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. Orodruin

    Insights A Geometrical View of Time Dilation and the Twin Paradox - Comments

    Orodruin submitted a new PF Insights post A Geometrical View of Time Dilation and the Twin Paradox Continue reading the Original PF Insights Post.
  2. Y

    Twin's Paradox: Who is Older A or B?

    Assume A and B are at rest on Earth initially. Then B travel to to one light year far away from Earth with an extremely low speed (even slower than a car). So I can assume their ages are the same after B has arrived, right? Then, B returns to Earth with an extremely fast speed (~0.9c) and A and...
  3. A

    What is the core problem of the information paradox?

    Can you please explain what the core problem of the information paradox is? Hi all! I've read many articles about it, watched videos, argued with some physicists, and yet I can't grasp at all where the paradox lies. For example, from the Wikipedia: "An important difference between the black...
  4. R

    A philosophical question regarding random numbers....

    A number can be random even if limitations are applied to the outcome - e.g. selecting a random integer between 1 and 5 restricts the outcome to one of 5 numbers, but the outcome is still random. The same would be true of between 1 and 2; although there are heavy restrictions, an unbiased...
  5. Q

    Immovable Object vs Unstoppable Object

    Admit it. It's a pretty dang hard question, but here it is compressed down. So theoretically it's impossible to have either one, but never mind that. A immovable object has to be an object that cannot have its own speed or velocity changed, so it is an object that cannot be accelerated, since...
  6. A

    Help with Twin Paradox: Understand Contradiction

    I was hoping I could get some help on wrapping my head around the twin paradox. The problem is I have never seen the following "contradiction" addressed. I understand (at least on paper) that events simultaneous in one frame needn't be simultaneous in another. But consider the following...
  7. V

    Fluid Shear Paradox: Is There Shear?

    A fluid with forced vortex flow and constant angular velocity is given. Newton's shearing says there must be strain due to differential linear velocity. The problem is, the difference of linear velocity is only visible to the external observer, the fluid particles themselves do not observe...
  8. T

    A thought experiment paradox

    I am pretty familiar with the theories of special and general relativity. I know how to add velocities, I know the main postulates and the experimental confirmation. However, I thought of the following thought experiment: There are 3 experimenters (at the same point in space), who adjust their...
  9. U

    Dielectric material in 'induced electric field'

    Hi everyone, I just wanted to know/understand that, why do the dielectrics don't get polarized, when subjected to induced electric field ? Because, according to the definition of electric field(which is a vector), it is the force per unit charge, which implies, that electric field has a unique...
  10. Kostik

    What is the Paradox of Faraday's Law and its Connection to Magnetic Fields?

    There's something very curious about Faraday's Law that results from considering a closed curve in space (and any surface whose boundary is that curve). Forget about conducting wires and EMFs: Faraday's Law gives the result of the integral of E along the curve in terms of the rate of change of...
  11. B

    Light and Doppler effect paradox?

    Hello, I just thought of something that looks like a paradox to me. Suppose you have a device which can detect a light source's frequency, and will explode if the frequency exceeds a threshold value f_t. Place this device stationary wrt the light source. Now, suppose there are two observers, one...
  12. K

    Sound standing waves paradox....

    If you seal a loudspeaker at the end of a tube and close the other end of the tube you will get standing waves; but what are the boundary conditions at the speaker for the sound pressure wave? Pressure =0 or Pressure = MAX? I find no mention of this in the literature. To find out I performed a...
  13. Einstein's Cat

    Gravitational Paradox: Solving the Unsolvable

    Galaxies outside the observable universe are moving away from the Earth faster than the speed of light. As the two bodies move apart, the gravitational force between them should weaken however as the speed of gravity is equal to the speed of light, the gravitational force would not do so. It is...
  14. marcus

