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. T

    Can a book from the future save a woman's life in the past?

    An immortal woman who is about to go back in time is mailed a book from an unknown address. Inside the book reveals explicit instructions on how not to die while in the past leading up to the present day. The book is written by her future self and mailed to herself by her future self who is now...
  2. B

    A discovered "paradox" in the double slit experiment

    Consider the classical double slit experiment where we are shooting electrons trough a double slit and then capture them on a photographic plate. We know that the pattern of electrons on the plate will differ depending on the state of knowledge of the observer. If he make a measurement to find...
  3. A

    Stern-gerlach vs zeeman effect = paradox?

    This may be a stupid question, but I am reviewing for the physics gre and can't help but see the zeeman effect and stern-gerlach experiments as contradictions. In the Zeeman effect, a neutral atom energy level will split into 3 levels (or 2 or more if take into account anomalous zeeman), but in...
  4. N

    Can someone please explain the elevator paradox?

    I tried searching it up but the only good place i found was wikipedia that actually talked about it and i hate wikipedia because it tries to explain complex things in complex ways instead of making them simple. Thanks!
  5. M

    Historical time and place paradox

    So, I have an idea to write a (sort of) "time travel" story in which future historians are able to transport a non-intrusive (possibly mass-less) viewport to various important events in history (and then accidentally incinerate Mohenjo-Daro with this technology, thus explaining certain Vedic...
  6. H

    Inverse square law explains Olbers' paradox?

    Hello, This is the thread I originally wanted to respond to, but it's closed: https://www.physicsforums.com/showthread.php?t=650126 I also found this on Wiki-talk page, which seems to be the same argument...
  7. Z

    Twins paradox and time dilatation

    I have already read about the twins paradox a lot of times, but what puzzles me is that how the Universe would "now" what twin had to be younger since, if the spaceship travels at high speed in relation to Earth, the planet would move the same with the ship as reference.
  8. wolram

    Faint Young Sun Paradox: Can Varying G Resolve It?

    Did gravity effect the suns output? arXiv:1405.4369 [pdf, ps, other] Can a variable gravitational constant resolve the Faint Young Sun Paradox ? Varun Sahni, Yuri Shtanov Comments: 9 pages, 1 figure Subjects: Solar and Stellar Astrophysics (astro-ph.SR); Cosmology and Nongalactic...
  9. C

    Charge vs Coulomb - A paradox?

    Hi I'm wondering: The symbol of charge is Q but the SI unit of charge is coulumb which is the Charge of approximately 6.241×1018 electrons. But charge is not itself defined, only in terms of Coulomb, and coulomb is defined in termes of Charge. Its SI definition of Coulomb is the charge...
  10. K

    The Hawking radiation and information paradox

    Here is my understanding, please correct me if I made any mistake Quantum physics theory suggests that information (the wave function, state, etc.) cannot be destroyed. All matters fall into a black hole will not be able to escape, which means all information of these particles stay inside...
  11. B

    Length Contraction Paradox Scenario

    Hi! I have been pondering a scenario involving a paradox with length contraction. I brought it up with my physics professor, and I somewhat understand what is supposed to happen, but I'm still somewhat confused, so I was wondering if you could help me figure out what is going on. In this...
  12. jk22

    EPR paradox and prediction time

    If we suppose we have an entangled pair in position/momentum and, following the argument, we measure position of particle A. We get a result let say xA. Then we want to predict the measurement of position of B, so up to now we have not measured particle B, but we know it's wave-function is a...
  13. Q

    Frame-dependency of aging rate in the twin paradox

    Hi, from what I understand about the twin paradox, Is the resolution essentially that since the traveling twin undergoes acceleration when the ship reverses direction, so since the velocity of the twin is no longer constant, the inertial reference frames are no longer valid? Then does that also...
  14. J

    A Negation of the Grandfather Paradox

    I believe I found a solution (or a negation) to one of temporal mechanics most enduring paradox: If you travel back in time, could you kill your own grandfather, thereby altering your future, even erasing yourself from existence? The short answer is NO. You can't. This is simply because...
  15. P

    Can Magnets in Equilibrium Defy Energy Conservation Laws?

