Philosophy of Quantum Physics for the Smart Shopper
Text of a lecture given at Burning Man, Sept. 1, 2005

Introduction

This essay is for smart shoppers for two reasons. One, it is about the relevance or lack thereof of quantum physics to everyday life. Currently there are misconceptions about the need of ordinary people to change their worldviews in response to new discoveries in science, and I’d like to set the record straight. And two, this is a “caveat emptor” statement to those shopping for world views. I show that some of these views are less useful than they purport to be.

Since this is an especially esoteric topic, and incompletely understood even by the most adept scientists and philosophers, the present discussion must necessarily be incomplete and oversimplified. Still, it is possible to say something meaningful that can be understood by most people. Also, I am presenting primarily my own viewpoint, developed over decades of working with quantum mechanics-related technology (lasers), and a few years of reading the philosophy of science. This is an engineer’s viewpoint, oriented toward the practical consequences of philosophy, and is probably in line with what most scientists believe.

I feel compelled to write about this topic because I see misleading statements being made in popular literature, and sales of bogus cures and devices based on obviously false claims. At least to me the falsity is obvious, while it might not be to those less familiar with the concepts at issue. I hope to provide some information that will inform the reader enough to perceive falsehoods buried in obscure language and flashy claims. Further, I want to communicate a sense of the wonderfully profound mysteries to be found in this topic. Unlike a murder mystery, none of the facts are hidden. All the cards are face up on the table and yet the best human minds falter at the task of understanding and explaining what they ultimately mean. No smug certainty is possible here without dishonesty.

The common sense worldview

A good starting point in this discussion is the origin of our everyday, common sense world view. Forming such a view is a practical matter, as we use it in all our interactions with the physical world, mainly to predict what will happen in response to our actions in that world. We organize our observations of the things around us, finding apparent links. Generalizing our perception of these links, they become abstracted into a world view. This view is built up from simple observations, as in the following instance. Let’s say I see a tree I’ve never seen before. If I turn away, I don’t see it anymore, but if I turn back I see it again. I could wonder why I see the same thing whenever I turn toward the place where it was, and reasonably conclude that the tree had continued to be present at that location irrespective of whether I was looking. I simply connect the dots, so to speak. I may draw the line further into the future, and expect that if I turn away again and turn back, I will see the tree yet again. Now I have useful knowledge that I can remember whenever I need a tree for some reason. With this expectation well established, I would be surprised to find the tree missing some day, and would look for evidence that it had been removed by some cause, finding sawdust on the ground for instance. Every time I stroll by the location of the tree and see it again, my mental model of the universe that includes the tree is confirmed, as is my method of constructing that mental model. A firm belief in this method and its results emerges from my experience.

This belief that things exist when we are not looking at them is called Realism. There are variants, depending on how far we extend our faith that things exist.  One could believe that things exist that we haven’t seen yet, or even things we will never see, or things that we could never see. This last is called Metaphysical Realism, since it applies to objects beyond our senses or instruments.

This method of gaining knowledge about the world through sensory experience is not absolutely certain, but instead represents a good bet. It is not certain that the tree will not disappear without a trace for no reason, but it’s unlikely given prior experience, and so we would bet that the tree will stay. The same could be said about the sun. We would bet our lives that it will rise tomorrow (in fact, we always do), although there is no ironclad proof. We could say that while it’s OK to draw the line between two dots we have seen, there is something shaky about drawing the line out to connect dots we only expect to see. Everything we know about the world through experience has this same minor flaw, if we were to nitpick. It begins to appear that certainty is not necessary, if we have a good enough bet to make reliable predictions.

Worldviews beyond experience

We would like to be able to draw the line out as far as we can reach, to describe everything we can imagine in the world, even though we might never even be able to see what’s there. Doing this would give us a complete picture, which would satisfy our curiosity. We therefore speculate about what can only be inferred, trying to stand outside of our known limits. (I see this as heroic.) The study of the phenomenon of existence, to ask the question “what, in general, exists and what does not?” is called Metaphysics. It’s important to distinguish this from the colloquial sense of that word, which refers more to the presumed world of disembodied spirits. There is a closely related field of study called Epistemology, which asks the questions “what is it possible to know?” and “how do we know anything?” and “what is truth?”

