Thought experiment Definition and 345 Threads

Suppose I could restrict an electron to a very small space byfor example using multiple magnetic fields, then could I not be sure with 100% probability that the electron was there before and after a measurement? Wouldn’t such a experimental set up dis prove the idea that the electron had freedom...

It has been mostly substantiated by virtue of experiments such as wheelers delayed choice quantum eraser experiment that we are able to retroactively impact past events of particles. However could this apply to the universe. When physicists are carrying out experiments today, which are creating...

Hello everyone, this is my first post on this forum, I am a new member and the other day was pondering on a question related to the passage of time. So, I have the following thought experiment: Suppose there is the following setup: We have two small toy cars, identical, each capable of...

This thought experiment has been bugging me for a very long time - I'm hoping someone can help me understand it. Premise: - Simple DC electrical circuit consisting of a battery, wire, light bulb, and another wire to complete the circuit. - Each wire has a length of 1 light-year (yes, very...

I'm a former physics student and I've been thinking about an interesting problem that eventually led me to the following thought experiment that I'm having trouble resolving. Imagine a two-compartment system, where one compartment is filled with He gas, and the other is filled with standard...

Hello All. This is driving me crazy and nobody can give me a straight answer, if there is one. I was daydreaming in my yard last week and came up with a weird question. Let's say I discovered a hole in my yard. The hole is plenty wide and well-constructed and has a series of rungs I can...

It has occurred to me that there's a pretty simple thought experiment, and was wondering if any proposed theory of quantum gravity can "handle" it. Imagine a completely empty universe with just 2 hydrogen atoms. They are set up to orbit the common center of mass, being attracted to each other by...

My daughter is 12 and we like to discuss black holes. Here is our thought experiment: Gravity bends space and time lengthening both from the observers perspective. Does time slow down the farther you get from objects with density? Is there a place way way out, out of the range of the Big...

Thought experiment: single use of "magic" Setup: Let's assume we have a giant ball of water in space. Magic: Let's assume the water does not compress its center under its own gravity. (Constant density of 1 g/cm^3) Basic stuff: The mass of this ball of water, (since it does not compress)...

Please move this if it belongs to other subforums. So i thought about some other stuff and then somehow this idea appeared to me, now according to physics it is impossible to communicate information faster than the speed of light through vacuum which is "c". So for any two bodies moving in...

Consider a box whose walls are mirrors. Suppose we trap a bunch (yes, it's vague) of photons inside the box. They will not escape, or assume that a major part of them will not escape the box. Now suppose we have a way of decreasing the size of the box at our will, but possibly obeying the laws...

Suppose we have a particle, let's say an electron, in a box of size D. And we add another one next to it at some distance L center to center. How do we solve for the wavefunctions of the electron. Can it be solved in normal QM or do we need QFT. Thanks.

Today, I had a thought experiment where I began to puzzle over inertia of very large masses being dropped. Imagine a scenario where the Moon was suspended 100 m from the surface of the Earth alongside a marble at the same height. Now ignoring air resistance and the gravity exerted by the Moon...

So as we know at the bottom of the ocean we have water cooled to 0-4 degrees celsius which is very dense and also compressed due to the pressure. Imagine we lower a few kilometres long pipe to the bottom of the ocean (it's made of material that is strong enough to sustain pressure). It's closed...

Hi, I arrived at a paradox today which I cannot explain myself. I was watching some physics videos on youtube and among them some were about lenz law and faraday disc workings. Now I know and understand the classical examples of why there is current generated when the magnet moves together with...

I'm an engineer who has an amateur interest in physics. I have been reading about Einsteins light clock experiment. I understand the principal that when a light clock on a train etc is moving relative to a standing still observer then the light must travel a longer distance per tick. given that...

A thought experiment about the speed of light. Say I build a 600,000 km long tube around the circumference of the Earth at the Equator. The tube's inner diameter is constant at 54.4505 mm. A snooker ball is perfectly manufactured to its lowest tolerance by a special new machine. Each one is...

