Paradox Definition and 1000 Threads

Hi Physics Forums, I've devised a thought experiment called the "Killer Crate Paradox" to put a spotlight on an issue I'm having, with regards to understanding length contraction, specifically in instances where multiple objects are observable and they have different velocities and directions...

Consider a Double Slits experiment in which the light source is monochromatic and each slit very narrow. There will be many fringes visible on either side of the axis. 1) If the light source is pulsed with very short, randomly spaced, pulses it will produce spectrally broadened radiation and...

This is the third time I try posting, and the first time after having written an Introduction. I hope it will work this time. Imagine we have a cuboid of mass ##M## and height ##2 r## that slides without friction on a horizontal surface. It is accelerated by a line or rod that is connected to...

We don't have a quantum theory of gravity. To my B level thinking, losing information at the EH of a black hole is just one of multiple known places where QM meets relativity and it becomes clear that our understanding is incomplete. I don't see it as any different than making the same...

Suppose you are participating in a game show, and at one point three doors are presented. It's announced that one of them has a car prize behind it and the other two have a goat, and for you to choose one of the doors. After choosing the host opens one of the other doors and reveals a goat, and...

Before introducing Special Relativity, a textbook highlights the inconsistency of Maxwell's Electrodynamics and Newtonian Mechanics through the standard discussion about the velocity of light in different frames of reference. A further inconsistency discussed. In some inertial frame of...

Summary: New black hole simulations that incorporate quantum gravity indicate that when a black hole dies, it produces a gravitational shock wave that radiates information, a finding that could solve the information paradox. Hello, Please excuse the rather "conversational" approach I'm using...

A rocket has length L with a separate head on top. The rocket lands in a cilinder on Earth with height L with speed v. From the point of view of the rocket, the cylinder undergoes a Lorentz contraction. The rocket will therefore collide with the bottom of the cilinder and damage it. From the...

Since QM is not deterministic, the future state B is not determined by the previous state A (at time A, B was only a possibility, not a certainty). Then, when we are at time B, and assuming we could move back in time (of course, we cannot do that, but let us make a Gedankenexperiment), it just...

I know the paradox is about a hypotethical hotel with hypotethical guests, how else could new people arrive, when everyone (infinite) is already inside;) But maybe the ones outside are aliens, I don't know.. My real point though, is that there's no need for the intricate shuffeling of guests...

In a recent thread, I said that if there was interest, I would post in a separate thread the calculations for the kinematic decomposition of the congruence of worldlines describing the rod in the "rod and hole" relativity paradox discussed in that thread. Since there was interest, I am posting...

Following up on a previous discussion: https://www.physicsforums.com/threads/conservation-of-momentum-in-a-closed-system.1009693/post-6570341 An uncontained system of particles interacting only by elastic collision is the same as a gas undergoing free expansion. If, for simplicity, the...

A rigid rod with length ## l_0## slides on a smooth and flat tabletop along the length at speed of ## ~\frac {\sqrt{3}}{2}c~ ##, there is a hole of width ##~l_0~##on the table. The observer who is stationary relative to the desktop thinks that the length of the rigid rod ##~ l=l_o...

The thread: https://www.physicsforums.com/threads/question-about-a-stronger-relativity-paradox-than-the-twin-paradox.1009978/ proposed an interesting SR scenario. The thread could have led to instructive discussion of exactly how relativity of simultaneity resolved a "false paradox" that...

I have a question about the Klein paradox in the massless case, for a potential step of height ##V_0## (this is exactly the situation described by Wikipedia). I don't have a problem to understand the "paradox", and I think the Wikipedia's illustration is quite telling. My question is : what...

The twin paradox can be explained by changing reference frames. But I’m really curious how this paradox can be explained. In the situation below there are three observers: A: Standing at a moving train platform moving at a speed of c/2 relative to “the ground”. B: Standing at a moving train...

