeit negligibly). If we postulate that the tree doesn't exist until the moment of observation, then we would also have to postulate that all the effects it causes on other objects, all the interactions it has with them, all come into existence solely at the moment of observation. And that completely contradicts what we know from both classical and quantum science. Because the quantum theory depends on certain physical "laws" as much as classical physics does. In particular, there are "conservation laws" which state that certain properties of objects are always conserved, that these properties don't simply appear out of nothing. Amongst such conserved properties are momentum, energy, electric charge and others.
Therefore we can say with certainty that the tree actually exists independently of whether anyone is actually looking at it or not, because we know that the properties associated with its physical existence are conserved and cannot simply appear out of nowhere at the moment someone just happens to be looking! If we postulate that the tree does not exist unless someone is looking, we then have a much stickier problem of having to explain where the energy / momentum / gravity / electric charge etc., come from at the moment of observation and also why their prior absence still caused other objects to act as though they were there all along!
And it is worth noting again that if anyone argues that quantum mechanics somehow shows that macroscopic objects only exist when observed, they are making a false assumption, simply because quantum mechanics itself is based on the very laws and assumptions that would be contradicted by that assumption. Therefore, if quantum mechanics were to hold that macroscopic objects do not exist independently of the observer, then quantum mechanics would invalidate itself on the same grounds!
However, the same argument becomes weaker when applied to microscopic objects at the quantum level.
Most people have heard of the mysterious "wavefunction" that is somehow at the heart of quantum mechanics. In reality, the wavefunction is nowhere near as mysterious and exotic as it sounds. All it is, is a mathematical equation that describes the relation between certain states of a system. For example, if we have a machine that has one inlet and two outlets, we could configure the machine to divert half of any objects that enter the inlet to one of the outlets, and the other half to the other outlet. Let's say that the objects are apples. We have a conveyer belt that feeds apples into the machine. The machine is designed so that every odd numbered apple is delivered to outlet #1 and every even numbered apple is delivered to outlet #2. So the first apple on the conveyer belt ends up at outlet #1, the second apple at outlet #2, the third apple at outlet #1 and so on.
We could even write an equation to describe this behaviour. We could say generally that if the number of apples input is x, then the number of apples output at outlet #1 is 1/2 x. The same equation works for outlet #2 as well. And so on. In a more general sense we could also work out that the probability that any apple will arrive at outlet #1 is 50%, similarly the same probability applies to outlet #2.
Although the wavefunction in quantum mechanics is much more complicated than this, in principle it is similar. A wavefunction effectively says that if we know certain things about the state of a system at some particular time, then we can make a guess about what will happen next.
However, a wavefunction effectively describes the behaviour of discrete objects (like our apple) as a combination of a set of waves. And that immediately causes a problem. What is the meaning of an apple expressed as "a wave"? We know that an apple is an apple. As far as we can see it doesn't behave like a wave! Yet at the quantum level we do know that very small objects often do behave as though they were waves. But not consistently. Sometimes they behave like particles, other times they behave like waves! So if our apple were a quantum object, we would see some wavelike behaviour, but not enough to conclude that it actually is uniquely a wave.
So where does that leave us with respect to what a quantum object actually is? Nowhere. The simple answer is that at the quantum level, we don't actually know what things really are - remember above we discovered that because our measurements are limited, nothing is absolutely clear and certain, everything appears "fuzzy" because our measurements can't go below a certain scale.
All this is quite confusing. Despite the fact that we don't know what things actually are, we need to make certain assumptions in order to be able to make predictions about these things. If we assume that a quantum object is a particle, then the wavefunction is a problem because the "answer" it gives is expressed as a wave amplitude. This caused a big headache for the early quantum scientists. It led to many arguments about what a wavefunction actually meant. In the end however, one of them (Max Born) came up with an acceptable interpretation. He said that the amplitude of the wavefunction (actually the square of the amplitude of the wavefunction, but it's not important for this explanation) represented the probability that a particle could be found at a particular place.
So in the case of our apples above, if we could apply the equivalent of a quantum wavefunction to our machine, the mathematical solution to the wavefunction would say that there was a 50% probability that an (unspecified) apple would end up at outlet #1 and a 50% probability that it would end up at outlet #2.
