The ‘observer with a hammer’ effect

Here is another short essay about quantum mechanics-related stuff. It’s a very high level essay, so any practising quantum physicists probably shouldn’t read it 😉 It is more aimed at a general audience (and news reporters!) and talks about the ‘spooky’ and ‘weird’ properties of superposition and decoherence that people seem to like to tie in with consciousness, cats, and ‘the observer effect’. It doesn’t really go into entanglement directly, I think that should be an issue for a separate post! It is also a fun introduction to some issues when trying to perform experimental quantum computing and quantum physics in general.

I’ve also put this essay in the Resources section as a permanent link.

The not-so spooky after all ‘observer-with-a-hammer’ effect

S. Gildert November 2010

I’m so sick of people using phrases like this:

“Looking at, nay, even thinking about a quantum computer will destroy its delicate computation. Even scientists do not understand this strange and counter-intuitive property of quantum mechanics”

or worse:

“The act of a conscious observer making a measurement on a quantum computer whilst it is performing a calculation causes the wavefunction to collapse. The spooky nature of these devices means that they just don’t work when we are looking at them!”


These kind of phrases spread like viral memes because they are easy to remember and they pique people’s curiosity. People like the idea of anthropomorphizing inanimate systems. It makes them seem unusual and special. This misunderstanding, the idea that a quantum system somehow ‘cares’ or is emotionally sensitive to what a human is doing, is actually what causes this meme to perpetuate.

So I’m going to put a new meme out there into the-internet-ether-blogosphere-tubes. Maybe someone will pick up on this analogy and it will become totally viral. It probably won’t, because it seems pretty dull in comparison to spooky ethereal all-seeing quantum systems, but if it flicks a light switch in the mind of but a single reader, if on contemplating my words someone’s conceptual picture of quantum mechanics as a mystical, ever elusive resource is reduced even by the tiniest amount, then my work here will be done.

Memetic surgery

Let’s start by cutting the yukky tumorous part from this meme and dissecting it on our operating table:

“Looking at a quantum system changes it.”

Now I don’t necessarily disagree with this statement, but I think you need to define what you mean by ‘looking’….

Usually when physicists ‘look’ at things, they are trying to measure something to extract information from it. To measure something, you need to interact with it in some way or other. In fact, everything in the world interacts with many other things around it (that’s why Physics is interesting!). Everything one could ever wish to measure is actually sitting in a little bath of other things that are constantly interacting with it. Usually, we can ignore this and concentrate on the one thing we care about. But sometimes this interacting-background property can cause unwanted problems.

Measuring small things

Brownian motion can give us a nice example of a nasty background interaction. Imagine that a scientist wanted to investigate the repulsion (or attraction) of some tiny magnetic particles in a solution that had just precipitated out of an awesomely cool chemical reaction. (I don’t know why you’d want to do this, but scientists have some weird ideas). So she starts to take measurements of the positions of the little magnetic particles over time, and finds that they are not obeying the laws of magnetism. How dare they! What could be wrong with the experiment? So our good scientist takes the solution in her beaker and you start to adjust various parameters to try and figure out what is going on. It turns out that when she cools the solution, the particles start to behave more in line with what is expected. She figures that the Brownian motion – all the other molecules jostling and wiggling around near the magnetic particles – are actually kicking the experiment around, ruining the results. But by lowering the temperature, it is possible to stop the environment in which the particles sit from disturbing them as much.

In this example, the scientist was able to measure the positions of the particles with something like a ruler or a laser or some other cool technique, and it was fairly easy, even though the environment had become irritatingly convolved with our experiment. Once she had got around how to stop the interaction with the environment, then our experiment worked well.

Quantum systems are small, and small things are delicate. But quantum systems are so small that the environment, the ‘background-interaction’ around them, is no longer something that they, or we, can ignore. It pushes them around. In order to have a chance at engineering quantum systems, researchers have to isolate them carefully from the environment (or at least the bits of the environment that kick them around). Scientists spend a lot of time trying to stop the environment from interacting with their qubits. For example, superconducting processors need to be operated at very cold temperatures, in extremely low magnetic field environments. But I won’t digress into the experimental details. The main idea is that no matter how you build your quantum computer, you will have to solve this problem in some way or other. And even after all this careful engineering, the darn things still interact with the environment to some degree.

