Paradox Definition and 1000 Threads

After making a couple of comments on this StackExchange question, and pointing yet again to this article, a thought occurred to me. I have been working on an Automatic Differentiation based ODE solver and equation analyzer, mentioned in this thread. Why not use it to solve equation (7) in the...

Hi! I'm an utter novice at physics, so please bear with me if I ask a foolish question. I just learned that velocities don't purely add: 2m/s + 2m/s does not equal 4m/s, but something like 3.9999999...9 m/s, and so on. Something to do with the upper limit of c. Logic makes me assume that this...

Homework Statement Let ##U_t = e^{-iHt/\hbar}## be the evolution operator associated with the Hamiltonian ##H##, and let ##P=\vert\phi\rangle\langle \phi\vert## be the projector on some normalized state vector ##\vert \phi\rangle##. Show that $$\underbrace{PU_{t/n}P\dots PU_{t/n}}_{n\text{...

https://en.m.wikipedia.org/wiki/Rietdijk%E2%80%93Putnam_argument Is the Andromeda Paradox accepted in physics? It seems to be based on the concept of relative simultaneity, but it seems quiet nonsensical. Wouldn't every observer seeing a different time period violate causality?

I've been trying to work out exactly what part of the experiment I'm fundamentally not getting. The experiment basically says that no information is being sent back in time because the coincidence counters are needed to isolate the signal photons and expose the interference pattern. But the...

Just a question: Can anybody give any information regarding the black hole paradox? There are so many theories behind it. Which one should we believe? Just a general question.

Does Hardy's paradox show that all realist interpretations cannot be made lorentz invariant? Or is it just realist hidden variable theories?

I have an obvious understanding failure here, so hopefully someone can help me clear this up. Thanks for reading this obnoxious drivel.Leading clocks lag So, if two clocks are fixed to a the ends of a barn, and they are set off with light pulses from the midpoint, in the frame of the barn the...

A traveler visits a location (or doesn't!) ##x## light years away at fractional [EDITED] speed ##v## and instantly returns at the same speed. After this her clock has progressed by ## \frac {2 x} {v} \sqrt {1 - v^2}## years. [EDITED] That really is all there is to be said. If the poster...

I've read the twin paradox and if I am correct the resolution is that one twin accelerates and decelerates so he comes back younger. But I have a different scenario that I would like to ask: What if you have two twins equally distant from a point in space and completely at rest relative to each...

I'm beginning to study the Matt Roots book Introduction to Cosmology and in the section 1.3 Olbers' Paradox he writes: "If the surface area of an average star is A, then its brightness is B=L/A. The sun may be taken to be such an average star, mainly because we know it so well. The number of...

Homework Statement a) Alice is observing a small ball of mass m in relativistic motion bouncing elastically back and forth between two parallel walls separated by a distance L with speed u. After each collision it reverses direction, thereby creating a clock. What does Alice observe as the...

Let us assume we have a cylindrical wind tunnel having a 0.5 m diameter fed by an electric fan. The cross-sectional area of the wind tunnel would be A1 = (PI/4) D1^2 = 0.196349541 m2. Let us suppose the motor driving the fan has a power rating of 1,500 W. At this stage, let us assume that the...

Homework Statement Compare bond energy of ethane/ene/yne 2. The attempt at a solution Comparing their acidity, ethyne has sp hybridized C so more polar CH bond, therefore H+ can be released easily. Therefore acidity order is ethyne>ethene>ethane which means CH bond is weakest in ethyne and so...

Homework Statement The points of interest are at point A and B, I want to calculate the pressures at that point. I am working in gage pressure so we can ignore atmospheric pressure. Homework Equations P = pgh P = sg x specific weight of water x height The Attempt at a Solution Attempting a...

A monochromatic gamma light source S emits photons with spherical symmetry. These photons have a little less energy than necessary to permit formation of particle - antiparticle couples (electron-positron couple) or “EPCs”. An inertial observer O moves towards S with a small fraction of light...