You may be scratching your head at this point and asking what is so mysterious about this? The simple answer is, nothing! But as we will see, given half a chance we can easily confuse ourselves!
The problem occurs when we look at the actual output of a wavefunction. It is a wave (or more properly a collection of waves). We have decided that (the square of) the wavefunction amplitude represents the probability of something being in a particular place at a particular time. But what about the wave itself? If we look at the wave that the wavefunction produces, we notice that it appears to be spread out over some area. If we could apply the wavefunction to our apple sorting machine, we would see a wave that is apparently spread out all over the inside of the machine and for some distance outside as well. And even the square of the wavefunction amplitude (our probability) is not sharply cut off precisely at each outlet. Even though the probability of an apple exiting from either outlet is overall pretty much 50%, we notice that there is a small but non-zero probability that the apple might exit from neither outlet! This, then leads us to another question. Is this simply a mathematical artefact or is there really a chance that an apple will simply disappear and stay inside the machine? It is this question which leads to further confusion.
Although our apple/machine example is somewhat absurd because quantum effects are not significant at the macroscopic level, at the quantum level we observe that real objects, particles like electrons etc., do sometimes behave like waves. And so the question of what the wavefunction is actually telling us, is not so clear cut as we might imagine. The key question, given that we only observe something like an electron as a "fuzzy" object (because of the measurement problem) is whether the electron really might be a "fuzzy" object spread out over some area. The simple answer is that we don't know, and we don't currently have any way of knowing. Therefore, since we don't know, it means that there are two possible ways we can interpret a wavefunction. We can take it as simply a mathematical expression that somewhat "fuzzily" tells us where a sharp, well defined object is, or we can interpret it as literally saying that the object is somehow spread out over an area, rather like a wave.
The latter view leads to a further confusion. If the object is really wavelike, then in wave mechanics, any complex wave can be considered to be a combination of other waves. We can in practice spilt a complex wave into a collection of simpler waves (Fourier analysis). Therefore, if the state of the object described by the wavefunction is a complex wave, then each of the probabilities inherent in the wavefunction can be considered to be a separate simpler wave (one for each different probability) and the state of the object itself can be considered to be a set of mutually contradictory probabilities all mixed together at the same time!
But, in practice it was always observed that although there appeared to be equal probabilities of two (or more) different things happening at the same time, in reality only one of them would ever be observed in practice. This then led some to speculate as to how the mixture of opposing probabilities contained in the wavefunction, would suddenly "solidify" into one specific event. This "solidification" of the wavefunction became known as "wavefunction collapse". So the question was, what causes wavefunctions to "collapse"? The only event that seems to differentiate a collapsed state from an uncollapsed one, is simply that the latter has been observed. This then led to the argument that it was the act of observation that caused the wavefunction to collapse. That a wavefunction contained all possibilities in equal measure and only one of the possibilities would suddenly become reality at the moment of observation.
But this interpretation is something of a stretch. This caused many arguments between quantum physicists from the moment it was first proposed. Although the argument is technically valid on purely mathematical grounds and may be supported philosophically, the real question is whether it is a valid description of reality. It is worth noting that Erwin Schrodinger, the scientist who developed the wavefunction, thought this argument was absurd. He spent much of the rest of his life actively campaigning against this interpretation. At one point he became so disgusted by what he saw as idiocy, he decided to propose an example of how absurd it really was. Unfortunately, that attempt backfired on him and only led to a whole new level of confusion!
In order to highlight how ridiculous he thought the idea of an "observer created reality" view of the wavefunction was, Schrodinger proposed a "thought experiment". He believed that it would be obvious to anyone just how absurd the idea was in the light of this example.
