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. Y

    Probability philosophical paradox?

    Hi, I am currently working on probability densities and one simple question came to my mind: Say we lived in an "2^aleph_0 world" which contains 2^aleph_0 mathematicans (dont screem already!). Now each mathematician chooses one real number between 0 and one in a bijective way. Now we can pick...
  2. C

    Resolving the Low Reynolds Number Paradox: Wake Formation

    The wake is made because the inertia forces in the system ,right? So if i have low Reynolds number the inertia forces are negligible and the flow doesn't separate ,right? So In every low Reynolds number the flow doesn't separate (no wake) but low Reynolds number also indicate a viscous flow...
  3. E

    Solve the paradox of set theory V7.4.1

    Solve the paradox of set theory V7.5 by LiJunYu 2010.12.25 email: myvbvc@tom.com or 165442523@qq.com Brief:All power sets of real number set R: P(R),P(P(R)),P(P(P(R))),...,Pn(R),...Because all Pn(R) does not contain its own,in Russell's paradox,"all sets which does not...
  4. A

    What was the original purpose of marriage?

    I've been quite potty these days and started couple of new threads, so I don't mind start another one, and I believe PF would very likely welcome such behavior. (Bring in potential clicks and members, although this is a little bit far out notion) You see, for every custom human society would...
  5. E

    Rolling Wheel Paradox: Is it True or a Model Problem?

    Hi, I'm trying to model a wheel that is placed on top of a moving platform. The problem is that I'm running into a situation that seems very counter intuitive. I'm not sure if its a problem with my model or not. I've attached a picture that demonstrates the problem. To begin, neither the...
  6. S

    Is the Grandfather Paradox Truly a Paradox if Feedback is Considered?

    Why is the "Grandfather Paradox" considered a paradox? Feedback exists in other disciplines, so why not in physics? Isn't disallowing feedback in time akin to stating that a negative feedback system can never exist in nature? (And, yet, they obviously do!) Why not assume that, as in other...
  7. S

    Pascal's Paradox: Pressure Differences Explained

    http://www.fas.harvard.edu/~scdiroff/lds/NewtonianMechanics/PascalsParadox/PascalsParadox002.gif the picture is from http://www.fas.harvard.edu/~scdiroff/lds/NewtonianMechanics/PascalsParadox/PascalsParadox.html The pressure on base of the first container (far left) and that of the second...
  8. K

    Electric Field Paradox: Unraveling the Gravity vs. Repulsion Debate in Physics

    Ok for the record I havn't studied physics in a year, I'm a math student. But I was reminded of a paradox I came up with once in physics: Suppose we place a positively charged ball above an infinite plane with positive charge. We know by Gauss law that the electric force on the ball ends up...
  9. I

    Twin paradox initial acceleration

    Hi, I've seen many variations of explanations of the twin paradox using special relativity, but i haven't yet seen an explanation that bothers to take into account the initial acceleration of the traveling twin away from planet Earth. Is it safe to say that this can be neglected...
  10. O

    Both think the other's time is slower Paradox

    Now I know there's another thread like this, and I read through it but still don't understand... So I'll present my own 'case' here. Two astronauts pass each other in space at speeds close to that of light (let's say one is at rest while the other one has a velocity greater than zero). As...
  11. J

    [Paradox] Spring, work, force problem

    so here is the problem The block in the figure below lies on a horizontal frictionless surface and is attached to the free end of the spring, with a spring constant of 40 N/m. Initially, the spring is at its relaxed length and the block is stationary at position x = 0. Then an applied force...
  12. Vorde

    Time Dilation Paradox: Exploring What Prevents it From Happening

    I was discussing the possibility of intergalactic travel with a friend and suddenly this occurred to me. Classically, if someone speeds away at the speed of light (or near to it), he returns without having aged as much as everyone else. But to him everything else sped away in the opposite...
  13. pellman

    Time independent operators and Heisenberg eq - paradox?

