Twin paradox Definition and 318 Threads

In physics, the twin paradox is a thought experiment in special relativity involving identical twins, one of whom makes a journey into space in a high-speed rocket and returns home to find that the twin who remained on Earth has aged more. This result appears puzzling because each twin sees the other twin as moving, and so, as a consequence of an incorrect and naive application of time dilation and the principle of relativity, each should paradoxically find the other to have aged less. However, this scenario can be resolved within the standard framework of special relativity: the travelling twin's trajectory involves two different inertial frames, one for the outbound journey and one for the inbound journey. Another way of looking at it is by realising that the travelling twin is undergoing acceleration, which makes him a non-inertial observer. In both views there is no symmetry between the spacetime paths of the twins. Therefore, the twin paradox is not a paradox in the sense of a logical contradiction.
Starting with Paul Langevin in 1911, there have been various explanations of this paradox. These explanations "can be grouped into those that focus on the effect of different standards of simultaneity in different frames, and those that designate the acceleration [experienced by the travelling twin] as the main reason". Max von Laue argued in 1913 that since the traveling twin must be in two separate inertial frames, one on the way out and another on the way back, this frame switch is the reason for the aging difference. Explanations put forth by Albert Einstein and Max Born invoked gravitational time dilation to explain the aging as a direct effect of acceleration. However, it has been proven that neither general relativity, nor even acceleration, are necessary to explain the effect, as the effect still applies to a theoretical observer that can invert the direction of motion instantly, maintaining constant speed all through the two phases of the trip. Such observer can be thought of as a pair of observers, one travelling away from the starting point and another travelling toward it, passing by each other where the turnaround point would be. At this moment, the clock reading in the first observer is transferred to the second one, both maintaining constant speed, with both trip times being added at the end of their journey.

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  1. Ookke

    Another twin paradox variation

    Sorry about twin paradox again, I'll try to keep this simple as simple as I can. Initial situation: All participants are at rest, A1 and A2 are together at midpoint between B1 and B2. All clocks are in sync. _____________A1, A2 _____B1____________________B2 ---- A1 and A2 move...
  2. A

    Twin Paradox: Understanding Who Ages Less

    We know what is twin paradox is, and also why it is not a paradox, but my question is, "if we can not define absolute motion, how can we decide that the twin which went to space will age less, and not the home one?" That is to say that, when peter at home sees paul's clock moving slow (in...
  3. K

    Twin Paradox: Exploring Relativity of Time Dilation

    Hi! I am studying special relativity and I still don't understand completely the relativity of time dilation: each twin sees that the time of the other twin is dilated, so how can exist the asimmetry in the measurements (only one twin at the end has really dilated his time)? I'll make an...
  4. GRB 080319B

    Twin Paradox: Can Age Asymmetry be Achieved on Earth?

    I understand if this question sounds juvenile, because I thought of it after seeing a science fiction movie called Clockstoppers. In this film, a device (stopwatch) is used to speed up the molecular motion of an person body so that from their frame of reference, the rest of the world has slowed...
  5. W

    Twin paradox in an empty universe

    The obvious objection to the famous thought experiment with one of a twins moving away from the Earth is, couldn't you have moved the twin together with the Earth in the opposite direction to yield the opposite conclusion. Thes standard answer is that the symmetry is broken when the returning...
  6. A

    Twin paradox and time dilation.

    When we read that two twins would age differently when one moves with relativistic speeds. i.e. When one twin travels at speed near to speed of light then the twin on Earth would see that time for the traveling twin has slowed down. Thats what we say time Dilation. Similar is the case with the...
  7. C

    Twin Paradox: Jerry vs Tom's Time Dilation

    form twin paradox, let say Jerry is the one go travel to outer space then back to Earth and Tom is the one stay in earth. From relativity time dilation,Tom will see time in Jerry will be slower and also for Jerry will see Tom time move slower. So, just at the time Jerry reach the earth(he...
  8. D

    Relativity and the twin paradox

    [SOLVED] Relativity and the twin paradox Homework Statement A friend of yours who is the same age as you travels to the star Alph Centauri, which is 4 light years away, and returns immediately. He claims that the entire trip took just 5 years. How fast did he travel? Homework Equations...
  9. K

    Exploring the Triplet Paradox: A Deeper Look into Time Dilation and Relativity

    This thread is another extending from the `Schwarzschild Metric` and `Climbing out of a Black Hole`. I hope the members of the physics forum will not object to me testing out some ideas against their wider knowledge in this subject area. Anybody reading about relativity bumps into the Twin...
  10. F

    Twin Paradox: Why Does the Traveling Twin Age Slower?

