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. PGaccount

    A Bohr's solution to the EPR paradox

    First, I will give my understanding of Bohr's resolution using an example that Bohr considers in his discussion. Then I will quote a passage where Bohr summarizes his resolution of the paradox. Finally, I will try to respond to John Bell's comments on this resolution. I would be interested in...
  2. Arkalius

    I Simultaneity Paradox in Space: What's Going On?

    I thought of yet another simultaneity paradox that I find even more confusing: We're just in space with spaceships. There's a ship moving past us at some relativistic speed. On the front and back of the ship there are thrusters at the top that can be activated by a pulse of laser light striking...
  3. P

    A Bell's spaceship paradox: after the thread breaks....

    When Bell says that the thread in put under "intolerable stress" and breaks, what happens then? Suppose that instead of the thread there is a light rod, which breaks at the point of attachment to the back spacecraft , so it is left sticking out backwards from the front spacecraft .. In the...
  4. WWW Mechanical PE

    A Can Somebody solve the Rich Investor's Paradox?

    The Rich Investor’s Paradox Let us assume you have been given an immense amount of money and you are worth $50 billion. In addition you have a clairvoyant that can read tomorrow’s edition of the Wall Street Journal. You decide to start investing in stock because you believe you have a sure...
  5. X

    I Relativity Paradox w/ Charged Spheres

    There is a similar thought experiment I imagined to help me begin to understand the Bell's spaceship paradox: Consider two positively charged spheres, placed side-by-side inside a frame S' with a string stretched to the point where it balances the repulsive electrostatic force between them. For...
  6. Grimble

    I Proper (and coordinate) times re the Twin paradox

    This was straying from the point in the original thread, but I thought it made a point... The stay-at -home twin is at rest in her frame and her clock must therefore measure proper time. The traveling twin, carries his clock with him; it is therefore at rest in his frame and must also measure...
  7. V

    B Error in Einstein's Biography on Twin Paradox?

    Hi, I am reading the biography "Einstein's greatest mistake" from David Bodanis. On page 39 the author explains some of the consequences of relativity by referring to (although he doesn't mention it by name) the twin paradox. He explains that someone accelerating at high speed away from Earth...
  8. Buckethead

    B Triplet Paradox and Thought: The Mystery of Time Dilation

    First off, let me just say I love this forum and all the people in it! The world is a better place because of all of you who take the time to post here and I thank you all! The most popular explanation to resolve the twin paradox seems to be the asymmetry that arises because the ship...
  9. B

    Paradox in calculating potential of a sphere

    Homework Statement Find electrostatic potential of a solid sphere with reference point of 0 statvolt at infinite. Homework EquationsThe Attempt at a Solution Potential energy of a solid sphere is ##\dfrac35 \dfrac{Q^2}{r}##. And I know ##\displaystyle U = {1\over 2} \int \rho \phi dv##. So...
  10. M

    A Can a Point-Like Particle Defy the Uncertainty Principle?

    Imagine a spatial frame of reference attached to a point-like particle. It has x=0 since it is at the origin and p=0 since it is at rest. Having definite position and momentum is normally considered a violation of the uncertainty principle. How would you resolve this paradox? 1. Position frames...
  11. Chestermiller

    Challenge Thermochemistry Challenge Problem - Chet's Paradox

    I have a reversible chemical reaction described by the balanced equation: ##aA+bB=cC+dD##. I devise a reversible process to take a closed system containing these species (and its surroundings) from thermodynamic equilibrium state 1 to thermodynamic equilibrium state 2: State 1: a moles of...
  12. trilobite

    Insights Exploring the Spectral Paradox - Comments

    trilobite submitted a new PF Insights post Exploring the Spectral Paradox Continue reading the Original PF Insights Post.
  13. A

    I Question: Proposed Solution to Two Envelope Paradox

    Su, Francis, et. al. have a short description of the paradox here: https://www.math.hmc.edu/funfacts/ffiles/20001.6-8.shtmlI used that link because it concisely sets forth the paradox both in the basic setting but also given the version where the two envelopes contain ( \,\$2^k, \$2^{k+1}) \...
  14. victor94

    I Exploring the EPR Paradox: What Does "Simultaneous Reality" Mean?

