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".

View More On Wikipedia.org
  1. Buzz Bloom

    I A new puzzle based on the "Blue-eye paradox"

    The puzzle presented below is derived as a variation of the Blue-eye paradox" which has been discussed in the following thread. https://www.physicsforums.com/threads/blue-eye-paradox.875870 THE PUZZLE Teams of N people each are each given the following challenge. The rules for the challenge...
  2. S

    B Twin Paradox: A and B at Different Speeds

    Hi, I'm trying to understand the twin paradox and time dilation. Someone told me that if observer A and observer B are traveling apart from each other with each having a uniform speed of .4c they will have the same age when they return back at the point of origin. Even though I'm unsure of...
  3. Quantum of Solace

    I Elitzur-Dolev Quantum Liar Paradox

    I've seen Elitzur's brief presentations on this. Two excited atoms pointed at a detector. The detector goes off, it isn't known which particle fired the photon, so you interrogate one, it gives a definite answer but violates bell's inequality? I'm sorry but I'm lost at such a vague...
  4. steveJOBS

    B The Firewall Paradox: Is it Possible?

    What is the firewall paradox?? is it possible in a black hole or in its event horizon ??
  5. E

    I What happens during acceleration in time dilation?

    I understand that the twin paradox isn't truly a paradox, and that the traveling twin ages since the universe can be "aware" of his traveling. However, my question is how does the time dilation formula break down? Why can't you integrate dT' = dT * Gamma for each velocity as the traveler...
  6. B

    B Help With the Twin Paradox: Why Does Time Dilation Apply?

    Forgive my naivete, but I've struggled with the twin paradox for a long time. If there is no privileged frame of reference, why does time dilation apply only to the traveling twin? I have been told (possibly erroneously) that the stay-at-home represents the entire universe, but this seems to...
  7. M

    Resolution to Gibbs' entropy paradox?

    It seems to me that Gibbs' Paradox (that the entropy of a classical ideal gas, calculated by phase-space volume, is not extensive) can be resolved without assuming that particles are indistinguishable. Suppose instead the opposite: that particles are distinguishable, meaning that each one can...
  8. A

    B Einstein's relativity of simultaneity & quantum paradox.

    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...
  9. micromass

    Insights Some Misconceptions about Indefinite Integrals - Comments

    micromass submitted a new PF Insights post Some Misconceptions on Indefinite Integrals Continue reading the Original PF Insights Post.
  10. S

    MHB Why is there a probability paradox in this bag of balls?

    A bag contains two balls. Either ball can be black or white. Without drawing any balls, determine the colors of the balls.Solution The bag could contain any of three contents, each with probabiity \tfrac{1}{3}. . . \boxed{B B} \qquad \boxed{BW} \qquad \boxed{WW} Add a black ball to the bag...
  11. soothsayer

    I Lines of simultaneity in Twin Paradox spacetime diagram

    I set up a Twin Paradox scenario and accompanying spacetime diagram to help better understand the resolution, but I had a question about the diagram I was hoping someone here could help answer. Please excuse the hastily drawn diagram! (Note: the ' frame corresponds to the outbound trip, the...
  12. Demystifier

    A Blue-Eye Paradox: Solution Not Unique

    The blue-eye puzzle (or paradox, or riddle) is a well known logical puzzle, explained and discussed in many places, including http://puzzling.stackexchange.com/questions/236/in-the-100-blue-eyes-problem-why-is-the-oracle-necessary https://en.wikipedia.org/wiki/Common_knowledge_%28logic%29...
  13. Dennis Plews

    I The information paradox and non-locality, ER = EPR

    I heard recently that Dr. Maldecena recently commented to Dr. Susskind, regarding the black hole information paradox, that ER = EPR. Can anyone illuminate this for us mere mortals? It seems to link all information via non-locality, which has interesting implications.
  14. Andy Resnick

    A Q: Stokes paradox (flow around a cylinder)

    Can anyone recommend a good (peer reviewed) reference that discusses low Reynolds number flow around a cylinder? I'm specifically looking for derivations of the drag coefficient. The usual 'gold standard' references...
  15. J

    I Free Particle: Time dependence of expectation values Paradox

    It would be really appreciated if somebody could clarify something for me: I know that stationary states are states of definite energy. But are all states of definite energy also stationary state? This question occurred to me when I considered the free particle(plane wave, not a Gaussian...
  16. R

    A Are there instances of Simpson's Paradox in Physics?