    Forgive me if this has been posted before, but looking through a page of search entries I found many topics that were related, but none that asked quite the same questions. I actually have two questions, but I feel they must be related. I hope you bear with me as I come to the subject from a...
  11. F

    The Twin Paradox: Why Does the Travelling Twin Age Less?

    As we all probably know, the twin paradox states that a twin goes off in a spaceship at c and returns, aging less than the twin on Earth because he traveled at c relative to Earth. However, relative to the spaceship, Earth is traveling away from it at c also, so technically, if I were on that...
  12. G

    Thoughts (of an amateur) on the Solution to the Twin Paradox

    Hello, All. I found this forum through a google search. This post could have been attached to the thread started by Bob Guerico on 09-Jan-08, but I felt it would be better to start a new thread. I've been reading about SR and GR for about a year now. I've been through several iterations of "I...
  13. W

    Exploring the Twin Paradox of Special Relativity

    Hi All, I was recently trying to understand the Special Theory of Relativity and my understanding of the resolution of the twin paradox is that the person who has accelerated away from the observer and accelerates again to join the observer is the person that grows older. I understand the...
  14. J

    Does the Twin Paradox Challenge Classical Relativity?

    I hate to bring this up again, but the twin paradox explanation based on acceleration does not hold water. Let's go back to Object A mentioned on the now locked thread posted earlier. Object A sees Object B fly by at close to the speed of light. A figures the clocks are moving more...
  15. N

    Mathematica There is no twin paradox - mathematical proof

    For the twin paradox to be considered a true paradox the framing of the scenario must be stringent, that is to say we cannot permit assumptions to be ignored. Therefore I must start with a short description of the twin paradox followed by identification of the inherent assumptions. From...
  16. A

    How Does the Twin Paradox Illustrate Time Dilation and Length Contraction?

    [SOLVED] Intro course Twin Paradox Homework Statement You probably already know. One twin stays on earth. One goes 4ly away at .8c. The question asked a bunch of different things. How long does the twin on the ship think it takes. How long does the twin on Earth think it takes. How long...
  17. U

    How Long is the Astronaut Gone in the Twin Paradox with Circular Motion?

    Homework Statement A variation on the twin paradox, with uniform circular motion. The traveling sibling moves so that his acceleration is g at all times, pointing to the centre of his circular path, constant velocity. There is given that the trip takes twenty years in the frame of the...
  18. R

    Twin Paradox: Simplifying Physics for Age Difference Explanation

    Primary Goals of Thread: (1) Eliminate all unnecessary concepts (2) Focus solely on the physics Tom and Bill are floating in space (that is, they are moving inertially). Let Bill meet Tom as they pass each other. They notice that they are both about the same age. After Bill and Tom...
  19. P

    Twin Paradox: Why Twin On Ship Ages Slower?

    The way the twin paradox is explained, the twin on the ship ages slower than the twin on Earth because he is moving at velocity with respect to the twin on earth. This makes sense from the twin on Earth's reference frame, but wouldn't the twin on the ship see it the opposite. From his...
  20. N

    About the Non-paradoxicality of the Twin Paradox

    When I wrote my paper on Special Relativity in my final year of high school, I explained the Twin Paradox as follows: Twin A stays on earth, twin B takes off to some star S. (I'm making this a very short version because I'm assuming we all know the structure of the paradox) Twin B measures...
  21. B

    Twin Paradox: Solving for Time Interval in Satellite Orbit | Special Relativity

    Homework Statement A clock is placed in a satellite that orbits Earth for a period of 5400 seconds. By what time interval will this clock differ from an identical clock on Earth after 1 year(assume that special relativity applies.) Homework Equations v(escape velocity)=11186 m/s...
  22. R

    Modified Twin Paradox. (Experts required).