    I'm reading the paper of the EPR paradox and I'm confused in the meaning of this: "The elements of the physical reality cannot be determined by a priori philosophical considerations, but must be found by an appeal to results of experiments and measurements......when the operators corresponding...
  15. J

    I A new solution to Olbers' Paradox?

    I read in a popular science magazine in the UK that "recent" observations of the universe indicate that the number of galaxies in the the universe is actually so vast that Olbers paradox is still a paradox. The short article postulated that they had solved the paradox by proving that light from...
  16. m4r35n357

    B If anyone here doesn't yet get the twin "paradox". .

    Jim al Khalili did a (basic level) TV programme in the UK last night where he featured a smartphone app which works as a space-time "odometer". Now you can experiment on your own version of the legendary brain-teaser with your friends, no need to go to Alpha Centauri and back! Go for a walk...
  17. B

    B Information paradox in black holes

    I have always been fascinated with black holes and information paradox. If quantum bits made up spacetime. Could the information getting inside a black hole be possibility encoded in its quantum bits? Look at https://www.quantamagazine.org/20150428-how-quantum-pairs-stitch-space-time/
  18. A

    B Zeno's arrow paradox and general relativity?

    I don't know much about general relativity, but I'm curious if Zeno somehow foresaw the reallty of the universe many many years before Einstein did(without any rigour ofc, but still the idea holds?). Understanding the Zeno's arrow paradox, stating that an arrow is motionless at a certain moment...
  19. S

    I A _perfectly_ symmetric twin paradox cases

    Case 1) Two rockets (no Earth involved) have an exactly the same acceleration profile/flight-plan during round trip but they dispatched to opposite directions. At the start both rockets are docked to the same space station...both rockets have an identical engine operation plan during the round...
  20. M

    Light as a Constant: Examining the Paradox

    How can light be a constant for any observer? I understand how it fits into equations and what not, but how can it be a constant. If I throw a baseball forward at 10m/s in a train going 40m/s. I perceive it as 10, an observer on the ground would perceive it as 50. Why doesn't the same apply to...
  21. J

    I Klein Paradox: Exploring E-mc^2 <V< E+mc^2

    Hello! I am trying to work out the various cases for the potential step problem in the context of the Klein Gordon equation. I was wondering if one must consider the situation where E<mc^2 when working out the situation of E-mc^2 <V< E+mc^2 where V is the value of the potential after the step...
  22. J

    I Twin Paradox: Comparing Lengths of Moving Rods

    Imagine that we have two metal rods, and both measure 1 meter, a measurement done from the same inertial system when they are at speed = 0. These two rods are equal, the extreme points of the first one are called a and b and its inertial system is called F, the extreme points of the other rod...
  23. michael879

    I Lagrangian Paradox: Uncovering an Issue

    Let me begin by saying I know I'm doing something wrong here, but I'm having trouble seeing what it is. This is a reformulation of https://www.physicsforums.com/threads/plugging-eom-into-lagrangian.905099/, where I've reduced the issue to a much simpler problem. Moderators, feel free to close...
  24. F

    I Russell's Paradox: Proving N is Normal if Abnormal

    Sets which doesn't contain themselves are called normal sets while sets that contain themselves are called abnormal. Let ##N## be a set of all normal sets. Prove that ##N## is normal if and only if ##N## is abnormal. Proof. ##~~\rightarrow ~~ ## Suppose ##N## is normal such that ##N \not\in N##...
  25. V

    I Can someone explain this? (bootstrap paradox)

    Hey! I am going to do a presentation about the bootstrap paradox in a few weeks and I need some help. I understand what the bootstrap paradox is but I need some help to sum up the theory so that i becomes easy (or at least easier) to understand. If you have any examples or facts that's fun...
  26. Old Chinaman

