Time dilation Definition and 999 Threads

In physics and relativity, time dilation is the difference in the elapsed time as measured by two clocks. It is either due to a relative velocity between them (special relativistic "kinetic" time dilation) or to a difference in gravitational potential between their locations (general relativistic gravitational time dilation). When unspecified, "time dilation" usually refers to the effect due to velocity.
After compensating for varying signal delays due to the changing distance between an observer and a moving clock (i.e. Doppler effect), the observer will measure the moving clock as ticking slower than a clock that is at rest in the observer's own reference frame. In addition, a clock that is close to a massive body (and which therefore is at lower gravitational potential) will record less elapsed time than a clock situated further from the said massive body (and which is at a higher gravitational potential).
These predictions of the theory of relativity have been repeatedly confirmed by experiment, and they are of practical concern, for instance in the operation of satellite navigation systems such as GPS and Galileo. Time dilation has also been the subject of science fiction works.

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  1. Benoit

    I Why is B's clock in advance instead of A's?

    Are you good with Lorentz' tranformations ? I tought I was, until I tried to do this exercice (it is really classical): Two planets, A and B, are at rest with respect to each other, a distance L apart, with synchronized clocks. A spaceship flies at speed v past planet A toward planet B and...
  2. John Fluharty

    B How does time dilation affect travel time at different speeds?

    Forgive me if this is the wrong place to ask this, but I am trying to do a mental exercise to understand time dilation relative to an observer's frame of reference. In my though experiment I am on a space station and someone is coming to meet me here. GST or Galactic Standard Time is always...
  3. S

    Calculating Muon's Time Dilation and Travel Distance in a Particle Accelerator

    Homework Statement The muon has been measured to have a mass of ##0.106\ \text{GeV}## and a rest frame lifetime of ##2.19 \times 10^{-6}## seconds. Imagine that such a muon is moving in the circular storage ring of a particle accelerator, ##1## kilometer in diameter, such that the muon's total...
  4. hypermental

    Shooting Video on Planet Z Near a Black Hole

    [Mentor's note: The thread title has been edited to change the level from "A" to the more appropriate "B"] Suppose there is planet Z revolving around black hole. Astronaut from Earth go in that Planet Z and start video recording and make a DVD . Suppose they played that DVD in the computer in...
  5. Sentosa

    I Does time dilation cause the speed of light to be invariant?

    I'm trying to understand why the speed of light is the same for all observers. I have found different answers on-line. This page claims that it relates to time dilation. But consider the following thought experiment: two ships flying at 98% c. Ship A is moving toward the sun, and ship B is...
  6. hypermental

    Time dilation and acceleration due to gravity

    If acceleration and acceleration due to gravity is equivalent , then by equivalence principle if we accelerate through universe at the equal to acceleration due to gravity near black hole , does that mean that there will be same time dilation while we accelerate in the universe like when we...
  7. G

    Entanglement and time dilation

    In entanglement, two electrons have the same spins measured at the same time. But how is same time defined, in light of special relativity's time dilation? Doesn't this mean that, from another frame of reference, they will not be simultaneous. That means, that person in point A, knows in...
  8. P

    How Long Does a Relativistic Journey to a Star 65 Light-Years Away Take?

    Homework Statement Suppose you decide to travel to a star 65 light-years away at a speed that tells you the distance is only 25 light-years. How many years would it take you to make the trip? Homework Equations ∆t=∆t0/(√ (1−v2/c2 )) / ∆t0 = ∆t √(1−v2/c2) L=L0√ (1−v2/c2) The Attempt at a...
  9. D

    B Who really understands time dilation and relativity?

    hi,so i posted a thought experiment on other fourms and it seems everyone is misunderstanding the big picture of the experiment.i would like to verify that i really understand relativity and time dilation.i will explain a thought experiment in order to exsplain my understanding of relativity in...
  10. merwyn

    Time Dilation: Biologist's Question to Math & Relativity Experts

    Iam a Microbiologist, not an expert in math and relativity. I have a simple question. Assumption Mr 'X' travels to the star 'S' In Earth reference the star is 5 light years ie 9,500,000,000,000 x 5 Kms from earth Mr X travels @ 80% of lights speed (80% speed from leaving and reaching back...
  11. Ananay Wadehra

    Conditions of Big Bang & Light Speed Travel: Exploring Relativity

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  12. A

    Can Classical Mechanics Calculate Time Dilation?