As I understand it with an orthodox interpretation of Special Relativity, if in flat space there was a velocity difference between two inertial frames of reference, then observers in either could calculate the clocks in the other to be going slower. And it could be said that both views are...

Here is a diagram from the Wikipedia. I'm sure you understand what this represents. Those who don't, can go to the Wikipedia page (https://en.wikipedia.org/wiki/Twin_paradox) and see all the details. After my prior post, I have a better appreciation for simultaneity. Originally, when I looked...

The resolution for Maxwell's demon paradox is that the demon has limited memory and the demon will eventually run out of information storage space and must begin to erase the information it has previously gathered. Erasing information is a thermodynamically irreversible process that increases...

You and two identical spaceships are all at rest with respect to each other. You note that the two engines start up at the same time, and the thrust curve and acceleration profile of both spaceships are identical. As the ships pick up speed, would you measure the ships to be shorter than their...

Can a "thing" go through the event horizon of a black hole? I mean, everything inside a black hole can travel only in one direction: inward. That destroys the "thing" itself, since independent parts of the "thing" are no longer connected to one each others. Perhaps it's impossible for a "thing"...

This paradox may have come from Feynman's Lectures on Physics, or I may have dreamed it up myself. I am not sure. It has been around for a while and if you have already seen it, I apologize. I am not aware of any resolution. An electron is at rest in a gravitational field. We know from...

The BE-distribution for the case of only one state per energy level (gi = 1) is ni = 1 / (exp(ui - μ)β - 1) This is a reasonable and well defined distribution as far as I can see. On the other hand the number of possibilities to realize a given distribution of bosons among k energy levels with...

Greg Bernhardt submitted a new PF Insights post A New Interpretation of Dr. Walter Lewin's Paradox Continue reading the Original PF Insights Post.

Good evening. The problem states: Spring paradox. What is wrong with the following argument? Consider a mass m held at rest at y = 0, the end of an unstretched spring hanging vertically. The mass is now attached to the spring, which will be stretched because of the gravitational force mg on the...

well since gravity waves are supposed to have mass, they are supposed to be effected by gravity itself, and :/ how are we supposed to detect gravitational waves emitted from a black hole when none can get out?

Right answer for the Walter Lewin demo/paradox about electromagnetic induction in Lecture 16 ?

Bridge fall paradox Another thread urges me to think of stress in materials in TOR and let me make a "paradox" to think of it as follows. --------------- A train is running on a bridge over a wide river. Evil terrorists switch on the bombs set on legs of the bridge to crash whole the bridge...

Okay, so if two identical twins put on a heart rate monitor that after let's say 400 million beats were detected (at 80bpm that's about 10 years) the monitor killed them. Now one gets in a spaceship and the other stays on earth. The one in the spaceship travels at say 95% of the speed of light...

I am posting this paradox as a brain teaser If we drilled a tunnel through the earth, to the other side, and measured gravity in the tunnel, gravity would be zero in the center of mass. This is Newtonian gravity and is connected to the vector addition of the gravitational force; cancels in...

Two paradoxes from different domains generate huge number of would-be solutions, and I am not starting this thread in order to promote one solution over the other or to proclaim that I have a new solution. I just wonder whether the techniques used for certain would-be solutions of one could be...

Hello, I'm a beginner on SGR and I'm struggeling with this, probably, simple problem. I'm interested on exploring Field Theory ( relativistic) so I started reading http://www.elegio.it/mc2/LandauLifshitz_TheClassicalTheoryOfFields_text.pdf which was suggested and reccomended by a PF's member...

I know this publication is not peer reviewed, but when I saw this article it was exactly the same way I came to “understand” the twin paradox myself. I literally did this exact calculation (with a different gamma value). So I was wondering if the article was valid. If it isn’t, where isn’t it...