Suppose you wanted a thought experiment about a variation on the vacuum (i.e., the spatial slice of spacetime) in which the quantum effects were absent or negligible, and the vacuum energy was zero . What would you call it? You can't call it the vacuum, because this Newtonian version of the...

I have a thought experiment that i need a answer to. In my experiment, I am in a bathroom with a mirror along one wall. I also have a laser that emits a single file line of photons. The laser is attached to the ceiling and emits a line of photons parallel to the mirror. What property of light...

I know this won't work, I'm having trouble explaining why to someone who thinks it will. Make a ring around a planet. Give it low walls. Fire countless pellets at hypersonic speeds around the inside of the ring. The pellets are moving at super-orbital speed, pushing the ring outward, making it...

Hi, Physics Forum! I've been wondering what would happen in the following thought experiment. I am not physicist and may have made some incorrect assumptions. Please explain if any of these assumptions are wrong. What would happen if you threw a piece of (very long and strong) rope into a...

Suppose we have two charged particles on the laboratory and two observers A and B. ##A## is inside one of the charges (never mind how) ##B## is sitting at the laboratory In the lab reference frame we accelerate the particles. According to ##A## there will be only electric attraction or...

I met with a little conflict between Pauli and Einstein? Can you please help. Its a thought experiment. Consider a single crystal which is 1km long. During its formation, due to Pauli’s exclusion principle, no two electron will have same quantum state. Now consider two electron, one with E and...

Hello all, I have a question that's been bothering me the last few days and wasn't sure where to turn. Recall the original Special Relativity thought experiment: A spaceship travels at constant velocity v, moving in the positive x direction. An observer on the spaceship emits a photon directly...

I am sorry but this question I have described is a long one. Ok so before I start a quick background , I have read and understand the Meissner effect of the superconductor expelling it’s magnetic field , also I understand that superconductor has zero resistance so a once induced or applied...

Hi! We were recently discussing if time appears quantified. I found the theory about "chronons" (quantums of time) on Wikipedia and I know, those are very theoretical constructs and as far as I found out there is no current research if chronons even exist. But I was wondering if somebody has an...

Hey all, I was re-reading my quantum mechanics books and I noticed that different books have different scenarios for the Einstein Train thought experiment. And I was just wondering if I understood it correctly. Scenario 1: A person inside a moving train flashes a light beam that goes in both...

Hello all, I'm starting to learn the math in physics and have the following thought experiment I want to use to work through something I own. The setup: There is a wall 10m from the center of a 1m diameter sphere. There is a 1m diameter light source casting a 1m diameter shadow on the wall...

Hi everyone, Recently I randomly thought of a thought experiment of something going faster than light, along the lines of a shadow or some other "non-information carrying object". In this case it would be an empty seat. The idea is to take 800 million and one chairs of half a meter breadth...

Let's say a memory qubit inside a quantum computer is in state ## α \left|1\right>+β\left|0\right> ## This computer is equipped with a device that emits photons that carry the same qubit as the aforementioned memory location. Alice and Bob, that are very far from each other, receive and...

I wonder if my thought experiment in proving the finite speed of field lines is valid. Say a spherical conductor has a cavity with positive charge Q inside as shown. say that the beginning of the universe starts at time 0, where there is the charge Q in the cavity and that the conductor is not...

Hi, I have a thought experiment which seems inconsistent with the 2nd Law of Thermodynamics, so there is probably a flaw in the idea somewhere. Imagine a single molecule of a heavy gas (such as SF6) in a pipe 2.5 metres high and 100mm diametre. The pipe is upright and under the normal...

I am puzzled over einstein's thought experiment on simultaneity. In this experiment, a man is standing on a train platform. A woman is sitted in the middle of a moving train traveling towards the man. When the train is half past the man, lightning strikes at the same instant at both ends of...

