A Thought Experiment is a mental tool that helps us investigate the nature of things. They help us engage in deliberate reasoning by exploring various circumstances and (often impossible) situations, and predict their implications and outcomes without conducting any real life experiments. In most cases, real life experiments aren’t feasible. Mastering thought experiments can not only help us stretch our minds but also make better decisions by confronting difficult questions.


In the 16th century, the Italian scientist Galileo Galilei is said to have dropped two spheres of different masses from the Leaning Tower of Pisa to demonstrate that their time of descent was independent of their mass. Contrary to popular belief, Galileo never actually climbed the tower. He didn’t have to.

Galileo reckoned, suppose we connect two bodies—a heavy body (H) and a lighter body (L)—by a string, thereby making the compound object H+L, one would predict that H+L should fall faster than H by itself, therefore H+L > H. However, it’s also possible to use the same logic to claim that the compound body should fall at a slower pace than H because of the drag created by L, thereby concluding H+L < H. Both the statements cannot be correct at the same time. This contradiction eventually lead to the conclusion that the assumption—that heavy objects fall faster than lighter objects—is false.

This whole experiment follows a series of logical experiments which were conducted inside Galileo’s head. Physicists discover laws, mathematicians prove theorems, philosophers construct world views, and decision makers choose the best course of action using thought experiments.

When we say “if money were no object” or “if you had all the time in the world,” we are conducting a thought experiment. Actually removing money or time to find empirical evidence is impossible, thus we turn to thought experiments to make sense of complex concepts.

Philosophers use thought experiments to explore ethical and moral issues all the time. One of the most famous is the Trolley Experiment. It goes like this: you are the driver of a trolley whose brakes have failed, and the trolly is out of control. Ahead, on the tracks, are five people tied up and unable to move. However, if you pull a lever, the trolley will switch to a different set of tracks where there is one person. You have two options:

  1. Do nothing and allow the trolley to kill the five people on the main track.
  2. Pull the lever, diverting the trolley onto the side track where it will kill one person.

Now, which is the more ethical option? Or, more simply: what is the right thing to do?

Obviously, there’s no one right answer to this problem. The purpose of this experiment is to encourage ethical speculation and logical thinking. It’s to push us outside our comfort zone by forcing us to confront questions we cannot answer with ease.

The difference between a thought experiment and aimless rumination is its structure. Thought experiments are always organised and targeted.

Let’s take one more example to understand this. If you were a king, how would you design a society of free, equal and moral people? Most importantly, how would you make sure that the process is not vulnerable to your personal biases, and there’s zero potential for majority groups to gang up on minority groups in the new society? This is the famous “veil of ignorance” thought experiment proposed by philosopher John Rawls.

According to Rawls, in order to figure out the most fair and impartial way to structure a society, you should operate behind a veil of ignorance. This means that you cannot know who you would be in the new society you’re creating. If you designed the society without knowing your economic status, your ethnic background, or even your gender, you are forced to create a structure that is as fair as possible in order to guarantee the best possible outcome for yourself.

Not only this, a thought experiment can make complex concepts and ideas more accessible so that even those who are not knowledgeable about a particular field can build an understanding.

One of Einstein’s notable thought experiments involved an elevator. Imagine you are in a closed elevator, your feet glued to the floor. Absent any other information, would you be able to know whether the elevator is in outer space with a string pulling the elevator upwards at an accelerating rate, or sitting on earth, being pulled down by gravity? By running the thought experiment, Einstein concluded that you would not.

The force you feel from acceleration and the force you feel from gravity don’t just feel the same—they are the same! Gravity works similarly to the accelerating elevator.

Now we don’t have any empirical evidence to prove this since we cannot build elevators in space, but this thought experiment gives us enough information to test this hypothesis logically.

You see it’s a mistake to use statistics without logic, but the reverse does not hold. It is not a mistake to use logic without statistics. Which means you don’t need to back up the claims in your thought experiments with data, graphs, diagrams, tables, numbers, etc. That’s the beauty! If your logic is rock solid, the data will eventually add up.

After he landed on the moon, Neil Armstrong showed the whole world that Galileo was right when he let go of a hammer and a feather while standing on the moon. Absent any atmospheric friction, sure enough they hit the Moon’s surface at the same time.