    B Understanding the EPR Paradox - Exploring the Gamma Factor

    I am not a physicist but interested in the decade long debate between Einstein and Niels Bohr, especially in the philosophical implication of the EPR Effect. I've been wondering if anyone could explain why Einstein, Podolsky and Rosen didn't applied the Lorentz Transformation formula - the...
  27. Mausam

    Solving the Thermodynamics Paradox with a Ball-Earth System

    I have learned that ΔG is the amount of available energy. So to understand it i used a simmple body system rather than chemical reaction,which is the sliding of a block on a fixed wedge(height h and inclination angleθ). 1)my system is ball -earth and rest surrounding both in thermal eqilibrium...
  28. nomadreid

    I Bauer's Paradox in General Theory of Relativity?

    Has anyone heard of "Bauer's Paradox" in Einstein's working out his equations for General Relativity? The description I came across was extremely fuzzy (something about an expression for a certain tensor adding up to be zero when it shouldn't, or vice-versa), so I am looking for a better...
  29. stevendaryl

    A Information Paradox for Unruh Radiation?

    I'm sure that there are limits to the analogy between the event horizon of black holes and the "Rindler horizon" for an accelerated observer, but there are a number of similarities: For Schwarzschild spacetime as described in Schwarzschild coordinates: Spacetime is static, and a rocket must...
  30. G

    I Gibbs paradox for a small numbers of particles

    Hi. Trying to solve the Gibbs paradox for two identical volumes of ideal gas with ##N## particles each, I found the mixing entropy to be $$\Delta S=2N \log(2)-\log((2N)!)+2\log(N!)\enspace .$$ The usual approach now uses Stirling's approximation to the order ##\log (n!)\approx n\log (n)-n##...
  31. I

    I Resolution to the Tachyonic Antitelephone paradox

    Wikipedia has this interesting article about a physics "paradox" that Einstein came up with: https://en.wikipedia.org/wiki/Tachyonic_antitelephone It shows that if you were able to send a signal faster than the speed of light, then you could send a message back in time leading to a causality...
  32. arupel

    I Explanation of the EPR paradox

    I am not sure I understand exactly what was the situation was with the EPR paradox Example: for simplicity: two electrons are coupled. One with spin up and the other with spin down. Since they are coupled there are one state. Separate the electrons one in one galaxy and the other in another...
  33. J

    I Solving Length Contraction Paradox

    Hello there, Suppose there are two inertial frames of reference ##S## and ##S'## with coordinates ##(x,ct)## and ##(x',ct')## such that ##S'## is moving relative to ##S## with velocity ##v##. Suppose ##v>0##, that implies ##\gamma >1##. We know that a Lorentz boost is given by: $$ x' = \gamma...
  34. FallenApple

    I Where does the angular momentum go in Feynman's disk paradox?

    There is a solenoid on top of a disk with charges attached to it. and there is a clockwise current through the solenoid. So by disconnecting the battery, the current will lower, and hence the flux of the magnetic field though the disk will lower, and according to faraday's law, there will be...
  35. Jeff B L

    B Special case of the twin paradox in special relativity

    There is something about the twin paradox in special relativity that has always bothered me. One twin sets out on a journey at a large fraction of the speed of light, turns around and returns. The fact that the returning twin is the one who is younger is explained by the fact that they are the...
  36. Chris Miller

    B Do Twins Age Differently in Space?

    Twins leave Earth in opposite directions, accelerate at the same rate until their relative v = ~c, hold this v for 20 years (or however long), then decelerate at the same rate to v=0, and accelerate at the same rate back towards Earth until their relative v again =~c, hold for same amount of...
  37. A

    B Can a "Cat paradox" exist inside a nucleus?