    Okay so I have a question about time dilation, kinetic energy and classical mechanics. My question is, if an object were traveling at very high relativistic speeds and experienced time dilation, would the time it experience and measure during the travels be equivalent to the travel time if it...
  13. D

    Proving Time Dilation: Troubleshooting Tips

  14. J

    Gravitational Time Dilation Problem

    Homework Statement A person lived 75 years in a city located 3.1km above sea level. How much longer could they have lived at sea level? (Times are measured by an observer at infinite distance). Homework Equations tr/t∞ = {1 - [ (2GM) / (r(c^2)) ]}^(1/2) Rc (Radius at city) = Rearth + 3.1km...
  15. R

    Time dilation magnitude in orbit around a black hole

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  16. Erland

    Gravitational time dilation, how much?

    OK, I could probably find the answer of this simple question somewhere, but... If an astronaut stays on space station, in a weightless state, for 30 years, how much older does he/she become compared to a person who stays on the Earth all the time? I think it is about one second. Am I...
  17. A

    Understanding Time Dilation: Exploring the Twin Paradox in Special Relativity

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  18. W

    Confusion about the gravitational time dilation formula

    Homework Statement I'm reading the book Relativity, Gravitation, Cosmology by Ta-Pei Cheng. I'm in the part where he derived the gravitational time dilation formula for static gravitational field, τ1=[1+(Φ1-Φ2)/c2]τ2. This implies that clocks at a higher gravitational potential will run...
  19. M

    Velocity-Based Time Dilation: Teen's $400k Video Correct?

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  20. M

    I Questions about time dilation, special relativity, etc.

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  21. S

    Falling Into a Black Hole: Time Dilation & Survival

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  22. I

    How does the time dilation equation work?

    Hi all! I've been doing some studying length contraction and time dilation and I came across this link http://hyperphysics.phy-astr.gsu.edu/hbase/relativ/tdil.html . I completely understand what it did with length contraction but when I got to time dilation I couldn't figure out one thing. They...
  23. S

    Time Dilation for Interplanetary Migration: Can We Go?

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  24. N

    Special Relativity: Time dilation

    Hello. This is not a concrete problem, rather conceptual question. Homework Statement 2. Homework Equations 3. The Attempt at a Solution [/B] Spaceship with speed v with respect to the Earth is traveling from the Earth to say some distant star, which is distant L apart from the Earth looking...
  25. T

    B How Can Time Dilation Be Explained Without Math?

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  26. M

    I Is the relativity of simultaneity the reason for time dilation?

    A yes answer can cause conceptual problems. What is your opinion?
  27. sunrah

    Ratio of time dilation relation in different potentials

    In the weak field limit, we have dt = (1 + 2\phi)^{-\frac{1}{2}}d\tau where the usual meaning of the symbols applies. This means that in GR dτ < dt analogous to SR. Let suppose we measure the period dtS of a photon emitted at the surface of the Sun as well as the same photon, i.e. same atomic...
  28. Warfen

    Gravitational Time Dilation & Orbits of Objects

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  29. N

    Time Dilation at ISCO for Kerr Black Holes

    Hello, I like to calculate the time dilatation at the ISCO of a Kerr black hole: According to general relativity the time dilation is given by following formula: d \tau = \sqrt{g_{\mu \nu} \dot{x^{\mu}} \dot{x^{\nu}}} If I'm interestet in the time dilation at the ISCO I set \Theta =...
  30. I

    Special Relativity - time dilation and length contraction

    Homework Statement The highest energy protons have gamma factors around ##1.0*10^{12}##. (a) Our galaxy has a disk diameter of 30 kpc, which is ##9.3*10^{20}m##. If a photon and one of these high energy protons start traversing the galaxy at the same time, by how long will the arrival of the...
  31. P

    Attempting to understand relativity and time dilation

    Homework Statement t = t0/(1-v2/c2)1/2 Homework Equations t = 10/(1-.95c^2/c^2)1/2 The Attempt at a Solution [/B] The provided solutiojn to the example given above is: t = 10/(1- (.95c)2/c2)1/2 t = 10/(1- .952)1/2 t = 10/ .312 t = 32 Unfortunately, no matter what I do the answer I...
  32. D

    Relativity time dilation and length contraction

    Homework Statement can somebody help my figure out what t0 l0 l and t is? For instance: A girl an her dad are in an airplane, the girl starts running 20m in 8 seconds. There is also a boy standing beneath the plane (lets pretend that the airplanes floor is seethrough. Homework EquationsThe...
  33. E

    Does time dilation occur between comoving galaxies?

