Thought Experiments

Galileo’s Leaning Tower of Pisa

Although there is some debate about whether Galileo actually performed this experiment, it is often attributed to him. The thought experiment involves dropping two objects of different masses from the Leaning Tower of Pisa to demonstrate that both objects fall at the same rate due to gravity.

Newton’s Cannonball

Proposed by Isaac Newton in his book “Mathematical Principles of Natural Philosophy” (1687), this thought experiment involves imagining a cannonball fired horizontally from a high mountain. If the cannonball is fired with sufficient velocity, it will fall around the Earth and continue orbiting, illustrating the concept of orbital motion.

Faraday’s Iron Ring

This thought experiment, devised by Michael Faraday, demonstrated electromagnetic induction. It involves a coil of wire wound around one side of an iron ring and a battery connected to the wire. When the battery is switched on and off, an induced current is observed in the other side of the ring, showing the relationship between magnetic fields and electric currents.

Maxwell’s Demon

Proposed by Scottish physicist James Clerk Maxwell in 1867, this thought experiment involves a hypothetical intelligent being (the demon) capable of sorting and controlling the movement of gas particles in a way that violates the second law of thermodynamics. It challenges our understanding of entropy and the principles of thermodynamics.

Imagine you are chasing a beam of light

Consider that you are pursuing a light beam. When he was just 16 years old, Einstein began to consider this. What would occur if you followed a light beam as it traveled across space? According to Einstein, if you could somehow keep up with the light, you could see it frozen in space. However, light cannot be stopped in space because it would stop being light. After some time, Einstein understood that light cannot be slowed down and must always be traveling at the speed of light. Therefore, another adjustment was required. After some time, Einstein came to the conclusion that time itself needed to evolve, which served as the foundation for his special theory of relativity.

Einstein’s Train

Another thought experiment by Albert Einstein, this one is used to explain the concept of time dilation in special relativity. It involves two observers on a moving train and a platform, where the observer on the train perceives time differently than the observer on the platform due to their relative motion.

Lightning on a train

Imagine you’re standing on a train while your friend is standing outside the train, watching it pass by. If lightning struck on both ends of the train, your friend would see both bolts of lightning strike at the same time. But on the train, you are closer to the bolt of lightning that the train is moving toward. So you see this lightning first because the light has a shorter distance to travel. This thought experiment showed that time moves differently for someone moving than for someone standing still, cementing Einstein’s belief that time and space are relative, and simultaneity doesn’t exist. This is a cornerstone in Einstein’s special theory of relativity.

Einstein’s Elevator

This thought experiment is used to illustrate the principle of equivalence in Einstein’s general theory of relativity. It involves an observer inside a windowless elevator in free-fall, experiencing apparent weightlessness. The observer cannot distinguish between the effects of gravity and the acceleration of the elevator, demonstrating the equivalence between gravitational and inertial mass.

Imagine you are standing in a box

Think of yourself as being in a box: Consider yourself suspended inside a box with no visibility of the outside world. You suddenly fall to the ground. So what took place? Is gravity causing the box to fall? Or is a rope pulling up on the box, accelerating it? Einstein came to the conclusion that there is no difference between gravity and acceleration – they are the same thing because these two effects would result in the same outcomes. Now recall Einstein’s earlier claim that space and time are relative. Gravity can alter time and space if motion has the ability to do so and gravity and acceleration are equivalent concepts. Einstein’s general theory of relativity contains a significant component that describes how gravity may bend spacetime.