I am currently going through a friend's Mechanics II notes and homework before I take the course at a different university next semester. I have a few problems that I am having trouble understanding and am posting here for help. 1. Homework Statement 1. A solenoid is on, Flux is Φ. 2. The...

I'm just trying to develop a general understanding of the 'twin paradox', so my description of this is will be a bit poor. I feel like I have a sound understanding so far on the topic, but the only thing that I can't seem to find an answer for is this scenario; Say you have the classic twin...

I've noticed that for every prime and every composite number on the number line that is not a perfect power, ( I am referring to positive whole numbers only), that there are infinitely many perfect powers (PPs) that can be generated using that number. This suggests that the PPs should swamp the...

I will soon start with the course introduction to QFT and are hence an amateur on the subject. However I could not help but wonder, If particles are describes by oschlliations in a field, how can a "bigger body" be made up of several such oscillation? (A bigger particle is made out of several...

Credit to this thread - https://www.physicsforums.com/threads/flash-open-manhole-cover-paradox.936632/ I did not think this one up myself. Per suggestion from @pervect I am creating a thread for this. Antman is sitting on top of a hockey puck trying to hide from Hulk. Hulk has seen him and...

The superhero "Flash" races over a 3' diameter open manhole at 0.999 the speed of light. I realize that this exceeds escape velocity on earth, so assume the running is being done on Terry Pratchett's "Discworld" https://en.wikipedia.org/wiki/Discworld From Flash's point of view, the manhole...

Bondi K-Calculus very depend on who was send the signal. If two twin A and B make a journey, A send a signal and B receiving the signal then yes after the journey A will see B younger, and this applied too for the case B sending a signal and A reflecting, then after the journey A will younger.

Homework Statement In a vessel is a 5 cent coin and two 1-cent coins. If someone takes up two randomly chosen of these coins, and we let X be the total value of the coins taken, what is the probability function for X? Homework Equations I know that X has a value {2,6} The Attempt at a...

Consider a spring-mass oscillator on a train moving at relativistic speed. According to SR, to a stationary observer, both the mass and the period will appear to have increased by a factor of γ. But the period is supposed to be proportional to the square root of the mass. Something is wrong...

https://en.wikipedia.org/wiki/Fitch's_paradox_of_knowability It begins by assuming that 'All truths are knowable' and then logically proves that that assumption means 'All truths are already known.' The proof is like this: Suppose p is a sentence that is an unknown truth; that is, the sentence...

Homework Statement One person that we will call him - A is standing on an infinite charged non conductive panel with velocity V=(-Vx0,0). A is throwing a particle q with V=(Vx0,Vy0). The other person - B, is start running below the particle at t=t0. A thinks that B will see the particle above...

In the information loss paradox, people say that in quantum mechanics , time evolution is unitary. They usually do not say anything about the measurement process of if they do, they briefly say that the measurement process does not violate unitarity either if one takes into account the...

The following reasoning leads to an apparent paradox; explain what’s wrong with the logic. A baseball player hits a ball. The ball and the bat spend a fraction of a second in contact. During that time they’re moving together, so their accelerations must be equal. Newton’s third law says that...

Hello, layman here, I have a simple question, could you please clear this up for me? Whenever I read about the information paradox, it always appears to me that it is automatically assumed that quantum fluctuations / virtual particle pairs are predictably random. Which leads to the loss of...

Hi, thanks to a different thread/question on this forum I've come to appreciate time dilation ..somewhat. And from that I wondered if, given the range of locally measured times aboard any and all particles in the universe, given their different trajectories and histories since the big bang...

Hi people! (Sorry for my poor english). I found everywhere that twin paradox need aceleration to explain it. Let me change the twin paradox a little: Suppouse that in Earth and before the traveller twin start his trip, you take two photos with old Polaroid camera, one to each twin. As we...

Interesting new derivation of ##E=mc^2## from an experiment of moving atoms emitting photons. http://flip.it/AfcjP9 http://flip.it/AfcjP9