    I have gone through the previous posts on the subject in this forum but still have an issue. So please tell me what is wrong with my following (qualitative) reasoning: Assume the standard paradox is replaced with: Twin A at origin of x-axis in free space. Twin B accelerates away to speed...
  23. A

    GPS Satellites & the Twin Paradox: Time Dilation Explored

    The satellites of GPS sysstem had been adjusted so they compensate for GR and SR dilation of time due their velocity and less gravity. This is what I found on Internet ( Not all agree ). Is that true ? But I´d like to know if the frequency of the ground stations that control the...
  24. N

    Twin Paradox: Exploring A's & B's Frame of Time Dilated Age

    Hai ,I am new to the forum. I have some basic questions regarding the same old twin paradox. Twin A stays at Earth and Twin B is the traveller. from the A,s frame we all agree that Time is dilated for B because it is moving(relative to A) near to the speed of light. Now switch on to B,s...
  25. L

    Can Special Relativity Solve the Twin Paradox in a Gravitational Field?

    It is possible to draw world-lines of the two twins in the non-accelerating one (A) frame of ref. The aging of the other (B), with respect to the first, is evaluated integrating its proper time differential (and comparing it with A's proper time). My question is (certainly already asked): is...
  26. O

    Twin paradox again (yes again)

    There is a simple truth to this world. Some people are dumb. I am one of them. I'm sorry to ask this but yet again but I just don't get it. Here is the latest explanation of the twin paradox that I have read. http://mentock.home.mindspring.com/twins.htm" I understand the three...
  27. R

    Twin Paradox Theory: Explained for 9th Graders

    I know there are a few threds already on this subject, but it seems to me that all of them require preknowlage on the subject busides a wikipedia search which only seems to tell you that If one twin leave Earth vie. space ship, and travels .99c to a Galaxy 2 light years away, turns around, and...
  28. M

    Is there a way to intuitively understand proper time in special relativity?

    i have a question... according to time dilation...as an object travels close to the speed of light, relative to antoher observer, the time goes slower in the moving object and it will appear to be "younger' if it was a person on the space travel... however, relative to the person on the...
  29. M

    Exploring the Twin Paradox: General Relativity & Time Travel

    How many of you over here are familiar with the twin paradox? I am personally quite fascinated with this phenomenon predicted by General Relativity. In a nut shell, since your relative time slows down at speeds close to the speed of light, it implies that if, say, your twin brother were to go...
  30. K

    Twin Paradox in 3-sphere (S^3)

    X and Y reside in the 3-sphere. Y is accelerated to near the speed of light; say, 0.9c. He does not ever change direction. In a little while, he meets X, who happens to be residing on the great circle upon which Y is traveling. When they meet, they give each other high-fives. At that...
  31. A

    How Has the Twin Paradox Been Resolved?

    News Story: "Twin Paradox Solved" This makes me even sadder than the 0/0 story a few months ago: http://www.physorg.com/news90697187.html edit: mirror: http://duggmirror.com/general_sciences/LSU_professor_resolves_Einstein_s_twin_paradox_2/
  32. D

    The Twin Paradox: Exploring Its Complexity

    The twin paradox is very confusing, and even after reading the explanation, I still get questions. The only explanation of the paradox is when an object is first moving away from earth, and then moving towards the earth. They make it very complicated. How about just moving one direction, and...
  33. K

    Twin Paradox: Special Relativity Theory Explained

    Hi all, I am taking a grade 12 physics course and we just covered special relativity theory however one thing troubles me; the twin paradox. The thought experiment proposes that a one twin travels to a distant star and back at a speed approaching that of light while the other twin remains on...
  34. resurgance2001

    Symetry, time dilation, twin paradox and all that stuff

    I spent several months last year trying to understand the twins paradox and didn't get anywhere. The standard answer given is that symetry is broken a/ becuase one of the twins has to accelerate and b/ becuase on the return journey she is actually in a different inertial frame to the outward...
  35. B

    How Does Jane Receive 30 Messages from Dick in the Twin Paradox Scenario?

    please help its urgent hi can someone please solve this paradox related to the twin paradox?? jane continues to be on Earth and dick goes to a planet 20 light years away at a speed of 0.8 c. Every year dick sends a message to Jane. Now for Jane due to time dilation the time taken by...
  36. B

    Relativity Question (Twin Paradox)

    Hi all, Most of you are probably familiar with the twin paradox of relativity, which is the basis of this problem. I think I understand it fairly well but am having trouble with one specific detail. Here is the setup: Problem We have two planets, the Earth and canopus, that are...
  37. michael879