    Stephen Hawking offers new resolution of black hole paradox

    Bee Hossenfelder was live-blogging from Stockholm Conference on BH info puzzle today Tuesday 25 August. Herewith: http://backreaction.blogspot.com/2015/08/hawking-proposes-new-idea-for-how.html The conference is 24-29 August. Hawking presented his idea Tuesday, based on joint work with Malcolm...
  15. A

    Paradox of Magnetic Force: Exploring the Relationship between Magnetism and Work

    Imagine an infinitely long wire carrying current i1 in west to east direction. At a small distance 'd' above the wire there is another small current carrying wire of length 'l' carrying current i2 from east to west direction (opposite to the direction of current in the below placed wire)...
  16. Dadface

    B Bell spaceship paradox - qualitatively

    [Mentor's note: This thread is forked from https://www.physicsforums.com/threads/bell-spaceship-paradox-quantitatively.828670/ for discussion of the basic principles behind the spaceship paradox] Suppose the string was replaced by some structure which linked the ships together to make a longer...
  17. vanhees71

    A Bell spaceship paradox quantitatively

    Yesterday, I found the time to write a bit further on my SRT FAQ and wanted to give a quantitative analysis of the Bell space-ship paradox on the example of the two rockets accelerating with constant proper acceleration, and I found a problem, I cannot solve. So I took this section out from my...
  18. Y

    Question regarding a twin paradox related example

    Since I am new to the forum here, I apologize in advance that in case similar example has been explained in another thread. If so, please kindly refer me to the appropriate place to read further. In my example, there will be four reference objects, earth, E, distant star, S, spaceship A, and...
  19. bcrowell

    Insights What Is the Bell Spaceship Paradox, and How Is It Resolved? - Comments

    bcrowell submitted a new PF Insights post What Is the Bell Spaceship Paradox, and How Is It Resolved? Continue reading the Original PF Insights Post.
  20. D

    I Is the Planck length the smallest measurable length?

    I read somewhere that you cannot tell the difference in position between a photon (Or any other particle) at some point in time and the same photon (Or other particle) less than a Planck time later, because it would not have traveled further than a Planck length, which apparently is the smallest...
  21. D

    Square root function: x intercept paradox?

    Here's my equation y= sqrt (x+4)+1 I want to find the x intercept. Ok so i replace y with 0 and solve for x 0= √(x+4)+1 -1=√(×+4) (-1)2=×+4 1=×+4 -3=× So it looks like the x intercept is (-3,0) But then when i go back and plug in -3 in place of x... y=√(-3+4)+1 y=1+1 y=2 I now have a point...
  22. Stephanus

    Twins Paradox: Nature Cheats but B Gets Fooled

    Dear PF Forum, After all these post'. I want to know that my understanding of twins paradox is close enough. So, Green travels, Blue stays. Blue keeps sending signal, Green bounces the signal. Doppler factor = 1/4, so ##\frac{1}{4} = \frac{1-v}{1+v}; v = 0.6## And at event T0 (from B), Green...
  23. C

    Maxwell equation at the surface of a conductor - paradox?

    Assume that we have a conductor of any shape, say a ball of copper. At electrostatic equilibrium, it is well known that the potential inside this conductor is constant, for otherwise free charges would move from points of highest potential to points of lowest potential (this includes the surface...
  24. M

    A Solution To The Grandfather Paradox

    Hey There, I would like to share something that crossed my mind the other day, a solution to the grandpa paradox. My solution is quite basic, The Man in the future is going to shoot himself in the past through a portal, He will not do so because if he did, he wouldn't exist in the future to...
  25. A

    Bertrand Paradox Method-1 and Method-2 may be equal

    I think that both methods (1 and 2) of Bertrand Paradox may be equivalent if the probability is represented by area of the circle enclosed by each method rather than by distances. Please see the attached file. In both methods, the probability is approximately 0.6.
  26. Graeme M

    Simple explanation of the Boltzmann Brain paradox

    Mods: I am not sure if this is a Physics question or more appropriate for Cosmology. I read a short discussion (on another forum) about the Boltzmann Brain paradox. I did a little further reading on the web but most explanations were a bit too deep (read: over my head). I wonder if someone...
  27. Toby N