There are metaphysical pictures of the world other than Realism. The following list summarizes generally the positions that are relevant to our present discussion.

Realism:    The world exists independent of our observations
Idealism:    The world exists because of our observations
Positivism:    Talk about things you can’t observe is nonsense. Metaphysics is bunk

To expand on idealism, one could say that the objects I see appear every time I look and then disappear, because the whole of my experience is being cooked up by a clever force that makes illusions look real (which might be a dark but powerful aspect of my own mind, a nasty God, or some vague, universal “intelligence”). People have tried to refute this position with logic, but can’t. This doesn’t make it true, only irrefutable by pure reason, which is insufficient grounds for a truth. Expanding on positivism we could say that if our only real knowledge of the world comes from observation, idle speculation about unobservables is a waste of time. This position is also taken by Pragmatism, Instrumentalism, etc., but Positivism was in vogue when the early quantum theorists were first wrestling with their philosophical questions. While this position seems overly practical, seemingly tying a ball and chain around the feet of angels, it makes a lot of perplexing, thousands of years old questions conveniently disappear.

Science’s view of knowledge

Scientists are typically realists but some are positivists or pragmatists, and a very few are idealists. What scientists do to determine physical facts is not dependent on their metaphysical worldview. The scientific method is very much like our common sense way of learning about the world, although more thorough and precise, and has checks to keep people from fooling themselves. The list of steps in the method is as follows:

1. Observe something in the world and wonder why it’s that way
2. Take a guess
3. Set up a controlled observation that tests the prediction you would make based on that guess
4. If the prediction is borne out, the guess might be right. If not, then the guess is probably wrong
5. The test has to be cross-checked by others, using different methods, to be accepted as reliable

This all results in knowledge that has the same basic flaw as our common sense knowledge, namely that it is not ever certain, only a good bet. But science gives us results that are a better bet than most, having been checked more thoroughly. Some of our most reliable laws (such as those governing the flow of energy) have been tested thousands of times, implicitly by their being used all the time in technology. Nothing would work if these laws were unreliable. On the other hand, there is no guarantee that even these laws won’t be found to be mere approximations to a more generally applicable truth. We can only build our picture of the world out of what we know at the time, so it may change depending on what we find out later. This doesn’t mean we were wrong to begin with, only ignorant of what we would later encounter. After all, the theories we had were only accepted because they were useful at the time, so they must have had some truth to them, even if it was a limited truth.

What is quantum physics, then? It is the study of the smallest pieces of what exists, of matter and energy, time and space. We now believe that everything, time and space included, comes in small units called quanta. The discrete nature of the microscopic world determines its sometimes counterintuitive characteristics, just as the apparently continuous nature of the macroscopic world determines its apparent characteristics. That is, in our everyday “macroscopic” world we can’t see that things are made of tiny particles. The most relevant science of that world works because it treats things as if they were continuous, not made of particles. Good old science works very well until you look very close. Then you begin to see the particles, and they act in ways that are different from the apparently continuous objects we are used to. This is where “quantum weirdness” comes from; the unfamiliar rules that small, unitary objects follow. It’s what makes quantum physics so hard to swallow, but also makes it such an exciting philosophical challenge. We now know the world is subtly different from what we previously thought.

From the familiar to the unfamiliar: two versions of the same experiment

It’s possible to illustrate some central concepts of quantum physics with a simple example that—in a continuous, macroscopic sense—you can do at home. In our example, the little quanta are pieces of light called “photons,” but the argument applies to other types of particles as well.