    As an astronomer observes a galaxy, which is receding, Does time dilation occur between the two comoving galaxies? If so, which (rf) is (t) longer in, as observed here on Earth (Our local Milkyway galaxy or the remote galaxy)? Thank you.
  34. E

    Signal time in Twin Paradox: Fast clocks? Redshift/blueshift

    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...
  35. M

    Explanation of time dilation due to c being the maximum speed

    I have seen a video in which the time dilation due to velocity is explained by saying that light and light interactions inside a moving body must travel a longer distance in space, which reduces the passage of time. Video: This explanation is new to me, and in fact, I recently heard an almost...
  36. D

    What time dilation do muon observers experience?

    Re. time dilation muons, CERN. Given the accelerated muons were observed to have a lifetime increased by approximately x 29, What happens to the observers life span? Thank you.
  37. B

    Time Dilation: Rel. Ref. Frames and Universal Reference Frame

    I understand that if someone is traveling away from Earth at a very high speed, time will slow down for the traveler relative to the people on earth. However, why is it not the other way around? If there is no universal reference frame, could this situation not also be thought of as the traveler...
  38. seb7

    Exploring the Truth Behind Time Dilation: Debunking Common Misconceptions

    The video is pretty popular and being spread by science channels. Is the last bit about the cause of time dilation correct? I used to think like this, but came to the concoction its wrong, but seeing this video makes me wonder once again how could this be correct. If the video is true then -...
  39. D

    Basic Questions on Time Dilation Implications

    I'm relatively new here, and was told that the GP group was a good place to ask some basic questions. If this isn't he right place for the question, please direct me to the proper group. For years I have been fascinated with the implications of the time dilation mental experiment -- the...
  40. writer

    I Time dilation time travel for novel - I need a calculation

    Hi! I've written a novel in which my main character travels through time (into the future) 18 years. While the concept of time travel is necessary to the plot, the details are not. Meaning, the book isn't sci-fi, but contains elements that wouldn't normally exist in a contemporary novel, so...
  41. iForget

    Time Dilation for Slower Objects - Physics Explained

    Good day, I'm a high schooler so my knowledge of physics is futile and still expanding. Please correct me when I'm wrong, I love physics. Now to my question. I'm still a bit fuzzy on this theory of time dilation and the speed of light etc. But if time dilation happens at the speed of light can...
  42. m4r35n357

    I Is it time to "retire" time dilation and length contraction?

    Considering the enormous number of questions posed on this forum and other places, the concepts seem fundamentally flawed (because both are formally and practically unobservable). The calculations themselves (together with the Lorentz Transform) are highly error-prone and the results misleading...
  43. 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.
  44. SuperfundMatt

    B How does time dilation appear to a third observer?

    Let’s assume it is 5,000,000 years in the future and we have created a quantum synchronization box that can broadcast a signal, used to synchronize two clocks and video feeds, no matter where they are in the universe. The third observer watches a split TV screen, which features the faces of two...
  45. T

    How Does Time Dilation Affect Spacecrafts Traveling at High Speeds?

    1. A spacecraft going at .99c is heading straight towards a star that's at a distance of 60,000 light years. Another ship 25,000 light years below the first one also is heading towards the star also at .99c. What what is the related rate between the time dilation of the first spacecraft to...
  46. Smattering

    Time dilation at the event horizon of a black hole

    Dear all, As far as I understand, for a distant observer, time stands still at the event horizon of a black hole, right? In particular, nothing will ever pass the EH. Instead, everything that approaches the BH will get stuck at the EH and stay there forever from the perspective of the distant...
  47. K

    Which Quintuplet Returns to Earth Last Based on Time Dilation Ranking?

    Homework Statement Five identical quintuplets leave Earth when they reach the age of 21, in the year 2121. Each quintuplet goes on a spaceship journey that takes T years, as measured by a clock in each spaceship. During the journey they travel at a constant speed v, as measured on earth, except...
  48. D

    Time Dilation and different clock types

    Hello PF. A moving clock is seen by the platform observer to run slow. This applies to all clock constructions. A light clock runs slow because the light path lengthens and the clock takes longer to tick over. Other types of clocks don't have a light path to lengthen. By what mechanism do...
  49. H

    Gravitational Time Dilation: A Layman's Explanation

    I think I have a layman's understanding of time and length contraction. However, I don't really understand gravitational time delay or distance contraction. If we were to put two clocks at the front and end of a rocket, the one on the top would experience time more quickly than would the one on...
  50. S

    Time Dilation by Light Alone? A Software Engineer's Exploration

    Let me first preface this with a couple facts about me. I am not a physicist, nor have I ever taken any classes in my life to warrant any extensive knowledge on the subject. I'm a software engineer by trade but have a great interest in physics (or at the very least, spacetime and how it all...
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