    Twin Paradox: Can You Outrun Time?

    famous paradox, everyone should knows it. Whenever I've heard it though its been dismissed as not really being a paradox since the two twins paths arent identical. The twin in the rocket accelerates off Earth and then accelerates back. With a hyper-spherical universe however you could have...
  38. N

    A quick question on the twin paradox (quick I promise)

    I am reading ''Modern Physics`by Tipler and Llewellyn, 4th edition, page 52. They say something which, unless I am completely confused, is completely wrong. I cite (Ulysses is the twin in the spaceship, they use \Delta t_{Earth}= \gamma \Delta_{spaceship} and then say: ''...we cannot...
  39. B

    Twin Paradox: Earth-Twin vs Space-Twin Aging

    The Twin Paradox: If a twin on a rocket travels at high speed for a while, and then returns to the Earth, the Earth-twin would have aged much more than the space-twin. But isn't it just as valid to say that the Earth is moving away from the rocket? Then the situation would be switched. Why would...
  40. T

    The Twin Paradox: Reconciling Time Dilation and Relative Velocity

    Just an easy question.. What does each observer see? The Earth one obviously sees time running slower on the spaceship. When the spaceship observer heads out, I assume he sees time running slower on the Earth frame? As he heads back, what does he see? I'm finding it hard to reconcile the...
  41. U

    Circular Twin Paradox: Non-Linear Acceleration and Age Differences Explained

    As we know, the twin paradox states that an astronaut that accelerates away from the Earth, stops, turns around, and then accelerates back to the Earth ages less than his twin that remains behind (on Earth). How about in the case where the acceleration isn't linear? Let's say our astronaut...
  42. S

    Kumar's Explanation of the Twin Paradox

    Guys can anybody explain me the famous "Twin Paradox" --->Sampath
  43. D

    A variation on the twin paradox

    OK, so I'm pretty familliar with the regular twin paradox and the explinations of how you decide which twin is younger by noticing which one accelerated, and the geometrical view of this using k-calculus and minkowsky diagrams, etc. I just thought of something though, and I guess my relativity...
  44. T

    Twin paradox? HA I'm an only child.

    Correct me if I'm wrong, please. If I travel at near the speed of light in my new spaceship then an observer here on Earth would age 20 years while I'd only age a small fraction of that. I understand that (well, I believe that). Here's where I start running into questions. The observer on Earth...
  45. Q

    Curtailed length and the twin paradox

    Hello, I've got two quick questions. Why is it so that they say "if a object moves extremely fast then we see it curtailed/shortened a little bit"? But if it moves that fast that the length even may be noticeable, how on Earth do we SEE it shortened when it moves THAT fast past us? If a...
  46. G

    How do you explain the twin paradox to a friend

    How do you explain the "twin paradox" to a friend Talking with a friend at work I encountered a problem, "No, he was wrong. There is no way possiable that someone can age at a diffrent rate because they are moving at a diffrent speed." We all know a person that has said this and have spent a...
  47. G

    How do you explain the twin paradox to a friend

    How do you explain the "twin paradox" to a friend Talking with a friend at work I encountered a problem, "No, he was wrong. There is no way possiable that someone can age at a diffrent rate because they are moving at a diffrent speed." We all know a person that has said this and have spent a...
  48. R

    Resolving the Twin Paradox: A Mathematical Approach

    I am not sure if this is the right place to ask this question. I am an amateur but I enjoy reading and trying to understand relativity. If anyone is aware of an article that addresses this question, I would appreciate the reference so that I can read up on it. Unfortunately, there are a lot...
  49. Pengwuino

    Twin paradox, live via satellite

    Ok I was trying to explain special relativity to a friend and I was wondering about something (he said someone explained to him why special relativity was wrong :rolleyes: ). Lets say you have 3 people, A, B, and C. Person A sits on earth. Person B is in a rocket ship. Person C is with...
  50. chronon

    Twin Paradox and the Logical Foundation of Relativity Theory

    I just noticed the following on the Philsci archive. Judit, X. Madárasz and István, Németi and Gergely, Székely (2005) Twin Paradox and the Logical Foundation of Relativity Theory. http://philsci-archive.pitt.edu/archive/00002358/ They seem to be saying that inertial frames can be dealt...
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