    If three circular or ring type magnets are placed such tnat centeral magnet is having its center at origin and other two are placed at its aperture repeling each other but they are just at enough distance such that the whole system is in equillibrium, placed on surface having friction. If i...
  16. D

    Klein Paradox - Dirac equation with step potentional

    Hi all! I was reading up on the Klein paradox in Itzykson & Zuber's Quantum Field Theory (but I think this is a pretty standard part that's probably present in most QFT textbooks) and on page 62 they have a pretty straight forward solution to the Dirac equation with a step potential. I've...
  17. S

    The Measure Problem and the Youngness Paradox

    I have read Max Tegmark's book "The Mathematical Universe" and he describes this thing called The Measure Problem as the biggest problems in physics. I am having difficulty understanding the problem so I will try to sum up my understanding of what he said. As a result of inflation, the volume...
  18. F

    Energy conservation paradox for constrained mass

    Consider the following setup (see illustration above): a mass m is connected to a circular section of a rail by means of a rod (with negligible mass) of length r, where r is the radius of the rail. The connection point P of the rod can move frictionless along the rail but is mounted such that...
  19. V

    Too Simple & Short Solution of Twin Paradox

    Consider two points A and B (Fig.1) at rest in S frame having a distance L0 between them (a long scale may be imagined as placed between A and B). ------ (1) The ‘traveler’ twin (S-frame) starts from A at time t = 0 and suddenly accelerates to attain a constant velocity v in the view...
  20. J

    Relativistic Compressor Paradox

    Relativistic compressor "paradox" Let's say we have a metro tunnel that is a circular loop with 1 m x 1 m rectangular cross section. The tunnel is 100 m long. There's a 50 m long train in the tunnel, the train fits snuggly in the tunnel. And there's air in the tunnel, at 1 atm pressure, and...
  21. S

    MHB Probability Paradox: One White and One Black Marble

    I saw this "proof" many years ago. .I thought you might enjoy it.A bag contains two marbles. Either can be Black or White. Determine the colors of the marbles. Answer: one Black marble and one White marble.\text{Proof} \text{There are three equally likely situtations.} . . \text{The bag...
  22. nearc

    Is the Traveling Signal Paradox Real or Just a Misunderstanding of Relativity?

    Traveling signal “paradox” Most relativity paradoxes are not true paradoxes they merely require some clarification about frame of references, stationary observer, etc… I hope some folk could help me clarify my “paradox” or point out where someone as already discussed this concept. We...
  23. bcrowell

    Your preferred way of explaining this point about the twin paradox?

    A student asked me a question in class last week about the twin paradox, and I found that although I knew a valid answer, it wasn't an answer that my class had the background to understand, and I wasn't immediately able to come up with one that would work for them. The standard difficulty in...
  24. C

    Seeming paradox when squaring distance depending on units

    Hello all This is probably simple and I'm overlooking something 1 mile = 5280 feet 10% of a mile is 528 feet 528 feet squared is 278,784 feet which is 52.8 miles squared But 0.1 miles squared is .01 miles squared So depending on if you square it as 0.1 miles, or if you convert...
  25. Mentz114

    Solving the Spaceship Paradox: A New Explanation

    I'm sticking my neck out because I just worked this out and may regret this post later. The spaceship paradox arises because the expansion scalar of the 'Bell' congruence is always positive, implying that the thread will break, even when the ships are not separating. For this vector field...
  26. O

    Black Hole Information Paradox and Alcubierre Warp Drives

    Suppose Alcubierre warp drives or some alternative form of warp drive is possible. Then surely a warp drive could enter the event horizon of a black hole, observe the interior, and exit the horizon, returning with information from within the black hole. What about black holes never visited by a...
  27. Grimble

    Exploring the True Nature of Relativity & The Twin Paradox

    It is said that Relativity proves that if one travels near the speed of light that time slows down, i.e. that the twin who travels ages less than the twin who stays behind (Twin Paradox) and that distances/lengths contract, but only in the direction of travel. Yet a simple look at these two...
  28. PhysicoRaj

    Why Do These Math Paradoxes Seem to Defy Logic?