To get a feel for the experiment, it may be useful to actually do the home version first, so that the behavior of the light doesn’t seem too counterintuitive. Find a laser pointer of any color, and a “diagonal” wire cutter or nail clipper. You want a couple of blades that meet almost parallel at the cutting surface, not like scissors. They should be able to close down to a small gap with the blades next to each other. In dim light, point the laser pointer onto a white wall six feet away or more. Now “cut” the laser beam with the wire cutters, near the pointer, keeping the beam in the center of the gap. Gradually close down the cutters, slowly making the gap diminish to zero. You will see the beam begin to spread out perpendicular to the edge of the blades, finally getting largest as it is cut off completely. You may also notice that the edges of the spread out beam are dashed lines rather than continuous. The beam remains the same width parallel to the blades of the cutter. Cut and release several times, noting especially that the spreading of the beam is greater when the gap is smaller. The action you observe is due to the fact that light consists of waves, and waves act this way when you constrict them. For a certain size gap, the spread of the beam will be wider for longer waves of light (red versus green, for example) and the space between the dark zones in the wings will be longer. Try making a permanent gap using razor blades, thin wire for a spacer, pencils to hold it all, and glue.

laser pointer held against wire cutters, so that the beam is narrowed by the jaws

five beam patterns with different wire cutter jaw closings, showing spread of beam as jaws narrow

Figure above shows the apparatus; a pointer and a wire cutter. On right is a series of patterns observed three feet away, as the cutter is closed down (top is open, bottom is almost closed down). Note how the pattern expands when the gap is closed. The expanding central bright area relates to the uncertainty principle (mentioned later). Note also the dark places between the bright bars, where no light goes. Curious, but easily explained by the wave nature of light.

The home version of this experiment as described above only deals with many photons at a time (about ten million billion per second). It’s still in the familiar, macroscopic realm. All we have to do to descend into quantum weirdness is turn down the power to one ten million billionth until there’s only one photon per second going through. And of course we need a very sensitive light detector!

A real quantum experiment and the issues it raises

Now we can describe a more interesting experiment that shows the quantum version of this phenomenon. The figure below shows how the equipment is arranged. There’s a laser as a source of photons (because the light that comes out is so well organized). There’s a couple of blades with a gap in between, which we call a “slit,” although this gap could be made very large. Some distance away from the slit is an array of photon detectors in a line, each capable of detecting a single photon when it hits. The detectors are connected to some electronics that make the results (which detector has been hit by a photon, and how many photons each detector has received) available to a computer, and a scientist can view the results on a monitor. All this equipment exists, so the experiment could actually be performed, and has been.

chain of events in a quantum experiment, from source of particles (laser) to observer

The laser is turned way down in power (filters are put in front to absorb almost all the light) until only one photon comes out at a time. The experiment is done in total darkness. We see on the computer screen that each photon hits one detector only, and seemingly at random. We can’t predict which one will be hit next, although the ones near the center are hit more often, and the ones near the edge are hit less often. The ones in the dark zones (refer to the patterns shown in the photo above) are hit not at all.

If we add up each detector’s hits and plot them on a graph (a bar five high for position 1, a bar eight high for position 2, etc.), we get a pattern that looks like what we see when there are many photons coming from the laser at once. We are counting the photons one at a time, but if we counted up to ten million billion we would get exactly the picture shown for the wire cutter/laser pointer experiment (actually, we’d see the pattern long before then). Photons don’t notice each other, so each one behaves the same way when it’s with ten million billion others as it does when it’s alone. It therefore makes sense that we would get basically the same result in both experiments, except in the single-photon case we now need to think in terms of statistics.  

The statistics of where the photons tend to hit are given by assuming that each photon is a wave, and fills the gap. As this wave spreads out, it represents where the photon is likely to hit, but not where it actually will, since that’s random and cannot be known ahead of time. We say then that the photon actually is a wave in that part of the experiment, that’s how it knows what places it should go and which to avoid. We say that the wave represents at once all possible places the photon could hit, that it’s the total collection of possibilities, each with a related probability. At least, that’s how we use the concept in our calculations, and in physics, calculations represent reality.

But when it hits a detector, only one detector receives the entire energy of the photon. None of the other detectors light up, though this big wide wave was supposedly headed for all of them at once. It doesn’t matter how small the detectors are, since in fact a single electron in one atom is absorbing all the energy of the photon, and an electron is pretty small. How did something that had to fill the gap (to know how wide it was, thus creating the appropriate pattern) and could spread out from there to encompass all the possible places to hit, get absorbed by a tiny electron? We say that the wave collapses, down to a small thing that could be called a particle. From then on, we calculate and talk about it differently, and forget about the wave that it used to be.

