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. A

    Resolving the EPR Paradox: Exploring Signal Models and Special Relativity

    We consider a typical version of the EPR paradox where an electron and a positron are produced collinearly in the +y and -y with the spins polarized in the positive and negative z directions. The pair is emitted with zero linear and zero spin-angular momentum. If the positron is detected in the...
  2. J

    Discover the Pi Paradox: The Infinite Perimeter of a Circle with a Diameter of 1

    Suppose you have a circle with a diameter of 1. If you draw a square with all four sides touching the circle, the perimeter of the square is 4. Now suppose you indent each corner of the square so that they all touch the circle-this will make a cross shape, and the perimeter of it is still 4. Now...
  3. D

    The Twin Paradox: Mike & Angela's Frame of Reference

    I am confused about the twin paradox. Let's imagine Mike and Angela are twins. Mike stays on Earth, and Angela rockets off, away from Earth at close to the speed of light, with the intention of making a round trip back to Earth at the end of her voyage. My question is this: why wouldn't...
  4. K

    Is anyone good at special relativity? the twin paradox?

    Is anyone good at special relativity? the "twin paradox?" Homework Statement In the problem a pilot accelerates away from Earth for 10 years, then decelerates the same way for 10 years, then turns around and repeats the whole process to return to earth. His acceleration is given by...
  5. R

    Can someone help me understand this paradox please

    I am really trying to get my head around SR, in particular the twin paradox I have read so much about. From my very elementary understanding of the twin paradox, the basic reason for the twin that is traveling aging less is because he accelerates and thus breaks the symmetry between the two...
  6. D

    Negative pressure & Hydrostatic paradox

    2 parts: 1. What does it mean if you get a negative gauge pressure value when calculating from manometer containing compound liquid? When calculating absolute pressure how does atmospheric pressure affect this negative pressure ie. atmospheric pressure opposes the direction of force? 2...
  7. K

    Special Relativity - Twin Paradox

    Homework Statement Consider the following space flight. As seen by the pilot the ship accelerates for 10 years with an acceleration given by a=2g[1-exp(-rt)] where g = 9.8 m/sec^2 and r=1/(3 years). She then decelerates the same way for 10 years (begins with 0 acceleration and increases...
  8. T

    Twin Paradox: Explaining Symmetry & Age Difference

    Hi, i want to ask about the basic explanation of twin paradox. In the explanation it says one twin has to accelarate to come back and the symmetry is broken and so one twin is older than other. Could you explain this symmetry and aging relation?
  9. P

    Straight Line Case. My paradox. Sorry if I rewrite and start a new post.

    1. Suppose, a fast moving train (600,000 km long) running on straight line at speed 0.999c, perpendicular to A. 2. A is at point P. B stands in center of train. M point. Distance P to M is 300,000 km. C stands at end of train. D stands in head of train. 3. Now B flash light. According to B...
  10. P

    My paradox, dead or not according to different observers

    My paradox, dead or not according to different observers! 1. Suppose, a fast moving train (600,000 km long) circling on track (radius is 600,000 km, radius can be even more, this is just convenience reason) at speed 0.999c. A stands at center of the track. 2. B stands in center of train. C...
  11. V

    Why Does the Twin Paradox Not Invalidate the Theory of Relativity?

    Bob sets on a voyage with a velocity 0.8c for total 6 years, leaving back Dave on the space station. On return Dave finds him younger by 4 years. Reciprocal results in time measurements in relativity make the theory redundant but here we see application of time dilation equation. This is...
  12. P

    Why is the Andromeda Paradox flawed according to Penrose's book?

    i just realized, Andromeda paradox is flawed. I feel good, as compared with penrose, I am really just started in this subject. it is flawed becuase penrose mistakendly consider the"each day" for the person in moving (although very slow) and the person are the same. They are not same. the...
  13. A

    Solving the Infinite Time Paradox: Zeno's Argument Explained

    This has most likely been mentioned before and if so I apologise, I have seen a few similar discussions though didn't really see any answers that I was able to understand/accept. The problem is if there is an infinite amount of time in the past then how is there a present? (I know there can...
  14. D

    The Paradox of Oppositely Traveling Objects in Spacetime

    It is my understanding that all things travel through spacetime at the same speed. Additionally , I am told we are moving through space at some velocity. My question is this: If an object were made to travel in a direction opposite to our direction of motion , would that object not then be...
  15. B

    Faster than the speed of light paradox

    Ok, so I'm not a physicist by any means, and I don't actually understand the first thing about physics. So, I'm guessing that somebody's probably realized this before, and I just want to know the name of this "paradox" (i'm not even sure it's the right word) so I can read up on it. Here's the...
  16. G

    The Klein Paradox - Exploring Beyond the Negative Coefficient of Transmission

    The Klein Paradox is the name given to the following prediction of Klein Gordon's equations. If you send a current of electrons against a potential barrier of height V such that the energy of the incident electrons is less then V - m, you should observe a current of positrons coming out of the...
  17. S

    Can someone explain, simply, hidden nonlocality/locality? EPR Paradox?