    I'm sure there must be some explanation to why these kind of things appear.. firstly, consider a=b ab=b2 a2-ab=a2-b2 a(a-b)=(a+b)(a-b) a=a+b since a=b, b=b+b 1=2 !?? then this one- (100-100)/(100-100) =[(10+10)(10-10)/10(10-10)] =2 Anything has gone wrong?
  29. julcab12

    Competing model on Firewall Paradox

    http://arxiv.org/abs/1401.4097 Fuzzball "The fuzzball construction resolves the black hole information paradox by making spacetime end just before the horizon is reached. But if there is no traditional horizon, then do we lose the elegant relations of black hole thermodynamics? Using an...
  30. bcrowell

    Has the Firewall Paradox Finally Been Resolved?

    This blog post https://medium.com/starts-with-a-bang/df0a131d7b95 by Ethan Siegal claims that the firewall paradox is resolved. The papers it refers to are: Samuel L. Braunstein, Stefano Pirandola, Karol Życzkowski, "Better Late than Never: Information Retrieval from Black Holes,"...
  31. G

    Black hole information paradox?

    Would it be possible for a black hole to carve a trail of information on two dimensional space in the holographic universe? Could the black hole, acting as a conduit between the macro and micro universe, due to its properties at the singularity (at the plank scale) carve the the information...
  32. A

    Understanding the Twin Paradox: A Quick Question Answered

    Hey guys, I just want to ask a quick question that confuses me a bit regarding the twin paradox. During acceleration, the moving twin very quickly 'runs over' across a large segment of the worldtube of the stationary twin. But, what is the perspective of the stationary twin during the...
  33. R

    Twin paradox without acceleration - A different question

    Hi, I noticed this topic already being discussed but didn't want to hijack the thread with a different question. I don't know if this has been asked before but if it has I couldn't find it. I was watching something recently about quantum physics and entanglement and it mentioned something...
  34. p764rds

    Is Zeno's Paradox Relevant in Understanding Digital and Real-World Motion?

    Here is an ultra short repeat of the Zeno Paradox, but please google it for a longer version with pictures etc: Think of a moving arrow. In an instant of time an arrow cannot move (bc its an *instant*). An arrow's movement is given by the sum of the movements at every instant. But since in...
  35. J

    Does the Work-Energy Theorem hold true for objects in rotational motion?

    Consider a solid sphere and a cube of equal mass, both on a frictionless table. Now, you apply a force to both objects at the point of contact between the object and the table. Then the linear accelerations of both objects will be the same (since the same force is applied to the two objects of...
  36. stevmg

    Does Time Dilation Occur for Both Twins in the Twin Paradox?

    Two twins A and (evil) B. Twin A remains "stationary" while evil B goes at near light speed to-and-fro. Ignoring General Relativity (acceleration/deceleration) evil B experiences time dilation and as result, when they meet up again, B's clock is behind A's clock. Look at it from B's point...
  37. J

    The Anthropomorphized Time Traveling Paradox.

    The most famous time traveling paradox is the Grandfather Paradox, where the traveler goes back in time to kill his own grandfather and thus prevents his own birth--a paradox. An adaptation to this paradox is Hawking's Mad Scientist Paradox where a mad scientist opens up a wormhole one minute...
  38. D

    EPR Paradox Confusion: Understanding the Violation of Locality and Uncertainty

    Hello, I've read through several sources about the EPR Paradox but I'm not sure I'm understanding everything. I know that: -the paradox in question seems to be due to a violation of the principle of locality -there is no useful transferred faster than c regardless of which axes the two...
  39. T

    Twin paradox without accelerative frame.

