Welcome to another edition of Woo Enthymemes. This entry was inspired by remembering some guy on a news article comment thread who was rambling on in a superior tone of voice about how the Double Slit Experiment put us skeptics in our place in regards to the existence of the supernatural. Cue my rolling eyes. I have yet to meet a woo who can tell me something I didn't already find boring in an "old news" sort of way about quantum mechanics.
Put simply, the typical quantum woo's amazement at the Double Slit Experiment comes from being stuck in the "Middle World," full of medium-sized objects moving around at medium speeds over medium periods of time, many of which involve agents we can perceive with our standard array of senses. All the objects they observe aren't heavily affected by being observed. Our minds were "built" by evolution to live in that world because resources spent understanding the "Big World" (of galaxies, dark matter, and illions of years), the "Small World" (of electrons, quarks, and femtoseconds), and the "Dense World" (of singularities and the instant of the Big Bang) was not conducive to having and raising children.
There is still a piece of my mind left in the savanna that gapes in wonder when I hold two repelling magnets against one another: They're inanimate objects, and yet they "struggle" to avoid meeting one another, as if they have their own locomotion, pushing against my fingers in a desperate effort. I know intellectually, of course, that like magnetic charges repel like charges. There's no intention there, anymore than water "wants" to flow downhill.
The myth of passive observation is born of our heritage as inhabitants of the Middle World. Let's say I'm in a dark cave and I want to examine a particular rock. I can shine a flashlight on it to look at it. I can pick it up and feel its shape. I can chip off a tiny sliver of it and perform various tests to determine its composition. All of these methods of observation change the rock. Shining light on it warms it up ever so slightly. Picking it up leaves traces of my skin's oils on it while picking off dust. Removing a sliver subtracts from the rock's overall mass. Because a human can be very delicate in the Middle World, these changes can be quite minimal. The danger of this, however, is that it can lead us to the hubris of thinking we can observe the universe as if we are not a part of it.
That is where things go wrong when a thoughtless person looks at the results of experimenting in the Small World of Quantum Mechanics. The word "quantum" refers to the smallest possible changes. Warming up a rock by a fraction of a degree in the middle world may be negligible, but the same sort of energy addition in a Quantum experiment could very well excite an electron into the next orbital shell or pin down the uncertain particle to a particular location, collapsing its wave function. The latter is precisely what happens in the Double Slit Experiment: Electrons are extraordinarily tiny particles with tiny mass. When we experiment with single electrons, we don't have the messy interactions of the Middle World to average out all the strange individual behaviors. Working with fundamental particles could be akin to moving an egg with a piece of construction equipment: We're hamfisted Middle World creatures manipulating objects that can be altered with the most delicate of touches.
The reason I am repeatedly impressing that fact in this blog post is because this is an issue that we were not made to think about. We take it for granted that we can look at something without changing it, mostly because the changes we inflict when being delicate are so small we can't casually observe them. While scientists are aware of this fact, many laymen who read their work have not raised their awareness. That is why many quantum woos out there can act surprised that observation can have effects: If they naively believe that we are separate from the experiment, they can believe it's magic when "passive" observation can have active effects. There is no such thing as passive observation. There is only active observation that strives to have negligible effects. In the Small World of QM, there is no "negligible."