Schrodinger noted that although quantum effects do not occur directly at the macroscopic level of the everyday world (at least to any significant extent) that if the state of a macroscopic system depended upon a quantum condition, that it might be reasonable to say that the macroscopic state of that system was defined by a quantum wavefunction. So what he proposed was that a cat could be sealed in a box. Also inside the box there would be a vial of cyanide gas that was attached to a trigger mechanism, so that if the trigger went off, the cyanide would be released into the box, and of course it would then kill the cat. And the trigger itself was connected to a device that would measure a quantum event, like the radioactive decay of some element. The idea was that the radioactive decay was only predictable by wavefunction since it is a quantum problem. At any given moment in time there would only be some probability that the trigger event had occurred, but that the wavefunction could be interpreted as containing both the probability that it had happened, as well as the probability that it hadn't. If the real state was truly a combination of equally valid but contradictory probabilities then it followed that both states had to be true at the same time. And therein lay the absurdity. Since the triggering of the vial was dependent on a purely quantum event, then it followed that the state of the vial was also contained in the wavefunction of that event. But since the life of the cat depended on the state of the vial, then that also depended on the wavefunction. There was only one possible conclusion. That if the wavefunction was not collapsed until someone observed the system, then as long as nobody looked inside the box, then the cat had to be both alive and dead at the same time!
Schrodinger thought that would be the end of the matter, because it was clearly absurd. Unfortunately it wasn't. Instead of dropping the philosophical position that contradictory realities could be simultaneously valid, it simply prompted some others to extend the theory into even more philosophical speculations!
A whole host of inventive "explanations" appeared. One of them (the many worlds interpretation) stated that both events actually happened, but that the universe itself split into different timelines or realities, so that in one universe the cat was alive, and in another it was dead! There were others I won't go into, but the above is an example of one of many philosophical proposals that are inherently untestable.
Some time later, another scientist, Wigner, proposed a variation of the Schrodinger's Cat experiment, that became known as "Wigner's Friend". In his experiment he replaced the cyanide with a light, and the cat with a human being. So the idea was that the switching on of a light in the box was dependent on a quantum event, and that there was an intelligent, conscious observer inside the box. Without going into great detail, Wigner constructed an argument that there were multiple possibilities, not just two in this form of the experiment. But since the state of the man in the box depended on these possibilities, it implied that there would be many equal versions of the man present simultaneously in the box! Since the man was conscious, it followed that there had to be numerous conscious versions of the man simultaneously in the box while the quantum condition was undetermined (i.e. the wavefunction was not collapsed). But Wigner also reasoned that if this really happened, then whichever version of the man was finally discovered in the box when it was opened, should be conscious and aware of the splitting of his consciousness into many versions of himself. But, of course, this didn't happen in practice.
Wigner then made a leap of reasoning. If such a thing could happen, but didn't, then it was clearly due to some specific factor that would somehow cause the wavefunction to collapse before it actually did happen. And working from the point of view that it was the observer who somehow collapsed the wavefunction, Wigner came to the conclusion that the defining factor was whether the observer was conscious. So it was Wigner's proposal that it was somehow the consciousness of the man in the box, that caused the wavefunction to collapse even before someone else looked into the box!
Although this may be an entertaining philosophical argument, my personal view is that this is just rampant speculation which is essentially absurd. However, it has become part of the overall "genre" of quantum mechanics. Although most practising quantum physicists don't bother with these kind of questions in practical work, it appears that some of them do speculate about such things in their spare time, and worse, to the popular press. All of which has led to a popular misconception amongst the public that quantum physics is all about "consciousness" and the like, and also that quantum mechanics has somehow "proved" that reality depends entirely on the "consciousness" of an observer. This is not true. Such ideas are just the philosophical speculations of some people.
Observation and Decoherence
It is worth at this point just mentioning one of many possible arguments against the above view. As I mentioned earlier, an "observation" in quantum mechanics is to all intents and purposes an interaction of a quantum system with something else. Therefore, it can be said that the wavefunction actually "collapses" the moment the system it describes interacts with something else. That "something else" can be a photon or the like, it does not imply a person or any "consciousness".
If we take the Schrodinger's cat example, we have a trigger which is set off by a quantum decay event. But how does the trigger "know" that the event has occurred? It has to interact with the system in order to make the "observation". Therefore one possible argument against the "consciousness" interpretation is that the wavefunction collapses the moment the decaying radioactive material emits a particle or photon that interacts with the trigger apparatus. And so, the result (the cat being alive or dead) is not dependent on whether anyone looks in the box or not. When someone looks in the box, they will discover the cat either alive or dead, but that does not imply that the cat was somehow in both states before they looked.
