Gedankenexperiment

Amused by hearing the name? It’s the German term for thought experiment, which was first used in the year 1897.

So, what is this thought experiment mean? Let’s start with the most famous thought experiment- The Schrödinger’s cat as an example.

In this though experiment, a cat is kept in a closed chamber in which there is a glass bottle with a poisonous acid. Connected to a Geiger counter (detector-detects radioactivity), there is a hammer. A radioactive source is also kept inside the box. When the detector detects the radioactivity from the material, the glass bottle is shattered, releasing the poisonous acid and the cat is dead. As an observer we are not aware of the outcome of the experiment. Only if the chamber is opened, the outcome is revealed. So, we can say the cat is live and dead at the same time i.e., in a superposition state.

Nothing is real unless it is observed…there is no underlying reality to the world. “Reality,” in the everyday sense, is not a good way to think about the behavior of the fundamental particles that make up the universe; yet at the same time those particles seem to be inseparably connected into some invisible whole, each aware of what happens to the others.

― John Gribbin, In Search of Schrödinger's Cat: Quantum Physics and Reality

Why this thought experiment is so relevant? It’s because it helps to understand how weird quantum mechanics is.

Let me take you to your school days…

We have heard of the double slit experiment. An electron firing source, a double slit and a detector is arranged as shown in the figure below.

We all know that when the electrons are fired, a wave pattern is observed in the detector, showing the wave nature of electrons (interference pattern). 

But if we try to observe the path of the electron (to know through which slit the electron is passing) using any detector, the outcome of the experiment changes, giving the pattern given by a particle (wave collapsed) i.e., the act of observation affects the outcome of the experiment.

When we are not observing there is the chance that electron can pass through both the slits just like the waves. This implies that the electrons are in superposition- existing in more than one position. This experiment is very hard to understand in a logical way. So, in such circumstances, a thought experiment comes handy, it lightens the complexity. 

What exactly is thought experiment?

Thought experiments are devices in which an imaginary scenario is created with the aim to solve and understand an actual experiment. Unlike the thought experiment, we manipulate the features of the observed world in the actual experiment.

When hypotheses become subjective and impossible to prove through empirical evidence, a thought experiment can be employed. It is not just restricted to science but useful in real life also.

Is there any particular way of doing thought experiment?

No, there is no formal procedure to do thought experiments. They are just act of imagination where we do an experiment mentally with the available resources expecting all the possible outcomes. Simply, we can say that it is just a prediction.

How we can perform a thought experiment?

We have to logically design the experiment, which should be realistic, reasonable and based on known principles, theories and facts.

One good example I found was someone explaining the reason for the white, cloudy middle in the ice cubes.

Here the author says that most water is not pure. So, there are millions of particles and minerals along with different types of gases inside it. Logically we can say that this is what makes the ice appear white. So, why is it white and cloudy only on the inside? Well, next step is to think about how water freezes. If you live in a cold place in which temperatures commonly dip below freezing point, you might know that the lakes, ponds, and rivers only freeze on the top, creating an insulating layer for the ecosystem in the water. Same with ice cubes. They freeze on the outside first then inwards. This is all pushing the diffused gasses and particles to pack into the middle. 

Thus, the author has performed a thought experiment with all the realistic, reasonable, and logical facts and principles.

Here is one thought experiment I made – The dancing girl.

Imagine a girl who used to dance in a room and there is no space outside that room. She shoots her dance and posts it on Instagram. One day her performance gets viral and she gets a lot of followers. Eventually she begins to earns money from Instagram. She becomes happy, begins to buy new dresses, eats a lot of food and slowly she becomes fat. Now she has reached a state where the room no longer can contain her. Also, since there is no space outside the room, she can’t push the walls to the outside to make the room bigger. Will she survive or die?

This simple thought experiment is made to understand the expansion of universe. Think on it and do comment your ideas in the comment section. Also, make your own thought experiments and feel free to share that.

Here I am also attaching some videos of famous thought experiments. You can find more out there.

The grandfather paradox

Brain in a vat

Achilles and the tortoise

The impossible barber