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I remember when I first heard of the double-slit experiment and had to ask myself, “Am I reading this right.” What if I were to say that a particle changes behavior just by looking at it? When you’re not looking, a particle behaves like a wave.
The Double Slit Experiment is one of the best known experiments in physics. Let’s delve in.
Part 1: The Basic Setup
Imagine having a wall with two narrow slits and a screen behind it along with something to fire at the wall.
Case 1: Solid Objects
Imagine throwing something like small pellets at the wall. They go through one of the slits and on the screen behind it you can see two clear lines, one for each slit.
Case 2: Waves
Now let’s imagine that you send waves similar to water waves through the slits. This is where something different happens. The waves spread out and overlap which creates a pattern of alternating bright and dark bands. This is called an interference pattern. Waves go through both slits and interfere with themselves.
Part 2: Now Use Particles
Stay with me on this. Instead of using water or pellets, electrons are used. It would seem like that you’d expect two lines like as shown by the pellets. However, something different happens. When many electrons are sent through the slits, they get an interference pattern. Imagine that, a particle acting like a wave. This is a little bit weird, but it gets even more strange.
Now you send electrons one at a time. You still get the interference pattern. This means that each electron isn’t just going through one slit but it behaves like it is going through both.
Part 3: Let’s Observe It
Now comes the time that goes beyond intuition. A scientist might asked “What slit is the electron going through? In order to observe it, they set up a detector. We think at first that we have confirmed it’s a particle and nothing else changes. The interference disappears. You end up with two lines again, just like you did with solid particles.
However, the act of observing changes the outcome.
Part 4: What Does That Mean?
Take a deep breath. Without observation the electrons behave like waves, however, when they are observed, they behave like particles. The only think that changed was the observation. Some people will say that “reality is created through the mind.” However, that is a misunderstanding. Observation in physics involves interaction. When you measure something, it becomes disturbed.
Part 5: Wave-Particle Duality
This leads to one of the main ideas of quantum physics and that is there is wave-particle duality. This means that particles aren’t just particles, but they exist as probabilities and waves of possibility. Before measuring, the electron in spread out and not in one fixed space. Once it is measured, it “collapses” into a specific location.
Part 6: The Deeper Implication
This experiment suggests that reality is not as solid as it appears. At the quantum level things exist as possibilities rather than definite states. When they are measured, they take on a definite form.
Part 7: What This Does NOT Mean
As suggested earlier, this does not mean you can control reality with your thoughts nor is the world an illusion in a simple sense. Rather, it means that the rules at the smallest level of reality are quite different from our own reality and experience.
Part 8: Why We Don’t Notice This
In regular life, objects are large and interactions are constant. The result is that quantum effects average out. What we can see at the human level is a stable and predictable reality.
Final Summary
Let’s take a look at what we’ve learned. It is possible for particles to behave like waves. They can interfere with themselves and observation changes their behavior. At the quantum level, reality is probabilistic. So when you think that reality is certain, remember that reality is something that only becomes definite when it’s observed.
See Also:
Further Reading (Affiliate Links)
QED: The Strange Theory of Light and Matter by Richard Feynman
Something Deeply Hidden By Sean Carroll
The Quantum Story — Jim Baggott
Beyond Weird — Philip Ball
Introduction to Quantum Mechanics — David J. Griffiths
In Search of Schrödinger’s Cat
The Fabric of Reality by David Deutsch
Quantum Enigma by Bruce Rosenblum and Fred Kuttner
Beyond Weird by Phillip Ball
Alice and Bob Meet the Wall of Fire by Thomas Lin
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