Questions tagged [thought-experiment]

Hypothetical situation in which, for simplification, only some physical aspects are considered in order to further understand or reveal contradictions between the laws governing them.

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Under relitivity, does apparent acceleration decrease towards the front of an accelerating object?

As I understand it, the Bell's spaceship paradox thought experiment says that if you have two identical rockets aligned in the direction of travel, which start accelerating simultaneously (in frame S) ...
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Symmetry in the Simultaneity of events in Special Relativity

I have been bothered for long by this question and finally decided to ask it here. I am going to resort to the original thought experiment by Einstein, involving the moving railway carriage and two ...
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What about this Hubble volume thought experiment is unphysical?

I've been considering a situation with Hubble volumes that I'm having a difficult time resolving. For simplicity, assume the expansion of space is constant, rather than accelerating or decelerating. ...
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Is there a maximum speed you can travel through time? If so, could you ever reach such a speed?

I understand that everything in the universe travels at the speed of light through spacetime. As a layperson I'm going to refer to this velocity as the spacetime velocity. Some examples.. Objects ...
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Consider the famous thought experiment

If we consider two people A and B who both are conducting the famous Schroedinger's Cat Experiment. Person A tries to open the box to see if the cat is alive or dead, Chances of Cat's death are 50-50 ...
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How the time slows down? In thought experiment of special theory of relativity in which two mirrors are used how the time gets slow for moving person? [duplicate]

If experiment is observed from stationery frame of reference then light travels more distance than frame of reference of mirrors so to keep speed constant time for stationery frame of reference should ...
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Equilibrium change in the isotherms of real gasses

I am not sure I understand Isotherms of real gasses correctly (the equilibrium line to be specific): Imagine a closed container with a piston between two compartments filled with a real gas (top blue ...
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Photons travelling in parallel and colliding (Thought Experiment)

Suppose two photons displaced by a distance $\delta$ are travelling with momentum vectors that are parallel to each other, and further assume that no other particles exist such that the photons can ...
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When does a photon become part of a moving system? [closed]

I was wondering when a photon becomes part of a moving system. Does it need to be generated inside e.g a moving train? Or can it be a photon generated out-side the train but reflected by mirrors that ...
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Time period of a simple pendulum at the centre of earth

So I thought of this hypothetical experiment and wondered whether it be possible for it to even happen at center of earth even though gravity is zero. So considering a pendulum with length much much ...
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Who does all the calculation in Archimedes Principle? [closed]

Let's do an experiment. In the first half of the experiment, you ask some geometers to determine the volume of a pineapple. They would model the 3D shape of the pineapple, which is a pretty tricky ...
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Whats the relation of entropy with synchronisation

2 pendulums tied to a same rod and oscillating with different frequencies and phases synchronize over time. This could be done at home just to see how interesting it is that things try to sync their ...
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In special relativity, how do we know that distance doesn't change in the direction perpendicular to velocity?

In the theory of special relativity it is said that the distance in the direction of the speed changes by a factor of $$\gamma=\frac{1}{\sqrt{1-\frac{v^{2}}{c^{2}}}}$$ How do we know that the distance ...
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Thought experiments - a didactic tool?

I am wondering whether thought experiments (as from a didactic perspective) are being discussed in the context of teaching physics by using another term or notion? - since I think thought experiments (...
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Are results of a turbulent flow experiment repeatable?

Say I perform a simple pipe flow experiment. I make sure that the Reynolds No. is sufficiently high so that the flow is turbulent. I measure the velocity field using probes placed at different points ...
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How can we explain the concept of the buoyant force without using notion of pressure?

I wish to explain the concept of the buoyant force without using the concept of pressure. Particularly, I want to explain why some objects float in water while some others sink, but I am finding it a ...
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Measurement accuracy in quantum mechanics?

Here's some classical background to this thought experiment. Let us first consider a classical scale ruler (called A) of a continuous classical variable. Rulers must be discretised. Let's compare this ...
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Where would a bubble settle in a long glass tube along the earth's equator at constant altitude?

This question came about in a meme group I partake in; one of the memes was making fun of flat earther experiments and had a picture of a spirit level on the ground. Another member jokingly commented ...
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Can we use this experiment to distinguish between two inertial frames?

I saw a statement in my HC Verma's physics book. One should take smaller steps while walking on ice since it ensures smaller friction force. Now let us say there is a man M of mass 50kg standing on ...
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Why can't particles “remember” the past?

The question pertains to a point in Feynman Lectures, Vol III, 5 - 3, which is : We want to know whether all those that get through $T$ also get through $S′$. They do not. Once they have been ...
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Thought experiment in relativistic quantum mechanics?

Background Consider the following thought experiment in the setting of relativistic quantum mechanics (not QFT). I have a particle in superposition of the position basis: $$ H | \psi \rangle = E | \...
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What's wrong with this experiment to measure the one way speed of light? [closed]

It's pretty simple so there must be something obviously wrong with it but what is it? Starter is an electric signal emitter that sends a pulse to the laser source and the detector, starting a counter ...
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Will this spaceship collide with the star? (time dilation)

I thought of the above thought experiment and arrive on 2 conflicting conclusions. I can't seem to identify the flaw in my reasoning. Suppose there is a star 4 light years from earth that has will ...
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How to read voice clips off a glass plate?

This question comes from the context of two great works on popular science, one a book on cognition and artificial intelligence Gödel, Escher, Bach (GEB) And the other a fictional TV series Fringe. In ...
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Gravitational Time Dilation Paradox?