The argument can be extended to include any possible interaction. In real macroscopic systems there are many quantum interactions all the time. No system exists in complete isolation, therefore the activity of all interrelated events causes many quantum interactions at any moment. And since an interaction is effectively an "observation", then wavefunctions simply don't survive very long in the real world, and certainly not long enough for a "Schrodinger's Cat" type situation to actually occur. This is sometimes called "decoherence".
And of course we must not forget that it is only a theory that the wavefunction has any direct physical meaning. Schrodinger himself only considered it a purely artificial mathematical function. And if that is the case, all arguments about its reality, consciousness etc., are absurd.
I have mentioned several times that quantum events ("quantum weirdness") do not seem to occur at macroscopic level, or at least not significantly. The decoherence argument is one of various attempts to explain this. In a macroscopic system the complex and numerous interactions between matter and radiation etc., cause the immediate collapse of wavefunctions, so the "weirdness" inherent in the wavefunction simply never makes it to the macroscopic "real world" in any noticeable way.
It is important at this stage to mention a more modern development of quantum mechanics that also sheds some light on the relation between microscopic and macroscopic.
Quantum Electrodynamics, or "QED" for short, was the development of one of the greatest scientists of the 20th century, Richard Feynman. Despite the complicated sounding name, Feynman's clarity of exposition has made it one of the simplest and most well understood aspects of quantum mechanics.
Feynman was inspired by a classical observation that has been stated in various different ways by scientists since the 17th century. It is also worth noting that Schrodinger was also inspired by the same idea. In various forms this observation has become known as "Fermat's Principle" or "Hamilton's Principle". Feynman called it the "Principle of Least Action", which is not technically correct, but is a reasonable summary of it. I won't go into great detail but here is an outline.
In physics one can measure a quantity called "action" which is the product of energy and time, or alternatively, momentum and position. It was the great discovery of Planck that "action" is quantized in fundamental units of "h" which is called Planck's constant. It appears to be a fundamental law of nature at all scales, microscopic, macroscopic, relativistic, that any event will occur in such a way that its total "action" is minimised. Actually, it is truer to say that its action is "stationary", but that word "stationary" has a special mathematical meaning that would only confuse the issue so I won't state it here. "Minimised" is a reasonably true approximation for most cases.
So what this means in practice is that if there are several different "paths" via which an event "A" could lead to a result "B", then in general, the actual path that will be followed in reality is the one that involves the least overall "action". The action principle is central to classical physics. If someone throws a ball in the air, then the actual trajectory the ball will follow will be described exactly by the action principle.
Feynman realised that he could represent events in the quantum world simply by considering them as a combination of wavelike "amplitudes" and "phases". He discovered that if you assumed that any event could proceed along all possible paths simultaneously, then the amplitudes of those events and their phases would interact in such a way that the net result would be that only one path (or a small group of paths) would remain - because the amplitudes and phases of other paths would cancel each other out. He also found a way of drawing a simple diagram (the Feynman diagram) that would sum up specific interactions and allow the net amplitude and phase to be worked out by an extremely simple procedure.
It is difficult to understand the significance of this at first sight, but it solves a number of "quantum problems" in one go. And what is more, the method is so easy that any high school child could in principle apply it with a little instruction!
The first problem it solves is the difference between microscopic "quantum" rules and macroscopic "classical" rules. Feynman states that every event will follow all possible paths. Although this sounds absurd, it works in practice. But at the quantum level, the interactions between all the amplitudes and phases of the different paths will cause only a small subset of paths to be feasible. However, the more amplitudes and the more phases involved, the more sharply defined the final path will be. So that defines the difference between "quantum" and "classical". Since a classical macroscopic system involves astronomical numbers of quantum events at any one time, the final path is clearly and sharply defined. But at the quantum level, when one only considers single or small numbers of quantum events, there are not enough spare "amplitudes and phases" to cancel out and so the path remains "fuzzy" because you can't narrow down the possibilities enough.
This argument puts the final nail in the coffin of Schrodinger's Cat so to speak! It's perfectly clear, using QED, that Schrodinger's Cat is a non-event. There was never any uncertainty at all about whether the cat was either alive or dead because it is macroscopic. If you could add up all the amplitudes and phases of all the wavefunctions that describe the cat, the box, the trigger and everything else, then there would be only one definite possibility. The cat would be alive or it would be dead, never in between. Unfortunately the system is too complex to solve in practice so we still don't know which of the two is the one that would actually happen in any given case, but we do know that the idea of "superimposed" simultaneously alive and dead cats is ridiculous in practice!