    Suppose we have time-dependent operator a(t) with the equal-time commutator [a(t),a^{\dag}(t)]=1 and in particular [a(0),a^{\dag}(0)]=1 with Hamiltonian H=\hbar \omega(a^\dag a+1/2) The Heisenberg equation of motion \frac{da}{dt}=\frac{i}{\hbar}[H,a]=-i\omega a implies...
  14. M

    Black Hole time dilation + biological paradox

    If a spaceship housing humans were to travel near a black hole, time would slow down due to the increased gravity. However, with what we currently know about cellular biology and gravity, humans need to stay around 1g to proliferate properly. Now if the spaceship generates an artificial...
  15. G

    Quantum/Relativitiy and the Speed of Light Paradox

    In my opinion the key to dealing with the current cosmological problems require applying some of the ancient spiritual Philosophies like buddhism. As I understand the big bang: Nothing can travel faster than light. Light travels at 2.998E^8m/s. The universe is accelerating at an increasing...
  16. J

    Exploring the Mixing Paradox: Entropy Change

    Just learned about it recently, and I'm curious to understand more. The 'mixing' form of the paradox goes something like this: Imagine a box partitioned in the middle. The two partitions are the same volume. In each there is a gas, on one side labelled A, and on the other B. The are held at...
  17. Buckethead

    Yet another Twin Paradox thread

    I've read most of the Paradox within a Paradox thread but rather than hijack it to get to my point I thought I'd start a new thread. First, if this has already been addressed from this angle my apologies, but it is next to impossible to read through all the TP threads to try and find one from...
  18. C

    Paradox within the twin paradox

    1) So let's say we have twin A and twin B. 2) Twin A stays on Earth. 3) Twin B goes on a trip nearly at the speed of light. 4) Twin A sees twin's B clock moving slower. 5) Twin B sees twin's A clock moving slower. 6) When twin B returns, twin A is older. #6 Implies that twin B's clock...
  19. A

    Achiles and a tortoise (not Zeno's Paradox)

    Homework Statement When Achiles decided to race with the tortoise, it had already walked 64 meters. After Achiles lowered the distance between him and the tortoise 8 times, he realized that he was 15 times faster than his opponent. Achiles stopped the race. How far did Achiles run before he...
  20. N

    Varitaion on the twin paradox that just doesnt work out for me

    So if you were to take the twin paradox, but make it so instead of the ship turning around and going to earth, the ship bends space through higher dimensions to return to Earth with no movement, what happens then? I'm sure this has been thought up of before, but i can't find an explanation that...
  21. H

    Doppler effect and the twin paradox

    Hi. I am learning special Relativity and I am seeing that the answer to the twin paradox involves the Doppler effect, and I am struggling to understand what is going on. First let me explain what I know about the Doppler effect. If an object produces waves (might it be light waves or sound...
  22. H

    Solving the Time Dilation Paradox - Special Relativity Explained

    Consider A and B are moving in a linear motion, A claims B to move, and B claims that A is in motion, now when they look at each other they would clearly see which clock is running slower. Let us denote the resting object by x and the moving object by y. The special relativity explains, that...
  23. H

    Fluid Dynamics-D'Alembert's paradox

    Hi, I'm trying to prove D'alembert's paradox, but considering a nonviscous, irrotational flow of a fluid around a cylinder. I used the following webpage to help me, which was very good, but I got to a part where I can't seem to solve, perhaps cause my maths needs some brushing up...
  24. M

    What is Simpson's Paradox and Is It Truly a Paradox?

    Hello mates, I am posting this here because I didn't find a forum "Statistics". What is the main reason: My brother wish to discuss with people the Simpson's paradox. He believe there is no paradox and it is a just a "Manifestation of the properties of weighted average." You could...
  25. M

    Why does a clock appear to run slower on a space probe moving away from Earth?