What happened? No one knows. No one even knows if this “collapse” actually happens, only that if you calculate the photon as a wave before it hits a detector, and as a particle afterwards, you get the right result as compared with the experiment. You can successfully describe reality (at least as reflected in your particular experiment), but not know why you can describe it, or even what’s “actually happening.” This is called the “measurement problem,” and is an unsolved mystery, although in a few paragraphs we’ll list some suggestions as to how to understand it.

Philosophical responses to quantum physics

Maybe asking “what is really going on?” is not a good question, because it very likely pertains to things we can never know. I should mention at this point that the experiment also illustrates the quantum uncertainty principle. The better you know where the photon was when it went through the gap (since the width of the gap is your range of uncertainty in its position), the less you know where it will end up on the detectors (because the range of uncertainty is the spread of the beam, where the photon could possibly end up). The better you know one aspect of the photon’s behavior, the less you know another related aspect. This indicates you can’t precisely know both aspects at once, so your ultimate knowledge (admittedly, of things that might be completely inappropriate to ask) is limited. There is nothing anyone can do to improve this situation. Also, since the final location of the photon is random, where it will hit next is another thing that can’t be known. Quantum physics is full of frustrating brick walls like this, the result of all quantities being discrete units and at the same time acting like waves. Read it and weep.

To know what is “really going on” when the measurement is made, we would have to know what the photon is doing before it hits the detectors. But since this is before the actual measurement, a positivist would reject the idea that the photon there has any meaningful status as real or not real, allowing only that you ought to calculate where the particle will end up by assuming it’s a wave beforehand. Thus it is possible to sidestep the hard question of what’s actually going on, by rendering it nonsensical. Consider this quote from the one Niels Bohr’s group in Copenhagen (the city whose name is attached to their particular interpretation):

"There is no quantum world. There is only an abstract quantum physical description. It is wrong to think that the task of physics is to find out how Nature is. Physics concerns what we can say about Nature."

And this from Bohr’s closest collaborator and fellow pioneer Werner Heisenberg:

"In the experiments about atomic events, we have to do with things and facts, with phenomena which are just as real as any phenomena in daily life. But atoms or elementary particles are not as real; they form a world of potentialities or possibilities rather than one of things or facts."

Other quantum physics pioneers such as Erwin Schrödinger and Albert Einstein thought quite differently about the philosophical implications, sometimes challenging their positivist colleagues with paradoxes and thought experiments.

Yet more problems arise when we ask specific questions about the photon that we would ordinarily about any familiar object, such as “how wide is a photon?” Well, it’s as wide as the slit, when it’s going through, because it must “know” the width in order to create the appropriate pattern of probabilities. But as you vary the slit width, the photon must follow. Thus certain properties are dependent on the situation in which you put the photon. This is called “observer dependence,” although “context dependence” would be a better term. It is impossible to observe a quantum particle in a way that leaves it undisturbed, because its context determines certain of its properties. Still, if we thoroughly understand the relationship between context and behavior of the particle, we can untangle these things and preserve the goal of objectivity. We can be objective about the object of study plus the experiment that surrounds it, and know nature as a connected system rather than the impossible case of a particle in isolation.

The slide into idealism

Assuming we accept the idea that there is a wave (or a calculation made as if there was a wave) at some point in the experiment and then a particle after the wave (called the “wave function” to emphasize that it’s just a calculation) collapses, then when does this collapse happen? Certainly, most physicists would make their jobs easiest by collapsing the wave function at the detectors, because calculating complicated wave functions takes a lot of computer power. Plus, the photon is lost there and transfers its energy to an electron. But the electrons are waves too, and so might have their own wave functions that could continue the type of action we saw with the photon, namely that the electron wave is a combination of all the possible places the electron could appear in the detectors, and no choice has been made as to where there’s a “hit.” The wave just continues as an array of possibilities with probabilities, through the machine. Nothing in quantum physics prohibits this, so it’s possible in principle.