The second problem that it solves is really the same problem in a different disguise! In quantum mechanics there are certain known quantities that can be calculated in principle, but it is difficult to define them exactly based on real data, because the data is always incomplete or limited, so they always remain somewhat "fuzzy". Using Feynman's method it is possible to calculate almost anything to any desired degree of accuracy. If you require more accuracy in a problem, simply add more possible paths with their amplitudes and phases and keep adding them together!
There is one drawback however to this method (technically known as "Sum Over Histories"). Each possible path requires a Feynman diagram to be evaluated. If you have a few paths, then you only need a few diagrams and solving them, as I have mentioned, is easily within the capabilities of an average school child. The problem is, that as you require more accuracy, the number of diagrams required increases by a ridiculous amount. And so if you want to define a complex quantum variable, then you need a totally impractical number of Feynman diagrams to do it! The numbers easily rise into the realms of the astronomical. Which means in practice that you need banks of supercomputers to solve many problems and the processing can literally take years! However, the fact that it is possible and that it does work means that it is used in practice. And it is largely on the basis of the success of Feynman's methods that quantum mechanics has been called, "the most accurate theory in history" because it can allow the calculation of infinitesimally small things to theoretically unlimited degrees of accuracy.
It is worth pointing out that at the macroscopic level, the number of Feynman diagrams is not a problem. We have sufficiently good measurements of "ordinary" events that we can quickly eliminate most possibilities and approximate the true path to most levels of meaningful macroscopic accuracy with simpler formulae. Newton's equations are an example of the latter.
Entanglement and Non-Locality
To round off the description of quantum mechanics I need to cover two more recent developments. In any system which consists of one or more quantum "events" it is possible to describe that system by a single wavefunction. In reality you can construct a wavefunction for each separate event and then simply add them together (rather like Feynman's diagrams) to generate a composite wavefunction for the system as a whole. Sometimes the state of one quantum event in one system is interdependent with the quantum state of another event in another system. When that occurs you can similarly combine the wavefunctions into one, and we say that the events are "entangled".
Now, if two quantum states are "entangled" then if you change one of those states, then by definition, you must also change the state in the other system it is entangled with. For example, atomic particles like electrons have a mysterious property called "spin" (it doesn't literally mean they are spinning). It is possible to entangle the spin of one electron with the spin of a different electron. In an electron, spin has only two possible states that we call "up" and "down" (again don't take that literally). So when two electrons are entangled like this we know that when one has "spin up", the other will always have "spin down" and vice versa.
This is interesting in itself. But it becomes even more interesting when we realise that the wavefunction doesn't imply any limitation of distance or velocity. So in theory, if one of our electrons is here, and the other entangled one is on the opposite side of the universe, then if we change the spin of the one here, the spin of the one there should also change instantaneously!
This immediately causes a conflict with other theories like relativity which states that information can only travel at the speed of light and also that simultaneity is impossible. Needless to say, there is still much argument in physics circles as to what is really going here and whether there are as yet unrealised limitations. But so far, experiments have shown that it is possible to entangle particles like this and also to measure changes in mutually entangled states that seem to violate relativity. But as it is such a new and complex area it is difficult to give a definitive statement about what the current state of research is.
Einstein always objected to quantum mechanics. As a theory he thought it was at least incomplete if not totally wrong. In the 1930's he and two others (Podolsky and Rosen) had formulated an idea which they thought would prove quantum mechanics incomplete. In the 1960's, a scientist called Bell developed a mathematical theorem that should allow Einstein, Podolsky and Rosen's (commonly called EPR for short) idea to be tested directly against the predictions of quantum mechanics. In the early 1980's a French scientist, Alain Aspect, performed the first of a series of experiments which, by using Bell's theorem, showed that the quantum mechanical prediction was correct and the EPR prediction wasn't. This has been widely proclaimed as a vindication of quantum mechanics and a proof that Einstein was wrong. However, there remains sufficient ambiguity in the experiment, as well as legitimate objections to Bell's theorem, to ensure that the result is still widely disputed. It is therefore difficult to say with certainty that the "non-locality" predicted by entanglement is as complete and truly "non-local" as some scientists believe. In any event, entanglement as currently understood is not something that anyone could simply cook up in their kitchen at home!
