The electron double-slit interferometry experiment is one of the greatest experiments in the history of human physics, and it is also the most troublesome experiment for physicists, and the experimental process and results are so strange that physicists begin to doubt the true objectivity of the world.
The experimental process will not be described in detail, I think everyone knows something, and I will focus on it here. At the heart of the experiment is the "observer effect".
What is the "observer effect"? Specifically, when we are not observing, the electrons pass through the two slits in the form of waves, and when we observe, the electrons pass through the slits in the form of particles.
In other words, the presence or absence of observation affects the state in which the electrons appear: when not observed, the electrons exhibit a vague wave state, while when observed, the electrons exhibit a definite particle state.
Going deeper, the way the world looks depends on whether we observe it or not. Obviously, this is a big violation of our preconceived notion that the world exists objectively. Whether we observe it or not, the world is the way it is.
Just as Albert Einstein once asked: When we don't look at the moon, isn't the moon there?
Obviously, the electron double-slit interference experiment completely subverted the inherent cognition of human beings, but this was only the beginning, and the discoveries made by physicists in the process of continuous improvement of the experiment really subverted people's three views.
First refinement: Physicists wanted to see how electrons passed through two slits at the same time, so they installed detectors next to the slits to make observations. It is necessary to emphasize here that it is not a surveillance detector that we often see in our daily life, but an energized coil, you know, in short, physicists have a way to obtain information about the path of electrons.
But it doesn't matter if you don't look at it, physicists are even more confused: they don't see the electrons passing through both slits at the same time, but obediently passing through one of the slits, and the interference fringes on the electron receiving screen disappear. This means that when physicists observe electrons, they no longer behave as waves, but as particles.
Clearly, the observational behavior of physicists changes the state of electrons. In physical terms, observation causes the "wave function collapse" of electrons, from a wave state to a particle state.
Electrons seem to have consciousness, as if they already know what physicists are going to do, and react at any time in response to their observations.
The second improvement: Instead of directly observing how the electrons pass through the two slits, fearing that this will really affect the state of the electrons, physicists wait until the electrons pass through the two slits before making observations. This is the delayed experiment
However, the electrons still exhibit a particle state, and the original light and dark interference fringes are still gone.
Physicists began to doubt life: it is clear that electrons have passed through the slit, and it stands to reason that the state should be whatever it should be, and it is impossible for people to change the behavior of electrons through the slit, so why will the original interference fringes disappear?
Physicists were not willing to accept such a "madness" and were extremely intelligent people, so they modified the experiments, this time completely changing the effect of observation behavior on particles.
The third improvement: Physicists suspect that the first two experiments may have affected the electron to some extent, so is there any way to observe the electron without affecting the state of the electron?
Physicists have really come up with a solution: using the weird principle of quantum entanglement. How does it work?
The process is a bit complicated, so let's make a long story short in layman's terms. A pair of entangled electrons are processed and fly in two different directions, and for convenience, the two electrons are named A and B.
A and B travel a certain distance to reach the screen that receives electrons, but the distance of the two electrons is not the same, A travels a short distance, while B moves a slightly longer distance.
In this way, A will be the first to reach the receiving screen, forming interference fringes on the screen, which of course requires multiple electrons. And B will arrive at the screen a little later.
Here's how the physicists operated, after A reached the receiving screen to form interference fringes, and before B reached the screen, they observed electron B, and they found that the interference fringes that had been formed by electron A would magically disappear!
It's incredible, you know what that means?
It means that physicists have changed what had already happened, and the law of cause and effect has been broken!
At the same time, physicists did not directly observe electron A, but only observed electron B, which is entangled with A, but even so, it will affect the behavior of electron A.
And when physicists no longer observe electron B, the original interference fringes of electron A reappear.
This improved experiment is the legendary "quantum erasure experiment", which completely subverts the law of cause and effect in people's inherent impressions, and the future can affect the past!
Physicists are really overwhelmed by such a result, and they begin to wonder whether reality really exists objectively, whether the law of cause and effect is true at all times, and whether the existence of this world is really due to our observational behavior?
See, this is the electronic double-slit interference experiment that drove everyone crazy!
But madness is madness, and physicists must give corresponding explanations, whether the explanations themselves are convincing or not, there must be explanations.
Of course, there are many explanations in the scientific community for such crazy experiments, but the more orthodox explanation is the Copenhagen interpretation, which is accepted by the mainstream physics community.
The core of Copenhagen's interpretation is uncertainty, or "superposition", any microscopic particle has uncertainty and is in different superposition states, and this uncertainty and superposition state is the essence of the quantum world.
What does that mean?
Generally speaking, microscopic particles have "wave-particle duality", which can show both particle characteristics and wavelines, and the specific characteristics depend on whether we observe or not.
But in fact, the explanation of "wave-particle duality" is more of a helpless move by physicists, or the golden mean, and the unpleasant thing to say is that "human beings are very ignorant", and we do not know why microscopic particles have "wave-particle duality", but only based on the specific performance results of microscopic particles to invert the conclusion of "wave-particle duality".
It can also be understood in this way that microscopic particles such as photons and electrons are essentially waves, not particles, and theoretically they are everywhere and can even appear randomly in every corner of the universe. And when we make observations, microscopic particles such as photons and electrons just appear in the place where we observe, making us feel that the microscopic particles are there, allowing us to see the particle characteristics of microscopic particles instead of wave, and this is called "wave function collapse".
Since waves are everywhere, no matter where we look, we will see waves appear in the place where we observe! But why do microscopic particles that are originally waves collapse into particles in an instant because of our observations?
This explanation of "wave function collapse" is actually an "afterthought", just like "wave-particle duality". In fact, physicists do not know why the "wave function collapse" occurs, but they have deduced the conclusion of "wave function collapse" based on the observation results to explain the strange behavior of microscopic particles.
To put it bluntly, the so-called "wave function collapse" is only a hypothesis, and of course it can also be considered an axiom, and the axiom does not need to be explained, it is like that. Just like the axiom that "the line segment between two points is the shortest", this axiom does not need to be explained, because what people observe is what they see.
conclusion
In fact, physicists have long determined that strange phenomena in the quantum world really exist, such as uncertainty, superposition, quantum entanglement, quantum tunneling effect, etc., and have long used these strange properties for people's use, for example, transistors, superconducting materials, quantum communications, quantum computers, lasers, electron microscopes and other products contain quantum technology.
Although physicists do not know what the underlying logic of the strange phenomena in the quantum world is, they do know that those strange phenomena really exist, and can use those strange phenomena for human use.
At the same time, physicists have not given up on finding the "underlying logic" of the strange phenomena in the quantum world, because they firmly believe that there must be a deeper mystery of the universe hidden there!