Paradox Definition and 1000 Threads

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. A

    A & B's Time Paradox: A Space-Time Conundrum

    Suppose A travels in a spaceship and B is on earth. At the time of launch they both synchronise their clocks. When 30 secs have passed by in A's clock he reads the time in B's clock to be 40 secs.But when 30 secs have passed in B's clock A's clock shows 40 seconds. Isn't this a contradiction to...
  2. B

    The Necktie Paradox: A Different Perspective

    There's discussion on the 'necktie paradox' on this blog, where I'm a regular visitor. I don't agree with the perspectives of those who have responded on that blog. In the wikipedia, The necktie paradox states that each stands to either win or lose an expensive tie, each at 50%...
  3. B

    The Paradox of Choice: Is More Choice Better?

    Is more choice better? Ten years ago the answer seemed obvious: Yes. Now the conventional wisdom is the opposite: lots of choice makes people less likely to choose anything, and less happy when they do choose. In the The Paradox of Choice, Psychologist Barry Schwartz discusses the phenomena...
  4. U

    Twin Paradox: Can Barbara Reach XEON Alive?

    My query is this. In the twin paradox let's assume that one twin Barbara keeps on moving at a relative speed of "c" away from the stationary Earth twin Alex. If I were to be able to be at both Barbara's rocket and the Earth at the same instant ( meaning I could travel through space...
  5. T

    Zeno's Paradox Applied to Physics: Can Object B Catch Up?

    Ok, so I have been looking at Zeno's Paradox and it occurred to me that it could possibly be applied in physics. The way i worked it out is like so: If an object A is traveling at half the speed of light is given a head start in a race vs an object B that is traveling at exactly the speed...
  6. e2m2a

    Paradox of Energy Gain: Exploring a Thought Experiment

    The following thought experiment describes the energy gain of a system that defies a classical explanation. In this experiment we assume no friction and all velocities are at sub-relativistic speeds, hence, Newtonian mechanics applies and Galilean transformation is adequate. Suppose we...
  7. Jorrie

    Understanding the False Twin Paradox: An Alternative Explanation

    The "False Twin Paradox" I have no problems with the resolution of the classical 'Twin Paradox', but the following "False Twin Paradox" does have me puzzled. (If it was discussed and explained elsewhere, please just point me there.) Instead of the usual accelerating twin at the turnaround...
  8. F

    The Grand Father paradox is flawed.

    The “Grand Father” paradox is flawed. The time travel cliché of the “Grand Father” paradox is logically flawed and has driven the notion of the multiverse theory. In fact matter as information can be proven to be persistent through time travel and indifferent to events that created it. The fact...
  9. M

    Resolving Olbers' Paradox: Is That Quote Wrong?

    I understand Olbers' Paradox and its resolution, however such phrases as this - "If the universe extends infinitely, then eventually if we look out into the night sky, we should be able to see a star in any direction, even if the star is really far away" - which can be found...
  10. L

    Unravelling the Paradox of Chapter 5.3b in Wald's "General Relativity"

    I'm reading Chapter 5.3b in Wald's "General Relativity". (i) On p105, it says that if the integral t=\int \frac{d \tau}{a(\tau)} converges, the Robertson Walker will be conformally related to a section of Minkowski spacetime above a t=constant hypersurface. This makes sense to me...it's kind...
  11. N

    Solving for Time: Paradox Equations for Astronauts Near Light Speed

    Hi Do any of you guys know what equations or formulas I should be using for questions like "If A is on Earth and B is an Astronaut traveling near the speed of light". Calculate the duration of B's journey to A and the duration of B's journey according to B. I assume that B's time...
  12. Q

    Time Dilation Paradox (variant distance between two accelerating bodies)

    This question concerns a paradox I've come up with in GR. If somebody could tell me where it breaks down, I'd be much obliged. Thank you! Assume there is spaceship A hovering above a black hole, and spaceship B further away from a black hole The black hole, A, and B are all lined up. (The...
  13. P

    Bertrand's Paradox: Is There More to it?

    I've been reading a little bit into mathematical paradoxes lately, and I'm not sure what to make of Bertrand's paradox (regarding the extraordinary set R). I understand the proof, but does this paradox extend to other areas of thought (on that note, this question might belong in the philosophy...
  14. E

    What is the probability of two Los Angeles teams making it to the world series

    can anyone answer this one? The baseball series has 4 teams in it and two are from los angeles. What are the chances of a Los Angeles team making it to the world series, at first I said simple. 50% but is this true? The dodgers are playing Philly, and in theory Philly has a 50% chance of...
  15. T

    Noise Power Paradox: Explaining Limitations

    Homework Statement Explain why the noise power across a resistor in thermal equilibrium is limited in contradiction to the formula for the noise V_{RMS} = \sqrt{4RkT\Delta f} which states that if we measure with infinite bandwidth we have infinitely large power Homework Equations...
  16. H

    Who experiences the greatest time dilation in special relativity?

    hi there I am confused by the following setting on special relativity: Suppose there are 4 people, say A, B, C and D, in the deepest vacuum - essentially no gravity or any force at all. Suppose further that all move in one-dimension with constant velocities - A moves towards west with 0.8c...
  17. J