    The so-called Simpson's Paradox arises frequently in medicine, economics, decision sciences, demography and many policy fields. Have there been any instances of it in physics (or chemistry)? Perhaps the most newsworthy instance of the paradox was in connection with possible gender bias in...
  17. N

    MHB Proving No Set Contains All Sets Without Russell's Paradox

    Greetings: I am attempting to prove that no set contains all sets without Russell's paradox. What I have thus far is this: Let S be an arbitrary set and suppose S contains S. If X is in S for some X not=S, then S - S cannot be empty. But this is a contradiction; hence if S contains S, then...
  18. J

    B Twin Paradox Visualization: Understanding with Java & Diagrams

    I decided to work a bit on my Java program created to visualize the Twin Paradox. It shows two diagrams. One from the perspective of the stay at home/earth twin on the left side and the traveling twin on the right side/diagram. The accelerations are considered to be near instantaneous, hence why...
  19. W

    I Exploring the BB Paradox in an Evolving Universe

    I know this has come up before but there is still something puzzling me about the whole BB paradox. This is the problem phrased in the context of our evolving universe. As far we can tell the universe will expand forever ( assuming dark energy is not something variable but is a constant). In a...
  20. P

    B Does Schrödinger's paradox work with multiple boxes?

    I just read an article (linked below) today and found it to be quite curious and interesting. In short, physicists have taken Schrödinger's cat paradox to a whole new level by adding a second box. I’m still very new to all the ideas of quantum physics, but apparently this addition of another box...
  21. Battlemage!

    Hodor bootstrap Paradox? Spoilers for the Game of Thrones

    The night is dark and full of SPOILERS...... Okay, so in the last Game of Thrones episode, a massive twist involving what appears to me to be a bootstrap paradox occurred. I was wondering what anyone who saw thought about it and for those who did or didn't whether or not it makes sense. The only...
  22. G

    I Questions about Vsauce's Banach-Tarski video

    Hi, I have some questions about the video about the Banach-Tarski Paradox from the YouTube channel Vsauce: 10:09: Is this really a valid way of constructing the hyperwebster? In this order, one will never get past sequences of only "A". Shouldn't one follow an order like A, ... ,Z, AA, ... ...
  23. S

    Blackbody paradox applied to interaction of gravity with electrons

    Homework Statement How does the blackbody paradox argument show that the electromagnetic field cannot be classical while electrons and atoms are quantum mechanical? Should the same arguments apply to treating gravity classically and electrons quantum mechanically? Homework Equations The...
  24. M

    B Fermi Paradox: What are your opinions on the Fermi Paradox?

    Hi guys, So If any of you aren't familiar with the Fermi Paradox, I highly advise you read about it. It is easily one of the most interesting topics I've come across. IF you can't be bothered for this I have included a small summary of what the Fermi Paradox in my survey (see below). I'm doing...
  25. Wandelgart

    Funny similarities between a ball and the expanding universe

    A rubber ball is bouncing on a flat surface. Every time it bounces, it loses energy, while the sound of the ball hitting the surface accelerates (because the intervals of the ball impacting the surface become shorter with each bounce). The ball seems to be accelerating when, in fact, it is...
  26. I

    B The Paradox of Mass Distortion in Collider Experiments

    When a collider such as the lhc accelerates two protons side by side, would thy seem to gain mass and then distort st? And if so, would the lab frame see them attract each other? How would the attraction be explained from the perspective of each particle, if they don't see the other particle...
  27. nomadreid

    I Status of Adami's solution to Firewall paradox?