    Probably not but I'm too dumb to figure it out. I'll describe the scenario as clearly and concisely as I can: Suppose a space probe is sent out into space moving away from Earth at a relatively high velocity, but not high enough that there are any significant time dilation effects. Without...
  26. K

    Can an outside observer use electromagnets to solve the Barn-Pole Paradox?

    Please excuse me if I seem inexperienced (I am new to this forum), but lately I've been thinking a lot about a length contraction paradox called the Barn-Pole Paradox. The paradox: A pole and a barn are both at rest relative to each other. When both are at rest, the pole is slightly longer...
  27. K

    Confused about this blueshift/redshift paradox

    Confused about this blueshift/redshift "paradox" Say you had a light probe with a sensor that converts light energy into electricity and and uses electricity generated to draft a chart of energy converted on paper. Now you send the probe on a 1 LY round trip. The probe has an internal drive...
  28. G

    Grandfather Paradox: Debunking the Myth of Time Travel and Altering the Past

    The Grandfather Paradox Something that's been on my mind for sometime... If you were to travel back in time and kill your grandfather you would no longer exist...I believe this is false and What I'm saying is: If you travel back in time, you have removed yourself from your original...
  29. M

    I am missing something in the train paradox

    The train paradox used to demonstrate relativity of simulatneity says that ( I will assume most people are familiar with it and therefore be brief) the observer on the train moves into the light from the front of the train and away from the light coming from the back of the train, therefore...
  30. T

    Quick question about impedance paradox

    Homework Statement Hi! We have a parallel circuit on 230V, 60Hz voltage. One of the parallel's has a 0.0768H coil, the other has a 50 Ohm resistance on it. The question is: What is the effective I in the main current? Homework Equations Z = Lw The Attempt at a Solution OK, so I...
  31. A

    Is the Twin Paradox Real or Just Apparent in Relativity?

    Friends, I will be happy if anybody throws light on the following concepts: (1). In the case of time dilation it is said that a clock in a moving frame appears to go slow to an observer in a resting frame.It leads to the famous twin paradox in which 'A' who spends some time in a spaceship...
  32. A

    Paradox of Rolling: Exploring the Conflicting Forces on an Ideal Wheel

    When an ideal wheel rolls without slipping on a horizontal floor there is a frictional force exerted at the instantaneous point of contact between the wheel and the surface in the opposite direction to motion. But this frictional force does no work on the moving wheel because the point of...
  33. J

    What is the relationship between spacetime and energy?

    Hi everyone I was in philosophy class today and my professor was going over what he said was a paradox with E=mc^2. He said that as defined energy is the ability to do work and that it does work on matter and in turn the work done on the matter creates energy in a cyclic process. The professor...
  34. A

    Is the Cosmological Principle Limited to Space Only?

    The cosmological principled as applied to modern cosmology and the standard model concerns only the spatial part of spacetime, this has been criticized based on Minkowski's predicated non-separability of spacetime, that led(among other things) to the "perfect cosmological principle" that...
  35. A

    Can we use the Andromeda Paradox?

    Can we "use" the Andromeda Paradox? Perhaps the term I should be using is "relativity of simultaneity"... anyway :) Usually I see the Andromeda Paradox stated in terms of a stationary observer and another who is moving toward the galaxy. I did find one source that said the reverse effect...
  36. C

    Resolving the Paradox of Entropy and Energy

    we know that when the energy drops the entropy increases. but when the energy of a gas drops then it will become eventualy solid which has less degrees of freedem and therefore the entropy should decrease and not increase. Moreover high temp. has more entropy (gas for ex.) and as long as the...
  37. C

    Understand the Paradox of Rigid Body Acceleration

    I've read that the acceleration produced in the center of mass of a rigid body is equal to: AccelerationCenter of mass = Forceexternal / Mass However, that leads to a counter-intuitive conclusion. The reason that seems unintuitive to me is that I would expect some rotation to happen...
  38. mrspeedybob

    Contemplating an apparent paradox in the classic double slit experiment.

