Why is the interpretation of the double slit experiment that the electron went through both slits and interfered with itself?

What are our real facts about electrons?

Most people will have a billiard ball model in their head. This is why the question.

The idea of a particle is related to how we view matter and its divisibility. It is possible to divide matter into smaller and more manageable pieces. This limit can be referred to as the domain of electrons or atoms. It seems that little billiard balls is a good representation of matter.

This intuition has a problem. Many of the properties we call matter are not due to fundamental particles, but the bonds that connect them. Even though graphite and diamond appear to be quite different substances, they are both made up of carbon atoms.

At some point, the importance of atoms is less than their ability to bond with one another. At this point, visible light is no longer an option to see the constituents.

We could see the basic constituents most of the time with light, but we couldn’t see the details in the microscopic world. Only when we try to see the fundamental building blocks of things, do we lose our ability to see them. This is where our intuition can take us beyond what we see.

This is where the problem lies when we try to study these fundamental components. We can’t see the whole world at its fundamental level so we must poke and prod it to try and build a model.

Here is where the double-slit comes in.

Imagine that you can see individual electrons. One electron beam can be pointed at a screen to see the individual electrons hitting it, sometimes flashing light. It’s no surprise that we find it amusing! After all, electrons are like little billiard balls.

To confirm the billiard ball hypothesis, it is necessary to conduct more experiments. What about sending single electrons through an apparatus with a double slit? If we believe the billiard ball model, then it should be possible to predict the behavior of the electrons. They would pass through one or the other slit.

This experiment shows that single electrons can be detected in localized areas with very few flashes. So far so good. Let’s start to build a history of electrons and the places they have hit the screen. We now see something very strange. Some places are unable to detect electrons, while others seem to be more favoured. The pattern of electron detections appears to be consistent with wave-like interference. This is analogous to what Young’s double slit sees.

Young’s double-slit experiment was intended to demonstrate that light is a wave phenomenon. It seems that electrons can also be wave phenomena.

We now have two models of the electron that seem to be contradictory. The electron is highly localised upon detection, just like a billiard ball model. But electrons behave like waves before detection.

It is interesting that light can be approached from the opposite direction of intuition. Young’s double-slit method revealed that light is a wave. This informs our intuition about light. Knowing waves in water, we can use that knowledge to see light as a wave phenomenon.

Light presents the opposite problem. We can’t see beyond the limit of having no light at all. The light from a source of light is attenuated by a double-slit apparatus. Everything looks wavelike and familiar until it reaches the limit of very little light. We then see light arriving on the screen, one spatially localised photon at time.

Finally, we can see that light behaves as a particle and call this particle a photograph. The interference pattern is still evident in single photon detection events.

In the limit of single quantum detection, light and electrons behave exactly the same in exact the same way!

This is one the most amazing properties of quantum systems. This is called wave-particle duality. It should be considered as one of the fundamental property of a quantum system.

You can repeat the experiment over and over again to see the same behavior. Quantum objects behave differently to macroscopic classical phenomena and objects. It is incorrect to think of a particle like a tiny billiard ball. It’s not. It is not. Yet we kept extrapolating. We expected that everything would be consistent to the smallest scales. We now know that things are not the same.

It’s not worth asking how an electron can be able to take both slits. We can prove it. It is more important to abandon the billiard ball model of particle physics and embrace a quantum model for the world.

You don’t have to look far to realize that electrons are more than just a few billiard balls. Electron microscopes treat electrons like waves and use electron beams for images of nanoscopic objects beyond the capabilities of light.


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