I saw a book that uses special relativity to solve the twin paradox, the inference process is roughly as follows. Suppose a spacecraft sets off from the Earth to travel to a distance black hole and then return to the earth. We divide this process into three stages, that is, the process of...

This started from a fairly innocuous post until fresh42 posted this link. Perok gave me guidance to work through it and I would like views on this. I kind of get it now I think, breaking the statements down into assumptions and deductions, combining the two is not permitted because you are...

Imagine that there is a very tight string connected to the bottom of each barn door. Each barn door opens and closes vertically. If the string breaks the barn blows up. The doors have to close at the same time for the string not to break. If the doors open one at a time, the extra distance...

Consider two observers, Alice and Bob, standing on the Earth together with synchronized clocks. Bob asks Alice, “Is this now?” to which Alice replies, “Yes, it is”. They are clearly both in the present moment. Bob climbs a mountain and some time later, due to the lower gravitational field...

Zeno's paradox claims that you can never reach your destination or catch up to a moving object by moving faster than the object because you would have to travel half way to your destination an infinite number of times. The two conflicting elements in this paradox are: 1) We do reach...

~ Shower Thoughts ~ Twin A is in a spaceship, Twin B is in a spaceship. Both in 'deep space'. B follows a highly elliptical geodesic which goes around a planet (or black hole) with strong gravity, very far away. When they meet again, who is younger and why? I genuinely don't know what this...

Hi all, I've been exploring the concept of the Relativity of Simultaneity. However, I cannot grasp the Pole in the Barn Paradox. Here is the video to the version of this paradox I am referring to: https://worldscienceu.com/lessons/11-3-the-pole-in-the-barn-paradox/ In this situation, the...

Imagine civilization gets a positive feedback mechanism for wasting resources, like cryptocurrencies: “one gets $100 banknote if burning $99 worth resources”, leading to exponential growth of waste at individual gains. We can observe exponential growth of their energy consumption (below)...

. . Two distant observers at rest with one another synchronize their clocks utilizing the travel time of light (by first moving the clocks to their locations, then using a light signal to time when the second clock should be turned on, and setting the second clock ahead to account for the...

In the first version of their arxiv preprint, Frauchiger and Renner argued that only the many word interpretation of QM was consistent. https://arxiv.org/abs/1604.07422v1 In the second version, the famous one published in Nature Communications, they radically changed their conclusions. They...

Spacetime physics chapter 4 describes this wonderfully well chosen set of speeds/distances for the twin paradox. A traveler departs from Earth at a speed of 99/101 (1=speed of light), traveling to a star that is 99light years away. From Earth's perspective, the traveler takes 101 years to go...

Originally i just wanted to look at how much analogy can be made between light and sound waves using all that math has to offer to depict them in most similar framework possible - just so as to have a different perspective to understand some things better. Anyhow, no matter how well one tries to...

I have been looking through some of the threads about the twins paradox in relativity. It’s clear there’s a lot of confusion on this, and I am yet one more person very confused on this. So I was thinking about a hypothetical experiment, and I will lay out my hypothesis of what might...

So picture this, its 2500 and you want to time travel back to 2300 to kill your great grandfather, this obviously creates a paradox wherein you prevent yourself from being born right? Well why don't you use your year 2500 technology to create a clone of your grandfather to replace him after (or...

I want to make sure I have this right, and whatever I have wrong I would like to fix it. Part I: So in particular, I’m referring to a fast moving pole along the x-axis of an observer who is at rest with respect to the barn (the barn is a few feet away from the observer), and when the pole is...

When an anthropologist analyzes a culture he/she might influence it and so does not get an accurate understanding of that culture. Does that mean that there was no specific culture before the anthropologist arrived? NO! Similarly, why would someone say that a particle has no position before...

I understand entropy as a movement from order to less order and that the universe's entropy is increasing. So I was wondering, life takes molecules and organizes them into organisms, so isn't life a reversal of entropy?