    An Endless Fall: Exploring a Fictional Paradox

    So I'm just really curious and this question is fictional, I'm new so i don't know if this is the right place to post this. Anyway, if there is 2 portal facing each other vertically and a person jump on to it, end up falling forever, i wonders how much could that person reach and is there anyway...
  28. N

    Question Regarding the Twin Paradox

    Homework Statement In the twin paradox suppose the twins are named Dick and Jane. And they both are 20 years old.Dick takes off on a voyage at a speed of 0.8c to a star 20 light years away.Lets say that both the twins send each other signals once a year while Dick is away.How many signals does...
  29. Deepak K Kapur

    Exploring Zeno's Paradox: Is It Valid?

    Zeno said that you can't finish or start a race because there is an infinty of points between any two points. Let's take a distance of say 1meter. As per zeno there is an infinity of points in this distance. So, what is the size of each of these points. Of course, 1/infinity=0. i.e. each point...
  30. Stephanus

    Exploring Twins Paradox & Length Contraction

    Dear PF Forum I want to know about these questions that are still bothering me, Does the universe have preferred frame of refference? Why there's twins paradox? Motion is relative, why 1 clock experiences time dilation while the other doesn't? V = \sqrt\frac{3}{4} ≈ 86.6\% If V define ratio of...
  31. A

    Apparent paradox in no costants fields

    if there is an uniform, infinitly extended,magnetic field that is changing with a law B(t), I can calculte the induced electric field using an arbitrary circle; then the induced circuitation on the circle is \epsilon _i=-\pi r^2 \frac{dB(t)}{dt} , and since the symmetry of the system ( infact...
  32. Stephanus

    Twin Paradox and Time Asymmetry in Special Relativity

    Dear PF Forum, Can someone make it clear for me? Perhaps I should ask a very simple question. Concerning just one direction. The distance between Earth and Star T is 100 lys. The clock is synchronized for A and B And as PeterDonis pointed out at my previous thread. Which I believe 87% is an...
  33. Stephanus

    Does the Twin Paradox Break Symmetry in the Zig-Zag Scenario?

    Dear PF Forum, Sorry if I ask (again) about twin paradox, after so many question about this topic here. Supposed T is a star 100 ly from earth. If B travels to T from earth A. Is the symmetry broken? B. If B watches A's clock at Earth and A watches B's clock at T, do they see the other clock...
  34. C

    Twin Paradox - Question on Space Time Diagram Analysis Resolution

    I started a thread previously (https://www.physicsforums.com/threads/time-dilation-happens-on-moving-frame-but-which-one.814622/) around this concept but it got closed by one of the staff after helpfully pointing me to...
  35. mathyou9

    "Triplet Paradox" involving a single one-way trip

    The "triplet paradox" that comes up in my Googling and search results involve one triplet that stays at rest and the other two venture out and back again, but in opposite directions. Essentially two "twin paradoxes" occurring together. But what about a scenario in which triplets A and B are...
  36. nomadreid

    Fuzzy logic and the Liar paradox

    I have once again (this time in http://www.economist.com/node/2099851) come across the argument that a fuzzy logic solves the liar paradox by assigning the liar sentence a truth value N, other than T or F, with [[A]] = N ⇒[[~A]] = N. However, I don't see that this gets around the essential...
  37. K

    Can a Computer Recognize a Paradox?