I can't get this around my head it seem a paradox to me. In my thought experiment. Suppose there are two guys John and Jack. John start throwing a ball at near speed of light Meanwhile Jack stays very ...
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Einstein's train thought experiment

I know similar questions have been asked multiple times, hence I'll get straight to my doubt which I couldn't find cleared in the other ones. The earth frame observer sees the lightning flashes ...
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Does an angular acceleration applied to a large body affect any bodies orbiting it?

Imagine the Earth (large body) and a single satellite, let's exclude all other bodies for this example. The satellite is orbiting the Earth parallel to the equator and is maintaining a constant ...
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I just saw the Einstein's thought experiment about train

In the experiment, two lightning bolts strike at the same time and the stationary observer at the train sees the lightning simultaneously but the one in the middle of the train station would see at ...
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Are quantum fluctuations observable?

I know I am asking out of my limits, but i felt relaxed thinking about this. Now I read somewhere about quantum fluctuations (that energy can be generated in randomly at two positions where total sum ...
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Yet another question about Schrödinger's cat

I had always believed that the point of the (in)famous Schrödinger's cat thought experiment was pretty obvious: people, back then, were puzzled with the state space being (basically) a vector space. ...
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Feynman Lectures Chapter 4.2: Understanding the obtainment of free power

Excerpt: Call this reversible machine, Machine A. Suppose this particular reversible machine lifts the three-unit weight a distance X. Then suppose we have another machine, Machine B, which is not ...
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Feynman Lectures Chapter 4.2: Add or remove weights in a non-ideal machine?

Excerpt: A very simple weight-lifting is shown in Fig. 4-1. This machine lifts three units "strong". We place three units on one balance pan, and one unit on the other. However, in order to ...
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Feynman Lectures Chapter 4.2: Why is this a machine that only lifts three units?

I am having some trouble with the following passage in section 4.2 of vol. I of the Feynman Lectures on Physics: A very simple weight-lifting is shown in Fig. 4-1. This machine lifts three units &...
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Feynman Lectures Chapter 4.2: Understanding the weight-lifting machine visually

Why a non-reversible weight lifting machine cannot lift higher that a reversible one is related to my current post, but everyone in that thread seems to have understood how Feynman's simple machine ...
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What is wrong with this definition of ordered state?

It is written in my book that a disorederd state is more probable than an ordered state and hence every system tends to move spontaneously to a state of higher disorder or higher probability. But I ...
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Some doubts regarding electric field inside a hollow shell made of charges

This question is a follow up to this question. Here my doubt is about a shell made up entirely of charges. I am asking this question because all physics and electrostatics/electrodynamics books talk ...
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Electric field inside a non-conducting shell with a charge inside the cavity

I have read about conducting charged shells and spheres and know somewhat about the electric fields associated with them. But I have never found anything on non-conducting shells. I have searched ...
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Special relativity compounding transformations doesn't work? (thought experiment)

Take an earth-star and a spaceship frame. The spaceship is heading at near the speed of light towards the star from the earth. Now let's say that in the earth-star frame, there are three events the ...
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Implication of a third observer in time dilation derivation

View from A View from B View from C In the familiar experiment to derive time dilation we have observer A traveling with a light clock. The light clock sends a light pulse from the roof of the ...
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Quantum tunnelling time experiment, what would the times be either side of the barrier?

Having read Quantum Tunnels Show How Particles Can Break the Speed of Light in Quanta; I felt the need to ask some smarter people than I a question. Consider two pairs of rubidium emitters and ...
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Given a collapsed state, can we derive the prior shape of the wavefunction?

More or less the title. Assume that we have found a box containing a completely isolated system of particles. We do not know for how long this system has been allowed to evolve. We do know what ...
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Thought Experiments

Can anyone please explain to me the importance of thought experiments? How does one arrive at a conclusion in a thought experiment. Like for example, the electron through double slit experiment is a ...
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Wigner's friend question [closed]

This is probably a dumb question, but does anyone know whether both Wigner and Wigner's friend observe the same result once both have been in the room and measured?
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Calculating the Universe's change in entropy for irreversible processes involving a system and a heat bath

Water at temperature $T_s$ is added to a lake at temperature $T_0 > T_s$ until the total system reaches equilibrium. What is the change in entropy of the Universe? This is a homework question but ...
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If I heat up a ball, is the radial temperature gradient in the middle of it going to be zero in all directions?

Assume I have a uniform ball, heat transfer is solely governed by the heat equation ($\dot{u} = \alpha \Delta u$). It has an initial temperature distribution solely dependent on $r$, ie $T=T(r)$, ...
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All the information (photons) within a unit cube of space [closed]

So here is a thought, lets fix a cube of side 1cm, it contains light passing through it from all possible angles, be it stars or insect. If we change our angle of view we can see different objects due ...
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Is the Accretion Disk of a Black Hole just an illusion?

As a matter of fact, I recently learnt that as an object is approaching a black hole, to an outside observer the object seems to be getting slower and slower and will cross the event horizon after an ...
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Hidden variable special relativity paradox

Members of this community were kind enough to contribute to my last paradox post: Special relativity paradox involving two light clocks I'm creating this new post to address the issues raised in that ...
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Special relativity paradox involving two light clocks

I came up with this thought experiment that seems to exemplify a paradox. In this paradox, one clock is ticking unevenly for one observer and evenly for another. Essentially, the clocks record a “tick”...
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If everything slowed down around you, but you were just as fast you are normally, would you jump higher? [closed]

If everything slowed down around you, but you were just as fast you are normally, would you jump higher? I am thinking velocity would increase, thus the force generated would be stronger, but I am not ...

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