The Observer Effect

The celebrated Uncertainty Principle of quantum mechanics is something that has aroused much of my interest — and by that I mean it’s philosophical implications beyond physics. It’s kind of why I took quantum mechanics as an elective last semester.

We were first taught the principle back in 11th-12th standard. It seemed quite absurd for a student who was used to classical mechanics. But it never got me thinking to an extent I am now, until it was retold to us in our course this semester in a more verbal form of the statement: The more precisely the position of some particle is determined, the less precisely its momentum can be known, and vice versa.

Now, since this article is titled the “Observer Effect”, I’m obviously going to lead you there instead of the uncertainty principle. But I started with it because I realized that the Uncertainty Principle is more often than not, confused with the observer effect. (I’m guilty of this too!) But the difference is not as subtle as it may seem. Since, I began writing this with the eagerness to discuss what I understood as the observer effect, I shall begin with it first. I’ll save the Uncertainty Principle, and how it is confused with the Observer effect, for another article.

The Observer Effect states that simply observing a situation or phenomenon inevitably changes that situation or phenomenon.

A simple example of the observer effect: to measure the pressure of a tire, we actually deflate it a little bit and then measure the pressure in the process. By deflating the tire slightly, we are actually changing (decreasing) the pressure by a tiny bit, but that tiny bit is insignificant for all practical and engineering purposes, so we take it to be the actual pressure.

Descending into what this means philosophically:

I like to think of the Observer Effect as a humble reminder to us that we are not a separate entity from the environment we are observing, but we are essentially and inseparably a part of it. Why should it be that we consider ourselves to be incongruously separate from it? Just because we consider ourselves to be conscious beings, doesn’t mean we are above all else in terms of our actions and their environmental effects.

In an imaginative case, if you were a God or some otherworldly entity, sitting above all else, not a part of the universe, you probably would have been able to observe the environment, by making a non-interactive measurement. But such is not the case and the Observer effect keeps our feet on the ground and says that you are not a God, or rather, if you are a God, you’re still a part of the universe; and that you observing or interacting with the environment is going to change it. So no matter how advanced our science and technology and cool contraptions might get, at the end of the day, we are all a part of the universe, all our observations are a part of the universe and they change it in some way or the other while observing.

The Observer Effect is a humble reminder that we are not a separate entity from the environment, but a part of it.

Then comes the base of all our scientific theories. They fundamentally require observation. If our theories are describing the environment, and these theories are based on the observations that changed the environment, what exactly is our theory describing? We then hope, that at least it is describing an environment that is between what the environment was prior to observation and what it is now after observation, if not a completely outlandish environment.

In the case of the tire, when you start deflating the tire, the actual pressure is high, and when you’re done deflating it, the actual pressure is slightly lower. We expect that the pressure measured will be something between these two pressures and not something wildly different.

Did Newton take into account, while devising his three laws of motion, the fact he was observing the apple when it fell (assuming the apple story is true)? This is indeed an absurd question, if not given the background we just discussed.

Classical mechanics simply neglects the effect of the observation. This is so because the effect on the environment is so small, that we assumed situations to be described by measurements made on ideal instruments. These ideal instruments were conveniently assumed to not affect the environment. Eg. ideal voltmeters and ammeters assumed in electrical circuits. While in some other cases we didn’t notice the effect at all for years, like the fact that light has momentum and that it can impart it to particles.

This convenience had to be dealt with later when we started making observations that affected the environment noticeably. And so quantum mechanics was devised to attempt to explain these phenomenon. We started to observe particles so small, that merely watching them with light would drastically alter their momentum. We started talking in terms of probabilities, that the particle has a 40% chance of being in this region if measured, and a 60% chance in the other.

But did we ever specify how the particle is being measured? Is this emergence of probability due to the shortcoming in the theory not considering the observer and how he measured the particle? Do we even know what parameters are required to specify how the particle is measured?

Perhaps, if we are able to answer these questions, and incorporate the observer in the theory, we may be able to proceed further in understanding the environment and thus the universe as a whole.

Observer + Environment = Universe
If we understand the universe better, we’ll understand the observer better, that is, we’ll understand ourselves better.