    Simple question: Can a computer be taught to recognize a paradox? This assumes the computer has no cognizant reasoning or "self awareness". It is a plot device used in a lot of science fiction, that the intrepid "flawed" human hero defeats the computer or robot with a simple paradox making it...
  38. Jimster41

    Loschmidt's Paradox: Exploring Irreversibility in QM

    i hate to start a new thread. Is it correct to say there is nothing in the current SM (or SUSY?) that resolves Loschmidt's puzzle of where irreversibility comes from. Or is it (non-commutativity?) a basic feature feature of all QM? If it is a basic feature of all QM, is it thought to require an...
  39. B

    Twin paradox with acceleration

    A spaceship leaves earth. One twin stays back, the other is on the ship. The ship accelerates for 5 years with a constant acceleration (the 5 years are in the reference frame of the ship), then it decelerates for 5 years. Then, it turns around and does the same thing again. All the accelerations...
  40. blue_leaf77

    Twin Paradox (again(again(again )))

    When you see the title of this thread, I'm sure you will either be bored or excited because this is one of those famous 'paradoxes' in SR. So I read the book by Schutz on the part of explanation behind the twin paradox. There he gave an example of two sisters Diana and Artemis involved in the...
  41. Stephanus

    Twins Paradox: Exploring Clocks in a Closed Room

    Dear PF Forum, I have a tought experiment here. I'm asking about twins paradox, but instead of using twins, I'm using clocks to lock them up in a closed room. Sort of Einstein elevator. (unlike Schrödinger, even in tought experiment, I can't imagine locking human being -- or cat -- in a closed...
  42. H

    A puzzle on a Faraday cage "eating up" information

    Imagine an uncharged solid spherical conductor. Inside this spherical conductor, there is a cavity of a weird shape carved out of it. And somewhere inside this cavity, there is a charge +q. The charge +q induces an opposite charge -q on the wall of the cavity of the conductor, which distributes...
  43. N

    What is the Real Life Twin Paradox?

    Landed on this PBS page, and read that there is going to be a real life twin paradox. Excerpt from the article "Astronaut twins Scott and Mark Kelly are about to realize this experiment: when Scott returns from a year in orbit in 2016 he will be about 28 microseconds younger than Mark, who is...
  44. nuclearhead

    Can you answer this virtual photon paradox?

    In order to get my head around virtual particles I've created the following question. Maybe some bright person can answer this. If I can answer this question I feel I would have the required understanding to explain virtual particles to other people. In the diagram below, A is a radioactive...
  45. D

    Twin Paradox in Kerr Metric - Help Needed

    Hi. I've been struggling with a formulation of the twin paradox in the Kerr metric. Imagine there are two twins at some radius in a Kerr metric. One performs equatorial circular motion whilst the other performs polar circular motion. They separate from one another and the parameters of the...
  46. G

    How to Solve the Twin Paradox Problem Using Lorentz Transformations

    Homework Statement This is a typical twin paradox problem as laid out in Griffith's Introduction to Electrodynamics, problem 12.16. The problem states that, on their 21st birthday, one of two twins - we'll call her Alice - departs Earth for star X at (4/5)c. Upon arriving at star X, she...
  47. Vinay080

    Why can't a particle ever reach a non-terminating decimal form radian value?

    Consider a particle P moving in a circle of radius r as shown in the figure. Premise 1: Position of the particle can be described by the angle θ. Premise 2: Particle reaches the position with an angle θ if it has covered the angle lesser than θ. Premise 3: Particle can never reach...
  48. ShayanJ

    Information paradox, dismissed?

    One of the important problems in modern physics is BH information paradox, which is the problem with non-unitarity of Hawking radiation. But now there is this paper which says that this process is actually unitary and so BH information paradox is, not solved, but dismissed. I'm posting this...
  49. Vinay080

    Is the Length of an Arc Equal to its Straight Line Distance?

    Premise 1: Line is composed of points. Premise 2: Each point is associated with specific co-ordinates (x,y). Premise 3: Lines of equal length have equal number of points. Lines of greater length have greater number of points. Premise 4: Each value of x in the function f(x) gives a single...
  50. PeterDonis

    Using General Relativity to analyze the twin paradox

    In a previous thread, reference was made to an entertaining "defense" of relativity by Einstein, which can be found here: https://en.wikisource.org/wiki/Dialog_about_Objections_against_the_Theory_of_Relativity One of the arguments Einstein makes in this dialog is that the twin paradox can be...
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