    A bit over two years ago, Chris Adami et al. published their solution to the firewall paradox (referred to without source in http://msutoday.msu.edu/news/2014/plugging-the-hole-in-hawkings-black-hole-theory-1/, perhaps referring to http://arxiv.org/abs/1310.7914). But what has happened in the...
  28. Javier Chornet

    B Solving the Paradox of Rope: Transmission of Info in GR

    I was thinking about a gendanken experiment that I don't know how to solve: Imagine we tie one extrem of a rope in the Earth and the other one in the Sun, with some tension, and connected to a dynamometer (obviously in ideal conditions: no heat, no rotation etc.). My question is: when will the...
  29. Dbwh

    Fermi Paradox Solution: R1/C1 < R2/C2

    Homework Statement In the book "In searcg of life in the Universe" A.D. Ursula gave the following formula R1/C1 = R2/C2 (A) when the contact between two civilizations happens, where R - result from a contact and C - cost to make a contact for those civilizations. Homework Equations The key...
  30. J

    I Is the Linear Ehrenfest Paradox Accurate for Circular Motion?

    Here is a linear version of the Ehrenfest paradox with the goal of understanding the observations of someone in motion in the scenario, then solicit your views on whether the calculations are correct and whether one can extend it to circular motion.Consider a one dimensional train of proper...
  31. C

    I Twin Paradox Resolution -- Inertial frames

    Thinking and reading about the twin paradox recently, I encounter a lot of explanations and resolutions that don't make sense to me. At its most basic, the issue is- when two bodies are in different frames of reference, why shouldn't relativistic effects affect both equally, negating time...
  32. FallenApple

    Is the Gravitational Twin Paradox Solved by Calculating Geodesic Paths?

    So say that there are twins. Twin A is near a heavy planet and twin B is out far away in space. Why does time slow for twin A compared to B? Can't they say that they both are in inertial frames because there are no forces(gravity isn't a force) acting upon them? Therefore for each of them can...
  33. Isaac0427

    Zeno's Arrow Paradox: Resolving Motion Impossibility

    To quote from this wikipedia article: How is this resolved? It seems a little bit nonsensical but I do get the logic. This has me very confused...
  34. Abel Cavaşi

    The informational paradox of rectilinear motion

    If the torsion of the straight line is undefined what happens with the information about the torsion? It is known (https://en.wikipedia.org/wiki/Quantum_no-deleting_theorem, http://van.physics.illinois.edu/qa/listing.php?id=24045) that the information conserved in a system can be nor created...
  35. G

    How is information lost if nothing passes the event horizon?

    Hi. From an outside observer's view, any object approaching the event horizon of a black hole appears to slow down and never quite pass through the horizon. So information about those objects can always be retrieved (if you correct for the redshift). So what actually is the information paradox...
  36. I

    I Understanding the GR Twin Paradox: Explained in a Concise Video

    Hi, I just saw a video about the twin paradox, explained by using GR. I was wondering whether I understood the video correctly. The video states that when the rocket twin is first accelerating away from earth, his clock and his Earth twin's clock are different, but, roughly the same because of...
  37. Dennydont

    How does the doppler effect resolve the twin paradox?

