What is Paradox: Definition and 1000 Discussions

A paradox is a logically self-contradictory statement or a statement that runs contrary to one's expectation. It is a statement that, despite apparently valid reasoning from true premises, leads to a seemingly self-contradictory or a logically unacceptable conclusion. A paradox usually involves contradictory-yet-interrelated elements that exist simultaneously and persist over time.In logic, many paradoxes exist which are known to be invalid arguments, but which are nevertheless valuable in promoting critical thinking, while other paradoxes have revealed errors in definitions which were assumed to be rigorous, and have caused axioms of mathematics and logic to be re-examined. One example is Russell's paradox, which questions whether a "list of all lists that do not contain themselves" would include itself, and showed that attempts to found set theory on the identification of sets with properties or predicates were flawed. Others, such as Curry's paradox, cannot be easily resolved by making foundational changes in a logical system.Examples outside logic include the ship of Theseus from philosophy, a paradox which questions whether a ship repaired over time by replacing each and all of its wooden parts, one at a time, would remain the same ship. Paradoxes can also take the form of images or other media. For example, M.C. Escher featured perspective-based paradoxes in many of his drawings, with walls that are regarded as floors from other points of view, and staircases that appear to climb endlessly.In common usage, the word "paradox" often refers to statements that are ironic or unexpected, such as "the paradox that standing is more tiring than walking".

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  1. m4r35n357

    I Twin Paradox: Travel at Fractional Speed & Instantly Return ##v##

    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...
  2. I

    I A variation of the twin paradox

    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...
  3. alejandromeira

    B Exploring Olbers' Paradox in Matt Roots' Introduction to Cosmology

    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...
  4. B

    Twin Paradox from Moving Reference Frame- Return Journey

    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...
  5. eudesvera3

    Paradox of a convergent nozzle fed by an electric fan

    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...
  6. Krushnaraj Pandya

    Acidity and the bond energy paradox in ethane, ethene, ethyne

    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...
  7. B

    Pressure Calculations at Points A and B using Pascal's Paradox

    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...
  8. Alfredo Tifi

    B New Paradox: Gamma Light & Relativistic Doppler Effect

    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...
  9. N

    I Exploring the Paradox of Relative Truth in Special Relativity

    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...
  10. F

    I Simultaneity and the Twin Paradox

    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...
  11. Deepblu

    Maxwell's Demon Paradox: Solving the Puzzle Without Memory Requirements

    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...
  12. David Lewis

    B Bell's Spaceship Paradox & Length Contraction

    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...
  13. G

    B Can Anything Go Through a Black Hole?

    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"...
  14. Gene Naden

    I Paradox: Electron Radiates in a Gravitational Field

    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...
  15. Philip Koeck

    A A paradox for bosons with non-degenerate states?

    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...
  16. rude man

    Insights A New Interpretation of Dr. Walter Lewin's Paradox - Comments

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

    Solving the Spring Paradox: Uncovering the Error

    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...
  18. negative

    B Black Hole Paradox: Exploring Gravity Waves

    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?
  19. mabilde

    I Walter Lewin Demo/Paradox: Electromagnetic Induction Lecture 16

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

    B Exploring the Bridge Fall Paradox: A Look at Stress and Damage in Materials

    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...
  21. Orangeator

    B Theoretical Question On The Twins Paradox and Heart Rate

    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...
  22. P

    I A paradox connected to General Relativity

    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...
  23. nomadreid

    I Are Time-Travel and Logical Paradoxes Connected?

    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...
  24. Aleberto69

    B Lag of a clock coming back to its initial position (Twins Paradox)

    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...
  25. Sorcerer

    I Twin Paradox: Exploring Scientific American Article

    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...
  26. T

    Mechanics II: Feynman Paradox

    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...
  27. Daniepie

    B How Does the Twin Paradox Affect Aging?

    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...
  28. P

    I Is this a paradox on the number line

    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...
  29. F

    I Exploring Oscillations & Interference in Particle Physics

    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...
  30. Grinkle

    B Hockey Puck Paradox: Will Antman Fly or Cruise?

    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...
  31. A

    I Flash open manhole cover paradox

    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...
  32. Mohammad Fajar

    I Twin Paradox & Bondi K-Calculus: Who's Younger?

    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.
  33. Pouyan

    A paradox in probability theory and statistics

    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...
  34. A

    B Relativistic Spring-Mass Oscillator: A Paradox?

    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...
  35. K

    B Fitch's Paradox: Knowability of All Truths

    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...
  36. K

    Paradox - different results for different viewers

    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...
  37. K

    A A question about the information loss paradox

    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...
  38. S

    How Does Newton's Third Law Apply When a Bat Hits a Ball?

    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...
  39. A

    B Black hole information paradox and determinism

    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...
  40. S

    I Twin paradox in SR and its applicability to radioactive decay

    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...
  41. L

    I Twin paradox not including accelerations, it is wrong where?

    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...
  42. jedishrfu

    B Solving Mysterious Relativity Paradox: New Derivation of E=mc^2

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

    Particle defined "at rest" compared to a magnetic field?

    I am trying to understanding magnetism and I've been running into this thought problem A particle a in a magnetic field B responds with Force F=|q|v x B. frame S: The field is B1, caused by a moving charge/s - current at speed v. the particle is at rest, F=0. frame S' moves with speed v/2...
  44. P

    Light-beam propagation across impassable barrier?

    Hi all, (See attached image file) Two mutually coherent and collimated light beams intersect as shown, creating the stationary 'bright' and 'dark' fringes of fig.A. Suppose that, after the fringe pattern has formed, we insert a very thin (compared to the fringe-width) and (ideally) perfectly...
  45. M

    I Resolving the Three Colliding Observers Paradox in Special Relativity

    I have a random paradox I seem to have found with three colliding observers, though to explain it properly I'm going to use a bit of visual aid and a bit of abstracting it from the math (or setting the math so that it works according to my example). For anyone who wants the TLDR, read this...
  46. S

    I Time Dilation and the Twin Paradox: A Look at the Relativistic Doppler Effect

    Hello everyone, Reminder: The key of the explanation of the "twin paradox" resides in the acceleration. We know that the time runs slower for the twin in the spaceship (since it was accelerated)...
  47. V

    Twins Paradox: Solving for Total Time Lapse

    Homework Statement In the twins paradox, suppose that Florence begins at rest beside Methuselah, then accelerates in Methuselah’s x-direction with an acceleration a equal to one Earth gravity, “1g”, for a time ##T_F/4## as measured by her, then accelerates in the −x-direction at 1g for a time...
  48. R

    B Special relativity and expansion of the Universe, A paradox

    Consider two bodies A &B are moving apart with a velocity V due to the expansion of space. According to an observer in A the body B is moving away and an observer in B feels the body A is moving apart. Can some one answer in which body the time dilates and why?. ( I am specifying once again that...
  49. Andy_K

    I Twin Paradox - Observation at Turnaround Moment

    Dear All, I am doing the Special Relativity course at World Science U, and came across this question which I got wrong: When 100 nanoseconds have elapsed on traveling Gracie's watch, she immediately stops, turns around, and heads back toward George at the same speed of her outbound journey...
  50. M

    I Twin paradox in GR - negative time?

    I was reading the wikipedia page on the twin paradox (https://en.m.wikipedia.org/wiki/Twin_paradox). It says: The mechanism for the advancing of the stay-at-home twin's clock is gravitational time dilation. When an observer finds that inertially moving objects are being accelerated with...
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