Twin paradox Definition and 315 Threads

I've read the twin paradox and if I am correct the resolution is that one twin accelerates and decelerates so he comes back younger. But I have a different scenario that I would like to ask: What if you have two twins equally distant from a point in space and completely at rest relative to each...

Homework Statement a) Alice is observing a small ball of mass m in relativistic motion bouncing elastically back and forth between two parallel walls separated by a distance L with speed u. After each collision it reverses direction, thereby creating a clock. What does Alice observe as the...

Here is a diagram from the Wikipedia. I'm sure you understand what this represents. Those who don't, can go to the Wikipedia page (https://en.wikipedia.org/wiki/Twin_paradox) and see all the details. After my prior post, I have a better appreciation for simultaneity. Originally, when I looked...

I know this publication is not peer reviewed, but when I saw this article it was exactly the same way I came to “understand” the twin paradox myself. I literally did this exact calculation (with a different gamma value). So I was wondering if the article was valid. If it isn’t, where isn’t it...

I'm just trying to develop a general understanding of the 'twin paradox', so my description of this is will be a bit poor. I feel like I have a sound understanding so far on the topic, but the only thing that I can't seem to find an answer for is this scenario; Say you have the classic twin...

Bondi K-Calculus very depend on who was send the signal. If two twin A and B make a journey, A send a signal and B receiving the signal then yes after the journey A will see B younger, and this applied too for the case B sending a signal and A reflecting, then after the journey A will younger.

Hi, thanks to a different thread/question on this forum I've come to appreciate time dilation ..somewhat. And from that I wondered if, given the range of locally measured times aboard any and all particles in the universe, given their different trajectories and histories since the big bang...

Hi people! (Sorry for my poor english). I found everywhere that twin paradox need aceleration to explain it. Let me change the twin paradox a little: Suppouse that in Earth and before the traveller twin start his trip, you take two photos with old Polaroid camera, one to each twin. As we...

Pardon me if this has been asked before, but I'm confused with the implication that SR makes, that there is no objective moment of present. Do the science still believe that the time flows (i don't mean the arrow of time, but the phenomena of flowing/passing, eq. flowing of a river)? I mean, how...

Hello everyone, Reminder: The key of the explanation of the "twin paradox" resides in the acceleration. We know that the time runs slower for the twin in the spaceship (since it was accelerated)...

Consider two bodies A &B are moving apart with a velocity V due to the expansion of space. According to an observer in A the body B is moving away and an observer in B feels the body A is moving apart. Can some one answer in which body the time dilates and why?. ( I am specifying once again that...

Dear All, I am doing the Special Relativity course at World Science U, and came across this question which I got wrong: When 100 nanoseconds have elapsed on traveling Gracie's watch, she immediately stops, turns around, and heads back toward George at the same speed of her outbound journey...

I was reading the wikipedia page on the twin paradox (https://en.m.wikipedia.org/wiki/Twin_paradox). It says: The mechanism for the advancing of the stay-at-home twin's clock is gravitational time dilation. When an observer finds that inertially moving objects are being accelerated with...

This was straying from the point in the original thread, but I thought it made a point... The stay-at -home twin is at rest in her frame and her clock must therefore measure proper time. The traveling twin, carries his clock with him; it is therefore at rest in his frame and must also measure...

Hi, I am reading the biography "Einstein's greatest mistake" from David Bodanis. On page 39 the author explains some of the consequences of relativity by referring to (although he doesn't mention it by name) the twin paradox. He explains that someone accelerating at high speed away from Earth...

First off, let me just say I love this forum and all the people in it! The world is a better place because of all of you who take the time to post here and I thank you all! The most popular explanation to resolve the twin paradox seems to be the asymmetry that arises because the ship...

Jim al Khalili did a (basic level) TV programme in the UK last night where he featured a smartphone app which works as a space-time "odometer". Now you can experiment on your own version of the legendary brain-teaser with your friends, no need to go to Alpha Centauri and back! Go for a walk...

Case 1) Two rockets (no Earth involved) have an exactly the same acceleration profile/flight-plan during round trip but they dispatched to opposite directions. At the start both rockets are docked to the same space station...both rockets have an identical engine operation plan during the round...

This question based on the site located here: http://galileo.phys.virginia.edu/classes/252/srelwhat.html The question is: If the object (spaceship) moving close to the velocity of light and I'm as a static object. The time goes slower in the object moving with constant velocity (inertial frame)...