It gets worse

But with quantum systems, there is an extra problem. The problem is not just the environment. To illustrate this problem, I’ll propose another little story of the striving scientists.

Imagine that our scientists have developed a technique to measure the diameter of bird eggs using a robotic arm. The arm has a hand that grasps the eggs, measures them, and then displays the diameter on a neat built-in display. (Alternatively, you can Bluetooth the results to your iPhone, so the scientists tell me). Anyway, this robotic arm is so ridiculously precise that it can measure the diameter of eggs more accurately than any pair or vernier calipers, any laser-interferometer array or any other cool way of measuring eggs that has ever existed. The National Standards laboratories are intrigued.

However, there is a slight problem. Every time the robot tries to measure an egg, it breaks the darn thing. There is no way to get around this. The scientific breakthrough relating to the accuracy of the new machine comes from the fact that the robot squeezes the egg slightly. Try and change the way that the measurement is performed, and you just can’t get good results anymore. It seems that we just cannot avoid breaking the eggs. The interaction of the robot with the egg is ruining our experiment.

Of course, a robot-egg measuring system like this sounds ridiculous, but this is exactly the problem that we have with quantum systems. The measuring apparatus is huge compared to the quantum system, and it interacts with it, just like the pesky environment does. It pushes and squeezes our quantum system. The result is that anything huge that we use to try to perform a delicate measurement will break it. And worse still, we can’t just try to ‘turn it off completely’ like we could with the environment surrounding the particles in the solution. By the very nature of what we are trying to do, we need the measurement apparatus to interact with the qubits, otherwise how can we measure them? What a pain. We end up measuring a kind of qubit-environment-combination mess, just like trying to measure the diameter of a broken egg whose contents are running all over our robotic measurement apparatus.

I can’t stress enough how comparatively big and clumsy quantum measurement apparatus is. Whilst scientists are trying to build better measurement techniques that don’t have such a bad effect on quantum systems, ultimately you just can’t get around this problem, because the large-scale things that we care about are just not compatible with the small-scale of the quantum world.

This doesn’t mean that quantum computers aren’t useful. It just means that the information we can extract from such systems is not neat, clean and unique to the thing we were trying to measure. We have to ‘reconstruct’ information from the inevitable conglomerate that we get out of a measurement. In some cases, this is enough to help us do useful computations.

Hammering the message home

Nowhere here does one need to invoke any spookiness, consciousness, roles of the observer, or animal cruelty involving cats and boxes. In fact, the so-called ‘observer’ effect could perhaps be more appropriately termed the ‘observer-with-a-hammer’ effect. We take for granted that we can measure large classical systems, like the 0 or 1 binary states of transistors, without affecting them too much. But measuring a quantum system is like trying the determine the voltage states of a single transistor by taking a hammer to the motherboard and counting the number of electrons that ended up sticking to the end of it. It kind of upsets the computation that you were in the middle of. It’s not the observer that’s the problem here, it’s the hammer.

So, the perhaps-not-so-viral phraseology for one to take away from my relentless ranting is thus:

“When you try and measure a delicate quantum system with clumsy apparatus, you actually end up with a messy combination of both!”

Alternatively, you could say ‘you can’t make a quantum measurement without breaking a few eggs’ – But if that terrible pun sticks then I will forever be embarrassed.


7 thoughts on “The ‘observer with a hammer’ effect

  1. […] This post was mentioned on Twitter by Stephenie Noah, Robert P Reibold. Robert P Reibold said: The 'observer with a hammer' effect « Physics and cake: “The act of a conscious observer making a measurement on… […]

  2. Dr.Dom says:

    Hey Suz this is a great post!
    You are totally right about the misunderstanding of the measurement of quantum systems, and I think the analogies you use here are a brilliant way of talking about them.
    In fact I can see myself using them in the future when I need to explain this stuff (giving appropriate references of course).
    Excellent work!

  3. Ben says:


    (Am I right in thinking this explains the Heisenberg Uncertainty Principle, too?)

