Authors: Robert Kroese
You pull the trigger on the gun, trapping the atom. The question is: where is the
atom? Common sense would tell you that it’s either in Box A or Box B. But common sense doesn’t apply to quantum mechanics. The fact is, until you open one of the boxes,
the atom is in both boxes simultaneously
. It isn’t split in two, with half of it being in Box A and half of it in Box B; it’s both entirely in Box A and entirely in Box B.
Here
’s how we know this to be the case: let’s suppose that we have a large number of box pairs that have been prepared as described in the previous paragraph. We position a box pair in front of a screen on which an impacting atom would stick. We open a narrow slit in each box at the same time. An atom hits the screen. If we repeat this action with many identically positioned box pairs, we will find that atoms cluster in some areas of the screen and not others, demonstrating an interference pattern. Further, if we change the spacing of the box pairs, we will find that the regions where the atoms cluster together are spaced differently: the larger the spacing between the boxes of a pair, the smaller the spacing between the places where atoms hit. What does this mean?
Well, let
’s take the “common sense” explanation, which would tell us that for each box pair, the atom was either in Box A or Box B, and that when we opened the slits, the atom left that box and struck the screen. But if this is the case, why would the location of the
other
box determine the region on the screen where the atom was “allowed” to strike? How can we explain the location of an
empty box
affecting the location of the particle? We can’t. The “common sense” explanation leads us to an absurd conclusion. So we are left with the conclusion that the atom was somehow in both box A and box B simultaneously. More precisely, the probability of the atom being emitted from one box or the other was “smeared” across both boxes, so that until the atom hit the screen, it would be meaningless to say which box it was in.
But now, instead of opening the slits at the same time, let
’s open the slit in one of the boxes and then later open the slit in another box. What we will find in this case is that the atom will either come out of the first box or the second box, but not both. And if we actually look in the boxes one at a time, we will find the atom in one box or the other. If we look in Box A, we will either find the atom or not find it. You will never find
half
an atom. If we find the atom in Box A, then the atom is entirely in Box A and not in Box B. If we don’t find the atom in Box A, then we will find the atom in Box B.
I should note that this is not a hypothetical scenario. Experiments conceptually identical to this
“box pair experiment” have actually been carried out, producing the results that I have described here. Thus through experimentation, we have been able to show that an atom is in one box or another. But we have also shown,
under identical circumstances
, that an atom was in both boxes.
To understand the import of this statement, imagine Galileo dropping objects of different mass from the Tower of Pisa and finding that gravity acted differently depending on how he chose to
look
at it. Imagine that he could first do an experiment conclusively proving that the two objects hit the ground at the same time, and then immediately thereafter do another experiment proving that the heavier object struck the ground first. Imagine further that no matter how hard he tried to find a single authoritative law of gravitation, it eluded him, and he lived out his days never knowing whether all objects fall at the same rate or not – believing, in fact, that they must sometimes fall at the same rate and sometimes must not, and that the way the objects behaved seemed to be completely arbitrary. Imagine Galileo’s peers and successors, the most brilliant minds on earth, devoting their lives to understanding why gravity acted in this way and none of them being able to explain it. Imagine, finally, decades after Galileo’s death, that science had concluded it was impossible for anyone to understand why gravity acted in this capricious manner and that the best solution was to just accept the fact and stop trying to explain it.
If that had happened, there would have been no scientific revolution. The idea of using experimentation to
test hypotheses would have been dismissed as the quaint conceit of an eccentric. Newton would never have published his
Principia
, a cornerstone of modern science. Einstein would never have discovered general relativity. If any sort of technological progress occurred over the next 400 years, it wouldn’t have been based on a scientific method designed to get at basic laws underlying the universe, but rather a sort of technical trickery based on an arbitrary collection of randomly acquired facts about the material world. What passed for science would really be alchemy, an inexact but occasionally useful body of hermetic knowledge passed down from one generation to the next. Theoretical science would be even more divorced from empirical reality, becoming indistinguishable from mysticism.
To a large extent, we can see this very thing happening in theoretical physics today. By 1981, the field of physics had experienced two hundred years of dramatic growth. Successive discoveries deepened our understanding of nature, because in each case theory and experiment worked in tandem. New ideas were tested and confirmed and new experimental discoveries were explained in terms of theory. Then, in the early 1980s, progress ground to a halt. The last major, empirically verifiable discoveries in physics occurred prior to 1982. Since that time, we have seen a proliferation of theories in the absence of empirical evidence. The most fundamental of the sciences now flirts openly with mysticism.
I remember reading that Neils Bohr once remarked that if you aren
’t shocked by quantum theory, you haven’t understood it. I’m not sure I understand it, but I’m definitely a little weirded out by it. How can a particle be both entirely in Box A and in Box B? And how can looking in one of the boxes cause the particle to choose to be in one box or the other? What he is saying is that by looking, you are forcing the atom to “choose” to be either in Box A or Box B. In other words,
your observation seems to cause the atom to be in one place or the other
.