    Hi, A cat cannot be alive and dead at the same time. Is it possible for particles in a nucleus to be both protons and neutrons at the same time? How could you tell whether this is happening?
  38. Mausam

    Understanding the Paradox of Centripetal Force in a Frictionless System

    If we have a frictionless hollow tube and a ball which just fits into it. All the surfaces are frictionless. Now if we put in the ball about at the center of tube and rotate the tube about one of its ends with a constant angular velocity ,then the ball swoops out of the other end . If we see...
  39. Mary curie

    B Paradox in the nuclear activity

    good evening everybody! i'm studying these days the nuclear activity and this amazing world where an atom try to find its/her stability ! so i came across the famous radiations but then stopped by something i didn't quite understand! when an atom release a beta radiation a negative one for...
  40. S

    I Is the Drake Equation a Reliable Tool for Estimating Extraterrestrial Life?

    "The Fermi paradox or Fermi's paradox, named after physicist Enrico Fermi, is the apparent contradiction between the lack of evidence and high probability estimates, e.g. those given by the Drake equation, for the existence of extraterrestrial civilizations". I have always failed to understand...
  41. Toby_phys

    Paradox found in my first relativity sheet

    We have got some SR work to do, however we have only had 1 introductory lecture. I have a problem with one of the problems. Question: A rod of 1m parrallel to the x-axis, travels at un-relativistic speeds at 45 degrees. It passes through a slit - also parallel to the x-axis - that is 1.1 meters...
  42. Matternot

    I Special relativity timebomb on distant planet 'paradox'?

    I thought of this 'paradox' which is somewhat similar to the twin paradox but can't be explained by a lack of symmetry etc. It is very similar to many paradoxes I have heard before of which the resolution is known (which is why I am mostly sure this can be resolved) Bob is looking through his...
  43. A

    I Superluminal Messaging and Causality Paradox: Myth or Reality?

    If I could route a signal from here-and-now to an event in my past light cone, then clearly I could make an irresolvable causal paradox by having the arriving signal disable the button that sends it, so I'll choose to believe that I can't send messages back in time TO HERE. Now I've heard it...
  44. A

    I LIGO BH Merger & Black Hole Information Paradox

    Has anyone analysed the LIGO merger detection http://journals.aps.org/prl/abstract/10.1103/PhysRevLett.116.061102 in the context of the BH information paradox? Is there any evidence that the gravitational waves carried any information that could compensate for the change in areas of the initial...
  45. W

    I LQC and the Information Paradox

    From my limited reading I get the impression that the bouncing black holes proposed by Rovelli and Vidotto implies a solution to the information paradox. The information comes back out when the bounce happens. But how does this relate to the idea of complimentarity? It seems the latter was the...
  46. K

    I Galilean transformation paradox help

    I'm getting quite stuck on this problem here. Galileo said that Xb = Xa - V*Ta. (This follows from dv = dx/t --> Xa - Xb = t*dv --> the above formula) Thus, it is concluded Xa = Xb + V*Ta, but why? In my thought experiment the objects are moving relative to each other, thus if A is moving away...
  47. N

    I Understanding the Twin Paradox: Exploring Special Relativity and Time Dilation

    Hello. Thank you to everyone who helped me with my previous post where I had general questions on special relativity. Several users suggested that I start by trying to understand the relativity of simultaneity which I did. Although I haven't mastered it, I understand it better now. Also, someone...
  48. X

    I Solve SR 'Paradox': Find Flaw in Argument

    Hi, I found this 'paradox' which supposedly says that SR is incorrect, I have a hunch why it may be a flawed argument, but can't personally get the numbers right. Perhaps it's a fun exercise for some of you to destroy the argument. Here it is: So my hunch why this is incorrect:
  49. cnh1995

    Faraday's law and motional EMF paradox

    Consider the diagram below (sorry for the quality:frown:). The circle is the front view of a cylindrical iron rotor (highly ferromagnetic, very low reluctance). The orange part is a single turn of a conductor (very high reluctance) wound around the rotor body. The grey lines are magnetic field...
  50. G

    A Black Hole information paradox and evolution in time

    I refer to a Schwarzschild Black Hole as the simplest example, and a well defined time outside the hole, say the Schwarzschild time. The information paradox of BH deals with the question of what stuff has fallen into the hole, but I am not aware that it deals with the question when the...
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