By Adam J. Pearson
Figure 1.1: the graph of the probability wavefunction for an electron. The high peaks are places where the electron is most likely to be found when measured; the flat areas are places where the electron is least likely to be found when measured. Prior to measurement, this is all we can say about the electron’s position is that it likely to be found in certain positions and unlikely to be found in other positions; when we measure it, this wavefunction ‘collapses’ and we find it in a particular place.
The Copenhagen Interpretation of quantum mechanics states that prior to measurement, particles exist only in a probabilistic superposition (adding up) of possible positions. In other words, they have no definite positions prior to measurement; all we can say about them is that they more likely to be found in one place than in certain other places. This distribution of probable positions can be expressed mathematically in what’s called a ‘wavefunction.’
If we look at one of these wavefunctions visually, there are the equivalent of little mountain peaks that depict places where the particle is most likely to show up when measured. The flatter areas depict places that it is less likely to appear. When we do a measurement of it, this wavefunction of probable locations ‘collapses’; we now find the particle at a given location. It no longer exists in a superposition (adding up) of possible locations; it exists in a particular place. And that’s where we find it to be when we measure it. This phenomenon is called the ‘wavefunction collapse.’ I often hear people say that “quantum physics says that consciousness collapses the probabilistic wavefunction of an electron so that we find it at a given place.” This is a total misunderstanding. In fact, consciousness has absolutely nothing to do with the wavefunction collapse at all.
It is not consciousness that forces the collapse of the probabilistic wavefunction, but the measuring instrument, the detector, which is the physical tool that is used to measure either, for example, the position or the velocity of a given electron or set of electrons (never both at the same time, due to Heisenberg uncertainty). In fact, we can show the fact that consciousness is irrelevant to the collapse of the wavefunction experimentally. If we set up an electron gun to fire electrons through a double split and hit a detector afterwards to measure their position and then leave the room while the measurements are happening, the wavefunction still collapses; we still get the interference pattern. Thus, consciousness is irrelevant to the wavefunction collapse.
Figure 1.2: A section through a lattice showing a quark wavefunction density versus one space and the time axis of lattice. The high peak is where the probability density is highest; that is where we are most likely to measure the quark to be in that particular area of space at that particular time.
Moreover, contrary to the claims of the speakers in the film What the Bleep do We Know?, the Copenhagen Interpretation does not say that it is ‘the conscious observer’ that collapses the wavefunction; rather, it says that it is the physical act of measurement using a particular physical instrument that does.
If this is the case, then why do people tend to think that consciousness is responsible for the collapse of the probabilistic wavefunction? People tend to think that it is consciousness that causes the collapse because quantum physicists sometimes use the word “observe” when they describe the act of physical measurement. Thus, they will say things like “it is the act of observing the particle that causes the wavefunction collapse.” But we need to be clear about the meaning of the word ‘observe’ here; it does not mean ‘being aware’ or ‘being conscious.’ It means ‘physically measuring using a physical instrument.’
Another popular misunderstanding is that it is the Heinsenberg uncertainty relationship that causes the wavefunction to collapse. In fact, though, it is not the uncertainty relationship that causes the wavefunction collapse. It’s the act of measurement; it just so happens that some pairs of observables (measurable properties) are in an inverse relationship so that as we increase precision in measuring one, we decrease precision in measuring the other. This is the essence of the Heisenberg uncertainty principle: in quantum mechanical measurement, the uncertainty of a measurement of the velocity of a particle (or more accurately, ‘wavicle’) and the uncertainty of a measurement are inversely related. As one goes up, the other goes down. As the other goes up, the one goes down.