    I've asked this question a few times. This time i have tiny change in the question. Instead of people I'm using stopwatch & i have removed the accelerative frame. If you have any doubts I'll clear it but do not skip the topic. All i want is an answer that can be agreeable for all...
  40. nomadreid

    Morse-Kelley Class Comprehension axiom and Russell's paradox

    As I understand the ZFC solution to Russell's paradox, since {x|x\notinx} must be {x|x\notinx}\capS for some set S, the paradox goes away, but in Morse-Kelley, if I understand Class Comprehension correctly, although again there must be some M such that {x|x\notinx}\capM, this M may be a proper...
  41. jk22

    Is There a Mistake in the Spin Quantum Paradox Calculation?

    Suppose we consider the spin 1/2 measurement matrices B=\frac{1}{\sqrt{2}}\left(\begin{array}{cc} 1 & 1\\1&-1\end{array}\right) and A=diag(1,-1) it's easy to show that B^2=A and a normalized eigenstate of B |\Psi\rangle=\left(\begin{array}{c}a\\b\end{array}\right) with eigenvalue 1 ...
  42. H

    Understanding the Twin Paradox in Time Dilation

    Hello! I am currently learning the theory of relativity, but have a hard time understanding the time dilation concept. In my example down here, the subscript “A” will be used to denote “in the frame of reference of observer A”; the subscript “B” will be used to denote “in the frame of...
  43. C

    Mystery of the Moving Car: Solving the Speed Paradox

    First of all, Happy Thanksgiving to you all! Now, my question: I'm on Earth viewing through a telescope. I observe a car in outer space, traveling roughly at right angles to me (i.e., across my scope's field of view, let's say left to right). That car, a 1956 Chevy (irrelevant, but my...
  44. M

    C FOR Loop Paradox: Unraveling the Mystery

    <<Unacceptable Link>> Why in C's FOR object doesn't fit?
  45. F

    How does this affect the length contraction paradox?

    Hi, As is well known, Relativity claims that a rod of a given proper length will appear length contracted when measured by a moving observer. Now consider a rod of length L and observer initially at rest relatively to it, with one end of the rod at the observer's coordinate x1(0) and the...
  46. T

    Ehrenfest paradox debate, how does a pinning disk look like?

    I was in a debate with a guy about "how does a spinning disk may look like in relativity." His point was that the disk will be flat as always. But the radius will be curved, i couldn't actually imagine it. He gave me a picture too http://casa.colorado.edu/~ajsh/sr/cartbig_gif.html So i...
  47. atyy

    Gibbs paradox in the Bohmian interpretation

    The Gibbs paradox in statistical mechanics is usually resolved by saying that particles do not have distinct trajectories, and so are truly identical. For example, http://ocw.mit.edu/courses/physics/8-333-statistical-mechanics-i-statistical-mechanics-of-particles-fall-2007/lecture-notes/...
  48. Conservation

    Back EMF Paradox: Is There a Contradiction?

    Correct me if I am wrong. For a RL circuit, I know as a fact at t=0, there is a back emf that is almost equivalent to the original emf source. In order for the back emf to exist, there needs to be a magnetic field in the inductor. In order for there to be a magnetic field in the inductor...
  49. N

    Understanding the Twin Paradox: Time Dilation in Relativity

    Hey! So the formula for time dilation is: \gamma \Delta t_0 = \Delta t, where ##\Delta t_0## is the time elapsed for a traveller ##S'## who has a relative constant velocity ##u## compared to a stationary observer ##S##, while ##\Delta t## is the time elapsed for the stationary observer...
  50. A

    Why is 51 considered the first uninteresting number?

    I don't want to talk about interesting being a subjective quality but the main paradox. Since the first dull number is interesting, we classify it as interesting. But then the second dull number becomes the first dull number. So it is also interesting. But if we look again, we have two new...
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