    Scaling Paradox: Differential Geometry & General Relativity

    Differential geometry (which includes general relativity) often introduces the length differential, expressed as ds2=gabdxadxb, to introduce the covariant form of the metric tensor gab. However, this formulation scales ds2 incorrectly. The appearance of an index as a superscript, as in dxa...
  18. W

    Time Dilation/Twin paradox Question

    Homework Statement A 30 year old femal astronaut leaves her newborn child on Earth and goes on a round-trip voyage at a star that is 40 light-years away in a spaceship traveling at 0.90 c. What will be the ages of the astronaut and her son when she returns? Homework Equations t = to / {1...
  19. R

    Instructor's Algebra Paradox? : How far does a projectile go up a ramp?

    I'm also working on this other question, which I think my instructor has a paradox in his algebra for lack of what to call it. Can anyone suggest a logical way to answer this question? Homework Statement http://media.wiley.com/product_data/excerpt/19/04717580/0471758019.pdf See problem #43 on...
  20. D

    A & B Clocks: Why Velocity Time Dilation is Not a Paradox

    We have two clocks, A and B. B is moving with constant velocity with respect to A. From the reference frame of A, B is running slow. From the reference frame of B, A is running slow. Why is this not a paradox?
  21. D

    Russell's Paradox: Understanding the Set of all Sets

    Russels paradox says that the set of all sets not contained in themselves, i.e. x=\{ y \ : \ y \not \in y \} neither is or is not contained in itself. The set can be created based on an axiom saying that "The set of objects with a property Q exists". Let`s assume Q : "Is not contained within...
  22. D

    Free will, Determinism and Banach-Tarsky paradox

    I read many threads in this forum (in QM section), and in many cases I witnessed the same logical flaw over and over again. People conclude that, for example, if world is deterministic, than there is no free will, because our consciousness is deterministic too. Why? Because our brain is nothing...
  23. V

    Can the Ehrenfest Paradox Occur for a Rotating Body with Relativistic Speeds?

    For a body of m=1kg, v=0.1c, and rotating with r=1m, lorentz factor =1/0.99 the centripetal force is (c^2 *10^-2)/0.99 N This force creates enough stress in the body to break it apart This effect reduces at values of r comparable to c^2 which again is purely fictitious like the "superluminal...
  24. F.Turner

    Solving the Satellite Paradox: K+U=E

    1. {This paradox denotes the fact that a satellite in a near circular orbit suffers an increase in velocity when subject to a drag force.} The Specific energy of the satellite is K + U = E where K =v^2/2 is specific kinetic energy. U= -u/r is specific energy and E is specific total energy. If...
  25. C

    Relativistic paradox involving torsion.

    Some time ago someone introduced me to the following scenario. Imagine you ship loads of oil rig pipes into space, and you assemble them to a length of many kilometers, and you start that long pipe spinning on its long axis. You add vibration damping, to get rid of any transverse, longitudinal...
  26. S

    Gibbs Paradox - Does Entropy Increase or Not?

    Hi guys, I have a question regarding the Gibbs paradox. Let's say we take a container A of helium gas and place it next to another container B also containing helium gas at the same temperature and pressure. When we remove the partition (wall) between them, what happens? If we use classical...
  27. I_am_learning

    Modified Car and ditch paradox

    Modified Car and ditch paradox! Suppose there is a car moving on a road in relativistic speed. The road has a ditch (hole) which is litter bigger than the car when both are at rest. Modification: Assume that the car will fall on the ditch if all of its tyres are in the air at the same...
  28. I_am_learning

    How exactly to calculate the age difference in Twin paradox

    How exactly to calculate the age difference in "Twin paradox" In so much of the text I have seen the "twin paradox" is resolved by simply showing how the condition is asymmetrical, they make no calculation on how this asymmetry results in age difference. I have seen some claiming that its...
  29. zonde

    Can Quantum Mechanics Explain the Paradox in Modified EPR Experiments?

    Lets look at two mind experiments. Experiment 1. We generate pair of entangle photons in opposite polarization states. At Alice's wing we have polarizer with polarization axis oriented vertically and detector that registers "clicks". At Bob's wing we have the same setup - polarizer with...
  30. R

    Paradox of Rigid Body: Solve the Mystery

    There is a rod treating as rigid body, the rod which mass is m and lenghth is R rotate about one end of itself with the angular acceleration \alpha . Apply a tangential external force f on another end to make the rod rotate. Now divide the rod into elements of mass. For each mass element dm with...
  31. K

    From Cat Paradox to Multiple Worlds: What Gives?

