Imagine a thought experiment. Suppose that the detector is installed to observe which slit the photon passes through, so the path information can be obtained (whether the path information is really read or not), then the interference pattern will disappear. This path experiment demonstrates the complementary principle of particle property and volatility. Photons can show particle property and volatility, but they can't show particle property and volatility at the same time. Although this thought experiment is very important for the basic theory of quantum mechanics, until the 1970s, there was no proposal for any possible technology to embody this thought experiment. In fact, such experiments can not be set up simply because old detectors will absorb photons. But now, many experiments have been completed to show all aspects of complementarity, such as quantum erasure experiment.

An experiment completed in 1987 found a surprising result. If only part of the path information is obtained, the interference pattern will not disappear completely. This experiment shows that if the measured action does not excessively disturb the motion of particles, the interference pattern will only be changed accordingly. In the Engeler Greenberg dual relation, there is a detailed mathematical discussion on the quantum behavior in this regard.