Imagine that we have two metal rods, and both measure 1 meter, a measurement done from the same inertial system when they are at speed = 0. These two rods are equal, the extreme points of the first one are called a and b and its inertial system is called F, the extreme points of the other rod...

There is something about the twin paradox in special relativity that has always bothered me. One twin sets out on a journey at a large fraction of the speed of light, turns around and returns. The fact that the returning twin is the one who is younger is explained by the fact that they are the...

Definitions: Astronaut is A Person on Earth is B A travels to a star far away at near light speed, A would see B's time dilate. B would also see A's time dilate Twin paradox revived: What would happen if A returns to B at a very slow speed? Then both frames of reference would see each others'...

Hello. Thank you to everyone who helped me with my previous post where I had general questions on special relativity. Several users suggested that I start by trying to understand the relativity of simultaneity which I did. Although I haven't mastered it, I understand it better now. Also, someone...

Hi, I'm trying to understand the twin paradox and time dilation. Someone told me that if observer A and observer B are traveling apart from each other with each having a uniform speed of .4c they will have the same age when they return back at the point of origin. Even though I'm unsure of...

I understand that the twin paradox isn't truly a paradox, and that the traveling twin ages since the universe can be "aware" of his traveling. However, my question is how does the time dilation formula break down? Why can't you integrate dT' = dT * Gamma for each velocity as the traveler...

robphy submitted a new PF Insights post Relativity on Rotated Graph Paper Continue reading the Original PF Insights Post.

Forgive my naivete, but I've struggled with the twin paradox for a long time. If there is no privileged frame of reference, why does time dilation apply only to the traveling twin? I have been told (possibly erroneously) that the stay-at-home represents the entire universe, but this seems to...

I set up a Twin Paradox scenario and accompanying spacetime diagram to help better understand the resolution, but I had a question about the diagram I was hoping someone here could help answer. Please excuse the hastily drawn diagram! (Note: the ' frame corresponds to the outbound trip, the...

When I read that conditions were such and such 1 to .05 seconds after the big bang, is that duration somehow longer than 1/2 second is now (maybe because of the difference in density or like the twin paradox?)?

I decided to work a bit on my Java program created to visualize the Twin Paradox. It shows two diagrams. One from the perspective of the stay at home/earth twin on the left side and the traveling twin on the right side/diagram. The accelerations are considered to be near instantaneous, hence why...

I feel a difficulty in understanding SP at fundamental level which is somewhat related with twin paradox. Let me take a thought scenario: in empty space or vacuum two boxes(A and B) with their own light sources attached are separated from each other at a far distance r initially. If they are...

Thinking and reading about the twin paradox recently, I encounter a lot of explanations and resolutions that don't make sense to me. At its most basic, the issue is- when two bodies are in different frames of reference, why shouldn't relativistic effects affect both equally, negating time...

So say that there are twins. Twin A is near a heavy planet and twin B is out far away in space. Why does time slow for twin A compared to B? Can't they say that they both are in inertial frames because there are no forces(gravity isn't a force) acting upon them? Therefore for each of them can...

Hi, I just saw a video about the twin paradox, explained by using GR. I was wondering whether I understood the video correctly. The video states that when the rocket twin is first accelerating away from earth, his clock and his Earth twin's clock are different, but, roughly the same because of...

If you had twin 1 on the earth, and twin 2 fly to a star and back at a speed of v with the Earth and star separated by a distance L, twin 1 sends out flashes at intervals of t seconds (measured in his frame). Taking into consideration the numbers of redshifted and blueshifted flashes that the...

I just came across this video today with Brian Greene talking about how time slows down for an observer near a black hole relative to an observer who is farther away. See the first two minutes: It reminded me of another video I saw recently by David Butler where he states that the twin...

Here is a scenario in which two twins age at different rates even though both always have the same speed.Consider a train track that includes a circular segment with ground circumference minutely greater than 80. Two twins are on a train with synchronized watches (Frank at the front and Reba at...

NOTE: This is NOT a homework problem. I created this one myself based on some problems I have seen, with specific numbers used to make calculation clean and easy. Tl/dr version: in a round trip to a star, will the "moving clock" run slower on the way there but faster on the way back due to the...

Hey Friends, In Einstein's special relativity I find "Twin Paradox", where Dick and Jack, two twins . one of them went to space at a speed of 0.80c to a star 20 light year away (where c is the speed of light) and other remains on earth. When Jane returned to Earth his age was...

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

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...

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...

I'm working on a Time Travel novel. Need to know if anyone can express the paradoxes as equations.

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...

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...

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...

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...

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...

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...

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...