Define Slit

Young’s double-slit experiment is often drawn as a cartoon: a wave, two slits, and a screen.
In the cartoon, the slits are perfect, the screen is smooth, and the “wave” glides through like a ghost. In reality, we have atoms, rough edges, different metals, and finite particles. The story changes.

1. Three regions, not one picture

Think of Young’s experiment as a trilogy:

Pre-slit: how light or electrons travel from source to the slit plane.
In-slit: what happens inside the finite slit: near edges, inside matter’s fields.
Post-slit: how the outgoing beam(s) evolve and form patterns on the screen.

Textbooks mostly draw only the third part. The “in-slit” region is treated as a thin mathematical line. But in a discrete world, the slit has thickness, atoms, and real electromagnetic structure.

2. Symmetry is a choice, not a law

The standard picture is symmetric: two identical slits cut into one uniform material. If everything is idealized that way, it is no surprise that the interference pattern is drawn symmetric too. But this is a design choice in the story, not a law of nature.

In reality:

Edges are made of atoms, not lines.
Different materials (steel, copper, aluminum…) have different electromagnetic environments.
The “slit” is a region with finite thickness, not a zero-width cut in an abstract screen.

Once we allow the slits to be asymmetric, the pattern on the screen is allowed to be asymmetric too. The symmetry in the textbook lives in the drawing assumptions, not in physics itself.

3. Asymmetric slits: DIY experiment

A simple way to break the symmetry is to build slits from different metals. For example, you can:

stack washers and metal foils (e.g. copper on one side, steel on the other),
use a laser pointer as a light source,
and project the pattern onto a screen or wall.

Even with a modest setup, the pattern can show visible asymmetry: one side brighter or more spread, fringes shifted, or an overall tilt. This is not an error; it is the atom-scale personality of the slit materials showing up.

4. In-slit dynamics: particles must turn

In the wave cartoon, the wave simply “passes through” the slit. For a particle (photon or electron), this is not enough. If a particle arrives from a source and later lands at a point on the screen that is not on the straight line, its direction must change inside the slit region. Something in the slit must “decide” the outgoing angle.

That “something” is the combination of:

the electromagnetic fields of the edge atoms,
the finite thickness of the slit,
and the discrete interaction of a particle with an environment, not an abstract line.

Ignoring this entire in-slit story and then declaring “mystery” at the screen is like ignoring a whole chapter in a book and being shocked by the ending.

5. Hyperbolic patterns and exact geometry

At large distances and small angles, the usual formulas for fringe spacing work well as approximations. But if we zoom in on the exact geometry, the locus of equal path difference is not a set of straight stripes; it is closer to hyperbolic structures, especially near the slits.

Near-field behavior (close to the slits) is highly nonlinear and sensitive to discrete details: slit width, thickness, edge roughness, and material. The “nice” sinusoidal pattern on the screen is a late, smoothed-out summary of a much more complicated local story.

6. Continuous cartoons vs discrete reality

The continuous wave model is extremely useful for many calculations. Engineers and physicists use it because it is workable. But it is still a cartoon language:

It smears out all atom-level differences.
It wipes away the full electromagnetic structure of the slit material.
It replaces a finite set of particles with a smooth wave field.

Where the world behaves “smooth enough”, this language works well. Near sharp edges, in thin gaps, or in low-density media, the discrete structure refuses to be ignored. Young’s experiment, especially with asymmetric slits, lives right at that border.

7. A better question for the slit

Instead of asking “How can a particle interfere with itself?”, we can ask:

“How does a discrete particle explore different discrete paths through a discrete electromagnetic environment, and how do those paths add up to the pattern we see?”

Once we phrase it this way, it becomes natural to:

model the slit at the level of atoms and fields,
let a machine (AI) simulate many particle histories,
and compare discrete predictions with real, asymmetric experiments.

The slit turns from a mystical symbol into a concrete playground for discrete physics and thinking machines.

Part of the Define Physics project — see also Define Ether · Define Gravity · Define Cat · Continuous→Discrete