Whilst on the subject of non-locality, there is a further theorem that is often invoked in connection with it. That is the Aharonov Bohm theory. This theory is a purely mathematical theory based on some complex wavefunction mathematics. At the end however, it comes to two basic, mutually exclusive conclusions. The first is that non-locality is possible. The second is that a quantity which has always been considered an artificial mathematical construct, called the "Magnetic Vector Potential" is actually a real, measurable quantity. Following experiments by Japanese scientists, the Magnetic Vector Potential was finally isolated and proven to exist in accordance with the Aharonov Bohm prediction. However, it is very important to note that the conclusion about "non-locality" contained in Aharonov and Bohm's theorem was mutually exclusive to the prediction about the Magnetic Vector Potential. The fact that the latter has been shown to be true seems to explicitly show that the former is not - at least in the case of Aharonov and Bohm.
The Great Quantum Confidence Trick
Above I have attempted to give a brief(!) overview of some of the basic and major ideas behind quantum mechanics, particularly the more "weird" or controversial ones. Since this is aimed at lay people I have not attempted to make it rigorous or mathematical, and it would take more than a book to make it complete! But I hope it gives a basic idea of what quantum mechanics is all about. Most people have no real idea of quantum mechanics, and many popular accounts tend to concentrate on the more fantastic and outrageous ideas for sensational effect value. However, many such accounts are nothing more than idle speculation. Quantum mechanics is not about "consciousness" or "paranormal" effects. It is a legitimate branch of physics which although having certain unusual philosophical viewpoints, is nonetheless firmly grounded in the traditions and methods of classical physics and science in general.
I would now like to look at some examples of how quantum mechanics is "misused" by various people as a justification for "the paranormal". There is no doubt whatsoever that the majority of people who claim that something improbable is "justified by quantum mechanics", have absolutely no idea what quantum mechanics is all about. In many cases, such people know perfectly well that the average lay person doesn't either, and they rely on this ignorance to mislead people into buying bogus products or accepting improbable claims. I have observed many attempts by various people to promote dubious "products" based on misrepresentations of quantum mechanics. Based on those observations I think it is worth pointing out some common traits in such attempts.
1. "Quantum Mechanics proves ..."
Perhaps surprisingly for such an extensive discipline, quantum mechanics actually "proves" very little. More than anything, quantum mechanics is an attempt to describe certain aspects of the world that defy conventional methods of measurement. Central to QM is the idea of the "wavefunction" and its "probabilities" of certain events happening. More often than not, QM doesn't predict a specific outcome for any event, it just gives various probabilities for alternatives. In many cases, actual wavefunctions cannot even be actually solved! Most people would be surprised to hear for example, that there is no exact solution of any QM wavefunction for the energy states of any atom but the most simple one of all - Hydrogen!
The idea that "all things are possible" is fundamental to QM in many ways. In reality it is seen in the Feynman Sum Over Histories technique which assumes just that - but which then goes on to show that out of all possibilities there are very few real probabilities. In a more fanciful form it is seen in Schrodinger's Cat etc. In the real world however we know that certain things do happen and others don't. Just because something may theoretically be possible in some abstract sense does not imply that it ever can or will happen in the real world. This is often misrepresented by claimants of the improbable. I have seen many claims to the effect that something is "proved possible by quantum mechanics". But it follows that if all things are equally possible and equally probable, the world would be impossible to manage in an everyday sense. Engineers for example have no problem setting down exact and precise physical limits for equipment, we all have precision instruments from TV's to computers, cars etc., which would not work in a world where just anything was reasonably possible.
2. "This is the equation for ..."
Quantum mechanics certainly has some impressive looking equations. But the problem is that only advanced mathematicians understand more than the most basic interpretation of them. The average person confronted by complex equations wouldn't have any idea at all what they were looking at, or what it meant. It would be quite possible (and I've seen it done) for someone to present some totally meaningless collection of mathematical looking letters, numbers and mathematical signs and to claim it was a "quantum mechanics equation".