    So I understand local realism (the moon is there when we aren't seeing it) and the notion that Bell's Theorem says that if local realism is true, then we could perform experiments that show observation is independent of reality and that we should expect certain probabilities to arise. But we...
  18. G

    Twin Paradox (thorough explanation needed)

    Hi, I'm an undergraduate physics student trying to comprehend why the twin paradox is not a paradox. The standard reply usually amounts to this: the dude in the spaceship has to turn around at some point to come back to Earth. So he accelerated during his journey (by changing his direction...
  19. A

    Enropy paradox ? or , tell me why?

    Hi all, I've been around with this question for a while,I googled it and I found some information,But I want you to help me more, The question is : From the beginning of the universe,Anywhere of the Universe you see,there is reactions that due to them new materials are being produced,and...
  20. O

    Twin paradox, what about ageing?

    I may not be right exactly but however i stand corrected where necessary. Twin paradox experiment explains time dilation in space time. My understanding is like this, assuming twins at 10yrs each. If one makes a space travel and the other is at stationed on Earth (both being at initial...
  21. J

    The Gravity Paradox: Does Mass Affect Speed?

    So according to all if you drop a feather and a bowling ball on Earth in vacuum it falls at the same speed. So that says acceleration of gravity is not affected by mass only the momentum. And this says that even a moon size iron ball would fall at the same speed to the Earth as a feather(in...
  22. C

    My Train Paradox: Exploring Relativity

    Its my first post here so i say hello to you. I have a 'problem' with understanding relativity. Here is the thing: We have a train and a station. Station and train have same lengths measured in rest (v=0). Station has attached two detectors, one at rear and one at front. They have built...
  23. W

    The Andromeda Paradox: A Reflection of Quantum Mechanics?

    Hello, Can someone explain the http://demonstrations.wolfram.com/TheAndromedaParadox/" ? What does it mean, philosophically/etc? Local and non-local events. Time? Was this paradox an invitation for an explanation of the unknown concept at the time called "spooky action at a distance"? Which we...
  24. D

    Angular velocity and c: Is this a paradox? Can you explain it?

    I thought of this today while studying relativity. Imagine a very large disc spinning with an arbitrary angular velocity. Perhaps w=57 rad/s (this is the speed of a CD, got this from a random physics text, whatever, the speed is really not important).. The speed of light is c=3*10^8 m/s...
  25. K

    Is There a Superluminal Signal When Turning Off a Harmonic Potential?

    Consider we initially have a ground state particle of a harmonic oscillator: \psi = \exp ( - a{x^2}) (neglecting nomalization) And we have a detector far in space monitoring the local probability of finding a particle. Now if we suddenly turn off the harmonic potential, the wavefunction will...
  26. D

    Gravitation and Information, BH paradox

    When (almost any) system emits gravitational waves, does information carried by these waves also 'counted' as an information about a system? In case of BH informational paradox, when BH dissapears, we get not only Hawking radiation, but also information encoded in the gravitational waves of...
  27. A

    Russell's Paradox and the Axiom Schema of Separation

    As everybody I have read or heard on the matter claims, the Axiom Schema of Separation was concocted to resolve a paradox that results from the Axiom of Unrestricted Comprehension. The Axiom Schema of Unrestricted Comprehension as I understand it is stated as follows (forgive my lack of...
  28. F

    E & M Magnetism Relativity Paradox

    E & M Magnetism Relativity "Paradox" :confused:In theory the laws of magnetism are derivable from coulomb's law and special relativity. Right. While my physics homework group were doing a problem set, I came up with this seeming paradox. (This isn't a homework question). There are 2 senarios...
  29. G

    Explaining the Second Ace Paradox: Understanding the Math Behind It

    Could someone please explain the math behind the Second Ace Paradox? Here's the problem: http://www.futilitycloset.com/2009/02/06/the-paradox-of-the-second-ace/ I want to know how the poster got those probabilities... I can't figure it out on my own.
  30. T

    Help Explain Electromagnetic Induction Paradox

    ok, i just can't figure this one out. you have heard of the example of the 2 wires, and depending on their currents, they will attract or repel each other because they "see" different amounts of protons/neutrons. so, this is what we call "magnetism" I just can't tie in electromagnetic...
  31. K

    Can Students Guess Their Secret Number Using the Axiom of Choice?