Velocity addition paradox: In observer A's frame, observers B and C move away from him at the speed of light c, B to the left and C to the right. In B's, frame A and C are both moving away from him at c, i.e. at the same speed. In both A's and C's frames they are moving at different speeds...

In a thread I started awhile back, in the common twins paradox scenario, it was indicated to me that the actual time (paraphrasing) on Earth for any given time in the ship is basically “undefined” (as it can’t be verified) and/or time dilated (ticking slower) for the trip out and then shifted to...

Reading McGhee's excellent book on the Carboniferous period and he explains in detail the unique circumstances behind the creation of 90% of the world's coal deposits - receding ocean in an ice age that created low lying swamps, high concentrations of oxygen in the atmosphere that would have...

Consider two massive charged objects at rest with a large horizontal distance ##d## between them (object ##1##: mass ##m_1##, charge ##q_1## and object ##2##: mass ##m_2##, charge ##q_2##). I apply a constant vertical force ##\vec{f_1}## upwards to object ##1## so that it gains an acceleration...

This post builds on a previously closed thread here: https://www.physicsforums.com/threads/lightbulb-paradox.141191/#post-1145674 I will not describe the problem here without the copyright owner's permission. I, like the OP in the original thread, am keen to see if anyone else who has this text...

Engineers are confronted with two apparently true but contradictory statements for airplanes in flight: a) Lift must equal the weight of the airplane (Lift = Weight), based on Newtons 2nd Law of motion (i.e. Force = ma); where gravity is used to calculate weight (i.e. Weight = mass x...

There are 3 lights in the form of a triangle... A, B, and C are lights and are stationary with respect to each other. S1, S2, S3 are spaceships. B S1 S2 A S3...

There we read: "note that if Wigner did not know this phase due to the lack of control of it, he would describe the “spin + friend’s laboratory” in an incoherent mixture of the two possibilities". Why is this the case? Given that the author has propoede neither a citation nor a proof for this...

If two identical radioactive masses were subjected to the "twin paradox" experiment of Langevin, would the mass that traveled be really less radioactive than the one that did not? Radioactive decay is supposed to be independent of physical conditions and to only depend on the isotope.

Hi, I recently discovered that there is no real paradox in the question of the mixing of classical distinguishble particles. I was shocked. Most books and all my professors suggest that an extensible entropy could not be defined for distinguishble particles. I believe that many of you will be...

Hello, For many years, solving the twin paradox has not been a problem for me. I understood that it is the change of Galilean frame of reference that is responsible for the age difference, and this clearly appears on a Minkowski diagram. Okay. However, since yesterday, in wanting to explain...

I know this has been asked so many times, but would someone please answer why to this particular variation to the question. Tom is moving at constant velocity past Jerry on Earth (assume no acceleration). At the moment they pass each other they agree on the time seen on a clock. Tom thinks...

Hello, I am currently reading "The first Fifteen Lifes of Harry August" from Catherine Webb and really like it so far. I did not even read the half or so but there was an interesting idea I would like to discuss about. As far as I understand Harry August does return after dying to the same...

Paradoxical scenario. Suppose Jack and Jill are sitting safely a kilometer above the event horizon (EH) of a large black hole. Now suppose: Jack decides to head toward the center of the black hole, traveling at an easy pace (say 10 km per hour). Jill sees Jack (with her ultrasensitive infrared...

While I have have heard about it for years, I have just read a more-or-less clear description of the EPR "paradox" in David Lindley's Where Does the Weirdness Go? (1996), page 91, "The fatal blow?". Here is a summary (paraphrasing what I read) as I understand it. A pair of particles (say A and...

Let's start with a horizontal tube with a constant diameter. I'm not sure if it's important, but let's assume it's frictionless. I will have some fluid flowing in this tube and if it's important, we can make the fluid incompressible, inviscid, irrotational, etc. To create a flow in the tube...

Can anybody point to an experiment that shows that the total entropy increases if two different gas mix at constant pressure and temperature, whereas if two volumes of identical gases mix the total entropy doesn't change?