    Einstein, champion of the incompleteness of quantum mechanics, wrote a letter to Schrodinger describing a situation where gunpowder is in a half-exploded half-stable state. This was a reductio ad absurdum argument for the incompleteness of QM, since, according to Einstein, "in reality there is...
  32. P

    Resolution of the black hole information paradox

    What is the resolution of the black hole information paradox? According to quantum theory, information — whether it describes the velocity of a particle or the precise manner in which ink marks or pixels are arranged on a document — cannot disappear from the universe. But the physicists Kip...
  33. S

    Exploring the Puzzling Paradox of Special Relativity

    A/to special relativity if one is moving faster, he sees that the clocks w.r.t which he is having relative motion are ticking faster.It increases my curiosity to know what would an observer w.r.t whom the person is having relative motion see, if he observes the watch of the traveller.Will he...
  34. T

    Paradox which questions time travel to the future

    You all have heard of the paradox whereas when you travel to the past and kill your grandfather you should not have existed in the presence whatsoever because you have killed your origins. So far so good...but I thought of another case, which I believe is more interesting since so far the...
  35. M

    How is the twin paradox solved in the first model of the expanding universe?

    I already posted about this under a different thread (Time dilation for clock thrown up and caught back) but, after reading some of the replies, figured that that was not the right way of attacking my real problem, which is figuring out what happens to time during a Big Crunch. So I will restate...
  36. B

    Bell's spaceship paradox - reversed

    Bell's spaceship paradox --- reversed The "[URL was discussed already https://www.physicsforums.com/showthread.php?t=236681", but I would like to add a twist. I take for granted, that the thread breaks, as described by Bell himself. Suppose the experiment starts out with a bit of slack on...
  37. L

    Exploring Curry's Paradox: Does Flying Spaghetti Monster Exist?

    Curry's paradox can be used to (dis)prove the riemann hypothesis and string theory, and even prove the (non)existence of God... no, actually, Curry's paradox IS God. :biggrin: Just kidding... I am now (speaking somewhat hyperbolically) freaked out. Does Curry's paradox go like this (try "1 =...
  38. C

    Apparent paradox: e=mc^2 violates conservation of energy?

    Take two uncharged particles (e.g., neutrons) at rest with respect to one another in empty space. Now apply 1 Joule of energy to accelerating them apart. They will eventually come again to rest with 1 Joule of gravitational potential and accelerate back together due to gravity. Their kinetic...
  39. D

    Hardy's Paradox: Exploring Copenhagen & Bohm's Theories

    Can someone explain how Hardy's Paradox is resolved? As well, what could someone infer from this regarding both Copenhagen Interpretation and Bohm's theory?
  40. T

    Name for a particular time travel paradox

    I have thought of an interesting property of time travel based on Novikov's self-consistency principle. I'm sure it's not wholly original, but if someone has heard of it before, I'd really like to know the name given to it so I can research it: If you find yourself next to a future version of...
  41. P

    Understanding Einstein's Twin Paradox, past the usual level?

    I heard some scientists say special relativity may not be relative to your frame of reference, but rather possibly distant galaxies or great sources of gravity? I heard they sent a jet around the world with an atomic clock, and also decaying sub atomic particles down a tube, to test special...
  42. B

    Are Poisson and Uniform Distributions Paradoxical on a Finite Line?

    Hi, all, Let's say we deploy some random points on a line of finite length according to a poisson distribution of density \lambda. Can I say that these points are also "uniformly" distributed on the same line? thks
  43. L

    Twin Paradox (I know not again)

    I am new to the forums so hello everyone. I have spent time trying to understand the twin paradox, and I have only partially grasped it. What I specifically don't grasp is...what really happens when the traveler changes inertial frames from leaving Earth to heading towards Earth? I know...
  44. P

    Is There a Perpetual Motion Machine Hidden in the Capacitor Paradox?

    Please see if you can resolve the following relativistic paradox for me. Capacitor is being charged at rest and accelerated to relativistic velocity. If we turn capacitor plates perpendicular to the direction of motion, width of dielectric contracts and amount of energy, stored in the...
  45. R

    A little paradox in relativity.

    Einstein once upon a time said that the faster you go the slower time goes. Speed is Distance/Time. If Time goes slower as a cause of speed, then the Time variable would be smaller and thus the speed greater. This would cause an infinite acceleration as more speed would cause the time to...
  46. E

    Resolving the Pole & Barn Paradox with Relativity

    Homework Statement The Pole and Barn Paradox Suppose a very fast runner (v=0.600c) holding a long horizontal pole runs through a barn that is open at both ends. The length of the pole (in its rest frame) is 6.00m, and the length of the barn (in its rest frame) is 5.00m. In the barn's...
  47. S

    Is Hilbert's Paradox of the Grand Hotel Flawed?

    Well first hello, I'm not really into physics, learning computer science at uni atm. However wanted to get something off my mind. Was browsing wikipedia a while ago and came across Hilbert's Paradox, the idea that a hotel with infinite rooms that are all full can still accept new guests by...
  48. J

    Klein Paradox: Clarifying Concepts & Coefficients

    I've been doing quite a bit of reading on the Klein Paradox, though I have to admit a lot of the math goes over my head. So I was hoping you guys at PF could clarify a few things and help me check my conceptual understanding so far. I found this post...
  49. T

    EPR Paradox and implications for QM

    Can somehow confirm that my understanding of the EPR Paradox is correct. Here goes... Essentially you can entangle two photons, and send them in opposite directions. If we detect one of the photons, we can find out its properties, and since the properties of the two photons are linked, also...
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