    Here is a thought experiment to illustrate the problem... Suppose you have a light source capable of emitting single photons on command from a computer. these photons travel through a barrier with two parallel slits and then strike a charge coupled device. The computer records each strike and...
  39. J

    What is the paradox of guessing coin flips with probability 2/3?

    A warm up problem 1 Somebody flips two coins on table, and then hides them with some two pieces of clothing. You observe, when one of the coins is revealed, and it is heads or tails. You are then asked to guess what's the side of the unrevealed coin. Which ever answer you give, you are right...
  40. M

    Paradox: Who Will Be the Oldest After Travelling Near Light Speed?

    Here comes the model situation. I have a man on a planet and two ships. One ship will go straight to from a planet and another one will go opposite direction. Well that's for me very interesting. Because i will travel with ship near to speed of light from Earth the Earth time will be for me...
  41. J

    Resolve to the Twins Paradox – Frame of Origin

    I have read many arguments concerning the issue of the famed “Twin Clock Paradox”. Very many arguments go through considerably complex explanations so as to defend Special Relativity or dispute it. But the explanation is actually much simpler. In every proposed twins paradox, there is a Frame...
  42. R

    Uncovering the Math Behind a Mysterious Paradox

    I discovered a mathamatical truth that seems to have no clear logical foundation. Could anyone here explain the math behind the following? A.Given the following recursive series: S(1) = 3 S(2) = 2 S(n) = 6*S(n-1) - S(n-2) - 4 Define a new series as follows N(i) = (S(i) + S(i+1) +...
  43. K

    Mechanical Paradox: Weightless Rod w/ Wheel & Weight

    You have a weightless rod with a wheel attached to one end (weightless, frictionless) and a weight attached to the other. The weight is mounted on a short axle, and can rotate freely. With the wheel on the floor, the rod is held at 45 degrees to the horizontal and then released. Since the rod...
  44. M

    Time travel paradox only due to choice

    The title is the best way I could group this thought. And the following is most likely sloppy so I do apologize. I get the 'feeling' (subjective I know), that the measurement effecting the outcome i.e. only being able to measure position over velocity, collapsing wave functions, etc... comes...
  45. A

    Grandfather Paradox: Exploring Cause & Effect in Time Travel

    Just an amateur (and hardly even that)... so take it easy on me... but I have some questions about the Grandfather Paradox. Assuming time travel to your past were otherwise possible, doesn't that imply that each moment in time is its own unique physical state existing simultaneously...
  46. M

    Resolving the Paradox in Deriving Gravitational Potential Energy Function

    I'll first derive here the gravitational pot. energy by my method, and then I'll give the method that has been formally used in books. My answer differs from the actual one by a minus sign. My derivation: Let mass M be at the origin O. Let another mass m be at an arbitrary position r from...
  47. Y

    Can an electric switch function differently at relativistic speeds?

    This relates to another thread about trains and manhole covers at relativistic speeds falling (or not) down gaps that would be normally be too small. Consider two hollow cylinders aligned with each other along their long axes with a short gap between the hollow cylinders. They are designed...
  48. K

    Magnetic Force Paradox: How Does Einstein's Theory of Relativity Solve It?

    Hi We've just begun studying magnetic force in school. Our teacher told us to explore the possibility of a paradoxical situation as F=qBv From different inertial frames, the apparent force will be different, won't it ? Our teacher told us that Einstein's theory of relativity solved the...
  49. C

    Repositioning clocks: continuing from the switch paradox

    In this hypothetical, an experiment is going to be conducted concerning the repositioning of clocks. two clocks are placed at the leading end of a vessel, that is 1 light second long, to an observer at rest relative to it. This vessel is shot into space from an observation station at...
  50. C

    The Switch Paradox: Resolving Relativity of Simultaneity

    This is a paradox that I have derived based on my understanding of relativity of simultaneity. Upon someone resolving it, I should be better able to understand the concept, which seems rather contradictory of the greater theory at this point in time. If events are considered to be...
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