Not sure where the best place to post this is, but here it goes. Imagine you were sent back in time, far enough back when a lot of the now known scientific laws, rules equations etc, haven't been discovered yet. You're someone who is intelligible with many scientific fields, and you have...

You have a glass (or plastic) dish (like a small transparent dish). You shine light onto its flat surface. Your lab partner discovers that 55% of the light has been transmitted, 55% is reflected. What is the absorbance of the dish (not in the log scale, just as a regular %age)? State a...

I am not a physicist but I was curious if there was any information on the following thought experiment. Say a beam of light emitted from a far away star passed a black hole at just the right direction that it became entrapped in a sort of orbit like the moon around the earth. Is this possible...

Hi, I studied undergrad pure maths now post grad philosophy, not quantum physics, but please consider the following experiment: Suppose you set up a double slits experiment with a photon detector attached to each slit, and the photon detector attached to a photon transmitter, so the photon can...

Einstein's relativity of simultaneity & quantum measurement paradox. Suppose a rocket traveling close to the velocity of light which emits a single photon from its midpoint at point A, illustrated below. The rocket is equipped with a single detector drawn in green at the front of the rocket...

Hi everyone, I've been working on developing a crypto-currency called eQualityCoin for a while now and hoped someone here might be able to help me "classify" the system in a formal mathematical sense. The system's main feature is a simple rule for how it determines a purchaser's exchange...

I decided to perform a little thought experiment -- without the mathematics. Assume we have two Schrodingers' Cats. After a while, they will be in a superposition of being alive and dead at the same time. Now assume that they are entangled, and we open the boxes at the exact same time. Cases...

Following scenario: One million entangled photon pairs are created and are sent to Alice's and Bob's laboratory such that Alice receives 1 million photons(or any other large number) of which each is entangled to one of the million photons Bob receives, their laboratories being at a distance to...

Once, someone had asked two interesting (though absolutely hypothetical) questions: 1) What should happen during the collision of two BHs, one consisting of matter (BH+) and the other consisting of antimatter (BH-)? Should they form a larger BH or should they be annihilated? My personal...

The following question/thought experiment is based on the dual nature (particle/wave) of electromagnetic radiation. Consider the emisson of a single photon on a 3D grid along the x-axis with its origin at (0,0,0). The only matter in this experiment consists of “electrons” found only in...

Imagine a test particle (say a golf ball) just floating in flat space-time. Now have a sunlike star instantly appear some distance away. From the perspective of a distant observer, (using very distant background stars for reference), the golf ball will be shifted towards the star a certain...

This is a thought experiment I came up with this evening. It must surely have been considered before but I couldn't find any reference and I've come up with it independently. NASA has positioned a clock in Earth's thermosphere that can be viewed from outer space with a powerful enough telescope...

In attempt to refute quantum mechanics, Einstein proposed a thought experiment where a box containing a particle is weighted before and after opening a small hole to release that particle. The precision of measuring the time and the energy of the particle can thus be known accurately which...

Suppose we have an elementary double-slit experiment: A laser fires individual photons through a double slit at a detectionscreen made of atoms. As we fire photons, an interference pattern emerges, exposing the momentum of the photons (the frequency of the laser). So, we have registration of...

Refer to this image: http://imgur.com/xT20HOv The white nodes are 'stations' which broadcast signals at light speed. The blue circles around them represent the particle horizon relative to these nodes. The pink nodes are intermediary stations in between these stations that pass on the signal...

Let us first review Einstein’s train and platform thought experiment which consists of one observer midway inside a speeding train car and another observer standing on a platform as the train moves past. A flash of light is given off at the center of the train car just as the two observers pass...

The subject of relativity has been haunting me for while now. Everytime i feel i understand a concept, there comes questions withtin that contradict the undestanding. Have been trying to digest the time dilation & symmetry of how it is felt mutually by observers in two different frame of...