One photon hitting a detector liberates only one electron, but standard electronics can’t deal with an electric signal that small. We need an amplifier that multiplies one electron into many, making a stronger signal. Here is where the microscopic becomes macroscopic. As more electrons get into the act, the original wave gets lost in the cacophony, and interesting quantum effects begin to look more like mundane effects from classical physics. Maybe the wave function can be said to collapse here.

But if we take to its extreme the assertion that any physical system—no matter how complex—can be described by a quantum wave function, then it needn’t collapse even when accounting for big machines like computers and monitors. The entire experimental apparatus could be just a complicated wave that embodies all the possible outcomes of the experiment, just as the original photon did. The only problem with this is that we never see such a thing, only that one of the possible outcomes has occurred. At that point we know for sure it has collapsed, from many possibilities to one certainty. The last point at which the collapse could happen is when we know it has happened. What then, made it do so? Maybe our knowing was the cause! Maybe knowing is a physical phenomenon of some sort, that collapses wave functions. Proof again that sentient beings like us are really special.

chain of quantum experiment events, now with indications of where the status of "wave" or "particle" is ambiguous

Hardly anyone takes this last position (i.e. “the wave function collapses at consciousness”), because it requires everything to act in strange ways when we’re not looking. It violates the mind-independence that we assume for solid things in the world. Yet, it is one of the very few answers to a vexing question, so we keep it around.

Yet, this apparently silly suggestion contributes to an argument for idealism. Add to it the position of the positivists regarding the wave function: since the wave is prior to any measurement it has no proper status as real. It would be easy to misinterpret this statement as suggesting that the wave is known to be not real. We would then be led to the belief that the unreal becomes real when the wave function collapses, and since this happens at the point of our knowing (at “consciousness” they say), our mind somehow makes the unreal real. We are then back to idealism, the assertion that the world exists because we perceive it. Things are not only not what they appear to be, they are not there at all until they appear to our senses.

As noted above, the particular properties of quantum objects are not independent of our probing, and so are called “observer dependent.” This too lends credence to the idea that we determine reality by our observations. The realist belief that the world is independent of our minds seems untenable. Of course, if we say “context dependent” instead, our minds are not the issue and objectivity again becomes possible.

It’s important to note that even if all this was true and our minds caused the collapse of the wave function to produce a certain outcome, we could not know or determine that outcome beforehand. It is a random selection from among the possibilities, weighted by their respective probabilities. We could not exercise will to make the quantum world what we want, even if we could make it appear. Thus some aspect of even the quantum idealist world is independent of our wills.

It is clear that we must try to accommodate what we have learned from quantum physics into an overall worldview somehow, whether we accept idealism or not. One might characterize a world view as a list of attributes of the physical universe, related by a consistent theory. Changing that world view would mean changing some of the attributes, discarding some while adding or keeping others. Since we are only changing things in order to cover our new experiences with quantum experiments, we needn’t change or world view regarding everyday experience because nothing new has been seen there. We could characterize the currently available suggestions for new world views in a table, listing only two attributes in order to show a sample of the differences:

Quantum world view Something to keep Something to discard
Copenhagen Unidirectional time Causality
Pilot wave Relativity Locality
Many worlds Causality Single universe
Decoherence Locality Unidirectional time

Without explaining all these positions, one can say that the debate about the alternatives is fierce and exciting. At the same time, most people who actually use quantum physics go about their work as usual, predicting experiments and designing gadgets with great success.

Pitfalls of idealism

I have only listed the reasonable, serious positions on the philosophical implications of quantum mechanics. There are some unreasonable ones also. Usually they derive from the idealist metaphysical orientation, which can be used to validate mysticism and other pursuits unrelated to science, while claiming scientific support. A popular example is the writing of Deepak Chopra, who loves the word “quantum” and puts it frequently on the covers of his books. Chopra is an admitted idealist, as a quote from a recent book reveals:

"The physical world, including our bodies, is a response of the observer. We create our bodies as we create the experience of our world. … Einstein taught us that the physical body, like all material objects, is an illusion…The unseen world is the real world."