    I heard this interesting paradox, which I haven't been able to find anywhere online! Now, bear with me while I set it up! Suppose a professor has a countably infinite number of students. This professor secretly assigns to each student a real number in the interval [0,1], and thus ends up with...
  32. Q

    The paradox, is basically a theory about time travel.

    The paradox, is basically a theory about time travel. This thread requires the assumption of making time travel possible. Supposedly, you go back in time and kill your grandfather before he gets married. How did you end up there in the first place?
  33. K

    Does a Thermometer Truly Reflect Air Temperature in Kinetic Theory?

    Let’s take an ordinary household thermometer and expose it to the air. The molecules of the air impact on the surface of the thermometer and transfer kinetic impulses. The thermometer transfers kinetic impulses to the impacting molecules as well. Eventually, thermal equilibrium is reached and...
  34. K

    Solving Twin Paradox: Earth's Motion in Astronaut's Frame

    Again on twin paradox! Hi! I'm trying to definitely solve the twin paradox (after 5 years of efforts :) ) In every physics textbook, it is studied the motion of the twin in an inertial frame (so the proper time is that measured in the twin frame), so we can express time delta t in the Earth...
  35. Y

    Does Schrodinger's Cat Paradox Suck?

    Is Schrodinger's cat paradox a poor pedagogical example for students of QM? In the traditional formulation of the paradox, the cat is declared to be both alive and dead at the same time, but no proof is offered of how the paradox can not be resolved by simply assuming the cat is either dead or...
  36. C

    Paradox in isentropic expansion? (statistical mechanics)

    If I have a container containing a liquid mixed with some other substance that has much a higher boiling point (i.e. water and salt). This liquid will be in equilibrium with its vapor (the salt vapor pressure is negligible). Now I quasi-statically adiabatically expand this vapor. Isentropic...
  37. C

    Time Dilation Paradox: Interstellar Race

    Hi, I asked a theoretical question here a month or two ago and someone was able to help me. I have another: Imagine an interstellar race. Starship 1 heads from Earth toward Alpha Centauri at a constant rate close to the speed of light, then makes a loop and returns home. Ship 2 is faster, and...
  38. Z

    Gravity - an accelerating frame paradox

    If the equivalence principle is true then it means that the Earth's gravity field is a constantly accelerating frame of reference. In any accelerating frame of reference the direction of acceleration is always opposite to the direction of attraction. That means that for all observers on the...
  39. D

    Twin Paradox Revisited: Exploring Time Dilation

    Folks, apologies for reviving a thread that I know has been picked over, but I am a bit confused. I understand the explanation that "solves" the Twin Paradox -- Twin B in the rocketship flying close to light speed undergoes acceleration and deceleration on his outbound trip away from Earth...
  40. T

    Can somebody please explain Olbers' paradox to me?

    In general terms, but not too general.
  41. Mueiz

    How to send a faster-than-light signal (spot Paradox)?

    Suppose you have a source that send a very strong straight beam of light (say laser ) Then you direct the light toward a distant wall with angle 45 degree as show in the drawing below Then if you rotate the source 90 degree in one second, what is the velocity of the visual effect (spot)on...
  42. N

    Relative Information and Time Paradox?

    Is this a paradox? We have a satellite orbiting at a significant amount of the speed of light around the earth. Hypothetical numbers: The satellite ages 6 years; while the; earth ages 7000 years. How does the satellite communicate with Earth or vice versa? How is information...
  43. L

    Is the Boltzmann Brain Paradox a valid explanation for our existence?

    Hi guys. I'm new here and pretty much a layman when it comes to physics and astronomy. I came across this hypothesis a few months ago, but have been looking at it the last few days. Anyway, I'm hoping you guys know about this so you can help me. Search wikipedia for it if not. I'm not...
  44. 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...
  45. 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...
  46. 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...
  47. 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...
  48. 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...
  49. S

    Grandfather Paradox vs. Feedback

    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...
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