Looking means intervening
One of the most bizarre premises of quantum theory, which has long fascinated both philosophers and physicists, states that the observer influences the observed reality simply by the act of observation. In fact, in a new experiment, electrons were more affected the more precisely scientists measured their properties. Researchers at the Weizmann Institute of Science, led by Mordehai Heiblum, have demonstrated how an electron beam was affected by the observation in an experiment whose conditions they could tightly control (Nature 26 February 1998).
According to quantum mechanics, particles can also behave like waves. Electrons can do various things as a wave that particles of matter could not do. For example, as they make their way, they can simultaneously slip through multiple openings in an obstacle and rejoin on the other side-a process known as interference.
It may sound strange, but interference can only happen when no one is looking. As soon as an observer wants to measure how the particles pass through the openings, the picture changes dramatically. If a particle is shown to pass through one orifice, then it is clear that it will not pass through the other at the same time. In other words, observation "forces" electrons to behave like particles rather than waves. Therefore, the mere act of observation affects the experimental results.
To demonstrate this, researchers at the Weizmann Institute built a tiny device less than a billionth of a meter in diameter that had a two-aperture barrier. They then sent a stream of electrons onto the obstacle. In this experiment, the "observer" was not human. For this purpose, the researchers used their sophisticated electronic detector, which can detect the electrons passing through. The quantum "observer's" ability to detect electrons could be adjusted by changing its electrical conductivity or the strength of the current flowing through it. The device looked more or less closely, so to speak.
The detector had no further effect on the electrons, it was only able to detect them. But the scientists found that the mere presence of the "observer" near one of the apertures caused changes in the interference pattern of the electron waves. In fact, this effect depended on the intensity of the observation. As the "observer's" ability to detect electrons increased, the interference weakened. On the other hand, if the measurement was not carried out so precisely, the interference behind the openings increased. So, by controlling the properties of the quantum observer, scientists were able to control the extent of its influence on the behavior of the electrons.
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