Whatever position one takes on his idealism, Chopra is quite wrong about Einstein, who was a staunch realist, but who represents for Chopra what he thinks he knows about the weird mysteries of the quantum world. Chopra seems to take the word “quantum” to mean “subjective” and to validate the subjective insights of Indian mysticism. He sees the physical world as a shadow of the spiritual world supposedly perceived by mystics, which he calls the quantum world. Chopra confuses quantum mechanics with relativity, and snares the reader in a swirl of facts, half truths, myths, science, philosophy, religion, and anecdotes connected by skillful but logically vacuous rhetoric. Contrary to his frequent appeals to Einstein’s ghost, Chopra’s claims are not supported by scientific evidence, since no evidence can verify metaphysical claims such as the illusory status of material objects.

Another outlet for idealist interpretations of quantum physics is the movie What the Bleep do We Know? This half documentary-half narrative shows a woman who takes on a new attitude and becomes aware of her own wave function, seeing possible alternate selves with husbands or boyfriends. Lest the viewer interpret this as a quaint metaphor, this extreme interpretation is bolstered by learned physicists who claim to be on the cutting edge, but more probably hail from the lunatic fringe. Their respective websites and comments in the film clearly identify them as idealists in the manner of Chopra, though more familiar with physics. Central to the film is the idea that quantum physics tells us we can control our world through acts of will. While this is true in the familiar regard that we can move matter with our hands and decide whether to take a bubble bath, the film’s pundits go further and suggest that walking on water is just a matter of the right attitude. Like Chopra, they claim that science endorses a particular metaphysical world view. If science leans in any particular direction, it would be toward realism and away from idealist mysticism.

Why does this idealist position appeal, given its contradiction with our common sense experience? It may be that people’s reasoning is emotionally motivated. We are social animals, most comfortable among friends. A cold, harsh world is scary, especially when one considers how little of the universe we can comfortably live in. We would like to anthropomorphize the world, to have a friend where there is none. Children show this tendency strongly, preferring pictures of the world where everything has a human face and voice, as in Pee Wee’s Playhouse. This was a television show where all the furniture and flowers and trees could talk to a man who acted like a child. In children’s stories, all animals talk, making it unnecessary to imagine a completely foreign mind. The idealist’s world is full of projections of ourselves, reacting to our thoughts and desires. This world loves or hates us, either of which is more comforting than a mindless vacuum. Early idealists such as George Berkeley saw the universe as a creation of the mind of God, which is not much different from Chopra’s “universal intelligence.”

Pee Wee had Chairy the chair to talk to, and Floorie the floor. Chopra wants Celly the cell and Universy the universe. Personally I feel it’s an insult to nature to reduce it to just another self portrait, preventing any insight into the real nature of physical reality. Where we should be seeking a window to look beyond our human limitations, we instead find a mirror and revel in them.

Recommendations

How should the ordinary person react to all this? Unless you are looking for an inspiring view of the great beyond, forget all this quantum stuff and learn classical (that is, 19th century) physics. In the U.S. we have some of the worst public education of all the industrialized nations. California, where I come from, is one of the worst states for primary science and math education, yet boasts some of the worlds best universities and high tech industries. Our own students can’t go to our universities or find technical jobs. It’s a scandal. In the near term, people will have to teach themselves, and a good place to start is to learn how the world around you works. Start maybe with your refrigerator or your TV or your car (leading to the basics of thermodynamics, electromagnetics, and classical mechanics, respectively). Quantum physics may be fashionable but it is irrelevant to explaining these things on a practical level. The old physics that explains these things is not invalidated by the new, only revealed to be limited in scope. But you almost always live within those limitations, so the old physics is sufficient.

It’s not “empowering” to be led on a wild goose chase in search of unattainable goals, while remaining ignorant of why the sky is blue and the sunset is orange. To know things like this changes one’s relationship to the outside world, even providing some measure of transcendence, in that it’s possible to reach beyond oneself conceptually, living for a moment in a cloud’s reflections on the sea, or a flash of color in winter air. One can internalize the knowledge of what is making the world what it is, paradoxically coming to invert that relationship and expand consciousness to encompass the landscape beyond. If one was to seek a spiritual aspect to science it could be found here. In contrast, idealism blocks such transcendence by encouraging one to see only oneself everywhere.