# Specific version of the observer effect

I have a practical experiment in mind which would test whether human minds can function as quantum mechanical observers. My question is then: has a similar experiment been performed, and if so what was the outcome?

In the experiment, there is some quantum mechanical process P. This process is observed by a machine M. The machine plots the results so far on a laptop during the process. After P is finished, it has an outcome O, which might for example be a normally distributed number. As for every experiment, there is also a human observer H.

There are two phases of the experiment. In the first phase, P is carried out. When P is running, the human experimenter H is not watching the results on the laptop. Only after P is done, H observes O. This is repeated a number of times to measure the probability distribution of O.

In the second phase, P is also carried out, but this time H is observing the laptop all the time. This is the only difference between the two phases. The second phase also yields a probability distribution for O.

Now in the first phase, there is only M that observes while the process is running (H observes at the end). But in the second phase, both M and H are observing the whole time. This may or may not influence the wave function of P (and hence the resulting O) in a different way.

If the two measured probability distributions of O turn out to differ significantly from each other, then this would imply that humans can function as quantum mechanical observers. On the other hand, if the two probability distributions coincide, then it seems that humans do not function as quantum observers.

What you are describing is precisely the Wigner's friend experiment.

EDIT: The question has changed the question and is addressed in another answer.

• The setup of the experiment seems to be similar to the Wigner’s friend experiment. But the goal might be different. The goal of the experiment I have in mind, is to influence the distribution of the outcome O when repeating the experiment many times. I have rewritten my question to try to make this more clear Jun 17 at 18:51
• In the Modern interpretation of QM: a machine and a person both can function as an observer, so changing which is which doesn't make a difference. The main difference in this new part you added is that now you are saying that in one case someone is constantly measuring something, while the other the person is not measuring for some time until the very end. This is very different from your origional question - and is infact a different effect called the "quantum zeno effect" Jun 17 at 23:59

The user added a second part to his question, so this answer is to address that:

The example you are describing is basically the quantum zeno effect.

You get a different result when you are continuously making a measurement of a quantum state (constantly looking at the result) than if you didn't look at it and instead waited for some time.

In fact, this effect is so strong that by constantly "looking" at a state, you can force it to essentially freeze in one place as a result.

• Thank you for your answer. I am sorry that my questions are so badly formulated. I think we are coming closer. So I read the wikipedia page on the quantum zeno effect, especially the part ‘experiments and discussion’. The experiments which are cited, seem to have one thing in common: the ‘observer’ is always a machine. In that point, my question seems to be different. Has the quantum zeno effect also been researched where the observer is a human, in the way described in my question? Jun 18 at 8:20
• I think you should try to understand the Wigner's friend problem better. If the machine isn't looked at, then it remains in a superposition state in your perspective until it is checked. It remains in a superposition of having measured both outcomes. Jun 18 at 12:41
• I will try to be more clear. As far as I understand it, usual quantum zeno experiments work as follows. An experiment is carried out twice. In the control version of the experiment, the result is measured by a machine at the end of the process. After that, this is measured by a human. In the other version of the experiment, there is a continual measurement of the process by a machine. After the process, this is observed by a human. So the difference in the two phases, is whether the machine is measuring the whole time or not. Jun 19 at 9:18
• Whereas in the experiment that I have in mind, the machine does a continual measurement in both phases of the experiment. The difference between the two phases is then, whether a human is looking during the process, or not Jun 19 at 9:22