    Now, if you could just explain entanglement in similarly easy-to-understand terms…

  4. Randal Koene says:

    @Ben: While I think Suzanne has done a great service by writing this very lucid article… I (with my non-quantum mechanics expertise) do not believe that the Heisenberg Uncertainty Principle is explained in quite the same manner. Said principle relates – if I understand correctly – to the nature of the system involved, not to a researcher’s ability to perform measurements. It is my understanding that this has more to do with waves/particles.

    I’m sure Suz can provide a much more descriptive explanation. 🙂

  5. zwenkwiel says:

    very informative post because I was one of these people being told about the spooky observer effect going on
    and I was like wtf that makes absolutely no sense whatsoever

    however after reading this it suddenly makes a lot more sense

  6. quantengott says:

    Mrs Gildert, your high level article seems to ignore EPR and after that Bell´s inequality violation ? ( proving, that reality is NOT local, in contrast to your egg metaphor )

    This is my lyrical point of view….

    Quantum Reality

    Lately I asked god
    if he is real or not

    Realism he replied
    makes me and quantums cry

    Since qubits were invented
    Yes and NO are superintended

    This makes the worlds reality
    toggeling until eternity

    And towards this strange big theory
    God pops up instantaniously

    But if you want to throw him out
    Just watch ! and he was just a cloud.

  7. Dr David Mannock says:

    Sue, I am confused, but I’m not quite sure how confused I am, or even if confusion is the appropriate term! The concept of self-learning AI is a nice one, but I wonder to what extent it is practical. I say this because, if mankind is to be part of the process, we must start off with machines serving us and by then evolving to either a null role in which the machines do the thinking for us or where we exist to serve the machine. As an experimental scientist, I found that there was a bit of a disconnect between the theory and the practical side of the problem. The initial idea of computers were that they were going to make our lives easier and give us better quality time for life’s pleasures, but this has not proved to be the case. You seem to be revisiting this idea and extending it to a level where self-learning AI machines will be taking over the human role in innovation and discovery. I cannot imagine who (singular or plural) would be able to write this code in a cohesive manner encompassing so many intellectual variables (Just look at Microsoft software), as well as lists of reference data for real time comparison in decision making.

    Part of my enjoyment in doing experimental science is designing and performing the experiment to provide an answer to a problem. I then learn from all of these actions and revisit the problem to refine/improve the answer. I get annoyed by people who tell me generalities and recently was told that a series of Phys chem experiments were not worth doing. I explained to this person (my boss) why he was wrong. Having done the expts with a student, he now wants to keep up the appearance that he directed the work to get an award. 🙂 Having presented a paradigm shift in an important area, by coming in as a new observer and ignoring the existing dogma, I am wondering if a computer will be able to distinguish between shades of grey in which some conclusions are correct and others are not. Ignoring the difficulties of writing the code for the moment, inputting data and making new predictions is not that straightforward in many cases. I say this because from a historical perspective in my research area, the conclusions drawn from measurements often seek to support the existing dogma. Moreover, any code writer looking to input that data into a machine (I am reviewing a model in my area this evening), would also introduce a bias, potentially distorting the decision making process until the AI system could correct itself. From my own perspective, the human has the ability to do all of this and “read between the lines”, intuition if you like, which machines do not have and will not for the foreseeable future. I do not know that this is something that the human race should or even can give up.

    Also, science everywhere is iterative, we have to revisit the problem several times over many generations to provide increasingly accurate models of systems. Can machines do this for us? Do we want them to do this for us? How invasive will they be and what will we, as human beings, be left with? I am reminded of many farm animals whose intelligence has been “bred out” of their behaviour. Are we destined to have the same fate and merely exist to reproduce ourselves?

    Incidentally, as a threadbare cleric of some 35 years in science, I can tell you that only some people want the money and the awards, I am of a generation that came from the British education system that encouraged my intellectual curiosity, something which is becoming increasingly rare. Personally, if I had to surrender these qualities to a machine, I would be better off dead. I recall my GP telling me that I should take better care of myself, so that I could live longer and die of something else 25 yrs hence. I replied that I would rather be in control of my faculties than be a bed-wetting, drooling vegetable in a hospital ward waiting for God, whoever she may be! Dave

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