    If you had twin 1 on the earth, and twin 2 fly to a star and back at a speed of v with the Earth and star separated by a distance L, twin 1 sends out flashes at intervals of t seconds (measured in his frame). Taking into consideration the numbers of redshifted and blueshifted flashes that the...
  38. S

    Another newbie question: paradox: size vs. age

    I've never understood this: we measure the edge of the observable universe to be around 13 billion LY away, so we are seeing the state of things 13 billion years ago. But 13 billion years ago, wasn't the universe much, much smaller? Did distant quasars and galaxies look like they do "now" so...
  39. rjbeery

    "Randomness Through Entropy" Paradox

    In Information Theory, entropy is defined as the unpredictability of information content and, as such, the entropy of the output from so-called pseudo random number generators (PRNG) is often measured as a test of their "randomness". An interesting paradox arises with this definition... Start...
  40. T

    EPR paradox and time of collapse

    According to the EPR-paradox, if we have a pair of two entangled spin-1/2 fermions A and B and measure z-component of A, B collapses immediately as well(i'm using these letters for both particles and their observers). The 'canonical' solution is then to state that it is not possible to transfer...
  41. DiracPool

    More twin paradox and acceleration

    I just came across this video today with Brian Greene talking about how time slows down for an observer near a black hole relative to an observer who is farther away. See the first two minutes: It reminded me of another video I saw recently by David Butler where he states that the twin...
  42. R

    Lorentz Transformation Equation Paradox

    Hi All; I was trying to understand Lorentz Transformation equation and special theory of relativity, but as I compared the derivation with a thought experiment which I imagined I found the whole Lorentz Transformation Equation fails. The details of the problem is given below. I know I m wrong...
  43. R

    B Lorentz Transformation Equation Paradox - Find Where I Went Wrong

    Hi All; I was trying to understand Lorentz Transformation equation and special theory of relativity, but as I compared the derivation with a thought experiment I created I found the whole Lorentz Transformation Equation fails. The details of the problem is given in the pdf file attached. I know...
  44. M

    B FTL Paradox: Grandfather Paradox Explained

    So here it goes: 2 points in space A & B. 1 superluminal object (fixed at 10c, no acceleration) that periodically transmits photons as soon as it starts moving. 1 observer with a very high accuracy photon counter removed a sufficiently large distance from the 2 points for light to take a small...
  45. Kostik

    Free particle propagation: paradox?

    Shankar ("Principles of Quantum Mechanics", 2nd ed.) shows that the free particle propagator "matrix element" is given by (see p. 153): ## \qquad \langle x | U(t) | x' \rangle = U(x,t;x') = \left(\frac{m}{2\pi\hbar it}\right)^{1/2} e^{im(x-x')^2/2m\hbar} ##, which can be used to evaluate the...
  46. J

    Does the Circular Twin Paradox Challenge Our Understanding of Time Dilation?

    Here is a scenario in which two twins age at different rates even though both always have the same speed.Consider a train track that includes a circular segment with ground circumference minutely greater than 80. Two twins are on a train with synchronized watches (Frank at the front and Reba at...
  47. E

    Signal time in Twin Paradox: Fast clocks? Redshift/blueshift

    NOTE: This is NOT a homework problem. I created this one myself based on some problems I have seen, with specific numbers used to make calculation clean and easy. Tl/dr version: in a round trip to a star, will the "moving clock" run slower on the way there but faster on the way back due to the...
  48. Aero_Arnendu

    Twin Paradox: Relation between Age and Speed of light .

    Hey Friends, In Einstein's special relativity I find "Twin Paradox", where Dick and Jack, two twins . one of them went to space at a speed of 0.80c to a star 20 light year away (where c is the speed of light) and other remains on earth. When Jane returned to Earth his age was...
  49. H

    Can Resolving Forces Differently Lead to Contradictory Equations?

    Hi ! So a friend and I were solving some mechanics problems in class today. And we came across a pretty funny mathematical paradox. So basically we tackled the problem in different ways...but we ended up with different equations...and none of us could prove the other wrong ! So here goes... The...
  50. S

    Viscous Disc Paradox: How Does Friction Operate?

    Which way does friction in a viscous disc operate? Imagine a ring consisting of ringlets. First consider a case of a pair of nearby ringlets - in the same plane, both circular orbits. If all particles of both ringlets are in circular orbits in the same plane, then they can never collide and...
Back
Top