And if that isn
’t weird enough, Heller then goes on to explain something called a “delayed-choice experiment,” which seems to indicate that observing which path a particle took can retroactively alter its behavior. That is, let’s say you do a double slit experiment but don’t observe the results. Since the experiment is unobserved, all of the light going through the slits will act as waves rather than particles. But if you store information about which slit a photon went through and later look at that information,
you will create a history of the photon having gone one slot or the other
. If you observe the results of the experiment after looking at the information, you will see that the photon went through the correct slot. If, however, you destroy the information without looking at it and then look at the results of the experiment, you will see that the photon went through both slots. Heller says that no matter how many times you perform the experiment, the results of the experiment will always correlate with your later decision to either look at or destroy the information about the photon’s path. Again, if you’re willing to set aside the complete absurdity of that statement and just go with it, you can skip the next few paragraphs:
This means that on a subatomic scale, cause and effect can apparently go backwards. That’s the only possible explanation if we accept that our choice of observation caused the photon’s behavior. If we deny the possibility of causation moving backwards through time, we are left with an even more troubling possibility: that the behavior of the photon determined our choice of observation. In that case, free will is an illusion: our apparent choice was in fact constrained by the behavior of the photon. (Another possibility is that both our choice and the photon’s behavior were caused by some other factor outside of our control, which also negates the possibility of free will.)
On
e could argue that these experiments are “special cases,” and that we might therefore still have free will in other cases, but it’s hard to see how this could be. If the subjective perception of free will can be demonstrated to be an illusion in one case, what reason do we have to think that free will exists in other cases? Further, to say that the observation of quantum phenomena is a “special case” has the matter backwards. We expect principles deduced from observing the subatomic level to apply universally. Quantum physics is the general case; classical physics is the special case. We know for a fact that classical physics is
wrong
. Classical physics is only a useful approximation. The sensible conclusion, it seems to me, is that our perception of free will is a similar sort of approximation, a useful concept that nevertheless fails to conform to reality at a basic level.
This is not some esoteric problem purely of academic interest. All of science is based on experimentation, which is to say performing an experiment and then observing the results. If how we observe the results can retroactively affect the experiment, then we have a very fundamental problem in the scientific method. It may be reassuring to think that the problem
occurs only at the quantum level, but how can we know? That’s simply the only arena in which we’ve observed the problem, and it’s the reliability of observation that is in question here. It’s fine to say that we will perform multiple experiments and gauge how observation affects the experiment, but all this does is kick the problem up a level. By observing how observation affects an experiment, we are essentially conducting another experiment, a “meta-experiment,” if you like. How can we know that the way we are observing the results of this meta-experiment isn’t affecting the outcome?
Let
’s suppose that we perform a double slit experiment a hundred times, each time observing which path a particular photon takes. Every time, the photon acts as a particle, traveling through either one slit or the other. Now let’s suppose that we perform another double slit experiment a hundred times, without observing which slit the photon travels through. Every time, the photon acts as a wave, seeming to travel through both slits. Thus our hypothesis is confirmed: if we observe a photon, it will act as a particle, but if we do not observe a photon, it will act as a wave. But how do we know that the confirmation of this hypothesis isn’t the consequence of the way we set up our meta-experiment? How do we know, in fact, that the 200 double slit experiments would act the way they did if we weren’t observing the meta-experiment? We don’t. Not only that, but we have some pretty solid evidence, based on our knowledge of the way light behaves, that our observations cause reality to act differently than it would if we weren’t observing.
If, on the other hand, we refuse to admit the possibility of reverse-chronological causation, how can we explain the exact correlation between our choice of experiment and the behavior of the photons? As I see it, there are two possibilities. The first is that rather than our observation causing the photon
’s behavior, the photon’s behavior is constraining our choice of which experiment to perform. The second is that both the photon’s behavior and our choice of which experiment to perform are both determined by some other, unknown phenomenon. In either case, our choice of which experiment to perform is not free but is instead determined by some force outside our control. If that’s the case, then we have an even bigger problem.
Science is based on the possibility of the experimenter making free choices. We assume, for example, that we could freely choose to perform either an interference experiment or a which-path experiment. If, however, light is objectively two completely different things at different times and it (or something else) arbitrarily prevents us from performing certain experiments by somehow controlling our choice of which experiment to perform, then we live in a conspiratorial universe that actively resists certain types of scientific endeavors.
Both the reverse-causation hypothesis and the conspiratorial universe hypothesis are counterintuitive and highly troubling. Further, it is clear that we can no longer accede to the fiction that the universe can be neatly divided into the “physical” and the “mental.” Either our observations contribute to the creation of reality or our seemingly free choices are in fact completely constrained by that reality.
My personal intuition is that these two possibilities are complementary, and that they both obtain to some extent. Thus the duality of mind and matter is replaced with the duality of volition versus determinism. This comports with the Jainist idea that human beings are constantly struggling against the weight of karma. And yet, if we take this notion to its logical conclusion, a strange inversion takes place: to conceive of a force that is capable of anticipating and thwarting my efforts to understand the universe, I cannot help but to imagine an intelligent, volitional being or beings guiding that force. This idea is implicit in the idea of a
“conspiratorial universe.” If the universe is conspiratorial, then what is conspiring against me? A purely passive, mechanistic force cannot conspire, cannot anticipate nor intentionally thwart my intended actions. Only something that is a mirror of my own intentions – a sort of anti-intention – could do this.
The situation is reminiscent of the ancient Chinese concept of Yin-Yang. Yin is cold, dark, and passive and Yang is hot, bright, and energetic, and the two swirl around each other, one becoming the other. Western science since Descartes has insisted on a false dichotomy, with science (Yang) studying the natural world (Yin) from outside. It was assumed that the natural world was ess
entially passive and mechanical – that it had no intelligence or intentions, and therefore it would sit still for us to contemplate it safely from within the objective realm of science. As our knowledge of Yin expanded, however, we came up against the border between Yin and Yang and realized to our surprise that while Yang pushes on Yin, Yin is pushing back. Further, it’s not always clear who is pushing whom. Does the existence of a photon cause us to observe it, or does our observation cause the photon to exist? I don’t believe there’s any definite answer, because as with Yin-Yang, the border is a continuum.