3. "This machine operates on quantum mechanical principles ..."
It is amazing how many people are willing to sell "advanced" machines that can (allegedly) do all kinds of fantastic things like manipulate theoretical particles predicted by variants of quantum mechanics. Or which can precisely perform non-local QM communication etc. It is even more amazing considering that the world's greatest scientists with all their knowledge and equipment can't even decide what an electron actually looks like! Or solve the wavefunction for the second simplest element, Helium! And of course, don't forget that quantum level effects don't scale up to the macroscopic world.
Unfortunately, it seems that real science simply hasn't caught up with any of these amazing people. And strangely enough, their fancy "quantum machines" always seem to not work when somebody who knows what they are doing actually tries to test them!
Although some people are easily conned into buying or accepting rubbish on the basis of "quantum" claims, at the same time the very word "quantum" provides an excellent red flag for a wary person. As soon as you see the word "quantum" used in connection with some improbable product, you can usually safely assume it's pure BS.
4. "Non-locality is proved by the Aharonov Bohm Effect ..."
Not exactly. The opposite is true! The Aharonov Bohm paper explicitly predicted non-locality or the existence of Magnetic Vector Potential. Since experiments subsequently proved the existence of Magnetic Vector Potential it follows that Aharonov and Bohm explicitly excluded non-locality since they are mutually exclusive options in that paper. The proven Aharonov Bohm Effect relates to the action of Magnetic Vector Potential on other systems, not non-locality.
5. "Quantum mechanics proves that consciousness ..."
Again, not exactly. Quantum mechanics has nothing to do with "consciousness". Some people, including some scientists have made purely philosophical speculations that certain aspects of quantum events may interact with the "consciousness" of an observer. But it's important to recognise mere speculation for what it is. Quantum mechanics does not have even a definition of what "consciousness" is! Which says little for all the claims about "quantum consciousness" and the like.
Look it up! It is amazing how often famous scientists are completely misquoted, usually out of context. Half the time they never even said what has been attributed to them. It is worth noting that Einstein had serious reservations about quantum mechanics and never really accepted it. Similarly Schrodinger, who is considered by many to be the "father of quantum mechanics" was also convinced that it had got out of hand, and in one famous statement actually did say that he didn't like it and wished he had never had anything to do with it!
7. "If a tree falls in the forest when no-one is looking ..."
This has already been covered above. It is a common misconception arising from a confusion of a lack of knowledge of events intermediate to quantum states, with the macroscopic world. There is no indication in QM (apart from philosophical speculation) that macroscopic reality is "observer dependent". And also it confuses the very idea of an "observation" at the quantum level with our everyday belief in an "observer".
So what is the real problem?
Just to round off, the real "problem" with quantum mechanics is that it is an attempt to make sense of things that are almost inevitably uncertain. We cannot, for example, directly measure the shape of an electron, or see what it looks like. All we can do is make some guesses about it. And the same applies to most things on a quantum scale. Whilst quackery and pseudoscience of various sorts has always attempted to infiltrate and subvert legitimate scientific results to its own ends, with most exact sciences it is very difficult to do. If someone makes a specific testable claim about some well known scientific area, it is easy to simply put it to the test and show whether it actually does what it says or not. But quantum mechanics is a real boon to the con artist. Most things in quantum mechanics are difficult if not impossible to test, and at best the results will always be ambiguous or "fuzzy". This is a real prize to the "professional pseudoscientist", a way of claiming scientific legitimacy without having to risk being proved wrong by simple testing! Fortunately, even though it suffers from areas of ambiguity, quantum mechanics as a whole, is a well defined discipline that can be tested in various ways. The pseudoscience hiding behind the veil of quantum mechanics can usually be seen through quite easily by someone actually familiar with the area.
I encourage everyone to learn what they can about this fascinating area. You don't need to be a maths genius to "get it". There are excellent introductory presentations by people like Richard Feynman, and a lot can be learned simply by reading the histories of the scientists involved - in many ways that will explain concepts better than any course in advanced quantum mathematical theory.
For anyone interested in learning more, there are four actual video recordings of lectures by Richard Feynman available freely online and viewable on an ordinary computer. They can be found at the following link: http://www.vega.org.uk/series/lectures/feynman/